Base station device and terminal device

Abstract

This base station device is provided with: a first beam search instruction unit that instructs execution of first beam search processing in which a beam identification signal containing an identical beam identifier is simultaneously transmitted from a plurality of antennas to a wireless station, for each beam identifier, using a transmission beam linked to the relevant beam identifier; a second beam search instruction unit that instructs execution of second beam search processing in which, on the basis of a report signal that includes selected beam identifiers indicating a plurality of beam identifiers selected on the basis of the quality of reception by the wireless station of the beam identification signals for each beam identifier, obtained through the first beam search processing, a beam identification signal that includes the selected beam identifiers is individually transmitted, for each selected beam identifier, at least from among the plurality of the antennas; and a transmission / reception unit that, on the basis of results of the first beam search processing and results of the second beam search processing, determines a combination of an antenna and a transmission beam to be used for wireless communication with the wireless station.　

Description

Base station device and terminal device

[0001] The present invention relates to a base station device and a terminal device.

[0002] (Beamforming in high frequency bands) There is a beamforming technology that forms a beam that concentrates power in a specific direction. In particular, 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, it is necessary to use beamforming technology that forms a beam that concentrates power in a specific direction to compensate for the free space propagation loss.

[0003] In the case of point-to-point (PP) type communications, where the combination of wireless stations communicating with each other is always fixed, and where the relative positions of the wireless stations and the propagation environment around the wireless stations do not change, beamforming can be used in a fixed manner, with beams formed in advance in a specific direction when the wireless stations are installed, etc. However, in the case of point-to-multipoint (P-MP) type communications, which accommodates multiple wireless stations, or in cases where at least one of the wireless stations moves, or in cases where at least one of the wireless stations communicating with each other moves, the appropriate direction of the beam changes, and therefore it is not possible to use a fixed beam formed in a specific direction.

[0004] In such cases, it is necessary to adaptively change the beam formation direction in accordance with the relative positions of the two wireless stations and changes in the propagation environment around the two wireless stations. Beamforming that adaptively controls the beam formation direction in this way is called adaptive beamforming. Generally, adaptive beamforming does not require a mechanical driver to change the beam formation direction. Adaptive beamforming forms a directional beam by adjusting the phase relationship between the radio waves emitted from multiple antenna elements.

[0005] However, in order to properly adjust this phase relationship, it is necessary to grasp the phase relationship for each combination of multiple antenna elements at the transmitting wireless station and multiple antenna elements at the receiving wireless station, and derive the optimal phase relationship from among the multiple phase relationships. In other words, it is necessary to grasp the state of the propagation path for each combination of antenna elements at the transmitting side and antenna elements at the receiving side.

[0006] It is possible to grasp the state of the propagation path for all of the above combinations by, for example, transmitting and receiving a known signal between a transmitting radio station and a receiving radio station. However, this method increases communication overhead because other communications cannot be performed while the known signal is being transmitted and received and because the state of the propagation path must be accurately transmitted.

[0007] For this reason, in general adaptive beamforming, multiple discrete beams are set in advance. Each of the multiple beams is associated with a beam ID (Identifier) ​​that allows the beam to be uniquely identified. For example, in adaptive beamforming, a beam-specific signal including a beam ID is transmitted and received between two wireless stations using each beam associated with the beam ID. Then, based on the results of the transmission and reception of the beam-specific signal by each beam, the optimal beam and the beam ID associated with that beam are identified between the two wireless stations. Adaptive beamforming can suppress an increase in overhead through such beam selection.

[0008] The above-described beam selection is defined in 3GPP (registered trademark) 5G (5th Generation) and IEEE (Institute of Electrical and Electronics Engineers) 802.11ad, and has been implemented in wireless communication systems that have been put into practical use in recent years.

[0009] (Beam Selection Procedure) Generally, beam selection is performed in the following procedure. First, one wireless station (transmitting wireless station) transmits a beam identification signal to the other wireless station (receiving wireless station). The beam identification signal here is a signal that enables the other wireless station to identify the beam used to transmit the beam identification signal transmitted by the other wireless station. Here, the one wireless station controls transmission so that the beam identification signals transmitted by each beam do not interfere with each other. Specifically, the one wireless station transmits the beam identification signals for each beam in sequence, shifting the transmission timing. Hereinafter, the act of a wireless station transmitting the beam identification signals for each beam in sequence, shifting the transmission timing, may be referred to as a "sweep."

[0010] Next, the other wireless station measures the reception quality of each beam-specific signal transmitted sequentially from the first wireless station via each beam. The other wireless station selects, for example, the beam-specific signal with the best reception quality. The other wireless station transmits a signal (hereinafter referred to as a "feedback signal") containing information based on the selected beam-specific signal to the first wireless station. With the above configuration, adaptive beamforming allows one wireless station to determine which beam is optimal to use when transmitting data to the other wireless station.

[0011] The beam identification signal may be, for example, a beam search signal including a beam ID (Identifier) ​​that identifies the beam used by one of the wireless stations. The beam search signal here is, for example, a signal specified in the Sector Sweep Frame (SSW) specified in IEEE 802.11ay (see, for example, Non-Patent Document 6) or the Synchronization Signal / Physical Broadcast Channel (SS / PBCH) specified in 5G.

[0012] In the following description, the reception quality measured by a wireless station may be any of received power, RSSI (Received Signal Strength Indicator), SNR (Signal to Noise Ratio), RSRP (Reference Signal Received Power), RSRQ (Reference Signal Received Quality), SIR (Signal to Interference Ratio), and SINR (Signal to Interference plus Noise Ratio).

[0013] Regarding beam selection at the receiving radio station, in a system such as TDD (Time Division Duplex) that uses the same frequency for transmission and reception, it is possible to select the same beam as the beam used by the transmitting radio station. In contrast, in a system such as FDD (Frequency Division Duplex) that uses different frequencies for transmission and reception, the receiving radio station must also select a beam similar to the beam selection performed by the transmitting radio station.

[0014] When a receiving radio station selects a beam, the receiving radio station transmits a signal to the transmitting radio station requesting a receiving beam search procedure. The signal requesting a receiving beam search procedure is a signal that requests the transmitting radio station to transmit a signal in order to select a beam to be used to receive the signal at the receiving radio station. The receiving radio station receives the signal by switching the beam reception direction over time in accordance with the signal transmitted by the transmitting radio station, and measures the reception quality of the received signal. This allows the receiving radio station to select the beam to be used by the receiving radio station by identifying the beam with the best reception quality.

[0015] (Distributed Antenna System) Fig. 17 is a diagram showing the configuration of a distributed antenna system 500, which is an example of a conventional general distributed antenna system. In Fig. 17, as an example, the distributed antenna system 500 includes five antenna devices 200-1 and five digital signal processing devices 210-1. As shown in Fig. 17, the digital signal processing devices 210-1 that transmit and receive signals are connected to the antenna devices 200-1 in a one-to-one relationship. That is, in this case, one cell 100 is formed for one antenna device 200. In this configuration, one terminal device is connected to the only one antenna device 200 that exists in the cell.

[0016] Looking at cell 100-1, antenna device 200-1 and digital signal processing device 210-1 constitute what is known as a base station device, and when a terminal station is located in cell 100-1, for example, the terminal station is connected to one antenna device 200-1 via radio waves.

[0017] As mentioned above, in high frequency bands such as the millimeter wave band and the terahertz band, the effects of reflected and diffracted waves are reduced by using beamforming technology. Therefore, in high frequency bands, the possibility of communication interruption increases if the beam is blocked, and line-of-sight communication becomes the norm. Meanwhile, MIMO (Multiple Input Multiple Output) is a powerful 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, since line-of-sight communication is the norm in high frequency bands, applying MIMO technology increases the spatial correlation between multiple transmitting and receiving antennas, making spatial multiplexing difficult.

[0018] Therefore, for wireless communications using high frequency bands, wireless communication systems using distributed antennas (hereinafter referred to as "distributed antenna systems") that have the effect of improving shielding resistance are being considered. Fig. 18 is a diagram showing the configuration of a distributed antenna system 500a, which is an example of a high frequency band distributed antenna system. As shown in Fig. 18, a digital signal processing device 210a that transmits and receives signals is connected to multiple distributed antenna devices 200a in a one-to-multiple relationship. That is, in the distributed antenna system, one cell 100 is formed by multiple distributed antenna devices 200a. In this configuration, one terminal device is connected to one of the multiple distributed antenna devices 200a present in the cell.

[0019] In cell 100-1, multiple distributed antenna devices 200a-1-1 to 200a-1-4 are installed in a distributed manner, and one digital signal processing device 210a-1 is connected to the multiple distributed antenna devices 200a-1-1 to 200a-1-4. In distributed antenna system 500a, the multiple distributed antenna devices 200a-1-1 to 200a-1-4 and digital signal processing device 210a-1 form so-called base station devices, and similar configurations are also used in other cells 100-2 to 100-5. In distributed antenna system 500a, when one terminal station is located in cell 100-1, for example, the terminal device is connected to the multiple distributed antenna devices 200a-1-1 to 200a-1-4 by radio waves.

[0020] Therefore, each of the multiple distributed antenna devices 200a must perform a beam search for the terminal device and select multiple beams. As a result, in a high-frequency band distributed antenna system, overhead increases due to the number of beam searches required for the distributed antenna devices 200a, reducing the efficiency of data transmission. That is, the overhead increases in proportion to the number of distributed antenna devices 200a, which is an issue. Furthermore, if the standard specifications impose an upper limit on the number of beams that can be searched, it is necessary to reduce the number of beams that can be searched per distributed antenna device 200a, which results in a smaller coverage area.

[0021] By applying MIMO (distributed MIMO) between multiple antennas provided in one terminal device and multiple distributed antenna devices 200a, spatial correlation is reduced and spatial multiplexing becomes possible (single-user MIMO). However, it is essential to select a beam in advance for each link between the terminal device and each of the multiple distributed antenna devices 200a.

[0022] Here, we will explain a general transmission beam selection method for performing high-frequency band distributed MIMO. A transmitting wireless station temporally switches and transmits a beam search signal, which contains digital information including a transmission beam ID associated with each of multiple candidate beams discretely set in advance for each transmitting antenna and an antenna ID associated with each transmitting antenna.

[0023] The receiving radio station measures the reception quality of each beam search signal at each receiving antenna, reads the transmission beam ID and antenna ID embedded in the beam search signal, and transmits a feedback signal including information on the transmitting and receiving antenna pair, the transmission beam ID, and the reception quality to the transmitting radio station. The transmitting radio station, upon receiving the feedback signal, selects multiple transmission beams equal to the number of spatial multiplexed beams by MIMO based on the reception quality. In addition, the receiving radio station sequentially selects multiple reception beams by receiving beam selection, thereby performing MIMO processing between the multiple transmission and reception beams and enabling high-frequency band MIMO transmission.

[0024] The above configuration has a problem in that the time required for one beam selection increases as the number of distributed antenna devices increases. Therefore, a method of beam searching that is independent of the number of distributed antenna devices by simultaneously sweeping and beam searching using multiple distributed antenna devices has been studied (see, for example, Patent Document 1). Fig. 19 is a diagram showing an overview of a distributed antenna system in which multiple distributed antenna devices simultaneously sweep and beam search. Fig. 19 shows a sweep state between one terminal device 300 and three distributed antenna devices 200a-1-1 to 200a-1-3.

[0025] First, as shown in FIG. 19A, all of the distributed antenna apparatuses 200a-1-1 to 200a-1-3 transmit the same beam-identifying signal including the same beam ID for each beam at the same timing in a time-division manner. For example, the distributed antenna apparatuses 200a-1-1 to 200a-1-3 transmit the same beam-identifying signal including the same beam ID for each beam at a certain timing (for example, at time t １ ), the distributed antenna devices 200a-1-1 to 200a-1-3 transmit the same beam identifying signal including beam ID #1 to the terminal device 300. ２ ), the distributed antenna devices 200a-1-1 to 200a-1-3 transmit the same beam identifying signal including the same beam ID for each beam in a time-division manner by switching between these processes over time.

[0026] In such a distributed antenna system, the distributed antenna devices 200a-1-1 to 200a-1-3 transmit the same beam-specific signal without including information that can identify the distributed antenna device 200a in each transmitted beam-specific signal. As a result, the same beam-specific signal is transmitted simultaneously from the multiple distributed antenna devices 200a. However, when the terminal device 300 receives beam-specific signals transmitted from the multiple distributed antenna devices 200a, the simultaneously transmitted beam-specific signals can be regarded as multipath interference. Therefore, by applying to the distributed antenna system general multipath interference compensation techniques, such as guard intervals used in general distributed antenna systems, degradation of the quality of wireless communication can be avoided.

[0027] The terminal device 300 selects, from among the multiple beam identification signals received, the beam identified by the beam ID included in the beam identification signal that provides the highest reception quality as the optimal beam. In the example shown in FIG. 19A, the terminal device 300 selects the beam identified by beam ID #4 as the optimal beam. Beam ID #4 indicates a result based primarily on the beam identification signal transmitted from the distributed antenna device 200a-1-2. Here, (1) shown in FIG. 19A indicates a result based primarily on the beam identification signal transmitted from the distributed antenna device 200a-1-3. (2) shown in FIG. 19A is an adjacent beam of beam ID #4, and indicates a result based primarily on the beam identification signal transmitted from the distributed antenna device 200a-1-2. (3) shown in FIG. 19A indicates a result based primarily on the beam identification signal transmitted from the distributed antenna device 200a-1-1. (4) shown in FIG. 19A shows the results based mainly on the reflected wave of the beam-specifying signal transmitted from the distributed antenna unit 200a-1-2.

[0028] Then, as shown in FIG. 19B , the terminal device 300 feeds back to the base station device a feedback signal including information indicating beam ID #4 corresponding to the selected optimal beam (hereinafter referred to as the “optimal beam ID”). In the distributed antenna system, the feedback signal transmitted from the terminal device 300 is received by each distributed antenna device 200a, and the reception quality of the feedback signal is measured for each distributed antenna device 200a. Then, based on the measurement results, the distributed antenna system selects the optimal distributed antenna device 200a to use for wireless communication with the terminal device 300. Hereinafter, the optimal distributed antenna device to use for wireless communication may also be referred to as the best DA. With this configuration, the distributed antenna system can perform optimal beam selection for the optimal antenna without increasing the time required for beam selection, even if the number of distributed antenna devices increases.

[0029] International Publication No. 2023 / 286187

[0030] As described above, in a high-frequency band distributed antenna system, spatial correlation can be reduced by having multiple distributed antenna devices cooperate to perform distributed MIMO transmission to a single terminal device. However, to do this, the terminal device must select the beam of another distributed antenna device (a distributed antenna device excluding the best DA) that has the best reception quality. Furthermore, from the perspective of shielding countermeasures, detecting the beams of different distributed antenna devices may also stabilize communications.

[0031] Here, an overview of the case where the conventional technology is extended to include the selection of the second or subsequent beam for the terminal device 300 will be described. First, as shown in FIG. 19A, all distributed antenna devices 200a-1-1 to 200a-1-3 transmit the same beam identification signal including the same beam ID for each beam at the same timing in a time-division manner. The terminal device 300 selects multiple candidate beam IDs based on the beam identification signals for each beam transmitted in a time-division manner from the distributed antenna devices 200a-1-1 to 200a-1-3. The candidate beam IDs include an optimal beam ID and a predetermined number of beam IDs from the second or subsequent beams with the best reception quality. In the example shown in FIG. 19B, the beam ID corresponding to the beam with the second best reception quality is beam ID #5, and the beam ID corresponding to the beam with the third best reception quality is beam ID #7.

[0032] Next, the terminal device 300 transmits a feedback signal including information indicating multiple candidate beam IDs to the base station device. In the high-frequency band distributed antenna system, the reception quality of the feedback signal received by each distributed antenna device 200a is measured. At this time, the high-frequency band distributed antenna system selects not only the best DA but also the second or subsequent distributed antenna devices with the best reception quality. Then, the high-frequency band distributed antenna system combines the optimal beam ID with the best DA, and combines the beam ID determined by the terminal device 300 to have the second best reception quality with the distributed antenna device with the second best reception quality of the feedback signal. However, there is a high possibility that the combination of the second or subsequent distributed antenna devices and beam IDs selected using this method will be inaccurate.

[0033] For example, assume that, as a result of measuring the reception quality of the feedback signal, the distributed antenna device 200a with the second best reception quality is the distributed antenna device 200a-1-1, and the distributed antenna device 200a with the third best reception quality is the distributed antenna device 200a-1-3. Also assume that the beam ID with the second best reception quality of the beam-identified signal in the terminal device 300 is beam ID #5, and the beam ID with the third best reception quality of the beam-identified signal is beam ID #7.

[0034] In this case, distributed antenna device 200a-1-1 is linked to beam ID #5, and distributed antenna device 200a-1-3 is linked to beam ID #7. However, as explained in (A) of Figure 19, beam ID #5 has the highest reception quality of the beam-identified signal transmitted from distributed antenna device 200a-1-2, and beam ID #7 has the highest reception quality of the beam-identified signal transmitted from distributed antenna device 200a-1-1. Thus, the combinations of the second and subsequent distributed antenna devices and beam IDs are not accurate.

[0035] The reason for this is that due to the influence of adjacent beams of the best DA or beams in the direction of the reflected wave of the best DA, radio waves with a higher signal strength than beams of other distributed antenna devices 200a may arrive at the terminal device 300, and if the terminal device 300 selects beams in order of highest reception quality, this will not match the order of the distributed antenna device 200a, which has the highest reception quality when receiving a feedback signal.

[0036] If the conventional technology were to be extended to detect the second or subsequent beams, the accuracy of the search for beams other than the optimal beam would be reduced, resulting in the loss of the spatial multiplexing effect achieved by distributed MIMO.

[0037] In view of the above circumstances, an object of the present invention is to provide a technology that can accurately perform a search for a beam other than the optimum beam.

[0038] One aspect of the present invention is a base station device comprising: a first beam search instruction unit that instructs the execution of a first beam search process in which beam identification signals including the same beam identifier are simultaneously transmitted from multiple antennas to a radio station for each beam identifier using transmission beams linked to the beam identifier; a second beam search instruction unit that instructs the execution of a second beam search process in which, based on a report signal including a selected beam identifier indicating multiple beam identifiers selected based on the reception quality of the beam identification signal for each beam identifier at the radio station obtained by the first beam search process, a beam identification signal including the selected beam identifier is individually transmitted for each selected beam identifier from at least the multiple antennas; and a transceiver unit that determines a combination of antennas and transmission beams to be used for wireless communication with the radio station based on the results of the first beam search process and the results of the second beam search process.

[0039] One aspect of the present invention is a base station device comprising: a beam search instruction unit that instructs the execution of a beam search process in which beam identification signals including the same beam identifier are simultaneously transmitted from multiple antennas to a radio station for each beam identifier using transmission beams linked to the beam identifier; a report signal receiving unit that forms a receiving beam at a pre-assigned timing for each transmission beam linked to the beam identifier and receives, via the multiple antennas, report signals corresponding to each of multiple beam identifiers selected based on the reception quality of the beam identification signal for each beam identifier at the radio station; and a transceiver unit that determines a combination of antennas and transmission beams to be used for wireless communication with the radio station based on the multiple report signals received by the report signal receiving unit.

[0040] One aspect of the present invention is a terminal device comprising: a first beam identifying signal receiving unit that extracts multiple first beam identifiers that satisfy a condition indicating that high transmission capacity is expected based on the reception quality of beam identifying signals including the same beam identifier that are transmitted simultaneously for each beam identifier from multiple antennas provided in a base station device by transmission beams linked to the beam identifiers; and a second beam identifying signal receiving unit that extracts one or more second beam identifiers that satisfy a condition indicating that high transmission capacity is expected at each of the multiple antennas based on the reception quality of beam identifying signals that include at least any first beam identifier of the multiple first beam identifiers that are transmitted at different times from the multiple antennas by transmission beams linked to each of the multiple first beam identifiers.

[0041] One aspect of the present invention is a terminal device comprising: a beam-specific signal receiving unit that extracts multiple beam identifiers that satisfy conditions indicating that high transmission capacity is expected based on the reception quality of beam-specific signals including the same beam identifier that are transmitted simultaneously for each beam identifier from multiple antennas provided in a base station device by transmission beams linked to the beam identifiers; and a report signal transmitting unit that transmits report signals at pre-assigned timings for each reception beam linked to the multiple beam identifiers.

[0042] According to the present invention, it becomes possible to perform a search for a beam other than the optimum beam with high accuracy.

[0043] 1 is a diagram illustrating an example of the configuration of a conventional base station device. FIG. 2 is a diagram illustrating conventional beam assignment information. FIG. 3 is a diagram illustrating an example of the configuration of a conventional terminal device. FIG. 4 is a flowchart illustrating a processing flow of a conventional base station device. FIG. 5 is a flowchart illustrating a processing flow of a conventional terminal device. FIG. 6 is a schematic diagram illustrating an overview of beam selection by a distributed antenna system in a first embodiment of the present invention. FIG. 7 is a diagram illustrating an example of the configuration of a distributed antenna system in a first embodiment of the present invention. FIG. 8 is a diagram illustrating an example of the configuration of a base station device in a first embodiment of the present invention. FIG. 9 is a diagram illustrating an example of the configuration of a terminal device in a first embodiment of the present invention. FIG. 10 is a flowchart illustrating a processing flow of a base station device in a first embodiment. FIG. 11 is a flowchart illustrating a processing flow of a terminal device in a first embodiment. FIG. 12 is a sequence diagram illustrating a processing flow of a distributed antenna system in a first embodiment. FIG. 13 is a diagram illustrating an example of the configuration of a base station device in a second embodiment of the present invention. FIG. 14 is a diagram illustrating an example of the configuration of a terminal device in a second embodiment of the present invention. FIG. 15 is a flowchart illustrating a processing flow of a base station device in a second embodiment. FIG. 16 is a flowchart illustrating a processing flow of a terminal device in a second embodiment.

[0044] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. For ease of understanding, the configuration of a conventional distributed antenna system will be described first for comparison.

[0045] The overall configuration of a conventional distributed antenna system will be described below. A conventional distributed antenna system is a wireless communication system in which multiple distributed antenna devices are arranged for one cell and communication is performed using a high frequency band. The conventional distributed antenna system includes one or more base station devices and one or more terminal devices. The configurations of the base station device and the terminal device will be described below.

[0046] [Configuration of a conventional base station device] Fig. 1 is a diagram showing an example of the configuration of a conventional base station device. As shown in Fig. 1, the base station device includes a digital-analog signal processing device 250 and P (P is an integer of 2 or more) distributed antenna devices 260-1 to 260-P. Hereinafter, when there is no need to particularly distinguish between the distributed antenna devices 260-1 to 260-P, they will be simply referred to as "distributed antenna device 260."

[0047] The digital-analog signal processing device 250 performs communication control related to beam selection, which selects from a plurality of beams a beam to be used in wireless communication between each of the distributed antenna devices 260-1 to 260-P and the terminal device. The digital-analog signal processing device 250 also transmits and receives wireless signals to and from the terminal device using the distributed antenna devices 260-1 to 260-P.

[0048] The distributed antenna device 260 is an antenna device capable of adaptive beamforming, and can select one of a plurality of types of beams to communicate with a terminal device.

[0049] The digital / analog signal processing device 250 includes a communication control unit 270, a digital signal processing unit 280, and an analog signal unit 290. The communication control unit 270 performs communication control related to the beam selection described above. The digital signal processing unit 280 performs digital signal processing. The analog signal unit 290 converts the digital signal that has been digitally processed by the digital signal processing unit 280 into an analog signal and transmits it from each distributed antenna device 260. The analog signal unit 290 converts a signal (e.g., a feedback signal) received by each distributed antenna device 260 into a digital signal and outputs it to the digital signal processing unit 280.

[0050] The communication control unit 270 includes a beam search instruction unit 271 , a feedback signal receiving unit 272 , a determination unit 273 , and a data transmission instruction unit 274 .

[0051] The beam search instruction unit 271 assigns a beam ID, which is an identifier for uniquely identifying all beams used in the distributed antenna devices 260-1 to 260-P, to each beam. An example of beam assignment information indicating the beam ID assigned by the beam search instruction unit 271 is shown in FIG. 2.

[0052] 2 is a diagram showing conventional beam assignment information 275. As shown in Fig. 2, the beam assignment information 275 is data in a table format in which combinations of distributed antenna devices 260 and beams are associated with beam IDs. The beam assignment information 275 is held in, for example, the beam search instruction unit 271.

[0053] 2 is an example of beam assignment information generated when the number of distributed antenna devices 260 is P and the number of beams used by each distributed antenna device 260 is n. For example, when four distributed antenna devices 260 are configured to use three types of beams each, P=4 and n=3.

[0054] The beam search instruction unit 271 outputs a beam search signal transmission instruction, which is an instruction to transmit a beam search signal from each of the distributed antenna units 260-1 to 260-P, to the digital signal processing unit 280. The beam search signal transmission instruction includes information indicating the beam ID assigned to each beam.

[0055] In response to the beam search signal transmission instruction, the digital signal processing unit 280 causes the distributed antenna units 260-1 to 260-P, which are distributed, to simultaneously transmit beam search signals for each beam assigned the same beam ID. Note that, depending on the locations of the distributed antenna units 260-1 to 260-P, there is a possibility that an error will occur in the timing at which the instruction from the digital signal processing unit 280 arrives at the distributed antenna units 260-1 to 260-P. Therefore, the digital signal processing unit 280 may notify time information indicating the timing at which to transmit a beam search signal for each beam ID. The beam search signal transmitted from each distributed antenna unit 260 includes information indicating the beam ID associated with the beam used to transmit the beam search signal.

[0056] The feedback signal receiving unit 272 acquires information indicating the optimum beam ID contained in the feedback signal from the digital signal processing unit 280. The feedback signal is transmitted from the terminal device, received by each distributed antenna device 260, and then decoded by the digital signal processing unit 280. The optimum beam ID is, for example, the beam ID contained in the beam search signal with the best reception quality among multiple beam search signals (beam identification signals) received by the terminal device as described above.

[0057] Furthermore, the feedback signal receiving unit 272 acquires information indicating the measurement results of the reception quality of the feedback signal in each distributed antenna device 260 from the digital signal processing unit 280. The feedback signal receiving unit 272 outputs the information indicating the optimal beam ID and the acquired measurement results of the reception quality of the feedback signal to the determining unit 273.

[0058] The determination unit 273 determines, for example, the distributed antenna device 260 with the best reception quality as the best DA based on the measurement result of the reception quality of the feedback signal acquired by the feedback signal receiving unit 272. The determination unit 273 outputs information indicating the combination of the beam (optimal beam) linked to the acquired optimal beam ID and the best DA to the data transmission instruction unit 274.

[0059] The data transmission instruction unit 274 issues an instruction to transmit data using the optimal beam in the best DA based on the information indicating the combination of the optimal beam and the best DA output from the judgment unit 273.

[0060] [Configuration of a conventional terminal device] Fig. 3 is a diagram showing an example of the configuration of a conventional terminal device 300. As shown in Fig. 3, terminal device 300 includes a terminal communication control unit 310, a digital signal processing unit 320, an analog signal unit 330, and Q (Q is an integer of 2 or more) antenna units 340-1 to 340-Q. Hereinafter, when there is no need to particularly distinguish between antenna units 340-1 to 340-Q, they will be simply referred to as "antenna unit 340."

[0061] The terminal communication control unit 310 performs communication control related to beam selection, which selects from a plurality of beams a beam to be used in wireless communication between each of the antenna units 340-1 to 340-Q and the base station device. The terminal communication control unit 310 also transmits and receives wireless signals to and from the base station device using the antenna units 340-1 to 340-Q.

[0062] The digital signal processing unit 320 acquires the radio signal output from the antenna unit 340. Furthermore, the digital signal processing unit 320 measures the reception quality of the beam-specific signal for each beam ID included in the beam-specific signal received by the antenna unit 340. The digital signal processing unit 320 outputs information indicating the measurement results of the reception quality of the beam-specific signal for each beam ID to the terminal communication control unit 310.

[0063] Furthermore, the digital signal processing unit 320 acquires a feedback signal transmission instruction output from the terminal communication control unit 310. The feedback signal transmission instruction includes information indicating the optimal beam ID. Upon acquiring the feedback signal transmission instruction, the digital signal processing unit 320 generates a feedback signal including information indicating the optimal beam ID. The digital signal processing unit 320 outputs the generated feedback signal to the analog signal unit 330.

[0064] The analog signal unit 330 converts the feedback signal output from the digital signal processing unit 320 into an analog signal and transmits it from each antenna unit 340. The analog signal unit 330 converts the signal (e.g., beam identification signal) received by each antenna unit 340 into a digital signal and outputs it to the digital signal processing unit 320.

[0065] The antenna unit 340 receives the radio signal transmitted from the distributed antenna device 260. For example, the antenna unit 340 receives a beam-identifying signal transmitted from the distributed antenna device 260. The antenna unit 340 outputs the received radio signal to the analog signal unit 330.

[0066] Furthermore, the antenna unit 340 acquires the feedback signal output from the analog signal unit 330. The antenna unit 340 transmits the acquired feedback signal to the base station device side.

[0067] The terminal communication control unit 310 includes an optimum beam ID selection unit 311 , a feedback signal transmission instruction unit 312 , and a data transmission instruction unit 313 .

[0068] The optimal beam ID selection unit 311 acquires information indicating the measurement results of the reception quality of the beam-identifying signal for each beam ID output from the digital signal processing unit 320. The optimal beam ID selection unit 311 identifies, for example, the optimal beam ID included in the beam-identifying signal with the best reception quality. The optimal beam ID selection unit 311 outputs information indicating the identified optimal beam ID to the feedback signal transmission instruction unit 312.

[0069] The feedback signal transmission instruction unit 312 acquires information indicating the optimal beam ID output from the optimal beam ID selection unit 311. The feedback signal transmission instruction unit 312 outputs a feedback signal transmission instruction, which is an instruction to transmit a feedback signal including information indicating the optimal beam ID to the base station device, to the digital signal processing unit 320.

[0070] The data transmission instruction unit 313 instructs data transmission between the base station device and the base station device.

[0071] An example of the operation of the base station device will be described below. Fig. 4 is a flowchart showing the flow of processing in a conventional base station device. The beam search instruction unit 271 instructs all distributed antenna devices 260 to transmit the same beam identifying signal simultaneously from all distributed antenna devices 260 (step S11). For example, the beam search instruction unit 271 instructs all distributed antenna devices 260 to transmit the same beam identifying signal (including the same beam ID) at the same timing. The beam search instruction unit 271 performs this processing for each beam of the distributed antenna device 260. As a result, at time t １ At time t ２ At time t ｎ In this case, all distributed antenna devices 260 can transmit the same beam-specific signal (e.g., including beam ID #n).

[0072] The processing flow of step S11 will be described in more detail. The beam search command unit 271 determines the value of the number P of distributed antenna devices 260 that will perform beam selection and the value of the number n of beams used by each distributed antenna device 260. For example, let P = 4 and n = 3. At this time, as shown in FIG. 2 , the beam search command unit 271 assigns a beam ID that can uniquely identify each beam that is simultaneously used by multiple distributed antenna devices 260 to transmit beam search signals. For example, the beam search command unit 271 assigns beam IDs that can uniquely identify each of three beams, such as beam ID #1, beam ID #2, and beam ID #3.

[0073] Next, the beam search instruction unit 271 initializes the value of counter i, which counts the beams that transmit the beam search signal, to i = 0. Next, in order to transmit the beam search signal with the next beam (i.e., to sweep the beams), the beam search instruction unit 271 increments the value of counter i by 1, to set i←i+1. Next, the beam search instruction unit 271 outputs to the digital signal processing unit 280 an identical beam search signal simultaneous transmission instruction, which is an instruction to transmit the same beam search signal, including information indicating the beam ID linked to the i-th beam, from all P distributed antenna devices 260 using the i-th beam.

[0074] The beam search instruction unit 271 repeatedly outputs instructions to the digital signal processing unit 280 to simultaneously transmit the same beam search signal until beam search signals are transmitted from all P distributed antenna devices 260 using n types of beams (i.e., until i = n).

[0075] Next, the feedback signal receiving unit 272 waits for a feedback signal transmitted from the terminal device 300 in response to the transmitted beam search signal to be received by all P distributed antenna devices 260. Here, the feedback signal includes information indicating the optimal beam ID.

[0076] Next, when the feedback signal has been received by all P distributed antenna devices 260, the feedback signal receiving unit 272 acquires information indicating the optimal beam ID contained in the feedback signal from the digital signal processing unit 280. The feedback signal receiving unit 272 outputs the acquired optimal beam ID to the determining unit 273.

[0077] Next, the feedback signal receiving unit 272 acquires information indicating the measurement results of the reception quality of the feedback signal in each distributed antenna device 260 from the digital signal processing unit 280. The feedback signal receiving unit 272 outputs the acquired measurement results to the determining unit 273.

[0078] The determination unit 273 determines, for example, the distributed antenna device 260 with the best reception quality as the best DA based on the measurement results acquired by the feedback signal receiving unit 272. The determination unit 273 detects a combination of the optimal beam and the best DA (step S12). The determination unit 273 outputs combination information indicating the detected combination of the optimal beam and the best DA to the data transmission instruction unit 274.

[0079] The data transmission instruction unit 274 selects a combination of the terminal device 300, the distributed antenna device 260, and the beam ID for cooperative transmission using the same time-frequency resource based on the combination information output from the determination unit 273, and instructs data transmission (step S13). Note that the data transmission instruction unit 274 may select the combination of the terminal device 300, the distributed antenna device 260, and the beam ID for cooperative transmission so as to maximize the transmission capacity, or may select the combination in descending order of reception quality.

[0080] An example of the operation of the terminal device 300 will now be described. Fig. 5 is a flowchart showing the flow of processing by the conventional terminal device 300.

[0081] The digital signal processing unit 320 waits for the antenna unit 340 to receive the beam identification signal for each beam ID transmitted from each distributed antenna device 260. Note that the beam identification signals for each beam ID transmitted from the distributed antenna device 260 are sequentially received by the antenna unit 340 using, for example, an omnidirectional or low-directivity beam.

[0082] When the beam-identifying signal for each beam ID transmitted from each distributed antenna device 260 is received by the antenna unit 340, the digital signal processing unit 320 measures the reception quality of the beam-identifying signal for each beam ID included in the beam-identifying signal received by the antenna unit 340. The optimal beam ID selection unit 311 selects the optimal beam ID based on the reception quality of the beam-identifying signal for each beam ID measured by the digital signal processing unit 320 (step S21). For example, the optimal beam ID selection unit 311 selects the beam ID included in the beam-identifying signal with the best reception quality as the optimal beam ID.

[0083] Next, the feedback signal transmission instruction unit 312 outputs a feedback signal transmission instruction to the digital signal processing unit 320, which is an instruction to transmit a feedback signal including information indicating the optimal beam ID to the base station device. The digital signal processing unit 320 generates a feedback signal including information indicating the optimal beam ID. The antenna unit 340 transmits the generated feedback signal to the base station device (step S22). Thereafter, the data transmission instruction unit 313 instructs data transmission with the base station device (step S23).

[0084] First Embodiment A first embodiment of the present invention will be described below. In the conventional distributed antenna system described above, when the terminal device 300 selects the second or subsequent beam with good reception quality, the combination of the beam ID corresponding to the second or subsequent beam selected by the terminal device 300 and the second or subsequent distributed antenna device 260 with good reception quality of the feedback signal, which is selected based on the reception result of the feedback signal, may not be accurate.

[0085] In contrast, the distributed antenna system of the present embodiment described below can improve the accuracy of the combination of the beam ID corresponding to the second or subsequent beam selected by the terminal device 300 with the second or subsequent distributed antenna device 260 having good reception quality of the feedback signal, which is selected based on the reception result of the feedback signal. Fig. 6 is a schematic diagram showing an overview of beam selection by the distributed antenna system of the first embodiment of the present invention.

[0086] As shown in (A) of Figure 6, in the distributed antenna system of this embodiment, similar to the conventional system, multiple distributed antenna devices 30 simultaneously transmit the same beam identification signal. Based on the beam identification signal transmitted from each distributed antenna device 30, the terminal device 40 selects K (K is an integer greater than or equal to 2) beam IDs as candidate beam IDs from among the multiple beam IDs in order of best reception quality. For example, when K = 3, the terminal device 40 selects the optimal beam ID, the beam ID with the second best reception quality, and the beam ID with the third best reception quality as candidate beam IDs based on the beam identification signal transmitted from each distributed antenna device 30. In this case, the terminal device 40 selects, for example, K candidate beam IDs in order of best reception quality among the local maxima.

[0087] In the example shown in Figure 6A, the terminal device 40 selects the beam identified by beam ID #4 as the optimal beam, selects the beam identified by beam ID #7 as the beam with the second best reception quality, and selects the beam identified by beam ID #2 as the beam with the third best reception quality. (1) shown in Figure 6A shows the result based mainly on the beam identification signal transmitted from the distributed antenna device 30-3. (2) shown in Figure 6A shows the result based mainly on the beam identification signal transmitted from the distributed antenna device 200a-1-1.

[0088] As shown in (B) of Fig. 6, the terminal device 40 feeds back a feedback signal including information indicating candidate beam IDs to the base station device side. The feedback signal fed back to the base station device side includes information indicating beam ID #4 corresponding to the optimal beam, information indicating beam ID #7 corresponding to the second best beam, and information indicating beam ID #2 corresponding to the third best beam.

[0089] In this way, the terminal device 40 in this embodiment feeds back to the base station device not only the optimum beam ID, but also information on the beam IDs corresponding to the beams with the second best reception quality or later.

[0090] In the distributed antenna system, a feedback signal transmitted from a terminal device 40 is received by each distributed antenna device 30, and the reception quality of the feedback signal is measured for each distributed antenna device 30. Then, based on the measurement results, the distributed antenna system selects the optimal distributed antenna device 30 (best DA) to use for wireless communication with the terminal device 40. Then, the distributed antenna system associates the selected best DA with the optimal beam ID included in the feedback signal. Here, the distributed antenna device 30-2 is assumed to be the best DA.

[0091] Thereafter, in the distributed antenna system, each of the distributed antenna devices 30 except for the best DA (e.g., the distributed antenna device 30-2) individually performs a beam search based on the candidate beam ID included in the feedback signal. For example, in the example shown in Fig. 6C, the distributed antenna device 30-1 and the distributed antenna device 30-3 individually perform a beam search based on the candidate beam ID.

[0092] For example, the distributed antenna unit 30-1 receives the ２ The distributed antenna device 30-3 transmits a beam specifying signal including the beam ID #7 with the second best reception quality and an identifier for identifying the distributed antenna device 30-1 to the terminal device 40. The distributed antenna device 30-3 transmits a beam specifying signal including the beam ID #7 with the second best reception quality and an identifier for identifying the distributed antenna device 30-1 to the terminal device 40 at a time different from that of the distributed antenna device 30-1 (for example, at time t ３ ), the distributed antenna device 30-3 transmits to the terminal device 40 a beam identification signal including beam ID #7 with the second best reception quality and an identifier for identifying the distributed antenna device 30-3.

[0093] The distributed antenna device 30-1 and the distributed antenna device 30-3 perform the above process for all candidate beam IDs included in the feedback signal. The terminal device 40 selects the top M (M is an integer equal to or greater than 1) beam IDs with the best reception quality based on the beam identification signals including each candidate beam ID transmitted from each distributed antenna device 30. For example, the terminal device 40 may select M beam IDs for each distributed antenna device 30 in descending order of reception quality.

[0094] In the above example, a beam identifying signal including beam ID #7 and a beam identifying signal including beam ID #2 are transmitted from each of the distributed antenna devices 30-1 and 30-2. Therefore, the terminal device 40 measures the reception quality of each of the beam identifying signals including beam ID #7 and beam ID #2 for each distributed antenna device 30. The terminal device 40 transmits to the base station device a feedback signal including information indicating the M beam IDs, the reception qualities corresponding to the M beam IDs (the reception qualities for each of the M beam IDs), and an identifier for identifying the distributed antenna device 30.

[0095] For example, the terminal device 40 transmits to the base station device information indicating M beam IDs, the reception qualities corresponding to the M beam IDs, a feedback signal including the identifier of the distributed antenna device 30-1, and information indicating the M beam IDs, the reception qualities corresponding to the M beam IDs, and a feedback signal including the identifier of the distributed antenna device 30-3. Note that the information indicating the M beam IDs included in the feedback signal including the identifier of the distributed antenna device 30-1 may differ from the information included in the feedback signal including the identifier of the distributed antenna device 30-3. This is because, in the terminal device 40, the reception quality of the beam-specific signal transmitted from the distributed antenna device 30-1 differs from the reception quality of the beam-specific signal transmitted from the distributed antenna device 30-3. Furthermore, although a feedback signal including the identifier of the distributed antenna device 30-1 and a feedback signal including the identifier of the distributed antenna device 30-3 are transmitted in the above example, they may also be transmitted together.

[0096] In the distributed antenna system, the feedback signal transmitted from the terminal device 40 for each distributed antenna device 30 (for example, the distributed antenna device 30-1 and the distributed antenna device 30-3) is received by the distributed antenna device 30. As a result, the selected second and subsequent distributed antenna devices 30 are associated with the beam ID included in the feedback signal and its reception quality.

[0097] The above configuration can solve the problems of the related art. A specific configuration for realizing the above processing will be described below.

[0098] [Configuration of Distributed Antenna System] The overall configuration of the distributed antenna system 1 in this embodiment will be described below. Fig. 7 is a diagram showing an example of the configuration of the distributed antenna system 1 in the first embodiment of the present invention. The distributed antenna system 1 is a wireless communication system in which a plurality of (four in Fig. 7) distributed antenna devices 30 are arranged for one cell 100 and communication is performed using a high frequency band.

[0099] As shown in Fig. 7, the distributed antenna system 1 includes a digital / analog signal processing device 20, distributed antenna devices 30-1 to 30-4, and a plurality of terminal devices 40. The distributed antenna system 1 is a communication system equipped with a plurality of distributed antenna devices on the accommodation station side. However, the configuration is not limited to this, and a distributed antenna system in which both opposing radio stations each include a plurality of distributed antennas may also be used. The digital / analog signal processing device 20 and the distributed antenna devices 30-1 to 30-4 constitute a so-called base station device.

[0100] 7, the digital-analog signal processing device 20 is connected to distributed antenna devices 30-1 to 30-4. Hereinafter, when there is no need to particularly distinguish between the distributed antenna devices 30-1 to 30-4, they will simply be referred to as "distributed antenna device 30."

[0101] 7 shows only one cell 100 for the sake of simplicity, the distributed antenna system 1 may be configured to include multiple cells 100. In this case, the distributed antenna system includes digital-analog signal processing devices 20 in the same number as the cells 100, and each of the digital-analog signal processing devices 20 is connected to a distributed antenna device 30-1 to 30-4 in the corresponding cell 100.

[0102] Each of the distributed antenna units 30-1 to 30-4 includes one distributed antenna 31-1 to 31-4 and one main unit 32-1 to 32-4. Each of the distributed antennas 31-1 to 31-4 is assigned a unique distributed antenna ID in advance to uniquely identify it.

[0103] Each of the main devices 32-1 to 32-4 transmits and receives radio frequency analog signals through the distributed antennas 31-1 to 31-4 connected to it. That is, each of the main devices 32-1 to 32-4 transmits the analog signal of the transmission data output by the digital-analog signal processing device 20 by radio waves from the distributed antennas 31-1 to 31-4.

[0104] Each of the main devices 32-1 to 32-4 receives radio waves from the distributed antennas 31-1 to 31-4 connected thereto and outputs analog signals to the digital / analog signal processor 20.

[0105] The distributed antenna device 30 is an antenna capable of adaptive beamforming. The distributed antenna device 30 can select one of a plurality of types of beams to communicate with the terminal device 40. Note that although the number of distributed antenna devices 30 is four in Fig. 7, the number may be two, three, five or more.

[0106] The digital-analog signal processing device 20 is configured to include an information processing device such as a general-purpose computer. The digital-analog signal processing device 20 performs communication control related to beam selection, which selects from among beams a beam to be used in wireless communication between the distributed antenna devices 30-1 to 30-4 and the terminal device 40. Furthermore, the digital-analog signal processing device 20 transmits and receives wireless signals to and from the terminal device 40 using the distributed antenna devices 30-1 to 30-4.

[0107] [Configuration of Base Station Device] The configuration of the base station device will be described below. Fig. 8 shows an example of the configuration of base station device B in the first embodiment of the present invention. As shown in Fig. 8, base station device B includes a digital-analog signal processing device 20 and P distributed antenna devices 30-1 to 30-P.

[0108] The digital / analog signal processing device 20 includes a communication control unit 21, a digital signal processing unit 22, and an analog signal unit 23. The communication control unit 21 performs communication control related to the beam selection described above. The digital signal processing unit 22 performs digital signal processing. The analog signal unit 23 converts the digital signal that has been digitally processed by the digital signal processing unit 22 into an analog signal and transmits it from each distributed antenna device 30. The analog signal unit 23 converts a signal (e.g., a feedback signal) received by each distributed antenna device 30 into a digital signal and outputs it to the digital signal processing unit 22.

[0109] The communication control unit 21 includes a first beam search instruction unit 24 , a feedback signal receiving unit 25 , a determination unit 26 , a second beam search instruction unit 27 , and a data transmission instruction unit 28 .

[0110] The first beam search command unit 24 assigns a beam ID, which is an identifier for uniquely identifying all beams used in the distributed antenna devices 30-1 to 30-P, to each beam by referring to the stored beam assignment information 275. For example, the first beam search command unit 24 assigns beam ID #1 to beam #1 and beam ID #n to beam #n.

[0111] The first beam search instruction unit 24 generates a first beam search signal transmission instruction for causing all distributed antenna devices 30 to simultaneously transmit the same beam identifying signal. In this way, the first beam search instruction unit 24 causes a plurality of distributed antenna devices 30 to simultaneously transmit the same beam identifying signal, thereby executing a beam search process (first beam search process).

[0112] As a result, the first beam search instruction unit 24 causes all distributed antenna devices 30 to simultaneously transmit a common beam identifying signal to one terminal device 40. The common beam identifying signal is a beam identifying signal including the same beam ID (e.g., beam ID #1) that is simultaneously transmitted by all distributed antenna devices 30. The first beam search instruction unit 24 outputs the generated first beam search signal transmission instruction to the digital signal processing unit 22. The first beam search signal transmission instruction includes information indicating the beam ID assigned to each beam.

[0113] The common beam-specific signal may be a Synchronization Signal / Physical Broadcast Channel (SS / PBCH) of the 3GPP standard, or a directional multi-gigabit (DMG) beacon frame of IEEE 802.11ad or IEEE 802.11ay.

[0114] The feedback signal receiving unit 25 acquires a first feedback signal from the digital signal processing unit 22. The first feedback signal is a signal including the result of a beam search using a common beam identification signal. For example, the first feedback signal includes information indicating K candidate beam IDs. Note that the first feedback signal may indicate information indicating the K candidate beam IDs in order of best reception quality at the terminal device 40, or may indicate the K candidate beam IDs together with the reception quality values ​​for each candidate beam ID.

[0115] The feedback signal receiving unit 25 acquires information indicating the candidate beam ID included in the first feedback signal. The first feedback signal is transmitted from the terminal device 40, received by each distributed antenna device 30, and then decoded by the digital signal processing unit 22.

[0116] Furthermore, the feedback signal receiving unit 25 acquires information indicating the measurement results of the reception quality of the first feedback signal in each distributed antenna device 30 from the digital signal processing unit 22. The feedback signal receiving unit 25 outputs information indicating the candidate beam ID and the acquired measurement results of the reception quality of the first feedback signal to the determining unit 26. Furthermore, the feedback signal receiving unit 25 outputs information indicating the candidate beam ID to the second beam search instructing unit 27.

[0117] Furthermore, the feedback signal receiving unit 25 acquires a second feedback signal from the digital signal processing unit 22. The second feedback signal is a signal including the result of a beam search using an individual beam identifying signal. For example, the second feedback signal includes an identifier of the distributed antenna device 30, M beam IDs, and information indicating the reception quality values ​​of each of the M beam IDs. This allows the feedback signal receiving unit 25 to determine whether the second feedback signal is addressed to the distributed antenna device 30.

[0118] The feedback signal receiving unit 25 obtains information indicating the identifier of the distributed antenna device 30, the M beam IDs, and the reception quality values ​​of each of the M beam IDs, which are included in the second feedback signal. The second feedback signal is transmitted from the terminal device 40, received by each distributed antenna device 30, and then decoded by the digital signal processing unit 22.

[0119] In addition, the feedback signal receiving unit 25 outputs to the data transmission instruction unit 28 the identifier of the distributed antenna device 30, information indicating the M beam IDs, and feedback results indicating the reception quality of each of the M beam IDs.

[0120] The determination unit 26 determines, for example, the distributed antenna device 30 with the best reception quality as the best DA based on the measurement result of the first feedback signal acquired by the feedback signal receiving unit 25. The determination unit 26 outputs information indicating the combination of the optimal beam and the best DA to the data transmission instruction unit 28.

[0121] The second beam search instruction unit 27 refers to the beam assignment information 275 it holds, and assigns the candidate beam IDs identified by the information indicating the candidate beam IDs output from the feedback signal receiving unit 25 to the corresponding beams. For example, if the candidate beam IDs identified by the information indicating the candidate beam IDs are beam ID #2 and beam ID #7, the second beam search instruction unit 27 assigns beam ID #2 to beam #2 and beam ID #7 to beam #7.

[0122] The second beam search instruction unit 27 generates a second beam search signal transmission instruction for causing all distributed antenna devices 30 (hereinafter referred to as "candidate distributed antenna devices") except for the best DA to transmit beam identification signals including candidate beam IDs at different timings. In this way, the second beam search instruction unit 27 executes beam search processing (second beam search processing) by causing each candidate distributed antenna device among the multiple distributed antenna devices 30 to individually transmit a beam identification signal including a candidate beam ID at a different timing. In this way, the second beam search instruction unit 27 generates a second beam search signal transmission instruction for causing each candidate distributed antenna device to transmit a beam identification signal.

[0123] In this way, the second beam search instruction unit 27 causes each candidate distributed antenna device to transmit an individual beam identifying signal at different timing to one terminal device 40. An individual beam identifying signal is a beam identifying signal including a candidate beam ID that is transmitted by each distributed antenna device 30 at a transmission timing that does not overlap with that of other distributed antenna devices 30.

[0124] The second beam search instruction unit 27 outputs the generated second beam search signal transmission instruction to the digital signal processing unit 22. The second beam search signal transmission instruction includes information indicating the beam ID assigned to each beam and identification information for identifying the distributed antenna device 30.

[0125] The individual beam-specific signal may be a CSI-RS (Channel Status Information-Reference Signal) of the 3GPP standard, or an SSW frame or a BRP (Beam Refinement Protocol) frame of IEEE 802.11ad or IEEE 802.11ay.

[0126] The data transmission instruction unit 28 issues an instruction to transmit data using the optimal beam in the best DA, based on the information indicating the combination of the optimal beam and the best DA output from the determination unit 26. Furthermore, the data transmission instruction unit 28 issues an instruction to transmit data using the beam associated with the second or subsequent distributed antenna device 30 having the best reception quality, based on the feedback result for each candidate distributed antenna device output from the feedback signal receiving unit 25.

[0127] [Configuration of Terminal Device] Fig. 9 is a diagram showing an example of the configuration of terminal device 40 in the first embodiment of the present invention. As shown in Fig. 9, terminal device 40 includes a terminal communication control unit 41, a digital signal processing unit 42, an analog signal unit 43, and Q (Q is an integer of 2 or more) antenna units 44-1 to 44-Q. Hereinafter, when there is no need to particularly distinguish between antenna units 44-1 to 44-Q, they will be simply referred to as "antenna unit 44."

[0128] The terminal communication control unit 41 performs communication control related to beam selection, which selects from a plurality of beams a beam to be used in wireless communication between each of the antenna units 44-1 to 44-Q and the base station device B. The terminal communication control unit 41 also transmits and receives wireless signals to and from the base station device B using the antenna units 44-1 to 44-Q.

[0129] The digital signal processing unit 42 acquires the radio signal output from the antenna unit 44. The digital signal processing unit 42 also measures the reception quality of the beam-specific signal for each beam ID included in the beam-specific signal received by the antenna unit 44. The digital signal processing unit 42 outputs information indicating the measurement results of the reception quality of the beam-specific signal for each beam ID to the terminal communication control unit 41.

[0130] Furthermore, the digital signal processing unit 42 acquires a feedback signal transmission instruction output from the terminal communication control unit 41. Upon acquiring the feedback signal transmission instruction, the digital signal processing unit 42 generates a feedback signal including information indicating a beam ID. For example, the feedback signal transmission instructions acquired by the digital signal processing unit 42 include a first feedback signal transmission instruction and a second feedback signal transmission instruction.

[0131] The first feedback signal transmission instruction includes information indicating K beam IDs. Upon receiving the first feedback signal transmission instruction, the digital signal processing unit 42 generates a first feedback signal including information indicating the K beam IDs. The digital signal processing unit 42 outputs the generated first feedback signal to the analog signal processing unit 43.

[0132] The second feedback signal transmission instruction includes information indicating M beam IDs, information indicating the reception quality of each of the M beam IDs, and an identifier of the candidate distributed antenna device. Upon receiving the second feedback signal transmission instruction, the digital signal processing unit 42 generates a second feedback signal for each candidate distributed antenna device, the second feedback signal including information indicating M beam IDs, information indicating the reception quality of each of the M beam IDs, and an identifier of the candidate distributed antenna device. The digital signal processing unit 42 outputs the generated second feedback signal for each candidate distributed antenna device to the analog signal unit 43.

[0133] The feedback signals (first feedback signal and second feedback signal) may be any of PRACH (Physical Random Access Channel), PUCCH (Physical Uplink Control Channel), or PUSCH (Physical Uplink Shared Channel) of the 3GPP standard, or may be an SSW frame, Sector Sweep Feedback (SSW-Feedback) frame, or BRP frame of IEEE802.11ad or IEEE802.11ay.

[0134] The analog signal unit 43 converts the feedback signal output from the digital signal processing unit 42 into an analog signal and transmits it from each antenna unit 44. The analog signal unit 43 converts the signal received by each antenna unit 44 (e.g., a beam identification signal, etc.) into a digital signal and outputs it to the digital signal processing unit 42.

[0135] The antenna unit 44 receives the radio signal transmitted from the distributed antenna device 30. For example, the antenna unit 44 receives the beam identification signal transmitted from the distributed antenna device 30. The antenna unit 44 outputs the received radio signal to the analog signal unit 43.

[0136] Furthermore, the antenna unit 44 acquires a feedback signal (to be described later) output from the analog signal unit 43. The antenna unit 44 transmits the acquired feedback signal to the base station device B.

[0137] The terminal communication control unit 41 includes a common beam specifying signal receiving unit 45 , a feedback signal transmission instruction unit 46 , an individual beam specifying signal receiving unit 47 , and a data transmission instruction unit 48 .

[0138] The common beam identifying signal receiving unit 45 acquires information indicating the measurement results of the reception quality of the beam identifying signal (common beam identifying signal) for each beam ID output from the digital signal processing unit 42. Based on the acquired measurement results, the common beam identifying signal receiving unit 45 extracts a local maximum value in the beam identifying signal for each beam ID. Then, the common beam identifying signal receiving unit 45 identifies K beam IDs, which is the number of peaks of the extracted local maximum values. The K beam IDs are, for example, an optimal beam ID, which is the beam ID included in the beam identifying signal with the best reception quality, or the second or subsequent beam IDs with the best reception quality. The common beam identifying signal receiving unit 45 outputs information indicating the identified K beam IDs to the feedback signal transmission instruction unit 46.

[0139] The feedback signal transmission instruction unit 46 acquires information indicating the K beam IDs output from the common beam identification signal receiving unit 45. The feedback signal transmission instruction unit 46 outputs a first feedback signal transmission instruction, which is an instruction to transmit a first feedback signal including information indicating the K beam IDs to the base station device B, to the digital signal processing unit 42.

[0140] Furthermore, the feedback signal transmission instruction unit 46 acquires information indicating the M beam IDs output from the individual beam identification signal receiving unit 47, information indicating the reception qualities corresponding to the M beam IDs output from the individual beam identification signal receiving unit 47, and identifiers of the candidate distributed antenna devices. The feedback signal transmission instruction unit 46 outputs to the digital signal processing unit 42 a second feedback signal transmission instruction, which is an instruction to transmit to base station device B a second feedback signal including the acquired information indicating the M beam IDs, the information indicating the reception qualities corresponding to the M beam IDs, and the identifiers of the candidate distributed antenna devices.

[0141] The individual beam identification signal receiver 47 acquires, for each candidate distributed antenna device, information indicating the measurement results of the reception quality of the individual beam identification signal output from the digital signal processor 42. Based on the acquired measurement results for each candidate distributed antenna device, the individual beam identification signal receiver 47 extracts, for each candidate distributed antenna device, the top M beam IDs with the best reception quality. The individual beam identification signal receiver 47 then outputs, to the feedback signal transmission instruction unit 46, information indicating the top M beam IDs extracted for each candidate distributed antenna device and information indicating the reception quality corresponding to the top M beam IDs extracted for each candidate distributed antenna device, together with the identifiers of the candidate distributed antenna devices.

[0142] The data transmission instruction unit 48 instructs data transmission between the base station device and the base station device.

[0143] [Operation of Base Station Device B] An example of the operation of the base station device B will be described below. Fig. 10 is a flowchart showing the flow of processing of the base station device B in the first embodiment. The first beam search command unit 24 commands all distributed antenna devices 30 to transmit the same beam identifying signal simultaneously from all distributed antenna devices 30 (step S101). For example, the first beam search command unit 24 commands all distributed antenna devices 30 to transmit the same beam identifying signal (including the same beam ID) at the same timing. The first beam search command unit 24 performs this processing for each beam of the distributed antenna device 30. As a result, at time t １ At time t ２ At time t ｎ In this case, all distributed antenna devices 30 can transmit the same beam-specific signal (including, for example, beam ID #n).

[0144] The processing flow of step S101 will be described in more detail. The first beam search command unit 24 determines the value of the number P of distributed antenna devices 30 that will perform beam selection and the value of the number n of beams used by each distributed antenna device 30. For example, let P = 4 and n = 3. At this time, the first beam search command unit 24 assigns a beam ID that can uniquely identify each beam that is simultaneously used by multiple distributed antenna devices 30 to transmit beam search signals. For example, the first beam search command unit 24 assigns beam IDs that can uniquely identify three beams, such as beam ID #1, beam ID #2, and beam ID #3.

[0145] Next, the first beam search instruction unit 24 initializes the value of counter i, which counts the beams that transmit the beam search signal, to i = 0. Next, in order to transmit the beam search signal with the next beam (i.e., to sweep the beams), the first beam search instruction unit 24 increments the value of counter i by 1, to set i←i+1. Next, the first beam search instruction unit 24 outputs to the digital signal processing unit 22 an identical beam search signal simultaneous transmission instruction, which is an instruction to transmit the same beam search signal, including information indicating the beam ID associated with the i-th beam, from all P distributed antenna devices 30 using the i-th beam.

[0146] The first beam search instruction unit 24 repeatedly outputs an instruction to simultaneously transmit the same beam search signal to the digital signal processing unit 22 until beam search signals are transmitted from all P distributed antenna devices 30 using n types of beams (i.e., until i = n).

[0147] Next, the feedback signal receiving unit 25 waits for a first feedback signal transmitted from the terminal device 40 in response to the transmitted beam search signal to be received by all P distributed antenna devices 30. The first feedback signal transmitted from the terminal device 40 is sequentially received by the distributed antenna device 30 using, for example, an omnidirectional or low-directivity beam. The first feedback signal transmitted from the terminal device 40 is received. Here, the first feedback signal includes information indicating K candidate beam IDs.

[0148] Next, when the first feedback signal has been received by all P distributed antenna devices 30, the feedback signal receiving unit 25 acquires information indicating the K beam IDs contained in the first feedback signal from the digital signal processing unit 22. The feedback signal receiving unit 25 outputs the acquired information indicating the K beam IDs to the determining unit 26 and the second beam search instructing unit 27.

[0149] Next, the feedback signal receiving unit 25 acquires information indicating the measurement results of the reception quality of the first feedback signal in each distributed antenna device 30 from the digital signal processing unit 22. The feedback signal receiving unit 25 outputs the acquired measurement results of the reception quality of the first feedback signal to the determining unit 26.

[0150] The determination unit 26 determines the best DA based on the measurement result of the reception quality of the first feedback signal output from the feedback signal receiving unit 25. Furthermore, the determination unit 26 determines an optimal beam ID from among the beam IDs identified by the information indicating the K beam IDs output from the feedback signal receiving unit 25. For example, the determination unit 26 determines, as the optimal beam ID, the beam ID identified as having the highest reception quality in the terminal device 40 from among the beam IDs identified by the information indicating the K beam IDs. In this way, the determination unit 26 detects a combination of the best DA and the optimal beam identified by the optimal beam ID (step S102). The determination unit 26 outputs combination information indicating the combination of the detected optimal beam and the best DA to the data transmission instruction unit 28.

[0151] The second beam search instruction unit 27 acquires candidate beam IDs excluding the optimal beam ID from among the candidate beam IDs identified by the information indicating the K candidate beam IDs output from the feedback signal receiving unit 25. The second beam search instruction unit 27 instructs the candidate distributed antenna devices to transmit individual beam identification signals including the acquired candidate beam IDs for each candidate beam ID (step S103). For example, the second beam search instruction unit 27 instructs the candidate distributed antenna devices to individually transmit beam identification signals including the candidate beam IDs at different timings.

[0152] The second beam search instruction unit 27 performs this process for each candidate distributed antenna device as many times as the number of candidate beam IDs. If there are k (1≦k≦K−1) candidate beam IDs, the second beam search instruction unit 27 instructs one candidate distributed antenna device to transmit a beam identification signal k times. To avoid interference, it is desirable for multiple candidate distributed antenna devices to transmit beam identification signals at different times.

[0153] As a result, for example, at time t １ At time t ２ In this case, the distributed antenna device 30-3 can individually transmit a beam identifying signal including a candidate beam ID (for example, candidate beam ID #2).

[0154] Next, the feedback signal receiving unit 25 waits until second feedback signals for all candidate distributed antenna devices in response to the transmitted beam identification signal are received from the terminal device 40. Here, the second feedback signals include information indicating M beam IDs, information indicating reception qualities corresponding to the M beam IDs, and identifiers of the candidate distributed antenna devices.

[0155] Next, when the second feedback signals for all the candidate distributed antenna devices have been received, the feedback signal receiving unit 25 obtains from the digital signal processing unit 22 information indicating the M beam IDs contained in each second feedback signal, information indicating the reception quality corresponding to the M beam IDs, and the identifier of the candidate distributed antenna device.

[0156] Next, the feedback signal receiving unit 25 outputs to the data transmission instruction unit 28 the feedback results for each candidate distributed antenna device, which include information indicating the acquired M beam IDs, information indicating the reception quality corresponding to the M beam IDs, an identifier of the candidate distributed antenna device, and the measurement results of the reception quality of the second feedback signal.

[0157] The data transmission instruction unit 28 selects a combination of terminal device 40, distributed antenna device 30, and beam ID for coherent cooperative transmission using the same time-frequency resource based on the combination information output from the judgment unit 26 and the feedback results for each candidate distributed antenna device output from the feedback signal receiving unit 25, and instructs data transmission (step S105).

[0158] The data transmission instruction unit 28 may select the combination of the terminal device 40, the distributed antenna device 30, and the beam ID for coherent cooperative transmission so as to maximize the transmission capacity, or may select the combination in descending order of reception quality. For example, the data transmission instruction unit 28 determines the combination of each beam corresponding to the second or subsequent beam IDs with the best reception quality and the candidate distributed antenna device based on the measurement results of the reception quality of each second feedback signal acquired by the feedback signal receiving unit 25, the M beam IDs, and the identifiers of the candidate distributed antenna devices. For example, the data transmission instruction unit 28 selects the candidate distributed antenna device with the best measurement result of the reception quality of the second feedback signal as the distributed antenna device to be used for coherent cooperative transmission.

[0159] Furthermore, the data transmission instruction unit 28 selects the beam ID identified as having the best reception quality at the terminal device 40 from among the M beam IDs corresponding to the distributed antenna devices to be used. The data transmission instruction unit 28 associates the selected distributed antenna device to be used with the selected beam ID. The data transmission instruction unit 28 executes this process until the distributed antenna device 30 to be used for coherent cooperative transmission is determined.

[0160] [Operation of Terminal Device 40] An example of the operation of the terminal device 40 will be described below. Fig. 11 is a flowchart showing the flow of processing by the terminal device 40 in the first embodiment. The digital signal processing unit 42 waits for the antenna unit 44 to receive a beam identification signal (common beam identification signal) for each beam ID transmitted from each distributed antenna device 30. Note that the beam identification signals for each beam ID transmitted from the distributed antenna device 30 are received in order by the antenna unit 44, for example, using an omnidirectional or low-directivity beam.

[0161] When the beam identifying signal for each beam ID transmitted from each distributed antenna device 30 is received by the antenna unit 44, the digital signal processing unit 42 measures the reception quality of the beam identifying signal for each beam ID included in the beam identifying signal received by the antenna unit 44. The common beam identifying signal receiving unit 45 extracts local maximum values ​​based on the reception quality of the beam identifying signal for each beam ID measured by the digital signal processing unit 42, and extracts K beam IDs, which is the number of peaks, as candidate beam IDs (step S201). The common beam identifying signal receiving unit 45 outputs the extracted K candidate beam IDs to the feedback signal transmission instruction unit 46.

[0162] The feedback signal transmission instruction unit 46 instructs the transmission of a first feedback signal including the K beam IDs extracted by the common beam identification signal receiving unit 45 (step S202). As a result, the first feedback signal is transmitted to the base station device B via the antenna unit 44.

[0163] The digital signal processing unit 320 waits for the antenna unit 44 to receive a beam identification signal (individual beam identification signal) including a beam ID individually transmitted from a candidate distributed antenna device. Note that the beam identification signals including the beam ID transmitted from the candidate distributed antenna devices are sequentially received by the antenna unit 44, for example, by an omnidirectional or low-directivity beam.

[0164] When the beam identifying signal for each beam ID transmitted from each candidate distributed antenna device is received by the antenna unit 44, the digital signal processing unit 42 measures the reception quality of the beam identifying signal for each beam ID included in the beam identifying signal received by the antenna unit 44. The individual beam identifying signal receiving unit 47 extracts M beam IDs in descending order of reception quality based on the reception quality of the beam identifying signal for each candidate beam ID measured by the digital signal processing unit 42 (step S203). The individual beam identifying signal receiving unit 47 performs this process for each candidate distributed antenna device.

[0165] The individual beam identification signal receiver 47 associates information indicating the M beam IDs for each extracted candidate distributed antenna device and information indicating the reception quality corresponding to the beam IDs with the identifiers of the candidate distributed antenna devices, and outputs the information to the feedback signal transmission instruction unit 46. The feedback signal transmission instruction unit 46 instructs transmission of a second feedback signal for each candidate distributed antenna device, based on the information indicating the M beam IDs for each candidate distributed antenna device and the information indicating the reception quality corresponding to the beam IDs output from the individual beam identification signal receiver 47. As a result, the second feedback signal for each candidate distributed antenna device is transmitted to base station device B via the antenna unit 44. Thereafter, the data transmission instruction unit 48 performs data transmission with base station device B (step S204).

[0166] [Operation of Distributed Antenna System 1] An example of the overall operation of the distributed antenna system 1 will now be described. Fig. 12 is a sequence diagram showing the processing flow of the distributed antenna system 1 in the first embodiment. The base station device B simultaneously transmits the same beam identification signal from all distributed antenna devices 30 (step S301). The base station device B executes this processing the number of times corresponding to all beam IDs.

[0167] The terminal device 40 receives beam identification signals for the number of beam IDs transmitted from the base station device B. The terminal device 40 generates a first feedback signal based on the beam identification signals for the number of received beam IDs. The terminal device 40 transmits the generated first feedback signal to the base station device B (step S302). The base station device B receives the first feedback signal transmitted from the terminal device 40. The base station device B detects a combination of the best DA and the optimal beam ID based on the received first feedback signal and outputs the combination to the data transmission instruction unit 28 (step S303).

[0168] Next, base station device B transmits a beam identification signal including candidate beams excluding the optimum beam ID at different timings for each candidate distributed antenna device (step S304). Base station device B performs this process a number of times equal to the number of candidate beams excluding the optimum beam ID multiplied by the number of candidate distributed antenna devices. Terminal device 40 receives the beam identification signal transmitted from base station device B. Terminal device 40 generates second feedback signals based on the received beam identification signal for the number of candidate distributed antenna devices. Terminal device 40 transmits the generated second feedback signals for each candidate distributed antenna device to base station device B (step S305).

[0169] The base station device B receives the second feedback signal for each candidate distributed antenna device transmitted from the terminal device 40. The base station device B outputs the candidate distributed antenna device (candidate DA) included in the received second feedback signal for each candidate distributed antenna device, information indicating the beam ID for each candidate distributed antenna device, and information indicating the reception quality of each beam ID for each candidate distributed antenna device to the data transmission instructing unit 28 (step S306). Thereafter, the data transmission instructing unit 28 instructs data transmission based on the obtained information (step S307).

[0170] Here, when data transmission is performed from base station device B, base station device B transmits the data instructed by the data transmission instructing unit 28 using one or more distributed antenna devices 30 (step S308). For example, when one or more distributed antenna devices 30 are used for data transmission, the data transmission instructing unit 28 transmits data from the best DA based on a combination of the best DA and the optimal beam ID. For example, when two or more distributed antenna devices 30 are used for data transmission, the data transmission instructing unit 28 transmits data based on a combination of the best DA and the optimal beam ID, and a combination of the candidate distributed antenna device with the second best reception quality and the beam ID of that candidate distributed antenna device.

[0171] When data is to be transmitted from the terminal device 40, the base station device B allocates data transmission resources to the terminal device 40 (step S309). The terminal device 40 transmits data to the base station device B using the allocated resources (step S310).

[0172] According to the distributed antenna system 1 configured as described above, the base station device B is equipped with a first beam search instruction unit 24 that instructs the execution of a first beam search process in which beam identification signals including the same beam ID are simultaneously transmitted from multiple distributed antenna devices 30 to terminal devices 40 for each beam ID using transmission beams linked to the beam ID, a second beam search instruction unit 27 that instructs the execution of a second beam search process in which beam identification signals including candidate beam IDs are individually transmitted for each candidate beam ID from at least multiple distributed antenna devices 30 based on the second feedback signal obtained by the first beam search process, and a data transmission instruction unit 28 that determines the combination of distributed antenna devices 30 and transmission beams to be used for wireless communication with the terminal device 40 based on the results from the first beam search instruction unit 24 and the results from the second beam search instruction unit 27.

[0173] In this way, base station device B performs a beam search in two stages. Specifically, in the first stage of beam measurement, base station device B synchronizes and simultaneously performs beam measurement on all distributed antenna devices 30. In the second stage, base station device B performs beam measurement individually on each candidate distributed antenna device for candidate beam IDs other than the optimal beam ID. This makes it possible to suppress the influence of beams adjacent to the best DA or beams in the direction of the reflected wave of the best DA. Then, base station device B uses the results obtained from the second stage of beam measurement to determine the combination of the second or subsequent distributed antenna devices 30 and beam ID with the best reception quality to be used for wireless communication with terminal device 40. This makes it possible to accurately perform beam searches other than the optimal beam.

[0174] The terminal device 40 also includes a common beam identification signal receiving unit 45 that extracts multiple candidate beam IDs (e.g., the top K beam IDs with good reception quality) that satisfy a condition indicating good reception quality based on the reception quality of beam identification signals including the same beam ID that are transmitted simultaneously for each beam ID from multiple distributed antenna devices 30 provided in the base station device B using transmission beams linked to the beam IDs, and an individual beam identification signal receiving unit 47 that extracts one or more beam IDs that satisfy a condition indicating good reception quality in each of the multiple distributed antenna devices 30 based on the reception quality of beam identification signals that include at least any of the multiple candidate beam IDs that are transmitted at different times from the multiple distributed antenna devices 30 using transmission beams linked to each of the multiple candidate beam IDs.

[0175] In this way, the terminal device 40 feeds back to the base station device B information that can be used to determine a combination of the best DA and the optimal beam ID based on the reception quality of beam identification signals including the same beam ID that are simultaneously transmitted from each distributed antenna device 30. Then, the terminal device 40 feeds back, for each distributed antenna device 30, the top M candidate beam IDs based on the measurement results of the reception quality of beam identification signals including each candidate beam ID transmitted from each candidate distributed antenna device 30 excluding the best DA. In this way, information that can be used to determine a combination of the second or subsequent distributed antenna devices 30 with the best reception quality and the beam ID is fed back to the base station device B. As a result, the base station device B can obtain a spatial multiplexing effect using distributed MIMO.

[0176] (Variation 1 of the First Embodiment) In the above-described embodiment, the second beam search instruction unit 27 instructs the first feedback signal to perform a beam search on candidate beam IDs (second and subsequent candidate beams) excluding the optimal beam ID among the K candidate beam IDs included in the first feedback signal. In contrast, the second beam search instruction unit 27 may perform a beam search on all of the K candidate beam IDs that have been fed back.

[0177] (Variation 2 of the First Embodiment) In the above-described embodiment, the best DA is selected based on the reception quality of the first feedback signal without using an individual beam identification signal, and individual beam identification signals are transmitted to candidate distributed antenna devices other than the best DA. In contrast, the second beam search command unit 27 may cause all candidate distributed antenna devices, including the best DA, to perform a search based on the candidate beam ID. That is, the second beam search command unit 27 may cause all candidate distributed antenna devices, including the best DA, to perform a search based on the candidate beam ID by transmitting individual beam identification signals. In this case, beams corresponding to all candidate beam IDs, including the best beam ID included in the first feedback signal, may be searched.

[0178] (Variation 3 of the First Embodiment) In the above-described embodiment, the second beam search instruction unit 27 is configured to transmit individual beam identification signals to all candidate distributed antenna devices other than the best DA. In contrast, the second beam search instruction unit 27 may transmit individual beam identification signals to some of the candidate distributed antenna devices, rather than to all candidate distributed antenna devices other than the best DA. For example, the second beam search instruction unit 27 may select a combination of candidate distributed antenna devices that is expected to have high reception power, and transmit individual beam identification signals to the candidate distributed antenna devices included in the selected combination.

[0179] (Variant 4 in the first embodiment) As a method of notifying a terminal device 40 that simultaneous searches are being performed by multiple distributed antenna devices 30, the base station device B may attach a flag to a common beam identification signal indicating that simultaneous searches are being performed, or may use a signal in a low frequency band, or if the terminal device 40 has previously established a connection, may use a signal in that frequency, or may use another wireless communication system.

[0180] (Variation 5 of the First Embodiment) In the above-described embodiment, a method of extracting a local maximum value was shown as a peak detection method, but a peak may also be detected by selecting a beam ID close to the center of gravity position using machine learning clustering.

[0181] (Variation 6 of the First Embodiment) In the above-described embodiment, the terminal device 40 has been configured to extract a local maximum value and select the top K beam IDs as candidate beam IDs. The terminal device 40 may select K candidate beam IDs in descending order of the reception quality of all beam IDs, rather than the local maximum value. Alternatively, the terminal device 40 may extract candidate beams based on the local maximum value, and then extract, as a new candidate beam direction, the maximum value from among the beam directions whose angle difference with the nearest candidate beam is equal to or greater than a set angle threshold and whose level difference with the nearest candidate beam is within a set level difference threshold, and continue extracting candidate beams until no beam direction satisfies the above conditions. Alternatively, if the reception quality of a beam adjacent to the beam with the highest reception quality is high, there is a possibility that the signal is from another distributed antenna device 30. Therefore, the top K candidate beam IDs may be selected from the local maximum value and the adjacent beam with the highest reception quality among the local maximum values.

[0182] (Variation 7 of the First Embodiment) In the above-described embodiment, the terminal device 40 selects the top K beam IDs, but the number of candidate beam IDs does not have to be K. For example, the terminal device 40 may set a number to be further extracted from the K and select candidate beam IDs, or may set the number to be extracted and then select only beam IDs that exceed a threshold value for reception quality as candidate beam IDs.

[0183] (Variation 8 of the First Embodiment) In the above-described embodiment, the terminal device 40 selects the top K beam IDs. However, the terminal device 40 may control the number K of candidate beam IDs to be extracted based on the number of distributed antenna devices 30 to be simultaneously searched, which is notified in advance by the base station device B. For example, the terminal device 40 may estimate that there are the same number of strong paths as the number of distributed antenna devices 30, and set the number K of extracted paths to the number of distributed antenna devices 30. Furthermore, for example, in an environment with many reflected waves, the terminal device 40 may detect the number K of extracted paths as being greater than the number of distributed antenna devices 30 (for example, the number of distributed antenna devices 30 + α) by assuming that there are a small number of reflected waves in addition to the number of distributed antenna devices 30. This notification method may use signals in a low frequency band, or, if a connection has been established with the terminal in advance, may use signals at that frequency, or may use another wireless communication system.

[0184] (Ninth Modification of the First Embodiment) The terminal device 40 may feed back the first feedback signal using an omnidirectional antenna, or may form a beam in a direction searched in advance and feed back the signal if the antenna unit 44 has directionality, or may feed back the signal while searching in multiple directions. Furthermore, the terminal device 40 may feed back the first feedback signal in a different frequency band to which a connection has been established, or may feed back the signal using another wireless communication system.

[0185] (Variation 10 of First Embodiment) In the above-described embodiment, the terminal device 40 is configured to feed back to the base station device B all of the M beam IDs for each distributed antenna device 30 obtained based on individual beam identification signals and information indicating the reception quality of each of the M beam IDs. However, there is a high possibility that information with clearly low reception quality will not be used even if it is fed back to the base station device B. Therefore, the terminal device 40 may be configured to feed back some of the M beam IDs for each distributed antenna device 30. For example, the terminal device 40 acquires the reception quality of each of the M beam IDs multiplied by the number of distributed antenna devices 30 (the number of DAs multiplied by the M reception qualities), but may be configured to feed back only a number designated from the top of the acquired overall reception quality, or may feed back only a number designated from the top of the reception quality for each distributed antenna device 30, or may feed back information whose reception quality is equal to or higher than a threshold.

[0186] (Second embodiment) A second embodiment of the present invention will be described below. In the distributed antenna system 1 in the first embodiment described above, a configuration has been shown in which a candidate distributed antenna device individually transmits a beam identification signal including a candidate beam ID based on a candidate beam ID included in a first feedback signal transmitted from a terminal device 40. In contrast, in the distributed antenna system 1 in the second embodiment, a configuration will be described in which the terminal device 40 transmits a signal in accordance with the timing of the received beam of the distributed antenna device 30, thereby feeding back a beam ID. In the second embodiment, the base station device will be described as base station device Ba, the distributed antenna device 30 as distributed antenna device 30a, and the terminal device 40 as terminal device 40a.

[0187] In this embodiment, the terminal device 40a feeds back the beam ID by transmitting a signal in accordance with the timing of the received beam of the distributed antenna device 30a, so the distributed antenna device 30a does not transmit an individual beam-identifying signal as in the first embodiment.

[0188] The base station device Ba forms a receive beam at a timing pre-assigned to each beam, and receives a feedback signal transmitted from the terminal device 40a at each distributed antenna device 30a. The timing pre-assigned to each beam is known to both the base station device Ba and the terminal device 40a. For example, the timing may be shared by including timing information of the receive beam corresponding to each beam ID in a common beam identification signal and notifying it, or by notifying the terminal device 40a at the time of connection, etc. The base station device Ba associates the reception quality of the feedback signal for beam ID #i received by each distributed antenna device 30a with the quality of each distributed antenna device 30a for beam ID #i. For example, the base station device Ba measures the reception quality of the feedback signal for beam ID #1 received by the distributed antenna device 30a-1, and associates the measurement result with the quality of the distributed antenna device 30a-1 for beam ID #1.

[0189] As in the first embodiment, the terminal device 40a receives the same beam identification signal transmitted simultaneously from all distributed antenna devices 30 from the base station device Ba. The terminal device 40a extracts K candidate beam IDs based on the received multiple beam identification signals. The terminal device 40a sequentially feeds back the extracted K candidate beam IDs to the base station device Ba. For example, the terminal device 40a feeds back feedback signals to the base station device Ba in ascending order of numbers among the K candidate beam IDs at timings previously assigned to beam #i corresponding to beam ID #i.

[0190] In this way, the terminal device 40a transmits a feedback signal to the base station device Ba at a timing pre-assigned to a beam corresponding to one of the K candidate beam IDs. The terminal device 40a executes this process as many times as the number of K candidate beam IDs. Note that the terminal device 40a transmits the feedback signal without including the candidate beam ID in the feedback signal.

[0191] This is because the base station device Ba forms a receiving beam at a timing assigned to each beam in advance, and therefore the base station device Ba can determine which beam the feedback signal corresponds to even if the feedback signal does not include a candidate beam ID.

[0192] As a result, the base station device Ba receives feedback signals corresponding to the K candidate beam IDs at each of the distributed antenna devices 30. The base station device Ba measures the reception quality of the feedback signal for each received candidate beam ID for each distributed antenna device 30. Then, the base station device Ba determines the best DA for each candidate beam ID based on the measured reception quality.

[0193] [Configuration of Distributed Antenna System] The overall configuration of the distributed antenna system 1 in the second embodiment is basically the same as the overall configuration of the distributed antenna system 1 in the first embodiment shown in FIG. 7 described above, and therefore description thereof will be omitted.

[0194] [Configuration of Base Station Device] The configuration of the base station device will be described below. Fig. 13 shows an example of the configuration of base station device Ba in the second embodiment of the present invention. As shown in Fig. 13, base station device Ba includes a digital-analog signal processing device 20a and P distributed antenna devices 30-1 to 30-P. Base station device Ba differs from base station device B in that it includes a digital-analog signal processing device 20a instead of the digital-analog signal processing device 20. The following description will focus on the differences from base station device B.

[0195] The digital-analog signal processing device 20a includes a communication control unit 21a, a digital signal processing unit 22, and an analog signal unit 23. The communication control unit 21a includes a first beam search instruction unit 24, a feedback signal receiving unit 25a, a determination unit 26a, and a data transmission instruction unit 28.

[0196] The feedback signal receiving unit 25a receives a feedback signal from the digital signal processing unit 22. The feedback signal received by the feedback signal receiving unit 25a does not include information indicating a beam ID, as in the first embodiment. The feedback signal is transmitted from the terminal device 40a, received by each distributed antenna device 30, and then decoded by the digital signal processing unit 22.

[0197] Furthermore, the feedback signal receiving unit 25a acquires information indicating the measurement results of the reception quality of the feedback signal in each distributed antenna device 30 from the digital signal processing unit 22. For example, the feedback signal receiving unit 25a acquires information indicating the measurement results of the reception quality of each feedback signal received by each distributed antenna device 30 at a timing assigned in advance for each beam from the digital signal processing unit 22. The feedback signal receiving unit 25a outputs the acquired measurement results of the reception quality of the feedback signal for each beam ID to the determining unit 26a.

[0198] The determination unit 26a determines the best DA for each beam ID based on the measurement results of the reception quality of the feedback signal for each beam ID acquired by the feedback signal receiving unit 25a. For example, the determination unit 26a identifies, for each beam ID, the distributed antenna device 30 with the best reception quality, for example, based on the measurement results of the reception quality of the feedback signal for each beam ID. Then, the determination unit 26a determines the identified distributed antenna device 30 for each beam ID as the best DA for each beam ID. In this way, the determination unit 26a links the beam corresponding to each beam ID with the best DA for each beam ID. The determination unit 26a outputs information indicating the best DA for each beam ID to the data transmission instruction unit 28.

[0199] [Configuration of Terminal Device] Fig. 14 is a diagram showing an example of the configuration of a terminal device 40a in the second embodiment of the present invention. As shown in Fig. 14, the terminal device 40a includes a terminal communication control unit 41a, a digital signal processing unit 42, an analog signal unit 43, and Q antenna units 44-1 to 44-Q. The terminal device 40a differs from the terminal device 40 in that it includes a terminal communication control unit 41a instead of the terminal communication control unit 41. The following description will focus on the differences from the terminal device 40.

[0200] The digital signal processing unit 42 acquires the radio signal output from the antenna unit 44. The digital signal processing unit 42 also measures the reception quality of the beam-specific signal for each beam ID included in the beam-specific signal received by the antenna unit 44. The digital signal processing unit 42 outputs information indicating the measurement results of the reception quality of the beam-specific signal for each beam ID to the terminal communication control unit 41.

[0201] Furthermore, the digital signal processing unit 42 acquires a feedback signal transmission instruction output from the terminal communication control unit 41. Upon acquiring the feedback signal transmission instruction, the digital signal processing unit 42 generates a feedback signal. At this time, the digital signal processing unit 42 generates a feedback signal that does not include information on the candidate beam ID.

[0202] The terminal communication control unit 41 a includes a common beam identification signal receiving unit 45 , a feedback signal transmission instruction unit 46 a , and a data transmission instruction unit 48 .

[0203] The feedback signal transmission instruction unit 46a acquires information indicating the K beam IDs output from the common beam identification signal receiving unit 45. The feedback signal transmission instruction unit 46a outputs a feedback signal transmission instruction, which is an instruction to transmit a feedback signal to base station device B at a timing assigned in advance to the beam corresponding to each of the K beam IDs, to the digital signal processing unit 42. This allows the terminal device 40a to transmit a feedback signal corresponding to beam #i at a timing when base station device Ba can receive beam #i.

[0204] [Operation of Base Station Device Ba] An example of the operation of the base station device Ba will now be described. Fig. 15 is a flowchart showing the flow of processing by the base station device Ba in the second embodiment. The first beam search command unit 24 commands all distributed antenna devices 30 to transmit the same beam identifying signal simultaneously from all distributed antenna devices 30 (step S401). For example, the first beam search command unit 24 commands all distributed antenna devices 30 to transmit the same beam identifying signal (including the same beam ID) at the same timing. The first beam search command unit 24 performs this processing for each beam of the distributed antenna device 30. Here, the total number of beams is assumed to be N.

[0205] As a result, at time t １ At time t ２ At time t ｎ In this case, all distributed antenna devices 30 can transmit the same beam-specific signal (including, for example, beam ID #n).

[0206] Next, the feedback signal receiving unit 25a initializes the value of a counter i, which counts the reception beams for which a feedback signal corresponding to each beam is to be received, to i = 0 (step S402). Next, the feedback signal receiving unit 25a increments the value of the counter i by 1, to i←i+1, in order to receive a feedback signal corresponding to the next beam (i.e., to sweep the beams) (step S403).

[0207] Next, base station device Ba causes each distributed antenna device 30 to form a receiving beam at the timing previously assigned to beam #i. As a result, base station device Ba receives the feedback signal transmitted from terminal device 40a at each distributed antenna device 30 (step S404). The digital signal processing unit 22 measures the reception quality of each feedback signal received by each distributed antenna device 30 for each distributed antenna device 30. The digital signal processing unit 22 outputs the measurement results of the reception quality for each distributed antenna device 30 to the feedback signal receiving unit 25a.

[0208] The feedback signal receiving unit 25a acquires the measurement result of the reception quality for each distributed antenna device 30 from the digital signal processing unit 22. The feedback signal receiving unit 25a outputs the acquired measurement result of the reception quality for each distributed antenna device 30 to the data transmission instruction unit 28. The data transmission instruction unit 28 associates the measurement result of the reception quality for each distributed antenna device 30 with beam #i (step S405).

[0209] The base station device Ba determines whether the receive beam sweep for all beams has been completed (step S406). That is, the base station device Ba determines whether the beam sweep for all beams has been performed by forming a receive beam at the timing assigned to each beam (step S406). If the base station device Ba determines that the receive beam sweep for all beams has not been completed (step S406-NO), the base station device Ba increments the value of counter i by 1. Then, the processing from step S404 onwards is executed.

[0210] On the other hand, if the base station device Ba determines that the reception beam sweep of all beams has been completed (step S406—YES), the data transmission instruction unit 28 selects a combination of the terminal device 40a, the distributed antenna device 30, and the beam ID for coherent cooperative transmission using the same time-frequency resource based on the linking result for each beam ID, and instructs data transmission (step S407). For example, the data transmission instruction unit 28 selects a combination in order of reception power or that maximizes transmission capacity, and instructs data transmission.

[0211] In addition, the data transmission instruction unit 28 may select the combination of terminal device 40a, distributed antenna device 30, and beam ID for coherent cooperative transmission so as to maximize the transmission capacity, or may select them in order of highest reception quality.

[0212] [Operation of Terminal Device 40a] An example of the operation of the terminal device 40a will be described below. Fig. 16 is a flowchart showing the processing flow of the terminal device 40a in the second embodiment. The digital signal processing unit 42 waits for the antenna unit 44 to receive a beam identification signal (common beam identification signal) for each beam ID transmitted from each distributed antenna device 30. Note that the beam identification signals for each beam ID transmitted from the distributed antenna device 30 are received in sequence by the antenna unit 44, for example, using an omnidirectional or low-directivity beam.

[0213] When the beam identifying signal for each beam ID transmitted from each distributed antenna device 30 is received by the antenna unit 44, the digital signal processing unit 42 measures the reception quality of the beam identifying signal for each beam ID included in the beam identifying signal received by the antenna unit 44. The common beam identifying signal receiving unit 45 extracts local maximum values ​​based on the reception quality of the beam identifying signal for each beam ID measured by the digital signal processing unit 42, and extracts K beam IDs, which is the number of peaks, as candidate beam IDs (step S501). The common beam identifying signal receiving unit 45 outputs the extracted K candidate beam IDs to the feedback signal transmission instruction unit 46a.

[0214] The feedback signal transmission instruction unit 46a initializes the value of a counter j that counts candidate beam IDs for which a feedback signal is to be transmitted, setting j = 0 (step S502). Next, the feedback signal transmission instruction unit 46a increments the value of the counter j by 1, setting j ← j + 1, in order to count the next candidate beam ID (step S503).

[0215] The feedback signal transmission instruction unit 46a outputs a feedback transmission instruction, which is an instruction to transmit a feedback signal at a timing pre-assigned to the i-th beam among the extracted K candidate beam IDs, to the digital signal processing unit 22. As a result, the digital signal processing unit 22 transmits the feedback signal from each antenna unit 44 at the timing pre-assigned to the i-th beam (step S504).

[0216] The feedback signal transmission instruction unit 46a determines whether the transmission of the feedback signal for each beam corresponding to the extracted K candidate beam IDs has been completed (step S505). If the feedback signal transmission instruction unit 46a determines that the transmission of the feedback signal has not been completed (step S505-NO), the feedback signal transmission instruction unit 46a increments the value of the counter j by 1 to count the next candidate beam ID (step S503). Then, the processing from step S504 onwards is executed.

[0217] On the other hand, if the feedback signal transmission instruction unit 46a determines that the transmission of the feedback signal has been completed (step S505-YES), the data transmission instruction unit 48 performs data transmission with the base station apparatus Ba (step S506).

[0218] According to the distributed antenna system 1 of the second embodiment configured as described above, the base station device Ba is equipped with: a first beam search instruction unit 24 that instructs the execution of a beam search process in which beam identification signals including the same beam ID are simultaneously transmitted from multiple distributed antenna devices 30 to terminal devices 40a for each beam ID using transmission beams linked to the beam ID; a feedback signal receiving unit 25a that forms a reception beam at a timing pre-assigned for each transmission beam linked to the beam ID and receives, via the multiple distributed antenna devices 30, feedback signals corresponding to each of multiple candidate beam IDs selected based on the reception quality of the beam identification signal for each beam ID in the terminal device 40a; and a data transmission instruction unit 28 that determines a combination of the distributed antenna device 30 and the transmission beam to be used for wireless communication with the terminal device 40 based on the multiple feedback signals received by the feedback signal receiving unit 25a.

[0219] In this way, the base station device Ba detects the reception qualities of the multiple distributed antenna devices 30 while forming reception beams for beams corresponding to K candidate beam IDs. This makes it possible to obtain reception quality information equal to K x the number of distributed antenna devices 30 x the number of terminal devices 40a. As a result, it is possible to determine the beam to be used during multi-user MIMO.

[0220] Furthermore, the terminal device 40 is equipped with a common beam identification signal receiving unit 45 that extracts multiple candidate beam IDs that satisfy conditions indicating good reception quality based on the reception quality of beam identification signals including the same beam ID that are transmitted simultaneously for each beam ID from multiple distributed antenna devices 30 provided in the base station device using transmission beams linked to the beam IDs, and a feedback signal transmission instruction unit 46a that transmits feedback signals at pre-assigned timings for each reception beam linked to each of the multiple candidate beam IDs.

[0221] In this way, the terminal device 40a extracts the top K candidate beam IDs with the best reception quality based on the reception quality of beam-specific signals containing the same beam ID simultaneously transmitted from each distributed antenna device 30. Then, the terminal device 40a transmits a feedback signal at a timing assigned in advance for each reception beam associated with each candidate beam ID. This allows the base station device Ba to be notified of the beam ID with the best reception quality. As a result, the base station device Ba can obtain the spatial multiplexing effect using distributed MIMO.

[0222] (Variation 1 of the Second Embodiment) In the above-described embodiment, a method of extracting a local maximum value was shown as a peak detection method, but a peak may also be detected by selecting a beam ID close to the center of gravity position using machine learning clustering.

[0223] (Variation 2 of the Second Embodiment) In the above-described embodiment, the terminal device 40 has been configured to extract the local maximum value and select the top K beam IDs as candidate beam IDs. The terminal device 40 may select the top K candidate beam IDs in terms of the reception quality of all beam IDs instead of the local maximum value, or may extract candidate beams based on the local maximum value, and then extract as a new candidate beam direction the maximum value from among the beam directions whose angle difference with the nearest candidate beam is equal to or greater than a set angle threshold and whose level difference with the nearest candidate beam is within a set level difference threshold, and continue extracting candidate beams until there are no more beam directions that satisfy the above conditions.

[0224] (Variation 3 of the Second Embodiment) In the above-described embodiment, the terminal device 40a selects the top K beam IDs, but the number of candidate beam IDs does not have to be K. For example, the terminal device 40a may set a number to be further extracted from the K and select candidate beam IDs, or may set the number to be extracted and then select only beam IDs that exceed a threshold value for reception quality as candidate beam IDs.

[0225] (Variation 4 of the Second Embodiment) In the above-described embodiment, the terminal device 40a selects the top K beam IDs. However, the terminal device 40a may control the number K of candidate beam IDs to be extracted based on the number of distributed antenna devices 30 to be simultaneously searched, which is notified in advance by the base station device Ba. For example, the terminal device 40a may estimate that there are the same number of strong paths as the number of distributed antenna devices 30, and set the number K of extracted paths to the number of distributed antenna devices 30. Furthermore, for example, in an environment with many reflected waves, the terminal device 40a may detect the number K of extracted paths as being greater than the number of distributed antenna devices 30 (for example, the number of distributed antenna devices 30 + α) by assuming that there are a small number of reflected waves in addition to the number of distributed antenna devices 30. This notification method may use signals in a low frequency band, or, if a connection has been established with the terminal in advance, may use signals at that frequency, or may use another wireless communication system.

[0226] (Fifth Modification of the Second Embodiment) The terminal device 40a may feed back a feedback signal using an omnidirectional antenna, or may form a beam in a direction searched in advance and feed back the signal if the antenna unit 44 has directionality, or may feed back the signal while searching in multiple directions. Furthermore, the terminal device 40a may feed back a feedback signal in a different frequency band to which a connection has been established, or may feed back the signal using another wireless communication system.

[0227] (Variant 6 in the second embodiment) The terminal device 40a transmits a feedback signal carrying K-1 candidate beam IDs only at the timing of feedback of the optimal beam among the K candidate beams, and the base station device Ba may separately perform a beam search using individual beam identification signals from the candidate distributed antenna device, as in the first embodiment.

[0228] (Variant 7 in the second embodiment) As a method of notifying a terminal device 40a that simultaneous searches are being performed by multiple distributed antenna devices 30, the base station device Ba may attach a flag to a common beam identification signal indicating that simultaneous searches are being performed, or may use a signal in a low frequency band, or if the terminal device 40a has previously established a connection with the terminal device 40a, may use a signal in that frequency, or may use another wireless communication system.

[0229] (Variant 8 in the second embodiment) When there are multiple terminal devices 40a, the data may be fed back to each terminal device 40a in a time-division manner, in a frequency-division manner, separated by code multiplexing and fed back, or fed back by random access.

[0230] The base station devices B, Ba in each of the above-described embodiments can be interpreted as a "base station (BS)," a "wireless base station," a "fixed base station," a "NodeB," an "eNodeB," a "gNodeB," an "access point," a "transmission point (TP)," a "reception point (RP)," a "transmission / reception point (TRP)," a "distributed antenna (DA)," a "cell," a "sector," a "macrocell," a "small cell," a "femtocell," and a "picocell."

[0231] (Variant 1 common to the first and second embodiments) In each of the above embodiments, a configuration is shown in which all distributed antenna devices 30 transmit the same beam-identifying signal simultaneously, but it may also be configured so that some of the distributed antenna devices 30 transmit the same beam-identifying signal.

[0232] (Modification 2 common to the first and second embodiments) In each of the above embodiments, depending on the terminal device 40, 40a, there may be cases where improving received power takes priority over improving capacity through spatial multiplexing. Therefore, the base station device B, Ba may transmit, together with the beam ID, a flag indicating whether or not to execute the feedback process of the present invention.

[0233] (Variation 3 common to the first and second embodiments) In S1-6, a method was shown in which K peaks, which are the number of peaks when extracting local maxima, are selected from the top. However, the number of peaks selected from the top may be determined taking into consideration the number of distributed antennas around the terminal notified in advance by the base station. For example, the number may be the same as the number of distributed antennas, or may be greater than the number of distributed antennas, taking into consideration the possibility that adjacent beam directions of the same distributed antenna may be detected but the direction of a different distributed antenna may not be detected. As a notification method, if a connection has not yet been established in that frequency band, notification may be made in a different frequency band in which a connection has been established, or notification may be made using another wireless communication system. If a connection has already been established in that frequency band, notification may be made in advance.

[0234] (Variation 4 common to the first and second embodiments) The terminal device 40a may receive beam identification signals (common beam identification signals) including the same beam ID simultaneously transmitted from each distributed antenna device 30 for each candidate beam of the terminal device 40a. In this case, when selecting the top K beam IDs, the terminal device 40a extracts and links the candidate beams of the terminal device 40a that have the highest reception quality for each candidate beam of the distributed antenna device 30, and then selects the top K beam IDs based on the highest reception quality for each candidate beam of the distributed antenna device 30. Furthermore, the terminal device 40a may transmit and receive signals using beams that are linked in advance at timings corresponding to the signals transmitted and received for each of the top K beam IDs. However, when the terminal device 40a receives signals using the beams that are linked in advance, the timings at which signals linked to the top K beam IDs are transmitted from each distributed antenna device 30 must be communicated to the terminal device 40a in advance. However, a method in which the signals are transmitted at a timing requested by the terminal device 40a may be used, or each distributed antenna device 30 may communicate the signals to the terminal device 40a in advance. This notification method may be a notification in a different frequency band to which a connection has already been established, or may be a notification using another wireless communication system. Notification may also be made in advance in that frequency band.

[0235] The digital-analog signal processing devices 20, 20a and the terminal devices 40, 40a in the first and second embodiments described above may be partially or entirely implemented by a computer. In this case, a program for implementing these functions may be recorded on a computer-readable recording medium, and the program may be loaded into a computer system and executed. Note that the term "computer system" as used herein includes hardware such as an operating system (OS) and peripheral devices. Furthermore, the term "computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, read-only memories (ROMs), and CD-ROMs, as well as storage devices such as hard disks built into computer systems.

[0236] 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 certain 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 some of the above-mentioned functions, or one that can realize the above-mentioned functions in combination with a program already stored in the computer system, or one that can be realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0237] Although an embodiment of the present invention has been described in detail above 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.

[0238] The present invention can be applied to a distributed antenna system that performs beam search.

[0239] DESCRIPTION OF SYMBOLS 1...Distributed antenna system, 20, 20a...Digital / analog signal processing device, 30, 30-1 to 30-P...Distributed antenna device, 40, 40a...Terminal device, 21, 21a...Communication control unit, 22...Digital signal processing unit, 23...Analog signal unit, 24...First beam search instruction unit, 25, 25a...Feedback signal receiving unit, 26, 26a...Determination unit, 27...Second beam search instruction unit, 28...Data transmission instruction unit, 41, 41a...Terminal communication control unit, 42...Digital signal processing unit, 43...Analog signal unit, 44, 44-1 to 44-Q...Antenna unit, 45...Common beam identification signal receiving unit, 46, 46a...Feedback signal transmission instruction unit, 47...Individual beam identification signal receiving unit, 48, 48a...Data transmission instruction unit

Claims

1. A base station device comprising: a first beam search instruction unit that instructs the execution of a first beam search process in which beam identification signals including the same beam identifier are simultaneously transmitted from multiple antennas to a radio station for each beam identifier using transmission beams linked to the beam identifier; a second beam search instruction unit that instructs the execution of a second beam search process in which, based on a report signal including a selected beam identifier indicating multiple beam identifiers selected based on the reception quality of the beam identification signal for each beam identifier at the radio station obtained by the first beam search process, a beam identification signal including the selected beam identifier is individually transmitted for each selected beam identifier from at least the multiple antennas; and a transceiver unit that determines a combination of antennas and transmission beams to be used for wireless communication with the radio station based on the results of the first beam search process and the results of the second beam search process.

2. A base station device comprising: a beam search instruction unit that instructs the execution of a beam search process in which beam identification signals including the same beam identifier are simultaneously transmitted from multiple antennas to a radio station for each beam identifier using transmission beams linked to the beam identifier; a report signal receiving unit that forms a reception beam at a pre-assigned timing for each transmission beam linked to the beam identifier and receives, via the multiple antennas, a report signal corresponding to each of multiple beam identifiers selected based on the reception quality of the beam identification signal for each beam identifier at the radio station; and a transceiver unit that determines a combination of antennas and transmission beams to be used for wireless communication with the radio station based on the multiple report signals received by the report signal receiving unit.

3. A terminal device comprising: a first beam identification signal receiving unit that extracts multiple first beam identifiers that satisfy a condition indicating that high transmission capacity is expected based on the reception quality of beam identification signals including the same beam identifier that are transmitted simultaneously for each beam identifier from multiple antennas provided in a base station device by transmission beams linked to the beam identifier; and a second beam identification signal receiving unit that extracts one or more second beam identifiers that satisfy a condition indicating that high transmission capacity is expected at each of the multiple antennas based on the reception quality of beam identification signals that include at least any first beam identifier of the multiple first beam identifiers that are transmitted at different times from the multiple antennas by transmission beams linked to each of the multiple first beam identifiers.

4. A terminal device comprising: a beam identification signal receiving unit that extracts multiple beam identifiers that satisfy conditions indicating that high transmission capacity is expected based on the reception quality of beam identification signals including the same beam identifier that are transmitted simultaneously for each beam identifier from multiple antennas provided in a base station device using transmission beams linked to the beam identifiers; and a report signal transmitting unit that transmits report signals at pre-assigned timings for each reception beam linked to each of the multiple beam identifiers.

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