Patent ID: 12250031

DETAILED DESCRIPTION

A communication relay apparatus according an embodiment includes a detector and a controller. The detector detects a mobile station located in a coverage area formed by a plurality of remote units. The controller controls, for the plurality of remote units, communication resources used by the remote units for communication with the mobile station, based on a detection result of the detector.

Hereinafter, a communication relay system according to an embodiment will be described with reference to the drawings.

FIG.1shows a part of a fifth generation mobile communication system, so-called 5G. The mobile communication system includes a 5th generation core network (5G core network) 5GC and a radio access network New Radio (NR). In the example ofFIG.1, the radio access network NR includes a communication relay system.

The 5G core network 5GC controls the radio access network NR, collects traffic, performs communication between the collected traffic and an external network (the Internet IN, an external telephone network EN, or the like), and includes a core apparatus C as its center. The core apparatus C performs, for example, authentication/security management, session management, policy control, packet transfer, and the like.

On the other hand, the radio access network NR includes a plurality of base station apparatuses (for example, gNodeB (gNB)1and gNB2inFIG.1). The base station apparatuses gNB1and gNB2are controlled by the core apparatus C, and each forms a radio communication area (a so-called cell) capable of communicating with mobile station user equipment (UE).

To be more specific, the base station apparatus gNB1wirelessly communicates with the mobile station UE through an antenna apparatus AN provided on a roof of a building or a dedicated tower, and connects the mobile station UE to the 5G core network 5GC through the core apparatus C. In addition, the base station apparatus gNB1performs beam forming by a massive MIMO which controls phases of signals in a large number of antenna elements on the antenna apparatus AN, and contributes to an increase in communication volume and the like.

The base station apparatus gNB2has the same function as that of the base station apparatus gNB1, but wirelessly communicates with the mobile station UE through the distributed antenna system DAS instead of the antenna apparatus AN, and connects the mobile station UE to the 5G core network 5GC through the core apparatus C.

The distributed antenna system DAS is used in a special place to form a relatively small-scale radio communication area compared to that of the antenna apparatus AN (for example, an inside of a building, an underground mall, or other structures, a sparsely or densely populated area, an area in which tower construction is difficult or limited, and a site such as an event hall where the antenna apparatus AN is not permanently placed). As illustrated inFIG.1, the distributed antenna system DAS includes a master unit MU, remote units RU1to RU3, and antennas AN1to AN3.

The master unit MU collectively controls each portion of the distributed antenna system DAS, and serves as a communication relay apparatus that enables the mobile station UE to communicate with the base station apparatus gNB2via the antennas (AN1to AN3) and the remote units (RU1to RU3). In a case where the master unit MU is connected to each of the remote units RU1to RU3through an optical communication line, the master unit MU may be generally referred to as an optical repeater.

The antennas AN1to AN3are respectively connected to the corresponding remote units RU1to RU3in a one-to-one correspondence, each antenna being formed of a large number of antenna elements, and support a massive MIMO in which directivity is controlled (beam forming is performed) by adjusting phases of transmission RF signals and/or reception RF signals.

In this embodiment, in order to simplify the description, it is assumed that each of the antennas AN1to AN3perform beam forming to form a maximum of four beams at a time in arbitrary directions. Further, in order to simplify the description, it is assumed that the master unit MU, which will be described in detail later, processes (relays) a maximum of four streams corresponding to the four beams at a time.

In an actual apparatus, the maximum number is not limited to four, and may be three or less, or five or more. In addition, the number of beams formed by each of the antennas AN1to AN3is not fixed, and may be dynamically changed by, for example, changing the number of antenna elements to be used.

The remote units RU1to RU3are respectively connected to the corresponding antennas AN1to AN3in a one-to-one correspondence, and can be connected so as to be able to communicate with the master unit MU via an optical communication line. In addition, the remote units RU1to RU3can perform beam forming by phase adjustment on the corresponding antennas AN1to AN3, respectively, and can also detect (search for) a direction in which the mobile station UE is located by measurement of reception intensity and beam forming.

More specifically, for the uplink, the remote units RU1to RU3perform phase adjustment (beam forming) on RF signals obtained by the corresponding antennas AN1to AN3, and obtain reception RF signals respectively corresponding to four beams at a maximum. In the beam forming in the remote units RU1to RU3, among the four beams at the maximum, beams corresponding to the number of streams allocated to each mobile station UE by the master unit MU are formed toward the mobile station UE. The remote units RU1to RU3down-convert the reception RF signals corresponding to the respective beams and simultaneously demodulate the reception RF signals into four reception signals respectively corresponding to four beams at the maximum. The remote units RU1to RU3serially bundle the respective demodulated reception signals, convert the reception signals from electrical signals into optical signals (modulate optical carriers), and transfer the optical signals to the master unit MU through the optical communication line. A stream included in the reception signal is referred to as a UL stream signal.

On the other hand, regarding the downlink, the remote units RU1to RU3convert optical signals transferred from the master unit MU through the optical communication line into electrical signals, and simultaneously demodulate the electrical signals into signals (hereinafter, referred to as DL stream signals) respectively corresponding to four streams at the maximum.

Then, the remote units RU1to RU3generate transmission RF signals obtained by modulating carriers using the DL stream signals, and output the transmission RF signals respectively to the antennas AN1to AN3connected thereto, to radiate the transmission RF signals into a space. Note that each of the remote units RU1to RU3can perform beam forming to simultaneously form four beams at a maximum, and each forms a beam for each DL stream signal to perform transmission. That is, in a case where four DL stream signals are obtained by demodulation, the remote units RU1to RU3form four beams and each beam transmits one DL stream signal.

Next, the master unit MU will be described in detail.FIG.2shows a configuration example of the master unit MU. The master unit MU includes ports P1to P3, a transfer unit10, an uplink (UL) signal processor20, a downlink (DL) signal processor30, and a controller100.

The ports P1to P3, respectively corresponding to the remote units RU1to RU3, can be connected to the optical communication line in a one-to-one correspondence, and are connected to the UL signal processor20and the DL signal processor30.

For the uplink, the ports P1to P3convert optical signals transmitted from the corresponding remote units RU1to RU3into electrical signals, demodulate the electrical signals into a maximum of four reception signals (reception signals of the respective beams demodulated by the remote units RU1to RU3) corresponding to the beams, and output the demodulated reception signals in parallel. The demodulated reception signals are output to the UL signal processor20.

The ports P1to P3function as an information acquirer that acquires, from the reception signals, information transmitted from the remote units RU1to RU3, to monitor the demodulated reception signals, and detect a communication start request (PRACH) from the mobile station UE included in the reception signals and stream IDs allocated to the reception signals (UL stream signals). Further, the ports P1to P3function as a position detector, and detect a presence of the mobile station UE located in a coverage area formed by each of the remote units RU1to RU3from results of the aforementioned detection or the like. These detection results are reported to the controller100.

On the other hand, for the downlink, four DL stream signals at a maximum are simultaneously input from the DL signal processor30to the ports P1to P3. Then, the ports P1to P3serially bundle the input DL stream signals, convert the electrical signals into optical signals (modulate optical carriers), and transfer the optical signals to the corresponding remote units RU1to RU3through the optical communication line.

The transfer unit10accommodates a communication line connected to the base station apparatus gNB2and communicates with the base station apparatus gNB2through the communication line. To be more specific, for the uplink, the transfer unit10transfers UL signals (four signals at a maximum at a time) input from the UL signal processor20to the base station apparatus gNB2. On the other hand, for the downlink, the transfer unit10receives DL signals (four signals at a maximum at a time) transferred from the base station apparatus gNB2through the communication line, and outputs the DL signals to the DL signal processor30.

Under the control of the controller100, the UL signal processor20performs a signal addition process of selectively adding the reception signals of the respective beams input from the ports P1to P3, and outputs the resultant signal αs a UL signal to the transfer unit10. The signal addition process will be described in detail later.

Under the control of the controller100, the DL signal processor30performs a signal distribution process of selectively distributing and outputting the DL signals input from the transfer unit10to the ports P1to P3. The signal distribution process will be described in detail later.

The controller100is a control center that collectively controls each portion of the master unit MU. The controller100includes a memory (not shown) that stores a control program and control data, and a processor (not shown) that executes processing based on the control program and the control data, thereby realizing various control functions. Note that the control program may be provided by a storage medium other than the memory. Details of the control will be described later in the description of the operation.

Next, a configuration example of the UL signal processor20will be described with reference toFIG.3.

The UL signal processor20includes uplink multiplexer switches (UL MUX SW)211to213and addition processors221to224.

The UL MUX SW211to213are in one-to-one correspondence with the ports P1to P3, respectively, receive four reception signals at a maximum output from the ports P1to P3, respectively, selectively multiplex these signals in accordance with UL switching signals α, β, and γ from the controller100, and output the multiplexed signals.

Here, a configuration example of the UL MUX SW211will be described with reference toFIG.4. The configurations of the UL MUX SW212and213are the same, and thus the description thereof will be omitted. However, the UL switching signals α, β, and γ may be different from one another.

The UL MUX SW211includes a switching controller2110, multiplexers2111to2114, and an output switch2115.

Each of the multiplexers2111to2114includes four input terminals, and four reception signals at a maximum output from the port P1are input thereto. Then, in accordance with an instruction from the switching controller2110, the input reception signals are selectively multiplexed and output to the output switch2115as multiplexed reception signals.

The output switch2115includes four independent switches corresponding to the multiplexers2111to2114, and multiplexed reception signals are input from the corresponding multiplexers2111to2114to the respective switches. Then, in accordance with an instruction from switching controller2110, the multiplexed reception signals are output from the output terminals of the switches. These output terminals serve as output terminals of the UL MUX SW211.

The switching controller2110controls the multiplexers2111to2114and the output switch2115in accordance with the UL switching signal α from the controller100to control multiplexing and output. That is, under the control in accordance with the UL switching signal α, a maximum of four reception signals output from the port P1are selectively multiplexed, and outputs and destinations of the multiplexed reception signals are controlled.

Reference is again made toFIG.3. Each of the addition processors221to224includes three input terminals and is connected to one of four output terminals of each of the UL MUX SW211to213, and the multiplexed reception signals are input to the three input terminals. Then, the addition processors221to224add (combine) a maximum of three multiplexed reception signals and output the added multiplexed reception signals to the transfer unit10as UL signals.

Next, a configuration example of the DL signal processor30will be described with reference toFIG.5.

The DL signal processor30includes downlink multiplexer switches (DL MUX SW)311to313.

The DL MUX SW311to313are in one-to-one correspondence with the ports P1to P3, respectively, receive four DL signals at a maximum output from the transfer unit10, selectively multiplex these DL signals in accordance with DL switching signals χ, ψ, and ω from the controller100, and output the multiplexed signals to the corresponding ports P1to P3. The DL MUX SW311to313may output signals without multiplexing.

A configuration example of the DL MUX SW311will be described with reference toFIG.6. The configurations of the DL MUX SW212and313are the same, and thus the description thereof will be omitted. However, the DL switching signals χ, ψ, and ω may be different from one another.

The DL MUX SW311includes a switching controller3110and multiplexers3111to3114.

Each of the multiplexers3111to3114includes four input terminals, and four DL signals at a maximum output from the transfer unit10are distributed and input to the multiplexers. Then, in accordance with an instruction from the switching controller2110, the multiplexers3111to3114selectively multiplex the input DL signals and output the multiplexed signals as one signal. The multiplexers3111to3114respectively correspond to four input terminals of the port P1in a one-to-one correspondence, and output a signal obtained by the multiplexing to the corresponding input terminals of the port P1.

The switching controller3110controls the multiplexers3111to3114in accordance with the DL switching signal χ from the controller100to control multiplexing and output. That is, under the control of the switching controller3110in accordance with the DL switching signal χ, a maximum of four DL signals can be selectively multiplexed and output to any or all of the four input terminals of the port P1.

Next, the operation of the communication relay system will be described. In the following description, the operation of the distributed antenna system DAS will be described in particular.FIG.7is a flowchart for explaining a control flow of the controller100of the master unit MU.

At the start of the operation of the distributed antenna system DAS, the controller100executes the processing illustrated inFIG.7, monitors detection results reported from the ports P1to P3, and monitors communication (communication start, communication in progress, and communication end) through each of the remote units RU1to RU3. That is, the controller100monitors and stands by for a generation of a communication start request from the mobile station UE located in the coverage area formed by each of the remote units RU1to RU3or an end of a communication session performed by the mobile station UE in the coverage area.

For example, if the mobile station UE located in the coverage area of the remote unit RU1transmits a communication start request, the communication start request is received by the antenna AN1and the remote unit RU1, and the communication start request reaches the port P1of the master unit MU through the optical communication line. As an example of the communication start request, a signal such as a physical random access channel (PRACH) is conceivable.

The port P1at which the communication start request arrived detects the generation of the communication start request and reports the detection to the controller100. The controller100recognizes that the port which reported the detection is the port P1, and proceeds to step701.

In the above description, the case where the communication start request through the remote unit RU1is detected has been described as an example. However, the remote unit RU2(or RU3) also performs a report in a similar operation from the port P2(or P3), and the controller100recognizes that the report was received from P2(or P3).

In an initial state of the operation of the distributed antenna system DAS, the master unit MU distributes and outputs the DL signal from the base station apparatus gNB2to each of the remote units RU1to RU3for the downlink stream. In addition, the remote units RU1to RU3in the initial state form beams in the same direction and transmit DL signals according to the same algorithm. However, as an initial setting, it is also possible to apply different settings to the remote units RU1to RU3so as to form beams in a predetermined direction.

In step701, the controller100acquires detection results from all of the ports P1to P3, counts the number of mobile stations UE in a state of communication in progress for each of the remote units RU1to RU3based on the detection results, and proceeds to step702.

As a method of counting the number of mobile stations UE in a state of communication in progress, for example, the PRACH transmitted from the mobile station UE to the base station apparatus gNB2may be monitored by the ports P1to P3or the controller100, and the number of PRACHs may be counted for each of the remote units RU1to RU3by distinguishing the mobile stations UE.

In step702, the controller100executes a stream allocation process, and then proceeds to step703. To be more specific, in accordance with a predetermined stream allocation algorithm, the controller100allocates the streams ID1to ID4to the mobile stations UE that made the communication start request and the mobile stations UE that are already in communication, and proceeds to step703. For the mobile stations UE that are already in communication, the stream IDs to be allocated are reviewed, but may not be changed.

The stream allocation algorithm may be determined in consideration of various factors. For example, the stream IDs to be allocated to the respective mobile stations UE are determined based on the number of streams that can be processed by the master unit MU (four in this example), the number of the remote units accommodated by the master unit MU (three, corresponding to RU1to RU3, in this example), the number of the mobile stations UE located in the coverage area of each of the remote units RU1to RU3(for example, the number of PRACHs recognized by the controller100), the maximum number of streams between the master unit MU and each of the remote units RU1to RU3(four in this example), the maximum number of streams between each of the remote units RU1to RU3and the mobile stations UE (four in this example), communication qualities of the respective resources, types of communication used by the mobile stations UE, communication capabilities of the mobile stations UE, and the like.

Among these items of information, the information on the master unit MU and the remote units RU1to RU3may be stored in a storage unit (not shown) of the master unit MU in advance. The information on the remote units RU1to RU3and the mobile stations UE may be dynamically acquired by the controller100from the remote units RU1to RU3and the mobile stations UE through the ports P1to P3.

In step703, the controller100reports the stream IDs allocated to the mobile stations UE in step702to each of the remote units RU1to RU3, and proceeds to step704. To be specific, the controller100reports to each of the remote units RU1to RU3, for example, the identification information of the mobile stations UE and the allocated stream IDs in association with each other.

Here, each of the remote units RU1to RU3that received the report secures a communication resource corresponding to the number of reported stream IDs for each mobile station UE, and establishes a communication link with each mobile station UE according to a predetermined procedure.

In step704, the controller100performs the signal addition process on the four signals output from each of the ports P1to P3based on the stream IDs allocated to the mobile stations UE in step702, thereby generating four UL signals, and proceeds to step705.

In the signal addition process, four signals output from each of the ports P1to P3are selectively added to generate four UL signals, and the addition process is performed by excluding a part or all of the signals not including the streams transmitted from the mobile stations UE. Accordingly, at least a signal including a stream transmitted from a mobile station UE is included in one of the four UL signals.

To be more specific, based on the stream IDs allocated to the mobile stations UE in step702, the controller100generates the UL switching signals α, β, and γ for adding the signals corresponding to the allocated stream IDs among the four signals output from each of the ports P1to P3, and controls the signal addition process of the UL signal processor20.

In step705, the controller100controls the UL signal processor20and the transfer unit10to start transferring the four UL signals obtained by the signal addition process of the UL signal processor20to the base station apparatus gNB2by the transfer unit10, and terminates the process.

Thereafter, the controller100starts the processing shown inFIG.7again, monitors detection results reported from the ports P1to P3, and monitors communication (communication start, communication in progress, and communication end) for each of the remote units RU1to RU3. If a communication start request is generated from the mobile station UE located in the coverage area formed by each of the remote units RU1to RU3or the communication session performed by the mobile station UE in the same coverage area is terminated, the controller100executes the processing of step701and subsequent steps again.

Next, with reference toFIG.8, the operation will be described using a specific example.

As shown inFIG.8(a), a case is considered in which the mobile station UE1that requests communication is present only in the coverage area of the remote unit RU1among the remote units RU1to RU3, that is, a case in which a communication start request is transmitted from the mobile station UE1and there is no mobile station in the coverage areas of the other remote units RU2and RU3.

In this case, the controller100recognizes that the mobile station UE1is present only in the coverage area of the remote unit RU1based on the detection result of each of the ports P1to P3obtained in step701, allocates, for example, all of the four streams ID1to ID4to the remote unit RU1by the stream allocation algorithm of step702, and allocates no streams to the remaining remote units RU2and RU3.

Accordingly, the remote unit RU1reports that the streams ID1to ID4are allocated to the mobile station UE1in step703, secures communication resources for the four streams (UL stream signals), and establishes a communication link for communicating with the mobile station UE1using the four streams in accordance with a predetermined procedure. To be more specific, in order to receive the four UL stream signals, the remote unit RU1forms all of the four beams that can be formed by the antenna AN1, that is, the beams respectively corresponding to the streams ID1to ID4, in the direction toward the mobile station UE1.

On the other hand, in the master unit MU, since the streams ID1to ID4are allocated to the mobile station UE1in step702, the controller100recognizes that the streams allocated to the remote unit RU1are the streams ID1to ID4and no streams are allocated to the remaining remote units RU2and RU3, and generates the UL switching signals α, β, and γ for adding signals corresponding to the allocated stream IDs.

At this time, the UL switching signal α is a signal for instructing the UL MUX SW211to output four signals input from the port P1and respectively corresponding to four beams of the remote unit RU1to the corresponding addition processors221to224.

On the other hand, the UL switching signal β is a signal for instructing the UL MUX SW212not to output some or all of the four signals input from the port P2and respectively corresponding to four beams of the remote unit RU2to the addition processors221to224. Similarly, the UL switching signal γ is a signal for instructing the UL MUX SW213not to output some or all of the four signals input from the port P3and respectively corresponding to four beams of the remote unit RU3to the addition processors221to224.

As a result, the addition processors221to224respectively output the signals of the four streams ID1to ID4of the remote unit RU1input from the port P1to the transfer unit10, with little or no addition of signals from the other remote units RU2and RU3. In this way, in the addition processors221to224, addition of a signal that is not expected to be used for communication to a signal that is actually used for communication is suppressed.

Next, an example shown inFIG.8(b)will be described.

In this example, one mobile station UE (UE1, UE2, UE3) is located in each of the coverage areas of the remote units RU1to RU3. Alternatively, it may be considered that the mobile stations UE2and UE3moved from the state shown inFIG.7(a)(only the mobile station UE1is present) to the respective coverage areas of the remote units RU2and RU3(or that the mobile stations UE2and UE3that were originally located in the respective coverage areas of the remote units RU2and RU3made a communication start request from a state in which they are not communicating).

In this case, based on the detection result of each of the ports P1to P3obtained in step701, the controller100recognizes that one mobile station UE (UE1, UE2, and UE3) is located in each of the coverage areas of the remote units RU1to RU3, and that each of the three mobile stations requests communication. Then, the controller100allocates, for example, two streams ID1and ID2to the remote unit RU1, and allocates one stream ID3or ID4to each of the remaining remote units RU2and RU3according to the stream allocation algorithm in step702.

The number of streams allocated to the remote unit RU1is larger than that allocated to the remote units RU2and RU3for various reasons, for example, as in the following cases: (1) the mobile station UE1is already in communication before the mobile stations UE2and UE3, (2) the environment of the radio transmission path is better (or worse) in the mobile station UE1than in the mobile stations UE2and UE3, (3) the type of communication requires more resources in the mobile station UE1than in the mobile stations UE2and UE3, (4) the mobile station UE1is a device (an administrator, a user of a special service, or the like) having priority over the mobile stations UE2and UE3, and (5) the mobile station UE1is a device having higher communication capability than the mobile stations UE2and UE3(for example, the mobile stations UE2and UE3are not capable of using two streams). It is conceivable to execute the stream allocation process of step702by weighting these conditions with priority.

Accordingly, the remote unit RU1reports that the streams ID1and ID2are allocated to the mobile station UE1in step703, secures communication resources for the two streams (UL stream signals), and establishes a communication link for communicating with the mobile station UE1using the two streams in accordance with a predetermined procedure. To be more specific, in order to receive the two UL stream signals, the remote unit RU1forms two beams among the four beams that can be formed by the antenna AN1, that is, the beams respectively corresponding to the streams ID1and ID2in the direction toward the mobile station UE1.

Similarly, the remote unit RU2reports that the stream ID3is allocated to the mobile station UE2in step703, secures a communication resource for the one stream (UL stream signal), and establishes a communication link for communicating with the mobile station UE2using the one stream in accordance with a predetermined procedure. To be more specific, in order to receive the one UL stream signal, the remote unit RU2forms one beam among four beams that can be formed by the antenna AN2, that is, the beam corresponding to the stream ID3in the direction toward the mobile station UE2.

Similarly, the remote unit RU3reports that the stream ID4is allocated to the mobile station UE3in step703, secures a communication resource for the one stream (UL stream signal), and establishes a communication link for communicating with the mobile station UE3using the one stream in accordance with a predetermined procedure. To be more specific, in order to receive the one UL stream signal, the remote unit RU3forms one beam among four beams that can be formed by the antenna AN3, that is, the beam corresponding to the stream ID4in the direction toward the mobile station UE3.

On the other hand, in the master unit MU, the controller100generates the UL switching signals α, β, and γ based on the allocation of the two streams ID1and ID2to the mobile station UE1and the allocation of one stream ID3or ID4to each of the mobile stations UE2and UE3in step702.

At this time, the UL switching signal α is a signal for instructing the UL MUX SW211to output, to the addition processors221and222, signals corresponding to the streams ID1and ID2among four signals input from the port ID1and respectively corresponding to the four beams of the remote unit RU1.

On the other hand, the UL switching signal β is an instruction signal for causing the UL MUX SW212to output, to the addition processor223, a signal corresponding to the stream ID3without fail among four signals respectively corresponding to the four beams of the remote unit RU2input from the port P2and not to output some or all of the remaining three signals to the addition processors221to224.

Similarly, the UL switching signal γ is an instruction signal for causing the UL MUX SW213to output, to the addition processor223, a signal corresponding to the stream ID4without fail among four signals respectively corresponding to the four beams of the remote unit RU3input from the port P3and not to output some or all of the remaining three signals to the addition processors221to224.

That is, the UL switching signals α, β, and γ are signals including an instruction not to output some or all of the signals not used for communication to the addition processors221to224.

As a result, the addition processors221and222output the signals of the two streams ID1and ID2of the remote unit RU1input from the port P1to the transfer unit10, with little or no addition of signals from the other remote units RU2and RU3.

Similarly, the addition processor223outputs the signal of the one stream ID3of the remote unit RU2input from the port P2to the transfer unit10, with little or no addition of signals from the other remote units RU1and RU3.

Similarly, the addition processor224outputs the signal of the one stream ID4of the remote unit RU3input from the port P3to the transfer unit10, with little or no addition of signals from the other remote units RU1and RU2.

That is, in the addition processors221to224, addition of a signal that is not used for communication (a signal for which communication is not expected) to a signal that is actually used for communication is suppressed.

As described above, in the communication relay system having the aforementioned configuration, necessary stream allocation is autonomously performed for each remote unit, and each remote unit autonomously performs beam forming for the allocated stream in the distributed antenna system DAS including the remote units RU1to RU3.

Therefore, according to the communication relay system having the aforementioned configuration, since the communication resource is allocated to each remote unit in accordance with the presence of the mobile station, it is possible to efficiently use the communication resources in the distributed antenna system DAS, which contributes to improvement in communication quality.

In addition, in the communication relay system having the aforementioned configuration, when the master unit MU that connects the remote units RU1to RU3to the base station apparatus gNB2adds (combines) the reception signals by the remote units RU1to RU3and transfers the signals to the base station apparatus gNB2, some or all of the signals that are not used for communication (signals for which communication is not expected) are not added.

Therefore, according to the communication relay system having the aforementioned configuration, addition of unnecessary signal components to a signal transferred from the master unit MU to the base station apparatus gNB2is suppressed, which suppresses NF degradation and contributes to improvement of a quality of communication.

The present invention is not limited to the embodiment described above and can be embodied in practice by modifying the structural elements without departing from the gist of the invention. In addition, various inventions can be made by suitably combining the structural elements disclosed in connection with the above embodiments. Furthermore, for example, a configuration may be considered in which some structural elements of all the structural elements described in the embodiment are deleted. Furthermore, structural elements of different embodiments may be suitably combined.

For example, in the aforementioned embodiment, the case where the base station apparatus gNB2is directly connected to the distributed antenna system DAS has been described as an example. However, a relay for increasing the number of distributions may be provided between the base station apparatus gNB2and the distributed antenna system DAS, and a plurality of distributed antenna systems DAS may be connected to the base station apparatus gNB2.

Furthermore, in the aforementioned embodiment, the controller100of the master unit MU determines a stream to be allocated to each of the remote units RU1to RU3, but the embodiment is not limited thereto. For example, the controller included in each of the remote units RU1to RU3may determine the number of streams to be used by the remote unit based on the number of mobile stations UE located in the coverage area of the remote unit, the number of available streams reported from the master unit MU, or the like. Alternatively, the aforementioned relay may perform the same process as that of the controller100, and may allocate a stream to each distributed antenna system DAS.

In the above embodiment, in the initial state of the control illustrated inFIG.7, the master unit MU distributes and outputs the DL signal from the base station apparatus gNB2to the remote units RU1to RU3for the downlink stream. However, as shown inFIGS.5and6, the master unit MU has a function of selectively outputting a maximum of four DL signals transmitted from the base station apparatus gNB2to arbitrary ports P1to P3according to the DL switching signals χ, ψ, and ω from the controller100.

Therefore, for example, after the uplink stream allocation is performed by the stream allocation process of step702, the same number of downlink streams may be allocated to the remote units (RU1to RU3) to which the uplink streams are allocated with reference to the allocation result, and each of the remote units RU1to RU3may be caused to transmit the corresponding downlink streams.

It is needless to say that various modifications can be made without departing from the scope of the present invention.

While several embodiments have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. The novel embodiments described herein can be implemented in a variety of other forms; furthermore, various omissions, substitutions, and changes can be made without departing from the spirit of the invention. The embodiments and their modifications are included in the scope and spirit of the invention and are included in the scope of the claimed inventions and their equivalents.