Distributed unit

Abstract

A distributed unit that is a constituent of a base station in a mobile communication system, the base station being constituted by a radio unit, the distributed unit, and a central unit, the distributed unit including: an allocation unit for allocating radio resources by limiting a number of allocated user signals among control signals and user signals, the control signals and the user signals being allocated to radio frames to be transmitted from the radio unit to a terminal.　

Description

distributed station

[0001] The present invention relates to a distributed station.

[0002] Conventionally, in a 5G mobile communication system, a base station is composed of a radio unit (RU), a distributed unit (DU), and a central unit (CU), and the fronthaul between the RU and the DU is connected by optical fiber (see, for example, Patent Document 1). In the fronthaul, signals are transmitted using the Ethernet (registered trademark) method based on the enhanced Common Public Radio Interface (eCPRI) (see, for example, Non-Patent Documents 1 and 2).

[0003] Currently, the fronthaul transmission bandwidth is determined depending on the maximum data transmission volume (IQ (In-Phase / Quadrature-Phase) signal size) exchanged between the RU and DU. For example, in O-RAN (Open Radio Access Network), 10G or 25G is used as the maximum data transmission volume. In OFDM (Orthogonal Frequency Division Multiplexing) methods such as LTE (Long Term Evolution) or 5G, IQ signals are arranged on two axes: frequency (subcarrier) and time. The maximum data transmission volume is then calculated based on the case where all IQ signals are used, and this is used as the fronthaul transmission bandwidth (see, for example, Non-Patent Document 3).

[0004] International Publication No. 2022 / 020495

[0005] IOWN Global Forum, "Mobile Fronthaul over APN PoC Reference", July 2022. Umesh Anil, Tatsuro Yajima, Toru Uchino, and Taku Okuyama, "O-RAN Fronthaul Specifications Overview", NTT DOCOMO Technical Journal, Vol. 27, No. 1, pp. 43-55, April 2019. Naoto Okubo, Umesh Anil, Mikio Iwamura, and Hiroyuki Arakawa, "LTE Radio System Overview: High Speed, Large Capacity, and Low Latency", NTT DOCOMO Technical Journal, Vol. 19, No. 1, pp. 11-19, April 2010.

[0006] Reducing the amount of data transmitted in the fronthaul would enable a reduction in the number of fibers used, and in the case of multiplexing and transmission using techniques such as WDM (Wavelength Division Multiplexing), it would also enable a reduction in the number of wavelengths. As a result, it would be possible to increase the number of RUs that can be connected to a DU. However, simply reducing the IQ signals would also reduce the control signals related to communication connectivity between the terminal and the RU, making it impossible to maintain communication.

[0007] In view of the above circumstances, the present invention aims to provide a technology that can reduce the transmission bandwidth used in the fronthaul of the fronthaul section without affecting communication connectivity.

[0008] One aspect of the present invention is a distributed station in a radio station, a distributed station, and a central station that constitute a base station in a mobile communication system, the distributed station comprising an allocation unit that allocates radio resources by limiting the number of allocations of user signals among control signals and user signals that are allocated to radio frames transmitted from the radio station to terminals.

[0009] According to the present invention, it is possible to reduce the transmission bandwidth used in the fronthaul of the fronthaul section without affecting communication connectivity.

[0010] It is a diagram showing an example of the configuration of a communication system in an embodiment. It is a diagram showing an example of a radio frame in an embodiment. It is a diagram showing an example of the configuration of a remote station in an embodiment. It is a flowchart showing the flow of a user signal allocation operation performed by a conventional remote station. It is a flowchart showing the flow of a user signal allocation operation performed by a remote station in an embodiment.

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] Fig. 1 is a diagram illustrating an example of the configuration of a communication system 100 according to an embodiment. The communication system 100 includes a radio station 10, a remote station 20, and a central station 30. In Fig. 1, the communication system 100 includes N (N is an integer equal to or greater than 1) radio stations 10, one remote station 20, and one central station 30, but the numbers of the radio stations 10, the remote stations 20, and the central station 30 are not particularly limited.

[0013] The wireless station 10, the remote station 20, and the central station 30 function as base stations in a 5G mobile communication system. While Fig. 1 shows an example in which the wireless station 10 is a child station and the remote station 20 and the central station 30 are parent stations, the wireless station 10 and the remote station 20 may be child stations and the central station 30 may be parent stations.

[0014] The communication system 100 configures a radio access network (RAN) that connects a base station and one or more terminals 35. A core network 40 is also connected to the central station 30. The section between the radio station 10 and the remote station 20 is called a fronthaul, and the section between the central station 30 and the core network 40 is called a backhaul. The radio station 10, the remote station 20, the central station 30, and the terminal 35 are RU, DU, CU, and UE (User Equipment), respectively, in a fifth-generation mobile communication system.

[0015] The wireless station 10 receives uplink data via a wireless signal transmitted from the terminal 35. The wireless station 10 sets the received uplink data as an uplink signal and transmits the uplink signal to the remote station 20 via the wired interface. The wireless station 10 also receives a downlink signal from the remote station 20 via the wired interface. The wireless station 10 transmits the downlink data addressed to the terminal 35, which is set in the received downlink signal, to the terminal 35 via a wireless signal.

[0016] In an OFDM transmission system such as LTE, the radio signal transmitted from the radio station 10 has a two-dimensional radio frame structure of frequency (subcarrier) and time. The type of IQ signal to be transmitted based on the combination of frequency (subcarrier) and time within the radio frame is defined in advance by specifications.

[0017] Control signals are transmitted in the hatched region R1 in the radio frame shown in Fig. 2, and user signals are transmitted in the white region R2 (non-hatched region). Fig. 2 is a diagram showing an example of a radio frame in an embodiment. Currently, a control signal or user signal is set in each region indicated by a single square in Fig. 2. As a result, control signals or user signals are set in all regions.

[0018] In contrast to this, in this embodiment, allocation of user signals is limited in the remote station 20. By limiting the allocation of user signals in the remote station 20 in this way, the transmission band in the fronthaul section is suppressed.

[0019] The remote station 20 receives uplink signals from each wireless station 10. The uplink signals received by the remote station 20 include uplink data received from terminals 35 subordinate to each wireless station 10. The remote station 20 generates an uplink signal that aggregates the uplink data and transmits the generated uplink signal to the central station 30 to which the remote station 20 is connected. The remote station 20 also receives a downlink signal (user signal) from the central station 30 to which the remote station 20 is connected, in which downlink data addressed to the terminal 35 subordinate to the central station 20 is set. The remote station 20 converts the received downlink signal into a downlink signal corresponding to the wireless signal to be transmitted from each wireless station 10. The remote station 20 transmits the converted downlink signal to the wireless station 10 corresponding to the downlink signal.

[0020] As described above, the fronthaul transmission bandwidth is determined depending on the maximum amount of data (IQ signal size) between the radio station 10 and the remote station 20. The remote station 20 imposes restrictions on the allocation of user signals so as to reduce the amount of data transmitted over the fronthaul. IQ signals are divided into control signals and user signals. Control signals are signals related to communication connectivity. Therefore, the remote station 20 does not impose restrictions on the allocation of control signals and transmits them all. In other words, the remote station 20 allocates all IQ signals corresponding to control signals and does not reduce them.

[0021] On the other hand, the remote station 20 limits the allocation of user signals based on the amount of data to be transmitted to the terminal 35. The remote station 20 sets a threshold for the fronthaul transmission band, calculates the number of IQ signals that can be used based on the set threshold, and allocates user signals within the range of the number of IQ signals obtained by the calculation.

[0022] The central station 30 aggregates uplink signals received from the subordinate remote stations 20 and transfers them to the core network 40. The central station 30 also receives downlink signals from the core network 40, in which downlink data addressed to a terminal 35 is set, and transfers the received downlink signals to the remote stations 20 connected to the destination terminal 35.

[0023] The terminal 35 transmits and receives radio signals to and from the radio station 10 using radio resources allocated by the remote station 20. The allocated radio resources include information indicating the start and end timings of time intervals during which radio signal transmission and reception are permitted. The start and end timings are represented by, for example, slots. A slot is a unit of scheduling for data transmission and reception in a radio frame. The allocated radio resources may further include information indicating a coding rate and a modulation scheme.

[0024] The core network 40 is a network that connects external networks. The core network 40 transfers upstream signals transmitted from the central station 30 to the external networks. The core network 40 also receives downstream signals directed to the terminal 35 and transferred from the external networks, and transfers the received downstream signals to the central station 30.

[0025] (Configuration of the Distributed Station 20) Fig. 3 is a diagram showing an example of the configuration of the distributed station 20 in the embodiment. The distributed station 20 includes a wireless station 12 and a control unit 22. The control unit 22 communicates with other devices. The communication unit 21 communicates with, for example, the wireless station 10 or the central station 30. The control unit 22 includes a setting unit 23 and an allocation unit 24.

[0026] The setting unit 23 sets a coefficient α, which is a ratio of the limit to the maximum value of the fronthaul transmission band. The coefficient α is 0<α<1. When the coefficient α is 1, it corresponds to the conventional method, in which control signals and user signals are allocated to the entire area of ​​the radio frame (reduction 0).

[0027] The allocation unit 24 allocates control signals and user signals to radio frames (frame length 10 ms). The allocation unit 24 allocates user signals based on the coefficient α set in the setting unit 23. A radio frame is made up of multiple subframes. For example, a radio frame is made up of 10 subframes, each 1 ms long.

[0028] The allocation unit 24 calculates the number of areas (the number of squares shown in FIG. 2) that can be allocated to user signals in a subframe. Hereinafter, the number of areas that can be allocated to user signals will be referred to as the number of user signal allocations. Here, the allocation unit 24 calculates the number of user signal allocations in the remaining area RC (RC = RA - RB) of the area RA that can be allocated in the subframe, excluding the number of allocation areas RB for all control signals. As described above, because control signals affect communication connectivity, the allocation unit 24 first allocates all control signals and then allocates user signals.

[0029] The allocation unit 24 updates the calculated number of user signals that can be allocated by the set coefficient α. The allocation unit 24 allocates user signals to be transmitted to the terminals 35 that are the transmission targets of the radio frame, with the updated number of user signals that can be allocated as an upper limit. In this way, the allocation unit 24 does not allocate user signals to all areas of the radio frame after the control signals have been allocated, but allocates a limited number of user signals.

[0030] (Conventional Allocation Operation) Before explaining the allocation operation of the present invention, a conventional allocation operation will be explained first. Fig. 4 is a flowchart showing the flow of a conventional user signal allocation operation performed by a remote station.

[0031] The remote station calculates an allocable amount A to be allocated to user signals in a subframe (step S101). The remote station selects a terminal to which the signal is to be transmitted (step S102). The remote station calculates an allocable amount B based on the amount of data of the user signal to be transmitted to the selected terminal (step S103). The remote station determines whether the value obtained by subtracting the allocable amount B from the allocable amount A is equal to or greater than 0 (step S104).

[0032] If the value obtained by subtracting the allocation amount B from the allocation amount A is 0 or more, it means that all of the user signals to be transmitted to the selected terminal can be allocated. If the value obtained by subtracting the allocation amount B from the allocation amount A is not 0 or more, it means that some of the user signals to be transmitted to the selected terminal can be allocated.

[0033] If the remote station determines that the value obtained by subtracting the allocation amount B from the allocable amount A is equal to or greater than 0 (step S104-YES), the remote station allocates all user signals (step S105). The remote station outputs the downlink data to which the allocation of user signals has been completed to the wireless station. The wireless station transmits a wireless signal containing the downlink data to the terminal.

[0034] On the other hand, if the remote station determines that the value obtained by subtracting the allocation amount B from the allocation amount A is not equal to or greater than 0 (step S104-NO), the remote station allocates some of the user signals (step S106). For example, the remote station allocates user signals equivalent to the allocation amount A. The remaining user signals that have not been allocated (allocation amount B-allocation amount A) will be allocated when the next radio frame is transmitted.

[0035] 5 is a flowchart showing the flow of the user signal allocation operation performed by the remote station 20 in this embodiment. The setting unit 23 sets a coefficient α, which is a ratio limiting the maximum value of the transmission bandwidth in the fronthaul section (step S201). The coefficient α may be input to the remote station 20 by a user operating an external device, or may be set in the remote station 20 in advance. The setting unit 23 sets the coefficient α, which has been input or set in this way, in the allocation unit 24.

[0036] The allocation unit 24 calculates an allocable amount A to be allocated to user signals in a subframe constituting a radio frame (step S202). Specifically, the allocation unit 24 calculates the remaining area of ​​the area allocated to the subframe after all control signals have been allocated as the allocable amount A. The allocation unit 24 updates the allocable amount A by multiplying the allocable amount A by the coefficient α set by the setting unit 23 (step S203). Thereafter, the allocation unit 24 selects a terminal to which the signal is to be transmitted (step S204).

[0037] For example, the allocation unit 24 may preferentially select terminals 35 for which it is desired to minimize communication delay time. This reduces the impact on delay time. Alternatively, for example, the allocation unit 24 may select terminals 35 in descending order of the amount of data in user signals to be transmitted. This reduces the impact on throughput. Alternatively, for example, the allocation unit 24 may select terminals 35 in descending order of the amount of data in user signals to be transmitted. This increases the number of terminals 35 to communicate with.

[0038] The allocation unit 24 calculates an allocation amount B based on the data amount of the user signal to be transmitted to the selected terminal 35 (step S205). The allocation unit 24 determines whether the value obtained by subtracting the allocation amount B from the allocable amount A is equal to or greater than 0 (step S206). If the allocation unit 24 determines that the value obtained by subtracting the allocation amount B from the allocable amount A is equal to or greater than 0 (step S206-YES), the allocation unit 24 allocates all of the user signals (step S207). The allocation unit 24 outputs the downlink data for which the allocation of the user signals has been completed to the wireless station 10. The wireless station 10 transmits a wireless signal in which the downlink data is set to the terminal 35.

[0039] On the other hand, if the allocating unit 24 determines that the value obtained by subtracting the allocation amount B from the allocable amount A is not equal to or greater than 0 (step S206—NO), the allocating unit 24 allocates some of the user signals (step S208). For example, the allocating unit 24 allocates the user signals equivalent to the allocable amount A. The remaining user signals that have not been allocated (allocation amount B−allocable amount A) will be allocated when the next radio frame is transmitted.

[0040] According to the communication system 100 configured as described above, the remote station 20 includes an allocation unit 24 that allocates radio resources by limiting the number of allocations of user signals among the control signals and user signals allocated to the radio frame transmitted from the radio station 10 to the terminal 35.

[0041] In this way, the remote station 20 does not use the entire area of ​​the radio frame that can be allocated to user signals, but limits the number of user signal allocations. Furthermore, the remote station 20 allocates all control signals by limiting only the number of user signal allocations. This allows all signals related to communication connectivity to be transmitted. Therefore, it is possible to reduce the transmission bandwidth used in the fronthaul of the fronthaul section without affecting communication connectivity. As a result, it is possible to reduce the number of fibers in the fronthaul section and the number of wavelengths when multiplexing and transmitting using WDM or the like. This also makes it possible to increase the number of radio stations 10 that can be accommodated.

[0042] The remote station 20 further includes a setting unit 23 that sets a coefficient indicating the desired ratio of the maximum value of the transmission bandwidth in the fronthaul section. The allocation unit 24 then limits the number of user signals to be allocated based on the coefficient set by the setting unit 23. In this way, the remote station 20 allocates radio resources by limiting user signals based on the transmission volume in the fronthaul section. This makes it possible to reduce the data transmission volume in the fronthaul section compared to conventional designs based on the maximum data transmission volume.

[0043] The distributed station 20 is realized as software by a processor such as a central processing unit (CPU) executing a program stored in a storage device having a non-volatile storage medium (non-transitory storage medium) and memory. The program may be recorded on a computer-readable storage medium. Examples of computer-readable storage media include portable media such as flexible disks, magneto-optical disks, read-only memories (ROMs), and compact disc read-only memories (CD-ROMs), and non-transitory storage media such as hard disks or solid-state drives (SSDs) built into computer systems.

[0044] Some or all of the functions of the remote station 20 may be realized using hardware including an electronic circuit (electronic circuit or circuitry) using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0045] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0046] The present invention is applicable to wireless access networks.

[0047] 10, 10-1 to 10-N...radio station, 20...remote station, 30...central station, 40...core network, 21...communication unit, 22...control unit, 23...setting unit, 24...allocation unit, 100...communication system

Claims

1. A distributed station in a radio station, a distributed station, and a central station that constitute a base station in a mobile communication system, the distributed station comprising an allocation unit that allocates radio resources by limiting the number of allocations of user signals among control signals and user signals allocated to radio frames transmitted from the radio station to terminals.

2. A distributed station as described in claim 1, further comprising a setting unit that sets a coefficient indicating a desired ratio of the maximum value of the transmission bandwidth of the fronthaul section between the radio station and the distributed station, and the allocation unit limits the number of allocations of the user signals based on the coefficient set by the setting unit.

3. The remote station according to claim 2, wherein the allocation unit calculates the updated number of user signals that can be allocated by multiplying the coefficient by the number of user signals that can be allocated after the control signal has been allocated, and allocates the user signals within the range of the calculated updated number of user signals that can be allocated.

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