Communication control method and communication control device

Abstract

Provided is a communication control method including: a transmission step of simultaneously transmitting, from multiple antennas to a radio station, beam identification signals including the same beam identifier for each of multiple beam identifiers by using a transmission beam associated with the beam identifier; a reception step of receiving, by each of the multiple antennas, a report signal including a selected beam identifier indicating one of the beam identifiers selected on the basis of the reception quality, at the radio station, of the beam identification signals for each of the beam identifiers; and a selection step of selecting an antenna for communication with the radio station on the basis of the reception quality of the report signal received by each of the multiple antennas and selecting a transmission beam associated with the selected beam identifier for communication with the radio station.

Description

[Technical field]

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

[0002] 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 the terahertz band, the free space propagation loss is large compared to low frequency bands such as the microwave band, so it is necessary to use beamforming to compensate for the free space propagation loss (for example, see Non-Patent Document 1).

[0003] In the case of PP (Point-to-Point) type communication in which the combination of wireless stations communicating with each other is always fixed, and in the case where the relative positions of the wireless stations and the propagation environment around the wireless stations do not change, beam forming can use a fixed beam formed in a specific direction in advance when the wireless stations are installed, etc. However, in the case of P-MP (Point-to-Multi Point) type communication in which multiple wireless stations are accommodated, or in the case where at least one of the wireless stations communicating with each other moves, the appropriate direction of beam formation changes, and therefore the fixed beam formed in a specific direction cannot be used.

[0004] In such a case, it is necessary to control the beam forming direction to change adaptively 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 forming direction in this way is called adaptive beamforming. Generally, adaptive beamforming does not require a mechanical drive unit to change the beam forming direction. In adaptive beamforming, a directional beam is formed by adjusting the phase relationship of radio waves radiated from multiple antenna elements.

[0005] However, in order to appropriately adjust this phase relationship, it is necessary to grasp the phase relationship for each combination of multiple antenna elements of the transmitting wireless station and multiple antenna elements of 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 on the transmitting side and antenna elements on the receiving side.

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

[0007] For this reason, in general adaptive beamforming, multiple discretely set beams are set in advance. Each of the multiple beams is associated with a beam ID (identifier) ​​that can uniquely identify the beam. For example, in adaptive beamforming, a beam-specific signal including a beam ID is transmitted and received between both wireless stations by the 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 the beam are identified between both wireless stations. Adaptive beamforming can suppress an increase in overhead by such beam selection.

[0008] The above-mentioned beam selection is defined in 3GPP (Third Generation Partnership Project) 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 (see, for example, Non-Patent Documents 1, 2, and 3).

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

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

[0011] As the beam identification signal, for example, a beam search signal including a beam ID (Identifier) ​​for identifying a beam used by one of the wireless stations can be used. The beam search signal here is, for example, a signal defined in the SSW (Sector Sweep Frame) defined in IEEE802.11ay (see, for example, Non-Patent Document 6) or the SS / PBCH (Synchronization Signal / Physical Broadcast Channel) defined in 5G (see, for example, Non-Patent Document 2).

[0012] A typical system configuration of a conventional wireless communication system is shown in Fig. 13. As shown in Fig. 13, a digital signal processing device that transmits and receives signals and a base station antenna are connected to each other on a one-to-one basis. That is, in this case, one cell is formed for one base station antenna. In this configuration, one terminal device is connected to the only one base station antenna in the cell.

[0013] Here, as described above, beamforming technology is used in high frequency bands such as the millimeter wave band and the terahertz band, so the influence of reflected waves and diffracted waves is reduced. On the other hand, in this case, there is a characteristic that the possibility of communication being interrupted increases when the line of sight between wireless stations is blocked. In this way, in the case of a conventional cell configuration, the possibility of communication being interrupted increases when the line of sight from one base station antenna is blocked. Therefore, in wireless communication using high frequency bands, the use of a wireless communication system using distributed antennas (hereinafter referred to as a "distributed antenna system") that has the effect of improving shielding resistance is being considered (for example, see Non-Patent Documents 4 and 5, and Patent Document 1).

[0014] A typical system configuration of a conventional distributed antenna system is shown in Fig. 14. As shown in Fig. 14, digital signal processing devices that transmit and receive signals and distributed antennas are connected to each other in a one-to-many relationship. That is, in the distributed antenna system, one cell is formed by multiple distributed antennas. In this configuration, one terminal device is connected to any one of multiple distributed antennas that exist in the cell.

[0015] As shown in Fig. 14, a communication control device is connected to the digital signal processing device. The communication control device controls distributed antennas connected to each terminal device via wireless communication, and controls beams used by the distributed antennas. Particularly in a cellular communication system, the communication control device is used for centralized control. In this case, the communication control device further performs processes such as user scheduling and resource control.

[0016] With such a distributed antenna system, even if a terminal device is blocked from the line of sight of one distributed antenna in a cell, the terminal device can wirelessly connect to other distributed antennas in the cell. In order to realize such a distributed antenna system, in addition to selecting an optimal beam, it is necessary to select an optimal distributed antenna from among multiple distributed antennas in a cell. Hereinafter, the selection of the optimal distributed antenna and the optimal beam is referred to as "antenna beam selection."

[0017] Generally, antenna beam selection in a distributed antenna system is performed in the following procedure. First, one wireless station (e.g., an accommodating station) transmits a beam-specific signal to the other wireless station (e.g., a terminal device). Here, the one wireless station sweeps so that the beam-specific signals transmitted by each beam do not interfere with each other, as shown in Fig. 15. Fig. 15 is a schematic diagram showing an overview of sweeping by a conventional distributed antenna system.

[0018] Next, the other wireless station measures the reception quality of each beam-specific signal transmitted by each distributed antenna and each beam in turn. The other wireless station identifies, for example, the beam-specific signal with the best reception quality. The other wireless station transmits a feedback signal indicating the identification result to the one wireless station. With the above configuration, the one wireless station can recognize which beam of which distributed antenna is optimal to use when transmitting data to the other wireless station. [Prior art documents] [Patent documents]

[0019] [Patent Document 1] JP 2019-207210 A [Non-patent literature]

[0020] [Non-Patent Document 1] “5G Multi-Antenna Technology,” NTT DOCOMO Technical Journal, Vol. 23, No. 4, pp. 30-39, January 2016. [Non-Patent Document 2] Kazuaki Takeda et al., "Status of study on physical layer elemental technologies and high frequency band utilization in 5G," NTT DOCOMO Technical Journal, Vol. 25, No. 3, pp. 23-32, October 2017. [Non-Patent Document 3] Koji Takinami et al., "Standardization Trends and Elemental Technologies of Millimeter-Wave Wireless LAN Systems," Communications Society Magazine, Institute of Electronics, Information and Communication Engineers, No. 38, Autumn, pp. 100-106, 2016. [Non-Patent Document 4] Daisei Uchida et al., "A Study on High-Frequency Distributed Antenna System in High-Density / Shielded Environments," Proceedings of the IEICE General Conference, Communications Lecture Series 1, B-5-87, p.375, March 2020 [Non-Patent Document 5] Masashi Iwabuchi et al., "Proposal of High-Frequency Band Multipath Formation Control Using Multiple Diverse Relay Systems," Proceedings of the IEICE General Conference, Communications Lecture Series 1, B-5-101, p.389, March 2020 [Non-Patent Document 6] Y. Ghasempour, et al., "IEEE 802.11ay: Next-Generation 60 GHz Communication for 100 Gb / s Wi-Fi," in IEEE Communications Magazine, Vol.55, No.12, pp.186-192, December 2017. Summary of the Invention [Problem to be solved by the invention]

[0021] As shown in Figure 15, in a distributed antenna system using high frequency bands in which multiple distributed antennas are arranged for one cell, it is necessary to perform antenna beam selection by sweeping each distributed antenna in order so that the beam-specific signals transmitted from each of the multiple distributed antennas do not interfere with each other. Therefore, the time required for beam selection becomes longer, especially when the number of distributed antennas increases. This causes the problem of increased overhead and reduced data transmission efficiency.

[0022] In addition, in general, a distributed antenna system using a high frequency band needs to periodically perform beam selection at an appropriate frequency in order to follow the propagation path fluctuations caused by the movement of a terminal device and changes in the surrounding environment. However, if the time required for one beam selection becomes too long due to an increase in the number of distributed antennas, the time required for the beam selection may become longer than the execution period of the beam selection. In this case, it becomes impossible to complete the beam selection within the execution period of the beam selection, making it difficult to carry out the data transmission itself.

[0023] In view of the above circumstances, an object of the present invention is to provide a communication control method and a communication control device that can perform beam selection without increasing the time required for beam selection when the number of distributed antennas is increased. [Means for solving the problem]

[0024] One aspect of the present invention is a communication control method comprising: a transmitting step of simultaneously transmitting beam identifying signals including the same beam identifier from multiple antennas to a wireless station for each beam identifier using a transmission beam linked to the beam identifier; a receiving step of receiving, by the multiple antennas, a report signal including a selected beam identifier indicating a beam identifier selected based on the reception quality of the beam identifying signal for each beam identifier at the wireless station; and a selection step of selecting an antenna to be used for communication with the wireless station based on the reception quality of the report signal received by the multiple antennas, and selecting a transmission beam linked to the selected beam identifier as the transmission beam to be used for communication with the wireless station.

[0025] One aspect of the present invention is a communication control method comprising: a transmitting step of transmitting a beam identifying signal from multiple antennas to a radio station using multiple transmission beams in sequence at a predetermined transmission timing for each of the transmission beams; a receiving step of receiving, by the multiple antennas, a report signal including information based on a beam identifying signal selected based on the reception timing and reception quality of the beam identifying signal for each of the transmission beams at the radio station; and a selection step of selecting an antenna to be used for communication with the radio station based on the reception quality of the report signal received by the multiple antennas, and selecting a transmission beam to be used for communication with the radio station based on the information included in the report signal.

[0026] One aspect of the present invention is a communication control method for a wireless communication system having a first wireless station and a second wireless station, comprising: a first transmission step in which the first wireless station simultaneously transmits beam-specific signals including the same beam identifier from multiple antennas to a second wireless station for each beam identifier using a transmission beam linked to the beam identifier; a first reception step in which the second wireless station receives the beam-specific signals transmitted from the first wireless station for each beam identifier; and a second reception step in which the second wireless station selects a beam-specific signal from the multiple beam identifiers using a specific beam identifier based on a reception quality of the beam-specific signal for each beam identifier. A communication control method comprising: a first selection step of selecting a selected beam identifier; a second transmission step of the second radio station transmitting a report signal including the selected beam identifier to the first radio station; a second reception step of the first radio station receiving the report signal by each of the multiple antennas; and a second selection step of the first radio station selecting an antenna to be used for communication with the second radio station based on the reception quality of the report signal received by each of the multiple antennas, and selecting a transmission beam linked to the selected beam identifier as the transmission beam to be used for communication with the second radio station.

[0027] One aspect of the present invention is a communication control device that includes a transceiver unit that simultaneously transmits beam identification signals including the same beam identifier from multiple antennas to a radio station for each beam identifier using a transmission beam linked to the beam identifier, and receives a report signal using each of the multiple antennas including a selected beam identifier indicating a beam identifier selected based on the reception quality of the beam identification signal for each beam identifier at the radio station, and a selection unit that selects an antenna to be used for communication with the radio station based on the reception quality of the report signal received by each of the multiple antennas, and selects the transmission beam linked to the selected beam identifier as the transmission beam to be used for communication with the radio station.

[0028] One aspect of the present invention is a communication control device that includes a transceiver unit that uses multiple transmission beams in sequence to transmit a beam identifying signal from multiple antennas to a radio station at a predetermined transmission timing for each of the transmission beams, and receives a report signal by each of the multiple antennas, the report signal including information based on a beam identifying signal selected based on the reception timing and reception quality of the beam identifying signal for each of the transmission beams at the radio station, and a selection unit that selects an antenna to use for communication with the radio station based on the reception quality of the report signal received by each of the multiple antennas, and selects a transmission beam to use for communication with the radio station based on the information included in the report signal. Effect of the Invention

[0029] According to the present invention, it becomes possible to perform beam selection without increasing the time required for beam selection even when the number of distributed antennas is increased. [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 is a block diagram showing a functional configuration of a communication control device 600 of a conventional distributed antenna system 6. [Diagram 2] FIG. 6 is a diagram showing beam assignment information 611 generated by a beam identifying signal transmission instruction unit 601 of a conventional distributed antenna system 6. [Diagram 3] FIG. 9 is a block diagram showing a functional configuration of a terminal device 900 in a conventional distributed antenna system 6. [Figure 4] 13 is a flowchart showing an operation of a communication control device 600 of a conventional distributed antenna system 6. [Diagram 5] 13 is a flowchart showing an operation of a terminal device 900 in a conventional distributed antenna system 6. [Figure 6] FIG. 1 is a schematic diagram showing an overview of beam selection by a distributed antenna system in a first embodiment of the present invention. [Figure 7] 1 is an overall configuration diagram of a distributed antenna system 1 according to a first embodiment of the present invention. [Figure 8]FIG. 2 is a block diagram showing a functional configuration of a communication control device 100 of the distributed antenna system 1 in the first embodiment of the present invention. [Figure 9] 1 is a diagram showing beam assignment information 111 generated by an identical beam search signal simultaneous transmission instruction unit 101 of a distributed antenna system 1 in a first embodiment of the present invention. FIG. [Figure 10] 5 is a flowchart showing an operation of the communication control device 100 of the distributed antenna system 1 in the first embodiment of the present invention. [Figure 11] FIG. 11 is a block diagram showing a functional configuration of a communication control device 100a in a distributed antenna system according to a second embodiment of the present invention. [Figure 12] 10 is a flowchart showing an operation of a communication control device 100a in a distributed antenna system in a second embodiment of the present invention. [Figure 13] FIG. 1 is a diagram showing a general system configuration of a conventional wireless communication system. [Figure 14] FIG. 1 is a diagram showing a general system configuration of a conventional distributed antenna system. [Figure 15] FIG. 1 is a schematic diagram showing an overview of a sweep by a conventional distributed antenna system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Hereinafter, a configuration of a distributed antenna system according to 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.

[0032] The following describes the overall configuration of the conventional distributed antenna system 6. As shown in Fig. 14, the distributed antenna system 6 includes a communication control device 600, a digital signal processing device 700, distributed antennas 800-1 to 800-4, and a plurality of terminal devices 900.

[0033] 14, the digital signal processing device 700 is connected to the communication control device 600 and distributed antennas 800-1 to 800-4. The communication control device 600 and the distributed antennas 800-1 to 800-4 are configured to be able to communicate with the digital signal processing device 700. Hereinafter, when there is no need to particularly distinguish the distributed antennas 800-1 to 800-4 from one another, they will simply be referred to as "distributed antenna 800."

[0034] The distributed antenna 800 is an antenna capable of performing adaptive beamforming. The distributed antenna 800 can perform wireless communication with the terminal device 900 by selectively using one of a plurality of types of beams.

[0035] The communication control device 600 is a control device for performing communication control related to beam selection, which selects a beam to be used in wireless communication between the distributed antennas 800-1 to 800-4 and the terminal device 900 from a plurality of beams.

[0036] Digital signal processing device 700 is a communication device that transmits and receives signals to and from terminal device 900 using distributed antennas 800-1 to 800-4.

[0037] The following describes the configuration of the communication control device 600. Fig. 1 is a block diagram showing the functional configuration of the communication control device 600 of the conventional distributed antenna system 6. As shown in Fig. 1, the communication control device 600 includes a beam identification signal transmission instruction unit 601, a feedback result receiving unit 602, an optimal antenna beam selecting unit 603, and an optimal antenna beam storing unit 604.

[0038] The beam identification signal transmission instruction unit 601 assigns an identifier (hereinafter, referred to as a "beam ID") to each beam so that all beams used in the distributed antennas 800-1 to 800-4 can be uniquely identified. An example of beam assignment information indicating the beam IDs assigned by the beam identification signal transmission instruction unit 601 is shown in FIG.

[0039] 2 is a diagram showing beam assignment information 611 generated by the beam identification signal transmission instruction unit 601 of the conventional distributed antenna system 6. The beam assignment information 611 is stored in, for example, the optimum antenna beam storage unit 604 or the like.

[0040] Beam assignment information 611 shown in FIG. 2 is an example of beam assignment information generated when the number of distributed antennas is m and the number of beams used by each distributed antenna is n.

[0041] 2, the beam identification signal transmission instruction unit 601 assigns beam IDs from #1 to #n to each of the n types of beams formed by the first distributed antenna (distributed antenna #1). Next, the beam identification signal transmission instruction unit 601 assigns beam IDs from #n+1 to #2×n to each of the n types of beams formed by the second distributed antenna (distributed antenna #2). The beam identification signal transmission instruction unit 601 repeats beam ID assignment in this manner, and finally assigns beam IDs from #(m-1)×n+1 to #m×n to each of the n types of beams formed by the mth distributed antenna (distributed antenna #m).

[0042] That is, the beam identification signal transmission instruction unit 601 assigns beam IDs from #(j-1)×n+1 to #j×n to each of the n types of beams formed by the j-th distributed antenna (distributed antenna #j). This allows the beam identification signal transmission instruction unit 601 to assign a beam ID that can uniquely identify each combination of multiple distributed antennas 800 and multiple beams.

[0043] The beam identifying signal transmission instruction unit 601 outputs a beam identifying signal transmission instruction, which is an instruction for transmitting a beam identifying signal from each of the distributed antennas 800-1 to 800-4, to the digital signal processing device 700. The beam identifying signal transmission instruction includes information indicating beam IDs assigned to all combinations of the multiple distributed antennas 800 and the multiple beams.

[0044] In response to receiving the beam identifying signal transmission instruction, the digital signal processing device 700 transmits a beam identifying signal using each beam from the distributed antennas 800-1 to 800-4. Each beam identifying signal to be transmitted is a beam search signal including information indicating a beam ID associated with the combination of the distributed antenna 800 and the beam used to transmit the beam identifying signal.

[0045] The feedback result receiving unit 602 acquires information indicating an optimal beam ID contained in the feedback signal from the digital signal processing device 700. The feedback signal is transmitted from the terminal device 900, received by the distributed antenna 800, and then decoded by the digital signal processing device 700. The feedback result receiving unit 602 outputs information indicating the acquired optimal beam ID to the optimal antenna / beam selecting unit 603.

[0046] The optimal beam ID is, for example, a beam ID included in a beam identifying signal having the best reception quality among beam identifying signals received by the terminal device 900. The reception quality here is, for example, a value of reception power or received signal strength (RSSI: Received Signal Strength Indicator), etc.

[0047] The optimum antenna / beam selector 603 acquires the optimum beam ID output from the feedback result receiver 602. The optimum antenna / beam selector 603 refers to the beam assignment information 611 and identifies a combination of a distributed antenna 800 and a beam linked to the optimum beam ID. The optimum antenna / beam selector 603 stores information indicating the identified combination of a distributed antenna 800 and a beam in the optimum antenna / beam storage unit 604.

[0048] The optimum antenna / beam storage unit 604 stores information indicating the combination of the specified distributed antenna 800 and beam. The digital signal processing device 700 performs wireless communication with the terminal device 900 using the distributed antenna 800 and beam stored in the optimum antenna / beam storage unit 604. The optimum antenna / beam storage unit 604 may store beam ID assignment information 611 shown in FIG. 9.

[0049] With the above-described configuration, on the distributed antenna 800 side (accommodating station side), settings are made so that a signal is transmitted to the terminal device 900 using the distributed antenna 800 and beam associated with the optimal beam ID.

[0050] The configuration of the terminal device 900 will be described below. Fig. 3 is a block diagram showing the functional configuration of the terminal device 900 of the conventional distributed antenna system 6. The terminal device 900 is an information processing device such as a smartphone, a tablet terminal, or a notebook PC. As shown in Fig. 3, the terminal device 900 includes an antenna unit 901, a digital signal processing unit 902, an optimal beam ID selection unit 903, and a feedback signal transmission instruction unit 904.

[0051] The antenna unit 901 receives a radio signal transmitted from the distributed antenna 800. For example, the antenna unit 901 receives a beam-specific signal transmitted from the distributed antenna 800. The antenna unit 901 outputs the received radio signal to the digital signal processing unit 902.

[0052] Furthermore, the antenna unit 901 acquires a feedback signal, described later, output from the digital signal processing unit 902. The antenna unit 901 transmits the acquired feedback signal to the distributed antenna 800 (the accommodating station side).

[0053] The digital signal processing unit 902 acquires the radio signal output from the antenna unit 901. The digital signal processing unit 902 also measures the reception quality of the beam-specific signal received by the antenna unit 901 for each beam ID contained in the beam-specific signal. As described above, the reception quality is, for example, a value such as received power or received signal strength. The digital signal processing unit 902 outputs information indicating the measurement result of the reception quality of the beam-specific signal for each beam ID to the optimal beam ID selection unit 903.

[0054] Furthermore, the digital signal processing unit 902 acquires a feedback signal transmission instruction output from a feedback signal transmission instruction unit 904. The feedback signal transmission instruction includes information indicating an optimal beam ID. Upon acquiring the feedback signal transmission instruction, the digital signal processing unit 902 generates a feedback signal including information indicating an optimal beam ID. The digital signal processing unit 902 outputs the generated feedback signal to the antenna unit 901.

[0055] The optimal beam ID selection unit 903 acquires information indicating the measurement result of the reception quality of the beam-specific signal for each beam ID output from the digital signal processing unit 902. The optimal beam ID selection unit 903 identifies an optimal beam ID, which is, for example, a beam ID included in a beam-specific signal having the best reception quality. The optimal beam ID selection unit 903 outputs information indicating the identified optimal beam ID to the feedback signal transmission instruction unit 904.

[0056] The feedback signal transmission instruction unit 904 acquires information indicating the optimal beam ID output from the optimal beam ID selection unit 903. The feedback signal transmission instruction unit 904 outputs, to the digital signal processing unit 902, a feedback signal transmission instruction, which is an instruction for transmitting, to the distributed antenna 800, a feedback signal including the information indicating the optimal beam ID.

[0057] Hereinafter, a description will be given of an example of the operation of the communication control device 600 in selecting an antenna beam in the conventional distributed antenna system 6. Fig. 4 is a flowchart showing the operation of the communication control device 600 of the conventional distributed antenna system 6.

[0058] First, the beam identification signal transmission instruction unit 601 determines the value of the number m of distributed antennas 800 that perform beam selection and the value of the number n of beams used by each distributed antenna 800 (step S001). At this time, as shown in Fig. 2, the beam identification signal transmission instruction unit 601 assigns a beam ID that can uniquely identify each combination of multiple distributed antennas 800 and multiple beams.

[0059] Next, the beam identifying signal transmission instruction unit 601 initializes the value of a counter j that counts the distributed antennas 800 that are to transmit a beam identifying signal, setting j to 0 (step S002).

[0060] Next, in order to cause the next distributed antenna 800 to transmit a beam identifying signal, the beam identifying signal transmission instruction unit 601 increments the value of the counter j by 1, setting j←j+1 (step S003).

[0061] Next, the beam identifying signal transmission instruction unit 601 initializes the value of a counter i that counts the beams for which a beam identifying signal is to be transmitted, setting i=0 (step S004).

[0062] Next, the beam identifying signal transmission instruction unit 601 increments the value of counter i by 1 to make i←i+1 in order to cause the distributed antenna 800 to transmit a beam identifying signal with the next beam (i.e., to sweep the beam) (step S005).

[0063] Next, the beam identifying signal transmission instruction unit 601 outputs a beam identifying signal transmission instruction, which is an instruction to transmit a beam identifying signal including information indicating a beam ID linked to the combination of the jth distributed antenna 800 and the ith beam by the jth distributed antenna 800 using the ith beam, to the digital signal processing device 700 (step S006).

[0064] The beam identifying signal transmission instruction unit 601 repeats outputting a beam identifying signal transmission instruction to the digital signal processing device 700 (steps S005 to S007) until the beam identifying signal is transmitted in sequence by all n types of beams, starting from the jth distributed antenna 800 (i.e., until i = n).

[0065] Furthermore, the beam identifying signal transmission instruction unit 601 repeats outputting the beam identifying signal transmission instruction to the digital signal processing device 700 (steps S003 to S008) until beam identifying signals are transmitted from all m distributed antennas 800 using n types of beams (i.e., until j = m).

[0066] Next, the feedback result receiving unit 602 waits for a feedback signal transmitted from the terminal device 900 in response to the transmitted beam identification signal to be received by the distributed antenna 800 (step S009). Here, the feedback signal includes information indicating the optimal beam ID as described above.

[0067] In addition, the feedback signal transmitted from the terminal device 900 is simultaneously received, for example, by each distributed antenna 800 used in transmitting the beam-specific signal, using an omnidirectional or low-directional beam.

[0068] Next, when the feedback signal is received by the distributed antenna 800 (step S009: YES), the feedback result receiving unit 602 acquires the optimum beam ID contained in the received feedback signal. The feedback result receiving unit 602 outputs the acquired optimum beam ID to the optimum antenna beam selecting unit 603.

[0069] The optimum antenna / beam selection unit 603 refers to the beam assignment information 611 and identifies a combination of the distributed antenna 800 and beam associated with the optimum beam ID. The optimum antenna / beam selection unit 603 stores information indicating the identified combination of the distributed antenna 800 and beam in the optimum antenna / beam storage unit 604 (step S010). This completes the operation of the communication control device 600 shown in the flowchart of FIG.

[0070] Hereinafter, a description will be given of an example of the operation of the terminal device 900 in antenna beam selection in the distributed antenna system 6. Fig. 5 is a flowchart showing the operation of the terminal device 900 in the conventional distributed antenna system 6.

[0071] First, the digital signal processing unit 902 waits for the antenna unit 901 to receive a beam identifying signal for each beam ID transmitted from each distributed antenna 800 (step S021).

[0072] In addition, the beam identifying signals for each beam ID transmitted from the distributed antenna 800 are sequentially received by the antenna unit 901 using, for example, an omnidirectional or low-directivity beam.

[0073] When a beam-specific signal for each beam ID transmitted from each distributed antenna 800 is received by the antenna unit 901 (step S021: YES), the digital signal processing unit 902 measures the reception quality of the beam-specific signal for each beam ID contained in the beam-specific signal received by the antenna unit 901.

[0074] The optimal beam ID selection unit 903 selects an optimal beam ID based on the reception quality of the beam identifying signal for each beam ID measured by the digital signal processing unit 902 (step S022). For example, the optimal beam ID selection unit 903 selects the beam ID included in the beam identifying signal having the best reception quality as the optimal beam ID.

[0075] Next, the feedback signal transmission instruction unit 904 outputs a feedback signal transmission instruction, which is an instruction for transmitting a feedback signal including information indicating the optimal beam ID to the distributed antenna 800, to the digital signal processing unit 902. The digital signal processing unit 902 generates a feedback signal including information indicating the optimal beam ID. The antenna unit 901 transmits the generated feedback signal to the distributed antenna 800 (step S023). This completes the operation of the terminal device 900 shown in the flowchart of FIG. 5.

[0076] <First embodiment> A first embodiment of the present invention will now be described.

[0077] In the above-mentioned conventional distributed antenna system 6, the time required for beam selection increases proportionately as the number of distributed antennas 800 increases. For example, when q types of beams are used in each distributed antenna 800, if the number of distributed antennas 800 is increased by p, an additional time is required for transmitting the beam identifying signal p×q times.

[0078] In contrast, the distributed antenna system in the present embodiment described below can suppress the increase in time required for beam selection that accompanies an increase in distributed antennas. Fig. 6 is a schematic diagram showing an overview of beam selection by the distributed antenna system in the first embodiment of the present invention.

[0079] As shown in Fig. 6(A), the distributed antenna system in this embodiment transmits the same beam-specific signal simultaneously from multiple distributed antennas, respectively. This makes it possible for the distributed antenna system in this embodiment to increase the number of distributed antennas without increasing the time required for beam selection.

[0080] The distributed antenna system of this embodiment having the above configuration can include information (e.g., a beam ID for identifying a beam) that enables the receiving side (wireless terminal side) to identify the beam used to transmit the beam identifying signal in the beam identifying signal, like the above-mentioned conventional distributed antenna system 6. However, since the distributed antenna system of this embodiment transmits the same beam identifying signal simultaneously from multiple distributed antennas, the receiving side (wireless terminal side) cannot identify from which distributed antenna the received beam identifying signal was transmitted.

[0081] Therefore, as shown in Fig. 6(B), the distributed antenna system in this embodiment receives a feedback signal transmitted from a terminal device by each distributed antenna, and measures the reception quality of the feedback signal for each distributed antenna. Then, the distributed antenna system in this embodiment selects a distributed antenna that is optimal for wireless communication with the terminal device based on the measurement result. By having such a configuration, the distributed antenna system in this embodiment can perform beam selection without increasing the time required for beam selection even if the number of distributed antennas increases.

[0082] In addition, the distributed antenna system in this embodiment transmits the same beam-specific signal simultaneously from multiple distributed antennas, but when the terminal device receives the beam-specific signals transmitted from the multiple distributed antennas, the simultaneously transmitted beam-specific signals can be regarded as multipath interference. Therefore, by applying a multipath interference compensation technique used in a general wireless communication system to the distributed antenna system in this embodiment, it is possible to avoid deterioration in the quality of wireless communication. At this time, the setting may be made taking into consideration the arrival time difference of the beam-specific signals from multiple distributed antennas that utilize the allowable delay time difference of multipath interference.

[0083] Moreover, the distributed antenna system 1 in the first embodiment uses a beam search signal as a beam identifying signal. The beam search signal is a beam identifying signal including information indicating a beam ID. Specifically, a beam search signal including a beam ID for identifying a beam is transmitted from each distributed antenna to a terminal device by each beam. The terminal device can identify the beam ID associated with the beam used to transmit the beam search signal by receiving and decoding the beam search signal.

[0084] [Configuration of distributed antenna system] The overall configuration of the distributed antenna system 1 in this embodiment will be described below. Fig. 7 is an overall configuration diagram 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 multiple (four in Fig. 7) distributed antennas are arranged for one cell and communication is performed using a high frequency band.

[0085] 7, the distributed antenna system 1 includes a communication control device 100, a digital signal processing device 200, distributed antennas 300-1 to 300-4, and a plurality of terminal devices 400. The distributed antenna system 1 is a communication system equipped with a plurality of distributed antennas on the accommodating station side. However, the distributed antenna system is not limited to this configuration, and may be a distributed antenna system in which both of the opposing wireless stations each have a plurality of distributed antennas.

[0086] 7, the digital signal processor 200 is connected to the communication control device 100 and the distributed antennas 300-1 to 300-4. The communication control device 100 and the distributed antennas 300-1 to 300-4 are configured to be able to communicate with the digital signal processor 200. Hereinafter, when there is no need to particularly distinguish the distributed antennas 300-1 to 300-4 from one another, they will simply be referred to as "distributed antenna 300."

[0087] The distributed antenna 300 is an antenna capable of performing adaptive beamforming. The distributed antenna 300 can select one of a plurality of types of beams to communicate with the terminal device 400. In addition, in Fig. 7, three types of beams are formed by each distributed antenna 300, and are illustrated by dashed lines.

[0088] Here, the number of distributed antennas 300 is four, but it may be two, three, or five or more. Also, although five terminal devices 400 are shown in Fig. 7, the number of terminal devices 400 may be any number.

[0089] Each of the communication control device 100 and the digital signal processing device 200 includes an information processing device such as a general-purpose computer, etc. The communication control device 100 and the digital signal processing device 200 may be an integrated device.

[0090] The communication control device 100 is a control device that performs communication control related to beam selection, which selects from among beams a beam to be used in wireless communication between the distributed antennas 300-1 to 300-4 and the terminal device 400. In other words, the communication control device 100 is a control device that controls processing related to beam selection in adaptive beamforming performed by the digital signal processing device 200, which is a communication device, using the distributed antennas 300-1 to 300-4.

[0091] The digital signal processing device 200 is a communication device that transmits and receives radio signals to and from the terminal device 400 by using the distributed antennas 300-1 to 300-4.

[0092] [Configuration of communication control device] The following describes the configuration of the communication control device 100. Fig. 8 is a block diagram showing the functional configuration of the communication control device 100 of the distributed antenna system 1 in the first embodiment of the present invention. As shown in Fig. 8, the communication control device 100 includes an identical beam search signal simultaneous transmission instruction unit 101, a distributed antenna feedback result receiving unit 102, an optimal antenna beam selecting unit 103, and an optimal antenna beam storing unit 104.

[0093] The same beam search signal simultaneous transmission instruction unit 101 assigns a beam ID, which is an identifier for uniquely identifying all beams used in the distributed antennas 300-1 to 300-4, to each beam. An example of beam assignment information indicating the beam ID assigned by the same beam search signal simultaneous transmission instruction unit 101 is shown in FIG.

[0094] Fig. 9 is a diagram showing beam assignment information 111 generated by the same beam search signal simultaneous transmission instruction unit 101 of the distributed antenna system 1 in the first embodiment of the present invention. As shown in Fig. 9, the beam assignment information 111 is table-format data in which combinations of distributed antennas 300 and beams are associated with beam IDs. The beam assignment information 111 is stored, for example, in the optimal antenna / beam storage unit 104 or the like.

[0095] The beam allocation information 111 shown in Fig. 9 is an example of beam allocation information generated when the number of distributed antennas is m and the number of beams used by each distributed antenna is n. For example, in the distributed antenna system 1 in this embodiment shown in Fig. 7, four distributed antennas 300 are configured to use three types of beams each, so in this case, m=4 and n=3.

[0096] 9, the same beam search signal simultaneous transmission instruction unit 101 assigns beam IDs #1 to #n to each of the n types of beams formed by the first distributed antenna (distributed antenna #1). Similarly, the same beam search signal simultaneous transmission instruction unit 101 assigns beam IDs #1 to #n to each of the n types of beams formed by the second to mth distributed antennas (distributed antennas #2 to #m).

[0097] That is, the same beam search signal simultaneous transmission instruction unit 101 assigns the same beam ID from #1 to #n to each of the n types of beams formed by each distributed antenna 300, regardless of which distributed antenna 300 forms the beam. In this way, the same beam search signal simultaneous transmission instruction unit 101 can assign beam IDs that can uniquely identify beams used to transmit beam search signals. However, the beam IDs assigned by the same beam search signal simultaneous transmission instruction unit 101 cannot identify the distributed antenna 300 used to transmit the beam search signal.

[0098] The same beam search signal simultaneous transmission instruction unit 101 outputs a beam search signal transmission instruction, which is an instruction for transmitting a beam search signal from each of the distributed antennas 300-1 to 300-4, to the digital signal processing device 200. The beam search signal transmission instruction includes information indicating a beam ID assigned to each beam.

[0099] In response to this beam search signal transmission instruction, the digital signal processing device 200 causes the distributed antennas 300-1 to 300-4 to simultaneously transmit beam search signals for each beam to which the same beam ID is assigned. Each transmitted beam search signal includes information indicating the beam ID associated with the beam used to transmit the beam search signal.

[0100] The distributed antenna feedback result receiving unit 102 acquires information indicating an optimal beam ID included in a feedback signal from the digital signal processing device 200. The feedback signal is transmitted from the terminal device 400, received by the distributed antenna 300, and then decoded by the digital signal processing device 200. The optimal beam ID is, for example, a beam ID included in a beam search signal having the best reception quality among beam search signals received by the terminal device 400.

[0101] Furthermore, the distributed antenna feedback result receiving unit 102 acquires information indicating measurement results of the reception quality of the feedback signal in each distributed antenna 300 from the digital signal processing device 200. Based on the acquired measurement results, the distributed antenna feedback result receiving unit 102 determines, for example, the distributed antenna 300 with the best reception quality as the optimal distributed antenna for wireless communication with the terminal device 400.

[0102] The distributed antenna feedback result receiving unit 102 outputs information indicating the acquired optimal beam ID and information identifying the distributed antenna determined as the optimal distributed antenna (hereinafter referred to as the "optimal antenna ID") to the optimal antenna / beam selecting unit 103.

[0103] The optimum antenna beam selection unit 103 acquires the optimum beam ID and the optimum antenna ID output from the distributed antenna-specific feedback result receiving unit 102. The optimum antenna beam selection unit 103 identifies the beam linked to the acquired optimum beam ID and the distributed antenna 300 linked to the optimum antenna ID. The optimum antenna beam selection unit 103 stores information indicating the identified combination of the distributed antenna 300 and the beam in the optimum antenna beam storage unit 104.

[0104] The optimum antenna / beam storage unit 104 stores information indicating a combination of the distributed antennas 300 and beams. The digital signal processing device 200 performs wireless communication with the terminal device 400 by using the combination of the distributed antennas 300 and beams stored in the optimum antenna / beam storage unit 104. The optimum antenna / beam storage unit 104 may store beam ID assignment information 111 shown in FIG. 9.

[0105] The optimal antenna beam storage unit 104 is composed of a storage medium such as a hard disk drive (HDD), flash memory, electrically erasable programmable read only memory (EEPROM), random access read / write memory (RAM), read only memory (ROM), or any combination of these storage media.

[0106] With the above-described configuration, the distributed antenna 300 (accommodating station) is configured to transmit a radio signal to the terminal device 400 using the distributed antenna 300 that had good reception quality of the feedback signal and the beam associated with the optimal beam ID.

[0107] [Terminal device configuration] The configuration of the terminal device 400 of the distributed antenna system 1 in this embodiment is basically similar to the configuration of the terminal device 900 of the conventional distributed antenna system 6 shown in FIG. 3 described above, and therefore a description thereof will be omitted.

[0108] [Operation of communication control device] Hereinafter, there will be described an example of the operation of the communication control device 100 in antenna beam selection of the distributed antenna system 1. Fig. 10 is a flowchart showing the operation of the communication control device 100 of the distributed antenna system 1 in the first embodiment of the present invention.

[0109] First, the same beam search signal simultaneous transmission instruction unit 101 determines the value of the number m of distributed antennas 300 that perform beam selection and the value of the number n of beams used by each distributed antenna 300 (step S101). At this time, as shown in Fig. 9, the same beam search signal simultaneous transmission instruction unit 101 assigns a beam ID that can uniquely identify each beam to each beam that is used simultaneously by the multiple distributed antennas 300 to transmit a beam search signal.

[0110] Next, the same beam search signal simultaneous transmission instruction unit 101 initializes the value of a counter i that counts the beams that transmit the beam search signal, setting i=0 (step S102).

[0111] Next, in order to transmit a beam search signal with the next beam (i.e., to sweep the beams), the same beam search signal simultaneous transmission instruction unit 101 increments the value of the counter i by 1, setting it to i←i+1 (step S103).

[0112] Next, the same beam search signal simultaneous transmission instruction unit 101 outputs a same 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 m distributed antennas 300 using the i-th beam, to the digital signal processing device 200 (step S104).

[0113] The same beam search signal simultaneous transmission instruction unit 101 repeats output of the same beam search signal simultaneous transmission instruction to the digital signal processing device 200 until beam search signals are transmitted from all m distributed antennas 300 using n types of beams (i.e., until i = n) (steps S103 to S105).

[0114] Next, the distributed antenna feedback result receiving unit 102 waits for the feedback signal transmitted from the terminal device 400 in response to the transmitted beam search signal to be received by all of the m distributed antennas 300 (step S106). Here, the feedback signal includes information indicating the optimal beam ID.

[0115] The feedback signal transmitted from the terminal device 400 may be received simultaneously by, for example, each of the distributed antennas 300 used in transmitting the beam search signal, using an omnidirectional or low-directional beam.

[0116] Next, when the feedback signal is received by all m distributed antennas 300 (step S106: YES), the distributed antenna-specific feedback result receiving unit 102 acquires information indicating an optimum beam ID contained in the feedback signal from the digital signal processing device 200. The distributed antenna-specific feedback result receiving unit 102 outputs the acquired optimum beam ID to the optimum antenna / beam selecting unit 103. The optimum antenna / beam selecting unit 103 stores information indicating the beam associated with the optimum beam ID in the optimum antenna / beam saving unit 104 (step S107).

[0117] Next, the distributed antenna feedback result receiving unit 102 acquires information indicating the measurement results of the reception quality of the feedback signal in each distributed antenna 300 from the digital signal processing device 200. Based on the acquired measurement results, the distributed antenna feedback result receiving unit 102 determines, for example, the distributed antenna 300 with the best reception quality as the optimal distributed antenna for wireless communication with the terminal device 400.

[0118] The distributed antenna feedback result receiver 102 outputs information indicating the distributed antenna 300 determined as the optimal distributed antenna to the optimal antenna beam selector 103. The optimal antenna beam selector 103 stores the acquired information indicating the distributed antenna 300 in the optimal antenna beam storage unit 104 (step S108). This completes the operation of the communication control device 100 shown in the flowchart of FIG.

[0119] As described above, in the distributed antenna system 1 in the first embodiment of the present invention, the radio station on the distributed antenna 300 side (accommodating station side) generates, for each beam, a beam search signal in which a beam ID capable of uniquely identifying each beam used in the distributed antenna 300 is embedded as digital information. The radio station on the distributed antenna 300 side (accommodating station side) transmits each generated beam search signal simultaneously from each distributed antenna 300, superimposed on a beam associated with the beam ID formed by each distributed antenna 300, while switching over time for each beam ID.

[0120] However, in the distributed antenna system 1 in the first embodiment of the present invention, since the same beam search signal is transmitted from a plurality of distributed antennas 300, the beam search signal can include information for identifying the beam used in the transmission, but cannot include information for identifying the distributed antenna 300 used in the transmission. Therefore, in the distributed antenna system 1 in this embodiment, the feedback signal transmitted from the terminal device 400 is simultaneously received by each distributed antenna 300, the reception quality of the feedback signal is measured for each distributed antenna 300, and it is determined which distributed antenna 300 is optimal for wireless communication with the terminal device 400.

[0121] The terminal device 400 receives beam search signals simultaneously transmitted from each distributed antenna 300 for each beam ID, and measures the reception quality (e.g., received power). The terminal device 400 also reads out the beam ID included in the received beam search signal. Based on the measurement result of the reception quality of the beam search signal for each beam ID, the terminal device 400 identifies the beam ID included in the beam search signal having the best reception quality. The terminal device 400 embeds the identified beam ID in a feedback signal as an optimal beam ID. The terminal device 400 transmits a feedback signal including the optimal beam ID to the distributed antenna 300 side (the accommodating station side).

[0122] The distributed antenna 300 side (accommodating station side) receives a feedback signal transmitted from the terminal device 400 and reads out an optimal beam ID included in the received feedback signal. The distributed antenna 300 side (accommodating station side) performs setting so that the beam associated with the read optimal beam ID is used in wireless communication with the terminal device 400. The distributed antenna 300 side (accommodating station side) also receives the feedback signal transmitted from the terminal device 400 by all the distributed antennas 300. The distributed antenna 300 side (accommodating station side) identifies the distributed antenna 300 that received the feedback signal with the best reception quality (e.g., received power) among the feedback signals received by each distributed antenna 300. The distributed antenna 300 side (accommodating station side) performs setting so that the identified distributed antenna 300 is used in wireless communication with the terminal device 400.

[0123] As mentioned above, in the conventional wireless communication system using high frequency bands in which multiple distributed antennas are arranged for one cell, it was necessary for the multiple distributed antennas to sweep their beams at different time periods so that the beam search signals transmitted from each of the multiple distributed antennas would not interfere with each other. Therefore, especially when the number of distributed antennas increases, the time required for beam selection becomes longer, which increases overhead and reduces data transmission efficiency. In addition, the longer time required for beam selection makes it difficult to make the distributed antenna follow the directionality of the terminal device in response to its movement, which can make wireless communication between the distributed antenna side (accommodating station side) and the terminal device difficult.

[0124] In contrast, the distributed antenna system 1 in the first embodiment of the present invention has the above-mentioned configuration, and transmits beam search signals from the multiple distributed antennas 300 to the terminal device 400 at the same time, so that the transmission of the beam search signals from the multiple distributed antennas 300 can be completed in only the time required for one distributed antenna 300 to transmit the beam search signal. As a result, even if the number of distributed antennas 300 is increased, the distributed antenna system 1 in this embodiment does not require a long time for beam selection, so that overhead is not increased and data transmission efficiency is not reduced. Furthermore, even if the number of distributed antennas 300 is increased, the distributed antenna system 1 in this embodiment does not require a long time for beam selection, so that it is not difficult to make the directivity of the distributed antenna 300 follow the movement of the terminal device 400, and it is possible to prevent the wireless communication itself between the distributed antenna side (accommodating station side) and the terminal device from becoming difficult.

[0125] In the distributed antenna system 1 in this embodiment, the same beam search signal is simultaneously transmitted from the multiple distributed antennas 300, so that the terminal device 400 can regard it as multipath interference when receiving the same beam search signal transmitted from the multiple distributed antennas 300. This makes it possible to avoid deterioration of wireless quality due to multipath interference by using a multipath interference compensation technique used in general wireless communication systems.

[0126] In wireless communication systems, in order to compensate for multipath interference, it is common to apply equalization processing in terminal devices and a compensation technique for multipath interference by a communication method. For example, as a method for compensating for multipath interference, there is a method of using OFDM (Orthogonal Frequency Division Multiplexing) + GI (Guard Interval) to set the GI length to be equal to or greater than the multipath delay difference, and a method of performing SC (Single Carrier) + TDE (Time Domain Equalization) with a sufficient number of taps.

[0127] In the distributed antenna system 1 of the present embodiment, the number of beams used by the multiple distributed antennas 300 is the same, but a different number of beams may be used for each distributed antenna 300. In this case, there may be a beam search signal transmitted only by a distributed antenna 300 that uses a larger number of beams than the other distributed antennas 300.

[0128] In the distributed antenna system 1 in this embodiment, the beam search signals are transmitted simultaneously from all the distributed antennas 300. However, the beam search signals may be transmitted simultaneously from only some of the distributed antennas 300.

[0129] In the distributed antenna system 1 in the present embodiment, as an example, a case where beam selection is not performed on the terminal device 400 side has been described, but the present invention is not limited to this. For example, the terminal device 400 may be configured to perform adaptive beamforming using multiple beams in the same manner as the distributed antenna 300. In this case, for example, the terminal device 400 may transmit a feedback signal including a beam ID to the distributed antenna 300 for each beam ID by a beam to which the beam ID is linked. Then, on the distributed antenna 300 side (accommodating station side), the reception quality of the feedback signal may be measured for each beam ID on the terminal device 400 side, and the beam ID included in the feedback signal with the best reception quality may be fed back to the terminal device 400 as the optimal beam ID (on the terminal device 400 side). In addition, when receiving a beam search signal from the distributed antenna 300, the terminal device 400 may specify a beam to be used by switching the reception beam and measuring the reception quality (for example, reception power) of each beam.

[0130] <Second embodiment> A second embodiment of the present invention will now be described.

[0131] In the distributed antenna system 1 in the first embodiment described above, a beam search signal including information indicating a beam ID is used as a beam identifying signal. On the other hand, in the distributed antenna system 1 in the second embodiment described below, an unmodulated wave (CW) signal is used as a beam identifying signal.

[0132] In this embodiment, since an unmodulated wave signal is used as the beam identifying signal, the beam identifying signal itself does not include information indicating a beam ID. Therefore, in this embodiment, it is necessary for the distributed antenna 300 side (accommodating station side) to notify the terminal device 400 in advance of information indicating the transmission timing of the unmodulated wave signal for each beam ID (hereinafter referred to as "transmission timing information") so that the terminal device 400 can identify the beam ID linked to the beam used when the distributed antenna 300 transmits the unmodulated wave signal.

[0133] Specifically, all the distributed antennas 300 simultaneously sweep the beams to transmit unmodulated wave signals at the transmission timing of the unmodulated wave signal for each beam ID based on the transmission timing information notified in advance from the distributed antenna 300 side (the accommodating station side) to the terminal device 400. The terminal device 400 receives the unmodulated wave signal at a reception timing synchronized with the transmission timing of the unmodulated wave signal for each beam ID, thereby being able to identify the beam ID of the beam used to transmit each received unmodulated wave signal.

[0134] As a method for notifying the transmission timing information, for example, a method can be used in which, like the above-mentioned beam-specific signal, which is an unmodulated wave signal, a signal including common transmission timing information is simultaneously transmitted and notified by sweeping beams from multiple distributed antennas at the same time. Alternatively, as a method for notifying the transmission timing information, a non-directional antenna can be used by a low-frequency wireless communication system.

[0135] In addition, when it is necessary to follow the propagation path fluctuation accompanying the movement of the terminal device 400 and the surrounding environmental changes, it is desirable to perform beam selection periodically at an appropriate frequency. In this case, the transmission timing information may be notified each time the beam selection is performed periodically. In addition, when the terminal device 400 side is notified in advance that the beam selection is performed periodically, the overhead can be reduced by notifying the transmission timing information only once at the beginning.

[0136] In this embodiment, the transmission timing information indicating the transmission timing of the unmodulated wave signal for each beam ID is notified in advance to the terminal device 400. Specifically, the transmission timing information including information indicating the timing of starting transmission of the unmodulated wave signal, the beam ID switching interval, and the beam ID switching sequence is notified in advance from the distributed antenna 300 side (accommodating station side) to the terminal device 400. This makes it possible for the terminal device 400 side to specify the transmission timing of the unmodulated wave signal for each beam ID.

[0137] In addition, transmission timing information including only information indicating the timing of starting transmission of the unmodulated wave signal and the switching interval of the beam ID may be notified to the terminal device 400 in advance. In this case, the terminal device 400 may identify which unmodulated wave signal had the best reception quality and transmit a feedback signal indicating the order to the distributed antenna 300 side (the accommodating station side). In this way, the communication control device 100a in the second embodiment can identify the optimal beam ID based on the switching sequence order of the beam ID of the beam used when transmitting the unmodulated wave signal and the order included in the feedback signal. In addition, the unmodulated wave signal may be a signal having a certain bandwidth. For example, the unmodulated wave signal may be a spread signal.

[0138] [Configuration of distributed antenna system] The overall configuration of the distributed antenna system 1 in this embodiment is basically similar to the overall configuration of the distributed antenna system 1 in the first embodiment shown in FIG. 7 described above, and therefore a description thereof will be omitted.

[0139] [Configuration of communication control device] The configuration of the communication control device 100a of this embodiment will be described below. Fig. 11 is a block diagram showing the functional configuration of the communication control device 100a of the distributed antenna system in the second embodiment of the present invention.

[0140] As shown in FIG. 11, the communication control device 100a includes an unmodulated wave signal simultaneous transmission instruction unit 101a, a distributed antenna feedback result receiving unit 102, an optimal antenna beam selecting unit 103, and an optimal antenna beam storing unit 104.

[0141] The unmodulated wave signal simultaneous transmission instruction unit 101a outputs an instruction to the digital signal processing device 200 to sweep the beams and transmit unmodulated wave signals simultaneously from multiple distributed antennas 300 at the transmission timing of the unmodulated wave signal for each beam ID, which has been notified to the terminal device 400 in advance by the transmission timing information.

[0142] The distributed antenna feedback result receiving unit 102 acquires information indicating an optimal beam ID included in the feedback signal from the digital signal processing device 200. In addition, the distributed antenna feedback result receiving unit 102 acquires information indicating measurement results of the reception quality of the feedback signal in each distributed antenna 300 from the digital signal processing device 200. Based on the acquired measurement results, the distributed antenna feedback result receiving unit 102 determines the distributed antenna 300 with the highest reception quality as the optimal distributed antenna for communication with the terminal device 400.

[0143] The distributed antenna feedback result receiving unit 102 outputs information indicating the acquired optimum beam ID and the optimum antenna ID to the optimum antenna / beam selecting unit 103.

[0144] The optimum antenna beam selection unit 103 acquires the optimum beam ID and the optimum antenna ID output from the distributed antenna-specific feedback result receiving unit 102. The optimum antenna beam selection unit 103 identifies the beam linked to the acquired optimum beam ID and the distributed antenna 300 linked to the optimum antenna ID. The optimum antenna beam selection unit 103 stores information indicating the identified combination of the distributed antenna 300 and the beam in the optimum antenna beam storage unit 104.

[0145] The optimum antenna / beam storage unit 104 stores information indicating a combination of the distributed antennas 300 and beams. The digital signal processing device 200 performs wireless communication with the terminal device 400 by using the combination of the distributed antennas 300 and beams stored in the optimum antenna / beam storage unit 104. The optimum antenna / beam storage unit 104 may store beam ID assignment information 111 shown in FIG. 9.

[0146] The optimum antenna beam storage unit 104 is configured by, for example, a storage medium such as a HDD, a flash memory, an EEPROM, a RAM, a ROM, or any combination of these storage media.

[0147] With the above-described configuration, the distributed antenna 300 is configured to transmit a signal to the terminal device 400 using the distributed antenna and beam associated with the optimal beam ID.

[0148] [Terminal device configuration] The terminal device 400 receives an unmodulated wave signal at each reception timing synchronized with the transmission timing of the unmodulated wave signal for each beam ID in the distributed antenna 300. The terminal device 400 can identify the beam ID associated with the unmodulated wave signal based on the reception timing of the unmodulated wave signal and the transmission timing information notified in advance.

[0149] Other configurations of the terminal device 400 of the distributed antenna system 1 in this embodiment are basically the same as the configurations of the terminal device 900 of the conventional distributed antenna system 6 shown in FIG. 3 described above, so that the description will be omitted.

[0150] [Operation of communication control device] An example of the operation of the communication control device 100a in antenna beam selection of the distributed antenna system of the second embodiment will be described below. Fig. 12 is a flowchart showing the operation of the communication control device 100a in the distributed antenna system of the second embodiment of the present invention.

[0151] First, the unmodulated wave signal simultaneous transmission instruction unit 101a determines the value of the number m of distributed antennas 300 that perform beam selection and the value of the number n of beams used by each distributed antenna 300 (step S201). At this time, as shown in Fig. 9, the unmodulated wave signal simultaneous transmission instruction unit 101a assigns a beam ID that can uniquely identify each beam to each of the beams that are used simultaneously by the multiple distributed antennas 300 to transmit unmodulated wave signals.

[0152] Next, the unmodulated wave signal simultaneous transmission instruction unit 101a notifies the terminal device 400 of the transmission timing information in advance (step S202). As described above, the transmission timing information is information indicating the transmission timing of the unmodulated wave signals that are simultaneously transmitted for each beam ID from the m distributed antennas.

[0153] Next, the unmodulated wave signal simultaneous transmission instruction unit 101a initializes the value of a counter i that counts the beams that transmit the unmodulated wave signal, setting it to i=0 (step S203).

[0154] Next, in order to transmit an unmodulated wave signal with the next beam (i.e., to sweep the beam), the unmodulated wave signal simultaneous transmission instruction unit 101a increments the value of the counter i by 1, setting it to i←i+1 (step S204).

[0155] Next, the unmodulated wave signal simultaneous transmission instruction unit 101a outputs to the digital signal processing device 200 a simultaneous unmodulated wave signal transmission instruction, which is an instruction to transmit unmodulated wave signals from all m distributed antennas 300 using the i-th beam at the transmission timing of the i-th beam based on the transmission timing information previously notified to the terminal device 400 (step S205).

[0156] The unmodulated wave signal simultaneous transmission instruction unit 101a repeats outputting the same unmodulated wave signal transmission instruction to the digital signal processing device 200 until unmodulated wave signals are transmitted from all m distributed antennas 800 using n types of beams (i.e., until i = n) (steps S204 to S206).

[0157] Next, the distributed antenna feedback result receiving unit 102 waits for the feedback signal transmitted from the terminal device 400 in response to the transmitted unmodulated wave signal to be received by all the m distributed antennas 300 (step S207). Here, the feedback signal includes information indicating the optimal beam ID.

[0158] Next, when the feedback signal is received by all m distributed antennas 300 (step S207: YES), the distributed antenna-specific feedback result receiving unit 102 acquires information indicating an optimum beam ID contained in the feedback signal from the digital signal processing device 200. The distributed antenna-specific feedback result receiving unit 102 outputs the acquired optimum beam ID to the optimum antenna / beam selecting unit 103. The optimum antenna / beam selecting unit 103 stores information indicating the beam associated with the optimum beam ID in the optimum antenna / beam saving unit 104 (step S208).

[0159] Next, the distributed antenna feedback result receiving unit 102 acquires information indicating the measurement results of the reception quality of the feedback signal in each distributed antenna 300 from the digital signal processing device 200. Based on the acquired measurement results, the distributed antenna feedback result receiving unit 102 determines, for example, the distributed antenna 300 with the best reception quality as the optimal distributed antenna for wireless communication with the terminal device 400.

[0160] The distributed antenna feedback result receiver 102 outputs information indicating the distributed antenna 300 determined as the optimal distributed antenna to the optimal antenna beam selector 103. The optimal antenna beam selector 103 stores the acquired information indicating the distributed antenna 300 in the optimal antenna beam storage unit 104 (step S108). This completes the operation of the communication control device 100 shown in the flowchart of FIG.

[0161] [Operation of terminal device] The operation of the terminal device 400 of the distributed antenna system in this embodiment is basically similar to the operation of the terminal device 900 of the conventional distributed antenna system 6 shown in FIG. 3 described above, and therefore a description thereof will be omitted.

[0162] As described above, in the distributed antenna system 1 in the second embodiment of the present invention, transmission timing information indicating the transmission timing of the unmodulated wave signal for each beam ID is notified in advance from the distributed antenna 300 side (accommodating station side) to the terminal device 400 so that the terminal device 400 can identify the beam ID linked to the beam used when the distributed antenna 300 transmits the beam identifying signal, which is an unmodulated wave signal. On the distributed antenna 300 side (accommodating station side), all the distributed antennas 300 simultaneously sweep the beams and transmit the unmodulated wave signal to the terminal device 400 at the transmission timing of the unmodulated wave signal for each beam ID based on the transmission timing information notified in advance to the terminal device 400.

[0163] The terminal device 400 can identify the beam ID of the beam used to transmit each received unmodulated wave signal by receiving the beam identifying signal at a reception timing synchronized with the transmission timing of the unmodulated wave signal for each beam ID. The terminal device 400 identifies the beam ID with the best reception quality based on the measurement result of the reception quality of the unmodulated wave signal for each beam ID. The terminal device 400 embeds the identified beam ID in the feedback signal as an optimal beam ID. The terminal device 400 transmits the feedback signal including the optimal beam ID to the distributed antenna 300 side (the accommodating station side).

[0164] The distributed antenna 300 side (accommodating station side) receives a feedback signal transmitted from the terminal device 400 and reads out an optimal beam ID included in the received feedback signal. The distributed antenna 300 side (accommodating station side) performs setting so that the beam associated with the read optimal beam ID is used in wireless communication with the terminal device 400. The distributed antenna 300 side (accommodating station side) also receives the feedback signal transmitted from the terminal device 400 by all the distributed antennas 300. The distributed antenna 300 side (accommodating station side) identifies the distributed antenna 300 that received the feedback signal with the best reception quality (e.g., received power) among the feedback signals received by each distributed antenna 300. The distributed antenna 300 side (accommodating station side) performs setting so that the identified distributed antenna 300 is used in wireless communication with the terminal device 400.

[0165] The distributed antenna system 1 in the second embodiment of the present invention has the above-mentioned configuration, and transmits a beam-specific signal, which is an unmodulated wave signal, from the multiple distributed antennas 300 to the terminal device 400 at the same time. Therefore, the transmission of the unmodulated wave signal from the multiple distributed antennas 300 can be completed in only the time required for one distributed antenna 300 to transmit the unmodulated wave signal. As a result, even if the number of distributed antennas 300 is increased, the distributed antenna system 1 in this embodiment does not require a long time for beam selection, so that overhead is not increased and data transmission efficiency is not reduced. Furthermore, even if the number of distributed antennas 300 is increased, the distributed antenna system 1 in this embodiment does not require a long time for beam selection, so that it is not difficult to make the directivity of the distributed antenna 300 follow the movement of the terminal device 400, and it is possible to prevent the wireless communication itself between the distributed antenna side (accommodating station side) and the terminal device from becoming difficult.

[0166] In this way, in the distributed antenna system 1 in the second embodiment, it is possible to use an unmodulated wave (CW) signal since there is no need to include information indicating a beam ID in the beam identification signal. By using an unmodulated wave signal to select a beam, for example, it becomes possible to evaluate the reception quality of a feedback signal more fairly and with higher accuracy. As a result, according to the distributed antenna system 1 in this embodiment, it becomes possible to select an optimal distributed antenna 300 for wireless communication with the terminal device 400 with higher accuracy.

[0167] The radio waves used in the beam selection by the distributed antenna system 1 in the second embodiment are not limited to unmodulated waves (CW) under the condition that the beam identification signal does not need to include information indicating a beam ID. For example, a sounding reference signal (SRS) may be used in the beam selection by the distributed antenna system in this embodiment.

[0168] In the distributed antenna system 1 of the present embodiment, the multiple distributed antennas 300 use the same number of beams, but a different number of beams may be used for each distributed antenna 300. In this case, there may be an unmodulated wave signal transmitted only by a distributed antenna 300 that uses a larger number of beams than the other distributed antennas 300.

[0169] In the distributed antenna system 1 of the present embodiment, unmodulated wave signals are transmitted simultaneously from all of the distributed antennas 300. However, unmodulated wave signals may be transmitted simultaneously from only some of the distributed antennas 300.

[0170] In the distributed antenna system 1 in the present embodiment, as an example, a case where beam selection is not performed on the terminal device 400 side has been described, but the present invention is not limited to this. For example, the terminal device 400 may be configured to perform adaptive beamforming using multiple beams in the same manner as the distributed antenna 300. In this case, for example, the terminal device 400 may transmit a feedback signal including a beam ID to the distributed antenna 300 for each beam ID by a beam to which the beam ID is linked. Then, on the distributed antenna 300 side (accommodating station side), the reception quality of the feedback signal may be measured for each beam ID on the terminal device 400 side, and the beam ID included in the feedback signal with the best reception quality may be fed back to the terminal device 400 as the optimal beam ID (on the terminal device 400 side). In addition, when receiving an unmodulated wave signal from the distributed antenna 300, the terminal device 400 may specify a beam to be used by switching the reception beam and measuring the reception quality (for example, reception power) of each beam.

[0171] The distributed antenna system 1 in each of the above-mentioned embodiments performs wireless communication using adaptive beamforming. The distributed antenna system 1 in each of the above-mentioned embodiments selects an optimal beam from among a plurality of beams. As mentioned above, the optimal beam is a beam with the best reception quality, for example, a beam with the maximum value of the received power. In each of the above-mentioned embodiments, it is assumed that each distributed antenna 300 has a plurality of antenna elements and each distributed antenna 300 is capable of forming a plurality of types of beams.

[0172] According to the above-mentioned embodiment, the communication control device includes a transmission / reception unit and a selection unit. For example, the communication control device is the communication control device 100 in the first embodiment, the transmission / reception unit is the same beam search signal simultaneous transmission instruction unit 101 and the distributed antenna feedback result receiving unit 102 in the first embodiment, and the selection unit is the optimal antenna beam selection unit 103 in the first embodiment.

[0173] The transceiver transmits beam identifying signals including the same beam identifier from multiple antennas to a wireless station by a transmission beam linked to the beam identifier simultaneously for each beam identifier. For example, the beam identifier is a beam ID in the first embodiment, the beam identifying signal is a beam search signal in the embodiment, the antenna is a distributed antenna 300 in the first embodiment, and the wireless station is a terminal device 400 in the first embodiment.

[0174] The transmitter / receiver receives, by the multiple antennas, a report signal including a selected beam identifier indicating a beam identifier selected based on the reception quality of a beam-identifying signal for each beam identifier in the wireless station. For example, the report signal is a feedback signal in the first embodiment, and the selected beam identifier is an optimal beam ID in the first embodiment.

[0175] The selection unit selects an antenna to be used for communication with the wireless station based on the reception quality of report signals received by each of the multiple antennas, and selects a transmission beam linked to the selected beam identifier as the transmission beam to be used for communication with the wireless station.

[0176] According to the above-described embodiment, the communication control device includes a transmission / reception unit and a selection unit. For example, the communication control device is the communication control device 100a in the second embodiment, the transmission / reception unit is the unmodulated wave signal simultaneous transmission instruction unit 101a and the distributed antenna feedback result receiving unit 102 in the second embodiment, and the selection unit is the optimal antenna beam selection unit 103 in the second embodiment.

[0177] The transmitting / receiving unit transmits a beam-specific signal from a plurality of antennas to a wireless station at a predetermined transmission timing for each transmission beam by using a plurality of transmission beams in sequence. For example, the beam-specific signal is an unmodulated wave signal in the second embodiment, the antenna is the distributed antenna 300 in the second embodiment, and the wireless station is the terminal device 400 in the second embodiment.

[0178] The transmitter / receiver receives, by the multiple antennas, a report signal including information based on a beam-specific signal selected based on the reception timing and reception quality of the beam-specific signal for each transmission beam at the wireless station. For example, the report signal is a feedback signal in the second embodiment.

[0179] The selection unit selects an antenna to be used for communication with the wireless station based on reception qualities of report signals received by the multiple antennas, and selects a transmission beam to be used for communication with the wireless station based on information included in the report signal.

[0180] In addition, in the above-mentioned communication control device, the information included in the report signal may be information indicating the order in which the selected beam identifying signals were received.

[0181] In the above communication control device, the beam identifying signal may be transmitted from a plurality of antennas using an unmodulated wave.

[0182] In addition, in the above communication control device, the beam identifying signal may be a sounding reference signal.

[0183] A part or all of each of the communication control device, the digital signal processing device, and the terminal device in each of the above-mentioned embodiments may be realized by a computer. In that case, a program for realizing the function may be recorded in a computer-readable recording medium, and the program recorded in the recording medium may be read into a computer system and executed to realize the function. The term "computer system" as used herein includes hardware such as an OS and peripheral devices. The term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into a computer system. The term "computer-readable recording medium" may also include a medium that dynamically holds a program for a short period of time, such as a communication line when a program is transmitted via a network such as the Internet or a communication line such as a telephone line, and a medium that holds a program for a certain period of time, such as a volatile memory inside a computer system that is a server or client in that case. The above-mentioned program may be a program for realizing a part of the above-mentioned function, or may be a program that can realize the above-mentioned function in combination with a program already recorded in the computer system, or may be a program that is realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0184] 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 designs that do not deviate from the gist of the present invention are also included. [Explanation of symbols]

[0185] 1,6...Distributed antenna system, 100, 100a...Communication control device, 101...Same beam search signal simultaneous transmission instruction unit, 101a...Unmodulated wave signal simultaneous transmission instruction unit, 102...Feedback result receiving unit for each distributed antenna, 103...Optimal antenna / beam selecting unit, 104...Optimal antenna / beam storing unit, 200...Digital signal processing device, 300...Distributed antenna, 400...Terminal device, 600...Communication control device, 601...Beam specific signal transmission instruction unit, 602...Feedback result receiving unit, 603...Optimal antenna / beam selecting unit, 604...Optimal antenna / beam storing unit, 700...Digital signal processing device, 800...Distributed antenna, 900...Terminal device, 901...Antenna unit, 902...Digital signal processing unit, 903...Optimal beam ID selecting unit, 904...Feedback signal transmission instruction unit

Claims

1. a transmitting step of simultaneously transmitting beam-specific signals including the same beam identifier from a plurality of antennas to wireless stations for each beam identifier by transmission beams associated with the beam identifier; a receiving step of receiving, by each of the plurality of antennas, a report signal including a selected beam identifier indicating a beam identifier selected based on a reception quality of the beam-identifying signal for each of the beam identifiers in the wireless station; a selection step of selecting an antenna to be used for communication with the wireless station based on reception qualities of the report signals received by the plurality of antennas, and selecting a transmission beam associated with the selected beam identifier as a transmission beam to be used for communication with the wireless station; A communication control method comprising the steps of:

2. a transmitting step of simultaneously transmitting a beam-specific signal from a plurality of antennas to a wireless station for each of the transmission beams at a predetermined transmission timing by sequentially using the plurality of transmission beams; a receiving step of receiving, by each of the plurality of antennas, a report signal including information based on a beam identifying signal selected based on a receiving timing and a receiving quality of the beam identifying signal for each of the transmission beams in the wireless station; a selection step of selecting an antenna to be used for communication with the wireless station based on reception qualities of the report signals received by the plurality of antennas, and selecting a transmission beam to be used for communication with the wireless station based on information included in the report signal; A communication control method comprising the steps of:

3. The information included in the report signal is information indicating the order in which the selected beam identification signal was received. The communication control method according to claim 2.

4. The beam-specific signals are transmitted from the plurality of antennas using unmodulated waves. The communication control method according to claim 2 or 3.

5. The beam-specific signal is a sounding reference signal. The communication control method according to claim 2 or 3.

6. A communication control method for a wireless communication system having a first wireless station and a second wireless station, comprising: a first transmission step in which the first wireless station simultaneously transmits beam-specific signals including the same beam identifier from a plurality of antennas to a second wireless station for each beam identifier by using transmission beams associated with the beam identifier; a first receiving step in which the second wireless station receives the beam identifying signal transmitted from the first wireless station for each beam identifier; a first selection step in which the second wireless station selects a selected beam identifier, which is a specific beam identifier, from the plurality of beam identifiers based on a reception quality of the beam-specific signal for each of the beam identifiers; a second transmission step in which the second wireless station transmits a report signal including the selected beam identifier to the first wireless station; a second receiving step in which the first wireless station receives the report signal by each of the plurality of antennas; a second selection step in which the first wireless station selects an antenna to be used for communication with the second wireless station based on reception qualities of the report signal received by each of the plurality of antennas, and selects a transmission beam associated with the selected beam identifier as a transmission beam to be used for communication with the second wireless station; A communication control method.

7. a transceiver unit that simultaneously transmits beam identifying signals including the same beam identifier from a plurality of antennas to a wireless station for each beam identifier by a transmission beam linked to the beam identifier, and receives, by the plurality of antennas, a report signal including a selected beam identifier indicating a beam identifier selected based on a reception quality of the beam identifying signal for each beam identifier at the wireless station; a selection unit that selects an antenna to be used for communication with the wireless station based on reception qualities of the report signals received by the plurality of antennas, and selects a transmission beam associated with the selected beam identifier as a transmission beam to be used for communication with the wireless station; A communication control device comprising:

8. a transceiver unit that uses a plurality of transmission beams in sequence to simultaneously transmit a beam identifying signal from a plurality of antennas to a wireless station for each transmission beam at a transmission timing predetermined for each of the transmission beams, and receives, by the plurality of antennas, a report signal including information based on a beam identifying signal selected based on the reception timing and reception quality of the beam identifying signal for each of the transmission beams at the wireless station; a selection unit that selects an antenna to be used for communication with the wireless station based on reception qualities of the report signals received by the plurality of antennas, and selects a transmission beam to be used for communication with the wireless station based on information included in the report signal; A communication control device comprising:

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