Communication control device, wireless communication system, communication control method, and program

Abstract

According to the present invention, in a beam search period for using search to determine a beam to be used for wireless communication with a terminal device, each of a plurality of distributed antennas is caused to perform an all-beam search, which is performed by transmitting a beam in all directions in which transmission is possible in an order of the distributed antennas that differs for each beam search period. When one beam identifier indicating the best beam has been acquired by the all-beam search, the all-beam search is stopped, and the beam identified by the acquired beam identifier and information indicating the distributed antenna that has transmitted the beam indicated by the beam identifier is set to a detection reference beam. A beam identifier of a distributed antenna which has not performed the all-beam search and which has been selected together with the detection reference beam is detected from a beam combination history storing unit as a candidate beam identifier of this distributed antenna, and it is determined, on the basis of a result of the detection, whether or not to cause the distributed antenna that has not performed the all-beam search during the beam search period to perform the all-beam search.

Description

Technical Field

[0001] The present invention relates to a communication control device, a wireless communication system, a communication control method, and a program.

Background Art

[0002] (Beamforming in High Frequency Bands) In high frequency bands such as the millimeter wave band and the terahertz band, the free space propagation loss is large compared to low frequency bands such as the microwave band. Therefore, it is necessary to use beamforming technology to form a beam that concentrates power in a specific direction in order to compensate for this loss (see, for example, Non-Patent Document 1).

[0003] In P-P (Point-to-Point) type communication where the combination of wireless stations that always communicate is fixed, and the positional relationship of the wireless stations and the propagation environment around the wireless stations do not change, beamforming can be performed fixedly by determining the beam formation direction in advance, such as at the time of installation of the wireless stations. On the other hand, in a P-MP (Point-to-Multi Point) type that accommodates a plurality of wireless stations, or when at least one of the wireless stations moves, beamforming cannot be performed fixedly. In this case, it is necessary to perform adaptive beamforming that adaptively controls the beam formation direction in accordance with the position of the wireless station that requires communication among the plurality of wireless stations, the movement of the wireless station, and the change in the propagation environment around the wireless station.

[0004] Adaptive beamforming is generally performed by adjusting the phase relationship of radio waves radiated between a plurality of antenna elements without using a mechanical drive unit to control the beam formation direction. However, in order to appropriately adjust the phase relationship, it is necessary to grasp the phase relationship between each antenna element of both the transmitting and receiving wireless stations and then derive an appropriate phase relationship. That is, it is necessary to grasp the state of the propagation path between each antenna element of both the transmitting and receiving wireless stations in all combinations of each antenna element.

[0005] The state of the propagation path can be grasped by transmitting and receiving a known signal between the transmitting radio station and the receiving radio station. However, during this transmission and reception, other communications cannot be carried out, and since it is necessary to accurately transmit the state of the propagation path from the receiving radio station to the transmitting radio station, the communication overhead increases.

[0006] In order to suppress the increase in overhead, in adaptive beamforming, a signal including a beam identifier (hereinafter referred to as beam ID (Identifier)) associated with a plurality of candidate beams set in advance discretely is transmitted in each candidate beam, and the beam ID of the beam determined to be the most suitable for communication is selected from among them. This technology is defined as the specification of wireless communication systems such as 3GPP (registered trademark) 5G (5th Generation) and IEEE802.11ad, and has also been implemented (see, for example, Non-Patent Documents 1, 2, and 3).

[0007] (Beam selection procedure) When selecting the transmitting beam of the radio station, the transmitting radio station transmits a signal that allows the receiving radio station to uniquely identify each beam used for transmission. Such a signal includes, for example, a beam search signal in which the beam ID of the beam used for transmission is embedded as digital information. The transmitting radio station transmits each beam carrying a beam search signal embedded with a different beam ID by switching the direction in time. The receiving radio station receives a plurality of beams, reads out the beam IDs included in the beam search signals of each of the received plurality of beams, measures the reception quality of each beam, and determines which transmitting beam has the best reception quality. The receiving radio station transmits a feedback signal that allows the transmitting radio station to uniquely identify the beam ID of the transmitting beam with the best reception quality to the transmitting radio station, so that the transmitting radio station can select the transmitting beam.

[0008] Regarding the reception-side beam selection of a radio station, in a system such as TDD (Time Division Duplex) that uses the same frequency for transmission and reception, it is also possible to select the same beam as the transmission side. On the other hand, in a system such as FDD (Frequency Division Duplex) that uses different frequencies for transmission and reception, similar to the transmission-side beam selection, it is necessary to perform beam selection for the reception-side beam as well. When selecting the reception-side beam of a radio station, the radio station on the reception side transmits a signal requesting a reception beam search procedure to the radio station on the transmission side. The radio station on the reception side switches the direction temporally in accordance with the signal transmitted by the radio station on the transmission side and receives it, and measures the reception quality of the received signal. Thereby, the radio station on the reception side can select the reception-side beam by determining which reception beam has the best reception quality.

[0009] (Distributed Antenna System) FIG. 36 is a diagram showing the configuration of a wireless communication system 500, which is an example of a conventional general wireless communication system. In FIG. 36, as an example, a configuration is shown in which five cells 100-1 to 100-5 exist in the wireless communication system 500. The wireless communication system 500 has a configuration in which one antenna is installed for each cell. That is, in the wireless communication system 500, antenna devices 200-1 to 200-5 are installed in each of the cells 100-1 to 100-5. Digital signal processing devices 210-1 to 210-5 for transmitting and receiving signals are connected to each of the antenna devices 200-1 to 200-5. Looking at cell 100-1, the antenna device 200-1 and the digital signal processing device 210-1 form a so-called base station device. When one terminal station is located in cell 100-1, for example, the terminal station will be connected by radio waves from one antenna device 200-1.

[0010] Here, as described above, in high-frequency bands such as the millimeter-wave band and the terahertz band, since beamforming technology is used, the influence of reflected waves and diffracted waves is reduced. Therefore, in high-frequency bands, when the beam is blocked, the possibility of communication interruption increases, and line-of-sight communication is basically required. By the way, there is a technology called MIMO (Multiple Input Multiple Output), which is a powerful spatial multiplexing technology. In MIMO, by using multiple antennas for transmission and reception, the transmission speed can be improved by several times the maximum number of antennas through spatial multiplexing at the same time and on the same frequency resource. However, since line-of-sight communication is fundamental in high-frequency bands, when applying MIMO technology, the spatial correlation between multiple antennas for transmission and reception increases, making spatial multiplexing difficult.

[0011] Therefore, in high-frequency bands, distributed antenna systems that have an effect of improving shielding resistance and reducing spatial correlation have been studied (see, for example, Non-Patent Documents 4 and 5). FIG. 37 is a diagram showing the configuration of a wireless communication system 500a, which is an example of a high-frequency band distributed antenna system. Similar to the wireless communication system 500 in FIG. 36, there are five cells 100-1 to 100-5 in the wireless communication system 500a. However, unlike the wireless communication system 500, the wireless communication system 500a has a configuration in which a plurality of antennas are distributed and installed for one cell. Hereinafter, each of the plurality of antennas distributed and installed is referred to as a distributed antenna. Looking at cell 100-1, distributed antenna devices 200a, ~200a-1-4, each having one distributed antenna, are distributed and installed, and one digital signal processing device 210a-1 is connected to the distributed antenna devices 200a-1-1 to 200a-1-4. In the wireless communication system 500a, the distributed antenna devices 200a-1-1 to 200a-1-4 and the digital signal processing device 210a-1 form a so-called base station device, and the same configuration is used in cells 100-2 to 100-5. In the wireless communication system 500a, when a terminal station is located in, for example, cell 100-1, the terminal station is connected by radio waves from a plurality of distributed antenna devices 200a-1-1 to 200a-1-4.

[0012] (Beam Selection Procedure in Distributed Antenna) By applying MIMO, i.e., single-user MIMO, between a radio station equipped with a plurality of antennas installed dispersedly, i.e., a distributed antenna, and a terminal station equipped with a plurality of antennas, spatial correlation is reduced and spatial multiplexing becomes possible. However, it is essential to select a beam in advance in the link between each of the plurality of antennas of the radio station and each of the plurality of antennas of the terminal station. In the following description, MIMO between a radio station equipped with a distributed antenna and a terminal station equipped with a plurality of antennas is referred to as distributed MIMO.

[0013] Here, a general transmission beam selection method for performing distributed MIMO in a high-frequency band will be described. A beam search signal in which a beam ID associated with each of a plurality of candidate beams set discretely in advance for each of the plurality of transmission antennas of the radio station and an antenna ID associated with each of the plurality of transmission antennas are embedded as digital information is generated in a plurality for each combination of the beam ID and the antenna ID. Each of the generated plurality of beam search signals is transmitted on a transmission beam in which the transmission antenna corresponding to the antenna ID included therein is switched over time and is superimposed on the transmission beam corresponding to the beam ID included therein.

[0014] The terminal station on the communication partner side receives a plurality of beams with each of a plurality of receiving antennas, reads out the beam ID included in the beam search signal of each of the received plurality of beams and the transmission antenna ID, and measures the reception quality of the received beam. The terminal station selects the beam ID with the best reception quality for each transmission antenna ID, and feeds back data combining the transmission antenna ID, the beam ID selected for the transmission antenna ID, and the reception quality corresponding to the beam ID to the wireless station on the transmission side. The wireless station that has received this feedback selects a plurality of transmission beams corresponding to the number of spatial multiplexing by MIMO based on the reception quality. In addition, the terminal station on the communication partner side sequentially selects a plurality of received beams by reception-side beam selection. As a result, in the high-frequency band, transmission and reception by MIMO between a plurality of transmission and reception beams becomes possible.

[0015] It is assumed that distributed MIMO is applied to the wireless communication system 500a shown in FIG. 37. For example, when one terminal station is located in cell 100-1, each of the plurality of distributed antenna devices 200a-1-1 to 200a-1-4 located in cell 100-1 performs a beam search for transmitting a beam search signal to the terminal station, and it is necessary to select the beam with the best reception quality from among the plurality of beams obtained by the beam search. Therefore, in the wireless communication system 500a, the overhead increases for the number of beam searches of the distributed antenna devices 200a-1-1 to 200a-1-4, and the efficiency of data transmission decreases. That is, the problem is that the overhead increases by increasing the distributed antenna devices 200a-1-1 to 200a-1-4.

[0016] Regarding the problem of this increase in overhead, for example, a method of storing the combination of beams selected for each of the plurality of distributed antennas and reducing the number of beam searches based on the history of the beam combination is disclosed in Non-Patent Document 6.

[0017] FIG. 38 and FIG. 39 are diagrams showing an overview of the technology disclosed in Non-Patent Document 6. In the wireless communication system 500b shown in FIG. 38(a), there is a cell 100 corresponding to any one of the cells 100-1 to 100-5 in the wireless communication system 500a shown in FIG. 37. In the cell 100, three distributed antenna devices 200a-1 to 200a-3 are distributed and installed, and one digital signal processing device 210 is connected to the distributed antenna devices 200a-1 to 200a-3. The communication control device 220 stores the history of the combination of beams selected for the plurality of distributed antenna devices 200a-1 to 200a-3. The communication control device 220 is a device that executes a method for reducing the number of beam searches based on the history of the combination of beams, and is connected to the digital signal processing device 210. In the cell 100, there is one terminal device 300 corresponding to the above-described terminal station, and it moves within the cell 100.

[0018] In the high frequency band, due to large free space propagation loss and diffraction loss and the use of beamforming, a small number of paths centered on the line-of-sight wave become dominant. Therefore, the beam combination selected by each of the distributed antenna devices 200a-1 to 200a-3 for distributed MIMO is a limited combination at each position of the terminal device 300. Therefore, one of the distributed antenna devices 200a-1 to 200a-3 transmits a beam with a beam search signal placed in all directions that can be transmitted. One beam selected based on the beam search signal and the beams of the other distributed antenna devices 200a-1 to 200a-3 that were selected in combination in the past are used as candidate beams, and the number of beam searches can be reduced by performing a partial beam search only for the candidate beams. In order to perform this process of reducing the number of beam searches, the communication control device 220 performs two types of mode processes: a storage mode for storing the combination of beams selected for the distributed antenna devices 200a-1 to 200a-3, and a reference mode for reducing the number of beam searches based on the history of the combination of beams. FIG. 38 is a diagram showing an overview of the process in the storage mode, and FIG. 39 is a diagram showing an overview of the process in the reference mode.

[0019] In the memory mode, the communication control device 220 instructs the digital signal processing device 210 to transmit a beam with beam search signals in all directions that each of the distributed antenna devices 200a-1 to 200a-3 can transmit. When the terminal device 300 receives each of the beams with the beam search signals transmitted by each of the distributed antenna devices 200a-1 to 200a-3, it reads out the beam ID included in the beam search signal and measures the reception quality of the beam. The terminal device 300 determines for each of the distributed antenna devices 200a-1 to 200a-3 based on the value indicating the reception quality measured for which beam has the best reception quality, and transmits a feedback signal that allows the communication control device 220 to uniquely identify the beam ID with the best reception quality.

[0020] When the communication control device 220 acquires the feedback signal through the distributed antenna devices 200a-1 to 200a-3 and the digital signal processing device 210, it generates a record in the beam combination history table shown in Fig. 38(b) based on the acquired feedback signal. In the table shown in Fig. 38(b), "1" under the item "Antenna" indicates the distributed antenna device 200a-1, "2" indicates the distributed antenna device 200a-2, and "3" indicates the distributed antenna device 200a-3. The numbers with "#" in the table indicate the beam ID. For example, the record in the first row indicates that in each of the distributed antenna devices 200a-1 to 200a-3, the beams with beam IDs "#3", "#4", and "#5" were selected as the best beams. While the terminal device 300 moves within the cell 100 and the communication control device 220 repeatedly performs the processing in the memory mode, records of different combinations will be added in the row direction to the beam combination history table.

[0021] In the reference mode, as shown in, for example, FIG. 39(a), the communication control device 220 instructs the digital signal processing device 210 to transmit the beam of the beam search signal in all directions that can be transmitted to the distributed antenna device 200a-1. Thus, it is assumed that the beam with the beam ID "#3" is selected as the best beam in the distributed antenna device 200a-1. In this case, the communication control device 220 uses the beam with the beam ID "#3" of the distributed antenna device 200a-1 as the detection reference beam, and as shown in FIG. 39(b), detects the beam IDs "#4" and "#5", which indicate the beams of the distributed antenna device 200a-2 that have been selected in combination with the detection reference beam from the table of the beam combination history, as the beam IDs indicating the candidate beams. The communication control device 220 detects the beam IDs "#4", "#5", and "#6", which indicate the beams of the distributed antenna device 200a-3 that have been selected in combination with the detection reference beam, as the beam IDs indicating the candidate beams. The communication control device 220 instructs the digital signal processing device 210 to transmit the beam of the beam search signal in the directions corresponding to the beam IDs "#4" and "#5" to the distributed antenna device 200a-2. The communication control device 220 instructs the digital signal processing device 210 to transmit the beam of the beam search signal in the directions corresponding to the beam IDs "#4", "#5", and "#6" to the distributed antenna device 200a-3. In this way, without performing beam search in all directions that can be transmitted in the distributed antenna devices 200a-2 and 200a-3, the beam search is narrowed down to the candidate beams and partially performed, so that the number of beam searches can be reduced.

Prior Art Documents

Non-Patent Documents

[0022]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0023] The total number of combinations of the beams transmitted by the plurality of distributed antenna devices 200a-1 to 200a-3 is determined by the range where the terminal device 300 exists, the positions of the distributed antenna devices 200a-1 to 200a-3, the angular interval of the discrete beams transmitted by the distributed antenna devices 200a-1 to 200a-3, and the like. Therefore, when the communication control device 220 performs the process in the storage mode, for example, in an area such as the area indicated by reference numeral 400 in FIG. 40, in the vicinity of an area where the terminal device 300 did not exist in the past, it may not be possible to acquire candidate beams that have been selected in combination with the detection reference beam. In this case, since a sufficient number of records are not accumulated in the table of the beam combination history, appropriate beam search and beam selection may not be possible, and in such a case, the transmission capacity may decrease. In order not to decrease the transmission capacity, for example, as shown in FIG. 41, when performing the process in the storage mode, the terminal device 300 is moved little by little at intervals that do not decrease the transmission capacity over the entire cell 100 that is the service providing area, and a sufficient number of records are accumulated in the table of the beam combination history. As a method for accumulating a sufficient number of records, for example, there are a method performed by a service provider and a method performed using the user's terminal device 300.

[0024] When performed by a service provider, there is a problem that it is very costly to move the terminal device 300 little by little at intervals that do not decrease the transmission capacity over the entire cell 100 that is the service providing area. On the other hand, when using the user's terminal device 300, the cost can be suppressed, but there is a low possibility that the user moves in an ideal manner on the operator side of the wireless communication system 500b. Therefore, when using the user's terminal device 300, there is a problem that it takes an enormous amount of time to obtain a sufficient number of records. In particular, as the carrier frequency increases, the beam width decreases. Therefore, in order not to decrease the transmission capacity, it is necessary to shorten the length of the interval when moving the terminal device 300, and the time required to obtain a sufficient number of records will further increase.

[0025] Therefore, when performing beam search processing, it is required to be able to accumulate a sufficient number of records for reducing the number of beam searches without reducing the transmission capacity, without generating records showing the history of beam combinations by moving the terminal devices little by little at intervals that do not reduce the transmission capacity throughout the service area in advance. For such a problem, for example, a method of defining a search period (mode) and recording the communication quality in the search period as a history for each beam combination can be considered. Also, for example, a method of measuring the communication quality at any time without providing a search period and updating the communication quality history for each beam combination each time the measurement is performed can be considered.

[0026] However, in the above method, it is assumed that the processing is performed with the order of the radio stations (outdoor stations) and distributed antenna devices performing beam search fixed. In such beam search with the processing order fixed, even if the beam search is repeated, the combination of beams to be searched may be fixed in a state deviated from the combination of beams that can actually obtain the best quality.

[0027] In view of the above circumstances, an object of the present invention is to provide a technique capable of reducing the number of beam searches while preventing the fixation of the combination of beams searched in beam search in a distributed antenna system.

Means for Solving the Problems

[0028] One aspect of the present invention is that, in a beam search period for searching for a beam used for wireless communication with a terminal device, for each of a plurality of distributed antennas, a full beam search is performed by transmitting beams in all directions that can be transmitted, and the full beam search is performed in an order of the distributed antennas that is different for each beam search period. When one beam identifier indicating the best beam among the beams obtained by the full beam search is acquired, the full beam search is stopped, and a beam specified by the acquired beam identifier and information indicating the distributed antenna that transmitted the beam indicated by the beam identifier is set as a detection reference beam. A candidate beam detector that detects, from a beam combination history storage unit, a beam identifier of a beam that is a beam identifier of a distributed antenna that has not performed the full beam search during the beam search period and that has been selected together with the detection reference beam as a candidate beam identifier for the distributed antenna; a beam search execution determination unit that determines whether to perform a full beam search for the distributed antennas that have not performed the full beam search during the beam search period based on the detection result of the candidate beam detector; and a beam combination recorder that generates a record indicating a combination of beam identifiers indicating the beams that have been the best beams in each of the distributed antennas during the beam search period and records the generated record in the beam combination history storage unit.

[0029] One aspect of the present invention is a wireless communication system including a terminal device, a plurality of distributed antenna devices each including one distributed antenna, and a communication control device. In a beam search period for searching for a beam used for wireless communication with the terminal device, the communication control device performs a full beam search in which beams are transmitted in all directions that can be transmitted for each of the plurality of distributed antennas in a different order of the distributed antennas for each beam search period. When one beam identifier indicating the best beam among the beams obtained by the full beam search is acquired, the full beam search is stopped, and a beam specified by the acquired beam identifier and information indicating the distributed antenna that transmitted the beam indicated by the beam identifier is set as a detection reference beam. A candidate beam detector that detects, from a beam combination history storage unit, a beam identifier of a beam that is a beam identifier of a distributed antenna that has not performed the full beam search during the beam search period and has been selected together with the detection reference beam as a candidate beam identifier for the distributed antenna; a beam search execution determination unit that determines whether to perform a full beam search for the distributed antennas that have not performed the full beam search during the beam search period based on the detection result of the candidate beam detector; and a beam combination recorder that generates a record indicating a combination of beam identifiers indicating the beams that have been the best beams in each of the distributed antennas during the beam search period and records the generated record in the beam combination history storage unit.

[0030] In one aspect of the present invention, during a beam search period for searching for a beam used for wireless communication with a terminal device, for each of a plurality of distributed antennas, a full beam search is performed by transmitting beams in all directions that can be transmitted. The full beam search is performed in an order of the distributed antennas that is different for each beam search period. When one beam identifier indicating the best beam among the beams obtained by the full beam search is acquired, the full beam search is stopped, and a beam specified by the acquired beam identifier and information indicating the distributed antenna that transmitted the beam indicated by the beam identifier is set as a detection reference beam. A candidate beam detection step of detecting, from a beam combination history storage unit, a beam identifier of a beam that is a beam identifier of a distributed antenna that has not performed the full beam search during the beam search period and that has been selected together with the detection reference beam as a candidate beam identifier for the distributed antenna; a beam search execution determination step of determining whether to perform a full beam search for the distributed antennas that have not performed the full beam search during the beam search period based on the detection result of the candidate beam detection step; and a beam combination recording step of generating a record indicating a combination of beam identifiers indicating the beams that are the best beams in each of the distributed antennas during the beam search period and recording the generated record in the beam combination history storage unit. This is a communication control method including these steps.

[0031] One aspect of the present invention is to cause a computer, during a beam search period for searching for a beam used for wireless communication with a terminal device, to perform a full beam search in which beams are transmitted in all directions that can be transmitted for each of a plurality of distributed antennas in a different order of the distributed antennas for each beam search period. When one beam identifier indicating the best beam among the beams obtained by the full beam search is acquired, the full beam search is stopped, and a beam specified by the acquired beam identifier and information indicating the distributed antenna that transmitted the beam indicated by the beam identifier is set as a detection reference beam. A candidate beam detection step of detecting, from a beam combination history storage unit, a beam identifier of a beam that is a beam identifier of a distributed antenna that has not performed the full beam search during the beam search period and that has been selected together with the detection reference beam as a candidate beam identifier for the distributed antenna; A beam search execution determination step of determining whether or not to perform a full beam search on the distributed antennas that have not performed the full beam search during the beam search period based on the detection result of the candidate beam detection step; A beam combination recording step of generating a record indicating a combination of beam identifiers indicating the beams that are the best beams in each of the distributed antennas during the beam search period and recording the generated record in the beam combination history storage unit. It is a program for causing

Effect of the Invention

[0032] According to the present invention, in beam search in a distributed antenna system, it is possible to reduce the number of beam searches while preventing the fixation of the combination of beams to be searched.

Brief Description of the Drawings

[0033]

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Embodiments for Carrying Out the Invention

[0034] (First Embodiment) Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an example of the configuration of a wireless communication system 1 in the first embodiment. The wireless communication system 1 includes at least one cell 100. Inside the area of the cell 100, distributed antenna devices 30-1, 30-2, 30-3, 30-4 and a terminal device 40 are provided. The wireless communication system 1 includes a communication control device 10 and a digital signal processing device 20. The communication control device 10 is connected to the digital signal processing device 20. The digital signal processing device 20 is connected to each of the distributed antenna devices 30-1 to 30-4. The communication control device 10, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4 will constitute a so-called base station device.

[0035] Note that the wireless communication system 1 shown in FIG. 1 is a configuration as an example. The wireless communication system 1 may be configured such that a plurality of distributed antenna devices 30-1 to 30-N are installed in the cell 100 and the digital signal processing device 20 is connected to each of the distributed antenna devices 30-1 to 30-N. Here, N is an integer of 2 or more. The wireless communication system 1 may have a configuration as shown in FIG. 18, that is, a configuration including a plurality of cells 100. In this case, the wireless communication system 1 includes the digital signal processing devices 20 and the communication control device 10 in a number corresponding to the number of cells 100. Each of the communication control devices 10 is connected to the corresponding digital signal processing device 20, and each of the digital signal processing devices 20 is connected to the distributed antenna devices 30-1 to 30-N in the corresponding cell 100.

[0036] Each of the distributed antenna devices 30-1 to 30-4 is capable of beamforming to switch directions and form a radio wave beam, and is connected to the terminal device 40 by radio waves. In FIG. 1, as an example, an example in which the distributed antenna devices 30-1 to 30-4 form beams in nine directions is shown. However, the number of directions in which the distributed antenna devices 30-1 to 30-4 can form beams may be two or more. The maximum number of directions in which the distributed antenna devices 30-1 to 30-4 can form beams is predetermined according to the specifications of the distributed antenna devices 30-1 to 30-4, and the operator may be able to arbitrarily determine the number of beams. Each of the distributed antenna devices 30-1 to 30-4 includes one distributed antenna 31-1 to 31-4 and one main body device 32-1 to 32-4. Each of the distributed antennas 31-1 to 31-4 is pre-assigned a distributed antenna ID that can uniquely identify each of them.

[0037] Each of the main body devices 32-1 to 32-4 transmits and receives radio frequency analog signals through the distributed antennas 31-1 to 31-4 connected to each of them. That is, each of the main body devices 32-1 to 32-4 modulates a carrier wave based on the digital signal of the transmission data output by the digital signal processing device 20 to generate a radio frequency analog signal. Each of the main body devices 32-1 to 32-4 transmits the generated analog signal by radio waves from the distributed antennas 31-1 to 31-4 connected to each of them. Each of the main body devices 32-1 to 32-4 demodulates the analog signal output when the distributed antennas 31-1 to 31-4 connected to each of them receive radio waves and converts it into a digital signal. Each of the main body devices 32-1 to 32-4 outputs the converted digital signal to the digital signal processing device 20.

[0038] From the perspective of beamforming, each of the main body devices 32-1 to 32-4 captures the digital signal of the beam search signal as the transmission data output by the digital signal processing device 20. Each of the main body devices 32-1 to 32-4 modulates the carrier wave based on the beam search signal so as to form a beam in the direction corresponding to the beam ID included in the captured beam search signal. Each of the main body devices 32-1 to 32-4 transmits the analog signal of the radio frequency with the beam search signal generated by modulation through the distributed antennas 31-1 to 31-4 connected to each of them.

[0039] Here, the beam ID is an identifier to which a character string "Beam ID#" is assigned to a continuous integer value starting from, for example, 1, and is an identifier predetermined for each of the distributed antenna devices 30-1 to 30-4. For example, when the distributed antenna device 30-1 can form beams in 40 different directions, beam IDs from "Beam ID#1" to "Beam ID#40" are fixedly assigned in advance to each of the 40-direction beams, and the data indicating the correspondence between the beam ID and the direction is stored in advance in the storage area inside the main body device 32-1. In other words, when "Beam ID#1" is specified by the beam search signal for the main body device 32-1 of the distributed antenna device 30-1, the direction of the beam formed by the distributed antenna 31-1 of the distributed antenna device 30-1 is uniquely determined. This is the same for the other distributed antenna devices 30-2 to 30-4. In this case, there may be the same beam ID in each of the distributed antenna devices 30-1 to 30-4.

[0040] The digital signal processing device 20 outputs the digital signal of the transmission data to the main body devices 32-1 to 32-4. When the digital signal processing device 20 receives a beam search instruction signal from the communication control device 10, it uses the distributed antenna ID included in the beam search instruction signal as the transmission source antenna ID, and generates a beam search signal including the transmission source antenna ID and the beam ID included in the beam search instruction signal. The digital signal processing device 20 outputs the generated beam search signal to the main body devices 32-1 to 32-4 corresponding to the distributed antenna ID included in the beam search instruction signal. Thereby, the terminal device 40 that receives the beam with the beam search signal can identify the distributed antennas 31-1 to 31-4 of the transmission source of the beam search signal by referring to the transmission source antenna ID included in the beam search signal, and further, can identify the beam on which the beam search signal is carried by referring to the beam ID included in the beam search signal.

[0041] The digital signal processing device 20 detects the received data included in the digital signal from the digital signal output by the main body devices 32-1 to 32-4. When the detected received data is a feedback signal transmitted by the terminal device 40 on a radio wave, the digital signal processing device 20 outputs the feedback signal to the communication control device 10.

[0042] (Configuration of the communication control device according to the first embodiment) As shown in FIG. 2, the communication control device 10 includes a beam search execution instruction unit 11, a feedback signal reception unit 12, a beam combination history generation unit 13, a beam combination history storage unit 14, a candidate beam detection unit 15, a beam search execution determination unit 16, and a beam combination recording unit 17.

[0043] The beam search execution instruction unit 11 causes each of the distributed antenna devices 30-1 to 30-4 to perform a full beam search in which beams are transmitted by switching time for each of all directions in which each can transmit, or causes a partial beam search in which beams are transmitted by switching time for one or a plurality of specific directions, via the digital signal processing device 20. The beam search execution instruction unit 11 stores in advance in its internal storage area a beam number table 110 shown in FIG. 3. The beam number table 110 has items of "distributed antenna ID" and "maximum beam ID". In the item of "distributed antenna ID", "distributed antenna ID #1", "distributed antenna ID #2", "distributed antenna ID #3", and "distributed antenna ID #4", which are the distributed antenna IDs assigned to each of the distributed antennas 31-1 to 31-4, are written in advance. Here, "distributed antenna ID #1" corresponds to the distributed antenna ID assigned to the distributed antenna 31-1, "distributed antenna ID #2" corresponds to the distributed antenna ID assigned to the distributed antenna 31-2, "distributed antenna ID #3" corresponds to the distributed antenna ID assigned to the distributed antenna 31-3, and "distributed antenna ID #4" corresponds to the distributed antenna ID assigned to the distributed antenna 31-4.

[0044] In the item of "maximum beam ID", the maximum value of the beam ID for each of the distributed antennas 31-1 to 31-4, that is, the number of transmission directions of the beams that each of the distributed antennas 31-1 to 31-4 can transmit, is written in advance. In FIG. 3, the values of the "maximum beam ID" of the distributed antennas 31-1 to 31-4 are all set to "40", but different values may be used.

[0045] When the beam search execution instruction unit 11 receives all beam search request signals including the distributed antenna ID, it refers to the beam number table 110 and reads out the maximum beam ID value corresponding to the distributed antenna ID included in all beam search request signals. The beam search execution instruction unit 11 generates beam search instruction signals in a number that matches the read maximum beam ID value, and each beam ID included in each of them is different, and includes beam ID signals one by one from 1 to the maximum beam ID value. The beam search execution instruction unit 11 writes the distributed antenna ID included in all beam search request signals to each of the generated beam search instruction signals.

[0046] For example, when the beam search execution instruction unit 11 receives all beam search request signals with the distributed antenna ID being "Distributed Antenna ID #1", it will generate 40 beam search instruction signals. More specifically, since the beam search execution instruction unit 11 generates "Beam ID #1" to "Beam ID #40", each of the 40 generated beam search instruction signals will include ("Distributed Antenna ID #1", "Beam ID #1"), ("Distributed Antenna ID #1", "Beam ID #2"), …, ("Distributed Antenna ID #1", "Beam ID #40"). Note that "Beam ID #1" to "Beam ID #40" generated by the beam search execution instruction unit 11 are fixedly associated in advance with each of the 40-direction beams formed by the distributed antenna 31-1 in the main body device 32-1 of the distributed antenna device 30-1 as described above. Therefore, the process of generating beam IDs performed by the beam search execution instruction unit 11 is not to generate and associate new beam IDs with the directions of the beams transmitted by the distributed antenna device 30-1 again, but simply to perform the process of generating beam IDs for all directions.

[0047] When the beam search execution instruction unit 11 receives a partial beam search request signal including a distributed antenna ID and one or more beam IDs, it generates beam search instruction signals in a number corresponding to the number of beam IDs included in the partial beam search request signal. The beam search execution instruction unit 11 writes the beam IDs included in the partial beam search request signal one by one to each of the generated beam search instruction signals so that all the beam IDs included in each of the generated beam search instruction signals are different beam IDs. The beam search execution instruction unit 11 writes the distributed antenna ID included in the partial beam search request signal to each of the generated beam search instruction signals. The beam search execution instruction unit 11 outputs the beam search instruction signals generated by receiving the full beam search request signal or the partial beam search request signal to the digital signal processing device 20 one by one in the order of generation at a predetermined fixed time interval.

[0048] When the beam combination history generation unit 13 starts the beam combination generation process for generating beam combinations, for each trial period, it causes all of the distributed antenna devices 30-1 to 30-4 to perform a full beam search, thereby generating a record indicating a combination of beam IDs indicating the beams that are the best beams in each of the distributed antenna devices 30-1 to 30-4.

[0049] The beam combination history storage unit 14 stores, for example, the beam combination history table 140 shown in FIG. 4. As shown in FIG. 4, the beam combination history table 140 has an item of "distributed antenna ID" on the horizontal axis and an item of "record ID" on the vertical axis. In the item of "distributed antenna ID", "distributed antenna ID #1", "distributed antenna ID #2", "distributed antenna ID #3", and "distributed antenna ID #4", which are the distributed antenna IDs assigned to each of the distributed antennas 31-1 to 31-4, are written in advance.

[0050] In the "Record" item, a record ID is written, which is given to the records generated for each trial period and each has a different identifier. For example, "Record ID #1" is the record ID given to the record generated in the first trial period, and "Record ID #2" is the record ID given to the record generated in the second trial period. Information indicating the beam ID is written in each element specified by the distributed antenna ID on the horizontal axis and the record ID on the vertical axis. That is, the "Beam ID #23" of the element of "Record 1" of "Distributed Antenna ID #1" indicates that the beam ID of the beam determined to be the best in the distributed antenna device 30-1 in the first trial period is "Beam ID #23".

[0051] When receiving an output destination switching instruction signal, the feedback signal receiving unit 12 sets any one of the beam combination history generation unit 13, the candidate beam detection unit 15, and the beam search execution determination unit 16 specified by the output destination switching instruction signal as the output destination of the feedback signal. When the feedback signal receiving unit 12 captures the feedback signal output by the digital signal processing device 20, it outputs the captured feedback signal to the set output destination.

[0052] When the beam search process for searching for a beam starts, the candidate beam detection unit 15 causes each of the distributed antenna devices 30-1 to 30-4 to perform a full beam search one by one in order. That is, the candidate beam detection unit 15 sequentially designates one by one the distributed antenna IDs of the distributed antennas 31-1 to 31-4, and outputs a full beam search request signal including the designated one distributed antenna ID to the beam search execution instruction unit 11. After starting the beam search process, when the candidate beam detection unit 15 captures the first feedback signal, it stops the full beam search, and sets the beam specified by the transmission source antenna ID and the beam ID included in the feedback signal as the detection reference beam. The candidate beam detection unit 15 detects, from the beam combination history table 140, the beam IDs of the distributed antenna devices 30-1 to 30-4 that have not performed a full beam search during the beam search period, which are the beam IDs of the beams that have been selected together with the detection reference beam, and the distributed antenna IDs corresponding to the beam IDs. Here, the beam search period is, for example, the time allocated to one round of processing of the beam search process. The beam search process is a periodically performed process, and this period is referred to as the beam search period. In each of the beam search periods, there are a beam search period in which one round of the beam search process is performed, and a data transmission period that is performed between the distributed antennas 31-1 to 31-4 of the distributed antenna devices 30-1 to 30-4 and the terminal antennas 41-1 to 41-M of the terminal device 40 after the beam search period. Note that the above-mentioned "beam search period" and the "beam search period" described below refer to the one-round beam search period included in the period of one beam search cycle, unless otherwise specified as having a different meaning. The candidate beam detection unit 15 sets the detected beam ID as the beam ID (hereinafter also referred to as the candidate beam ID) indicating the candidate beam in the distributed antenna devices 30-1 to 30-4 corresponding to the detected distributed antenna ID, and sets the combination of the detected distributed antenna ID and the candidate beam ID as the detection result.

[0053] Based on the detection results of the candidate beam detection unit 15, the beam search execution determination unit 16 determines whether to cause the distributed antenna devices 30-1 to 30-4 that have not performed full beam search during the beam search period to perform full beam search. More specifically, the beam search execution determination unit 16 determines, as the distributed antenna devices 30-1 to 30-4 that will perform full beam search, the distributed antenna devices 30-1 to 30-4 that have not performed full beam search during the beam search period and whose detection results do not include the candidate beam ID in the detection results of the candidate beam detection unit 15.

[0054] For the distributed antenna devices 30-1 to 30-4 whose detection results of the candidate beam detection unit 15 include the candidate beam ID, the beam search execution determination unit 16 causes them to perform partial beam search using the candidate beam ID included in the detection results. That is, the beam search execution determination unit 16 outputs a partial beam search request signal including the distributed antenna ID and the candidate beam ID included in the detection results to the beam search execution instruction unit 11. Based on the received power value included in the feedback signal transmitted by the terminal device 40 that has received the beam by partial beam search and a predetermined threshold value, the beam search execution determination unit 16 determines whether to cause the distributed antenna devices 30-1 to 30-4 corresponding to the transmission source antenna ID included in the feedback signal to perform full beam search. When the beam search execution determination unit 16 determines to perform full beam search, it designates the transmission source antenna ID included in the feedback signal to be determined. The beam search execution determination unit 16 outputs a full beam search request signal including the designated transmission source antenna ID to the beam search execution instruction unit 11.

[0055] During the beam search period, the beam combination recording unit 17 generates one record based on the combination of the beam ID of the beam finally determined to be the best beam in each of the distributed antenna devices 30-1 to 30-4 and the transmission source antenna ID corresponding to the beam ID. The beam combination recording unit 17 assigns a new record ID to the generated one record and writes it into the beam combination history table 140.

[0056] (Configuration of the terminal device according to the first embodiment) FIG. 5 is a block diagram showing the configuration of the terminal device 40. The terminal device 40 includes M terminal antennas 41-1 to 41-M, an analog signal transceiver unit 42, a digital signal processing unit 43, a beam search signal receiving unit 44, an optimal beam selection unit 45, and a feedback signal generation unit 46. Here, M is an integer of 2 or more. Wireless communication by distributed MIMO is performed between the terminal antennas 41-1 to 41-M and the distributed antennas 31-1 to 31-4 included in each of the distributed antenna devices 30-1 to 30-4.

[0057] The analog signal transceiver unit 42 modulates a carrier wave based on the digital signal of the transmission data output by the digital signal processing unit 43 to generate an analog signal of a radio frequency. The analog signal transceiver unit 42 transmits the generated analog signal as radio waves through the terminal antennas 41-1 to 41-M. The analog signal transceiver unit 42 demodulates the analog signal output when the terminal antennas 41-1 to 41-M receive radio waves and converts it into a digital signal. The analog signal transceiver unit 42 outputs the converted digital signal to the digital signal processing unit 43. The analog signal transceiver unit 42 measures the received power of the beam received by the terminal antennas 41-1 to 41-M. The analog signal transceiver unit 42 outputs the received power value obtained by the measurement to the digital signal processing unit 43 in association with the digital signal corresponding to the beam to be measured.

[0058] The digital signal processing unit 43 outputs the digital signal of the feedback signal output by the feedback signal generation unit 46 to the analog signal transceiver unit 42. The digital signal processing unit 43 takes in the digital signal output by the analog signal transceiver unit 42 and the received power value associated with the digital signal. The digital signal processing unit 43 associates the received power value taken in with the beam search signal included as reception data in the taken-in digital signal and outputs it to the beam search signal receiving unit 44.

[0059] The beam search signal receiving unit 44 captures the beam search signal output by the digital signal processing unit 43 and the received power value associated with the beam search signal. The beam search signal receiving unit 44 combines the transmission source antenna ID and beam ID included in the captured beam search signal with the captured received power value, writes the combination as a set of data into an internal storage area, and stores it. When the beam search signal receiving unit 44 captures all the beam search signals for any one of the distributed antenna devices 30-1 to 30-4, among the data stored in the internal storage area, it detects and reads out all the data including the transmission source antenna ID corresponding to the distributed antenna devices 30-1 to 30-4 that have captured all the beam search signals. The beam search signal receiving unit 44 outputs all the read data as a set of data to the best beam selection unit 45.

[0060] The best beam selection unit 45 captures a set of data output by the beam search signal receiving unit 44. The best beam selection unit 45 selects the data corresponding to the maximum received power value among the captured set of data. In other words, the best beam selection unit 45 selects the beam indicated by the beam ID corresponding to the selected maximum received power value as the best beam in the distributed antenna devices 30-1 to 30-4 corresponding to the transmission source antenna ID. The best beam selection unit 45 outputs the transmission source antenna ID, beam ID, and received power value included in the selected data to the feedback signal generation unit 46. The feedback signal generation unit 46 generates a feedback signal including the transmission source antenna ID, beam ID, and received power value output by the best beam selection unit 45. The feedback signal generation unit 46 outputs the generated feedback signal to the digital signal processing unit 43.

[0061] (Processing by the terminal device according to the first embodiment) The processing by the terminal device 40 will be described with reference to FIGS. 6 and 7. FIG. 6 is a flowchart showing the flow of processing performed when the terminal device 40 receives the beams transmitted by the distributed antenna devices 30-1 to 30-4.

[0062] The analog signal transceiver unit 42 waits for reception of the beams transmitted by the distributed antennas 31-1 to 31-4 of the distributed antenna devices 30-1 to 30-4 (step Sta1), and repeatedly determines whether or not it has received a beam through the terminal antennas 41-1 to 41-M (step Sta2). When the analog signal transceiver unit 42 determines that it has not received a beam (step Sta2, No), it continues the process of step Sta1, that is, waits for reception of a beam.

[0063] On the other hand, when the analog signal transceiver unit 42 determines that it has received a beam (step Sta2, Yes), it measures the reception power of the beam received through the terminal antennas 41-1 to 41-M. The analog signal transceiver unit 42 converts the received beam into a digital signal. The analog signal transceiver unit 42 associates the reception power value obtained by measurement with the digital signal obtained by the conversion and outputs the result to the digital signal processing unit 43. The digital signal processing unit 43 takes in the digital signal output by the analog signal transceiver unit 42 and the reception power value associated with the digital signal. The digital signal processing unit 43 detects reception data from the taken-in digital signal, thereby obtaining a beam search signal included as reception data in the digital signal. The digital signal processing unit 43 associates the obtained beam search signal with the taken-in reception power value and outputs the result to the beam search signal reception unit 44.

[0064] The beam search signal reception unit 44 takes in the beam search signal output by the digital signal processing unit 43 and the reception power value associated with the beam search signal. The beam search signal reception unit 44 reads out the transmission source antenna ID and the beam ID included in the taken-in beam search signal (step Sta3).

[0065] The beam search signal receiving unit 44 is capable of generating a plurality of timers internally, and determines whether the read transmission source antenna ID is associated with any of the timers (step Sta4). If the beam search signal receiving unit 44 determines that the read transmission source antenna ID is not associated with any of the timers (step Sta4, No), it generates and activates one timer in association with the read transmission source antenna ID. When activating the timer, the beam search signal receiving unit 44 sets, in the timer, the time required for all the distributed antenna devices 30-1 to 30-4 that transmit the largest number of beams to transmit all the beams. Note that this time is a predetermined time (step Sta5).

[0066] On the other hand, when the beam search signal receiving unit 44 determines that the read transmission source antenna ID is associated with any of the timers (step Sta4, Yes), or after the process of step Sta5, it combines the read transmission source antenna ID and beam ID with the captured received power value to form a set of data, and writes and stores the set of data in an internal storage area (step Sta6). Thereafter, the processes after step Sta1 are repeatedly performed.

[0067] Putting it another way for the determination process in step Sta4 above, in this determination process, the beam search signal receiving unit 44 determines whether the captured beam search signal is the first beam search signal in the full beam search or partial beam search performed by each of the distributed antenna devices 30-1 to 30-4, based on whether a timer is activated or not. If a timer is not generated in association with the transmission source antenna ID included in the beam search signal captured by the beam search signal receiving unit 44, the beam search signal is the first beam search signal, and if a timer is generated, the beam search signal is the beam search signal after the second time.

[0068] FIG. 7 is a flowchart showing the flow of processing performed when the timer started by the beam search signal receiving unit 44 expires. The beam search signal receiving unit 44 waits for the expiration of the timer started in the process of step Sta5 in FIG. 6. It is assumed that the timer outputs a timer expiration notification signal when the measured time reaches the set time (step Stb1).

[0069] The beam search signal receiving unit 44 repeatedly determines whether it has received a timer expiration notification from any of the timers (step Stb2). If it determines that it has not received a timer expiration notification (step Stb2, No), it continues the process of step Stb1, that is, waits for the expiration of the timer. On the other hand, when the beam search signal receiving unit 44 determines that it has received a timer expiration notification from any of the timers (step Stb2, Yes), it acquires the transmission source antenna ID associated with the expired timer and deletes the timer. The beam search signal receiving unit 44 detects and reads out all the data including the acquired transmission source antenna ID from the data stored in the internal storage area, that is, the data combining the transmission source antenna ID, the beam ID, and the received power value. After reading, the beam search signal receiving unit 44 deletes the data read from the internal storage area. The beam search signal receiving unit 44 outputs all the read data as a set of data to the best beam selection unit 45 (step Stb3).

[0070] The best beam selection unit 45 captures a set of data output by the beam search signal reception unit 44. The best beam selection unit 45 selects the data including the maximum received power value from the captured set of data (step Stb4). The best beam selection unit 45 outputs the transmission source antenna ID, beam ID, and received power value included in the selected data to the feedback signal generation unit 46. The feedback signal generation unit 46 captures the transmission source antenna ID, beam ID, and received power value output by the best beam selection unit 45, and generates a feedback signal including the captured transmission source antenna ID, beam ID, and received power value. The feedback signal generation unit 46 outputs the generated feedback signal to the digital signal processing unit 43 (step Stb5).

[0071] In the first embodiment, the feedback signal generation unit 46 does not necessarily include the received power value in the feedback signal. The feedback signal generation unit 46 may generate a feedback signal including only the captured transmission source antenna ID and beam ID. Similarly, in the third, fifth, seventh, and ninth embodiments described later, the feedback signal generation unit 46 does not necessarily include the received power value in the feedback signal.

[0072] The digital signal processing unit 43 captures the feedback signal output by the feedback signal generation unit 46. The digital signal processing unit 43 outputs the captured feedback signal to the analog signal transceiver unit 42. The analog signal transceiver unit 42 generates a radio frequency analog signal from the feedback signal output by the digital signal processing unit 43. The analog signal transceiver unit 42 transmits the generated analog signal by radio wave through the terminal antennas 41-1 to 41-M (step Stb6).

[0073] (Processing by the wireless communication system of the first embodiment) FIG. 8 is a flowchart showing the overall processing performed by the wireless communication system 1. In the communication control device 10, for example, in response to an operation by an operator who operates the wireless communication system 1, first, in order to generate the beam combination history table 140, the beam combination history generation unit 13 performs a beam combination generation process (step S1). When the beam combination generation process by the beam combination history generation unit 13 ends, in response to an operation by the operator, the candidate beam detection unit 15 starts a beam search process (step S2). When the beam search process ends, for example, between the communication device connected to the digital signal processing device 20 and the terminal device 40, data transmission processing using the beams of the distributed antenna devices 30-1 to 30-4 selected by the beam search process is started (step S3). During the data transmission process, the candidate beam detection unit 15 repeatedly determines whether a beam search cycle timer, which will be described later, has expired at regular intervals in order to determine whether the beam search cycle has elapsed (step S4). When the candidate beam detection unit 15 determines that the beam search cycle timer has not expired (step S4, No), the data transmission process continues. On the other hand, when the candidate beam detection unit 15 determines that the beam search cycle timer has expired (step S4, Yes), a data transmission end instruction signal for ending the data transmission process is output to the digital signal processing device 20. When receiving the data transmission end instruction signal, the digital signal processing device 20 stops outputting data to be transmitted to the distributed antenna devices 30-1 to 30-4. As a result, the data transmission process that has been performed between the communication device connected to the digital signal processing device 20 and the terminal device 40 via the distributed antenna devices 30-1 to 30-4 ends.

[0074] The operator determines whether to stop the beam search process by the communication control device 10 (step S5). If the operator determines not to stop the beam search process by the communication control device 10 (step S5, No), the process proceeds to step S2, and the candidate beam detection unit 15 starts the process for the next beam search cycle. On the other hand, if the operator determines to stop the beam search process by the communication control device 10 (step S5, Yes), the communication control device 10 is operated to stop the beam search process. Hereinafter, the details of the beam combination generation process in step S1 and the beam search process in step S2 will be described.

[0075] (Beam Combination Generation Process of the First Embodiment) FIG. 9 is a flowchart showing the flow of the beam combination generation process performed in the process of step S1 in FIG. 8. In response to the operation of the operator of the wireless communication system 1, the beam combination history generation unit 13 of the communication control device 10 starts the process for the first trial cycle of the beam combination generation process. The beam combination history generation unit 13 reads out all the distributed antenna IDs written in the distributed antenna ID item of the beam combination history table 140 stored in the beam combination history storage unit 14. The beam combination history generation unit 13 provides a counter i in its internal storage area and initializes it to i = 1. Here, i is an integer value from 1 to N. However, the wireless communication system 1 in FIG. 1 includes four distributed antenna devices 30-1 to 30-4. The beam combination history generation unit 13 reads out four distributed antenna IDs, namely, "Distributed Antenna ID #1", "Distributed Antenna ID #2", "Distributed Antenna ID #3", and "Distributed Antenna ID #4" from the beam combination history table 140. Therefore, hereinafter, the description will be made with N = 4. In the following description, the i-th distributed antenna device is the distributed antenna device 30-i, the i-th distributed antenna is the distributed antenna 31-i, and the i-th main body device is the main body device 32-i.

[0076] The beam combination history generation unit 13 outputs an output destination switching instruction signal whose output destination is the beam combination history generation unit 13 to the feedback signal reception unit 12. When the feedback signal reception unit 12 receives the output destination switching instruction signal whose output destination is the beam combination history generation unit 13 from the beam combination history generation unit 13, it sets the output destination of the feedback signal to the beam combination history generation unit 13.

[0077] In order to cause the distributed antenna device 30-i including the i-th distributed antenna 31-i to perform a full beam search, the beam combination history generation unit 13 outputs a full beam search request signal including the distributed antenna ID of the i-th distributed antenna 31-i to the beam search execution instruction unit 11. After the beam combination history generation unit 13 outputs the full beam search request signal to the beam search execution instruction unit 11, it activates a feedback signal timer provided therein. When activating the feedback signal timer, the beam combination history generation unit 13 sets the feedback signal timer to the time required to acquire the feedback signal from the full beam search performed by the distributed antenna devices 30-1 to 30-4 with the largest number of beams to be transmitted since the beam combination history generation unit 13 output the full beam search request signal to the beam search execution instruction unit 11. Note that the time is a predetermined time and is set in advance in the beam combination history generation unit 13.

[0078] The beam search execution instruction unit 11 captures the full beam search request signal output by the beam combination history generation unit 13 and reads out the distributed antenna ID of the i-th distributed antenna 31-i included in the captured full beam request instruction signal. The beam search execution instruction unit 11 reads out the maximum beam ID corresponding to the distributed antenna ID of the i-th distributed antenna 31-i read from the beam number table 110 in the internal storage area. Here, as an example, it is assumed that the beam search execution instruction unit 11 reads out "40" as the maximum beam ID.

[0079] The beam search execution instruction unit 11 generates beam search instruction signals that match the maximum value of the read beam IDs, that is, "40", and each contains a different beam ID from 1 to the maximum value of the beam IDs. The beam search execution instruction unit 11 writes the distributed antenna ID of the i-th distributed antenna 31-i read out to each of the generated beam search instruction signals. The beam search execution instruction unit 11 outputs the 40 generated beam search instruction signals to the digital signal processing device 20 one by one in the order of generation at a predetermined fixed time interval.

[0080] The digital signal processing device 20 sequentially captures the 40 beam search instruction signals output by the beam search execution instruction unit 11. The digital signal processing device 20 generates a beam search signal from the captured beam search instruction signal. The digital signal processing device 20 outputs the generated beam search signal to the i-th main body device 32-i corresponding to the distributed antenna ID included in the beam search instruction signal in the order of generation. The i-th main body device 32-i captures the beam search signal output by the digital signal processing device 20. The i-th main body device 32-i modulates the carrier wave based on the beam search signal so as to form a beam in the direction corresponding to the beam ID included in the captured beam search signal. The i-th main body device 32-i generates an analog signal of a radio frequency carrying the beam search signal generated by the modulation. By the i-th main body device 32-i outputting the generated analog signal of the radio frequency to the i-th distributed antenna 31-i, the i-th distributed antenna 31-i transmits a beam carrying the beam search signal in the direction of the beam ID included in the beam search signal (step Sa1).

[0081] The terminal device 40 receives all the beams transmitted by the distributed antenna 31-i. The terminal device 40 performs the processing described with reference to FIGS. 6 and 7 for each of the received beams. The distributed antenna 31-i receives the radio wave carrying the feedback signal transmitted by the terminal device 40. The distributed antenna 31-i outputs the received radio wave as an analog signal to the main body device 32-i. The main body device 32-i converts the analog signal including the feedback signal into a digital signal and outputs it to the digital signal processing device 20. The digital signal processing device 20 detects and acquires the feedback signal included in the digital signal output by the main body device 32-i. The digital signal processing device 20 outputs the acquired feedback signal to the feedback signal receiving unit 12 of the communication control device 10. The feedback signal receiving unit 12 takes in the feedback signal output by the digital signal processing device 20 and outputs it to the beam combination history generation unit 13 whose output destination is set.

[0082] The beam combination history generation unit 13 determines whether or not a feedback signal including the distributed antenna ID of the i-th distributed antenna 31-i as the transmission source antenna ID has been taken in before the time measured by the feedback signal timer reaches the time set in the feedback signal timer and the feedback signal timer expires (step Sa2).

[0083] When the beam combination history generation unit 13 determines that a feedback signal including the distributed antenna ID of the i-th distributed antenna 31-i as the transmission source antenna ID has been taken in before the feedback signal timer expires (step Sa2, Yes), the beam ID included in the taken-in feedback signal is set as the beam ID indicating the best beam in the i-th distributed antenna device 30-i. The beam combination history generation unit 13 writes and records the data obtained by combining the transmission source antenna ID included in the taken-in feedback signal and the beam ID in the internal storage area (step Sa3).

[0084] On the other hand, assume that the beam combination history generation unit 13 determines that it has not captured a feedback signal in which the distributed antenna ID of the i-th distributed antenna 31-i is included as the transmission source antenna ID before the feedback signal timer expires (step Sa2, No). Here, the case where the beam combination history generation unit 13 cannot capture the feedback signal means, for example, that there is no line of sight between the i-th distributed antenna 31-i and the terminal device 40, and the beam transmitted by the i-th distributed antenna 31-i does not reach the terminal device 40. When the beam transmitted by the i-th distributed antenna 31-i reaches the terminal device 40, but the reception level of the beam that has reached the terminal device 40 is lower than the reception sensitivity of the terminal device 40, the analog signal transceiver 42 of the terminal device 40 cannot demodulate it and discards it. When the reception level of the radio wave carrying the feedback signal transmitted by the terminal device 40 is lower than the reception sensitivity of the distributed antenna device 30-i, the main body device 32-i cannot demodulate it and discards it. When the transmission of the radio wave carrying the feedback signal is delayed due to a delay in the internal processing of the terminal device 40 or the like, and after the feedback signal timer expires, the feedback signal reception unit 12 outputs the feedback signal to the beam combination history generation unit 13. Such cases are assumed.

[0085] After the processing of step Sa3, or after making a "No" determination in the processing of step Sa2, if the value of i at that time is not N (here, N = 4), the beam combination history generation unit 13 sets the value obtained by adding 1 to i as the new value of i, and the processing of steps Sa1 to Sa3 is performed again (loops La1s to La1e). When the value of i at that time is N (here, N = 4), the beam combination history generation unit 13 ends the processing of loops La1s to La1e. The beam combination history generation unit 13 reads all the data written in the internal storage area, and after reading, deletes all the data from the internal storage area. The beam combination history generation unit 13 generates a record indicating the best beam combination in the distributed antenna devices 30-1 to 30-4 based on all the read data (step Sa4).

[0086] The beam combination history generation unit 13 detects the number of records in the beam combination history table 140 that match the combination of beam IDs in the generated record from the combination of beam IDs in the records already recorded in the beam combination history table 140, and determines whether the detected number is less than a predetermined number of records (step Sa5). When the beam combination history generation unit 13 determines that the detected number is less than the predetermined number of records (step Sa5, No), the beam combination history generation unit 13 generates a new row in the beam combination history table 140. The beam combination history generation unit 13 generates a new record ID. The beam combination history generation unit 13 writes the generated new record ID into the "Record ID" item of the new row. Based on the combination of the source antenna ID and the beam ID, the beam combination history generation unit 13 writes the corresponding beam ID into each element of "Distributed Antenna ID #1", "Distributed Antenna ID #2", "Distributed Antenna ID #3", and "Distributed Antenna ID #4" in the new row (step Sa6). Thereafter, as the processing for the next trial period, the beam combination history generation unit 13 performs the processing of loops La1s to La1e again.

[0087] On the other hand, assume that the beam combination history generation unit 13 determines that the detected number is not less than a predetermined number of records (step Sa5, Yes). In this case, during the beam combination generation process, it can be considered that within the range where the terminal device 40 has moved within the cell 100, the pattern of the best beam combination in the distributed antenna devices 30-1 to 30-4 has been sufficiently obtained. Therefore, the beam combination history generation unit 13 ends the process. Incidentally, before ending the process, if there are multiple records that are the same as the combination of beam IDs stored in the beam combination history table 140, the beam combination history generation unit 13 may delete all but one of the records. Also, in the beam combination generation process, even if the pattern of the best beam combination in the distributed antenna devices 30-1 to 30-4 has not been sufficiently obtained, the beam combination history generation unit 13 may perform the process of step Sa6 until the number of records stored in the beam combination history table 140 reaches a predetermined number of records, instead of the determination process of step Sa5, and when the predetermined number of records is reached, perform a determination process to end the process of FIG. 9. By doing so, it is possible to start the beam search process of step S2 in FIG. 8 in a state where the number of records stored in the beam combination history table 140 has reached a certain amount of records.

[0088] As a result, for example, when the beam combination history generation unit 13 repeats the processing of loops La1s to La1e M times, that is, when the trial period for M times ends, as shown in FIG. 4, M records are generated in the beam combination history table 140. Note that in the beam combination history table 140 shown in FIG. 4, beam IDs are not written in "Record ID#2", "Record ID#4", and "Record ID#6" of "Distributed Antenna ID#3". This indicates that in the trial periods of "Record ID#2", "Record ID#4", and "Record ID#6", any of the above events where the beam combination history generation unit 13 cannot capture the feedback signal occurred, and the beam combination history generation unit 13 could not acquire the feedback signal from all beam searches performed by the distributed antenna device 30-3 corresponding to "Distributed Antenna ID#3".

[0089] (Beam Search Processing of the First Embodiment) FIG. 10 is a flowchart showing the flow of the beam search processing performed in the processing of step S2 in FIG. 8. It is assumed that the beam combination history table 140 shown in FIG. 4 is generated in the beam combination history storage unit 14 as a premise for starting the beam search processing shown in FIG. 8.

[0090] In response to the operation of the operator of the wireless communication system 1, the candidate beam detection unit 15 of the communication control device 10 starts the beam search processing. The candidate beam detection unit 15 activates the beam search period timer provided therein. When activating the beam search period timer, the candidate beam detection unit 15 sets a time indicating the length of a preset one beam search period.

[0091] The candidate beam detection unit 15 reads out all the distributed antenna IDs written in the item of the distributed antenna ID in the beam combination history table 140 stored in the beam combination history storage unit 14. The candidate beam detection unit 15 provides a counter i in its internal storage area and initializes it to i = 1. Here, i is an integer value from 1 to N. However, the wireless communication system 1 in FIG. 1 includes four distributed antenna devices 30-1 to 30-4. The candidate beam detection unit 15 reads out four distributed antenna IDs, namely, "distributed antenna ID #1", "distributed antenna ID #2", "distributed antenna ID #3", and "distributed antenna ID #4" from the beam combination history table 140. Therefore, in the following description, N = 4 is assumed. In the following description, the i-th distributed antenna device is denoted as the distributed antenna device 30-i, the i-th distributed antenna is denoted as the distributed antenna 31-i, and the i-th main body device is denoted as the main body device 32-i.

[0092] The candidate beam detection unit 15 outputs an output destination switching instruction signal whose output destination is the candidate beam detection unit 15 to the feedback signal receiving unit 12. When the feedback signal receiving unit 12 receives the output destination switching instruction signal whose output destination is the candidate beam detection unit 15 from the candidate beam detection unit 15, it sets the output destination of the feedback signal to the candidate beam detection unit 15.

[0093] When i = 1, the candidate beam detection unit 15 performs the following processing. That is, the candidate beam detection unit 15 outputs a full beam search request signal including the "diversity antenna ID #1", which is the diversity antenna ID assigned to the first diversity antenna 31-1, to the beam search execution instruction unit 11 in order to cause the diversity antenna device 30-1 including the first diversity antenna 31-1 to perform a full beam search. After the candidate beam detection unit 15 outputs the full beam search request signal to the beam search execution instruction unit 11, it activates the feedback signal timer provided inside. When the candidate beam detection unit 15 activates the feedback signal timer, it sets the same time as that set by the beam combination history generation unit 13 for the feedback signal timer in the process of step Sa1 in FIG. 9. Note that the time is a predetermined time and is set in advance in the candidate beam detection unit 15. When the beam search execution instruction unit 11 captures the full beam search request signal output by the candidate beam detection unit 15, thereafter, in the process of step Sa1 in FIG. 9, the processing after the beam search execution instruction unit 11 captures the full beam search request signal is performed by the beam search execution instruction unit 11, the digital signal processing device 20, the main body device 32-1, the diversity antenna 31-1, and the terminal device 40 with i = 1 (step Sb1 when i = 1).

[0094] The candidate beam detection unit 15 determines whether or not it has captured a feedback signal including the "diversity antenna ID #1", which is the diversity antenna ID of the first diversity antenna 31-1, as the transmission source antenna ID before the feedback signal timer expires (step Sb2 when i = 1).

[0095] Here, assume that any event occurs when the beam combination history generation unit 13 described above cannot capture the feedback signal. In this case, the candidate beam detection unit 15 determines that it has not captured the feedback signal in which the "diversity antenna ID #1", which is the diversity antenna ID of the first diversity antenna 31-1, is included as the transmission source antenna ID before the feedback signal timer expires (step Sb2, No). If the value of i at that time is not N (here, N = 4), the candidate beam detection unit 15 sets the value obtained by adding 1 to i as the new value of i, and the processes of steps Sb1 and Sb2 are performed again (loops Lb1s to Lb1e). Here, since the value of i at that time is "1", the candidate beam detection unit 15 sets "2" as the new value of i.

[0096] When i = 2, the candidate beam detection unit 15 performs the following processing as the second processing of loops Lb1s to Lb1e. That is, the candidate beam detection unit 15 outputs a full beam search request signal including the "diversity antenna ID #2", which is the diversity antenna ID given to the second diversity antenna 31-2, to the beam search execution instruction unit 11 in order to cause the diversity antenna device 30-2 including the second diversity antenna 31-2 to perform a full beam search. After the candidate beam detection unit 15 outputs the full beam search request signal to the beam search execution instruction unit 11, it starts the feedback signal timer provided inside. When starting the feedback signal timer, the candidate beam detection unit 15 sets the same time as that set by the beam combination history generation unit 13 for the feedback signal timer in the process of step Sa1 in FIG. 9. When the beam search execution instruction unit 11 captures the full beam search request signal output by the candidate beam detection unit 15, then, in the process of step Sa1 in FIG. 9, after the beam search execution instruction unit 11 captures the full beam search request signal, the subsequent processing is performed by the beam search execution instruction unit 11, the digital signal processing device 20, the main body device 32-2, the diversity antenna 31-2, and the terminal device 40 with i = 2 (step Sb1 when i = 2).

[0097] The candidate beam detection unit 15 determines whether it has captured a feedback signal that includes the "diversity antenna ID #2," which is the diversity antenna ID of the second diversity antenna 31-2, as the transmission source antenna ID before the feedback signal timer expires (step Sb2 when i = 2). Here, it is assumed that none of the events occur when the beam combination history generation unit 13 described above cannot capture the feedback signal, and the feedback signal reception unit 12 outputs a feedback signal to the candidate beam detection unit 15. In this case, the candidate beam detection unit 15 determines that it has captured a feedback signal that includes the "diversity antenna ID #2," which is the diversity antenna ID of the second diversity antenna 31-2, as the transmission source antenna ID before the feedback signal timer expires (step Sb2 when i = 2, Yes).

[0098] The candidate beam detection unit 15 exits the processing of loops Lb1s to Lb1e, and sets the beam ID included in the captured feedback signal as the beam ID indicating the best beam in the second diversity antenna device 30-2. The candidate beam detection unit 15 designates the beam specified by the beam ID and the "diversity antenna ID #2," which is the transmission source antenna ID included in the feedback signal, as the detection reference beam. Here, it is assumed that the beam ID included in the feedback signal captured by the candidate beam detection unit 15 is "beam ID #33."

[0099] The candidate beam detection unit 15 combines the transmission source antenna ID, beam ID, and received power value included in the feedback signal into a set of data, and outputs the set of data to the beam combination recording unit 17. The beam combination recording unit 17 captures the set of data output by the candidate beam detection unit 15. The candidate beam detection unit 15 outputs an output destination switching instruction signal to the feedback signal reception unit 12 to change the output destination to the beam search execution determination unit 16. When receiving the output destination switching instruction signal from the candidate beam detection unit 15 to change the output destination to the beam search execution determination unit 16, the feedback signal reception unit 12 sets the output destination of the feedback signal to the beam search execution determination unit 16 (step Sb3).

[0100] Put another way regarding the processing of steps Sb2 and Sb3 above, the candidate beam detection unit 15 performs a process of causing all the distributed antenna devices 30-1 to 30-4 to perform a full beam search in order. During this process, when one feedback signal is captured, the processing of loops Lb1s to Lb1e ends, and the beam specified by the transmission source antenna ID and the beam ID included in the captured feedback signal is used as the detection reference beam.

[0101] At this point, during the beam search period, the distributed antenna devices for which the full beam search has not been performed are the two devices 30-3 and 30-4. If the wireless communication system 1 includes N distributed antenna devices 30-1 to 30-N, the number of distributed antenna devices 30-1 to 30-N for which the full beam search has not been performed is represented by N - i using the value of i at the time of exiting loops Lb1s to Lb1e and the value of N. The candidate beam detection unit 15 provides a counter k in its internal storage area and initializes it to k = i + 1. k is an integer value from (i + 1) to N. Here, k takes the values of "3" and "4".

[0102] When k = 3, the candidate beam detection unit 15 performs the following processing. That is, the candidate beam detection unit 15 detects, as candidate beams, beams that are the beams of the third distributed antenna device 30-3 and have been selected together with the detection reference beam from the beam combination history table 140. Here, the detection reference beam is the beam specified by "Beam ID #33" of "Distributed Antenna ID #2". In the beam combination history table 140, "Beam ID #33" of "Distributed Antenna ID #2" corresponding to the detection reference beam is included in "Record ID #2", "Record ID #4", and "Record ID #6", but the items of "Distributed Antenna ID #3" in "Record ID #2", "Record ID #4", and "Record ID #6" are blank. Therefore, the candidate beam detection unit 15 detects as a detection result that there is no candidate beam ID indicating a candidate beam that is a beam of the third distributed antenna device 30-3 and has been selected together with the detection reference beam. The candidate beam detection unit 15 generates data indicating a detection result including only "Distributed Antenna ID #3" (step Sb4 when k = 3).

[0103] The candidate beam detection unit 15 outputs data indicating a detection result including only "Distributed Antenna ID #3" to the beam search execution determination unit 16 (step Sb5 when k = 3). When the beam search execution determination unit 16 receives the data indicating the detection result from the candidate beam detection unit 15, it starts the subroutine of the all beam search execution determination process shown in FIG. 11 (step Sb6 when k = 3).

[0104] The beam search execution determination unit 16 fetches the data indicating the detection result output by the candidate beam detection unit 15 (step Sc1 when k = 3). The beam search execution determination unit 16 determines whether the candidate beam ID is included in the fetched data indicating the detection result (step Sc2 when k = 3). Here, since the candidate beam ID is not included in the data indicating the detection result, the beam search execution determination unit 16 determines that the candidate beam ID is not included in the fetched data indicating the detection result (step Sc2, No when k = 3).

[0105] Next, the processes of Step Sc3 to Step Sc6 will be described. The beam search execution determination unit 16 reads out the "distributed antenna ID #k" included in the data indicating the detection result, and based on the read "distributed antenna ID #k", in order to cause the distributed antenna device 30-k including the k-th distributed antenna 31-k to perform a full beam search, it outputs a full beam search request signal including the "distributed antenna ID #k" to the beam search execution instruction unit 11. After the beam search execution determination unit 16 outputs the full beam search request signal to the beam search execution instruction unit 11, it activates the feedback signal timer provided inside. When activating the feedback signal timer, the beam search execution determination unit 16 sets the same time as that set by the beam combination history generation unit 13 for the feedback signal timer in the process of Step Sa1 in FIG. 9. Note that the time is a predetermined time and is set in advance in the beam search execution determination unit 16. When the beam search execution instruction unit 11 captures the full beam search request signal output by the beam search execution determination unit 16, then, in the process of Step Sa1 in FIG. 9, after the beam search execution instruction unit 11 captures the full beam search request signal, the subsequent process is performed by the beam search execution instruction unit 11, the digital signal processing device 20, the main body device 32-k, the distributed antenna 31-k, and the terminal device 40 with i = k (Step Sc3).

[0106] The beam search execution determination unit 16 determines whether or not it has captured a feedback signal including the "distributed antenna ID #k", which is the distributed antenna ID of the k-th distributed antenna 31-k, as the transmission source antenna ID before the feedback signal timer expires (Step Sc4).

[0107] For example, assume that none of the events occur when the beam combination history generation unit 13 described above cannot capture the feedback signal, and the feedback signal reception unit 12 outputs the feedback signal to the beam search execution determination unit 16. In this case, the beam search execution determination unit 16 determines that it has captured the feedback signal in which the "diversity antenna ID #k", which is the diversity antenna ID of the k-th diversity antenna 31-k, is included as the transmission source antenna ID before the feedback signal timer expires (step Sc4, Yes). The beam search execution determination unit 16 sets the beam ID included in the feedback signal as the beam ID indicating the best beam in the k-th diversity antenna device 30-k. The beam search execution determination unit 16 combines the transmission source antenna ID, the beam ID, and the received power value included in the feedback signal into a set of data, and outputs the set of data to the beam combination recording unit 17. The beam combination recording unit 17 captures the set of data output by the beam search execution determination unit 16. (step Sc5).

[0108] On the other hand, assume that any one of the events occurs when the beam combination history generation unit 13 described above cannot capture the feedback signal. In this case, the beam search execution determination unit 16 determines that it has not captured the feedback signal in which the "diversity antenna ID #k", which is the diversity antenna ID of the k-th diversity antenna 31-k, is included as the transmission source antenna ID before the feedback signal timer expires (step Sc4, No).

[0109] After the process of step Sc5, or after making a "No" determination in the process of step Sc4, the beam search execution determination unit 16 outputs an end notification signal indicating that the process for the k-th diversity antenna device 30-k has ended, and the end notification signal including the value of the counter k to the candidate beam detection unit 15 (step Sc6), and ends the subroutine process.

[0110] Returning to FIG. 10, when the candidate beam detection unit 15 captures the end notification signal output by the beam search execution determination unit 16, if the value of k at that time is not N (here, N = 4), the value obtained by adding 1 to k is set as the new value of k, and the processes of steps Sb4 to Sb6 are performed again (loops Lb2s to Lb2e). Here, since the value of k at that time is "3", the candidate beam detection unit 15 sets "4" as the new value of k.

[0111] When k = 4, the candidate beam detection unit 15 performs the following process. That is, the candidate beam detection unit 15 detects from the beam combination history table 140 the beam ID of the beam that is the beam of the fourth distributed antenna device 30-4 and has been selected together with the detection reference beam. Here, the detection reference beam is the beam specified by "beam ID #33" of "distributed antenna ID #2". In the beam combination history table 140, "beam ID #33" of "distributed antenna ID #2" corresponding to the detection reference beam is included in "record ID #2", "record ID #4", and "record ID #6". In the items of "distributed antenna ID #4" of "record ID #2", "record ID #4", and "record ID #6", "beam ID #15", "beam ID #16", and "beam ID #15" are written.

[0112] Therefore, the candidate beam detection unit 15 detects "Beam ID #15" and "Beam ID #16" from the beam combination history table 140 as the beam IDs of the beams of the fourth distributed antenna device 30-4 that have been selected together with the detection reference beam. The candidate beam detection unit 15 sets "Beam ID #15" and "Beam ID #16" as candidate beam IDs indicating candidate beams of the distributed antenna device 30-4 corresponding to "Distributed Antenna ID #4". The candidate beam detection unit 15 generates data indicating a detection result including "Distributed Antenna ID #4", "Beam ID #15" which is the candidate beam ID, and "Beam ID #16" (step Sb4 when k = 4). The candidate beam detection unit 15 outputs the generated data indicating the detection result to the beam search execution determination unit 16 (step Sb5 when k = 4). When receiving the data indicating the detection result from the candidate beam detection unit 15, the beam search execution determination unit 16 starts a subroutine of the all beam search execution determination process shown in FIG. 11 (step Sb6 when k = 4).

[0113] The beam search execution determination unit 16 fetches the data indicating the detection result output by the candidate beam detection unit 15 (step Sc1 when k = 4). The beam search execution determination unit 16 determines whether the candidate beam ID is included in the fetched data indicating the detection result (step Sc2 when k = 4). Here, since the data indicating the detection result includes "Beam ID #15" and "Beam ID #16", the beam search execution determination unit 16 determines that the candidate beam ID is included in the fetched data indicating the detection result (step Sc2, Yes when k = 4).

[0114] The beam search execution determination unit 16 outputs a partial beam search request signal including "distributed antenna ID #4", "beam ID #15", and "beam ID #16" to the beam search execution instruction unit 11 in order to cause the distributed antenna device 30-4 including the fourth distributed antenna 31-4 to perform a partial beam search for the candidate beam ID. After outputting the partial beam search request signal to the beam search execution instruction unit 11, the beam search execution determination unit 16 activates a feedback signal timer provided therein. When activating the feedback signal timer, the beam search execution determination unit 16 sets the same time as that set by the beam combination history generation unit 13 for the feedback signal timer in the process of step Sa1 in FIG. 9.

[0115] The beam search execution instruction unit 11 captures the partial beam search request signal output by the beam search execution determination unit 16, and reads out "distributed antenna ID #4", "beam ID #15", and "beam ID #16" included in the captured partial beam request instruction signal. The beam search execution instruction unit 11 generates a beam search instruction signal including "distributed antenna ID #4" and "beam ID #15", and a beam search instruction signal including "distributed antenna ID #4" and "beam ID #16". The beam search execution instruction unit 11 outputs the two generated beam search instruction signals to the digital signal processing device 20 one by one in the order of generation at a predetermined fixed time interval. The digital signal processing device 20 sequentially captures the two beam search instruction signals output by the beam search execution instruction unit 11. Thereafter, in the process of step Sa1 in FIG. 9, after the digital signal processing device 20 captures the beam search instruction signal, the processing is performed by the digital signal processing device 20, the main body device 32-4, the distributed antenna 31-4, and the terminal device 40 with i = 4 (step Sc7 when k = 4).

[0116] The beam search execution determination unit 16 determines whether or not a feedback signal including "distributed antenna ID #4", which is the distributed antenna ID of the fourth distributed antenna 31-4, as the transmission source antenna ID has been captured before the feedback signal timer expires (step Sc8).

[0117] For example, assume that any event occurs when the beam combination history generation unit 13 described above cannot capture the feedback signal. In this case, the beam search execution determination unit 16 determines that it has not captured the feedback signal in which the "diversity antenna ID #4", which is the diversity antenna ID of the fourth diversity antenna 31-4, is included as the transmission source antenna ID before the feedback signal timer expires (step Sc8, No when k = 4), and proceeds to step Sc3.

[0118] On the other hand, assume that any event does not occur when the beam combination history generation unit 13 described above cannot capture the feedback signal, and the feedback signal reception unit 12 outputs the feedback signal to the beam search execution determination unit 16. In this case, the beam search execution determination unit 16 determines that it has captured the feedback signal in which the "diversity antenna ID #4", which is the diversity antenna ID of the fourth diversity antenna 31-4, is included as the transmission source antenna ID before the feedback signal timer expires (step Sc8, Yes when k = 4).

[0119] In this case, the beam search execution determination unit 16 determines whether the received power value included in the feedback signal exceeds a predetermined threshold (step Sc9 when k = 4). When the beam search execution determination unit 16 determines that the received power value included in the feedback signal does not exceed the predetermined threshold (step Sc9, No when k = 4), it proceeds to step Sc3. On the other hand, when the beam search execution determination unit 16 determines that the received power value included in the feedback signal exceeds the predetermined threshold (step Sc9, Yes when k = 4), it proceeds to step Sc5.

[0120] Putting it another way for the processes of steps Sc7, Sc8, and Sc9 above, the beam search execution determination unit 16 causes the distributed antenna device 30-4 corresponding to the "distributed antenna ID #4" to perform a partial beam search for transmitting the beam corresponding to the "beam ID #15" and the beam corresponding to the "beam ID #16". If a feedback signal from the partial beam search cannot be obtained, the beam search execution determination unit 16 advances the process to step Sc3, causing the distributed antenna device 30-4 corresponding to the "distributed antenna ID #4" to perform a full beam search to re-search for the best beam for the distributed antenna device 30-4. Also, in the full beam search in this case, the beam search execution determination unit 16 searches only for beams other than the beam corresponding to the "beam ID #15" and the beam corresponding to the "beam ID #16".

[0121] Then, if the beam search execution determination unit 16 captures a feedback signal including the "distributed antenna ID #4" as the transmission source antenna ID before the feedback signal timer expires in step Sc4, the process proceeds to step Sc5, and the beam ID included in the feedback signal is used as the data to be added to the beam combination history table 140.

[0122] On the other hand, when a feedback signal is obtained by the partial beam search, if the received power value included in the feedback signal, that is, the received power value of the beam selected as the best beam in the terminal device 40, does not exceed the threshold value, the beam search execution determination unit 16 determines that the beam indicated by the feedback signal is an inappropriate beam that cannot be used for normal operation. Therefore, the beam search execution determination unit 16 advances the process to step Sc3 and causes the distributed antenna device 30-4 corresponding to "distributed antenna ID#4" to perform a full beam search to re-search for the best beam for the distributed antenna device 30-4. Also, in the full beam search in this case, the beam search execution determination unit 16 searches only for beams other than the beam corresponding to "beam ID#15" and the beam corresponding to "beam ID#16".

[0123] Then, when the beam search execution determination unit 16 captures a feedback signal in which "distributed antenna ID#4" is included as the transmission source antenna ID before the feedback signal timer expires in step Sc4, the process proceeds to step Sc5, and the beam ID included in the feedback signal is used as data to be added to the beam combination history table 140.

[0124] On the other hand, when the received power value included in the feedback signal exceeds the threshold value, the beam search execution determination unit 16 advances the process to step Sc5 and determines that the beam is the best beam in the distributed antenna device 30-4. In this case, since the beam search execution determination unit 16 can use the beam as an appropriate beam that can be used for normal operation without performing a full beam search for the distributed antenna device 30-4, the number of beam searches can be reduced.

[0125] Returning to FIG. 10, when the candidate beam detection unit 15 captures the end notification signal output by the beam search execution determination unit 16, if the value of k at that time is N (here, N = 4), the processing of loops Lb2s to Lb2e is terminated, and the processing proceeds to step Sb7.

[0126] Based on the remaining data obtained by removing the received power value from the set of data captured in the processing of step Sb3 and step Sc5, that is, the data combining the transmission source antenna ID, the beam ID, and the received power value, the beam combination recording unit 17 generates one record in the beam combination history table 140. That is, the beam combination recording unit 17 generates a new row in the beam combination history table 140 to generate "record ID #M + 1" as a new record ID. The beam combination recording unit 17 writes "record ID #M + 1", which is the newly generated record ID, in the "record ID" item of the newly generated row. Based on the combination of the transmission source antenna ID and the beam ID, the beam combination recording unit 17 writes the corresponding beam ID in each of the elements of "diversity antenna ID #1", "diversity antenna ID #2", "diversity antenna ID #3", and "diversity antenna ID #4" in the row of "record ID #M + 1" (step Sb7).

[0127] In the wireless communication system 1 of the above-described first embodiment, during a beam search period in which the candidate beam detection unit 15 searches for a beam to be used for wireless communication with the terminal device 40, for each of the plurality of distributed antennas 31-1 to 31-4, a full beam search is performed by transmitting beams in all directions in which transmission is possible. When one beam identifier indicating the best beam among the beams obtained by the full beam search is acquired, the full beam search is stopped, and the beam specified by the acquired beam identifier and the information indicating the distributed antennas 31-1 to 31-4 that transmitted the beam indicated by the beam identifier is set as the detection reference beam. The beam identifier of a beam that is a beam identifier of the distributed antennas 31-1 to 31-4 that have not performed the full beam search during the beam search period and that has been selected together with the detection reference beam is detected from the beam combination history storage unit 14 as the candidate beam identifier for the distributed antennas 31-1 to 31-4. The beam search execution determination unit 16 determines whether to perform the full beam search for the distributed antennas 31-1 to 31-4 that have not performed the full beam search during the beam search period, based on the detection result of the candidate beam detection unit 15. The beam combination recording unit 17 generates a record indicating a combination of beam identifiers indicating the beams that have been the best beams at each of the distributed antennas during the beam search period. The beam combination recording unit 17 records the generated record in the beam combination history storage unit. As a result, in the beam combination generation process performed by the beam combination history generation unit 13, even if a sufficient number of records indicating the history of beam combinations cannot be generated by gradually moving the terminal device 40 at intervals that do not reduce the transmission capacity over the entire cell 100 within the service area, when performing the beam search process, it is possible to accumulate a sufficient number of records for reducing the number of beam searches without reducing the transmission capacity.

[0128] While referring to FIG. 12, the content of the beam search process of the above-described first embodiment is organized. For the distributed antenna device 30-1, in the process of step Sb2 when i = 1, the candidate beam detection unit 15 cannot obtain a feedback signal by all beam searches performed on the distributed antenna device 30-1 until the feedback signal timer expires, so it cannot search for a beam. For the distributed antenna device 30-2, in the process of step Sb2 when i = 2, the candidate beam detection unit 15 can obtain a feedback signal by all beam searches performed on the distributed antenna device 30-2, and the beam indicated by the beam ID of "Beam ID #33" included in the obtained feedback signal can be searched as the best beam in the distributed antenna device 30-2.

[0129] For the distributed antenna device 30-3, the candidate beam detection unit 15 cannot detect the beam ID of the beam that has been selected together with the best beam "Beam ID #33" in the distributed antenna device 30-2 from the beam combination history table 140. Therefore, as shown in FIG. 12(a), the beam search execution determination unit 16 proceeds to the process of step Sc3 in FIG. 11 to cause the distributed antenna device 30-3 to perform all beam searches. If the beam search execution determination unit 16 can obtain a feedback signal by all beam searches by the distributed antenna device 30-3, it can search for the best beam in the distributed antenna device 30-3, and if it cannot obtain a feedback signal, it cannot search for the best beam in the distributed antenna device 30-3.

[0130] Regarding the distributed antenna device 30-4, the candidate beam detection unit 15 can detect "Beam ID #15" and "Beam ID #16" from the beam combination history table 140 as the beam IDs of the beams that have been selected together with "Beam ID #33", which is the best beam in the distributed antenna device 30-2. Therefore, as shown in Fig. 12(b), the beam search execution determination unit 16 causes the distributed antenna device 30-4 to perform a partial beam search using the beams indicated by "Beam ID #15" and "Beam ID #16" as candidate beams in step Sc7 of Fig. 11. The beam search execution determination unit 16 has acquired a feedback signal through the partial beam search by the distributed antenna device 30-4. If the received power value included in the acquired feedback signal exceeds a predetermined threshold, the beam ID included in the feedback signal can be searched as the best beam in the distributed antenna device 30-4. On the contrary, if the beam search execution determination unit 16 has not obtained a feedback signal through the partial beam search by the distributed antenna device 30-4, or if the received power value included in the feedback signal does not exceed the predetermined threshold when the feedback signal is obtained, the beam search execution determination unit 16 proceeds to the process of step Sc3 in Fig. 11 and causes the distributed antenna device 30-4 to perform a full beam search. If the beam search execution determination unit 16 can obtain a feedback signal through the full beam search by the distributed antenna device 30-4, the best beam in the distributed antenna device 30-4 can be searched. If the feedback signal cannot be obtained, the best beam in the distributed antenna device 30-4 cannot be searched.

[0131] Therefore, all the beam search processes performed in the processes of steps Sb1 and Sb2 in FIG. 10 and steps Sc3 and Sc4 in FIG. 11 can be regarded as processes for covering the shortage of records when a sufficient number of records are not recorded in the beam combination history table 140 by the beam combination generation process by the beam combination history generation unit 13. On the other hand, the partial beam search process performed in the processes of steps Sc7 to Sc9 in FIG. 11 is a process for searching for beams while reducing the number of beam searches. However, when a sufficient number of records are not recorded in the beam combination history table 140, when the candidate beams are narrowed down, the best beam may not be included in the narrowed-down candidate beams, and the transmission capacity may decrease. In such a case, the process proceeds to step Sc3 to perform a full beam search to newly select the best beam. As a result, even when there are not a sufficient number of records in the beam combination history table 140, it is possible to accumulate a sufficient number of records for reducing the number of beam searches without reducing the transmission capacity when performing the beam search process.

[0132] (Second Embodiment) FIG. 13 is a block diagram showing the configuration of the communication control device 10a in the second embodiment. The communication control device 10a is a device used in place of the communication control device 10 in the first embodiment. Hereinafter, for convenience of explanation, a wireless communication system 1 including the communication control device 10a in place of the communication control device 10 is referred to as a wireless communication system 1a. In the communication control device 10a, the same components as those of the communication control device 10 in the first embodiment are denoted by the same reference numerals, and different components will be described below.

[0133] The communication control device 10a includes a beam search execution instruction unit 11, a feedback signal reception unit 12, a beam combination history generation unit 13a, a beam combination history storage unit 14a, a candidate beam detection unit 15a, a beam search execution determination unit 16a, and a beam combination recording unit 17a.

[0134] The beam combination history storage unit 14a stores a beam combination history table 140a shown in FIG. 14. The beam combination history table 140a has the same data format as the beam combination history table 140 of the first embodiment shown in FIG. 4, except that the data written to the elements is different. The beam combination history table 140 of the first embodiment has a data configuration in which only the beam ID is written as an element. On the other hand, in the beam combination history table 140a of the second embodiment, the beam ID and the received power value measured by the terminal device 40 when the terminal device 40 receives the beam indicated by the beam ID are written as elements. Note that, as the received power value, for example, a numerical value represented in the unit of "dBm" is written.

[0135] The beam combination history generation unit 13a has the same configuration as the beam combination history generation unit 13 of the first embodiment, except for the configuration described below. In the process of step Sa3 in FIG. 9, the beam combination history generation unit 13 of the first embodiment writes and records, in an internal storage area, data obtained by combining the transmission source antenna ID included in the captured feedback signal and the beam ID. On the other hand, in the process of step Sa3 in FIG. 9, the beam combination history generation unit 13a of the second embodiment adds the received power value included in the captured feedback signal, and writes and records, in an internal storage area, data obtained by combining the transmission source antenna ID, the beam ID, and the received power value.

[0136] In the record generated by the beam combination history generation unit 13 of the first embodiment in the process of step Sa4 in FIG. 9, the received power value is not included. On the other hand, the beam combination history generation unit 13a of the second embodiment generates a record in which the received power value is added to the transmission source antenna ID and the beam ID in the process of step Sa4 in FIG. 9. Therefore, the beam combination history generation unit 13a writes the record including the received power value into the beam combination history table 140a in the process of step Sa6. At that time, the beam combination history generation unit 13a writes each of the data obtained by combining the beam ID and the received power value included in the record as an element at the position specified by the newly generated row for the record in the beam combination history table 140a and the column of the transmission source antenna ID corresponding to the data obtained by combining the beam ID and the received power value. In the first embodiment, it is stated that when there are a plurality of records having the same combination of beam IDs stored in the beam combination history table 140 before the process ends, the beam combination history generation unit 13 may leave any one record and delete the other records. However, in the second embodiment, even if the combination of beam IDs is the same, the received power values may be different. Therefore, it is necessary to leave all the records written in the beam combination history table 140a.

[0137] The candidate beam detection unit 15a has the same configuration as the candidate beam detection unit 15 in the first embodiment, except for the configuration described below. When the candidate beam detection unit 15a detects the beam ID of the distributed antenna devices 30-1 to 30-4 that have not performed full beam search during the beam search period and that have been selected together with the detection reference beam, and the distributed antenna ID corresponding to the beam ID from the beam combination history table 140a, the candidate beam detection unit 15a detects the received power value written as an element together with the detected beam ID in the beam combination history table 140a. Based on the combination of the detected beam ID and the detected received power value, the candidate beam detection unit 15a calculates the average value of the received power values for each beam ID, and sets the maximum value of the calculated average values as the average received power value for the detected distributed antenna ID. The candidate beam detection unit 15a includes the calculated average received power value in the data indicating the detection result.

[0138] The beam search execution determination unit 16a has the same configuration as the beam search execution determination unit 16 in the first embodiment, except for the configuration described below. When the data indicating the detection result output by the candidate beam detection unit 15 includes the candidate beam ID, the beam search execution determination unit 16a performs the following process. That is, the beam search execution determination unit 16a reads the average received power value included in the data indicating the detection result, and sets the value obtained by adding a margin to the read average received power value as the threshold for the distributed antenna ID included in the data indicating the detection result. Here, the reason for setting the value obtained by adding a margin to the average received power value as the threshold is to allow a received power value slightly smaller than the average received power value. Specifically, the beam search execution determination unit 16a sets the value of the error occurring in the pre-calculated received power value as a predetermined value, and sets the subtraction value obtained by subtracting the predetermined value from the average received power value as the threshold.

[0139] When the beam search execution determination unit 16a causes any of the distributed antenna devices 30-1 to 30-4 to perform the partial beam search, it selects a threshold value for the transmission source antenna ID included in the feedback signal obtained at that time from among the calculated threshold values, and based on the selected threshold value and the received power value included in the feedback signal, determines whether to cause the distributed antenna devices 30-1 to 30-4 corresponding to the transmission source antenna ID included in the feedback signal to perform the full beam search.

[0140] The beam combination recording unit 17a has the same configuration as the beam combination recording unit 17 of the first embodiment for configurations other than those described below. The beam combination recording unit 17 of the first embodiment generated one record based on the remaining data obtained by removing the received power value from the data combining the transmission source antenna ID, the beam ID, and the received power value in the process of step Sb7 in FIG. 10. In contrast, the beam combination recording unit 17a of the second embodiment generates one record from the data combining the transmission source antenna ID, the beam ID, and the received power value without removing the received power value in the process of step Sd7 in FIG. 15 corresponding to the process of step Sb7 in FIG. 10. The beam combination recording unit 17a writes each of the data combining the beam ID and the received power value included in the record as an element at the location specified by the newly generated row for the record in the beam combination history table 140a and the column of the transmission source antenna ID corresponding to the data combining the beam ID and the received power value.

[0141] (Processing by the wireless communication system of the second embodiment) Similar to the first embodiment, in the wireless communication system 1a of the second embodiment, the beam combination generation process in step S1 and the beam search process in step S2 shown in FIG. 8 are also performed. However, the beam combination generation process and the beam search process performed in the second embodiment are different from the processes performed in the first embodiment in the points described below.

[0142] (Beam combination generation process of the second embodiment) In the beam combination generation process shown in FIG. 9, except that the processes of steps Sa3, Sa4, and Sa6 are replaced with the above-described processes, the same processes as those in the first embodiment are performed by the beam search execution instruction unit 11, the feedback signal reception unit 12, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4, and the process that was performed by the beam combination history generation unit 13 is performed by the beam combination history generation unit 13a.

[0143] (Beam Search Process of the Second Embodiment) FIG. 15 is a flowchart showing the beam search process of the second embodiment, and FIG. 16 is a flowchart showing the process of the subroutine for determining the execution of all beam searches performed in step Sd6 of FIG. 15. In FIG. 15, the processes of steps Sd1 and Sd2, the processes of the loop Ld1s to Ld1e that repeats the processes of steps Sd1 and Sd2, and the process of step Sd3 are the same processes as the processes of steps Sb1 and Sb2 and the process of the loop Lb1s to Lb1e that repeats the processes of steps Sb1 and Sb2 and the process of step Sb3 in FIG. 10, and are performed by the beam search execution instruction unit 11, the feedback signal reception unit 12, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4. The process that was performed by the candidate beam detection unit 15 is performed by the candidate beam detection unit 15a. The process of step Sd7 is performed by the beam combination recording unit 17a with the above-described process.

[0144] In the process of the loop Ld2s to Ld2e, when k = 3, similar to the first embodiment, the candidate beam detection unit 15a cannot detect the candidate beam ID corresponding to "distributed antenna ID #3" from the beam combination history table 140a. Therefore, in this case, the candidate beam detection unit 15a cannot detect the received power value either. Thus, the candidate beam detection unit 15a does not calculate the average received power value, and similar to the process of step Sb4 of the first embodiment, it is detected that there is no candidate beam ID indicating a beam of the third distributed antenna device 30-3 that has been selected together with the detection reference beam as a detection result. The candidate beam detection unit 15a generates data indicating a detection result including only "distributed antenna ID #3" (step Sd4 when k = 3).

[0145] The candidate beam detection unit 15a outputs data indicating a detection result including only "distributed antenna ID #3" to the beam search execution determination unit 16a (step Sb5 when k = 3). When receiving the data indicating the detection result from the candidate beam detection unit 15a, the beam search execution determination unit 16a starts a subroutine of the all beam search execution determination process shown in FIG. 16 (step Sd6 when k = 3).

[0146] The subroutine of the all beam search execution determination process performed in step Sd6 of the beam search process of the second embodiment will be described with reference to FIG. 16. The processes from step Se1 to step Se6 are the same as the processes from step Sc1 to step Sc6 shown in FIG. 11, which are performed by the beam search execution instruction unit 11, the feedback signal reception unit 12, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4. The process that was performed by the beam search execution determination unit 16 is now performed by the beam search execution determination unit 16a. Therefore, when k = 3, in the determination process of step Se2, the beam search execution determination unit 16a determines "No", and the process proceeds to step Se3. After that, the same process as in the case of k = 3 in the first embodiment is performed.

[0147] In the process of the loop Ld2s to Ld2e shown in FIG. 15, it is assumed that the process has advanced to k = 4. Similar to the first embodiment, the candidate beam detection unit 15a detects from the beam combination history table 140a the beam ID of the beam of the fourth distributed antenna device 30-4 that has been selected together with the detection reference beam. Here, the detection reference beam is the beam specified by "beam ID #33" of "distributed antenna ID #2". In the beam combination history table 140a, "beam ID #33" of "distributed antenna ID #2" corresponding to the detection reference beam is included in "record ID #2", "record ID #4", and "record ID #6". In the items of "distributed antenna ID #4" of "record ID #2", "record ID #4", and "record ID #6", "beam ID #15", "beam ID #16", and "beam ID #15" are written.

[0148] Therefore, the candidate beam detection unit 15a detects "beam ID #15" and "beam ID #16" from the beam combination history table 140 as the beam IDs of the beams of the fourth distributed antenna device 30-4 that have been selected together with the detection reference beam. The candidate beam detection unit 15a uses "beam ID #15" and "beam ID #16" as candidate beam IDs indicating candidate beams of the distributed antenna device 30-4 corresponding to "distributed antenna ID #4".

[0149] The candidate beam detection unit 15a further detects, for "Beam ID #15", "(Received power value 2 - 4)" of "Record ID #2" and "(Received power value 6 - 4)" of "Record ID 6", and for "Beam ID #16", detects "(Received power value 4 - 4)" of "Record ID #4". The candidate beam detection unit 15a calculates the average value of "(Received power value 2 - 4)" and "(Received power value 6 - 4)" corresponding to "Beam ID #15". For "Beam ID #16", since there is only one "(Received power value 4 - 4)", "(Received power value 4 - 4)" is used as the average value. The candidate beam detection unit 15a sets the maximum average value among the average value corresponding to "Beam ID #15" and the average value of "Beam ID #16" as the average received power value for "Diversity antenna ID #4". The candidate beam detection unit 15 generates data indicating the detection result including "Diversity antenna ID #4", "Beam ID #15" which is the candidate beam ID, "Beam ID #16", and the calculated average received power value (step Sd4 when k = 4). The candidate beam detection unit 15a outputs the data indicating the generated detection result to the beam search execution determination unit 16a (step Sd5 when k = 4).

[0150] In the process of step Se1 of the subroutine of the all beam search execution determination process of FIG. 16 performed in the subsequent step Sd6 process, the beam search execution determination unit 16a takes in the detection result data output by the candidate beam detection unit 15a, and in the process of step Se2, determines that the candidate beam ID is included in the data indicating the taken-in detection result (step Se2, Yes when k = 4).

[0151] The processes of steps Se7 and Se8 are the same as the processes of steps Sc7 and Sc8 in FIG. 11, respectively, and are performed by the beam search execution instruction unit 11, the feedback signal reception unit 12, the digital signal processing device 20, and the distributed antenna device 30-4. The process that was performed by the beam search execution determination unit 16 is performed by the beam search execution determination unit 16a. When the beam search execution determination unit 16a determines "Yes" in the determination process of step Se8, it reads out the average received power value included in the data indicating the detection result, gives a margin to the read average received power value, and calculates a threshold value for "distributed antenna ID #4" (step Se9). The beam search execution determination unit 16a determines whether the received power value included in the feedback signal exceeds the threshold value calculated for the transmission source antenna ID (here, "distributed antenna ID #4") included in the feedback signal (step Se10 when k = 4).

[0152] When the beam search execution determination unit 16a determines that the received power value included in the feedback signal exceeds the threshold value calculated for the transmission source antenna ID included in the feedback signal (step Se10, Yes), then it advances the process to the process of step Se5. On the other hand, when the beam search execution determination unit 16a determines that the received power value included in the feedback signal does not exceed the threshold value calculated for the transmission source antenna ID included in the feedback signal (step Se10, No), then it advances the process to the process of step Se3.

[0153] Accordingly, in the second embodiment, when the beam search execution determination unit 16a determines to cause any one of the distributed antenna devices 30-1 to 30-4 to perform a partial beam search, if the received power value included in the feedback signal acquired by the partial beam search is about the past average received power value of the distributed antenna devices 30-1 to 30-4 targeted by the partial beam search, the beam indicated by the beam ID included in the feedback signal can be searched for as the best beam of the distributed antenna devices 30-1 to 30-4 corresponding to the transmission source antenna ID included in the feedback signal. The beam search execution determination unit 16a can add data related to the beam to the beam combination history table 140a. On the other hand, if the received power value included in the feedback signal acquired by the partial beam search is not about the past average received power value of the distributed antenna devices 30-1 to 30-4 targeted by the partial beam search, the beam search execution determination unit 16a causes the distributed antenna devices 30-1 to 30-4 corresponding to the transmission source antenna ID included in the feedback signal to perform a full beam search. If the beam search execution determination unit 16 can acquire a feedback signal by the full beam search, the best beam in the distributed antenna devices 30-1 to 30-4 targeted by the full beam search can be searched for, and if the feedback signal cannot be acquired, the best beam in the distributed antenna devices 30-1 to 30-4 targeted by the full beam search cannot be searched for. Therefore, in the second embodiment, in addition to the effects achieved by the communication control device 10 of the first embodiment, when causing a partial beam search to be performed, the best beam can be searched for more accurately than in the first embodiment.

[0154] In the above-described first embodiment, by setting a threshold value of a reception power value determined in advance to be higher, it is possible to lower the possibility that a beam that is not the best in terms of communication quality is selected. However, in this case, in the first embodiment, since full beam search is performed for more distributed antenna devices, it becomes difficult to reduce the number of beam searches. In addition, since the optimal threshold value also varies depending on the position of the terminal device and the like, it is difficult to set the threshold value for selecting the best beam while reducing the number of beam searches as a uniform value. On the other hand, in the second embodiment, by changing the threshold value for each beam combination, the threshold value is substantially changed for each position of the terminal device 40, and the configuration is such that the threshold value is adaptively set.

[0155] In the second embodiment, the method in which the average value of the reception power values for each detected beam ID is used as a reference has been described, but it is not limited to the average value. For example, the value used as a reference may be the median, the mode, the maximum value, or the minimum value. Further, among these values, when the maximum value, the minimum value, or the average value is used as a reference, other records may be deleted by calculating each time for the same combination of beam IDs.

[0156] In the above-described first embodiment, in the beam search process shown in FIG. 10, the candidate beam detection unit 15 performs a process of causing all the distributed antenna devices 30-1 to 30-4 to perform full beam search in order. When the candidate beam detection unit 15 captures one feedback signal during the process, the processes of loops Lb1s to Lb1e are terminated, and the best beam specified by the transmission source antenna ID and the beam ID included in the captured feedback signal is set as the detection reference beam. Then, the candidate beam detection unit 15 detects, from the beam combination history table 140, a beam that has been selected together with the detection reference beam as a candidate beam.

[0157] Similarly, in the second embodiment described above, in the beam search process shown in FIG. 15, the candidate beam detection unit 15a performs a process of causing all the distributed antenna devices 30-1 to 30-4 to perform a full beam search in order. When the candidate beam detection unit 15a captures one feedback signal during the process, it ends the processes of loops Ld1s to Ld1e, and sets the best beam specified by the transmission source antenna ID and the beam ID included in the captured feedback signal as the detection reference beam. Then, the candidate beam detection unit 15a detects from the beam combination history table 140a a beam that has been selected together with the detection reference beam as a candidate beam.

[0158] In this way, in the first and second embodiments, a process of causing all the distributed antenna devices 30-1 to 30-4 to perform a full beam search in order is performed, and a detection reference beam is selected. Then, a partial beam search is performed on the candidate beam, which is a beam that has been selected together with the detection reference beam. In the partial beam search, if the received power value included in the feedback signal exceeds a predetermined threshold value, the beam based on the feedback signal is selected.

[0159] However, the beam selected in this way is merely a beam whose received power value exceeds a predetermined threshold value, and is not necessarily the best beam from the perspective of communication quality. When a beam whose received power value exceeds the threshold value is selected, a full beam search is not performed on the distributed antenna device that is the target of the beam search, and the beam combination history table is not updated either. Therefore, when a full beam search is performed on the distributed antenna devices 30-1 to 30-4 in a fixed order, it may happen that a combination of non-optimal beams continues to be selected.

[0160] On the other hand, by setting a higher threshold value, the possibility of selecting a beam that is not the best in terms of communication quality can be made lower. However, in this case, since full beam search is performed for a larger number of distributed antenna devices, it becomes difficult to reduce the number of beam searches.

[0161] In the wireless communication system 1b in the third embodiment and the wireless communication system 1c in the fourth embodiment described below, instead of performing full beam search in a fixed order for the distributed antenna devices 30-1 to 30-4 at the first stage of the beam search process, full beam search is performed in a random order for the distributed antenna devices 30-1 to 30-4. By having such a configuration, in the third and fourth embodiments described below, even for a distributed antenna device for which full beam search was not performed because a beam that is not the best beam but has a received power value exceeding the threshold value was selected by partial beam search, full beam search is performed at a random timing. Therefore, the beam combination history table is also updated. Thus, according to the third and fourth embodiments described below, it is possible to prevent a combination of non-optimal beams from being continuously and fixedly selected while reducing the number of beam searches.

[0162] (Third Embodiment) FIG. 17 is a block diagram showing the configuration of the communication control device 10b in the third embodiment. The communication control device 10b is a device used in place of the communication control device 10 in the first embodiment. Hereinafter, for convenience of explanation, a wireless communication system 1 including the communication control device 10b in place of the communication control device 10 is referred to as a wireless communication system 1b. In the communication control device 10b, the same components as those of the communication control device 10 in the first embodiment are denoted by the same reference numerals, and the different components will be described below.

[0163] Among the configurations of the wireless communication system 1b in the third embodiment, the difference from the configuration of the wireless communication system 1 in the first embodiment is that, in the first stage of the beam search process, instead of performing a full beam search by a plurality of distributed antenna devices in a fixed order, the distributed antenna devices are randomly selected to perform a full beam search.

[0164] The communication control device 10b includes a beam search execution instruction unit 11, a feedback signal reception unit 12, a beam combination history generation unit 13, a beam combination history storage unit 14, a candidate beam detection unit 15b, a beam search execution determination unit 16, and a beam combination recording unit 17.

[0165] When the beam search process for searching for a beam is started, the candidate beam detection unit 15b causes each of the distributed antenna devices 30-1 to 30-4 to perform a full beam search one by one in a random order. That is, the candidate beam detection unit 15b randomly designates one by one the distributed antenna IDs of the distributed antennas 31-1 to 31-4, and outputs a full beam search request signal including the designated one distributed antenna ID to the beam search execution instruction unit 11. After starting the beam search process, when the candidate beam detection unit 15b captures the first feedback signal, it stops the full beam search, and uses the beam specified by the transmission source antenna ID and the beam ID included in the feedback signal as the detection reference beam.

[0166] The candidate beam detection unit 15b detects from the beam combination history table 140 the beam IDs of the distributed antenna devices 30-1 to 30-4 that have not performed a full beam search during the beam search period and that have been selected together with the detection reference beam, and the distributed antenna IDs corresponding to the beam IDs. The candidate beam detection unit 15b sets the detected beam ID as a candidate beam ID indicating a candidate beam in the distributed antenna devices 30-1 to 30-4 corresponding to the detected distributed antenna ID, and sets the combination of the detected distributed antenna ID and the candidate beam ID as the detection result.

[0167] (Processing by the wireless communication system of the third embodiment) Similar to the first embodiment, in the wireless communication system 1b of the third embodiment, the beam combination generation process of step S1 and the beam search process of step S2 shown in FIG. 8 are also performed. However, in the points described below, the beam search process performed in the third embodiment is different from the process performed in the first embodiment.

[0168] (Beam combination generation process of the third embodiment) The same beam combination generation process as that of the first embodiment shown in FIG. 9 is performed by the beam search execution instruction unit 11, the feedback signal reception unit 12, the beam combination history generation unit 13, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4.

[0169] (Beam search process of the third embodiment) FIG. 18 is a flowchart showing the beam search process of the third embodiment. FIG. 18 is a flowchart showing the flow of the beam search process performed in the process of step S2 in FIG. 8. Assume that the beam combination history table 140 shown in FIG. 4 is generated in the beam combination history storage unit 14 as a prerequisite for starting the beam search process shown in FIG. 8.

[0170] In FIG. 18, the processes of steps Sf1 and Sf2 and the processes of loops Lf1s to Lf1e that repeat the processes of steps Sf1 and Sf2 are performed by the candidate beam detection unit 15b as described above. The process of step Sf3, the processes of steps Sf4 to Sf6, the processes of loops Lf2s to Lf2e that repeat the processes of steps Sf4 to Sf6, and the process of step Sf7 are the same as the process of step Sb3 in FIG. 10, the processes of steps Sb4 to Sb6, the processes of loops Lb2s to Lb2e that repeat the processes of steps Sb4 to Sb6, and the process of step Sb7, and are performed by the beam search execution instruction unit 11, the feedback signal reception unit 12, the beam combination recording unit 17, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4. The process that was performed by the candidate beam detection unit 15 is performed by the candidate beam detection unit 15b.

[0171] In response to the operation of the operator of the wireless communication system 1b, the candidate beam detection unit 15b of the communication control device 10b starts the beam search process. The candidate beam detection unit 15b activates the beam search cycle timer provided therein. When activating the beam search cycle timer, the candidate beam detection unit 15b sets a time indicating the length of a period of one predetermined beam search cycle.

[0172] The candidate beam detection unit 15b reads out all the distributed antenna IDs written in the distributed antenna ID item of the beam combination history table 140 stored in the beam combination history storage unit 14. The candidate beam detection unit 15b provides a variable i in its internal storage area. Here, i is a variable that can take integer values from 1 to N. However, the wireless communication system 1 in FIG. 1 includes four distributed antenna devices 30-1 to 30-4, and the candidate beam detection unit 15b reads out four distributed antenna IDs, namely, "Distributed Antenna ID #1", "Distributed Antenna ID #2", "Distributed Antenna ID #3", and "Distributed Antenna ID #4" from the beam combination history table 140. Therefore, in the following description, N = 4 is used for explanation. The i-th distributed antenna device is referred to as the distributed antenna device 30-i, the i-th distributed antenna is referred to as the distributed antenna 31-i, and the i-th main body device is referred to as the main body device 32-i for the following description.

[0173] The candidate beam detection unit 15b outputs an output destination switching instruction signal to the feedback signal receiving unit 12 with the output destination being the candidate beam detection unit 15b. When the feedback signal receiving unit 12 receives the output destination switching instruction signal with the output destination being the candidate beam detection unit 15b from the candidate beam detection unit 15b, it sets the output destination of the feedback signal to the candidate beam detection unit 15b.

[0174] The candidate beam detection unit 15b randomly selects one value from 1 to N as the value of the variable i. The candidate beam detection unit 15b writes and records the values that the variable i can take (that is, 1 to N) and the values that have already been selected in its internal storage area. Here, for example, it is assumed that the value "4" is selected as the value of the variable i. When i = 4, the following processing is performed. That is, the candidate beam detection unit 15b outputs a full beam search request signal including the "Distributed Antenna ID #4", which is the distributed antenna ID assigned to the fourth distributed antenna 31-4, to the beam search execution instruction unit 11 in order to cause the distributed antenna device 30-4 including the fourth distributed antenna 31-4 to perform a full beam search.

[0175] After the candidate beam detection unit 15b outputs the all-beam search request signal to the beam search execution instruction unit 11, it activates the feedback signal timer provided inside. When activating the feedback signal timer, the candidate beam detection unit 15b sets the same time as that set by the beam combination history generation unit 13 for the feedback signal timer in the process of step Sa1 in FIG. 9. Note that the time is a predetermined time and is set in advance in the candidate beam detection unit 15b. When the beam search execution instruction unit 11 captures the all-beam search request signal output by the candidate beam detection unit 15b, then, in the process of step Sa1 in FIG. 9, after the beam search execution instruction unit 11 captures the all-beam search request signal, the subsequent process is performed by the beam search execution instruction unit 11, the digital signal processing device 20, the main body device 32-4, the distributed antenna 31-4, and the terminal device 40 with i = 4 (step Sf1 when i = 4).

[0176] The candidate beam detection unit 15b determines whether it has captured a feedback signal in which the "distributed antenna ID #4", which is the distributed antenna ID of the fourth distributed antenna 31-4, is included as the transmission source antenna ID before the feedback signal timer expires (step Sf2 when i = 4).

[0177] Here, assume that any event occurs when the beam combination history generation unit 13 described above cannot capture the feedback signal. In this case, the candidate beam detection unit 15b determines that it has not captured the feedback signal in which the "diversity antenna ID #4", which is the diversity antenna ID of the fourth diversity antenna 31-4, is included as the transmission source antenna ID before the feedback signal timer expires (step Sf2, No). If the candidate beam detection unit 15b has not selected the values of the variable i in a random order for the number N of diversity antennas at that time (that is, if the state where all possible values that the variable i can take have not been selected), the candidate beam detection unit 15b randomly selects one value from 1 to N that has not been selected yet as the value of the variable i. Here, for example, assume that "2" is selected as the value of the variable i. Then, the processes of steps Sf1 and Sf2 are performed again (loops Lf1s to Lf1e).

[0178] When i = 2, the candidate beam detection unit 15b performs the following process as the second process of loops Lf1s to Lf1e. That is, the candidate beam detection unit 15b outputs a full beam search request signal including the "diversity antenna ID #2", which is the diversity antenna ID given to the second diversity antenna 31-2, to the beam search execution instruction unit 11 in order to cause the diversity antenna device 30-2 including the second diversity antenna 31-2 to perform a full beam search. After the candidate beam detection unit 15b outputs the full beam search request signal to the beam search execution instruction unit 11, it activates the feedback signal timer provided inside. When activating the feedback signal timer, the candidate beam detection unit 15b sets the same time as that set by the beam combination history generation unit 13 for the feedback signal timer in the process of step Sa1 in FIG. 9. When the beam search execution instruction unit 11 captures the full beam search request signal output by the candidate beam detection unit 15b, then, in the process of step Sa1 in FIG. 9, after the beam search execution instruction unit 11 captures the full beam search request signal, the subsequent process is performed by the beam search execution instruction unit 11, the digital signal processing device 20, the main body device 32-2, the diversity antenna 31-2, and the terminal device 40 with i = 2 (step Sf1 when i = 2).

[0179] The candidate beam detection unit 15b determines whether it has captured a feedback signal in which the "diversity antenna ID #2", which is the diversity antenna ID of the second diversity antenna 31-2, is included as the transmission source antenna ID before the feedback signal timer expires (step Sf2 when i = 2). Here, it is assumed that none of the events occur when the beam combination history generation unit 13 described above cannot capture the feedback signal, and the feedback signal reception unit 12 outputs the feedback signal to the candidate beam detection unit 15b. In this case, the candidate beam detection unit 15b determines that it has captured a feedback signal in which the "diversity antenna ID #2", which is the diversity antenna ID of the second diversity antenna 31-2, is included as the transmission source antenna ID before the feedback signal timer expires (step Sf2 when i = 2, Yes).

[0180] The candidate beam detection unit 15b exits the processing of loops Lf1s to Lf1e, and sets the beam ID included in the captured feedback signal as the beam ID indicating the best beam in the second diversity antenna device 30-2. The candidate beam detection unit 15b designates the beam specified by the beam ID and the "diversity antenna ID #2", which is the transmission source antenna ID included in the feedback signal, as the detection reference beam. Here, it is assumed that the beam ID included in the feedback signal captured by the candidate beam detection unit 15b is "beam ID #33".

[0181] The candidate beam detection unit 15b combines the transmission source antenna ID, beam ID, and received power value included in the feedback signal into a set of data, and outputs the set of data to the beam combination recording unit 17. The beam combination recording unit 17 captures the set of data output by the candidate beam detection unit 15b. The candidate beam detection unit 15b outputs an output destination switching instruction signal to the feedback signal reception unit 12 to change the output destination to the beam search execution determination unit 16. When the feedback signal reception unit 12 receives the output destination switching instruction signal whose output destination is changed to the beam search execution determination unit 16 from the candidate beam detection unit 15b, it sets the output destination of the feedback signal to the beam search execution determination unit 16 (step Sf3).

[0182] In other words, regarding the processing of steps Sf2 and Sf3 above, the candidate beam detection unit 15b performs a process of causing all the distributed antenna devices 30-1 to 30-4 to perform a full beam search in a random order. During this process, when one feedback signal is captured, the processing of loops Lf1s to Lf1e ends, and the beam specified by the transmission source antenna ID and beam ID included in the captured feedback signal is used as the detection reference beam.

[0183] At this point, during the beam search period, the two distributed antenna devices 30-1 and 30-3 have not performed a full beam search. If the wireless communication system 1b includes N distributed antenna devices 30-1 to 30-N, when exiting loops Lf1s to Lf1e, the value of variable i that has been selected so far and the value of N are used to identify the distributed antenna device 30-k that has not performed a full beam search. Here, the variable k takes the values of "1" and "3". The candidate beam detection unit 15b writes and records the possible values that the variable k can take and the values that have already been selected in an internal storage area.

[0184] When k = 1, the candidate beam detection unit 15b performs the following processing. That is, the candidate beam detection unit 15b detects from the beam combination history table 140 the beam ID of the beam of the first distributed antenna device 30-1 that has been selected together with the detection reference beam. Here, the detection reference beam is the beam specified by "beam ID #33" of "distributed antenna ID #2". In the beam combination history table 140, "beam ID #33" of "distributed antenna ID #1" corresponding to the detection reference beam is included in "record ID #2", "record ID #4", and "record ID #6". In the items of "distributed antenna ID #1" of "record ID #2", "record ID #4", and "record ID #6", "beam ID #13" and "beam ID #25" are written.

[0185] Therefore, the candidate beam detection unit 15b detects from the beam combination history table 140 "beam ID #13" and "beam ID #25" as the beam IDs of the beams of the first distributed antenna device 30-1 that have been selected together with the detection reference beam. The candidate beam detection unit 15b sets "beam ID #13" and "beam ID #25" as candidate beam IDs indicating candidate beams of the distributed antenna device 30-1 corresponding to "distributed antenna ID #1". The candidate beam detection unit 15b generates data indicating a detection result including "distributed antenna ID #1", candidate beam ID "beam ID #13", and "beam ID #25" (step Sf4 when k = 1). The candidate beam detection unit 15b outputs the data indicating the generated detection result to the beam search execution determination unit 16 (step Sf5 when k = 1). When receiving the data indicating the detection result from the candidate beam detection unit 15b, the beam search execution determination unit 16 starts the subroutine of the all beam search execution determination process shown in FIG. 11 (step Sf6 when k = 1).

[0186] The beam search execution determination unit 16 captures data indicating the detection result output by the candidate beam detection unit 15b (step Sc1 when k = 1). The beam search execution determination unit 16 determines whether the data indicating the captured detection result contains a candidate beam ID (step Sc2 when k = 1). Here, since the data indicating the detection result contains "Beam ID #13" and "Beam ID #25", the beam search execution determination unit 16 determines that the data indicating the captured detection result contains a candidate beam ID (step Sc2 when k = 1, Yes).

[0187] The beam search execution determination unit 16 outputs a partial beam search request signal including "Distributed antenna ID #1", "Beam ID #13", and "Beam ID #25" to the beam search execution instruction unit 11 in order to cause the distributed antenna device 30-1 including the first distributed antenna 31-1 to perform a partial beam search for the candidate beam ID. After the beam search execution determination unit 16 outputs the partial beam search request signal to the beam search execution instruction unit 11, it activates a feedback signal timer provided inside. When activating the feedback signal timer, the beam search execution determination unit 16 sets the same time as that set by the beam combination history generation unit 13 for the feedback signal timer in the process of step Sa1 in FIG. 9.

[0188] The beam search execution instruction unit 11 captures the partial beam search request signal output by the beam search execution determination unit 16, and reads out "distributed antenna ID #1", "beam ID #13", and "beam ID #25" included in the captured partial beam search request instruction signal. The beam search execution instruction unit 11 generates a beam search instruction signal including "distributed antenna ID #1" and "beam ID #13", and a beam search instruction signal including "distributed antenna ID #1" and "beam ID #25". The beam search execution instruction unit 11 outputs the two generated beam search instruction signals to the digital signal processing device 20 one by one in the order of generation at a predetermined fixed time interval. The digital signal processing device 20 sequentially captures the two beam search instruction signals output by the beam search execution instruction unit 11. Thereafter, in the process of step Sa1 in FIG. 9, after the digital signal processing device 20 captures the beam search instruction signal, the process is performed by the digital signal processing device 20, the main body device 32-1, the distributed antenna 31-1, and the terminal device 40 with i = 1 (step Sc7 when k = 1).

[0189] The beam search execution determination unit 16 determines whether or not it has captured a feedback signal including "distributed antenna ID #1", which is the distributed antenna ID of the first distributed antenna 31-1, as the transmission source antenna ID before the feedback signal timer expires (step Sc8).

[0190] For example, assume that any one of the events occurs when the beam combination history generation unit 13 described above cannot capture the feedback signal. In this case, the beam search execution determination unit 16 determines that it has not captured a feedback signal including "distributed antenna ID #1", which is the distributed antenna ID of the first distributed antenna 31-1, as the transmission source antenna ID before the feedback signal timer expires (step Sc8, No when k = 1), and advances the process to step Sc3.

[0191] On the other hand, assume that none of the events occur where the beam combination history generation unit 13 described above cannot capture the feedback signal, and the feedback signal reception unit 12 outputs the feedback signal to the beam search execution determination unit 16. In this case, the beam search execution determination unit 16 determines that it has captured a feedback signal in which the "diversity antenna ID #1", which is the diversity antenna ID of the first diversity antenna 31-1, is included as the transmission source antenna ID before the feedback signal timer expires (step Sc8, Yes when k = 1).

[0192] In this case, the beam search execution determination unit 16 determines whether the received power value included in the feedback signal exceeds a predetermined threshold (step Sc9 when k = 1). When the beam search execution determination unit 16 determines that the received power value included in the feedback signal does not exceed the predetermined threshold (step Sc9, No when k = 1), the process proceeds to step Sc3. On the other hand, when the beam search execution determination unit 16 determines that the received power value included in the feedback signal exceeds the predetermined threshold (step Sc9, Yes when k = 1), the process proceeds to step Sc5.

[0193] To put it another way regarding the processing of steps Sc7, Sc8, and Sc9 above, the beam search execution determination unit 16 causes the diversity antenna device 30-1 corresponding to the "diversity antenna ID #1" to perform a partial beam search for transmitting the beam corresponding to the "beam ID #13" and the beam corresponding to the "beam ID #25". When the feedback signal from the partial beam search cannot be obtained, the beam search execution determination unit 16 proceeds to step Sc3 and causes the diversity antenna device 30-1 corresponding to the "diversity antenna ID #1" to perform a full beam search to re-search for the best beam for the diversity antenna device 30-1. Also, in the full beam search in this case, the beam search execution determination unit 16 only searches for beams other than the beam corresponding to the "beam ID #13" and the beam corresponding to the "beam ID #25".

[0194] Then, when the beam search execution determination unit 16 captures a feedback signal including "distributed antenna ID #1" as the transmission source antenna ID before the feedback signal timer expires in step Sc4, the process proceeds to step Sc5, and the beam ID included in the feedback signal is set as the data to be added to the beam combination history table 140.

[0195] On the other hand, when a feedback signal is obtained by the partial beam search, if the received power value included in the feedback signal, that is, the received power value of the beam selected as the best beam in the terminal device 40, does not exceed the threshold value, the beam search execution determination unit 16 determines that the beam indicated by the feedback signal is an inappropriate beam that cannot be used for normal operation. Therefore, the beam search execution determination unit 16 proceeds with the process to step Sc3 to cause the distributed antenna device 30-1 corresponding to "distributed antenna ID #1" to perform a full beam search and re-search for the best beam for the distributed antenna device 30-1. Also, in the full beam search in this case, the beam search execution determination unit 16 searches only for beams other than the beam corresponding to "beam ID #13" and the beam corresponding to "beam ID #25".

[0196] Then, when the beam search execution determination unit 16 captures a feedback signal including "distributed antenna ID #1" as the transmission source antenna ID before the feedback signal timer expires in step Sc4, the process proceeds to step Sc5, and the beam ID included in the feedback signal is set as the data to be added to the beam combination history table 140.

[0197] On the other hand, when the received power value included in the feedback signal exceeds the threshold value, the beam search execution determination unit 16 proceeds with the process to step Sc5 and determines that the beam is the best beam in the distributed antenna device 30-1. In this case, the beam search execution determination unit 16 can use the beam for normal operation without performing a full beam search for the distributed antenna device 30-1, and can use the beam as an appropriate beam that can be used for normal operation, so the number of beam searches can be reduced.

[0198] If there is a value that can be taken by the variable k (here, "1", "3") at that time and has not been selected, the candidate beam detection unit 15b selects the unselected value, and the processes of steps Sf4 to Sf6 are performed again (loops Lf2s to Lf2e). Here, since "3" among the values that can be taken by the variable k (here, "1", "3") has not been selected yet, the candidate beam detection unit 15b sets "3" as the new value of k.

[0199] When k = 3 (for the other possible value of the variable k, which is "3"), the candidate beam detection unit 15b performs the following processing. That is, the candidate beam detection unit 15b detects, from the beam combination history table 140, as candidate beams, the beams of the third distributed antenna device 30-3 that have been selected together with the detection reference beam. Here, the detection reference beam is the beam specified by "Beam ID #33" of "Distributed Antenna ID #2". In the beam combination history table 140, "Beam ID #33" of "Distributed Antenna ID #2" corresponding to the detection reference beam is included in "Record ID #2", "Record ID #4", and "Record ID #6", but the items of "Distributed Antenna ID #3" in "Record ID #2", "Record ID #4", and "Record ID #6" are blank. Therefore, the candidate beam detection unit 15b detects as a detection result that there is no candidate beam ID indicating a candidate beam of the third distributed antenna device 30-3 that has been selected together with the detection reference beam. The candidate beam detection unit 15b generates data indicating a detection result including only "Distributed Antenna ID #3" (step Sf4 when k = 3).

[0200] The candidate beam detection unit 15b outputs data indicating a detection result including only "Distributed Antenna ID #3" to the beam search execution determination unit 16 (step Sf5 when k = 3). When the beam search execution determination unit 16 receives the data indicating the detection result from the candidate beam detection unit 15b, it starts the subroutine of the all beam search execution determination process shown in FIG. 11 (step Sf6 when k = 3).

[0201] When the candidate beam detection unit 15b captures the end notification signal output by the beam search execution determination unit 16, if there is a value among the possible values of the variable k at that time (here, "1" and "3") that has not been selected, it selects that unselected value, and the processing from step Sf4 to step Sf6 is performed again (loops Lf2s to Lf2e).

[0202] When the candidate beam detection unit 15b captures the end notification signal output by the beam search execution determination unit 16, if there is no value among the possible values of the variable k at that time (here, "1" and "3") that has not been selected, the processing of the loop Lf2s to Lf2e ends, and the processing proceeds to step Sf7. Here, since there is no longer a value among the possible values of the variable k at that time that has not been selected, the processing of the loop Lf2s to Lf2e ends, and the processing proceeds to the processing of step Sf7.

[0203] The beam combination recording unit 17 generates one record in the beam combination history table 140 based on the remaining data excluding the received power value from the set of data captured in the processing of step Sf3 and the processing of step Sc5, that is, the data obtained by combining the transmission source antenna ID, the beam ID, and the received power value. That is, the beam combination recording unit 17 generates a new row in the beam combination history table 140 to generate "record ID #M + 1" as a new record ID. The beam combination recording unit 17 writes "record ID #M + 1", which is the newly generated record ID, in the "record ID" item of the newly generated row. The beam combination recording unit 17 writes the corresponding beam ID in each of the elements of "diversity antenna ID #1", "diversity antenna ID #2", "diversity antenna ID #3", and "diversity antenna ID #4" in the row of "record ID #M + 1" based on the combination of the transmission source antenna ID and the beam ID (step Sf7).

[0204] In the wireless communication system 1b of the above-described third embodiment, during the beam search period in which the candidate beam detection unit 15b searches for a beam to be used for wireless communication with the terminal device 40, for each of the plurality of distributed antennas 31-1 to 31-4 in a random order, all beams are transmitted in all directions in which transmission is possible to perform a full beam search. When one beam identifier indicating the best beam among the beams obtained by the full beam search is acquired, the full beam search is stopped, and the beam specified by the acquired beam identifier and the information indicating the distributed antennas 31-1 to 31-4 that transmitted the beam indicated by the beam identifier is set as the detection reference beam. The beam identifier of a beam that has been selected together with the detection reference beam among the beam identifiers of the distributed antennas 31-1 to 31-4 for which the full beam search has not been performed during the beam search period is detected from the beam combination history storage unit 14 as the candidate beam identifier for the distributed antennas 31-1 to 31-4.

[0205] The beam search execution determination unit 16 determines whether to perform a full beam search for the distributed antennas 31-1 to 31-4 for which the full beam search has not been performed during the beam search period based on the detection result of the candidate beam detection unit 15b. The beam combination recording unit 17 generates a record indicating a combination of beam identifiers indicating the beams that have been the best beams in each of the distributed antennas during the beam search period. The beam combination recording unit 17 records the generated record in the beam combination history storage unit 14. Thereby, in the beam combination generation process performed by the beam combination history generation unit 13, even if a sufficient number of records indicating the history of beam combinations cannot be generated by slightly moving the terminal device 40 at intervals that do not reduce the transmission capacity over the entire cell 100 within the service area, when performing the beam search process, it is possible to accumulate a sufficient number of records to reduce the beam search count without reducing the transmission capacity, which has the effect of making this possible.

[0206] Also, in the wireless communication system 1b according to the third embodiment, instead of performing a full beam search in a fixed order for the distributed antenna devices 30-1 to 30-4 at the first stage of the beam search process, a full beam search is performed in a random order for the distributed antenna devices 30-1 to 30-4. By having such a configuration, the wireless communication system 1b can perform a full beam search at random timing even for a distributed antenna device for which the full beam search was not performed because a beam that is not the best beam but has a received power value exceeding the threshold is selected by the partial beam search. Thus, the update of the beam combination history table 140 is also performed. Accordingly, according to the wireless communication system 1b in the third embodiment, it is possible to reduce the number of beam searches and prevent a combination of non-optimal beams from being continuously and fixedly selected.

[0207] (Fourth Embodiment) FIG. 19 is a block diagram showing the configuration of the communication control device 10c in the fourth embodiment. The communication control device 10c is a device used in place of the communication control device 10a in the second embodiment. Hereinafter, for convenience of explanation, a wireless communication system 1a including the communication control device 10c in place of the communication control device 10a is referred to as a wireless communication system 1c. In the communication control device 10c, the same components as those of the communication control device 10a in the second embodiment are denoted by the same reference numerals, and different components will be described below.

[0208] Among the configurations of the wireless communication system 1c in the fourth embodiment, the difference from the configuration of the wireless communication system 1a in the second embodiment is that, at the first stage of the beam search process, instead of performing a full beam search by a plurality of distributed antenna devices in a fixed order, a distributed antenna device is randomly selected and a full beam search is performed.

[0209] The communication control device 10c includes a beam search execution instruction unit 11, a feedback signal reception unit 12, a beam combination history generation unit 13a, a beam combination history storage unit 14a, a candidate beam detection unit 15c, a beam search execution determination unit 16a, and a beam combination recording unit 17a.

[0210] When the beam search process for searching for a beam starts, the candidate beam detection unit 15c causes each of the distributed antenna devices 30-1 to 30-4 to perform a full beam search one by one in a random order. That is, the candidate beam detection unit 15c designates one distributed antenna ID of the distributed antennas 31-1 to 31-4 one by one in a random order, and outputs a full beam search request signal including the designated one distributed antenna ID to the beam search execution instruction unit 11. After starting the beam search process, when the candidate beam detection unit 15c captures the first feedback signal, it stops the full beam search, and sets the beam specified by the transmission source antenna ID and the beam ID included in the feedback signal as the detection reference beam. The candidate beam detection unit 15c detects, from, for example, the beam combination history table 140a shown in FIG. 14, the beam ID of the beam that is the beam ID of the distributed antenna devices 30-1 to 30-4 that have not performed the full beam search during the beam search period and that has been selected together with the detection reference beam, and the distributed antenna ID corresponding to the beam ID.

[0211] At that time, the candidate beam detection unit 15c detects the received power value written as an element together with the detected beam ID in the beam combination history table 140a. The candidate beam detection unit 15c sets the beam ID of the candidate beam in the distributed antenna devices 30-1 to 30-4 corresponding to the detected distributed antenna ID as the candidate beam ID, and sets the combination of the detected distributed antenna ID and the candidate beam ID as the detection result. The candidate beam detection unit 15c calculates the average value of the received power values for each beam ID based on the combination of the detected beam ID and the detected received power value, and sets the maximum value of the calculated average values as the average received power value for the detected distributed antenna ID. The candidate beam detection unit 15c includes the calculated average received power value in the data indicating the detection result.

[0212] (Processing by the wireless communication system of the fourth embodiment) Similar to the second embodiment, in the wireless communication system 1c of the fourth embodiment, the beam combination generation process in step S1 and the beam search process in step S2 shown in FIG. 8 are also performed. However, in the points described below, the beam search process performed in the fourth embodiment is different from the process performed in the second embodiment.

[0213] (Beam combination generation process of the fourth embodiment) The same beam combination generation process as that of the first embodiment shown in FIG. 9 is performed by the beam search execution instruction unit 11, the feedback signal reception unit 12, the beam combination history generation unit 13a, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4.

[0214] (Beam search process of the fourth embodiment) FIG. 20 is a flowchart showing the beam search process of the fourth embodiment. FIG. 20 is a flowchart showing the flow of the beam search process performed in the process of step S2 in FIG. 8.

[0215] In FIG. 20, the processes of steps Sg1 and Sg2, the loop Lg1s to Lg1e that repeats the processes of steps Sg1 and Sg2, and the process of step Sg3 are the same as the processes of steps Sd1 and Sd2 and the loop Ld1s to Ld1e that repeats the processes of steps Sd1 and Sd2 and the process of step Sd3 in FIG. 15, and are performed by the beam search execution instruction unit 11, the feedback signal reception unit 12, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4. The process that was performed by the candidate beam detection unit 15a is performed by the candidate beam detection unit 15c. The process of step Sg7 is performed by the beam combination recording unit 17a for the above-described process.

[0216] In response to the operation of the operator of the wireless communication system 1c, the candidate beam detection unit 15c of the communication control device 10c starts the beam search process. The candidate beam detection unit 15c activates the beam search period timer provided therein. When activating the beam search period timer, the candidate beam detection unit 15c sets a time indicating the length of a period of one predetermined beam search period.

[0217] The candidate beam detection unit 15c reads out all the distributed antenna IDs written in the distributed antenna ID item of the beam combination history table 140a stored in the beam combination history storage unit 14a. The candidate beam detection unit 15c provides a variable i in its internal storage area. Here, i is a variable that can take integer values from 1 to N. However, since the wireless communication system 1 in FIG. 1 includes four distributed antenna devices 30-1 to 30-4, the candidate beam detection unit 15c reads out four distributed antenna IDs, namely, "distributed antenna ID #1", "distributed antenna ID #2", "distributed antenna ID #3", and "distributed antenna ID #4" from the beam combination history table 140a. Therefore, in the following description, N = 4 is assumed. The i-th distributed antenna device is referred to as the distributed antenna device 30-i, the i-th distributed antenna is referred to as the distributed antenna 31-i, and the i-th main body device is referred to as the main body device 32-i for the following description.

[0218] The candidate beam detection unit 15c outputs an output destination switching instruction signal whose output destination is the candidate beam detection unit 15c to the feedback signal reception unit 12. When receiving the output destination switching instruction signal whose output destination is the candidate beam detection unit 15c from the candidate beam detection unit 15c, the feedback signal reception unit 12 sets the output destination of the feedback signal to the candidate beam detection unit 15c.

[0219] The candidate beam detection unit 15c randomly selects one value from 1 to N as the value of the variable i. The candidate beam detection unit 15c writes and records the possible values that the variable i can take (i.e., 1 to N) and the values that have already been selected in an internal storage area. Here, for example, it is assumed that the value "4" is selected as the value of the variable i. When i = 4, the following processing is performed. That is, the candidate beam detection unit 15c outputs a full beam search request signal including the "diversity antenna ID #4", which is the diversity antenna ID assigned to the fourth diversity antenna 31-4, to the beam search execution instruction unit 11 in order to cause the diversity antenna device 30-4 including the fourth diversity antenna 31-4 to perform a full beam search. After the candidate beam detection unit 15c outputs the full beam search request signal to the beam search execution instruction unit 11, it activates a feedback signal timer provided inside itself.

[0220] When the candidate beam detection unit 15c activates the feedback signal timer, it sets the same time as that set by the beam combination history generation unit 13a for the feedback signal timer in the process of step Sa1 in FIG. 9. Note that the time is a predetermined time and is set in advance in the candidate beam detection unit 15c. When the beam search execution instruction unit 11 captures the full beam search request signal output by the candidate beam detection unit 15c, then, in the process of step Sa1 in FIG. 9, the processing after the beam search execution instruction unit 11 captures the full beam search request signal is performed as i = 4 by the beam search execution instruction unit 11, the digital signal processing device 20, the main body device 32-4, the diversity antenna 31-4, and the terminal device 40 (step Sg1 when i = 4).

[0221] The candidate beam detection unit 15c determines whether or not it has captured a feedback signal including the "diversity antenna ID #4", which is the diversity antenna ID of the fourth diversity antenna 31-4, as the transmission source antenna ID before the feedback signal timer expires (step Sg2 when i = 4).

[0222] Here, assume that any event occurs when the beam combination history generation unit 13a described above cannot capture the feedback signal. In this case, the candidate beam detection unit 15c determines that it has not captured the feedback signal in which the "diversity antenna ID #4", which is the diversity antenna ID of the fourth diversity antenna 31-4, is included as the transmission source antenna ID before the feedback signal timer expires (step Sg2, No). If the values of the variable i have not been selected in a random order for the number N of diversity antennas at that time (that is, if the state is not such that all possible values that the variable i can take have been selected), the candidate beam detection unit 15c randomly selects one value from 1 to N that has not been selected yet as the value of the variable i. Here, for example, assume that "2" is selected as the value of the variable i. Then, the processes of steps Sg1 and Sg2 are performed again (loop Lg1s to Lg1e).

[0223] When i = 2, the candidate beam detection unit 15c performs the following process as the second process of loop Lg1s to Lg1e. That is, the candidate beam detection unit 15c outputs a full beam search request signal including the "diversity antenna ID #2", which is the diversity antenna ID assigned to the second diversity antenna 31-2, to the beam search execution instruction unit 11 in order to cause the diversity antenna device 30-2 including the second diversity antenna 31-2 to perform a full beam search. After the candidate beam detection unit 15c outputs the full beam search request signal to the beam search execution instruction unit 11, it activates the feedback signal timer provided inside. When activating the feedback signal timer, the candidate beam detection unit 15c sets the same time as that set by the beam combination history generation unit 13a for the feedback signal timer in the process of step Sa1 in FIG. 9. When the beam search execution instruction unit 11 captures the full beam search request signal output by the candidate beam detection unit 15c, then, in the process of step Sa1 in FIG. 9, after the beam search execution instruction unit 11 captures the full beam search request signal, the subsequent process is performed by the beam search execution instruction unit 11, the digital signal processing device 20, the main body device 32-2, the diversity antenna 31-2, and the terminal device 40 with i = 2 (step Sg1 when i = 2).

[0224] The candidate beam detection unit 15c determines whether it has captured a feedback signal that includes, as the transmission source antenna ID, "diversity antenna ID #2", which is the diversity antenna ID of the second diversity antenna 31-2, before the feedback signal timer expires (step Sg2 when i = 2). Here, it is assumed that none of the events occur when the beam combination history generation unit 13a cannot capture the feedback signal, and the feedback signal reception unit 12 outputs the feedback signal to the candidate beam detection unit 15c. In this case, the candidate beam detection unit 15c determines that it has captured a feedback signal that includes, as the transmission source antenna ID, "diversity antenna ID #2", which is the diversity antenna ID of the second diversity antenna 31-2, before the feedback signal timer expires (step Sg2 when i = 2, Yes).

[0225] The candidate beam detection unit 15c exits the processing of loops Lg1s to Lg1e, and sets the beam ID included in the captured feedback signal as the beam ID indicating the best beam in the second diversity antenna device 30-2. The candidate beam detection unit 15c sets the beam specified by the beam ID and "diversity antenna ID #2", which is the transmission source antenna ID included in the feedback signal, as the detection reference beam. Here, it is assumed that the beam ID included in the feedback signal captured by the candidate beam detection unit 15c is "beam ID #33".

[0226] The candidate beam detection unit 15c combines the transmission source antenna ID, beam ID, and received power value included in the feedback signal into a set of data, and outputs the set of data to the beam combination recording unit 17a. The beam combination recording unit 17a captures the set of data output by the candidate beam detection unit 15c. The candidate beam detection unit 15c outputs an output destination switching instruction signal to the feedback signal reception unit 12 to set the output destination to the beam search execution determination unit 16a. When the feedback signal reception unit 12 receives the output destination switching instruction signal from the candidate beam detection unit 15c to set the output destination of the feedback signal to the beam search execution determination unit 16a (step Sg3).

[0227] In other words, regarding the processing of steps Sg2 and Sg3 above, the candidate beam detection unit 15c performs a process of causing all the distributed antenna devices 30-1 to 30-4 to perform a full beam search in a random order. During this process, when one feedback signal is captured, the processing of loops Lg1s to Lg1e ends, and the beam specified by the transmission source antenna ID and beam ID included in the captured feedback signal is used as the detection reference beam.

[0228] At this point, during the beam search period, the two distributed antenna devices 30-1 and 30-3 have not performed a full beam search. If the wireless communication system 1c includes N distributed antenna devices 30-1 to 30-N, when exiting loops Lg1s to Lg1e, using the value of the variable i that has been selected so far and the value of N, the distributed antenna device 30-k that has not performed a full beam search is identified. Here, the variable k takes the values of "1" and "3". The candidate beam detection unit 15c writes and records the possible values that the variable k can take and the values that have already been selected in an internal storage area.

[0229] When k = 1, the candidate beam detection unit 15c performs the following processing. That is, the candidate beam detection unit 15c detects from the beam combination history table 140a the beam ID of the beam of the first distributed antenna device 30-1 that has been selected together with the detection reference beam. Here, the detection reference beam is the beam specified by "beam ID #33" of "distributed antenna ID #2". In the beam combination history table 140a, "beam ID #33" of "distributed antenna ID #2" corresponding to the detection reference beam is included in "record ID #2", "record ID #4", and "record ID #6". In the items of "distributed antenna ID #1" of "record ID #2", "record ID #4", and "record ID #6", "beam ID #13" and "beam ID #25" are written.

[0230] Therefore, the candidate beam detection unit 15c detects "beam ID #13" and "beam ID #25" from the beam combination history table 140a as the beam IDs of the beams of the first distributed antenna device 30-1 that have been selected together with the detection reference beam. The candidate beam detection unit 15c uses "beam ID #13" and "beam ID #25" as candidate beam IDs indicating candidate beams of the distributed antenna device 30-1 corresponding to "distributed antenna ID #1".

[0231] The candidate beam detection unit 15c further detects, for "Beam ID #25", "(Received power value 2-1)" of "Record ID #2" and "(Received power value 6-1)" of "Record ID #6", and for "Beam ID #13", detects "(Received power value 4-1)" of "Record ID #4". The candidate beam detection unit 15c calculates the average value of "(Received power value 2-1)" and "(Received power value 6-1)" corresponding to "Beam ID #25". For "Beam ID #13", since there is only one "(Received power value 4-1)", "(Received power value 4-1)" is used as the average value. The candidate beam detection unit 15c sets the maximum average value among the average value corresponding to "Beam ID #13" and the average value of "Beam ID #25" as the average received power value for "Diversity antenna ID #1". The candidate beam detection unit 15c generates data indicating the detection result including "Diversity antenna ID #1", candidate beam ID "Beam ID #13", "Beam ID #25", and the calculated average received power value (step Sg4 when k = 4). The candidate beam detection unit 15c outputs the data indicating the generated detection result to the beam search execution determination unit 16a (step Sg5 when k = 1).

[0232] In the process of step Se1 of the subroutine of the all beam search execution determination process of FIG. 16 performed in the subsequent step Sg6 process, the beam search execution determination unit 16a fetches the detection result data output by the candidate beam detection unit 15c, and in the process of step Se2, determines that the candidate beam ID is included in the data indicating the fetched detection result (step Se2, Yes when k = 1).

[0233] When the beam search execution determination unit 16a determines "Yes" in the determination process of step Se8, it reads out the average received power value included in the data indicating the detection result, gives a margin to the read average received power value, and calculates a threshold value for "diversity antenna ID #1" (step Se9). The beam search execution determination unit 16a determines whether the received power value included in the feedback signal exceeds the threshold value calculated for the transmission source antenna ID (here, "diversity antenna ID #1") included in the feedback signal (step Se10 in the case of k = 1).

[0234] When the beam search execution determination unit 16a determines that the received power value included in the feedback signal exceeds the threshold value calculated for the transmission source antenna ID included in the feedback signal (step Se10, Yes), then it advances the process to the process of step Se5. On the other hand, when the beam search execution determination unit 16a determines that the received power value included in the feedback signal does not exceed the threshold value calculated for the transmission source antenna ID included in the feedback signal (step Se10, No), then it advances the process to the process of step Se3.

[0235] If there is a value that has not been selected among the possible values of the variable k at that time (here, "1", "3"), the candidate beam detection unit 15c selects the value that has not been selected, and the processes of step Sg4 to step Sg6 are performed again (loops Lg2s to Lg2e). Here, since "3" among the possible values of the variable k (here, "1", "3") has not been selected yet, the candidate beam detection unit 15c sets "3" as the new value of k.

[0236] When k = 3 (for the case of "3", the other value that the variable k can take), the candidate beam detection unit 15c performs the following processing. In the processing of loops Lg2s to Lg2e, when k = 3, similar to the first and third embodiments, the candidate beam detection unit 15c cannot detect the candidate beam ID corresponding to "diversity antenna ID #3" from the beam combination history table 140a. Therefore, in this case, the candidate beam detection unit 15c also cannot detect the received power value. Thus, the candidate beam detection unit 15c does not calculate the average received power value, and similar to the processing of step Sb4 of the first embodiment and step Sd4 of the third embodiment, it is detected that there is no candidate beam ID indicating a candidate beam that has been selected together with the detection reference beam among the beams of the third diversity antenna device 30-3. The candidate beam detection unit 15c generates data indicating a detection result including only "diversity antenna ID #3" (step Sg4 when k = 3).

[0237] The candidate beam detection unit 15c outputs data indicating a detection result including only "diversity antenna ID #3" to the beam search execution determination unit 16a (step Sg5 when k = 3). When receiving the data indicating the detection result from the candidate beam detection unit 15c, the beam search execution determination unit 16a starts the subroutine of the all beam search execution determination process shown in FIG. 16 (step Sg6 when k = 3).

[0238] Regarding the subroutine of the all beam search execution determination process performed in step Sg6 of the beam search process of the fourth embodiment, it will be described with reference to FIG. 16. The processes from step Se1 to step Se6 are the same as the processes from step Sc1 to step Sc6 shown in FIG. 11, and are performed by the beam search execution instruction unit 11, the feedback signal reception unit 12, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4. The process that was performed by the beam search execution determination unit 16 is now performed by the beam search execution determination unit 16a. Therefore, when k = 3, in the determination process of step Se2, the beam search execution determination unit 16a determines "No", and the process proceeds to step Se3. After that, the same processes as those in the case of k = 3 in the first embodiment and the case of k = 3 in the third embodiment are performed.

[0239] Accordingly, in the fourth embodiment, when the beam search execution determination unit 16a determines to cause any one of the distributed antenna devices 30-1 to 30-4 to perform a partial beam search, if the received power value included in the feedback signal obtained by the partial beam search is about the past average received power value of the distributed antenna devices 30-1 to 30-4 targeted by the partial beam search, the beam indicated by the beam ID included in the feedback signal can be searched as the best beam of the distributed antenna devices 30-1 to 30-4 corresponding to the transmission source antenna ID included in the feedback signal. The beam search execution determination unit 16a can add the data related to the beam to the beam combination history table 140a.

[0240] On the other hand, if the received power value included in the feedback signal acquired by the partial beam search is not about the past average received power value of the distributed antenna devices 30-1 to 30-4 targeted by the partial beam search, the beam search execution determination unit 16a causes the distributed antenna devices 30-1 to 30-4 corresponding to the transmission source antenna ID included in the feedback signal to perform a full beam search. If the beam search execution determination unit 16a can acquire a feedback signal by the full beam search, the best beam in the distributed antenna devices 30-1 to 30-4 targeted by the full beam search can be searched. If the feedback signal cannot be acquired, the best beam in the distributed antenna devices 30-1 to 30-4 targeted by the full beam search cannot be searched. Therefore, in the fourth embodiment, in addition to the effects exhibited by the communication control device 10 of the first embodiment and the communication control device 10b of the third embodiment, when causing the partial beam search to be performed, the best beam can be searched more accurately than in the first embodiment and the third embodiment.

[0241] In the third embodiment described above, by setting a higher threshold value of the received power value determined in advance, the possibility of selecting a beam that is not the best from the viewpoint of communication quality can be made lower. However, in this case, in the third embodiment, since the full beam search is performed for more distributed antenna devices, it becomes difficult to reduce the number of beam searches. Further, since the optimal threshold value also changes depending on the position of the terminal device and the like, it is difficult to set the threshold value for selecting the best beam while reducing the number of beam searches as a uniform value. On the other hand, in the fourth embodiment, by changing the threshold value for each beam combination, the threshold value is substantially changed for each position of the terminal device 40, and the configuration is such that the threshold value is adaptively set.

[0242] In the fourth embodiment, a method was described in which the average value of the received power values for each detected beam ID is used as a reference, but it is not limited to the average value. For example, the value used as a reference may be the median, the mode, the maximum value, or the minimum value. Also, among these values, when the maximum value, the minimum value, or the average value is used as a reference, by calculating each time with the same combination of beam IDs, other records may be deleted.

[0243] Also, the wireless communication system 1c in the fourth embodiment does not perform a full beam search on the distributed antenna devices 30-1 to 30-4 in a fixed order at the first stage of the beam search process, but performs a full beam search on the distributed antenna devices 30-1 to 30-4 in a random order. By having such a configuration, the wireless communication system 1c can perform a full beam search on the distributed antenna devices for which the full beam search was not performed because a beam whose received power value exceeds the threshold but is not the best beam was selected by the partial beam search, at random timings. Thus, the update of the beam combination history table 140a is also performed. Thereby, according to the wireless communication system 1c in the fourth embodiment, it is possible to prevent a combination of non-optimal beams from being continuously and fixedly selected while reducing the number of beam searches.

[0244] As described above, the wireless communication system 1b in the third embodiment and the wireless communication system 1c in the fourth embodiment are configured to perform a full beam search one by one in a random order on the distributed antenna devices 30-1 to 30-4 at the first stage of the beam search process. By randomly selecting the distributed antenna devices 30-1 to 30-4 that perform the full beam search, it is possible to prevent a combination of non-optimal beams from being continuously and fixedly selected.

[0245] Instead of performing the full beam search one by one in a random order for the distributed antenna devices 30-1 to 30-4, it may be configured to perform the full beam search simultaneously using a plurality of randomly selected distributed antenna devices among the distributed antenna devices 30-1 to 30-4. Also in this case, since the combination of the distributed antenna devices 30-1 to 30-4 that perform the full beam search is randomly selected, it is possible to prevent the combination of beams that is not the best from being continuously and fixedly selected.

[0246] Note that, as a method of performing the full beam search simultaneously using the distributed antenna devices, for example, techniques such as frequency multiplexing or code multiplexing may be used. In addition, when the interference between the distributed antenna devices is small, etc., the full beam search using the same resource may be performed in a plurality of distributed antenna devices.

[0247] In the wireless communication system 1d in the fifth embodiment and the wireless communication system 1e in the sixth embodiment described below, in the first stage of the beam search process, the full beam search is performed simultaneously using a plurality of randomly selected distributed antenna devices among the distributed antenna devices 30-1 to 30-4. By having such a configuration, in the fifth embodiment and the sixth embodiment described below, even for the distributed antenna devices for which the full beam search was not performed because a beam that is not the best beam but has a received power value exceeding the threshold is selected by the partial beam search, the full beam search is performed at random timing. Therefore, the beam combination history tables 140 and 140a are also updated. Thus, according to the fifth embodiment and the sixth embodiment described below, it is possible to prevent the combination of beams that is not the best from being continuously and fixedly selected while reducing the number of beam searches.

[0248] (Fifth Embodiment) FIG. 21 is a block diagram showing the configuration of the communication control device 10d in the fifth embodiment. The communication control device 10d is a device used in place of the communication control device 10 in the first embodiment. Hereinafter, for convenience of explanation, a wireless communication system 1 including the communication control device 10d in place of the communication control device 10 is referred to as a wireless communication system 1d. In the communication control device 10d, the same components as those of the communication control device 10 in the first embodiment are denoted by the same reference numerals, and different components will be described below.

[0249] Among the configurations of the wireless communication system 1d in the fifth embodiment, the difference from the configuration of the wireless communication system 1 in the first embodiment is that, in the first stage of the beam search process, instead of performing a full beam search one by one in a fixed order for a plurality of distributed antenna devices, a full beam search is performed simultaneously using a plurality of randomly selected distributed antenna devices among the plurality of distributed antenna devices.

[0250] The communication control device 10d includes a beam search execution instruction unit 11, a feedback signal reception unit 12, a beam combination history generation unit 13, a beam combination history storage unit 14, a candidate beam detection unit 15d, a beam search execution determination unit 16, and a beam combination recording unit 17.

[0251] When the beam search process for searching for a beam is started, the candidate beam detection unit 15d randomly selects a plurality of (X pieces) of the N distributed antenna devices 30-1 to 30-N. For example, the candidate beam detection unit 15d randomly selects 2 (X = 2) of the 4 (N = 4) distributed antenna devices 30-1 to 30-4. Note that each time the beam search process is performed, the same number of (for example, 2 (X = 2)) distributed antenna devices may be randomly selected, or different numbers of (for example, 2 to 3 (X = 2 to 3)) distributed antenna devices may be randomly selected.

[0252] The candidate beam detection unit 15d causes all beam searches to be performed simultaneously for each of the selected plurality of distributed antenna devices. That is, the candidate beam detection unit 15d designates, for example, the distributed antenna IDs of two distributed antennas randomly selected, such as the distributed antennas 31-1 and 31-4, and outputs a full beam search request signal including the designated two distributed antenna IDs to the beam search execution instruction unit 11. After starting the beam search process, when the candidate beam detection unit 15d captures the first feedback signal, it stops the full beam search, and designates the beam specified by the transmission source antenna ID and the beam ID included in the feedback signal as the detection reference beam.

[0253] The candidate beam detection unit 15d detects, from the beam combination history table 140, the beam ID of the distributed antenna device among the distributed antenna devices 30-1 to 30-4 that has not performed a full beam search during the beam search period, and that has been selected together with the detection reference beam, and the distributed antenna ID corresponding to the beam ID. The candidate beam detection unit 15d designates the detected beam ID as the candidate beam ID indicating the candidate beam in the distributed antenna devices 30-1 to 30-4 corresponding to the detected distributed antenna ID, and sets the combination of the detected distributed antenna ID and the candidate beam ID as the detection result.

[0254] (Processing by the wireless communication system of the fifth embodiment) Similar to the first embodiment, in the wireless communication system 1d of the fifth embodiment, the beam combination generation process in step S1 and the beam search process in step S2 shown in FIG. 8 are also performed. However, the beam search process performed in the fifth embodiment is different from the process performed in the first embodiment in the points described below.

[0255] (Beam combination generation process of the fifth embodiment) The same beam combination generation process as that of the first embodiment shown in FIG. 9 is performed by the beam search execution instruction unit 11, the feedback signal reception unit 12, the beam combination history generation unit 13, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4.

[0256] (Beam Search Processing of the Fifth Embodiment) FIG. 22 is a flowchart showing the beam search processing of the fifth embodiment. FIG. 22 is a flowchart showing the flow of the beam search processing performed in the process of step S2 in FIG. 8. As a prerequisite for starting the beam search processing shown in FIG. 8, it is assumed that the beam combination history table 140 shown in FIG. 4 is generated in the beam combination history storage unit 14.

[0257] In FIG. 22, the processes of steps Sh1 and Sh2 and the processes of loop Lh1s to Lh1e that repeat the processes of steps Sh1 and Sh2 are performed by the candidate beam detection unit 15d as described above. The process of step Sh3, the processes of steps Sh4 to Sh6, the processes of loop Lh2s to Lh2e that repeat the processes of steps Sh4 to Sh6, and the process of step Sh7 are the same as the process of step Sb3 in FIG. 10, the processes of steps Sb4 to Sb6, the processes of loop Lb2s to Lb2e that repeat the processes of steps Sb4 to Sb6, and the process of step Sb7. The processes that were performed by the candidate beam detection unit 15 are now performed by the beam search execution instruction unit 11, the feedback signal reception unit 12, the beam combination recording unit 17, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4, and the processes that were performed by the candidate beam detection unit 15 are now performed by the candidate beam detection unit 15d.

[0258] In response to the operation of the operator of the wireless communication system 1d, the candidate beam detection unit 15d of the communication control device 10d starts the beam search processing. The candidate beam detection unit 15d activates the beam search cycle timer provided inside. When activating the beam search cycle timer, the candidate beam detection unit 15d sets a time indicating the length of a predetermined beam search cycle period.

[0259] The candidate beam detection unit 15d reads out all the distributed antenna IDs written in the distributed antenna ID item of the beam combination history table 140 stored in the beam combination history storage unit 14. The candidate beam detection unit 15d provides a variable i in its internal storage area. Here, i is a variable that can take integer values from 1 to N. However, the wireless communication system 1 in FIG. 1 includes four distributed antenna devices 30-1 to 30-4, and the candidate beam detection unit 15d reads out four distributed antenna IDs, namely, "distributed antenna ID #1", "distributed antenna ID #2", "distributed antenna ID #3", and "distributed antenna ID #4" from the beam combination history table 140. Therefore, in the following description, N = 4 is assumed. The i-th distributed antenna device is denoted as the distributed antenna device 30-i, the i-th distributed antenna is denoted as the distributed antenna 31-i, and the i-th main body device is denoted as the main body device 32-i, and the following description is given.

[0260] Also, the candidate beam detection unit 15d provides a variable X in its internal storage area. Here, X is a variable that can take integer values of 2 or more. X represents the number of distributed antenna devices for which all beam searches are performed simultaneously. In the following description, as an example, X = 2 is assumed.

[0261] The candidate beam detection unit 15d outputs an output destination switching instruction signal whose output destination is the candidate beam detection unit 15d to the feedback signal reception unit 12. When the feedback signal reception unit 12 receives the output destination switching instruction signal whose output destination is the candidate beam detection unit 15d from the candidate beam detection unit 15d, it sets the output destination of the feedback signal to the candidate beam detection unit 15d.

[0262] The candidate beam detection unit 15d randomly selects two values (X = 2) from among the values of 1 to N as the value of the variable i. The candidate beam detection unit 15d writes and records the possible values that the variable i can take (that is, 1 to N) and the values that have already been selected in an internal storage area. Here, for example, it is assumed that the values of "1" and "3" are selected as the value of the variable i. When i = 1 and 3, the following processing is performed. That is, the candidate beam detection unit 15d causes the distributed antenna device 30-1 including the first distributed antenna 31-1 and the distributed antenna device 30-3 including the third distributed antenna 31-3 to perform a full beam search simultaneously. Therefore, a full beam search request signal including the "distributed antenna ID #1", which is the distributed antenna ID assigned to the first distributed antenna 31-1, and the "distributed antenna ID #3", which is the distributed antenna ID assigned to the third distributed antenna 31-3, is output to the beam search execution instruction unit 11.

[0263] After the candidate beam detection unit 15d outputs the full beam search request signal to the beam search execution instruction unit 11, it activates a feedback signal timer provided inside. When activating the feedback signal timer, the candidate beam detection unit 15d sets the same time as that set by the beam combination history generation unit 13 for the feedback signal timer in the process of step Sa1 in FIG. 9. Note that the time is a predetermined time and is set in advance in the candidate beam detection unit 15d. When the beam search execution instruction unit 11 captures the full beam search request signal output by the candidate beam detection unit 15d, then, in the process of step Sa1 in FIG. 9, the processing after the beam search execution instruction unit 11 captures the full beam search request signal is performed by the beam search execution instruction unit 11, the digital signal processing device 20, the main body device 32-1, the main body device 32-3, the distributed antenna 31-1, the distributed antenna 31-3, and the terminal device 40 when i = 1 and 3 (step Sh1 when i = 1 and 3).

[0264] The candidate beam detection unit 15d determines whether it has captured a feedback signal that includes either "diversity antenna ID #1", which is the diversity antenna ID of the diversity antenna 31-1, or "diversity antenna ID #3", which is the diversity antenna ID of the diversity antenna 31-3, as the transmission source antenna ID before the feedback signal timer expires (step Sh2 when i = 1 and 3).

[0265] Here, it is assumed that any one of the events occurs when the beam combination history generation unit 13 described above cannot capture the feedback signal. In this case, the candidate beam detection unit 15d determines that it has not captured a feedback signal that includes "diversity antenna ID #1", which is the diversity antenna ID of the first diversity antenna 31-1, and "diversity antenna ID #3", which is the diversity antenna ID of the third diversity antenna 31-3, as the transmission source antenna ID before the feedback signal timer expires (step Sh2, No). If the values of the variable i have not been selected for all N diversity antennas at that time (that is, if the state is not such that all possible values that the variable i can take have been selected), the candidate beam detection unit 15d randomly selects two (X = 2) values from 1 to N as the values of the variable i. Here, the remaining "2" and "4" will be selected as the values of the variable i. Then, the processes of steps Sh1 and Sh2 are performed again (loops Lh1s to Lh1e).

[0266] As the second processing of the loops Lh1s to Lh1e, the candidate beam detection unit 15d performs the following processing. That is, the candidate beam detection unit 15d outputs a full beam search request signal including "diversity antenna ID #2", which is the diversity antenna ID given to the second diversity antenna 31-2, and "diversity antenna ID #4", which is the diversity antenna ID given to the fourth diversity antenna 31-4, to the beam search execution instruction unit 11 in order to cause the diversity antenna device 30-2 including the second diversity antenna 31-2 and the diversity antenna device 30-4 including the fourth diversity antenna 31-4 to perform a full beam search simultaneously.

[0267] After the candidate beam detection unit 15d outputs the all-beam search request signal to the beam search execution instruction unit 11, it activates the feedback signal timer provided inside. When activating the feedback signal timer, the candidate beam detection unit 15d sets the same time as that set by the beam combination history generation unit 13 for the feedback signal timer in the process of step Sa1 in FIG. 9. When the beam search execution instruction unit 11 captures the all-beam search request signal output by the candidate beam detection unit 15d, then, in the process of step Sa1 in FIG. 9, after the beam search execution instruction unit 11 captures the all-beam search request signal, the processes are performed by the beam search execution instruction unit 11, the digital signal processing device 20, the main body device 32-2, the main body device 32-4, the distributed antenna 31-2, the distributed antenna 31-4, and the terminal device 40 with i = 2 and 4 (step Sh1 in the case of i = 2 and 4).

[0268] The candidate beam detection unit 15d determines whether it has captured a feedback signal in which the "distributed antenna ID #2", which is the distributed antenna ID of the second distributed antenna 31-2, or the "distributed antenna ID #4", which is the distributed antenna ID of the fourth distributed antenna 31-4, is included as the transmission source antenna ID before the feedback signal timer expires (step Sh2 in the case of i = 2 and 4). Here, it is assumed that none of the events in the case where the above-described beam combination history generation unit 13 cannot capture the feedback signal occur, and the feedback signal reception unit 12 outputs a feedback signal in which the "distributed antenna ID #2", which is the distributed antenna ID of the second distributed antenna 31-2, is included as the transmission source antenna ID to the candidate beam detection unit 15d. In this case, the candidate beam detection unit 15d determines that it has captured a feedback signal in which the "distributed antenna ID #2", which is the distributed antenna ID of the second distributed antenna 31-2, is included as the transmission source antenna ID before the feedback signal timer expires (step Sh2 in the case of i = 2 and 4, Yes).

[0269] The candidate beam detection unit 15d exits the processing of loops Lh1s to Lh1e, and sets the beam ID included in the captured feedback signal as the beam ID indicating the best beam in the second distributed antenna device 30-2. The candidate beam detection unit 15d designates the beam specified by the beam ID and the "distributed antenna ID #2", which is the transmission source antenna ID included in the feedback signal, as the detection reference beam. Here, it is assumed that the beam ID included in the feedback signal captured by the candidate beam detection unit 15d is "beam ID #33".

[0270] The candidate beam detection unit 15d combines the transmission source antenna ID, beam ID, and received power value included in the feedback signal into a set of data, and outputs the set of data to the beam combination recording unit 17. The beam combination recording unit 17 captures the set of data output by the candidate beam detection unit 15d. The candidate beam detection unit 15d outputs an output destination switching instruction signal to the feedback signal reception unit 12 to set the output destination to the beam search execution determination unit 16. When receiving the output destination switching instruction signal whose output destination is set to the beam search execution determination unit 16 from the candidate beam detection unit 15d, the feedback signal reception unit 12 sets the output destination of the feedback signal to the beam search execution determination unit 16 (step Sh3).

[0271] Putting it another way for the processing of steps Sh2 and Sh3 above, the candidate beam detection unit 15d performs a process of causing simultaneous full beam search using a plurality of randomly selected distributed antenna devices among the distributed antenna devices 30-1 to 30-4. In the middle of the process, when the candidate beam detection unit 15d captures one feedback signal, it ends the processing of loops Lh1s to Lh1e, and designates the beam specified by the transmission source antenna ID and the beam ID included in the captured feedback signal as the detection reference beam.

[0272] If the wireless communication system 1d includes N distributed antenna devices 30-1 to 30-N, when passing through loops Lh1s to Lh1e, a distributed antenna device 30-k that has not performed a full beam search is identified using the value of variable i that has been selected up to that point and the value of N. The candidate beam detection unit 15d writes and records the possible values that variable k can take and the values that have already been selected in an internal storage area.

[0273] When k = 1, the candidate beam detection unit 15d performs the following processing. That is, the candidate beam detection unit 15d detects from the beam combination history table 140 the beam ID of the beam of the first distributed antenna device 30-1 that has been selected together with the detection reference beam. Here, the detection reference beam is the beam specified by "beam ID #33" of "distributed antenna ID #2". In the beam combination history table 140, "beam ID #33" of "distributed antenna ID #1" corresponding to the detection reference beam is included in "record ID #2", "record ID #4", and "record ID #6". In the "distributed antenna ID #1" item of "record ID #2", "record ID #4", and "record ID #6", "beam ID #13" and "beam ID #25" are written.

[0274] Therefore, the candidate beam detection unit 15d detects "Beam ID #13" and "Beam ID #25" from the beam combination history table 140 as the beam IDs of the beams of the first distributed antenna device 30-1 that have been selected together with the detection reference beam. The candidate beam detection unit 15d sets "Beam ID #13" and "Beam ID #25" as candidate beam IDs indicating candidate beams of the distributed antenna device 30-1 corresponding to "Distributed Antenna ID #1". The candidate beam detection unit 15d generates data indicating a detection result including "Distributed Antenna ID #1", "Beam ID #13" which is the candidate beam ID, and "Beam ID #25" (step Sh4 when k = 1). The candidate beam detection unit 15d outputs the generated data indicating the detection result to the beam search execution determination unit 16 (step Sh5 when k = 1). When receiving the data indicating the detection result from the candidate beam detection unit 15d, the beam search execution determination unit 16 starts a subroutine of the process of determining all beam searches shown in FIG. 11 (step Sh6 when k = 1).

[0275] The beam search execution determination unit 16 fetches the data indicating the detection result output by the candidate beam detection unit 15d (step Sc1 when k = 1). The beam search execution determination unit 16 determines whether the candidate beam ID is included in the fetched data indicating the detection result (step Sc2 when k = 1). Here, since the data indicating the detection result includes "Beam ID #13" and "Beam ID #25", the beam search execution determination unit 16 determines that the candidate beam ID is included in the fetched data indicating the detection result (step Sc2 when k = 1, Yes).

[0276] The beam search execution determination unit 16 outputs a partial beam search request signal including "distributed antenna ID #1", "beam ID #13", and "beam ID #25" to the beam search execution instruction unit 11 in order to cause the distributed antenna device 30-1 including the first distributed antenna 31-1 to perform a partial beam search for the candidate beam ID. After outputting the partial beam search request signal to the beam search execution instruction unit 11, the beam search execution determination unit 16 activates a feedback signal timer provided therein. When activating the feedback signal timer, the beam search execution determination unit 16 sets the same time as that set by the beam combination history generation unit 13 for the feedback signal timer in the process of step Sa1 in FIG. 9.

[0277] The beam search execution instruction unit 11 takes in the partial beam search request signal output by the beam search execution determination unit 16, and reads out "distributed antenna ID #1", "beam ID #13", and "beam ID #25" included in the taken-in partial beam request instruction signal. The beam search execution instruction unit 11 generates a beam search instruction signal including "distributed antenna ID #1" and "beam ID #13" and a beam search instruction signal including "distributed antenna ID #1" and "beam ID #25". The beam search execution instruction unit 11 outputs the two generated beam search instruction signals to the digital signal processing device 20 one by one in the order of generation at a predetermined fixed time interval. The digital signal processing device 20 sequentially takes in the two beam search instruction signals output by the beam search execution instruction unit 11. Thereafter, in the process of step Sa1 in FIG. 9, after the digital signal processing device 20 takes in the beam search instruction signal, the process is performed by the digital signal processing device 20, the main body device 32-1, the distributed antenna 31-1, and the terminal device 40 with i = 1 (step Sc7 when k = 1).

[0278] The beam search execution determination unit 16 determines whether or not it has taken in a feedback signal including "distributed antenna ID #1", which is the distributed antenna ID of the first distributed antenna 31-1, as the transmission source antenna ID before the feedback signal timer expires (step Sc8).

[0279] For example, assume that any event occurs when the beam combination history generation unit 13 described above cannot capture the feedback signal. In this case, the beam search execution determination unit 16 determines that it has not captured the feedback signal in which the "diversity antenna ID #1", which is the diversity antenna ID of the first diversity antenna 31-1, is included as the transmission source antenna ID before the feedback signal timer expires (step Sc8, No when k = 1), and proceeds to step Sc3.

[0280] On the other hand, assume that any event does not occur when the beam combination history generation unit 13 described above cannot capture the feedback signal, and the feedback signal reception unit 12 outputs the feedback signal to the beam search execution determination unit 16. In this case, the beam search execution determination unit 16 determines that it has captured the feedback signal in which the "diversity antenna ID #1", which is the diversity antenna ID of the first diversity antenna 31-1, is included as the transmission source antenna ID before the feedback signal timer expires (step Sc8, Yes when k = 1).

[0281] In this case, the beam search execution determination unit 16 determines whether the received power value included in the feedback signal exceeds a predetermined threshold (step Sc9 when k = 1). When the beam search execution determination unit 16 determines that the received power value included in the feedback signal does not exceed the predetermined threshold (step Sc9, No when k = 1), it proceeds to step Sc3. On the other hand, when the beam search execution determination unit 16 determines that the received power value included in the feedback signal exceeds the predetermined threshold (step Sc9, Yes when k = 1), it proceeds to step Sc5.

[0282] Putting it another way for the processes of steps Sc7, Sc8, and Sc9 above, the beam search execution determination unit 16 causes the distributed antenna device 30-1 corresponding to "distributed antenna ID #1" to perform a partial beam search for transmitting the beam corresponding to "beam ID #13" and the beam corresponding to "beam ID #25". When the feedback signal from the partial beam search cannot be obtained, the beam search execution determination unit 16 advances the process to step Sc3 to cause the distributed antenna device 30-1 corresponding to "distributed antenna ID #1" to perform a full beam search and re-search for the best beam for the distributed antenna device 30-1. Also, in the full beam search in this case, the beam search execution determination unit 16 searches only for beams other than the beam corresponding to "beam ID #13" and the beam corresponding to "beam ID #25".

[0283] Then, when the beam search execution determination unit 16 captures a feedback signal in which "distributed antenna ID #1" is included as the transmission source antenna ID before the feedback signal timer expires in step Sc4, the process advances to step Sc5, and the beam ID included in the feedback signal is used as the data to be added to the beam combination history table 140.

[0284] On the other hand, when a feedback signal is obtained by the partial beam search, if the received power value included in the feedback signal, that is, the received power value of the beam selected as the best beam in the terminal device 40, does not exceed the threshold value, the beam search execution determination unit 16 determines that the beam indicated by the feedback signal is an inappropriate beam that cannot be used for normal operation. Therefore, the beam search execution determination unit 16 advances the process to step Sc3 and causes the distributed antenna device 30-1 corresponding to "distributed antenna ID#1" to perform a full beam search to search for the best beam for the distributed antenna device 30-1 again. Also, in the full beam search in this case, the beam search execution determination unit 16 searches only for beams other than the beam corresponding to "beam ID#13" and the beam corresponding to "beam ID#25".

[0285] Then, when the beam search execution determination unit 16 captures a feedback signal including "distributed antenna ID#1" as the transmission source antenna ID before the feedback signal timer expires in step Sc4, the process proceeds to step Sc5, and the beam ID included in the feedback signal is set as data to be added to the beam combination history table 140.

[0286] On the other hand, when the received power value included in the feedback signal exceeds the threshold value, the beam search execution determination unit 16 advances the process to step Sc5 and determines that the beam is the best beam in the distributed antenna device 30-1. In this case, since the beam search execution determination unit 16 can set the beam as an appropriate beam that can be used for normal operation without performing a full beam search for the distributed antenna device 30-1, the number of beam searches can be reduced.

[0287] If there is a value among the possible values of variable k at that time (here, "1", "3", "4") that has not been selected, the candidate beam detection unit 15d selects that unselected value, and the processes of steps Sh4 to Sh6 are performed again (loops Lh2s to Lh2e). Here, among the possible values of variable k (here, "1", "3", "4"), "3" (and "4") has not been selected yet, so the candidate beam detection unit 15d sets "3" as the new value of k.

[0288] When k = 3, the candidate beam detection unit 15d performs the following processing. That is, the candidate beam detection unit 15d detects, as candidate beams, the beams of the third distributed antenna device 30-3 that have been selected together with the detection reference beam from the beam combination history table 140. Here, the detection reference beam is the beam specified by "Beam ID #33" of "Distributed Antenna ID #2". In the beam combination history table 140, "Beam ID #33" of "Distributed Antenna ID #2" corresponding to the detection reference beam is included in "Record ID #2", "Record ID #4", and "Record ID #6", but the items of "Distributed Antenna ID #3" in "Record ID #2", "Record ID #4", and "Record ID #6" are blank. Therefore, the candidate beam detection unit 15d determines as the detection result that there is no candidate beam ID indicating a candidate beam of the third distributed antenna device 30-3 that has been selected together with the detection reference beam. The candidate beam detection unit 15d generates data indicating a detection result including only "Distributed Antenna ID #3" (step Sh4 when k = 3).

[0289] The candidate beam detection unit 15d outputs data indicating a detection result including only "Distributed Antenna ID #3" to the beam search execution determination unit 16 (step Sh5 when k = 3). When receiving the data indicating the detection result from the candidate beam detection unit 15d, the beam search execution determination unit 16 starts the subroutine of the all beam search execution determination process shown in FIG. 11 (step Sh6 when k = 3).

[0290] When the candidate beam detection unit 15d captures the end notification signal output by the beam search execution determination unit 16, if there is a value among the possible values of the variable k at that time (here, "1", "3", "4") that has not been selected, the unselected value is selected, and the processes of steps Sh4 to Sh6 are performed again (loops Lh2s to Lh2e).

[0291] When the candidate beam detection unit 15d captures the end notification signal output by the beam search execution determination unit 16, if there is no value among the possible values of the variable k at that time (here, "1", "3", "4") that has not been selected, the processes of loops Lh2s to Lh2e are terminated, and the process proceeds to step Sh7.

[0292] Here, among the possible values of the variable k (here, "1", "3", "4"), "4" has not been selected yet, so the candidate beam detection unit 15d sets "4" as the new value of k. When k = 4, the candidate beam detection unit 15d performs the following processes. That is, the candidate beam detection unit 15d detects from the beam combination history table 140 the beam ID of the beam that is the beam of the fourth distributed antenna device 30-4 and has been selected together with the detection reference beam. Here, the detection reference beam is the beam specified by "beam ID #33" of "distributed antenna ID #2". In the beam combination history table 140, "beam ID #33" of "distributed antenna ID #2" corresponding to the detection reference beam is included in "record ID #2", "record ID #4", and "record ID #6". In the "distributed antenna ID #4" items of "record ID #2", "record ID #4", and "record ID #6", "beam ID #15", "beam ID #16", and "beam ID #15" are written.

[0293] Therefore, the candidate beam detection unit 15d detects "Beam ID #15" and "Beam ID #16" from the beam combination history table 140 as the beam IDs of the beams of the fourth distributed antenna device 30-4 that have been selected together with the detection reference beam. The candidate beam detection unit 15d sets "Beam ID #15" and "Beam ID #16" as candidate beam IDs indicating the candidate beams of the distributed antenna device 30-4 corresponding to "Distributed Antenna ID #4". The candidate beam detection unit 15d generates data indicating a detection result including "Distributed Antenna ID #4", "Beam ID #15" which is the candidate beam ID, and "Beam ID #16" (step Sh4 when k = 4). The candidate beam detection unit 15d outputs the generated data indicating the detection result to the beam search execution determination unit 16 (step Sh5 when k = 4). When receiving the data indicating the detection result from the candidate beam detection unit 15d, the beam search execution determination unit 16 starts a subroutine of the process of determining the execution of the full beam search shown in FIG. 11 (step Sh6 when k = 4).

[0294] The beam search execution determination unit 16 fetches the data indicating the detection result output by the candidate beam detection unit 15d (step Sc1 when k = 4). The beam search execution determination unit 16 determines whether the candidate beam ID is included in the fetched data indicating the detection result (step Sc2 when k = 4). Here, since the data indicating the detection result includes "Beam ID #15" and "Beam ID #16", the beam search execution determination unit 16 determines that the candidate beam ID is included in the fetched data indicating the detection result (step Sc2, Yes when k = 4).

[0295] The beam search execution determination unit 16 outputs a partial beam search request signal including "diversity antenna ID #4", "beam ID #15", and "beam ID #16" to the beam search execution instruction unit 11 in order to cause the diversity antenna device 30-4 including the fourth diversity antenna 31-4 to perform a partial beam search for the candidate beam ID. After outputting the partial beam search request signal to the beam search execution instruction unit 11, the beam search execution determination unit 16 activates a feedback signal timer provided therein. When activating the feedback signal timer, the beam search execution determination unit 16 sets the same time as that set by the beam combination history generation unit 13 for the feedback signal timer in the process of step Sa1 in FIG. 9.

[0296] The beam search execution instruction unit 11 takes in the partial beam search request signal output by the beam search execution determination unit 16, and reads out "diversity antenna ID #4", "beam ID #15", and "beam ID #16" included in the taken-in partial beam request instruction signal. The beam search execution instruction unit 11 generates a beam search instruction signal including "diversity antenna ID #4" and "beam ID #15", and a beam search instruction signal including "diversity antenna ID #4" and "beam ID #16". The beam search execution instruction unit 11 outputs the two generated beam search instruction signals to the digital signal processing device 20 one by one in the order of generation at a predetermined fixed time interval. The digital signal processing device 20 sequentially takes in the two beam search instruction signals output by the beam search execution instruction unit 11. Thereafter, in the process of step Sa1 in FIG. 9, after the digital signal processing device 20 takes in the beam search instruction signal, the process is performed by the digital signal processing device 20, the main body device 32-4, the diversity antenna 31-4, and the terminal device 40 with i = 4 (step Sc7 when k = 4).

[0297] The beam search execution determination unit 16 determines whether or not a feedback signal including "diversity antenna ID #4", which is the diversity antenna ID of the fourth diversity antenna 31-4, as the transmission source antenna ID has been taken in before the feedback signal timer expires (step Sc8).

[0298] For example, assume that any event occurs when the beam combination history generation unit 13 described above cannot capture the feedback signal. In this case, the beam search execution determination unit 16 determines that it has not captured the feedback signal in which the "diversity antenna ID #4", which is the diversity antenna ID of the fourth diversity antenna 31-4, is included as the transmission source antenna ID before the feedback signal timer expires (step Sc8, No when k = 4), and proceeds to step Sc3.

[0299] On the other hand, assume that any event does not occur when the beam combination history generation unit 13 described above cannot capture the feedback signal, and the feedback signal reception unit 12 outputs a feedback signal to the beam search execution determination unit 16. In this case, the beam search execution determination unit 16 determines that it has captured the feedback signal in which the "diversity antenna ID #4", which is the diversity antenna ID of the fourth diversity antenna 31-4, is included as the transmission source antenna ID before the feedback signal timer expires (step Sc8, Yes when k = 4).

[0300] In this case, the beam search execution determination unit 16 determines whether the received power value included in the feedback signal exceeds a predetermined threshold (step Sc9 when k = 4). When the beam search execution determination unit 16 determines that the received power value included in the feedback signal does not exceed the predetermined threshold (step Sc9, No when k = 4), the process proceeds to step Sc3. On the other hand, when the beam search execution determination unit 16 determines that the received power value included in the feedback signal exceeds the predetermined threshold (step Sc9, Yes when k = 4), the process proceeds to step Sc5.

[0301] Putting it another way for the processing of the above steps Sc7, Sc8, and Sc9, the beam search execution determination unit 16 causes the distributed antenna device 30-4 corresponding to the "distributed antenna ID #4" to perform a partial beam search for transmitting the beam corresponding to the "beam ID #15" and the beam corresponding to the "beam ID #16". When the feedback signal from the partial beam search cannot be obtained, the beam search execution determination unit 16 advances the process to step Sc3 to cause the distributed antenna device 30-4 corresponding to the "distributed antenna ID #4" to perform a full beam search, and re-searches for the best beam for the distributed antenna device 30-4. Also, in the full beam search in this case, the beam search execution determination unit 16 searches only for beams other than the beam corresponding to the "beam ID #15" and the beam corresponding to the "beam ID #16".

[0302] Then, when the beam search execution determination unit 16 captures a feedback signal including the "distributed antenna ID #4" as the transmission source antenna ID before the feedback signal timer expires in step Sc4, the process proceeds to step Sc5, and the beam ID included in the feedback signal is used as the data to be added to the beam combination history table 140.

[0303] On the other hand, when a feedback signal is obtained by the partial beam search, if the received power value included in the feedback signal, that is, the received power value of the beam selected as the best beam in the terminal device 40, does not exceed the threshold value, the beam search execution determination unit 16 determines that the beam indicated by the feedback signal is an inappropriate beam that cannot be used for normal operation. Therefore, the beam search execution determination unit 16 advances the process to step Sc3 and causes the distributed antenna device 30-4 corresponding to "distributed antenna ID #4" to perform a full beam search to re-search for the best beam for the distributed antenna device 30-4. Also, in the full beam search in this case, the beam search execution determination unit 16 searches only for beams other than the beam corresponding to "beam ID #15" and the beam corresponding to "beam ID #26".

[0304] Then, when the beam search execution determination unit 16 captures a feedback signal including "distributed antenna ID #4" as the transmission source antenna ID before the feedback signal timer expires in step Sc4, the process proceeds to step Sc5, and the beam ID included in the feedback signal is set as the data to be added to the beam combination history table 140.

[0305] On the other hand, when the received power value included in the feedback signal exceeds the threshold value, the beam search execution determination unit 16 advances the process to step Sc5 and determines that the beam is the best beam in the distributed antenna device 30-4. In this case, since the beam search execution determination unit 16 can set the beam as an appropriate beam that can be used for normal operation without performing a full beam search for the distributed antenna device 30-4, the number of beam searches can be reduced.

[0306] Returning to FIG. 22, when the candidate beam detection unit 15d captures the end notification signal output by the beam search execution determination unit 16, if there is a value that can be taken by the variable k (here, "1", "3", "4") that has not been selected at that time, the value that has not been selected is selected, and the processes of steps Sh4 to Sh6 are performed again (loops Lh2s to Lh2e). Here, since there is no longer a value that can be taken by the variable k at that time and has not been selected, the processes of loops Lh2s to Lh2e end, and the process proceeds to step Sh7.

[0307] The beam combination recording unit 17 generates one record in the beam combination history table 140 based on the remaining data obtained by removing the received power value from the set of data captured in the processes of step Sh3 and step Sc5, that is, the data combining the transmission source antenna ID, the beam ID, and the received power value. That is, the beam combination recording unit 17 generates a new record ID "Record ID#M + 1" by generating a new row in the beam combination history table 140. The beam combination recording unit 17 writes the generated new record ID "Record ID#M + 1" in the "Record ID" item of the generated new row. The beam combination recording unit 17 writes the corresponding beam ID in each of the elements of "Diversity Antenna ID#1", "Diversity Antenna ID#2", "Diversity Antenna ID#3", and "Diversity Antenna ID#4" in the row of "Record ID#M + 1" based on the combination of the transmission source antenna ID and the beam ID (step Sh7).

[0308] In the wireless communication system 1d of the fifth embodiment described above, during the beam search period in which the candidate beam detection unit 15d searches for a beam to be used for wireless communication with the terminal device 40, the candidate beam detection unit 15d causes a plurality of distributed antenna devices randomly selected from among the distributed antenna devices 30-1 to 30-4 to perform a full beam search simultaneously. When one beam identifier indicating the best beam among the beams obtained by the full beam search is acquired, the full beam search is stopped, and the beam specified by the acquired beam identifier and the information indicating the distributed antennas 31-1 to 31-4 that transmitted the beam indicated by the beam identifier is set as the detection reference beam. The candidate beam detection unit 15d detects, from the beam combination history storage unit 14, the beam identifier of a beam that is the beam identifier of the distributed antennas 31-1 to 31-4 that have not performed the full beam search during the beam search period and that has been selected together with the detection reference beam as the candidate beam identifier for the distributed antennas 31-1 to 31-4.

[0309] The beam search execution determination unit 16 determines whether to cause the distributed antennas 31-1 to 31-4 that have not performed the full beam search during the beam search period to perform the full beam search, based on the detection result of the candidate beam detection unit 15d. The beam combination recording unit 17 generates a record indicating a combination of beam identifiers indicating the beams that are the best beams in each of the distributed antennas during the beam search period. The beam combination recording unit 17 records the generated record in the beam combination history storage unit 14. As a result, in the beam combination generation process performed by the beam combination history generation unit 13, even if sufficient records indicating the history of beam combinations cannot be generated by gradually moving the terminal device 40 at intervals that do not reduce the transmission capacity over the entire cell 100 within the service area, when performing the beam search process, it is possible to accumulate a sufficient number of records to reduce the number of beam searches without reducing the transmission capacity.

[0310] Also, in the fifth embodiment, the wireless communication system 1d does not perform a full beam search in a fixed order for the distributed antenna devices 30-1 to 30-4 at the first stage of the beam search process. Instead, it simultaneously performs a full beam search using a plurality of randomly selected distributed antenna devices among the distributed antenna devices 30-1 to 30-4. By having such a configuration, the wireless communication system 1d can perform a full beam search at random timing even for a distributed antenna device for which the full beam search was not performed because a beam that is not the best beam but has a received power value exceeding the threshold was selected by the partial beam search, and thus the full beam search was not carried out. Therefore, the update of the beam combination history table 140 is also performed. Accordingly, according to the wireless communication system 1d in the fifth embodiment, it is possible to reduce the number of beam searches and prevent a combination of non-optimal beams from being continuously and fixedly selected.

[0311] (Sixth Embodiment) FIG. 23 is a block diagram showing the configuration of the communication control device 10e in the sixth embodiment. The communication control device 10e is a device used in place of the communication control device 10a in the second embodiment. Hereinafter, for convenience of explanation, a wireless communication system 1a including the communication control device 10e in place of the communication control device 10a is referred to as a wireless communication system 1e. In the communication control device 10e, the same components as those of the communication control device 10a in the second embodiment are denoted by the same reference numerals, and different components will be described below.

[0312] Among the configurations of the wireless communication system 1e in the sixth embodiment, the difference from the configuration of the wireless communication system 1a in the second embodiment is that, at the first stage of the beam search process, a full beam search is not performed in a fixed order for the distributed antenna devices, but a full beam search is simultaneously performed using a part of a plurality of randomly selected distributed antenna devices among the plurality of distributed antenna devices.

[0313] The communication control device 10e includes a beam search execution instruction unit 11, a feedback signal reception unit 12, a beam combination history generation unit 13a, a beam combination history storage unit 14a, a candidate beam detection unit 15e, a beam search execution determination unit 16a, and a beam combination recording unit 17a.

[0314] When the beam search process for searching for beams is started, the candidate beam detection unit 15e randomly selects a plurality of (X pieces) of the N distributed antenna devices 30-1 to 30-N. For example, the candidate beam detection unit 15e randomly selects 2 (X = 2) of the 4 (N = 4) distributed antenna devices 30-1 to 30-4. Note that each time the beam search process is performed, the same number of (for example, 2 (X = 2)) distributed antenna devices may be randomly selected, or different numbers of (for example, 2 to 3 (X = 2 to 3)) distributed antenna devices may be randomly selected.

[0315] The candidate beam detection unit 15e causes all beam searches to be performed simultaneously for each of the selected plurality of distributed antenna devices. That is, the candidate beam detection unit 15e designates, for example, the IDs of 2 distributed antennas such as distributed antennas 31-1 and 31-4 that are randomly selected, and outputs a full beam search request signal including the designated 2 distributed antenna IDs to the beam search execution instruction unit 11. After starting the beam search process, when the candidate beam detection unit 15e captures the first feedback signal, it stops the full beam search, and sets the beam specified by the transmission source antenna ID and the beam ID included in the feedback signal as the detection reference beam. The candidate beam detection unit 15e detects, from, for example, the beam combination history table 140a shown in FIG. 14, the beam IDs of the distributed antenna devices 30-1 to 30-4 that have not performed the full beam search during the beam search period, the beam IDs of the beams that have been selected together with the detection reference beam, and the distributed antenna IDs corresponding to the beam IDs.

[0316] At this time, the candidate beam detection unit 15e detects the received power value written as an element together with the detected beam ID in the beam combination history table 140a. The candidate beam detection unit 15e uses the candidate beam ID indicating the candidate beam in the distributed antenna devices 30-1 to 30-4 corresponding to the detected distributed antenna ID, and sets the combination of the detected distributed antenna ID and the candidate beam ID as the detection result. The candidate beam detection unit 15e calculates the average value of the received power values for each beam ID based on the combination of the detected beam ID and the detected received power value, and sets the maximum value of the calculated average values as the average received power value for the detected distributed antenna ID. The candidate beam detection unit 15e includes the calculated average received power value in the data indicating the detection result.

[0317] (Processing by the wireless communication system of the sixth embodiment) Similar to the second embodiment, in the wireless communication system 1e of the sixth embodiment, the beam combination generation process of step S1 and the beam search process of step S2 shown in FIG. 8 are also performed. However, in the points described below, the beam search process performed in the sixth embodiment is different from the process performed in the second embodiment.

[0318] (Beam combination generation process of the sixth embodiment) The same beam combination generation process as that of the first embodiment shown in FIG. 9 is performed by the beam search execution instruction unit 11, the feedback signal reception unit 12, the beam combination history generation unit 13a, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4. The process that was performed by the beam combination history generation unit 13a is now performed by the beam combination history generation unit 13e.

[0319] (Beam search process of the sixth embodiment) FIG. 24 is a flowchart showing the beam search process of the sixth embodiment. FIG. 24 is a flowchart showing the flow of the beam search process performed in the process of step S2 in FIG. 8.

[0320] In FIG. 24, the processes of steps Si1 and Si2, the processes of loops Li1s to Li1e that repeat the processes of steps Si1 and Si2, and the process of step Si3 are the same as the processes of steps Sd1 and Sd2 in FIG. 15, the processes of loops Ld1s to Ld1e that repeat the processes of steps Sd1 and Sd2, and the process of step Sd3. These processes are performed by the beam search execution instruction unit 11, the feedback signal reception unit 12, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4. The process that was performed by the candidate beam detection unit 15a is now performed by the candidate beam detection unit 15e. The process of step Si7 is performed by the beam combination recording unit 17a for the above-described processes.

[0321] In response to the operation of the operator of the wireless communication system 1e, the candidate beam detection unit 15e of the communication control device 10e starts the beam search process. The candidate beam detection unit 15e activates the beam search period timer provided inside. When activating the beam search period timer, the candidate beam detection unit 15e sets a time indicating the length of a predetermined one beam search period.

[0322] The candidate beam detection unit 15e reads out all the distributed antenna IDs written in the distributed antenna ID item of the beam combination history table 140a stored in the beam combination history storage unit 14a. The candidate beam detection unit 15e provides a variable i in its internal storage area. Here, i is a variable that can take integer values from 1 to N. Since the wireless communication system 1 in FIG. 1 includes four distributed antenna devices 30-1 to 30-4, and the candidate beam detection unit 15e reads out four distributed antenna IDs, namely, "Distributed Antenna ID #1", "Distributed Antenna ID #2", "Distributed Antenna ID #3", and "Distributed Antenna ID #4" from the beam combination history table 140a, hereinafter, the description will be made assuming N = 4. The i-th distributed antenna device is referred to as the distributed antenna device 30-i, the i-th distributed antenna is referred to as the distributed antenna 31-i, and the i-th main body device is referred to as the main body device 32-i for the following description.

[0323] Also, the candidate beam detection unit 15e provides a variable X in its internal storage area. Here, X is a variable that can take an integer value of 2 or more. X represents the number of distributed antenna devices for which full beam search is performed simultaneously. Below, as an example, it will be described assuming X = 2.

[0324] The candidate beam detection unit 15e outputs an output destination switching instruction signal to the feedback signal receiving unit 12 to set the output destination to the candidate beam detection unit 15e itself. When the feedback signal receiving unit 12 receives the output destination switching instruction signal from the candidate beam detection unit 15e to set the output destination to the candidate beam detection unit 15e itself, it sets the output destination of the feedback signal to the candidate beam detection unit 15e.

[0325] The candidate beam detection unit 15e randomly selects two values (X = 2) from among the values from 1 to N as the value of the variable i. The candidate beam detection unit 15e writes and records the values that the variable i can take (i.e., 1 to N) and the values that have already been selected in its internal storage area. Here, for example, it is assumed that the values "1" and "3" are selected as the value of the variable i. In the case of i = 1 and 3, the following processing is performed. That is, the candidate beam detection unit 15e outputs a full beam search request signal including the distributed antenna ID "Distributed Antenna ID #1" assigned to the first distributed antenna 31-1 and the distributed antenna ID "Distributed Antenna ID #3" assigned to the third distributed antenna 31-3 to the beam search execution instruction unit 11 in order to cause the distributed antenna device 30-1 including the first distributed antenna 31-1 and the distributed antenna device 30-3 including the third distributed antenna 31-3 to perform full beam search simultaneously.

[0326] After the candidate beam detection unit 15e outputs the all-beam search request signal to the beam search execution instruction unit 11, it activates the feedback signal timer provided inside. When activating the feedback signal timer, the candidate beam detection unit 15e sets the same time as that set by the beam combination history generation unit 13a for the feedback signal timer in the process of step Sa1 in FIG. 9. Note that the time is a predetermined time and is set in advance in the candidate beam detection unit 15e. When the beam search execution instruction unit 11 captures the all-beam search request signal output by the candidate beam detection unit 15e, thereafter, in the process of step Sa1 in FIG. 9, after the beam search execution instruction unit 11 captures the all-beam search request signal, the processing is performed by the beam search execution instruction unit 11, the digital signal processing device 20, the main body device 32-1, the main body device 32-3, the distributed antenna 31-1, the distributed antenna 31-3, and the terminal device 40 with i = 1 and 3 (step Si1 in the case of i = 1 and 3).

[0327] Until the feedback signal timer expires, the candidate beam detection unit 15e determines whether it has captured a feedback signal including either "distributed antenna ID #1", which is the distributed antenna ID of the distributed antenna 31-1, or "distributed antenna ID #3", which is the distributed antenna ID of the distributed antenna 31-3, as the transmission source antenna ID (step Si2 in the case of i = 1 and 3).

[0328] Here, assume that any event occurs when the beam combination history generation unit 13a described above cannot capture the feedback signal. In this case, the candidate beam detection unit 15e determines that the feedback signals including the "diversity antenna ID #1", which is the diversity antenna ID of the first diversity antenna 31-1, and the "diversity antenna ID #3", which is the diversity antenna ID of the third diversity antenna 31-3, have not been captured until the feedback signal timer expires (step Si2, No). If the value of the variable i has not been selected for the number N of diversity antennas at that time (that is, if not all the values that the variable i can take have been selected), the candidate beam detection unit 15e randomly selects two (X = 2) values from 1 to N as the value of the variable i. Here, the remaining "2" and "4" will be selected as the values of the variable i. Then, the processes of steps Si1 and Si2 are performed again (loop Li1s~Li1e).

[0329] As the second processing of the loop Li1s~Li1e, the candidate beam detection unit 15e performs the following processing. That is, the candidate beam detection unit 15e outputs a full beam search request signal including the "diversity antenna ID #2", which is the diversity antenna ID given to the second diversity antenna 31-2, and the "diversity antenna ID #4", which is the diversity antenna ID given to the fourth diversity antenna 31-4, to the beam search execution instruction unit 11 in order to cause the diversity antenna device 30-2 including the second diversity antenna 31-2 and the diversity antenna device 30-4 including the fourth diversity antenna 31-4 to perform a full beam search simultaneously.

[0330] After the candidate beam detection unit 15e outputs the all-beam search request signal to the beam search execution instruction unit 11, it activates the feedback signal timer provided inside. When activating the feedback signal timer, the candidate beam detection unit 15e sets the same time as that set by the beam combination history generation unit 13 for the feedback signal timer in the process of step Sa1 in FIG. 9. When the beam search execution instruction unit 11 captures the all-beam search request signal output by the candidate beam detection unit 15e, then, in the process of step Sa1 in FIG. 9, after the beam search execution instruction unit 11 captures the all-beam search request signal, the processes are performed by the beam search execution instruction unit 11, the digital signal processing device 20, the main body device 32-2, the main body device 32-4, the distributed antenna 31-2, the distributed antenna 31-4, and the terminal device 40 with i = 2 and 4 (step Si1 in the case of i = 2 and 4).

[0331] The candidate beam detection unit 15e determines whether it has captured a feedback signal that includes, as the transmission source antenna ID, the "distributed antenna ID #2" which is the distributed antenna ID of the second distributed antenna 31-2 or the "distributed antenna ID #4" which is the distributed antenna ID of the fourth distributed antenna 31-4 before the feedback signal timer expires (step Si2 in the case of i = 2 and 4). Here, assume that none of the events occur when the above-described beam combination history generation unit 13a cannot capture the feedback signal, and the feedback signal reception unit 12 outputs to the candidate beam detection unit 15e a feedback signal that includes, as the transmission source antenna ID, the "distributed antenna ID #2" which is the distributed antenna ID of the second distributed antenna 31-2. In this case, the candidate beam detection unit 15e determines that it has captured a feedback signal that includes, as the transmission source antenna ID, the "distributed antenna ID #2" which is the distributed antenna ID of the second distributed antenna 31-2 before the feedback signal timer expires (step Si2 in the case of i = 2 and 4, Yes).

[0332] The candidate beam detection unit 15e exits the processing of loops Li1s to Li1e, and sets the beam ID included in the captured feedback signal as the beam ID indicating the best beam in the second distributed antenna device 30-2. The candidate beam detection unit 15e designates the beam specified by the beam ID and the "distributed antenna ID #2", which is the transmission source antenna ID included in the feedback signal, as the detection reference beam. Here, it is assumed that the beam ID included in the feedback signal captured by the candidate beam detection unit 15e is "beam ID #33".

[0333] The candidate beam detection unit 15e combines the transmission source antenna ID, beam ID, and received power value included in the feedback signal into a set of data, and outputs the set of data to the beam combination recording unit 17a. The beam combination recording unit 17a captures the set of data output by the candidate beam detection unit 15e. The candidate beam detection unit 15e outputs an output destination switching instruction signal to the feedback signal receiving unit 12 to set the output destination to the beam search execution determination unit 16a. When receiving the output destination switching instruction signal from the candidate beam detection unit 15e to set the output destination to the beam search execution determination unit 16a, the feedback signal receiving unit 12 sets the output destination of the feedback signal to the beam search execution determination unit 16a (step Si3).

[0334] Putting it another way for the processing of steps Si2 and Si3 above, the candidate beam detection unit 15e performs a process of causing all the distributed antenna devices 30-1 to 30-4 to perform a full beam search in a random order. During this process, when one feedback signal is captured, the processing of loops Li1s to Li1e is terminated, and the beam specified by the transmission source antenna ID and the beam ID included in the captured feedback signal is set as the detection reference beam.

[0335] If the wireless communication system 1e includes N distributed antenna devices 30-1 to 30-N, when passing through loops Li1s to Li1e, the value of variable i that has been selected up to that point and the value of N are used to identify the distributed antenna device 30-k that has not performed full beam search. The candidate beam detection unit 15e writes and records the values that variable k can take and the values that have been selected in the past in the internal storage area.

[0336] When k = 1, the candidate beam detection unit 15e performs the following processing. That is, the candidate beam detection unit 15e detects from the beam combination history table 140a the beam ID of the beam of the first distributed antenna device 30-1 that has been selected together with the detection reference beam. Here, the detection reference beam is the beam specified by "beam ID #33" of "distributed antenna ID #2". In the beam combination history table 140a, "beam ID #33" of "distributed antenna ID #2" corresponding to the detection reference beam is included in "record ID #2", "record ID #4", and "record ID #6". In the "distributed antenna ID #1" item of "record ID #2", "record ID #4", and "record ID #6", "beam ID #13" and "beam ID #25" are written.

[0337] Therefore, the candidate beam detection unit 15e detects "beam ID #13" and "beam ID #25" from the beam combination history table 140a as the beam IDs of the beams of the first distributed antenna device 30-1 that have been selected together with the detection reference beam. The candidate beam detection unit 15e sets "beam ID #13" and "beam ID #25" as candidate beam IDs indicating the candidate beams of the distributed antenna device 30-1 corresponding to "distributed antenna ID #1".

[0338] The candidate beam detection unit 15e further detects, for "Beam ID #25", "(Received power value 2-1)" of "Record ID #2" and "(Received power value 6-1)" of "Record ID #6", and for "Beam ID #13", "(Received power value 4-1)" of "Record ID #4". The candidate beam detection unit 15e calculates the average value of "(Received power value 2-1)" and "(Received power value 6-1)" corresponding to "Beam ID #25". For "Beam ID #13", since there is only one "(Received power value 4-1)", "(Received power value 4-1)" is used as the average value. The candidate beam detection unit 15e sets the maximum average value among the average value corresponding to "Beam ID #13" and the average value of "Beam ID #25" as the average received power value for "Diversity antenna ID #1". The candidate beam detection unit 15e generates data indicating a detection result including "Diversity antenna ID #1", the candidate beam ID "Beam ID #13", "Beam ID #25", and the calculated average received power value (step Si4 when k = 1). The candidate beam detection unit 15e outputs the data indicating the generated detection result to the beam search execution determination unit 16a (step Si5 when k = 1).

[0339] In the process of step Se1 of the subroutine of the all beam search execution determination process of FIG. 16 performed in the subsequent step Si6 process, the beam search execution determination unit 16a fetches the detection result data output by the candidate beam detection unit 15e, and in the process of step Se2, determines that the candidate beam ID is included in the data indicating the fetched detection result (step Se2, Yes when k = 1).

[0340] When the beam search execution determination unit 16a determines "Yes" in the determination process of step Se8, it reads out the average received power value included in the data indicating the detection result, gives a margin to the read average received power value, and calculates a threshold value for "diversity antenna ID #1" (step Se9). The beam search execution determination unit 16a determines whether the received power value included in the feedback signal exceeds the threshold value calculated for the transmission source antenna ID (here, "diversity antenna ID #1") included in the feedback signal (step Se10 in the case of k = 1).

[0341] When the beam search execution determination unit 16a determines that the received power value included in the feedback signal exceeds the threshold value calculated for the transmission source antenna ID included in the feedback signal (step Se10, Yes), then it advances the process to the process of step Se5. On the other hand, when the beam search execution determination unit 16a determines that the received power value included in the feedback signal does not exceed the threshold value calculated for the transmission source antenna ID included in the feedback signal (step Se10, No), then it advances the process to the process of step Se3.

[0342] Thus, in the sixth embodiment, when the beam search execution determination unit 16a determines to cause any one of the diversity antenna devices 30-1 to 30-4 to perform a partial beam search, if the received power value included in the feedback signal obtained by the partial beam search is a value about the past average received power value of the diversity antenna devices 30-1 to 30-4 targeted by the partial beam search, then the beam indicated by the beam ID included in the feedback signal can be searched as the best beam of the diversity antenna devices 30-1 to 30-4 corresponding to the transmission source antenna ID included in the feedback signal. The beam search execution determination unit 16a can add the data related to the beam to the beam combination history table 140a.

[0343] On the other hand, if the received power value included in the feedback signal acquired by the partial beam search is not about the past average received power value of the distributed antenna devices 30-1 to 30-4 targeted by the partial beam search, the beam search execution determination unit 16a causes the distributed antenna devices 30-1 to 30-4 corresponding to the transmission source antenna ID included in the feedback signal to perform a full beam search. If the beam search execution determination unit 16a can acquire a feedback signal by the full beam search, the best beam in the distributed antenna devices 30-1 to 30-4 targeted by the full beam search can be searched. If the feedback signal cannot be acquired, the best beam in the distributed antenna devices 30-1 to 30-4 targeted by the full beam search cannot be searched. Therefore, in the sixth embodiment, in addition to the effects exhibited by the communication control device 10 of the first embodiment, the communication control device 10b of the third embodiment, and the communication control device 10d of the fifth embodiment, when causing the partial beam search to be performed, the best beam can be searched more accurately than in the first embodiment, the third embodiment, and the fifth embodiment.

[0344] In the fifth embodiment described above, by setting a higher threshold value of the received power value determined in advance, the possibility of selecting a beam that is not the best from the viewpoint of communication quality can be made lower. However, in this case, in the fifth embodiment, since the full beam search is performed for more distributed antenna devices, it becomes difficult to reduce the number of beam searches. Further, since the optimal threshold value also changes depending on the position of the terminal device and the like, it is difficult to set the threshold value for selecting the best beam while reducing the number of beam searches as a uniform value. On the other hand, in the sixth embodiment, by changing the threshold value for each beam combination, the threshold value is substantially changed for each position of the terminal device 40, and the configuration is such that the threshold value is adaptively set.

[0345] In the sixth embodiment, a method was described in which the average value of the received power values for each detected beam ID is used as a reference. However, it is not limited to the average value. For example, the value used as a reference may be the median, the mode, the maximum value, or the minimum value. Further, among these values, when the maximum value, the minimum value, or the average value is used as a reference, other records may be deleted by calculating each time with the same combination of beam IDs.

[0346] If there is a value that can be taken by the variable k at that time (here, "1", "3", "4") and has not been selected, the candidate beam detection unit 15e selects the unselected value, and the processes of steps Si4 to Si6 are performed again (loops Li2s to Li2e). Here, among the values that can be taken by the variable k (here, "1", "3", "4"), since "3" (and "4") has not been selected yet, the candidate beam detection unit 15e sets "3" as the new value of k.

[0347] When k = 3, the candidate beam detection unit 15e performs the following processing. In the processing of loops Li2s to Li2e, when k = 3, similar to the first embodiment, the third embodiment, and the fifth embodiment, the candidate beam detection unit 15e cannot detect the candidate beam ID corresponding to "diversity antenna ID #3" from the beam combination history table 140a. Therefore, in this case, the candidate beam detection unit 15e cannot detect the received power value either. Accordingly, the candidate beam detection unit 15e does not calculate the average received power value, and similar to the processing of step Sb4 in the first embodiment, step Sd4 in the third embodiment, and step Sh4 in the fifth embodiment, it is detected that there is no candidate beam ID indicating a candidate beam that has been selected together with the detection reference beam among the beams of the third diversity antenna device 30-3. The candidate beam detection unit 15e generates data indicating a detection result including only "diversity antenna ID #3" (step Si4 when k = 3).

[0348] The candidate beam detection unit 15e outputs data indicating a detection result including only "Distributed Antenna ID #3" to the beam search execution determination unit 16a (step Si5 when k = 3). When the beam search execution determination unit 16a receives the data indicating the detection result from the candidate beam detection unit 15e, it starts the subroutine of the all beam search execution determination process shown in FIG. 16 (step Si6 when k = 3).

[0349] The subroutine of the all beam search execution determination process performed in step Si6 of the beam search process according to the sixth embodiment will be described with reference to FIG. 16. The processes from step Se1 to step Se6 are the same as the processes from step Sc1 to step Sc6 shown in FIG. 11, and are performed by the beam search execution instruction unit 11, the feedback signal reception unit 12, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4. The process that was performed by the beam search execution determination unit 16 is now performed by the beam search execution determination unit 16a. Therefore, when k = 3, in the determination process of step Se2, the beam search execution determination unit 16a determines "No", and the process proceeds to step Se3. After that, the same processes as those in the case of k = 3 in the first embodiment, the case of k = 3 in the third embodiment, and the case of k = 3 in the fifth embodiment will be performed.

[0350]

[0351] Thus, in the sixth embodiment, when the beam search execution determination unit 16a determines to cause any one of the distributed antenna devices 30-1 to 30-4 to perform a partial beam search, if the received power value included in the feedback signal obtained by the partial beam search is about the same as the past average received power value of the distributed antenna device 30-1 to 30-4 targeted by the partial beam search, the beam indicated by the beam ID included in the feedback signal can be searched as the best beam of the distributed antenna device 30-1 to 30-4 corresponding to the transmission source antenna ID included in the feedback signal. The beam search execution determination unit 16a can add the data related to the beam to the beam combination history table 140a.In contrast, if the received power value included in the feedback signal obtained by the partial beam search is not about the past average received power value of the distributed antenna devices 30-1 to 30-4 targeted by the partial beam search, the beam search execution determination unit 16a causes the distributed antenna devices 30-1 to 30-4 corresponding to the transmission source antenna ID included in the feedback signal to perform a full beam search. If the beam search execution determination unit 16a can obtain a feedback signal by the full beam search, it becomes possible to search for the best beam in the distributed antenna devices 30-1 to 30-4 targeted by the full beam search. If the feedback signal cannot be obtained, it becomes impossible to search for the best beam in the distributed antenna devices 30-1 to 30-4 targeted by the full beam search. Therefore, in the sixth embodiment, in addition to the effects exhibited by the communication control device 10 of the first embodiment, the communication control device 10b of the third embodiment, and the communication control device 10d of the fifth embodiment, when causing the partial beam search to be performed, it becomes possible to search for the best beam more accurately than in the first embodiment, the third embodiment, and the fifth embodiment.

[0352] Also, the wireless communication system 1e in the sixth embodiment does not perform a full beam search on the distributed antenna devices 30-1 to 30-4 in a fixed order at the first stage of the beam search process, but simultaneously performs a full beam search using a plurality of randomly selected distributed antenna devices among the distributed antenna devices 30-1 to 30-4. By having such a configuration, the wireless communication system 1e can perform a full beam search on the distributed antenna devices for which the full beam search was not performed because a beam that is not the best beam but has a received power value exceeding the threshold was selected by the partial beam search, at random timings. Thus, the update of the beam combination history table 140a is also performed. According to the wireless communication system 1e in the sixth embodiment, it is possible to prevent a combination of non-optimal beams from being continuously and fixedly selected while reducing the number of beam searches.

[0353] Note that the wireless communication system in the above-described third to sixth embodiments repeats randomly selecting one or more distributed antenna devices 30-1 to 30-4 in the first stage of the beam search process and performs a full beam search in order. In contrast, in the first stage of the beam search process, the wireless communication system may randomly select one or more distributed antenna devices 30-1 to 30-4 only in the first time, and then shift the selection order by one each time.

[0354] That is, for example, the candidate beam detection units 15b and 15c first randomly select one value from 1 to N (here, N = 4) as the value of the variable i in the first stage of the beam search process. For example, here it is assumed that i = 2 is selected. Thereby, the candidate beam detection units 15b and 15c first cause the distributed antenna device 30-2 including the second distributed antenna 31-2 to perform a full beam search. After that, instead of randomly selecting one value from 1 to N as the value of the variable i, the candidate beam detection units 15b and 15c select i = 3 obtained by adding 1 to the value of the variable i. Thereby, the candidate beam detection units 15b and 15c next cause the distributed antenna device 30-3 including the third distributed antenna 31-3 to perform a full beam search. After that as well, the candidate beam detection units 15b and 15c sequentially add 1 to the value of the variable i and select in the order of i = 4 and i = 1. Thereby, the candidate beam detection units 15b and 15c next cause the distributed antenna device 30-4 including the fourth distributed antenna 31-4 to perform a full beam search, and then cause the distributed antenna device 30-1 including the first distributed antenna 31-1 to perform a full beam search.

[0355] In this way, when the candidate beam detectors 15b and 15c first select 2 as the value of the variable i by random selection, they will select the values of this variable i in the order of 2, 3, 4, 1. Then, in the next candidate beam detection process, the candidate beam detectors 15b and 15c will select 3, which is obtained by adding 1 to the randomly selected value 2 as the value of the variable i, and will select the values of this variable i in the order of 3, 4, 1, 2. Then, in the candidate beam detection process of the next time, the candidate beam detectors 15b and 15c will select 4, which is obtained by further adding 1 to the added value 3 as the value of the variable i, and will select the values of this variable i in the order of 4, 1, 2, 3.

[0356] Alternatively, for example, the candidate beam detectors 15d and 15e first randomly select two values (here, let X = 2) from 1 to N (here, let N = 8) as the value of the variable i at the first stage of the beam search process. For example, here it is assumed that i = 2 and 6 are selected. As a result, the candidate beam detectors 15d and 15e first cause the distributed antenna device 30-2 including the second distributed antenna 31-2 and the distributed antenna device 30-6 (not shown) including the sixth distributed antenna 31-6 (not shown) to perform a full beam search. After that, instead of randomly selecting one value from 1 to N as the value of the variable i, the candidate beam detectors 15d and 15e select i = 3 and 7, which are obtained by adding 1 to the value of the variable i. As a result, the candidate beam detectors 15d and 15e next cause the distributed antenna device 30-3 including the third distributed antenna 31-3 and the distributed antenna device 30-7 (not shown) including the seventh distributed antenna 31-7 (not shown) to perform a full beam search.

[0357] After that, the candidate beam detectors 15d and 15e also sequentially add 1 to the value of the variable i, and select in the order of i = 4 and 8, i = 5 and 1. As a result, the candidate beam detectors 15d and 15e next cause the distributed antenna devices 30-4 including the fourth distributed antenna 31-4 and the distributed antenna devices 30-8 (not shown) including the eighth distributed antenna 31-8 (not shown) to perform full beam search, and then cause the distributed antenna devices 30-5 (not shown) including the fifth distributed antenna 31-5 (not shown) and the distributed antenna devices 30-1 including the first distributed antenna 31-1 to perform full beam search.

[0358] Thus, when the candidate beam detectors 15d and 15e initially select 2 and 6 by random selection as the values of the variable i, they will select the values of this variable i in the order of 2 and 6, 3 and 7, 4 and 8, 5 and 1. Then, in the next candidate beam detection process, the candidate beam detectors 15d and 15e select 3 and 7, which are obtained by adding 1 to 2 and 6 respectively, which are the randomly selected values as the values of the variable i, and select the values of this variable i in the order of 3 and 7, 4 and 8, 5 and 1, 6 and 2. Then, in the candidate beam detection process of the next time after that, the candidate beam detectors 15d and 15e select 4 and 8, which are obtained by further adding 1 to 3 and 7 respectively, which are the added values as the values of the variable i, and select the values of this variable i in the order of 4 and 8, 5 and 1, 6 and 2, 7 and 3.

[0359] By having such a configuration, in the first stage of the beam search process, the wireless communication system randomly selects one or a plurality of distributed antenna devices 30-1 to 30-4 only for the first time, and then shifts the selection order one by one each time. By having such a configuration, even for a distributed antenna device for which the entire beam search is not performed because a beam that is not the best beam but has a received power value exceeding the threshold is selected by partial beam search, the entire beam search is performed at random timing. Therefore, the beam combination history table is also updated. Thus, according to the wireless communication system, it is possible to reduce the number of beam searches and prevent a non-optimal beam combination from being continuously and fixedly selected.

[0360] Generally, a distributed antenna system using a high-frequency band needs to perform beam selection periodically at an appropriate frequency in order to follow propagation path fluctuations due to the movement of the terminal device and changes in the surrounding environment. However, if the time required for one beam selection becomes too long due to an increase in the number of distributed antennas, the time required for the beam selection may become longer than the execution period of the beam selection. In this case, since the beam selection cannot be completed within the execution period of the beam selection, it becomes difficult to perform data transmission itself.

[0361] In contrast, the wireless communication system 1d in the fifth embodiment and the wireless communication system 1e in the sixth embodiment described above are configured to perform the entire beam search simultaneously using a plurality of randomly selected distributed antenna devices among the distributed antenna devices 30-1 to 30-4 in the first stage of the beam search process. At this time, as a method of performing the entire beam search simultaneously using the distributed antenna devices, for example, techniques such as frequency multiplexing or code multiplexing are used.

[0362] In the fifth and sixth embodiments, full beam search can be performed simultaneously by a plurality of distributed antennas using orthogonal radio resources. However, if this is implemented with all distributed antennas, since all beam searches are completed, the partial beam search using history becomes unnecessary, but the radio resources required for beam search become enormous. Therefore, the fifth and sixth embodiments are configured such that full beam search is performed simultaneously by a part of the plurality of distributed antennas, and partial beam search using history is performed for the remaining distributed antennas.

[0363] ...

Claims

1. In a beam search period for searching for a beam used for wireless communication with a terminal device, for each of a plurality of distributed antennas, perform a full beam search of transmitting beams in all directions that can be transmitted, in an order of the distributed antennas different for each beam search period. When one beam identifier indicating the best beam among the beams obtained by the full beam search is acquired, stop the full beam search, and use the beam specified by the acquired beam identifier and information indicating the distributed antenna that transmitted the beam indicated by the beam identifier as a detection reference beam. A candidate beam detector that detects, from a beam combination history storage unit, as a candidate beam identifier for the distributed antenna, a beam identifier of a beam that is a beam identifier of a distributed antenna that has not performed the full beam search during the beam search period and has been selected together with the detection reference beam; A beam search execution determination unit that determines whether to perform a full beam search for the distributed antennas that have not performed the full beam search during the beam search period, based on the detection result of the candidate beam detector; A beam combination recording unit that generates a record indicating a combination of beam identifiers indicating the beams that have been the best beams in each of the distributed antennas during the beam search period, and records the generated record in the beam combination history storage unit; A communication control device comprising the above.

2. The beam search execution determination unit: Determines, as the distributed antenna for which the full beam search is to be performed, a distributed antenna that has not performed the full beam search during the beam search period and for which the candidate beam identifier has not been detected by the candidate beam detector; The beam that has been the best beam in each of the distributed antennas during the beam search period is the beam that the terminal device has determined to be the best among the beams transmitted by the distributed antennas for which the full beam search has been performed during the beam search period. The communication control device according to Claim 1.

3. The beam search execution determination unit: Causing the partial beam search to transmit the beam indicated by the candidate beam identifier to the distributed antenna in which the candidate beam identifier has been detected by the candidate beam detector, and based on a value indicating the reception quality of the beam that the terminal device has determined to be the best among the beams obtained by the partial beam search and a threshold value, determining whether to cause the distributed antenna to perform a full beam search; The beam determined to be the best beam in each of the distributed antennas during the beam search period is, when it is determined by the beam search execution determination unit not to cause the distributed antenna to perform a full beam search, the beam that the terminal device has determined to be the best among the beams obtained by the immediately preceding partial beam search performed by the distributed antenna, or, when it is determined by the beam search execution determination unit to cause the distributed antenna to perform a full beam search, the beam that the terminal device has determined to be the best among the beams obtained by the full beam search to be performed by the distributed antenna; The communication control device according to claim 1 or claim 2.

4. In the beam combination history storage unit, a value indicating the reception quality when the terminal device receives the beam indicated by the beam identifier is stored in association with each of the beam identifiers for each distributed antenna; The beam search execution determination unit, Determines whether to cause the distributed antenna to perform a full beam search based on the threshold value calculated from the value indicating the reception quality associated with the candidate beam identifier in the beam combination history storage unit and the value indicating the reception quality of the beam indicated by the beam identifier; The communication control device according to claim 3.

5. Before the beam search period, a beam combination history generation unit that records, for each trial period, in the beam combination history storage unit, a record indicating a combination of beam identifiers indicating the beams that the terminal device has determined to be the best for each of the distributed antennas among the beams obtained by the full beam search to be performed on all of the distributed antennas for each trial period; The communication control device according to claim 1, further comprising:

6. A wireless communication system including a terminal device, a plurality of distributed antenna devices each having one distributed antenna, and a communication control device, The communication control device is, In a beam search period for searching for a beam used for wireless communication with the terminal device, for each of a plurality of distributed antennas, perform a full beam search by transmitting beams in all directions in which transmission is possible in a different order of the distributed antennas for each beam search period. When one beam identifier indicating the best beam among the beams obtained by the full beam search is acquired, stop the full beam search, and use the beam identifier and the information indicating the distributed antenna that transmitted the beam indicated by the beam identifier as a detection reference beam. A candidate beam detection unit that detects, from a beam combination history storage unit, as a candidate beam identifier for the distributed antenna, a beam identifier of a beam that is a beam identifier of the distributed antenna that has not performed the full beam search during the beam search period and that has been selected together with the detection reference beam. A beam search execution determination unit that determines whether to perform a full beam search for the distributed antennas that have not performed the full beam search during the beam search period based on the detection result of the candidate beam detection unit. A beam combination recording unit that generates a record indicating a combination of beam identifiers indicating the beams that have been the best beams in each of the distributed antennas during the beam search period, and records the generated record in the beam combination history storage unit. A wireless communication system comprising the above.

7. In a beam search period for searching for a beam used for wireless communication with a terminal device, for each of a plurality of distributed antennas, perform a full beam search by transmitting beams in all directions in which transmission is possible in a different order of the distributed antennas for each beam search period. When one beam identifier indicating the best beam among the beams obtained by the full beam search is acquired, stop the full beam search, and use the beam identifier and the information indicating the distributed antenna that transmitted the beam indicated by the beam identifier as a detection reference beam. A candidate beam detection step of detecting, from a beam combination history storage unit, as a candidate beam identifier for the distributed antenna, a beam identifier of a beam that is a beam identifier of the distributed antenna that has not performed the full beam search during the beam search period and that has been selected together with the detection reference beam. A beam search execution determination step of determining whether to perform a full beam search on the distributed antenna that has not performed the full beam search during the beam search period based on the detection result by the candidate beam detection step; A beam combination recording step of generating a record indicating a combination of beam identifiers indicating the beams that are the best beams in each of the distributed antennas during the beam search period, and recording the generated record in the beam combination history storage unit; A communication control method including the above.

8. A computer, During a beam search period for searching for a beam used for wireless communication with a terminal device, for each of a plurality of distributed antennas, perform a full beam search by transmitting beams in all directions that can be transmitted in a different order of the distributed antennas for each beam search period. When one beam identifier indicating the best beam among the beams by the full beam search is obtained, stop the full beam search, and use the obtained beam identifier and the information indicating the distributed antenna that transmitted the beam indicated by the beam identifier as a detection reference beam. A candidate beam detection step of detecting, from the beam combination history storage unit, as a candidate beam identifier for the distributed antenna, a beam identifier of a beam that has been selected together with the detection reference beam among the beam identifiers of the distributed antennas that have not performed the full beam search during the beam search period; A beam search execution determination step of determining whether to perform a full beam search on the distributed antenna that has not performed the full beam search during the beam search period based on the detection result by the candidate beam detection step; A beam combination recording step of generating a record indicating a combination of beam identifiers indicating the beams that are the best beams in each of the distributed antennas during the beam search period, and recording the generated record in the beam combination history storage unit; A program for causing the above to be executed.

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