Wireless communication system, communication control device, communication control method and program

Abstract

This wireless communication system comprises: at least one terminal device; a plurality of distributed antenna devices each comprising one distributed antenna; and a communication control device. The communication control device comprises: a report signal transmission unit that, in a beam search period which is for searching for a beam to be used in wireless communication with the at least one terminal device, allocates, to the at least one terminal device, a necessary resource for transmitting a reference signal, and reports information of the resource to the at least one terminal device; and a reference signal reception unit that receives, while changing a reception beam, a reference signal which is transmitted from the at least one terminal device at a timing indicated by the information of the resource having been reported by the report signal transmission unit, and which is received from each of the distributed antennas included in the the distributed antenna devices.　

Description

[Technical Field]

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

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

[0003] In Point-to-Point (PP) communications, where the combination of communicating wireless stations is always fixed and the relative positions of the wireless stations and the propagation environment around the wireless stations do not change, fixed beamforming can be performed by determining the beam forming direction in advance, such as when the wireless stations are installed. In contrast, in Point-to-Multipoint (P-MP) communications, which accommodate multiple wireless stations, or when at least one of the wireless stations moves, fixed beamforming cannot be performed. In these cases, adaptive beamforming is required, which adaptively controls the beam forming direction in accordance with the position of the wireless station that needs to communicate, the movement of the wireless station, and changes in the propagation environment around the wireless station.

[0004] Adaptive beamforming is generally performed by controlling the beam direction by adjusting the phase relationship of radio waves radiated between multiple antenna elements without using mechanical drivers. However, to properly adjust the phase relationship, it is necessary to understand the phase relationship between each antenna element at both the transmitting and receiving wireless stations and then derive the appropriate phase relationship. In other words, it is necessary to understand the state of the propagation path between each antenna element at both the transmitting and receiving wireless stations for all combinations of each antenna element.

[0005] The state of the propagation path can be determined by transmitting and receiving a known signal between the transmitting radio station and the receiving radio station, but other communications cannot be performed during this transmission and reception, and the receiving radio station must accurately convey the state of the propagation path to the transmitting radio station, which increases communication overhead.

[0006] To suppress the increase in overhead, adaptive beamforming uses a technique in which a signal including a beam identifier (hereinafter referred to as beam ID (Identifier)) associated with a plurality of candidate beams that are discretely set in advance is transmitted via each candidate beam, and the beam ID of the beam determined to be most suitable for communication is selected from among these candidate beams. This technique is defined as a specification for wireless communication systems that have been put into practical use in recent years, such as 3GPP (registered trademark) 5G (5th Generation) and IEEE802.11ad, and is also being implemented (for example, see Non-Patent Documents 1, 2, and 3).

[0007] (Beam selection procedure) When selecting a transmitting beam for a wireless station, the transmitting wireless station transmits a signal that allows the receiving wireless station to uniquely identify each beam used for transmission. One such signal is a beam search signal that embeds the beam ID of the beam used for transmission as digital information. The transmitting wireless station transmits each beam, carrying a beam search signal with a different embedded beam ID, by switching the direction over time.

[0008] The receiving radio station receives multiple beams, reads the beam ID included in the beam search signal for each of the received multiple 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 to the transmitting radio station that allows the transmitting radio station to uniquely identify the beam ID of the transmitting beam with the best reception quality, allowing the transmitting radio station to select the transmitting beam.

[0009] In systems such as TDD (Time Division Duplex), which use the same frequency for transmission and reception, it is possible for a wireless station to select the same beam as the transmitting side when selecting a receiving beam. In contrast, in systems such as FDD (Frequency Division Duplex), which use different frequencies for transmission and reception, the receiving side must also select a beam, just as it selects a beam for the transmitting side. When selecting a receiving beam for a wireless station, the receiving wireless station transmits a signal to the transmitting wireless station requesting a receiving beam search procedure. The receiving wireless station switches its direction in time to match the signal transmitted by the transmitting wireless station, receives the signal, and measures the reception quality of the received signal. This allows the receiving wireless station to select a receiving beam by determining which receiving beam provides the best reception quality.

[0010] (Distributed Antenna System) FIG. 25 is a diagram showing the configuration of wireless communication system 500, which is an example of a conventional general wireless communication system. FIG. 25 shows, as an example, a configuration in which five cells 100-1 to 100-5 exist in wireless communication system 500. Wireless communication system 500 is configured so that one antenna is installed for each cell. That is, wireless communication system 500 is configured so that antenna devices 200-1 to 200-5 are installed in each of cells 100-1 to 100-5. Digital signal processing devices 210-1 to 210-5 that transmit and receive signals are connected to each of antenna devices 200-1 to 200-5, respectively. Looking at cell 100-1, antenna device 200-1 and digital signal processing device 210-1 are so-called base station devices, and when one terminal station is located in cell 100-1, for example, the terminal station is connected to one antenna device 200-1 by radio waves.

[0011] As mentioned above, in high-frequency bands such as the millimeter wave and terahertz bands, the effects of reflected and diffracted waves are reduced by using beamforming technology. Therefore, in high-frequency bands, line-of-sight communication is essential, as there is a high possibility of communication interruption if the beam is blocked. Meanwhile, MIMO (Multiple Input Multiple Output) is a promising spatial multiplexing technology. MIMO uses multiple antennas for transmission and reception, and spatial multiplexing improves transmission speeds by up to several times the number of antennas using the same time and frequency resources. However, because line-of-sight communication is essential in high-frequency bands, applying MIMO technology increases the spatial correlation between multiple transmitting and receiving antennas, making spatial multiplexing difficult.

[0012] Therefore, distributed antenna systems that have the effect of improving shadowing resistance and reducing spatial correlation in high frequency bands are being studied (see, for example, Non-Patent Documents 4 and 5). Fig. 26 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 shown in Fig. 25, the wireless communication system 500a has five cells 100-1 to 100-5. However, unlike the wireless communication system 500, the wireless communication system 500a has a configuration in which multiple antennas are installed in a distributed manner for one cell. Hereinafter, each of the multiple antennas installed in a distributed manner will be referred to as a distributed antenna.

[0013] In cell 100-1, a plurality of distributed antenna apparatuses 200a-1-1 to 200a-1-4, each equipped with one distributed antenna, are installed in a distributed manner, and one digital signal processing device 210a-1 is connected to the plurality of distributed antenna apparatuses 200a-1-1 to 200a-1-4. In wireless communication system 500a, the plurality of distributed antenna apparatuses 200a-1-1 to 200a-1-4 and digital signal processing device 210a-1 form what is called a base station apparatus, and similar configurations are also used in other cells 100-2 to 100-5. In wireless communication system 500a, when one terminal station is located in cell 100-1, for example, the terminal station is connected to the plurality of distributed antenna apparatuses 200a-1-1 to 200a-1-4 by radio waves.

[0014] (Beam selection procedure for distributed antennas) By applying MIMO between a radio station equipped with multiple antennas (distributed antennas) installed in a distributed manner and a single terminal station equipped with multiple antennas, i.e., single-user MIMO, spatial correlation is reduced and spatial multiplexing becomes possible. However, it is essential to select a beam in advance for the link between each of the multiple antennas of the radio station and each of the multiple antennas of the terminal station. In the following description, MIMO between a radio station equipped with distributed antennas and a terminal station equipped with multiple antennas is referred to as distributed MIMO.

[0015] Here, we will explain a general transmit beam selection method for performing distributed MIMO in high frequency bands. A wireless station generates multiple beam search signals for each combination of beam ID and antenna ID, each of which embeds digital information including a beam ID associated with each of multiple candidate beams discretely set in advance for each of the wireless station's multiple transmit antennas and an antenna ID associated with each of the multiple transmit antennas. The wireless station transmits each of the multiple generated beam search signals on a transmit beam corresponding to the included beam ID, which is a transmit beam switched over time by the transmit antenna corresponding to the included antenna ID.

[0016] The terminal station, which is the communicating party, receives multiple beams with each of its multiple receiving antennas, reads the beam ID and transmitting antenna ID included in the beam search signal for each of the received multiple beams, and measures the reception quality of the received beam. The terminal station selects the beam ID with the best reception quality for each transmitting antenna ID, and feeds back to the transmitting radio station data combining the transmitting antenna ID, the beam ID selected for that transmitting antenna ID, and the reception quality corresponding to that beam ID. The radio station that receives this feedback selects multiple transmission beams equal to the number of spatial multiplexed beams using MIMO based on the reception quality. In addition, the terminal station, which is the communicating party, selects multiple reception beams in sequence using receiver beam selection. This enables MIMO transmission and reception between multiple transmission and reception beams in high frequency bands.

[0017] Assume that a two-stage beam search is applied to beam selection in wireless communication system 500a shown in Fig. 26. First, two-stage beam search will be described using Fig. 27. Fig. 27 is a diagram for explaining two-stage beam search. Two-stage beam search is a method in which, in the first stage, a wide beam (wide beam) is transmitted by switching the transmitting antenna over time to identify a rough beam direction for the terminal station, and in the second stage, a beam (narrow beam) narrower than that in the first stage is transmitted by switching the transmitting antenna over time more precisely within the range of the identified rough beam direction to identify the best beam for the terminal station.

[0018] In FIG. 27, similarly to FIG. 26, a plurality of distributed antenna apparatuses 200a-1-1 to 200a-1-4 are installed in a distributed manner. As shown in the left diagram of FIG. 27, the plurality of distributed antenna apparatuses 200a-1-1 to 200a-1-4 transmit beams with wide beam widths (wide beams) in a first stage by switching the transmitting antenna over time. At this time, the plurality of distributed antenna apparatuses 200a-1-1 to 200a-1-4 transmit beam search signals on the wide beams. The plurality of distributed antenna apparatuses 200a-1-1 to 200a-1-4 receive signals fed back from the terminal stations 220-1 and 220-2 to roughly identify the beam directions for the terminal stations 220-1 and 220-2. Generally, since there may be terminal stations that are initially connected, the plurality of distributed antenna apparatuses 200a-1-1 to 200a-1-4 periodically transmit beam search signals to all terminal stations.

[0019] 27, in the second stage, the plurality of distributed antenna devices 200a-1-1 to 200a-1-4 transmit beams (narrow beams) with narrower beam widths than those in the first stage by switching the transmitting antennas more precisely over time within the range of the identified rough beam direction. At this time, the plurality of distributed antenna devices 200a-1-1 to 200a-1-4 transmit reference signals on the narrow beams.

[0020] Fig. 28 is a sequence diagram showing a processing flow when a two-stage beam search is applied to beam selection in conventional wireless communication system 500a. In Fig. 28, the multiple distributed antenna apparatuses are described as distributed antenna apparatuses 200a-1-1 to 200a-1-3, and the multiple terminal stations are described as terminal stations 220-1 to 220-3.

[0021] The distributed antenna device 200a-1-1 switches the transmitting antenna over time and transmits the broadcast signal on a wide beam (step S11). The broadcast signal is a signal in which information on the beam ID and the antenna ID is embedded, similar to the beam search signal. Here, the number of wide beams transmitted by the distributed antenna device 200a is N w N wis an integer equal to or greater than 2. Similarly, the distributed antenna devices 200a-1-2 and 200a-1-3 switch the transmitting antennas over time to transmit the report signal on a wide beam (steps S12 and S13).

[0022] When each of the terminal stations 220-1 to 220-3 receives the wide beam, it transmits a feedback signal to the distributed antenna apparatuses 200a-1-1 to 200a-1-3 that transmitted the wide beam (steps S14 to S16). As a result, each of the distributed antenna apparatuses 200a-1-1 to 200a-1-3 identifies the beam direction for each of the terminal stations 220-1 to 220-3. Thereafter, the distributed antenna apparatus 200a-1-1 switches the transmitting antenna over time, and transmits the reference signal on a narrow beam to each of the terminal stations 220-1 to 220-3 (steps S17 to S19). The number of narrow beams that the distributed antenna apparatus 200a transmits to one terminal station 220 is N n N n is an integer equal to or greater than 2. Similarly, the distributed antenna devices 200a-1-2 and 200a-1-3 switch the transmitting antennas over time to transmit the reference signal on a narrow beam (steps S20 to S25). [Prior art documents] [Non-patent literature]

[0023] [Non-Patent Document 1] Satoshi Suyama et al., "5G Multi-Antenna Technology," NTT DOCOMO Technical Journal, Vol. 23, No. 4, pp. 30-39, January 2016 [Non-patent document 2] Kazuaki Takeda et al., "Status of Study on Physical Layer Elemental Technologies and High Frequency Band Utilization in 5G," NTT DOCOMO Technical Journal, Vol. 25, No. 3, pp. 23-32, October 2017 [Non-patent document 3] Koji Takinami et al., "Standardization Trends and Elemental Technologies of Millimeter-Wave Wireless LAN Systems," IEICE Communications Society Magazine, No. 38 Autumn Issue, pp. 100-106, 2016 [Non-patent document 4] Daisei Uchida et al., "A Study on High-Frequency Distributed Antenna Systems in High-Density / Shielded Environments," IEICE General Conference, Communications Lecture Papers 1, B-5-87, p.375, March 2020 [Non-Patent Document 5] Masashi Iwabuchi et al., "Proposal for High-Frequency Band Multipath Formation Control Using Multiple Diverse Relay Systems," Proceedings of the Institute of Electronics, Information and Communication Engineers General Conference, Communications Lecture Papers 1, B-5-101, p.389, March 2020 Summary of the Invention [Problem to be solved by the invention]

[0024] As described above, when a two-stage beam search is applied to beam selection in the wireless communication system 500a, a reference signal is transmitted using a narrow beam for each distributed antenna device in the second stage of the beam search to perform a precise beam search, which creates the problem that the overhead required for the beam search increases as the number of distributed antenna devices increases.

[0025] In view of the above circumstances, an object of the present invention is to provide a technique that can suppress an increase in overhead associated with beam search. [Means for solving the problem]

[0026] One aspect of the present invention is a wireless communication system comprising one or more terminal devices, a plurality of distributed antenna devices each having one distributed antenna, and a communication control device, wherein the communication control device comprises: a notification signal transmitting unit that allocates resources required to transmit a reference signal to the one or more terminal devices during a beam search period in which a beam to be used for wireless communication with the one or more terminal devices is searched for, and notifies each of the one or more terminal devices of information about the resources; and a reference signal receiving unit that receives the reference signal transmitted from each of the one or more terminal devices at a timing indicated by the resource information notified by the notification signal transmitting unit, the reference signal being received by all of the distributed antennas provided in each of the plurality of distributed antenna devices while changing the receiving beam.

[0027] One aspect of the present invention is a communication control device that includes: a notification signal transmitting unit that allocates resources necessary for transmitting a reference signal to one or more terminal devices during a beam search period in which a beam to be used for wireless communication with the one or more terminal devices is searched for, and notifies each of the one or more terminal devices of information about the resources; and a reference signal receiving unit that receives the reference signal transmitted from each of the one or more terminal devices at a timing indicated by the resource information notified by the notification signal transmitting unit, and that receives the reference signal by all distributed antennas provided in each of a plurality of distributed antenna devices while changing the receiving beam.

[0028] One aspect of the present invention is a signal control method that, during a beam search period in which beams to be used for wireless communication with one or more terminal devices are searched for, allocates resources necessary for transmitting reference signals to the one or more terminal devices, notifies each of the one or more terminal devices of information about the resources, and receives the reference signals transmitted from each of the one or more terminal devices at timings indicated by the notified resource information, the reference signals being received by all distributed antennas provided in each of a plurality of distributed antenna devices while changing the receiving beam.

[0029] One aspect of the present invention is a program for causing a computer to execute the following steps: a notification signal transmitting step of allocating resources necessary for transmitting a reference signal to one or more terminal devices during a beam search period in which beams to be used for wireless communication with the one or more terminal devices are searched for, and notifying each of the one or more terminal devices of information about the resources; and a reference signal receiving step of receiving the reference signal transmitted from each of the one or more terminal devices at a timing indicated by the resource information notified in the notification signal transmitting step, the reference signal being received by all distributed antennas provided in each of a plurality of distributed antenna devices while changing the receiving beam. [Effects of the Invention]

[0030] According to the present invention, it is possible to suppress an increase in overhead required for beam search. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a block diagram showing an example of the configuration of a wireless communication system according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of a communication control device according to the first embodiment. [Figure 3] FIG. 2 is a diagram illustrating an example of the configuration of a terminal device according to the first embodiment. [Figure 4] FIG. 3 is a sequence diagram showing a processing flow of the wireless communication system in the first embodiment. [Figure 5] 4 is a flowchart showing the flow of processing performed by the communication control device in the first embodiment. [Figure 6] 5 is a flowchart showing the flow of wide beam search processing performed by the communication control device in the first embodiment. [Figure 7] 5 is a flowchart showing the flow of narrow beam search processing performed by the communication control device in the first embodiment. [Figure 8] 5 is a flowchart showing the flow of processing performed by a terminal device in the first embodiment. [Figure 9] 10 is a flowchart showing the flow of wide beam search processing performed by the terminal device in the first embodiment. [Figure 10] 5 is a flowchart showing the flow of narrow beam search processing performed by the terminal device in the first embodiment. [Figure 11] FIG. 10 is a diagram illustrating an example of the configuration of a communication control device according to a second embodiment. [Figure 12] FIG. 10 is a diagram illustrating an example of the configuration of a terminal device according to a second embodiment. [Figure 13] FIG. 10 is a sequence diagram showing a processing flow of a wireless communication system according to the second embodiment. [Figure 14] 10 is a flowchart showing the flow of processing performed by a communication control device in the second embodiment. [Figure 15] 10 is a flowchart showing the flow of a receiving beam search process performed by a communication control device in the second embodiment. [Figure 16] 10 is a flowchart showing the flow of processing performed by a terminal device in the second embodiment. [Figure 17] 10 is a flowchart showing the flow of a receiving beam search process performed by a terminal device in the second embodiment. [Figure 18] FIG. 10 is a diagram illustrating an example of the configuration of a communication control device according to a third embodiment. [Figure 19] FIG. 10 is a diagram illustrating an example of the configuration of a terminal device according to a third embodiment. [Figure 20] FIG. 11 is a sequence diagram showing a processing flow of a wireless communication system according to the third embodiment. [Figure 21] 10 is a flowchart showing the flow of processing performed by a communication control device in the third embodiment. [Figure 22] 10 is a flowchart showing the flow of a receiving beam search process performed by a communication control device in the third embodiment. [Figure 23] 10 is a flowchart showing the flow of processing performed by a terminal device in the third embodiment. [Figure 24]10 is a flowchart showing the flow of a receiving beam search process performed by a terminal device in the third embodiment. [Figure 25] 1 is a diagram showing a configuration of a wireless communication system that is an example of a conventional general wireless communication system. [Figure 26] 1 is a diagram illustrating the configuration of a wireless communication system that is an example of a high-frequency band distributed antenna system. [Figure 27] FIG. 10 is a diagram for explaining a two-stage beam search. [Figure 28] FIG. 1 is a sequence diagram showing a processing flow when a two-stage beam search is applied to beam selection in a conventional wireless communication system. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (First embodiment) 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. The wireless communication system 1 is equipped with a communication control device 10, a digital signal processing device 20, and distributed antenna devices 30-1 to 30-4. Distributed antenna devices 30-1, 30-2, 30-3, and 30-4 and a terminal device 40 are located within the area of ​​the cell 100. 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 form a so-called base station device.

[0033] 1 is an example of a configuration of the wireless communication system 1, and the wireless communication system 1 may be configured such that a plurality of distributed antenna apparatuses 30-1 to 30-N are installed in a cell 100, and a digital signal processing device 20 is connected to each of the distributed antenna apparatuses 30-1 to 30-N. Here, N is an integer equal to or greater than 2. The wireless communication system 1 may be configured to include a plurality of cells 100 as shown in FIG. 26. In this case, the wireless communication system 1 includes a number of digital signal processing devices 20 equal to the number of cells 100, and a communication control device 10, and each of the communication control devices 10 is connected to a corresponding digital signal processing device 20, and each of the digital signal processing devices 20 is connected to a corresponding distributed antenna apparatus 30-1 to 30-N in the cell 100.

[0034] In the first embodiment, each of the distributed antenna devices 30-1 to 30-4 performs a two-stage beam search and is therefore capable of forming a wide beam with a first beam width and a narrow beam with a second beam width narrower than the first beam width. For example, the distributed antenna devices 30-1 to 30-4 can form wide beams in multiple directions and narrow beams in multiple directions. The number of directions in which the distributed antenna devices 30-1 to 30-4 can form wide beams and narrow beams may be two or more. The maximum number of directions in which the distributed antenna devices 30-1 to 30-4 can form wide beams and narrow beams is predetermined by 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.

[0035] Each of the distributed antenna devices 30-1 to 30-4 includes one distributed antenna 31-1 to 31-4 and one main device 32-1 to 32-4. Each of the distributed antennas 31-1 to 31-4 is assigned a distributed antenna ID in advance that allows each to be uniquely identified.

[0036] Each of main devices 32-1 to 32-4 transmits and receives radio frequency analog signals through distributed antennas 31-1 to 31-4 connected to it. That is, each of main devices 32-1 to 32-4 generates a radio frequency analog signal by modulating a carrier wave based on the digital signal of the transmission data output by digital signal processing device 20. Each of main devices 32-1 to 32-4 transmits the generated analog signal by radio waves from distributed antennas 31-1 to 31-4 connected to it.

[0037] Each of main devices 32-1 to 32-4 demodulates and converts into digital signals the analog signals that are received and output by distributed antennas 31-1 to 31-4 connected thereto, and outputs the converted digital signals to digital signal processing device 20.

[0038] From the viewpoint of beamforming, each of the main devices 32-1 to 32-4 receives a digital beam search signal as transmission data output from the digital signal processing device 20. Each of the main devices 32-1 to 32-4 modulates a carrier wave based on the beam search signal to form a beam in a direction corresponding to the beam ID included in the received beam search signal and transmit the beam search signal. Each of the main devices 32-1 to 32-4 transmits a radio frequency analog signal carrying the modulated beam search signal via the distributed antennas 31-1 to 31-4 connected to each of the main devices 32-1 to 32-4.

[0039] Here, the beam ID is, for example, an identifier in which a character string "beam ID#" is assigned to consecutive integer values ​​starting from 1, and is an identifier that is predetermined for each of the distributed antenna devices 30-1 to 30-4. For example, if the distributed antenna device 30-1 can form beams in 10 different directions, fixed beam IDs from "beam ID#1" to "beam ID#10" are assigned in advance to each of the beams in the 10 directions, and data indicating the correspondence between the beam IDs and the directions is stored in advance in an internal storage area of ​​the main device 32-1.

[0040] In other words, when "beam ID #1" is specified by a beam search signal to the main 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 also applies to the other distributed antenna devices 30-2 to 30-4, and in this case, the same beam ID may exist in each of the distributed antenna devices 30-1 to 30-4.

[0041] Each of the distributed antenna devices 30-1 to 30-4 in the first embodiment performs a beam search using a wide beam and a narrow beam. Therefore, data indicating the correspondence between beam IDs and beam directions is stored in advance in the internal storage areas of the main devices 32-1 to 32-4 for each wide beam and narrow beam. Furthermore, the correspondence between the beam IDs of the wide beams and the beam IDs of the narrow beams is also stored in advance. Since the correspondence between the beam IDs of the wide beams and the narrow beams is also stored in advance, each of the distributed antenna devices 30-1 to 30-4 can uniquely determine the narrow beam to be used when performing a beam search using a narrow beam based on the results of the beam search using the wide beam. For example, when each of the distributed antenna devices 30-1 to 30-4 identifies a beam direction for the terminal device 40 as a result of the beam search using the wide beam, it simply selects the beam ID of the narrow beam associated with the beam ID of the wide beam for the identified beam direction.

[0042] When performing a beam search using a wide beam, each of the distributed antenna devices 30-1 to 30-4 transmits a report signal carried on the wide beam. The report signal includes information on the antenna ID and the beam ID. Furthermore, each of the distributed antenna devices 30-1 to 30-4 transmits a report signal using the wide beam in a direction specified by an instruction from the communication control device 10. The report signal is a signal for notifying the terminal device 40 of resource allocation. The report signal includes an instruction to request transmission of a reference signal and information on time-frequency resources. In this way, the report signal includes information on time-frequency resources allocated to the terminal device 40 for transmitting a reference signal. When performing a beam search using a narrow beam, each of the distributed antenna devices 30-1 to 30-4 receives a reference signal transmitted from the terminal device 40 using the narrow beam by switching time in multiple specific directions specified by an instruction from the communication control device 10.

[0043] The digital signal processing device 20 outputs the digital signal of the transmission data to the main 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, the digital signal processing device 20 uses the distributed antenna ID included in the beam search instruction signal as the source antenna ID and generates a beam search signal including the source antenna ID and the beam ID included in the beam search instruction signal.

[0044] The digital signal processing device 20 outputs the generated beam search signal to the main device 32-1 to 32-4 corresponding to the distributed antenna ID included in the beam search instruction signal. As a result, the terminal device 40 receiving the beam carrying the beam search signal can identify the distributed antenna 31-1 to 31-4 that is the source of the beam search signal by referring to the source antenna ID included in the beam search signal, and can further identify the beam that carried the beam search signal by referring to the beam ID included in the beam search signal.

[0045] The digital signal processing device 20 detects received data contained in the digital signals output from the main devices 32-1 to 32-4. If the detected received data is a feedback signal transmitted by the terminal device 40 via radio waves, the digital signal processing device 20 outputs the feedback signal to the communication control device 10.

[0046] The terminal device 40 performs wireless communication with each distributed antenna device 30. In the first embodiment, the terminal device 40 is assumed to be used in a standalone state, not connected to any other wireless communication system. Note that in the first embodiment, the terminal device 40 may be in a non-standalone state, connected to any other wireless communication system. The terminal device 40 transmits a reference signal using time-frequency resources allocated based on the notification signal transmitted from the distributed antenna device 30.

[0047] (Configuration of communication control device of first embodiment) 2 is a diagram showing an example of the configuration of the communication control device 10 in the first embodiment. The communication control device 10 includes a wide beam search execution instruction unit 11, a narrow beam search execution instruction unit 12, a data signal transmission / reception instruction unit 13, a feedback signal receiving unit 14, and a narrow beam search reference signal receiving unit 15.

[0048] When the beam search process for searching for a beam is started, the wide beam search execution instruction unit 11 causes each of the distributed antenna devices 30-1 to 30-4 to perform an all-wide beam search or a partial wide beam search in turn, one by one. The all-wide beam search is a beam search performed by causing each of the distributed antenna devices 30-1 to 30-4 to transmit a beacon signal in each of all wide beam directions in which it can transmit, by switching the time, via the digital signal processing device 20. The partial wide beam search is a beam search performed by causing a beacon signal in a specific wide beam direction, by switching the time, to be transmitted.

[0049] The wide beam search execution instruction unit 11 generates a wide beam search instruction signal including one beam ID between 1 and the maximum beam ID value. For example, when performing a full wide beam search, the wide beam search execution instruction unit 11 generates a wide beam search instruction signal including all beam IDs between 1 and the maximum beam ID value. The wide beam search execution instruction unit 11 writes a distributed antenna ID into each of the generated wide beam search instruction signals. This makes it possible for the digital signal processing device 20 to identify the distributed antenna device 30 to which the wide beam search instruction signal is to be sent. The wide beam search execution instruction unit 11 is one aspect of a broadcast signal transmission unit.

[0050] The narrow beam search execution instruction unit 12 determines the distributed antenna device 30 to which a notification signal is to be transmitted based on reception quality information included in the feedback signal received by the feedback signal receiver 14. For example, the narrow beam search execution instruction unit 12 may determine the distributed antenna device 30 with the highest reception quality included in the feedback signal as the distributed antenna device 30 to which a notification signal is to be transmitted. The narrow beam search execution instruction unit 12 calculates the beam ID of a narrow beam for each terminal device 40, based on the beam ID of the best wide beam for each distributed antenna device 30 included in the feedback signal from each terminal device 40, and allocates to each terminal device 40 the time-frequency resources required for a reception beam search in which the maximum number of beams among the number of candidate narrow beams of the distributed antenna device 30 are switched to measure reception quality, and transmits the notification as a notification signal. The narrow beam search execution instruction unit 12 outputs a notification signal transmission instruction to the determined distributed antenna device 30 to cause the determined distributed antenna device 30 to transmit the notification signal using the wide beam with the highest reception quality. The notification signal transmission instruction in the first embodiment includes the notification signal, an instruction to transmit the notification signal, information for identifying the distributed antenna device 30, and information on the beam ID.

[0051] When allocating time-frequency resources to each terminal device 40, the narrow beam search execution instruction unit 12 may allocate the time-frequency resources so that radio information is included in the reference signal to be transmitted by each of the one or more terminal devices 40 and the reference signal is demodulated by the communication control device 10 to acquire the radio information of the one or more terminal devices 40, or may allocate the time-frequency resources so that radio information is not included in the reference signal to be transmitted by each of the one or more terminal devices 40 and only the received power is measured without being demodulated by the communication control device 10. Note that when the number of beams to be searched differs for each distributed antenna device 30, the resources required for the reference signal to be transmitted to each terminal device 40 may be determined according to the largest number.

[0052] The narrow beam search execution instruction unit 12 may determine the distributed antenna devices 30 to transmit the notification signal from among the plurality of distributed antenna devices 30 in descending order of reception quality. The narrow beam search execution instruction unit 12 is one aspect of the notification signal transmission unit.

[0053] Furthermore, the narrow beam search execution instruction unit 12 causes each of the distributed antenna devices 30-1 to 30-4 to perform a narrow beam search in which narrow beams are switched over time for reception in a plurality of specific directions via the digital signal processing device 20. The narrow beam search execution instruction unit 12 instructs each of the distributed antenna devices 30 to simultaneously switch over and receive candidate narrow beams for each of the distributed antenna devices 30 at the timing of the time-frequency resources that have been allocated and notified to each terminal device 40 in advance.

[0054] The data signal transmission and reception instruction unit 13 selects a distributed antenna device 30 to be used for transmitting and receiving a data signal based on the reception quality of a reference signal transmitted from the terminal device 40. The data signal transmission and reception instruction unit 13 instructs the selected distributed antenna device 30 to transmit and receive a data signal to and from the terminal device 40. At this time, the data signal transmission and reception instruction unit 13 sets the beam to be used by each distributed antenna device 30 to a narrow beam identified by the beam search result, and causes the distributed antenna device 30 to transmit and receive the data signal.

[0055] When the feedback signal receiving unit 14 receives the feedback signal output from the digital signal processing unit 20 , it outputs the received feedback signal to the narrow beam search execution instructing unit 12 .

[0056] The narrow beam search reference signal receiver 15 simultaneously switches between candidate narrow beams for each distributed antenna device 30 at the timing of time-frequency resources that have been allocated and notified to each terminal device 40 in advance, and receives reference signals transmitted from the terminal devices 40. Of the reception qualities for each narrow beam received in each distributed antenna device 30, the narrow beam with the highest reception quality becomes the best narrow beam for each distributed antenna device 30 for each terminal device 40. The narrow beam search reference signal receiver 15 outputs the narrow beam search results to the data signal transmission / reception instruction unit 13. The narrow beam search reference signal receiver 15 is one aspect of a reference signal receiver.

[0057] (Configuration of terminal device of first embodiment) 3 is a diagram showing an example of the configuration of a terminal device 40 in the first embodiment. The terminal device 40 includes P terminal antennas 41-1 to 41-P, an analog signal transmitting / receiving unit 42, a digital signal processing unit 43, a wide beam search broadcast signal receiving unit 44, a feedback signal transmitting unit 45, a narrow beam search notification signal receiving unit 46, a data signal transmitting / receiving unit 47, and a narrow beam search execution instruction unit 48. Here, P is an integer equal to or greater than 1. Wireless communication using distributed MIMO is performed between the terminal antennas 41-1 to 41-P and distributed antennas 31-1 to 31-4 included in each of the distributed antenna devices 30-1 to 30-4.

[0058] The analog signal transmitter / receiver 42 generates a radio frequency analog signal by modulating a carrier wave based on the digital signal of the transmission data output by the digital signal processor 43. The analog signal transmitter / receiver 42 transmits the generated analog signal by radio waves through the terminal antennas 41-1 to 41-P. The analog signal transmitter / receiver 42 demodulates and converts into a digital signal the analog signals that the terminal antennas 41-1 to 41-P receive and output by radio waves. The analog signal transmitter / receiver 42 outputs the converted digital signal to the digital signal processor 43. The analog signal transmitter / receiver 42 measures the received power of the beams received by the terminal antennas 41-1 to 41-P. The analog signal transmitter / receiver 42 associates the received power value obtained by the measurement with a digital signal corresponding to the beam to be measured and outputs the result to the digital signal processor 43.

[0059] The digital signal processing unit 43 outputs the digital signal of the feedback signal output by the feedback signal transmitting unit 45 to the analog signal transmitting / receiving unit 42. Furthermore, the digital signal processing unit 43 outputs the digital signal of the data signal output by the data signal transmitting / receiving unit 47 to the analog signal transmitting / receiving unit 42. Furthermore, the digital signal processing unit 43 outputs the digital signal of the reference signal output by the narrow beam search execution instructing unit 48 to the analog signal transmitting / receiving unit 42.

[0060] The digital signal processing unit 43 receives the digital signal output by the analog signal transmitting / receiving unit 42 and the received power value associated with the digital signal. If the received digital signal is a beam search signal (e.g., a wide beam search signal), the digital signal processing unit 43 associates the received received power value with the beam search signal (e.g., a wide beam) and outputs the beam search signal to the wide beam search notification signal receiving unit 44. Furthermore, if the received digital signal is a notification signal, the digital signal processing unit 43 outputs the notification signal to the narrow beam search notification signal receiving unit 46.

[0061] The wide beam search notification signal receiver 44 receives the beam search signal and the received power value associated with the beam search signal output by the digital signal processor 43. The wide beam search notification signal receiver 44 combines the antenna ID and beam ID contained in the received beam search signal with the received received power value, and writes and stores the combined data in an internal storage area.

[0062] When the wide beam search broadcast signal receiver 44 receives all beam search signals for one of the distributed antenna devices 30-1 to 30-4, it detects and reads all data stored in its internal storage area, including the source antenna ID corresponding to the distributed antenna device 30-1 to 30-4 that received all beam search signals. The wide beam search broadcast signal receiver 44 selects the data corresponding to the maximum received power value from the received set of data. In other words, the wide beam search broadcast signal receiver 44 selects the beam indicated by the beam ID corresponding to the selected maximum received power value as the best beam for the distributed antenna device 30-1 to 30-4 that corresponds to the source antenna ID. The wide beam search broadcast signal receiver 44 outputs the source antenna ID, beam ID, and received power value included in the selected data to the feedback signal transmitter 45.

[0063] The feedback signal transmitter 45 generates a feedback signal including the source antenna ID, the beam ID, and the received power value output by the wide beam search broadcast signal receiver 44. The feedback signal transmitter 45 outputs the generated feedback signal to the digital signal processor 43.

[0064] The narrow beam search notification signal receiving unit 46 receives the digital signal of the notification signal output from the digital signal processing unit 43. The narrow beam search notification signal receiving unit 46 outputs the received digital signal of the notification signal to the narrow beam search execution instruction unit 48.

[0065] The data signal transmitting / receiving unit 47 transmits and receives data signals to and from the distributed antenna device 30. The data signal transmitting / receiving unit 47 outputs to the digital signal processing unit 43 transmission data to be transmitted.

[0066] The narrow beam search execution instruction unit 48 generates a reference signal based on the digital signal of the notification signal output from the narrow beam search notification signal receiving unit 46. Specifically, the narrow beam search execution instruction unit 48 generates a reference signal based on the time-frequency resource allocated by the digital signal of the notification signal. The narrow beam search execution instruction unit 48 causes the terminal antennas 41-1 to 41-P to transmit the reference signal at the time frequency specified by the allocated time-frequency resource.

[0067] 4 is a sequence diagram showing the flow of processing in the wireless communication system 1 in the first embodiment. Note that in FIG. 4, the explanation will be given assuming that there are M distributed antenna devices 30 and K terminal devices 40. The distributed antenna device 30-1 switches the beam direction of the distributed antenna 31-1 over time in accordance with an instruction from the communication control device 10, and transmits the broadcast signal on the wide beam (step S101). The broadcast signal is a signal in which information on the beam ID and antenna ID is embedded, similar to the beam search signal. The distributed antenna device 30-1 switches the wide beam direction of the distributed antenna 31-1 over time, and transmits the N w The notification signal is transmitted.

[0068] Similarly, the distributed antenna devices 30-2 and 30-M switch the beam directions of the distributed antennas 31-2 and 31-M over time in accordance with an instruction from the communication control device 10, and transmit the report signal on the wide beam (steps S102 and S103). w The notification signal is transmitted.

[0069] Upon receiving the broadcast signal, each of the terminal devices 40-1 to 40-K transmits a feedback signal to the distributed antenna devices 30-1 to 30-M that transmitted the broadcast signal (steps S104 to S106). Each of the distributed antenna devices 30-1 to 30-M receives the feedback signal transmitted from each of the terminal devices 40-1 to 40-K via the distributed antennas 31-1 to 31-M. Each of the distributed antenna devices 30-1 to 30-M outputs the received feedback signal to the communication control device 10 via the digital signal processing device 20.

[0070] The communication control device 10 determines the distributed antenna device 30 to which the notification signal is to be transmitted, based on the feedback signal obtained from each of the distributed antenna devices 30-1 to 30-M. The communication control device 10 causes the determined distributed antenna device 30 to form a wide beam in a direction corresponding to the beam ID specified in the feedback signal and transmit the notification signal. Here, it is assumed that the distributed antenna device 30-1 is determined as the distributed antenna device 30 to which the notification signal is to be transmitted. The distributed antenna device 30-1 forms a wide beam in a direction corresponding to the beam ID instructed by the communication control device 10, and transmits the notification signal on the wide beam (steps S107 to S109).

[0071] Each of the terminal devices 40-1 to 40-K receives the notification signal transmitted from the distributed antenna device 30-1. Based on the time-frequency resource included in the notification signal, each of the terminal devices 40-1 to 40-K switches the terminal antennas 41-1 to 41-P over time to transmit the reference signal on a beam (steps S110 to S112). Here, the number of beams switched by the distributed antenna device 30 to receive the reference signal transmitted by the terminal device 40 is N n is.

[0072] Fig. 5 is a flowchart showing the flow of processing performed by the communication control device 10 in the first embodiment. Note that the processing in Fig. 5 shows processing performed by the communication control device 10 in one beam search cycle. Therefore, the communication control device 10 executes the processing in Fig. 5 for each beam search cycle. The communication control device 10 performs wide beam search processing (step S201). Details of the wide beam search processing will be described later. The communication control device 10 performs narrow beam search processing within the range of the beam direction identified in the wide beam search processing (step S202). Details of the narrow beam search processing will be described later.

[0073] The data signal transmission / reception instruction unit 13 of the communication control device 10 selects a distributed antenna device 30 to be used for transmitting and receiving the data signal based on the reception quality of the reference signal transmitted from each terminal device 40 (step S203). The data signal transmission / reception instruction unit 13 sets the beam to be used by the selected distributed antenna device 30 to the narrow beam resulting from the reception beam search, and transmits and receives the data signal (step S204).

[0074] FIG. 6 is a flowchart showing the flow of wide beam search processing performed by the communication control device 10 in the first embodiment. The wide beam search execution instruction unit 11 of the communication control device 10 provides a counter m in an internal storage area and initializes it to m=1 (step S251). Here, m is an integer value between 1 and M. Since the wireless communication system 1 of FIG. 1 includes four distributed antenna devices 30-1 to 30-4, the following description will be given assuming M=4. The following description will be given assuming that the mth distributed antenna device is distributed antenna device 30-m, the mth distributed antenna is distributed antenna 31-m, and the mth main device is main device 32-m.

[0075] After the process of step S251, the communication control device 10 performs the processes of loops L1s to L1e. The processes of loops L1s to L1e are repeatedly executed until the value of m becomes larger than M. Since M=4, the processes of loops L1s to L1e are repeatedly executed until the processes for distributed antenna devices 30-1 to 30-4 are completed.

[0076] The wide beam search execution instruction unit 11 provides a counter i in an internal storage area and initializes it to i=1 (step S252). In FIG. 6, i ranges from 1 to N.w It is an integer value up to N w is the maximum number of wide beams that the distributed antenna device 30 can transmit. w The value of N may be different for each distributed antenna apparatus 30. w The value of is the same (for example, N w = 10).

[0077] After the process of step S252, the communication control device 10 performs the process of the loop L2s to L2e. The process of the loop L2s to L2e is performed when the value of i is N w The wide beam search execution instruction unit 11 outputs an instruction to the m-th distributed antenna device 30-m to transmit a broadcast signal by wide beam i in the direction corresponding to beam ID "#i". In response to the instruction from the communication control device 10, the m-th distributed antenna device 30-m transmits the broadcast signal on wide beam i in the direction corresponding to beam ID "#i" (step S253). At this time, the m-th distributed antenna device 30-m includes in the broadcast signal a beam ID "#i" that can uniquely identify wide beam i.

[0078] After the process of step S253, the wide beam search execution instruction unit 11 adds 1 to the counter i to update the value of i (step S254). w (For example, N w If the updated value of i is not greater than N (=10), the process of steps S253 to S254 is repeated (loop L2s to L2e). w (For example, N w = 10), the processing of loops L2s to L2e is terminated. In this way, in the processing of loops L2s to L2e, the wide beam search execution command unit 11 executes the wide beam search command for the m-th distributed antenna device 30-m. w The wide beams transmit a warning signal.

[0079] After completing the processing of loops L2s to L2e, the wide beam search execution instruction unit 11 adds 1 to the counter m to update the value of m (step S255). If the updated value of m is not greater than M (for example, M=4), the wide beam search execution instruction unit 11 performs the processing of steps S252 to S255 again (loop L1s to L1e). If the updated value of m is greater than M (for example, M=4), the wide beam search execution instruction unit 11 ends the processing of loops L1s to L1e. In this way, in the processing of loops L1s to L1e, the communication control device 10 performs N w The wide beams transmit a warning signal.

[0080] After completing the processing of loops L1s to L1e, the wide beam search execution instruction unit 11 starts a timer (within a time T1 seconds) that waits for a feedback signal from the terminal device 40. The wide beam search execution instruction unit 11 waits for and receives a feedback signal from the terminal device 40 (step S256). If the time T1 set in the timer has not elapsed since the timer was started when the processing of step S256 ends, the wide beam search execution instruction unit 11 repeatedly executes the processing of step S256 again (loops L3s to L3e).

[0081] When the process of step S256 ends, if the time T1 set in the timer has elapsed since the timer was started, the wide beam search execution instruction unit 11 ends the loop L3s to L3e.

[0082] FIG. 7 is a flowchart showing the flow of narrow beam search processing performed by the communication control device 10 in the first embodiment. The feedback signal receiving unit 14 of the communication control device 10 receives a feedback signal in response to the notification signal transmitted in the wide beam search processing shown in Fig. 6. The feedback signal receiving unit 14 outputs the feedback signal to the narrow beam search execution instruction unit 12. Based on the feedback signal output from the feedback signal receiving unit 14, the narrow beam search execution instruction unit 12 identifies K' terminal devices 40 that have been able to receive the feedback signal.

[0083] Next, the narrow beam search execution instruction unit 12 identifies, for each distributed antenna device 30, the beam of the distributed antenna device 30 with the highest reception quality based on reception quality information (e.g., maximum received power) included in the feedback signal received from each of the identified K' terminal devices 40. Here, the beam identified by the narrow beam search execution instruction unit 12 is a wide beam. Furthermore, the narrow beam search execution instruction unit 12 extracts the wide beam with the highest reception quality for each distributed antenna device 30 included in the feedback signal received from each of the identified K' terminal devices 40, and calculates a narrow beam corresponding to each wide beam. Furthermore, the narrow beam search execution instruction unit 12 calculates time-frequency resources required for the distributed antenna device 30 to simultaneously perform a reception beam search for the maximum number of candidate beams of the distributed antenna device 30 that perform the narrow beam search for the identified K' terminal devices 40, allocates the time-frequency resources to each terminal device 40, and transmits a notification as a notification signal. The narrow beam search execution instruction unit 12 sequentially transmits a notification signal including an instruction to transmit a reference signal for the resources required for the narrow beam search using the beam of the identified distributed antenna device 30 to the identified K' terminal devices 40 (step S301).

[0084] For example, if the beam of the distributed antenna device 30 identified for a certain terminal device 40 (e.g., terminal device 40-1) among the K' number of terminal devices 40 is the beam of the distributed antenna device 30-1, the narrow beam search execution instruction unit 12 outputs information on the beam ID of the identified distributed antenna device 30 and an instruction to transmit a notification signal to the distributed antenna device 30-1. As a result, the distributed antenna device 30-1 transmits a notification signal to the terminal device 40 (e.g., terminal device 40-1) using a wide beam in the direction corresponding to the beam ID instructed by the communication control device 10. The best beam of the distributed antenna device 30 differs for each of the K' number of terminal devices 40. Therefore, the narrow beam search execution instruction unit 12 performs the above processing for each of the K' number of terminal devices 40, thereby extracting the best wide beam for each of the K' number of terminal devices 40 and calculating a narrow beam corresponding to each wide beam. The subsequent processing is as described above.

[0085] The narrow beam search execution instruction unit 12 may instruct a plurality of distributed antenna devices 30 to transmit a notification signal. In this case, the narrow beam search execution instruction unit 12 identifies, for each distributed antenna device 30, a beam that provides the highest reception quality for each distributed antenna device 30, and outputs beam ID information and an instruction to transmit a notification signal to each distributed antenna device 30.

[0086] The narrow beam search execution instruction unit 12 provides a counter k' in an internal storage area and initializes it to k'=1 (step S302). Here, k' is an integer value between 1 and K'. In the following description, K'=3 is used. The k'th terminal device 40 is assumed to be terminal device 40-k' in the following description. After processing step S302, the communication control device 10 performs processing of loop La1s to La1e. The processing of loop La1s to La1e is repeatedly executed until the value of k' becomes greater than K'.

[0087] The narrow beam search execution instruction unit 12 provides a counter i in an internal storage area and initializes it to i=1 (step S303). Here, in FIG. 7, i ranges from 1 to N n It is an integer value up to Nn is the maximum number of narrow beams that the distributed antenna device 30 can support in the direction of one wide beam (beam ID of the wide beam). Therefore, in FIG. 7, i=1 to N n means the i-th narrow beam among the narrow beams corresponding to the wide beam. N n The value of N may be different for each distributed antenna apparatus 30. n The following explanation will be given assuming that the values ​​of are the same.

[0088] After the process of step S303, the communication control device 10 performs the process of the loop La2s to La2e. The process of the loop La2s to La2e is performed when the value of i is N n The narrow beam search execution instruction unit 12 causes all distributed antenna devices 30 (hereinafter referred to as "beam search target distributed antenna devices 30") that perform narrow beam search for the terminal device 40 that is the sender of the k'th received feedback signal to receive the reference signal transmitted from the terminal device 40 that is the sender of the k'th received feedback signal, using the i-th narrow beam corresponding to the wide beam. For example, if there are four distributed antenna devices 30 that are the sender of beam search, the narrow beam search execution instruction unit 12 instructs each of the four distributed antenna devices 30 to receive the reference signal using the i-th narrow beam corresponding to the wide beam. It is assumed that the narrow beam searched by each of the four distributed antenna devices 30 will be in a different direction for each distributed antenna device 30.

[0089] The narrow beam search reference signal receiving unit 15 receives the reference signal received by the distributed antenna device 30 that is the target of the beam search (step S304). The narrow beam search reference signal receiving unit 15 holds the received reference signal for each distributed antenna device 30. Thereafter, the narrow beam search execution instruction unit 12 adds 1 to the counter i to update the value of i (step S305).

[0090] The narrow beam search execution instruction unit 12 determines whether the updated value of i is Nn If it is not greater than N, the process of steps S304 to S305 is repeated (loop La2s to La2e). n If it is greater than the predetermined value, the processing of loops La2s to La2e is terminated. In this way, in the processing of loops La2s to La2e, the communication control device 10 performs beam search on each distributed antenna device 30, and then performs beam search on each distributed antenna device 30, where i=1 to N corresponding to the wide beam of each distributed antenna device 30. n The narrow beam is switched over time in the direction corresponding to the first reference signal, and the reference signal transmitted from the terminal device 40 is received.

[0091] As shown in the processing of step S304, when i=1, the narrow beam search execution instruction unit 12 causes each distributed antenna device 30 that is the target of beam search to form a narrow beam 1 in the direction corresponding to the i-th narrow beam among the narrow beams that each distributed antenna device 30 directs toward the terminal device 40, and causes the narrow beam 1 to receive a reference signal transmitted from the terminal device 40. For example, if the beam ID of the narrow beam corresponding to the wide beam of each distributed antenna device 30 that is the target of beam search is 1 to N, n When up to the specified wide beam are allocated, the narrow beam search execution instruction unit 12 selects the beam ID of the narrow beam corresponding to the identified wide beam for each distributed antenna device 30 that is the target of the beam search, and forms a narrow beam. This allows a narrow beam to be formed in a direction corresponding to the wide beam for each distributed antenna device 30 that is the target of the beam search. In this way, the narrow beam search execution instruction unit 12 causes all distributed antenna devices 30 that are the target of the beam search to receive a reference signal at the same timing. Then, the narrow beam search execution instruction unit 12 causes all distributed antenna devices 30 that are the target of the beam search to receive a reference signal by switching the direction in which the narrow beam is formed at the same timing.

[0092] When the processing of loop La2s to La2e is completed, the narrow beam search execution instruction unit 12 adds 1 to the counter k' to update the value of k' (step S306). If the updated value of k' is not greater than K', the narrow beam search execution instruction unit 12 performs the processing of steps S303 to S306 again (loop La1s to La1e). If the updated value of k' is greater than K', the narrow beam search execution instruction unit 12 ends the processing of loop La1s to La1e.

[0093] Fig. 8 is a flowchart showing the flow of processing performed by the terminal device 40 in the first embodiment. Note that the processing in Fig. 8 shows processing performed by the terminal device 40 in one beam search cycle. Therefore, the terminal device 40 executes the processing in Fig. 8 for each beam search cycle. The terminal device 40 performs wide beam search processing (step S401). The wide beam search processing performed by the terminal device 40 will be described later. The terminal device 40 performs narrow beam search processing (step S402). The narrow beam search processing performed by the terminal device 40 will be described later. The terminal device 40 transmits and receives data signals (step S403).

[0094] FIG. 9 is a flowchart showing the flow of wide beam search processing performed by the terminal device 40 in the first embodiment. When the wide beam search process is started, the terminal device 40 performs the process of loop Laa1s to Laa1e. The process of loop Laa1s to Laa1e is repeatedly executed until the time T3 seconds set in the timer has elapsed. The wide beam search beacon signal receiver 44 starts a timer (within the time T3 seconds) that waits for beacons from multiple distributed antenna devices 30.

[0095] After starting the timer, the wide beam search broadcast signal receiver 44 waits for and receives broadcast signals transmitted from the plurality of distributed antenna devices 30 (step S451). Upon receiving a broadcast signal, the wide beam search broadcast signal receiver 44 measures the reception quality (e.g., reception power) of the received broadcast signal. The wide beam search broadcast signal receiver 44 outputs information on the measured reception quality and information on the beam ID and antenna ID included in the broadcast signal to the feedback signal transmitter 45.

[0096] When the process of step S451 ends, if the time T3 set in the timer has not elapsed since the timer was started, the wide beam search report signal receiving unit 44 repeatedly executes the process of step S451 again (loop Laa1s to Laa1e).

[0097] If the time T3 set in the timer has elapsed when the process of step S451 ends, the wide beam search broadcast signal receiver 44 ends the loop Laa1s to Laa1e. Thereafter, the feedback signal transmitter 45 generates a feedback signal including the combination of the beam and antenna ID for which the maximum received power has been obtained, and information about the maximum received power, for each distributed antenna device 30. The feedback signal transmitter 45 transmits the generated feedback signal to each distributed antenna device 30 (step S452).

[0098] FIG. 10 is a flowchart showing the flow of narrow beam search processing performed by the terminal device 40 in the first embodiment. When the narrow beam search process is started, the terminal device 40 performs the process of loop Lb1s to Lb1e. The process of loop Lb1s to Lb1e is repeatedly executed until the time T4 seconds set in the timer has elapsed. The narrow beam search notification signal receiver 46 starts a timer (within the time T4 seconds) that waits for an instruction (notification signal) from the distributed antenna device 30 to transmit a reference signal for narrow beam search.

[0099] After starting the timer, the narrow beam search notification signal receiving unit 46 waits for and receives notification signals transmitted from the multiple distributed antenna devices 30 (step S501). When the narrow beam search notification signal receiving unit 46 receives a notification signal, it outputs the received notification signal to the narrow beam search execution instruction unit 48. If, at the time when the processing of step S501 is completed, the time T4 set in the timer has not elapsed since the timer was started, the narrow beam search notification signal receiving unit 46 repeatedly executes the processing of step S501 again (loop Lb1s to Lb1e).

[0100] If the time T4 set in the timer has elapsed when the process of step S501 is completed, the narrow beam search notification signal receiving unit 46 ends the loop Lb1s to Lb1e. Thereafter, the narrow beam search execution instruction unit 48 transmits a reference signal using the allocated time-frequency resource based on the time-frequency resource included in the notification signal (step S502).

[0101] In the wireless communication system 1 configured as described above, the communication control device 10 includes a narrow beam search execution instruction unit 12 that allocates resources required for transmitting reference signals to one or more terminal devices 40 during a beam search period in which a beam to be used for wireless communication with one or more terminal devices 40 is searched for, and causes each of the one or more terminal devices 40 to transmit a notification signal including information on the allocated time-frequency resources to the distributed antenna device 30; and a narrow beam search reference signal receiving unit 15 that receives reference signals transmitted from each of the one or more terminal devices 40 at the timing indicated in the notification signal transmitted to the distributed antenna device 30 by the narrow beam search execution instruction unit 12, the reference signals being received by all of the distributed antennas 31 provided in each of the multiple distributed antenna devices 30 while changing the narrow beam. In this way, the communication control device 10 controls all distributed antenna devices 30 to simultaneously perform a receive beam search. This makes it possible to suppress the beam search overhead that increases depending on the number of distributed antenna devices 30.

[0102] The communication control device 10 causes each of the multiple distributed antenna devices 30 performing a two-stage beam search to perform a wide beam search process in which a report signal is transmitted in all directions possible using a wide beam with a first beam width, and receives a feedback signal including the result of the wide beam search process. The communication control device 10 causes a report signal to be transmitted to the terminal device 40 that is the source of the feedback signal, and causes all of the distributed antennas 31 provided in each of the multiple distributed antenna devices 30 to receive reference signals transmitted from one or more terminal devices 40 while changing narrow beams with a second beam width narrower than the wide beam, and receives the reference signals received by all of the distributed antennas 31. In this way, the communication control device 10 roughly identifies the beam direction for the terminal device 40 through the first-stage wide beam search process and transmits a report signal to the terminal device 40. The communication control device 10 then receives a reference signal within the range of the identified wide beam while switching narrow beams over time. This makes it possible to limit the reception range of the reference signal. This makes it possible to suppress the overhead of the beam search.

[0103] (Second embodiment) In the first embodiment, it is assumed that the terminal device is in a stand-alone state, and in the two-stage beam search, a second-stage beam search (narrow beam search) after notification to the terminal device is completed is performed to have each terminal device transmit a reference signal, and a plurality of distributed antenna devices simultaneously perform a receiving beam search. In contrast, in the second embodiment, a configuration is described that assumes a state in which the terminal device is connected to another wireless communication system (non-stand-alone state). In the following description, the same components as in the first embodiment are assigned the same reference numerals as in the first embodiment, and description thereof is omitted.

[0104] A wireless communication system 1 in the second embodiment includes at least one cell 100. The wireless communication system 1 in the second embodiment includes a communication control device 10a, a digital signal processing device 20, and distributed antenna devices 30-1 to 30-4. Distributed antenna devices 30-1, 30-2, 30-3, and 30-4 and a terminal device 40a are arranged within the area of ​​the cell 100. As shown in FIG. 11, the communication control device 10a is connected to a base station device 55 in addition 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 10a, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4 constitute a so-called base station device.

[0105] Each of the distributed antenna devices 30-1 to 30-4 in the second embodiment is capable of beamforming, which forms a beam of radio waves by switching the direction, and connects to the terminal device 40a via radio waves. 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 determined in advance by the specifications of the distributed antenna devices 30-1 to 30-4, and the operator may be able to determine the number of beams as desired.

[0106] The base station device 55 is a base station (BS) of a wireless communication system using a different frequency. In accordance with an instruction from the communication control device 10a, the base station device 55 transmits a notification signal to the terminal device 40a connected to the wireless communication system of the base station device 55.

[0107] In the wireless communication system 1 according to the second embodiment, the terminal device 40a is connected to the terminal device 60 as shown in Fig. 12. The terminal device 60 is a terminal device (UE: User Equipment) of a wireless communication system using a different frequency. The terminal device 60 receives a notification signal transmitted from the base station device 55, and transmits the received notification signal to the terminal device 40a to which it is connected.

[0108] (Configuration of communication control device of second embodiment) 11 is a diagram illustrating an example of the configuration of a communication control device 10a according to the second embodiment. The communication control device 10a includes a data signal transmission / reception instruction unit 13, a receiving beam search execution instruction unit 16, and a receiving beam search reference signal receiving unit 17.

[0109] The data signal transmission and reception instruction unit 13 selects a distributed antenna device 30 to be used for transmitting and receiving a data signal based on the reception quality of a reference signal transmitted from the terminal device 40a. The data signal transmission and reception instruction unit 13 instructs the selected distributed antenna device 30 to transmit and receive a data signal to and from the terminal device 40a. At this time, the data signal transmission and reception instruction unit 13 sets the beam to be used by each distributed antenna device 30 to the beam identified by the beam search result, and causes the distributed antenna device 30 to transmit and receive a data signal.

[0110] The receiving beam search execution instruction unit 16 transmits a notification signal transmission instruction to the base station device 55 to cause the base station device 55 to transmit a notification signal to the terminal device 40a that is already connected to the base station device 55 of a wireless communication system using a different frequency. The notification signal transmission instruction in the second embodiment includes an instruction to transmit a notification signal to the connected terminal device 40a, an instruction to request transmission of a reference signal, and information on time-frequency resources. In this way, in the second embodiment, information on time-frequency resources is notified to the terminal device 40a that is already connected to a wireless communication system using a different frequency via the base station device 55 of the wireless communication system using a different frequency. The receiving beam search execution instruction unit 16 is one aspect of a notification signal transmission unit.

[0111] When allocating time-frequency resources to each terminal device 40a, the receiving beam search execution instruction unit 16 may allocate the time-frequency resources so that radio information is included in the reference signal to be transmitted by each of the one or more terminal devices 40a and the reference signal is demodulated by the communication control device 10a to obtain the radio information of the one or more terminal devices 40a, or may allocate the time-frequency resources so that radio information is not included in the reference signal to be transmitted by each of the one or more terminal devices 40a and the reference signal is not demodulated by the communication control device 10a and only the received power is measured.

[0112] Furthermore, the receive beam search execution instruction unit 16 causes each of the distributed antenna devices 30-1 to 30-4 to perform a receive beam search by switching time in a plurality of specific directions via the digital signal processing device 20. The receive beam search execution instruction unit 16 instructs the distributed antenna devices 30 to simultaneously switch and receive candidate narrow beams for each of the distributed antenna devices 30 at the timing of the time-frequency resources that have been allocated and notified to each terminal device 40a in advance.

[0113] The reference signal receiver 17 for receiving beam search simultaneously switches between candidate beams for each distributed antenna device 30 at the timing of time-frequency resources that have been allocated and notified to each terminal device 40a in advance, and receives a reference signal transmitted from the terminal device 40a. Of the reception qualities for each reception beam in each distributed antenna device 30, the beam with the highest reception quality becomes the best beam for each distributed antenna device 30 for each terminal device 40a. The reference signal receiver 17 for receiving beam search outputs the beam search result to the data signal transmission / reception instruction unit 13. The reference signal receiver 17 for receiving beam search is one aspect of a reference signal receiver.

[0114] (Configuration of terminal device of second embodiment) 12 is a diagram showing an example of the configuration of a terminal device 40a in the second embodiment. The terminal device 40a includes P terminal antennas 41-1 to 41-P, an analog signal transmitting / receiving unit 42, a digital signal processing unit 43, a data signal transmitting / receiving unit 47, a reception beam search notification signal receiving unit 49, and a reception beam search execution instruction unit 50. Wireless communication using distributed MIMO is performed between the terminal antennas 41-1 to 41-P and the distributed antennas 31-1 to 31-4 included in the distributed antenna devices 30-1 to 30-4, respectively. Note that the analog signal transmitting / receiving unit 42, the digital signal processing unit 43, and the data signal transmitting / receiving unit 47 perform the same processing as the functional units with the same names in the first embodiment, and therefore description thereof will be omitted.

[0115] The receiving beam search notification signal receiving unit 49 receives a notification signal transmitted from the terminal device 60. The receiving beam search notification signal receiving unit 49 converts the received notification signal into a digital signal and outputs it to the receiving beam search execution instruction unit 50.

[0116] The receiving beam search execution instruction unit 50 generates a reference signal based on the digital signal of the notification signal output from the receiving beam search notification signal receiver 49. Specifically, the receiving beam search execution instruction unit 50 generates a reference signal based on the time-frequency resource allocated by the digital signal of the notification signal. The receiving beam search execution instruction unit 50 causes the terminal antennas 41-1 to 41-P to transmit the reference signal at the time specified by the allocated time-frequency resource.

[0117] 13 is a sequence diagram showing the flow of processing in the wireless communication system 1 in the second embodiment. In FIG. 13, the description will be given assuming that there are M distributed antenna devices 30 and K terminal devices 40a. Here, it is assumed that the K terminal devices 40a are connected to the base station device 55. The receiving beam search execution instruction unit 16 of the communication control device 10a transmits a notification signal transmission instruction to the base station device 55 to cause the base station device 55 to transmit a notification signal to the terminal devices 40a-1 to 40a-K that are already connected to the base station device 55. The base station device 55 receives the notification signal transmission instruction transmitted from the communication control device 10a. In accordance with the received notification signal transmission instruction, the base station device 55 transmits a notification signal to the connected terminal devices 40a-1 to 40a-K via the terminal device 60 (steps S601 to S603).

[0118] Each of the terminal devices 40a-1 to 40a-K receives the notification signal. Based on the time-frequency resource included in the notification signal, each of the terminal devices 40a-1 to 40a-K transmits a reference signal on a beam from each of the terminal antennas 41-1 to 41-P (steps S604 to S606). Here, the number of beams switched by the distributed antenna device 30 to receive the reference signal transmitted by the terminal device 40a is N.

[0119] Fig. 14 is a flowchart showing the flow of processing performed by the communication control device 10a in the second embodiment. Note that the processing in Fig. 14 shows processing performed by the communication control device 10a in one beam search cycle. Therefore, the communication control device 10a executes the processing in Fig. 14 for each beam search cycle. The communication control device 10a performs a receiving beam search process (step S701). The receiving beam search process performed by the communication control device 10a will be described in detail later. The data signal transmission / reception instruction unit 13 of the communication control device 10a selects a distributed antenna device 30 to be used for transmitting and receiving data signals based on the reception quality of the reference signal transmitted from each terminal device 40a (step S702). The data signal transmission / reception instruction unit 13 sets the beam to be used by each distributed antenna device 30 to the beam resulting from the receiving beam search, and transmits and receives data signals (step S703).

[0120] FIG. 15 is a flowchart showing the flow of the receiving beam search process performed by the communication control device 10a in the second embodiment. The receiving beam search execution instruction unit 16 of the communication control device 10a causes a notification signal to be transmitted to each terminal device 40a that can be connected to the distributed antenna system 1 through a base station device 55 of a wireless communication system using a different frequency (step S801). Specifically, the receiving beam search execution instruction unit 16 causes a notification signal to be transmitted to each terminal device 40a that can be connected to the distributed antenna system 1 through a base station device 55 of a wireless communication system using a different frequency by transmitting a notification signal transmission instruction to the base station device 55. The base station device 55 transmits a notification signal to each connected terminal device 40a in accordance with the instruction from the communication control device 10a.

[0121] The reference signal receiver 17 for receiving beam search provides a counter k in an internal storage area and initializes it to k=1 (step S802). Here, k is an integer value between 1 and K1'. In FIG. 15, K1' may be the total number of terminal devices connected to a wireless communication system using a different frequency, or may be the number of terminal devices narrowed down to those that require a receiving beam search, or may be the number of terminal devices narrowed down to those present in the vicinity of the distributed antenna device 30 if location information is available. In the following description, K1'=3 is used. The following description will be given assuming that the k-th terminal device 40a is terminal device 40a-k. After processing step S802, the communication control device 10a performs processing of loops Lc1s to Lc1e. The processing of loops Lc1s to Lc1e is repeatedly executed until the value of k becomes greater than K1'.

[0122] The receiving beam search execution instruction unit 16 provides a counter i in an internal storage area and initializes it to i=1 (step S803). Here, in FIG. 15, i is an integer value ranging from 1 to N. N is the maximum number of beams that each terminal device 40a can transmit. The value of N may be different for each terminal device 40a, but the following description will be given assuming that the value of N is the same for all terminal devices 40a.

[0123] After processing step S803, the communication control device 10a performs processing of loops Lc2s to Lc2e. The processing of loops Lc2s to Lc2e is repeatedly executed until the value of i becomes greater than N. The reception beam search execution command unit 16 causes the distributed antenna devices 30 that are connectable to the terminal devices 40a-k and that perform the beam search to receive the reference signal using the i-th beam. For example, if there are four distributed antenna devices 30 that perform the beam search, the reception beam search execution command unit 16 commands the four distributed antenna devices 30 to receive the reference signal using the i-th beam. It is assumed that the beam searched by each of the four distributed antenna devices 30 will be in a different direction for each distributed antenna device 30.

[0124] The reference signal receiver 17 for receiving beam search receives the reference signal received by the distributed antenna device 30 that is the target of the beam search (step S804). The reference signal receiver 17 for receiving beam search holds the received reference signal for each distributed antenna device 30. After that, the receiving beam search execution instruction unit 16 adds 1 to the counter i to update the value of i (step S805).

[0125] If the updated value of i is not greater than N, the reception beam search execution instruction unit 16 performs the processing of steps S804 to S805 again (loop Lc2s to Lc2e). If the updated value of i is greater than N, the reception beam search execution instruction unit 16 ends the processing of loop Lc2s to Lc2e. In this way, in the processing of loop Lc2s to Lc2e, the communication control device 10a performs the processing of loop Lc2s to Lc2e for each distributed antenna device 30 that is connectable to the terminal devices 40a-k and is a beam search target, by using i=1 to N corresponding to the beam for each distributed antenna device 30 that is a beam search target. n The beam is switched over time in the direction corresponding to the th direction to receive the reference signal transmitted from the terminal device 40a.

[0126] As shown in the processing of step S804, when i=1, the reception beam search execution instructing unit 16 causes each distributed antenna device 30 that is connectable to the terminal devices 40a-k and is the target of beam search to form beam 1 in a direction corresponding to the ith beam among the beams directed toward the terminal device 40a for each distributed antenna device 30, and causes the reference signal transmitted from the terminal device 40a to be received. Then, the reception beam search execution instructing unit 16 causes all distributed antenna devices 30 that are performing beam search to receive the reference signal by switching the direction in which the beam is formed at the same timing.

[0127] When the processing of loop Lc2s to Lc2e ends, the receive beam search execution instruction unit 16 adds 1 to counter k to update the value of k (step S806). If the updated value of k is not greater than K, the receive beam search execution instruction unit 16 performs the processing of steps S803 to S806 again (loop Lc1s to Lc1e). If the updated value of k is greater than K1', the receive beam search execution instruction unit 16 ends the processing of loop Lc1s to Lc1e.

[0128] Fig. 16 is a flowchart showing the flow of processing performed by the terminal device 40a in the second embodiment. Note that the processing in Fig. 16 shows processing performed by the terminal device 40a in one beam search cycle. Therefore, the terminal device 40a executes the processing in Fig. 16 for each beam search cycle. The terminal device 40a performs a receiving beam search process (step S901). The receiving beam search process performed by the terminal device 40a will be described in detail later. The terminal device 40a transmits and receives a data signal (step S902).

[0129] FIG. 17 is a flowchart showing the flow of the receiving beam search process performed by the terminal device 40a in the second embodiment. When the reception beam search process is started, the terminal device 40a performs the processes of loops Ld1s to Ld1e. The processes of loops Ld1s to Ld1e are repeatedly executed until the time T5 seconds set in the timer has elapsed. The reception beam search notification signal receiver 49 starts a timer (within the time T5 seconds) that waits for an instruction (notification signal) to transmit a reference signal for the reception beam search of the distributed antenna device 30 from the base station device 55 of the wireless communication system using a different frequency.

[0130] After starting the timer, the notification signal receiver 49 for receiving beam search waits for and receives a notification signal transmitted from the communication control device 10a (step S1001). When the notification signal receiver 49 for receiving beam search receives a notification signal, it outputs the received notification signal to the reception beam search execution instruction unit 50. If the time T5 set in the timer has not elapsed since the timer was started when the processing of step S1001 is completed, the notification signal receiver 49 for receiving beam search repeatedly executes the processing of step S1001 again (loop Ld1s to Ld1e).

[0131] If the time T5 set in the timer has elapsed when the process of step S1001 is completed, the receiving beam search notification signal receiver 49 ends the loop Ld1s to Ld1e. After that, the receiving beam search execution command unit 50 transmits a reference signal using the allocated time-frequency resource based on the time-frequency resource included in the notification signal (step S1002).

[0132] The wireless communication system 1 of the second embodiment configured as described above can achieve the same effects as those of the first embodiment. Specifically, in the wireless communication system 1 of the second embodiment, when the terminal device 40a is in a non-standalone mode and a wireless connection has already been established with another wireless communication system at a different frequency, a notification signal is transmitted to the terminal device 40a via the base station device 55 of the other wireless communication system. This makes it possible to transmit a notification signal to at least the terminal device 40a that has a wireless connection established with the other wireless communication system.

[0133] (Third embodiment) In the third embodiment, in a wireless communication system in which an initial connection can be initiated from a terminal device without waiting for a notification signal from the network side, a configuration will be described in which the terminal device requests permission to transmit a reference signal for a distributed antenna receiving beam search and performs a receiving beam search. Note that in the following description, the same components as in the first embodiment will be assigned the same reference numerals as in the first embodiment, and their description will be omitted.

[0134] A wireless communication system 1 in the third embodiment includes at least one cell 100. The wireless communication system 1 in the third embodiment includes a communication control device 10b, a digital signal processing device 20, and distributed antenna devices 30-1 to 30-4. Distributed antenna devices 30-1, 30-2, 30-3, and 30-4 and a terminal device 40b are located within the area of ​​the cell 100. The communication control device 10b 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 10b, the digital signal processing device 20, and the distributed antenna devices 30-1 to 30-4 constitute a so-called base station device.

[0135] (Configuration of communication control device of third embodiment) 18 is a diagram showing an example of the configuration of a communication control device 10b in the third embodiment. The communication control device 10b includes a data signal transmission / reception instruction unit 13, a receiving beam search execution instruction unit 16, a receiving beam search reference signal receiving unit 17, and a connection request signal receiving unit 18.

[0136] The data signal transmission and reception instruction unit 13 selects a distributed antenna device 30 to be used for transmitting and receiving a data signal based on the reception quality of a reference signal transmitted from the terminal device 40b. The data signal transmission and reception instruction unit 13 instructs the selected distributed antenna device 30 to transmit and receive a data signal to and from the terminal device 40b. At this time, the data signal transmission and reception instruction unit 13 sets the beam to be used by each distributed antenna device 30 to the beam identified by the beam search result, and causes the distributed antenna device 30 to transmit and receive a data signal.

[0137] The receiving beam search execution instruction unit 16 determines the distributed antenna device 30 that is to transmit the notification signal based on a combination of the connection request signal received by the connection request signal receiving unit 18 and the reception quality. For example, the receiving beam search execution instruction unit 16 may determine the distributed antenna device 30 with the highest reception quality of the connection request signal as the distributed antenna device 30 that is to transmit the notification signal. The receiving beam search execution instruction unit 16 outputs a notification signal transmission instruction to the determined distributed antenna device 30 to transmit the notification signal. The notification signal transmission instruction in the third embodiment includes an instruction to transmit the notification signal, information for identifying the distributed antenna device 30, and beam ID information. In this way, in the third embodiment, information on the time-frequency resource is notified to the terminal device 40b that is the source of the connection request signal.

[0138] Furthermore, the receive beam search execution instruction unit 16 causes each of the distributed antenna devices 30-1 to 30-4 to perform a receive beam search by switching time in a plurality of specific directions via the digital signal processing device 20. The receive beam search execution instruction unit 16 instructs the distributed antenna devices 30 to simultaneously switch and receive candidate narrow beams for each of the distributed antenna devices 30 at the timing of the time-frequency resources that have been allocated and notified to each terminal device 40b in advance.

[0139] The reference signal receiver 17 for receiving beam search simultaneously switches between candidate beams for each distributed antenna device 30 at the timing of the time-frequency resources previously allocated and notified for each terminal device 40b, and receives the reference signal transmitted from the terminal device 40b. Of the reception qualities for each reception beam in each distributed antenna device 30, the beam with the highest reception quality becomes the best beam for each distributed antenna device 30 for each terminal device 40b. The reference signal receiver 17 for receiving beam search outputs the beam search result to the data signal transmission / reception instruction unit 13.

[0140] The connection request signal receiving unit 18 receives a connection request signal transmitted from the terminal device 40b. The connection request signal receiving unit 18 outputs the received connection request signal to the reception beam search execution instructing unit 16.

[0141] (Configuration of terminal device of third embodiment) 19 is a diagram showing an example of the configuration of a terminal device 40b in the third embodiment. The terminal device 40b includes P terminal antennas 41-1 to 41-P, an analog signal transmitting / receiving unit 42, a digital signal processing unit 43, a data signal transmitting / receiving unit 47, a reception beam search notification signal receiving unit 49, a reception beam search execution instruction unit 50, and a connection request signal transmission instruction unit 51. Wireless communication using distributed MIMO is performed between the terminal antennas 41-1 to 41-P and distributed antennas 31-1 to 31-4 included in each of the distributed antenna devices 30-1 to 30-4.

[0142] Analog signal transmitting / receiving unit 42 generates a radio frequency analog signal by modulating a carrier wave based on the digital signal of the transmission data output by digital signal processing unit 43. Analog signal transmitting / receiving unit 42 transmits the generated analog signal by radio waves through terminal antennas 41-1 to 41-P. Analog signal transmitting / receiving unit 42 demodulates the analog signals that terminal antennas 41-1 to 41-P receive and output by radio waves and converts them into digital signals. Analog signal transmitting / receiving unit 42 outputs the converted digital signals to digital signal processing unit 43.

[0143] The digital signal processing unit 43 outputs the digital signal of the data signal output by the data signal transmitting / receiving unit 47 to the analog signal transmitting / receiving unit 42. Furthermore, the digital signal processing unit 43 outputs the digital signal of the reference signal output by the receiving beam search execution instruction unit 50 to the analog signal transmitting / receiving unit 42. Furthermore, the digital signal processing unit 43 outputs the digital signal of the connection request signal output by the connection request signal transmission instruction unit 51 to the analog signal transmitting / receiving unit 42.

[0144] The digital signal processing unit 43 receives the digital signal output from the analog signal transmitting / receiving unit 42. If the received digital signal is a notification signal, the digital signal processing unit 43 outputs the notification signal to the receiving beam search notification signal receiving unit 49. Furthermore, if the received digital signal is a data signal, the digital signal processing unit 43 outputs the data signal to the data signal transmitting / receiving unit 47.

[0145] The notification signal receiver 49 for receiving beam search receives the digital signal of the notification signal output from the digital signal processor 43. The notification signal receiver 49 for receiving beam search outputs the received digital signal of the notification signal to the reception beam search execution instruction unit 50.

[0146] The receiving beam search execution instruction unit 50 generates a reference signal based on the digital signal of the notification signal output from the receiving beam search notification signal receiver 49. Specifically, the receiving beam search execution instruction unit 50 generates a reference signal based on the time-frequency resource allocated by the digital signal of the notification signal. The receiving beam search execution instruction unit 50 causes the terminal antennas 41-1 to 41-P to transmit the reference signal at the time specified by the allocated time-frequency resource.

[0147] The connection request signal transmission instruction unit 51 generates a connection request signal for requesting a connection, and outputs the generated connection request signal to the digital signal processing unit 43.

[0148] Fig. 20 is a sequence diagram showing the flow of processing in the wireless communication system 1 in the third embodiment. Note that in Fig. 20, the explanation will be given assuming that there are M distributed antenna devices 30 and K terminal devices 40b. Each of the terminal devices 40b-1 to 40b-K transmits a connection request signal to each of the distributed antenna devices 30-1 to 30-M (steps S1101 to S1103). Each of the distributed antenna devices 30-1 to 30-M receives the connection request signal transmitted from each of the terminal devices 40b-1 to 40b-K. Each of the distributed antenna devices 30-1 to 30-M outputs the received connection request signal to the communication control device 10b via the digital signal processing device 20.

[0149] The communication control device 10b determines the distributed antenna device 30 to which a notification signal is to be transmitted, based on the connection request signals obtained from each of the distributed antenna devices 30-1 to 30-M. The communication control device 10b causes the determined distributed antenna device 30 to transmit a notification signal to the terminal devices 40b-1 to 40b-K that are the senders of the connection request signals. Here, it is assumed that the distributed antenna device 30-1 is determined as the distributed antenna device 30 to which the notification signal is to be transmitted. In accordance with an instruction from the communication control device 10b, the distributed antenna device 30-1 transmits a notification signal to the terminal devices 40b-1 to 40b-K that are the senders of the connection request signals (steps S1104 to S1106).

[0150] Each of the terminal devices 40b-1 to 40b-K receives the notification signal transmitted from the distributed antenna device 30-1. Each of the terminal devices 40b-1 to 40b-K receives the resource allocation notification. Each of the terminal devices 40b-1 to 40b-K transmits a reference signal on a beam from each of the terminal antennas 41-1 to 41-P based on the time-frequency resource included in the notification signal (steps S1107 to S1109). Here, the number of beams switched by the distributed antenna device 30 to receive the reference signal transmitted by the terminal device 40b is N.

[0151] Fig. 21 is a flowchart showing the flow of processing performed by the communication control device 10b in the third embodiment. Note that the processing in Fig. 21 shows processing performed by the communication control device 10b in one beam search cycle. Therefore, the communication control device 10b executes the processing in Fig. 21 for each beam search cycle. The communication control device 10b performs a receiving beam search process (step S1201). The receiving beam search process performed by the communication control device 10b will be described in detail later. The data signal transmission and reception instruction unit 13 selects a distributed antenna device 30 to be used for transmitting and receiving data signals based on the reception quality of the reference signal transmitted from each terminal device 40b (step S1202). The data signal transmission and reception instruction unit 13 sets the beam to be used by each distributed antenna device 30 to the beam resulting from the receiving beam search, and transmits and receives data signals (step S1203).

[0152] FIG. 22 is a flowchart showing the flow of the receiving beam search process performed by the communication control device 10b in the third embodiment. When the receiving beam search process is started, the communication control device 10b performs the process of the loop Le1s to Le1e. The process of the loop Le1s to Le1e is repeatedly executed until the time T6 seconds set in the timer has elapsed. The connection request signal receiving unit 18 starts a timer (within the time T6 seconds) that waits for a connection request signal from the terminal device 40b.

[0153] After starting the timer, the connection request signal receiving unit 18 waits for and receives a connection request signal transmitted from the terminal device 40b (step S1301). When the connection request signal receiving unit 18 receives the connection request signal, it outputs the received connection request signal to the reception beam search execution instructing unit 16. When the processing of step S1301 ends, if the time T6 set in the timer has not elapsed since the timer was started, the connection request signal receiving unit 18 repeatedly executes the processing of step S1301 again (loop Le1s to Le1e).

[0154] If the time T6 set in the timer has elapsed since the timer was started at the time the processing of step S1301 is completed, the connection request signal receiving unit 18 ends the loop Le1s to Le1e. Based on the connection request signal output from the connection request signal receiving unit 18, the receiving beam search execution instructing unit 16 identifies the terminal device 40b that has been able to receive the connection request signal.

[0155] The receiving beam search execution instruction unit 16 identifies the distributed antenna device 30 with the highest reception quality based on information on the reception quality (e.g., maximum reception power) of the connection request signal received from each of the identified terminal devices 40b. The receiving beam search execution instruction unit 16 causes the identified distributed antenna devices 30 to sequentially transmit a notification signal including an instruction to transmit a reference signal for the amount of resources required for the receiving beam search (step S1302).

[0156] For example, if the identified distributed antenna device 30 is the distributed antenna device 30-1, the communication control device 10b outputs to the distributed antenna device 30-1 an instruction to transmit a notification signal and information on the terminal devices 40b that have received the connection request signal. As a result, the distributed antenna device 30-1 transmits the notification signal instructed by the communication control device 10b to each of the terminal devices 40b that have received the connection request signal in turn.

[0157] The receiving beam search reference signal receiving unit 17 provides a counter k in an internal storage area and initializes it to k=1 (step S1303). Here, k is an integer value between 1 and K2'. In FIG. 22, K2' represents the number of terminal devices 40b that have received a connection request. In the following description, K2'=3 is used. After the processing of step S1303, the communication control device 10b performs processing of loop Le2s to Le2e. The processing of loop Le2s to Le2e is repeatedly executed until the value of k becomes greater than K2'.

[0158] The receiving beam search execution instruction unit 16 provides a counter i in an internal storage area and initializes it to i=1 (step S1304). Here, in FIG. 22, i is an integer value from 1 to N. N is the maximum number of beams that the terminal device 40b can transmit. The value of N may be different for each terminal device 40b, but the following description will be given assuming that the value of N is the same for all terminal devices 40b.

[0159] After the process of step S1304, the communication control device 10b performs the processes of loops Le3s to Le3e. The processes of loops Le3s to Le3e are repeatedly executed until the value of i becomes greater than N. The receiving beam search execution command unit 16 causes the distributed antenna devices 30 that have received the connection request signal and are performing the beam search to receive the reference signal using the i-th beam. For example, if there are four distributed antenna devices 30 performing the beam search, the receiving beam search command unit 16 commands the four distributed antenna devices 30 to receive the reference signal using the i-th beam. In other words, the communication control device 10b does not cause the distributed antenna devices 30 that have not received the connection request signal to receive the reference signal. Note that the receiving beam search execution command unit 16 may cause the distributed antenna devices 30 that are geographically close (within a radius of X m or less) to receive the reference signal from the terminal device 40b that is the source of the connection request signal.

[0160] The reference signal receiver for receiving beam search 17 receives the reference signal received by the distributed antenna device 30 performing the beam search (step S1305). The reference signal receiver for receiving beam search 17 stores the received reference signal for each distributed antenna device 30. After that, the receiving beam search execution instruction unit 16 adds 1 to the counter i to update the value of i (step S1306).

[0161] If the updated value of i is not greater than N, the receiving beam search execution command unit 16 performs the processing of steps S1305 to S1306 again (loop Le3s to Le3e). If the updated value of i is greater than N, the receiving beam search execution command unit 16 ends the processing of loop Le3s to Le3e. In this way, in the processing of loop Le3s to Le3e, the communication control device 10b, for each of all distributed antenna devices 30 that have received a connection request signal, searches for i=1 to N corresponding to the beam for each distributed antenna device 30 that has received a connection request signal. n The beam is switched over time in the direction corresponding to the th direction to receive the reference signal transmitted from the terminal device 40b.

[0162] As shown in the processing of step S1305, when i=1, the communication control device 10b causes all distributed antenna devices 30 that have received the connection request signal to form beam 1 in a direction corresponding to the ith beam among the beams directed toward the terminal device 40b for each distributed antenna device 30, and causes the distributed antenna devices 30 to receive the reference signal transmitted from the terminal device 40b. Then, the communication control device 10b causes all distributed antenna devices 30 that have received the connection request signal to receive the reference signal by switching the direction in which the beam is formed at the same timing.

[0163] When the processing of loop Le3s to Le3e is completed, the receive beam search execution instruction unit 16 adds 1 to counter k to update the value of k (step S1307). If the updated value of k is not greater than K, the receive beam search execution instruction unit 16 performs the processing of steps S1304 to S1307 again (loop Le2s to Le2e). If the updated value of k is greater than K2', the receive beam search execution instruction unit 16 ends the processing of loop Le2s to Le2e.

[0164] Fig. 23 is a flowchart showing the flow of processing performed by the terminal device 40b in the third embodiment. Note that the processing in Fig. 23 shows processing performed by the terminal device 40b in one beam search cycle. Therefore, the terminal device 40b executes the processing in Fig. 23 for each beam search cycle. The terminal device 40b performs a receiving beam search process (step S1401). The receiving beam search process performed by the terminal device 40b will be described in detail later. The terminal device 40b transmits and receives a data signal (step S1402).

[0165] FIG. 24 is a flowchart showing the flow of the receiving beam search process performed by the terminal device 40b in the third embodiment. The terminal device 40b transmits a connection request signal to the distributed antenna device 30 (step S1501). Thereafter, the terminal device 40b performs processing of loop Lf1s to Lf1e. The processing of loop Lf1s to Lf1e is repeatedly executed until the time T7 seconds set in the timer has elapsed. The notification signal receiver 49 for reception beam search starts a timer (within the time T7 seconds) that waits for an instruction (notification signal) to transmit a reference signal for reception beam search of the distributed antenna device 30.

[0166] After starting the timer, the notification signal receiver 49 for receiving beam search waits for and receives a notification signal transmitted from the communication control device 10b (step S1502). When the notification signal receiver 49 for receiving beam search receives a notification signal, it outputs the received notification signal to the reception beam search execution instruction unit 50. If the time T7 set in the timer has not elapsed since the timer was started when the processing of step S1502 is completed, the notification signal receiver 49 for receiving beam search repeatedly executes the processing of step S1502 again (loop Lf1s to Lf1e).

[0167] If the time T7 set in the timer has elapsed when the process of step S1502 is completed, the receiving beam search notification signal receiver 49 ends the loop Lf1s to Lf1e. Thereafter, the receiving beam search execution command unit 50 transmits a reference signal using the allocated time-frequency resource based on the time-frequency resource included in the notification signal (step S1503).

[0168] The wireless communication system 1 of the third embodiment configured as described above can achieve the same effects as those of the first embodiment. Specifically, the wireless communication system 1 of the third embodiment transmits a notification signal to the terminal device 40b that is the source of the connection request signal. This makes it possible to transmit the notification signal at least to the terminal device 40b that is the source of the connection request signal.

[0169] (Modification 1 common to the first to third embodiments) If communication has already been established, the distributed antenna device 30 may be configured to transmit information using another frequency with which communication has already been established, without transmitting a notification signal from the distributed antenna device 30, a connection request signal from the terminal device 40, or a feedback signal from the terminal device 40.

[0170] (Modification 2 common to the first to third embodiments) In the receiving beam search processing, the loop processing performed by the distributed antenna device 30 and the loop processing performed by the terminal device 40 may be reversed, and feedback from the terminal device 40 may be given without waiting for a search of all terminal devices 40.

[0171] The communication control devices 10, 10a, and 10b in the first to third embodiments described above may be implemented by a computer. In this case, a program for implementing this function may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read into a computer system and executed to implement the function. Note that the term "computer system" here includes hardware such as an OS and peripheral devices. Furthermore, the term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into a computer system.

[0172] Furthermore, the term "computer-readable recording medium" may include a medium that dynamically stores a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, or a medium that stores a program for a fixed period of time, such as a volatile memory within a computer system that serves as a server or client in such a case. The program may also be one that realizes part of the above-mentioned functions, or may be one that can realize the above-mentioned functions in combination with a program already stored in the computer system, or may be one that is realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0173] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Industrial Applicability]

[0174] The present invention is applicable to wireless communication systems equipped with distributed antennas. [Explanation of symbols]

[0175] 1...wireless communication system, 10, 10a, 10b...communication control device, 11...wide beam search execution instruction unit, 12...narrow beam search execution instruction unit, 13...data signal transmission / reception instruction unit, 14...feedback signal receiving unit, 15...narrow beam search reference signal receiving unit, 16...receiving beam search execution instruction unit, 17...receiving beam search reference signal receiving unit, 18...connection request signal receiving unit, 20...digital signal processing device, 30, 30-1 to 30-4...distributed antenna device, 31, 31-1 to 31-4...distributed antenna, 32, 32-1 to 32-4...main unit, 40, 40a, 40b...terminal device, 41, 41-1 to 41-P...terminal antenna, 42...analog signal transmitting / receiving unit, 43...digital signal processing unit, 44...wide beam search notification signal receiving unit 45...feedback signal transmitter, 46...narrow beam search notification signal receiver, 47...data signal transmitter / receiver, 48...narrow beam search execution instruction unit, 49...receiving beam search notification signal receiver, 50...receiving beam search execution instruction unit, 51...connection request signal transmission instruction unit, 55...base station device, 60...terminal device

Claims

1. A wireless communication system including one or more terminal devices, a plurality of distributed antenna devices each including one distributed antenna, and a communication control device, The communication control device a notification signal transmission unit that allocates resources required for transmitting a reference signal to the one or more terminal devices during a beam search period in which a beam to be used for wireless communication with the one or more terminal devices is searched for, and notifies each of the one or more terminal devices of information on the resources; a reference signal receiving unit that receives the reference signal transmitted from each of the one or more terminal devices at a timing indicated by the resource information notified by the notification signal transmitting unit, the reference signal being received by all distributed antennas included in each of the plurality of distributed antenna devices while changing a reception beam; A wireless communication system comprising:

2. The communication control device a beacon signal transmitter that causes each of the plurality of distributed antenna devices to perform a wide beam search process for transmitting a beacon signal in all directions that can be transmitted by a wide beam having a first beam width; a feedback signal receiving unit that receives a feedback signal including a result of the wide beam search process from each of the one or more terminal devices; Furthermore, the notification signal transmission unit transmits information about the resource to a terminal device that is a transmission source of the feedback signal, and further receives the reference signal transmitted from each of the one or more terminal devices by all of the distributed antennas provided in each of the plurality of distributed antenna devices while changing a narrow beam having a second beam width that is narrower than the wide beam as the reception beam; the reference signal receiving unit receives the reference signals received by all of the distributed antennas.

10. The wireless communication system of claim 1.

3. The notification signal transmission unit allocate time-frequency resources to the one or more terminal devices so that radio information can be included in the reference signal to be transmitted by each of the one or more terminal devices, demodulate the signal by the communication control device, and acquire the radio information of the one or more terminal devices, and notify the one or more terminal devices; or allocate time-frequency resources to the one or more terminal devices so that radio information is not included in the reference signal to be transmitted by each of the one or more terminal devices, but the communication control device can measure only the received power without demodulating the signal, and notify the one or more terminal devices.

3. The wireless communication system according to claim 1 or 2.

4. The notification signal transmission unit notifying the one or more terminal devices already connected in a wireless communication system of a different frequency of information about the resources via the wireless communication system of the different frequency; 10. The wireless communication system of claim 1.

5. The communication control device a connection request signal receiving unit that receives a connection request signal from the one or more terminal devices; Furthermore, The notification signal transmission unit notifying the one or more terminal devices that are the senders of the connection request signal of information about the resources; 10. The wireless communication system of claim 1.

6. a notification signal transmitting unit that allocates resources required for transmitting a reference signal to one or more terminal devices during a beam search period in which a beam to be used for wireless communication with one or more terminal devices is searched for, and notifies each of the one or more terminal devices of information on the resources; a reference signal receiving unit that receives the reference signal transmitted from each of the one or more terminal devices at a timing indicated by the resource information notified by the notification signal transmitting unit, the reference signal being received by all distributed antennas included in each of a plurality of distributed antenna devices while changing a reception beam; A communication control device comprising:

7. In a beam search period for searching for a beam to be used for wireless communication with one or more terminal devices, resources necessary for transmitting a reference signal to the one or more terminal devices are allocated, and information on the resources is notified to each of the one or more terminal devices; A signal control method for receiving the reference signal transmitted from each of the one or more terminal devices at a timing indicated by the notified resource information, the reference signal being received by all distributed antennas provided in each of a plurality of distributed antenna devices while changing the receiving beam.

8. On the computer, a notification signal transmission step of allocating resources required for transmitting a reference signal to one or more terminal devices during a beam search period in which a beam to be used for wireless communication with one or more terminal devices is searched for, and notifying each of the one or more terminal devices of information on the resources; a reference signal receiving step of receiving the reference signal transmitted from each of the one or more terminal devices at a timing indicated by the resource information notified in the notification signal transmitting step, the reference signal being received by all distributed antennas included in each of a plurality of distributed antenna devices while changing a reception beam; A program to execute.

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