Wireless communication system, control method for wireless communication system, and distributed unit program

Abstract

The present invention comprises a plurality of DUs (2), a plurality of RUs (6) that are connected to the DUs (2), and ANTs (7) that are connected to respective RUs (6) and transmit wireless signals to UE. The DUs (2) comprise a MAC Scheduler (31), an RLC (4), and a HiPHY (5). The MAC Scheduler (31) makes an ANT (7) connected to an RU (6) connected to a HiPHY (5) included in a DU (2) that does not include the MAC Scheduler (31) transmit a wireless signal via the HiPHY (5).

Description

Wireless communication system, wireless communication system control method, and distributed unit program

[0001] The present invention relates to wireless communication systems such as 5G networks.

[0002] 5G (fifth generation mobile communication system) has features such as high speed communication, high reliability, low latency, and multiple simultaneous connections, and various new services that take advantage of these features have been proposed. With the aim of streamlining capital investment, 5G's entire architecture is designed with virtualization in mind. O-RAN (Open RAN) has been proposed to realize vRAN (virtualized RAN), which virtualizes the Radio Access Network (RAN).

[0003] With the spread of vRAN, it is expected that a configuration in which multiple distributed units (DUs) are connected to one central unit (CU) of a RAN and multiple antennas are controlled by one CU will become widespread. The DU integrates a control signal processing unit and a data communication signal processing unit, and the data communication processing unit includes a buffer control unit and a scheduler.

[0004] Japanese Patent Publication No. 2021-111825 Publication of Japanese Special Publication No. 2023-542177 Publication of Japanese Special Publication No. 2023-543856

[0005] To achieve coordination between multiple antennas in large-scale cell (antenna) coordination technologies, such as Cell-Free Massive MIMO (Multi-Input Multi-Output) and distributed MIMO, signals to be transmitted to a UE (User Equipment) must be transmitted simultaneously from multiple antennas. Although it is possible to simultaneously transmit from multiple antennas, for example, to link the MAC layer of a DU housed in one housing with the PHY layer of a DU housed in another housing, increasing the number of antennas to be coordinated results in a large amount of traffic being generated between the DUs. Furthermore, since time synchronization is required between the DU's buffer control unit and scheduler, it is difficult to separate them, and therefore the DUs cannot be distributed to different housings. Therefore, antenna coordination is limited to antennas that can be housed in a single device.

[0006] One aspect of the present invention aims to realize a wireless communication system that eliminates the need for data signal exchange associated with the exchange of control signals between distributed units (DUs) and enables cooperation between large-scale cells (antennas) that is independent of the traffic volume of data signals.

[0007] In order to solve the above problem, a wireless communication system according to the present invention comprises a plurality of distributed units, a plurality of radio units connected to the distributed units, and an antenna unit connected to each of the radio units and transmitting a radio signal to a user terminal, wherein the distributed units comprise a control signal processor, a buffer controller, and an upper PHY layer, and the control signal processor transmits the radio signal to the antenna unit connected to the radio unit connected to the upper PHY layer via the upper PHY layer accommodated in the distributed unit that does not accommodate the control signal processor. Note that the operations of the distributed units and the radio units may be controlled by a RAN Intelligent Controller (RIC).

[0008] Furthermore, the present invention provides a control method for a wireless communication system comprising a plurality of distributed units, a plurality of wireless units connected to the distributed units, and an antenna unit connected to each of the wireless units and transmitting a wireless signal to a user terminal, wherein the distributed units further comprise a control signal processing unit, a buffer control unit, and an upper PHY layer, and the control signal processing unit has a step of causing the antenna unit connected to the wireless unit connected to the upper PHY layer to transmit the wireless signal via the upper PHY layer accommodated in the distributed unit that does not accommodate the control signal processing unit.

[0009] According to the present invention, the exchange of data signals accompanying the exchange of control signals between distributed units is no longer necessary, and cooperation between large-scale cells (antennas) that is independent of the traffic volume of data signals is possible.

[0010] It is a diagram showing an example of the configuration of a wireless communication system according to an embodiment of the present invention. It is a diagram showing a functional separation structure of a DU of the wireless communication system. It is a diagram showing an operation of the wireless communication system.

[0011] Hereinafter, one embodiment of the present invention will be described in detail.

[0012] (Configuration Example of Wireless Communication System) FIG. 1 shows a configuration example of a wireless communication system 1 according to this embodiment. As shown in the figure, the wireless communication system 1 includes CUs (Central Units) 8 (8a, 8b, ...), DUs (Distributed Units) 2 (2a, 2b, ...), RUs (Radio Units) 6 (6a, 6b, ...), ANTs (Antenna Units) 7 (7a, 7b, ...), and the like. Note that the wireless communication system 1 according to this embodiment is assumed to be a 5G network, but is not limited thereto, and can be applied to any wireless communication network having similar functions.

[0013] The CU8 is also called a master station or aggregation station, and mainly controls multiple DU2s and RRC (Radio Resource Control), a communication protocol between UEs (User Equipment) and base stations. Note that the CU8, like the DU2, is configured by being installed on a general-purpose server and virtualized.

[0014] DU2, also known as a slave station, mainly processes the upper PHY layer and MAC layer. DU2 is configured by being installed on a general-purpose server and virtualized. DU2 is connected to CU8, where it processes communications with the upper layer, and is also connected to RU6 installed at each site. As will be described in detail later, DU2 comprises a MAC Scheduler 31 and a data communication signal processing unit 21, which includes RLC4, MAC Multiplexing 32, and HiPHY5 (5a, 5b, ...; upper PHY layer), separated from each other. DU2a, 2b, 2c, and 2d are each housed in a single housing.

[0015] The RU 6 is a device that performs processing of the lower PHY layer of the base station. The RU 6 transmits and receives radio waves to and from the UE (not shown), and also communicates with the DU 2. The RU 6 is connected to the ANT 7. In FIG. 1, the RUs 6b, 6c, and 6d and the ANTs 7c to 7h connected thereto constitute a cell of a single frequency network (SFN).

[0016] An RIC (RAN Intelligent Controller) is provided above the CU 8 and controls the DU 2. As shown in Fig. 1, the RIC includes at least a Non-RT RIC 10 and a Near-RT RIC 9.

[0017] The Near-RT RIC 9 controls the RAN in short time units of 10 ms to 1 second. The Near-RT RIC 9 communicates with the CU 8 via the E2 interface. The Non-RT RIC 10 controls the RAN in long time units of about 1 second. The Non-RT RIC 10 communicates with the Near-RT RIC 9 via the A1 interface. The RIC communicates with the Non-RT RIC 10 and Near-RT RIC 9 and the DU 2 via the O1 interface. Control of QoS, etc. is performed from the Non-RT RIC 10 via the Near-RT RIC 9 and the E2 interface.

[0018] 2 shows the functional separation structure of the DU 2. As shown in the figure, in the DU 2, the MAC function is separated into a MAC Scheduler 31 and a MAC Multiplexing 32.

[0019] The MAC scheduler 31 performs scheduling related to wireless transmission and reception in accordance with the Media Access Control protocol.

[0020] On the other hand, the MAC Multiplexing 32 performs data multiplexing / demultiplexing processing, error correction processing using HARQ (Hybrid Automatic Repeat reQuest), etc., which are part of the MAC protocol. That is, the MAC Multiplexing 32 has both MUX and DeMUX functions.

[0021] RLC4 is in charge of the Radio Link Control protocol and performs retransmission control and the like.

[0022] The HiPHY 5 is a layer above the physical layer, and performs processes such as scrambling, layer mapping, etc. The layer below the physical layer (LowMAC) is included in the RU 6.

[0023] As shown in the figure, the MAC Multiplexing 32 and the HiPHY 5 constitute a radio signal processing unit 22. Furthermore, the RLC 4 and the radio signal processing unit 22 constitute a data communication signal processing unit .

[0024] With the above configuration, each DU2 operates as follows.

[0025] DU2 communicates with upper layers using MAC Scheduler 31 for control signals and RLC4 for data signals. Specifically, MAC Scheduler 31 receives control signals (Policies, QoS) from PCRF (Policy and Charging Rule Function) and performs QoS (bandwidth control) for each subscriber information and billing control according to the communication usage status. RLC4 transmits data signals received from upper layers to radio signal processing unit 22, and transmits data signals received from radio signal processing unit 22 to upper layers.

[0026] During downlink, the MAC scheduler 31 receives a resource request along with a buffer status from the RLC 4. During uplink, the MAC scheduler 31 receives a resource request along with a radio channel condition from the HiPHY 5. The MAC scheduler 31 also transmits scheduling information (scheduling decisions) such as time slots to the MAC multiplexing 32.

[0027] During uplink, an encoded data signal acquired by the RU 6 from a radio signal received by the ANT 7 is input to the HiPHY 5. The HiPHY 5 notifies the MAC scheduler 31 of the radio channel conditions using information indicating the state of the UE as a reference signal (Sounding Reference Signal).

[0028] During downlink, data signals as traffic for user UEs are input from the upper layer or core network side to the RLC 4. The RLC 4 creates a buffer for each UE and holds and controls the data signals processed by the MAC Multiplexing 32. Then, at a predetermined timing, the RLC 4 orders the buffered data as a data signal contained in one frequency and transmits it to the HiPHY 5.

[0029] (DU Internal Operation for Inter-Cell Coordination) Fig. 3 shows the internal operation performed by DU2... for inter-cell coordination. Although MAC Multiplexing 32 is omitted in the figure, it should be understood that it operates together with HiPHY 5.

[0030] In the figure, the MAC Scheduler 31R is a representative MAC Scheduler 31 (hereinafter referred to as the "representative MAC Scheduler 31R") designated from among the MAC Schedulers 31 of the DUs 2 that wish to cooperate between cells. The representative MAC Scheduler 31R is responsible for communication of control signals in the DUs 2 that wish to cooperate between cells. In other words, the representative MAC Scheduler 31R places the data communication signal processing units 21 of the DUs 2 that wish to cooperate between cells under its control.

[0031] A PTP GM (PTP Grandmaster) 11 is a network time server that distributes highly accurate time, and is provided in the wireless communication system 1. In the figure, the operations of a representative MAC Scheduler 31R, a Per-UE RLC 4, a Per-RU HiPHY 5, and an RU 6 are synchronized by a Time Sync signal distributed by the PTP GM 11.

[0032] The Per-UE RLC 4 is an RLC 4 included in a DU 2 for inter-cell coordination. A Per-UE RLC 4 exists for each UE that is a user.

[0033] The Per-RU HiPHY 5 is a HiPHY 5 included in the DU 2 that desires inter-cell coordination. A Per-RU HiPHY 5 exists for each connected RU 6.

[0034] With the above configuration, DU2..., which desires inter-cell cooperation, operates as follows.

[0035] In the downlink, the Per-UE RLC 4 notifies the representative MAC scheduler 31R of the downlink buffer status based on a downlink data signal input from a higher layer. In response, the representative MAC scheduler 31R notifies the Per-UE RLC 4 of downlink scheduling information (including which RU 6 to transmit to, i.e., which Per-RU HiPHY 5 to transmit to). Then, when the Per-UE RLC 4 transfers a data signal to the Per-RU HiPHY 5 (each HiPHY 5 of the DUs 2, etc. that require inter-cell coordination), it directly encodes a timestamp (time synchronization signal) into the downlink packet. This timestamp may be the time when each RU 6, etc. simultaneously transmits a radio signal to the UE.

[0036] On the other hand, in the uplink, the RU 6 acquires the signal received by the ANT 7, and the Per-RU HiPHY 5 notifies the representative MAC scheduler 31R of a reference signal (Sounding Reference Signal) indicating the UE state and an uplink scheduling request. In response, the representative MAC scheduler 31R notifies the Per-RU HiPHY 5 of uplink scheduling information. The Per-RU HiPHY 5 then transfers the data signal to the Per-UE RLC 4. Note that in the uplink, a timestamp is not encoded in the packet.

[0037] (Effects) 6G (6th generation mobile communication system) is premised on cooperation between cells (antennas). In other words, there is a shift from cells to distributed MIMO. For example, there is a concept such as Cell-Free Massive MIMO, where information from all antennas is centrally managed in one place.

[0038] In order to coordinate between cells (antennas), not only control signals but also data signals must be exchanged between different base stations, but the scale of the number of cells (antennas) that can cooperate is limited by the traffic volume of data signals.Furthermore, time synchronization is basically required between the RLC4 and the radio signal processing unit 22, making it difficult to separate them and making it impossible to distribute them between different housings, so the scale of cooperation is limited to the number of cells (antennas) that can be accommodated in a single housing.

[0039] To solve these problems, the wireless communication system 1 according to this embodiment particularly includes the following configurations (1) to (3).

[0040] (1) The MAC Scheduler 31 (control signal processing unit) in DU2 is separated from the RLC 4, MAC Multiplexing 32, and HiPHY 5 (data communication signal processing unit 21), and multiple data communication signal processing units 21 are placed under the control of a single MAC Scheduler 31. This enables coordination between large-scale cells (antennas) that is independent of the traffic volume of data signals.

[0041] In detail, conventionally, a DU contains a MAC and a PHY together. To coordinate the operation of a PHY in another DU from the MAC of one DU, a control signal must be sent. However, because the MAC and PHY are combined, data signals also flow together with the control signals. As a result, communication between different DUs requires a huge bandwidth for the data signals. This data signal traffic volume becomes a bottleneck, limiting the number of cells that can coordinate with each other.

[0042] A DU can be separated into a C-plane, which handles control signal communication, and a U-plane, which handles user-directed data signal communication. Therefore, a DU2 is separated into a MAC Scheduler 31, which handles control signals, and an RLC 4, MAC Multiplexing 32, and HiPHY 5, which handle data signals. This allows control signals to be exchanged between cooperating DUs 2, using the P5 interface; there is no need to exchange data signals using the P7 interface. For example, as shown in FIG. 1, when DUs 2c and 2b cooperate with each other, it is sufficient to send control signals from the MAC Scheduler 31d of DU 2c to the HiPHYs 5b and 5c of DU 2b using the P5 interface. In other words, there is no need to send data signals using the P7 interface, as in the past. Therefore, with regard to the communication of control signals from the MAC Scheduler 31, the number of RUs 6 accommodated in a DU2 can be expanded regardless of the traffic volume of user signal communication. In other words, it enables cooperation between large-scale cells (antennas) that is independent of the traffic volume of data signals, which is advantageous in terms of expanding the scale of Cell-Free Massive MIMO.

[0043] In this embodiment, the P5 (C-Plane) interface and P7 (U-Plane) interface of the FAPI (Femtocell Application Programming Interface) are assumed, but the present invention is not limited to this.

[0044] (2) The RLC 4 (buffer control unit) in DU 2 is separated from the MAC Multiplexing 32 and HiPHY 5 (radio signal processing unit 22), and multiple radio signal processing units 22 are placed under the control of a single RLC 4. This enables coordination between large-scale cells (antennas) that is independent of the traffic volume of data signals.

[0045] In detail, it is necessary for multiple cooperating ANTs 7 to emit beams to a specific UE at the same timing and with the same phase. To achieve this, the MAC scheduler 31 of the DU 2 that desires inter-cell coordination determines a representative MAC scheduler 31R to which the other DUs 2 are subordinate, and controls the HiPHYs 5 of the other cooperating DUs 2 through the RLC 4 housed in the same DU 2. Specifically, for example, as shown in FIG. 1, when coordination is performed between DUs 2c and 2b housed in different housings, the MAC scheduler 31d of DU 2c becomes the representative, and under its control, the HiPHYs 5b and 5c of DU 2b operate, and the RUs 6b and 6c connected to them transmit radio signals from ANTs 7c to 7f. The HiPHY 5d of the DU 2c also operates under the control of the MAC Scheduler 31d, and the RU 6d transmits wireless signals from the ANTs 7g to 7h.

[0046] At this time, as shown in FIG. 3, in communication between DUs 2c and 2b, the representative MAC scheduler 31R sends a control signal to the Per-UE RLC 4 of the same DU 2c, instructing ANTs 7c to 7h to transmit data radio signals at the transmission time. The Per-UE RLC 4 transmits data packets to the Per-RU HiPHYs 5b, 5c, and 5d of DUs 2c and 2b, which accommodate ANTs 7c to 7h. The ANTs 7c to 7h then transmit radio signals at the designated transmission time. In this way, by separating the RLC 4 from the HiPHY 5 in the DU 2, the HiPHYs 5 of other DUs 2, including DUs 2 accommodated in different housings, can operate cooperatively under the control of the RLC 4. This makes it possible to distribute ANTs 7 among DUs 2 that wish to cooperate, which is advantageous in terms of expanding the scale of Cell-Free Massive MIMO.

[0047] (3) Embedding timestamps in data signals exchanged between cooperating DUs 2.... This solves the problem of time synchronization that arises from separating the RLC 4 and HiPHY 5... in (2), on the premise that each distributed processing unit is time-synchronized by the PTP GM (PTP Grandmaster) 11.

[0048] In particular, if the HiPHY 5 is not separated from the MAC Scheduler 31 and the RLC 4 and is housed in a single housing, time synchronization is easy because it only requires referencing the time of the housing. However, if they are separated and distributed across different housings as in (2), time synchronization is necessary. Therefore, in the DU2, as shown in FIG. 3, under the control of the representative MAC Scheduler 31R, when transmitting a data packet to be transmitted from the ANT 7... to the Per-RU HiPHY 5... of the DU2... with which the Per-UE RLC 4 cooperates, a timestamp indicating the transmission time from the ANT 7... is embedded in the packet. Then, the RUs 6... that receive the packet with the embedded timestamp refer to the clocks in their respective housings and transmit a wireless signal from the ANT 7... at the specified transmission time. Note that each cooperating housing receives a synchronization signal from the PTP GM 11 to synchronize its time, so there is no need to individually adjust the time between the housings.

[0049] As described above, according to this embodiment, it is possible to provide a wireless communication network that eliminates the need for the exchange of data signals associated with the exchange of control signals between DUs, and enables cooperation between large-scale cells (antennas) that is independent of the traffic volume of data signals.

[0050] The representative MAC scheduler 31R may be statically set.

[0051] Furthermore, regarding the method of determining which DU2, RU6, and ANT7 will cooperate, an RU6 that wishes to cooperate can obtain a reference signal (Sounding Reference Signal) in uplink communication, thereby determining which UE is under which ANT7, and can then determine which ANT7 to use by further taking into account radio wave strength and channel information.

[0052] [Example of Implementation by Software] As described above, DU2 is configured by being installed on a general-purpose server and virtualized. The functions of DU2 (hereinafter referred to as "device") are realized by a program that causes a computer to function as the device, and by a program that causes the computer to implement each control function of the device.

[0053] In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., a memory) as hardware for executing the program. The functions described in each of the above embodiments are realized by executing the program using the control device and storage device.

[0054] The program may be non-transitory and may be recorded on one or more computer-readable recording media. The recording media may or may not be included in the device. In the latter case, the program may be supplied to the device via any wired or wireless transmission medium.

[0055] Furthermore, some or all of the functions of the control blocks can be realized by logic circuits. For example, an integrated circuit on which a logic circuit that functions as each of the control blocks is formed is also included in the scope of the present invention.

[0056] (Summary) A wireless communication system (1) according to aspect 1 of the present invention comprises a plurality of DUs (2...; distributed units), a plurality of RUs (6...; wireless units) connected to the DUs (2...), and ANTs (7...; antenna units) connected to each of the RUs (6) and transmitting wireless signals to a UE (user terminal), wherein the DUs (2...) comprise a MAC Scheduler (31; control signal processing unit), an RLC (4; buffer control unit), and a HiPHY (5; upper PHY layer), and the MAC Scheduler (31) causes the ANTs (7...) connected to the RUs (6...) connected to the HiPHYs (5...) to transmit the wireless signals via the HiPHYs (5...) accommodated in the DUs (2...) that do not accommodate the MAC Scheduler (31).

[0057] According to the above configuration, DU2 is separated into a MAC Scheduler 31 that handles control signals, and an RLC 4, MAC Multiplexing 32, and HiPHY 5 that handle data signals. That is, DU2 can be separated into a C-plane that handles control signal communication and a U-plane that handles user-directed data signal communication. As a result, for example, as shown in FIG. 1 , when coordinating between DU2c and 2b, it is sufficient to send control signals from the MAC Scheduler 31d of DU2c to the HiPHYs 5b and 5c of DU2b using the P5 interface. That is, there is no need to send data signals using the P7 interface, as in the past. This enables large-scale inter-cell (antenna) coordination that is independent of the data signal traffic volume.

[0058] A wireless communication system (1) according to aspect 2 of the present invention may be configured such that, in the above-mentioned aspect 1, the RLC (4) transmits a downlink data signal to the HiPHY (5...) contained in the DU (2...) that does not contain the RLC (4).

[0059] According to the above configuration, it is possible to distribute ANTs 7... among DUs 2... that wish to cooperate, thereby enabling cooperation between large-scale cells (antennas) that is independent of the traffic volume of data signals.

[0060] A wireless communication system according to Aspect 3 of the present invention may be configured in the above-described Aspect 2 such that the RLC (4) incorporates a timestamp (time synchronization signal) into the downlink data signal and transmits the data signal.

[0061] According to the above configuration, the RUs 6... that receive a data signal with an embedded timestamp can refer to the clock of each device and transmit a radio signal from the ANTs 7... according to the time specified in the timestamp.

[0062] A control method for a wireless communication system (1) according to aspect 4 of the present invention is a control method for a wireless communication system comprising a plurality of DUs (2...), a plurality of RUs (6...) connected to the DUs (2...), and ANTs (7...) connected to each of the RUs (6) and transmitting wireless signals to a UE, wherein the DUs (2) further comprise a MAC Scheduler (31), an RLC (4), and a HiPHY (5), and the MAC Scheduler (31) has a step of causing the ANTs (7...) connected to the RUs (6...) connected to the HiPHYs (5...) to transmit the wireless signals via the HiPHYs (5...) accommodated in the DUs (2...) that do not accommodate the MAC Scheduler (31).

[0063] According to the above method, DU2 is separated into a MAC Scheduler 31 that handles control signals, and an RLC4, MAC Multiplexing 32, and HiPHY 5 that handle data signals. That is, DU2 can be separated into a C-plane that handles control signal communication and a U-plane that handles user-directed data signal communication. As a result, for example, as shown in FIG. 1 , when coordinating between DU2c and 2b, it is sufficient to send control signals from the MAC Scheduler 31d of DU2c to the HiPHYs 5b and 5c of DU2b using the P5 interface. That is, there is no need to send data signals using the P7 interface, as in the past. This enables large-scale inter-cell (antenna) coordination that is independent of the data signal traffic volume.

[0064] The distributed unit program according to aspect 5 of the present invention is a distributed unit program for causing a computer to function as a DU (2) provided in a wireless communication system (1) in any of aspects 1 to 3 above, and may be configured to cause the computer to realize the functions provided by the DU (2).

[0065] The wireless communication system according to the embodiment of the present invention may be configured as follows: In the wireless communication system, the control signal processing unit (MAC Scheduler) and the data communication signal processing unit (RLC, MAC Multiplexing, HiPHY) in the wireless base station are separated, and a single control signal processing unit can control multiple data communication signal processing units. Also, the data communication signal processing unit is separated into a buffer control unit (RLC) and a wireless signal processing unit (MAC Multiplexing, HiPHY), and a time synchronization signal is incorporated into the data signal exchanged between them.

[0066] This ensures scalability that is independent of the data traffic volume and the number of cells (antennas), and also makes it possible to distribute the radio signal processing units and antenna units to different devices, improving the utilization efficiency of radio frequencies.

[0067] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0068] REFERENCE SIGNS LIST 1 Wireless communication system 2 (2a, 2b, ...) DU (Distributed Unit) 21 (21a, 21b, ...) Data communication signal processing unit 22 Wireless signal processing unit 31 (31a, 31b, ...) MAC Scheduler (Control signal processing unit) 31R Representative MAC Scheduler (Control signal processing unit) 32 MAC Multiplexing 4 RLC (Buffer control unit) 5 (5a, 5b, ...) HiPHY (Upper PHY layer) 6 (6a, 6b, ...) RU (Radio unit) 7 (7a, 7b, ...) ANT (Antenna unit)

Claims

1. A wireless communication system comprising: a plurality of distributed units; a plurality of radio units connected to the distributed units; and an antenna unit connected to each of the radio units and transmitting radio signals to a user terminal, wherein the distributed units comprise a control signal processing unit, a buffer control unit, and an upper PHY layer, and the control signal processing unit transmits the radio signals to the antenna unit connected to the radio unit connected to the upper PHY layer via the upper PHY layer accommodated in the distributed unit that does not accommodate the control signal processing unit.

2. The wireless communication system according to claim 1, wherein the buffer control unit transmits a downlink data signal to the upper PHY layer accommodated in the distributed unit that does not accommodate the buffer control unit.

3. The wireless communication system according to claim 2, wherein the buffer control unit transmits the downlink data signal by incorporating a time synchronization signal into the downlink data signal.

4. A control method for a wireless communication system comprising: a plurality of distributed units; a plurality of radio units connected to the distributed units; and an antenna unit connected to each of the radio units and transmitting radio signals to a user terminal, wherein the distributed units comprise a control signal processing unit, a buffer control unit, and an upper PHY layer, and the control signal processing unit causes the antenna unit connected to the radio unit connected to the upper PHY layer to transmit the radio signal via the upper PHY layer accommodated in the distributed unit that does not accommodate the control signal processing unit.

5. A distributed unit program for causing a computer to function as a distributed unit provided in a wireless communication system according to any one of claims 1 to 3, the distributed unit program causing the computer to realize the functions provided by the distributed unit.

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