Communication relay device and computer program

Abstract

To provide a communication relay device and a computer program that contribute to the improvement of communication quality in a system that relays between base stations and mobile stations.SOLUTION: A communication relay device of an embodiment includes an antenna, a signal strength detection unit, a first search unit, and a second search unit. The antenna forms a radio wave beam in an arbitrary direction. The signal strength detection unit detects signal strength received by the antenna. The first search unit changes the direction of the beam formed by the antenna in a first range, and detects a direction in which the mobile station is located based on the signal strength detected by the signal strength detection unit. The second search unit changes the direction of the beam formed by the antenna in a second range narrower than the first range, and detects the direction in which the mobile station is located based on the signal strength detected by the signal strength detection unit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a communication relay device and a computer program. [Background technology]

[0002] Commercial mobile phone services using 5G (5th generation mobile communications system) were launched in Japan in 2020. One of the technologies attracting attention in 5G is beamforming. This is a function that expands the coverage area and cell capacity by simultaneously communicating with multiple users by coordinating the operation of multiple antenna elements on a single antenna to form a radio wave beam in any direction, and is generally achieved in combination with a massively multi-element antenna (Massive MIMO).

[0003] Incidentally, Distributed Antenna Systems (DAS) have been used as a measure to cover indoor areas of mobile communication systems since before 5G. DAS systems relay between mobile stations and base stations and consist of a master unit and multiple slave units that are distributed. The master unit distributes the signal of one base station to multiple slave units, and each slave unit outputs the same downlink signal from its respective antenna to create an area as one cell.

[0004] If a DAS system is simply applied to a 5G system, as mentioned above, the same signal will be output from each slave unit, and the beams formed by the distributed slave units will also point in a common direction, and will not necessarily point in the direction of mobile stations within the coverage area. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6567438 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a communication relay device and a computer program that contribute to improving communication quality. [Means for solving the problem]

[0007] A communication relay device according to an embodiment includes an antenna, a signal strength detection unit, a first search unit, and a second search unit. The antenna forms a radio wave beam in an arbitrary direction, the signal strength detection unit detects the signal strength received by the antenna, the first search unit changes the direction of the beam formed by the antenna within a first range and detects the direction in which a mobile station exists based on the signal strength detected by the signal strength detection unit, and the second search unit changes the direction of the beam formed by the antenna within a second range that includes the direction detected by the first search unit and is narrower than the first range, and detects the direction in which a mobile station exists based on the signal strength detected by the signal strength detection unit. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 shows a mobile communication system including a communication relay system. [Diagram 2] FIG. 2 is a diagram showing an example of the configuration of the parent unit shown in FIG. 1; [Diagram 3] FIG. 2 is a diagram showing an example of the configuration of the slave unit shown in FIG. 1; [Figure 4] FIG. 2 is a diagram showing an example of beamforming by the slave unit shown in FIG. 1. [Diagram 5] 2 is a diagram showing an example of a search for a mobile station by the slave unit shown in FIG. 1; [Figure 6] 4 is a flowchart for explaining the process of the parent unit shown in FIG. 1 . [Figure 7] 2 is a diagram showing an example of a high-speed search for a mobile station by the slave unit shown in FIG. 1; [Figure 8] 2 is a diagram showing an example of a slow search for a mobile station by the slave unit shown in FIG. 1; [Figure 9] 2 is a diagram showing an example of a tracking search for a mobile station by the slave unit shown in FIG. 1; [Figure 10]2 is a diagram showing an example of a tracking search for a mobile station by the slave unit shown in FIG. 1; [Figure 11] 2 is a diagram showing an example of a search for a mobile station by the slave unit shown in FIG. 1; [Figure 12] 2 is a diagram showing an example of a search for a mobile station by the slave unit shown in FIG. 1; [Figure 13] 2 is a diagram showing an example of a search for a mobile station by the slave unit shown in FIG. 1; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A communication relay system according to an embodiment will be described below with reference to the drawings. FIG. 1 shows a part of a fifth generation mobile communication system, so-called 5G. This mobile communication system includes a 5th Generation Core network (5GC) and a radio access network (NR). In the example of FIG. 1, a communication relay system is included in the radio access network NR.

[0010] The 5G core network 5GC controls the radio access network NR, bundles traffic and communicates with external networks (Internet IN, external telephone network EN, etc.), and has a core device C as its central device. The core device C performs, for example, authentication and security management, session management, policy control, packet forwarding, etc.

[0011] Meanwhile, the radio access network NR includes a plurality of base station devices (for example, gNB (gNodeB) 1 and gNB 2 in FIG. 1). The base station devices gNB 1 and gNB 2 are controlled by a core device C, and each of them forms a wireless communication area (so-called a cell) capable of communicating with a mobile station UE (User Equipment).

[0012] More specifically, the base station device gNB1 wirelessly communicates with the mobile station UE through an antenna device AN installed on the rooftop of a building or on a dedicated tower, and connects the mobile station UE to the 5G core network 5GC through a core device C. The base station device gNB1 also performs beamforming using Massive MIMO, which controls the phase of signals in multiple antenna elements on the antenna device AN, thereby contributing to an increase in communication capacity.

[0013] The base station device gNB2 has the same functions as the base station device gNB1, but communicates wirelessly with the mobile station UE through a distributed antenna system DAS instead of the antenna device AN, and connects the mobile station UE to the 5G core network NW through the core device C.

[0014] The distributed antenna system DAS is an example of a communication relay system, and is used to form a wireless communication area that is relatively small compared to the antenna device AN in special locations (for example, inside buildings, underground shopping malls, and other structures, depopulated or overpopulated areas, areas where it is difficult or limited to construct steel towers, and temporary locations for the antenna device AN such as event venues), and as shown in Figure 1, it comprises a master unit MU (Master Unit), remote units RU (Remote Units) 1 to RU3, and antennas AN1 to AN3.

[0015] The master unit MU controls each unit of the distributed antenna system DAS and serves as a communication relay device that enables mobile stations UE connected via antennas (AN1-AN3) and slave units (RU1-RU3) to communicate with the base station apparatus gNB2. When the master unit MU is connected to the slave units RU1-RU3 via optical communication lines, it is generally referred to as an optical repeater.

[0016] Antennas AN1 to AN3 are connected one-to-one to their corresponding slave units RU1 to RU3, each consisting of a large number of antenna elements, and compatible with Massive MIMO, in which directivity is controlled (beamforming) by phase adjustment of the transmitted RF signal and / or received RF signal.

[0017] In this embodiment, for the sake of simplicity, each of the antennas AN1 to AN3 will be described as performing beamforming to simultaneously form up to four beams in any direction, and for the sake of simplicity, the parent unit MU, which will be described in detail later, will also be described as processing (relaying) up to four streams simultaneously corresponding to the above four beams.

[0018] In an actual device, the number is not limited to a maximum of four, and may be three or less, or five or more. Also, the number of beams formed by each of the antennas AN1 to AN3 is not fixed, and may be dynamically changed by varying the number of antenna elements used.

[0019] The slave units RU1 to RU3 are connected one-to-one to the corresponding antennas AN1 to AN3, respectively, and can be connected to the master unit MU so as to be able to communicate with the master unit MU via an optical communication line. As a connection method, as shown in Fig. 1, the slave units RU1 to RU3 can be connected to the master unit MU by a daisy chain method, or a method (not shown) in which the slave units RU1 to RU3 are each directly connected to the master unit MU can be considered.

[0020] In addition, the slave units RU1 to RU3 are capable of performing beamforming by adjusting the phase of the corresponding antennas AN1 to AN3, and can detect (search) the direction in which the mobile station UE is located by measuring the reception strength and performing beamforming, and can track and communicate with the moving mobile station UE.

[0021] More specifically, regarding beamforming, in the uplink, the slave units RU1 to RU3 perform phase adjustment (beamforming) on ​​the RF signals obtained by the corresponding antennas AN1 to AN3. In this example, received RF signals corresponding to up to four beams are obtained from each of the antennas AN1 to AN3.

[0022] The slave units RU1 to RU3 then down-convert the received RF signals corresponding to each beam, and simultaneously demodulate them into four received signals corresponding to up to four beams. The slave units RU1 to RU3 then serially bundle the demodulated received signals, convert them from electrical signals to optical signals (modulate the optical carrier), and transmit them to the master unit MU via the optical communication line. The stream included in the received signals is referred to as a UL stream signal.

[0023] On the other hand, for the downlink, the slave units RU1 to RU3 convert the optical signals transmitted from the master unit MU over the optical communication line into electrical signals and simultaneously demodulate them into signals corresponding respectively to a maximum of four streams (hereinafter referred to as DL stream signals).

[0024] The slave units RU1 to RU3 then generate transmission RF signals by modulating a carrier wave using the DL stream signals, and output these transmission RF signals to the connected antennas AN1 to AN3, respectively, for emission into space. Each of the slave units RU1 to RU3 is capable of beamforming, which forms up to four beams simultaneously, and forms a beam for each DL stream signal for transmission. In other words, when four DL stream signals are obtained by demodulation, four beams are formed, and each beam transmits one DL stream signal.

[0025] Next, the master unit MU will be described in detail. Fig. 2 shows an example of the configuration of the master unit MU. That is, the master unit MU includes a port P, a control unit 100, a transmission unit 110, a UL (Up Link) signal processing unit 120, and a DL (Down Link) signal processing unit 130.

[0026] Port P accommodates an optical communication line and is connectable to slave units RU1 to RU3 via this optical communication line, and is connected to UL signal processing unit 120 and DL signal processing unit 130. Note that in the example of Fig. 2, slave unit RU1 is physically connected directly via the optical communication line, but since optical signals exchanged between slave units RU2 and RU3 are also multiplexed onto the optical communication line, port P is essentially connected to slave units RU2 and RU3, and is capable of transmitting and receiving optical signals to and from any of slave units RU1 to RU3.

[0027] Regarding the uplink, port P demultiplexes the optical signal sent from slave unit RU1, separates it into multiple optical signals, converts each optical signal into an electrical signal, and demodulates it to obtain multiple electrical communication signals. These multiple electrical communication signals are received signals corresponding to the beams (or UL stream signals) of slave units RU1 to RU3, respectively, and are output in parallel to UL signal processor 120.

[0028] Port P also functions as an information detector that acquires information sent from slave units RU1-RU3 from each received signal, monitors each demodulated received signal, and detects a communication start request (PRACH) from the mobile station UE contained in the received signal and a stream ID assigned to each received signal (UL stream signal). Port P also functions as a position detector that detects the presence of a mobile station UE located within the coverage area formed by each slave unit RU1-RU3 from the above detection results. These detection results are notified to the control unit 100.

[0029] On the other hand, for the downlink, a maximum of four DL stream signals are simultaneously input to port P1 from the DL signal processing unit 130. Then, port P adds identification information of the destination slave units RU1-RU3 to the input DL stream signals, converts the signals from electrical signals to optical signals (modulates the optical carrier), multiplexes these optical signals, and transmits them to the slave units RU1-RU3 via the optical communication line.

[0030] The transmission unit 110 accommodates a communication line connected to the base station device gNB2, and communicates with the base station device gNB2 through this communication line. Specifically, for the uplink, the transmission unit 110 transmits UL signals (up to four at the same time) input from the UL signal processing unit 120 to the base station device gNB2. On the other hand, for the downlink, the transmission unit 110 receives DL stream signals (up to four at the same time) transmitted from the base station device gNB2 through the above-mentioned communication line, and outputs them to the DL signal processing unit 130.

[0031] The UL signal processing unit 120 performs signal addition processing to add up the reception signals of the respective beams input from port P according to the control of the control unit 100, and outputs the result to the transmission unit 110 as a UL signal. The DL signal processing unit 130 performs multiplexing processing to multiplex the DL stream signals input from the transmission unit 110 and output the multiplexed signal to a port P under the control of the control unit 100 .

[0032] The control unit 100 is a control center that controls each part of the parent unit MU, and is equipped with a memory (not shown) that stores control programs and control data, and a processor (not shown) that executes processing based on the control programs and the control data, thereby realizing various control functions.

[0033] As a specific control, the control unit 100 performs communication relay control between the mobile station UE and the base station device gNB2 via the slave units RU1 to RU3, and also performs stream allocation control and handover control for the slave units RU1 to RU3 based on the detection results notified from port P and the DL stream signals transmitted from the base station device gNB2.

[0034] In stream allocation control, the capabilities of the slave units RU1 to RU3 (e.g., the number of streams they can handle) and slave unit information including the number of streams currently allocated, as well as mobile station information including the location information of the mobile station UE, are stored and managed (updated), and streams are allocated to the slave units RU1 to RU3 based on this slave unit information and mobile station information.

[0035] In addition, in the handover control, based on the detection result notified from port P, a determination is made as to the need to change the slave units RU1-RU3 that should communicate with the mobile station UE, and based on this determination result, an instruction is given to each slave unit RU1-RU3 and the mobile station UE to perform handover between the slave units.

[0036] More specifically, for example, the signal strength of the received signal from the mobile station UE notified from each of RU1 to RU3 is compared, and when the signal strength notified from the communicating handset falls below a preset first threshold and the signal strength of the same mobile station UE notified from another handset exceeds a second threshold, an instruction is issued to both handset units to perform handover to the other handset unit. The conditions for determining the necessity of handover are not limited to this example, and various conditions may be considered depending on the installation environment, etc., and may be applied.

[0037] Next, the slave units RU1 to RU3 will be described in detail. In the following, in order to avoid redundancy in the description and confusion over the correspondence of the configurations, the slave units will be described as "slave unit RUn." When the description is made as "slave unit RUn," the description is common to all of the slave units RU1 to RU3. That is, in the following description, "n" can be read as any of 1 to 3.

[0038] 3 shows an example of the configuration of each slave RUn (RU1 to RU3). That is, each slave RUn includes a control unit 200, a communication unit 210, a signal processing unit 220, a wireless communication unit 230, a storage unit 240, and an antenna ANn.

[0039] The communication unit 210 transmits and receives optical communication signals through an optical communication line, has at least two ports, and functions as an optical communication repeater that amplifies an optical communication signal received through the optical communication line accommodated in one port and transmits it through the optical communication line accommodated in the other port, and also functions as a modulator / demodulator that converts between optical signals and electrical signals.

[0040] The modem has an optical / electrical conversion function for receiving an optical signal through an optical communication line and performing optical / electrical conversion to obtain an electrical communication signal (DL stream signal), and an electrical / optical conversion function for performing electrical / optical conversion of an electrical communication signal (UL stream signal) input from a signal processing unit 220 described later to an optical communication signal and transmitting it through the optical communication line.

[0041] The signal processing unit 220 communicates with the base station device gNB2 in accordance with a predetermined communication protocol. For the downlink of the system, the signal processing unit 220 demodulates and decodes the communication signal obtained by the communication unit 210, detects a DL stream signal addressed to the slave RUn, and outputs the DL stream signal to the control unit 200. For the uplink of the system, the signal addressed to the base station device gNB2 provided by the control unit 200 is used for carrier modulation to generate a UL stream signal, and outputs the UL stream signal to the communication unit 210.

[0042] The wireless communication unit 230 performs wireless communication with the mobile station UE through the antenna ANn, and adopts a wireless access method conforming to 5G. Therefore, even when the mobile station UE communicates through the distributed antenna system DAS, the mobile station UE can perform wireless communication using the same wireless access method as when communicating with the base station device gNB1 through the antenna AN shown in FIG. 1.

[0043] Further, according to instructions from the control unit 200, the wireless communication unit 230 performs beamforming by massive MIMO that controls the phases of signals (transmitted RF signals and / or received RF signals) in a large number of antenna elements on the antenna ANn. Furthermore, the wireless communication unit 230 measures the received signal strength (for example, RSSI) from the mobile station UE, and notifies the control unit 200 of the measurement result in association with the identification information of the mobile station UE.

[0044] The control unit 200 is a control center that controls all parts of the child unit RUn, and is equipped with a work memory (not shown) and a processor (not shown) that executes processing based on control programs and control data loaded into the work memory from the memory unit 240 described later, thereby realizing various control functions.

[0045] As specific control functions, the control unit 200 has at least a beamforming control function 200a, a search control function 200b, and a handover control function 200c, in addition to a communication control function that connects the mobile station UE, which is wirelessly connected to the slave unit RUn, to the 5G core network 5GC via the master unit MU and the base station device gNB2, as well as a processing function that integrates and executes these functions.

[0046] The beamforming control function 200a controls the massive MIMO performed by the wireless communication unit 230, and performs beamforming according to a predetermined algorithm in accordance with the number of streams assigned to the mobile station UE, etc.

[0047] An example of beamforming is shown in Fig. 4. In this example, the antenna ANn is divided into four groups Gr1 to Gr4 so that a large number of antenna elements correspond to four streams, as shown in Fig. 4(a), and the directivity of each group can be controlled in an arbitrary direction.

[0048] When a mobile station UE is present within the coverage area of ​​antenna ANn and two streams are assigned to the mobile station UE, for example, as shown in FIG. 4(b), beamforming is performed to direct the stream from group Gr1 and the stream from group Gr2 toward the direction in which the mobile station UE is located.

[0049] Furthermore, when one mobile station UE is present within the coverage area of ​​antenna ANn and four streams are allocated to the mobile station UE, for example, as shown in FIG. 4(c), beamforming is performed to direct each stream from groups Gr1 to Gr4 in the direction in which the mobile station UE is present.

[0050] The search control function 200b controls the wireless communication unit 230 to search and estimate (detect) the direction and distance of the mobile station UE. Specifically, it controls the massive MIMO by the wireless communication unit 230 to repeatedly sweep the direction of the beam in an arbitrary range every 20 ms as shown in Fig. 5(a), for example, and during this time, monitors the received signal strength successively detected by the wireless communication unit 230 to detect the direction and distance of the mobile station UE. Fig. 5(b) shows the timing of each beam shown in Fig. 5(a), and the correspondence between the shading in both figures indicates the correspondence.

[0051] The handover control function 200c is a control function that cooperates with the master unit MU to realize handover of the mobile station UE between the slave units RU1 to RU3. More specifically, the wireless communication unit 230 notifies the master unit MU of the received signal strength successively detected, and according to an instruction from the master unit MU (the handover control function thereof), ends communication with the mobile station UE with which it is currently communicating (for example, when moving outside the coverage area) or starts communication with a new mobile station UE (for example, when moving inside the coverage area).

[0052] The storage unit 240 stores the control program and control data used by the control unit 200, and also stores the UE location information table 240a. The control program and the control data are pre-installed at the time of manufacture, and are also installed or updated through an external interface (not shown) during manufacturing setup, or installed or updated by communicating with a server on the 5G core network 5GC such as the core device C.

[0053] The UE location information table 240a is a data table that records location information of mobile stations UE present within the coverage area of ​​the slave unit RUn, and stores information such as identification information, location information, update date and time of the mobile station UE in association with each other. Examples of the location information include, but are not limited to, a combination of the identification information of the above-mentioned antenna element groups Gr1 to Gr4, beam direction information, estimated distance information, and the like.

[0054] Next, the operation will be described. In the following description, search control and stream allocation for the mobile station UE in the slave unit RUn of the distributed antenna system DAS will be particularly described. Fig. 6 is a flowchart for explaining the control flow of control unit 200 of the slave unit RUn.

[0055] When the operation of the distributed antenna system DAS starts, in the slave RUn, the control unit 200 executes several control flows in parallel, one of which is the control flow shown in Fig. 6. The control flow shown in Fig. 6 is executed repeatedly until the operation of the slave RUn is stopped or a stop command is received from the master MU or the like.

[0056] First, in step 601, the control unit 200 starts or restarts the timer T, sets the parameter of the timeout flag F stored in the work memory to a value meaning OFF, and proceeds to step 602. That is, from the point in time when the control unit 200 proceeds to step 601, the control unit 200 starts or resumes the time count by the timer T.

[0057] In step 602, the control unit 200 judges whether or not a new stream has been allocated to the mobile station UE from the master unit MU. The new stream here refers to a stream for new communication at the request of the master unit MU. If a new stream has been allocated, the process proceeds to step 606. If a new stream has not been allocated, the process proceeds to step 603.

[0058] In step 603, the control unit 200 judges whether or not a new communication start request has been generated from the mobile station UE. The new communication start request here means a request for new communication by the mobile station UE. If a new communication start request has been generated, the control unit 200 proceeds to step 606, whereas if a new communication start request has not been generated, the control unit 200 proceeds to step 604.

[0059] In step 604, the control unit 200 checks the timer T started in step 601, and judges whether or not a preset time t has elapsed since step 601. If the time t has elapsed, the process proceeds to step 605, whereas if the time has not elapsed, the process proceeds to step 602 again.

[0060] In step 605, the control unit 200 sets a value meaning ON to the parameter of the above-mentioned timeout flag F, and proceeds to step 607. This setting (ON setting) of the timeout flag F indicates that the processing of the subsequent steps 607 to 609 was executed as a result of the timeout in step 604.

[0061] In step 606, the control unit 200 refers to the UE location information table 240a stored in the storage unit 240, compares the update date and time included in this table with the current time, and determines whether a preset time has elapsed.

[0062] Here, if there is no information in the UE location information table 240a or if the preset time has elapsed, the process proceeds to step 607. On the other hand, if the preset time has not elapsed, the process proceeds to step 611.

[0063] That is, if there is no location information of the mobile station UE in the UE location information table 240a or if the location information is old, it is determined that a search for the mobile station UE is necessary, and the process proceeds to step 607 to search for the mobile station UE. On the other hand, if there is location information of the mobile station UE that can be referred to in the UE location information table 240a, the process proceeds to step 611 to allocate streams.

[0064] In step 607 , the control unit 200 uses the search control function 200 b to execute a high-speed search for detecting the direction in which the mobile station UE is located, and then proceeds to step 608 . Specifically, the control unit 200 controls the massive MIMO by the wireless communication unit 230, and for example, as shown in Fig. 7(a), sets the variable range of the beam direction (for example, horizontal direction) to about 120°, and repeatedly sweeps every 20 ms as shown in Fig. 7(b), during which the wireless communication unit 230 monitors the received signal strength successively detected to detect the identification information of the mobile station UE and the direction and distance where the mobile station UE is located. Note that Fig. 7(b) shows the received signal strength corresponding to each beam shown in Fig. 7(a), and the matching of shading in both figures indicates the corresponding relationship.

[0065] This high-speed search is performed independently for each of the four groups Gr1 to Gr4 of antenna elements on the antenna ANn. The directions searched by each of the groups Gr1 to Gr4 may be arbitrarily set by an operator during setup, or may be set by the search control function 200b itself based on statistical data and learning data of the location information of the mobile station UE accumulated and stored in the storage unit 240, or may be updated by reviewing the settings.

[0066] In step 608 , the control unit 200 uses the search control function 200 b to execute a slow search to detect the direction in which the mobile station UE exists with higher accuracy, and then proceeds to step 609 . Specifically, the control unit 200 controls the massive MIMO by the wireless communication unit 230, and for example, as shown in Fig. 8(a), sets the variable range of the beam direction (for example, horizontal direction) to about 90° narrower than about 120° in the high-speed search, and repeatedly sweeps every 20 ms as shown in Fig. 8(b), during which the wireless communication unit 230 monitors the received signal strength successively detected at the same frequency as the high-speed search, and detects the identification information of the mobile station UE and the direction and distance where the mobile station UE is located. Note that, like Fig. 7, Fig. 8(b) shows the received signal strength corresponding to each beam shown in Fig. 8(a), and the matching of shading in both figures indicates the corresponding relationship.

[0067] This slow search is performed independently for each of the four groups Gr1 to Gr4 of antenna elements on the antenna ANn. The direction searched by each of the groups Gr1 to Gr4 is centered on the direction detected in the fast search in step 607. The range of the search direction may be limited by an operator during setup, or may be limited by the search control function 200b itself based on statistical data or learning data of the location information of the mobile station UE accumulated and stored in the storage unit 240, or the range of the limit may be reviewed.

[0068] At the time of moving to step 608, the parameter of the timeout flag F stored in the work memory is referenced, and if a value meaning ON is set, the low-speed search of step 608 may be skipped and the process may move to step 609. In other words, if a timeout occurs, the higher-precision search may be omitted.

[0069] In step 609, the control unit 200 records the identification information of the mobile station UE detected in step 608 in association with information on the direction and distance of the mobile station UE (location information), and the time of detection (update date and time) in the UE location information table 240a, and proceeds to step 610. If information on the same mobile station exists in the UE location information table 240a, the information may be overwritten and saved, or information may be cumulatively saved as a log for a certain period of time (certain number of times). The log can be used by the control unit 200 as the above-mentioned learning data.

[0070] In step 610, the control unit 200 refers to the parameter of the timeout flag F stored in the work memory, and judges whether or not a value meaning ON is set. If a value meaning ON is set, the process proceeds to step 601, whereas if a value meaning OFF is set, the process proceeds to step 611.

[0071] That is, if a value meaning ON is set, the information in the UE location information table 240a is merely updated, whereas if a value meaning OFF is set, the process proceeds to the subsequent stream allocation process.

[0072] In step 611, the control unit 200 allocates a stream to the mobile station UE, and proceeds to step 612. Specifically, if it is determined in step 602 that a new stream has been allocated from the master unit MU, the control unit 200 allocates the ID of the stream notified from the master unit MU to the mobile station UE, whereas if a request to start new communication is made from the mobile station UE in step 603, the control unit 200 allocates the ID of an available stream to the mobile station UE. It is assumed that the control unit 200 has received regular notification of the available stream ID in advance from the master unit MU.

[0073] In step 612, the control unit 200 uses the beamforming control function 200a to control massive MIMO by the wireless communication unit 230 for the stream assigned to the mobile station UE in step 611, and performs beamforming according to a predetermined algorithm, and then proceeds to step 613.

[0074] Specifically, the control unit 200 refers to the UE location information table 240a, and forms a beam directed in the direction in which the mobile station UE is located, based on the identification information of the mobile station UE to which the stream was assigned in step 611 and the location information associated therewith.

[0075] In step 613, the control unit 200 controls the wireless communication unit 230 to establish a wireless communication link with the mobile station UE to which the stream was allocated in step 611, and also controls the signal processing unit 220 to establish a communication link for the mobile station UE with the core device C, connects the mobile station UE to the core device C through these links, and proceeds to step 614. Thereafter, communication is started between the mobile station UE and the core device C via the stream allocated in step 611.

[0076] In step 614, the control unit 200 uses the search control function 200b to perform a slow search to track the direction in which the mobile station UE is located in order to maintain the wireless communication link established in step 613, and then proceeds to step 615.

[0077] Specifically, by controlling the massive MIMO by the wireless communication unit 230, for example, as shown in FIG. 9(a), the variable range of the beam direction (e.g., the horizontal direction) is set to a trackable range (approximately 45° in the example of FIG. 9(a)) narrower than the approximately 90° during the slow search in step 608.

[0078] The control unit 200 then repeatedly sweeps every 20 ms as shown in Fig. 9(b), during which it monitors the received signal strength successively detected by the wireless communication unit 230 to detect the identification information of the mobile station UE and the direction in which the mobile station UE is located. Fig. 9(b) shows the received signal strength corresponding to each beam shown in Fig. 9(a) in the same way as Fig. 8, and the correspondence between the shading in Fig. 9(a) and Fig. 9(b) indicates the correspondence.

[0079] The variable range may be varied based on data learned by the control unit 200 regarding the movement of the mobile station UE. Alternatively, the distance between the slave RUn and the mobile station UE may be estimated from the received signal strength, and the variable range may be varied. In this case, when the received signal strength is relatively high, it is determined that the slave RUn and the mobile station UE are close to each other, and the variable range is widened, whereas when the received signal strength is relatively low, it is determined that the slave RUn and the mobile station UE are far from each other, and the variable range is narrowed.

[0080] In step 615, the control unit 200 uses the beamforming control function 200a to perform beamforming to form a beam directed in the direction detected in step 614, thereby maintaining the wireless communication link established in step 613, and proceeds to step 616.

[0081] In step 614, the control unit 200 may estimate the moving direction of the mobile station UE, and in step 615, the control unit 200 may perform beamforming to form a beam directed in a direction based on the estimation result of step 614. For example, as shown in Fig. 10(a), when the mobile station UE moves, the control unit 200 can estimate the moving direction of the mobile station UE from the received signal strength of each beam, the magnitude relationship of the received signal strength in each direction, and the change therein.

[0082] In step 616, the control unit 200 determines whether or not the communication started in step 613 has ended. If the communication has ended, the process is started again from step 601, whereas if the communication has not ended, the process proceeds to step 614, where beamforming is continued to maintain the wireless communication link.

[0083] As described above, in the communication relay system configured as above, the beam direction is varied for each of the slave units RU1 to RU3, and the direction and distance to the mobile station UE are detected based on the signal strength received from the mobile station UE. Therefore, according to the communication relay system configured as above, the slave units RU1 to RU3 can detect the position of the mobile station UE present in each of their coverage areas.

[0084] Furthermore, in the communication relay system configured as above, the slave units RU1 to RU3 successively perform a high-speed search in which a beam is directed in a wide direction to detect the position of the mobile station UE, and a low-speed search in which a beam is directed in a narrower direction than the high-speed search to detect the position of the mobile station UE with higher accuracy. Therefore, according to the communication relay system configured as above, the slave units RU1 to RU3 can efficiently detect the location of the mobile station UE present in each of their coverage areas.

[0085] In the communication relay system configured as above, the slave units RU1 to RU3 change the direction of the beam to track the mobile station UE. Therefore, according to the communication relay system configured as above, the slave units RU1 to RU3 can perform stable communication with the mobile stations UE present in their respective coverage areas.

[0086] Furthermore, in the communication relay system configured as above, the slave units RU1 to RU3 divide the antenna elements on their respective antennas AN1 to AN3 into four groups Gr1 to Gr4, and independently vary the beam direction for each of the groups Gr1 to Gr4 to track the mobile station UE.

[0087] Therefore, according to the communication relay system having the above configuration, even if multiple mobile stations UE1, UE2 are present in approximately the same direction relative to antenna ANn, as shown in Figure 11(a), for example, two groups Gr1, Gr2 can search in the directions set for them. FIG. 11(b) and FIG. 11(c) show the received signal strengths corresponding to the beams shown in FIG. 11(a), and the correspondence between the shading in both figures indicates the correspondence.

[0088] In this case, the two groups Gr1 and Gr2 are controlled independently of each other by the control unit 200. Therefore, for example, as shown in FIG. 12(a), while group Gr1 is performing a slow search to track mobile station UE1 in step 614 of FIG. 6, group Gr2 can perform a high-speed search for mobile station UE2 in step 607 of FIG. 6. FIG. 12(b) and FIG. 12(c) show the received signal strengths corresponding to the beams shown in FIG. 12(a), and the correspondence between the shading in both figures indicates the correspondence.

[0089] It should be noted that the present invention is not limited to the above-described embodiment as it is, and in the implementation stage, the components can be modified and embodied without departing from the gist of the invention. In addition, various inventions can be formed by appropriately combining multiple components disclosed in the above-described embodiment. For example, a configuration in which some components are deleted from all the components shown in the embodiment can also be considered. Furthermore, the components described in different embodiments may be appropriately combined.

[0090] For example, in the above embodiment, for the sake of simplicity, an example has been described in which one group of antenna elements searches for one mobile station UE, but one antenna group may search for two or more mobile stations.

[0091] Specifically, for example, as shown in Fig. 13, group Gr1 on antenna ANn searches for two mobile stations UE1 and UE2. In this case, as shown in Fig. 13(b), two peaks appear in the received signal strength, so the control unit 200 can detect the number of mobile stations present and their directions by detecting the peaks in the received signal strength. FIG. 13(b) shows the received signal strength corresponding to each beam shown in FIG. 13(a), and the correspondence between the shading in both figures indicates the correspondence.

[0092] For example, in the above embodiment, in the high-speed search of step 607, the low-speed search of step 608, and the low-speed search of step 614, as illustrated in Figures 7, 8, and 9, a case has been described in which the range of directions in which the beam is pointed is controlled for the same antenna group, but this is not limited to this.

[0093] For example, different antenna groups may be used in some or all of the high-speed search in step 607, the low-speed search in step 608, and the low-speed search in step 614. That is, for example, group Gr1 is used in the high-speed search in step 607 and the low-speed search in step 608, and group Gr2 is used in the low-speed search in step 614. Alternatively, group Gr1 is used in the high-speed search in step 607, and group Gr2 is used in the low-speed search in step 614 and the low-speed search in step 608. Alternatively, group Gr1 is used in the high-speed search in step 607 and the low-speed search in step 614, and group Gr2 is used in the low-speed search in step 608. Alternatively, group Gr1 is used in the high-speed search in step 607, group Gr2 is used in the low-speed search in step 608, and group Gr3 is used in the low-speed search in step 614.

[0094] It goes without saying that various modifications can be made without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0095] 100...control unit, 110...transmission unit, 120...UL signal processing unit, 130...DL signal processing unit, 200...control unit, 200a...beamforming control function, 200b...search control function, 200c...handover control function, 210...communication unit, 220...signal processing unit, 230...wireless communication unit, 240...memory unit, 240a...UE location information table, 5GC...5G core network, AN1 to AN3...antennas, Gr1 to Gr4...antenna groups, P1...port, RU1 to RU3...child unit, UE1...mobile station, UE2...mobile station, gNB1...base station device, gNB2...base station device.

Claims

1. A communication relay device that relays communication between a base station and a mobile station connected to a network, an antenna having a large number of antenna elements, the directivity of which is controlled by adjusting the phase of signals passing through the antenna elements to form a radio wave beam in a desired direction; a signal strength detection unit for detecting a signal strength received by the antenna; a first search unit that changes a direction of a beam formed by the antenna within a first range by phase adjustment of a signal passing through a part of antenna elements among a large number of antenna elements included in the antenna, and detects a direction in which the mobile station is located based on the signal strength detected by the signal strength detection unit; a second search unit that changes the direction of the beam formed by the antenna within a second range that includes the direction detected by the first search unit and is narrower than the first range by phase adjustment of a signal passing through some of the antenna elements among a large number of antenna elements included in the antenna, and detects the direction in which the mobile station is located based on the signal strength detected by the signal strength detection unit; A communication relay device comprising:

2. The communication relay device described in claim 1, wherein the first search unit changes the direction of the beam formed by the antenna within a first range and detects the direction in which the mobile station is located based on the change in signal strength detected by the signal strength detection unit, and detects the direction in which the peak radio signal among the change in signal strength is received as the direction in which the mobile station is located.

3. Further, a third search unit that changes a direction of the beam formed by the antenna within a third range that is equal to or smaller than the second range to receive a radio signal transmitted from the mobile station, and detects movement of the mobile station based on the signal strength detected by the signal strength detection unit, The communication relay device according to claim 1 .

4. A computer used in a communication relay device that relays communications between a base station and a mobile station connected to a network, a signal strength detection unit that detects the strength of a signal received by an antenna that includes a large number of antenna elements and that forms a radio wave beam in a desired direction by controlling the directivity of the signal through the antenna elements by adjusting the phase of the signal; a first search unit that changes a direction of a beam formed by the antenna within a first range by phase adjustment of a signal passing through a part of antenna elements among a large number of antenna elements included in the antenna, and detects a direction in which the mobile station is located based on the signal strength detected by the signal strength detection unit; a second search unit that changes the direction of the beam formed by the antenna within a second range that includes the direction detected by the first search unit and is narrower than the first range by phase adjustment of a signal passing through some of the antenna elements among a large number of antenna elements included in the antenna, and detects the direction in which the mobile station is located based on the signal strength detected by the signal strength detection unit; A communication relay program that functions as a

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