JP6989768B2 - Wireless base station system and communication method - Google Patents

Description

The present invention relates to a radio base station system and a communication method.

As one of the radio access networks that make up an optical / mobile communication system, a large number of optical overhanging stations (DUs: Distributed Units) are arranged at high density, and wireless signals are aggregated by a wireless control device (CU: Central Unit). There is a centralized radio access network (C-RAN) that performs signal processing. The CU and DU are communicated and connected by an optical access network called a mobile fronthaul (MFH).

"CU-DU interface: U-plane aspects", 3GPP TSG-RAN Working Group 3 meeting # 95 R3-170620, 13-17 Feburary 2017 Yu Nakayama, Daisuke Hisano, Takahiro Kubo, Tatsuya Shimizu, Hirotaka Nakamura, Jun Terada, and Akihiro Otaka, "Novel Rank-Based Low-Latency Scheduling for Maximum Fronthaul Accommodation in Bridged Network", Optical Fiber Communication Conference 2017, 19-23 March 2017

In the conventional MFH, the time from the start of transfer of the radio signal to the completion of transfer is 250 microseconds (μs) or less. This is due to the fact that the hybrid RQ (Automatic repeat request) performed between the wireless terminal (UE: User Equipment) and the CU is performed at high speed. Specifically, within the delay request time of 250 μs provided for low delay transfer of the acknowledgment (ACK) signal and the negative response (NAK) signal, which are the control signals of the hybrid ARQ. The signal needs to be transferred.
Conventionally, there has been a problem that the upper limit of the number of DUs accommodated in the C-RAN is limited due to the short delay request time.

In view of the above circumstances, it is an object of the present invention to provide a radio base station system and a communication method capable of accommodating a larger number of optical overhanging stations by performing separate transfer of a main signal and a control signal.

One aspect of the present invention includes an optical overhang station of a radio base station that employs a time-divided duplex system and an aggregate station that aggregates the optical overhang stations, and there are a plurality of intervals between the optical overhang station and the aggregate station. It is a radio base station system that communicates and connects by a communication network via a transfer device of the above and transfers the flow of a plurality of the optical overhanging stations to the centralized station, and the optical overhanging station is transmitted from a wireless terminal and covers a wireless section. A receiving unit that receives the propagated radio signal, a channel separation unit that separates the radio signal received by the receiving unit into a data signal and a control signal, and the data signal and the control separated by the channel separation unit. An identifier that makes it possible to identify the priority set to transfer the control signal in preference to the data signal is assigned to the signal , and the data signal and the control signal are transferred according to the priority. An identifier assigning unit for transferring data to the aggregation station via the communication network is provided, and the identifier assigning unit transfers the data signal within a delay request time provided for low delay transfer of the control signal. It is a wireless base station system.

Further, one aspect of the present invention is the above-mentioned radio base station system, in which the aggregation station separates a downlink radio signal to be transferred to the optical overhanging station into a downlink data signal and a downlink control signal. And, with respect to the downlink data signal and the downlink control signal separated by the downlink channel separation unit, the downlink data signal and the downlink control signal can be distinguished from each other, and the priority in transfer can be identified. It is provided with a downlink identifier assigning unit that assigns an identifier and transfers the downlink data signal and the downlink control signal to the optical overhang station via the communication network according to different requirements for each downlink identifier.

Further, one aspect of the present invention is the above-mentioned radio base station system, in which the optical overhanging station gives priority to the control signal over the data signal according to the identifier given by the identifier assigning unit. Transfer to the aggregation station.

Further, one aspect of the present invention is the above-mentioned radio base station system, in which the aggregate station has priority over the downlink data signal according to the downlink identifier assigned by the downlink identifier assigning unit. The control signal is transferred to the optical overhang station.

Further, one aspect of the present invention has an optical overhanging station of a radio base station that employs a time-divided duplexing system and an aggregate station that aggregates the optical overhanging stations, and is located between the optical overhanging station and the aggregated station. Is a communication method by a computer of a radio base station system that connects the data by a communication network via a plurality of transfer devices and transfers the flow of the plurality of optical overhanging stations to the centralized station. A reception step for receiving the radio signal propagated in the above, a channel separation step for separating the radio signal received by the reception step into a data signal and a control signal, and the data signal and the data signal separated by the channel separation step. An identifier that makes it possible to identify the priority set to transfer the control signal in preference to the data signal is assigned to the control signal, and the data signal and the control signal are assigned according to the priority. The data signal within the delay request time provided for the low delay transfer of the control signal in the identifier assignment step of transferring the data from the optical overhang station to the aggregation station via the communication network and the identifier assignment step. Has a step of transferring and.

According to the present invention, more light overhanging stations can be accommodated.

It is a figure which shows the uplink structure of a radio base station. It is a figure which shows the transmission procedure in a downlink. It is a figure which shows the vertical link ratio of 7 kinds of TDD schemes defined by 3GPP. It is a figure which shows the list of the reply timing of the ACK signal and the NAK signal. It is a time chart which shows the data transmission procedure of an uplink. It is a figure which simplified the radio base station configuration shown in FIG. It is a figure which shows the radio base station configuration by 1st Embodiment. It is a flowchart which shows the operation of the radio base station by 1st Embodiment. It is a figure which shows the radio base station configuration by 2nd Embodiment.

<First Embodiment>
Hereinafter, the first embodiment of the present invention will be described.

First, FIG. 1 shows an uplink configuration of a radio base station system (hereinafter referred to as “radio base station”). The uplink configuration of the radio base station shown in FIG. 1 is based on the configuration of the radio base station (see Non-Patent Document 1) posted as a contribution to 3GPP (Third Generation Partnership Project).

In the C-RAN radio base station, the functions of the radio base station are separated and separated at the boundary between any of the five functional blocks (a) to (e) shown in FIG. The combined functional groups are deployed in the CU (aggregate station, wireless control device) and the DU (optical overhang station), respectively. For example, in the case of a C-RAN radio base station in which the functions of the radio base station are separated between the functional blocks shown in FIG. 1, the functions higher than the MAC (Media Access Control) layer are mounted on the CU side. Then, the functions lower than the Decoder are implemented on the DU side. In the conventional LTE (registered trademark) (Long term evolution), the functions of the radio base station are separated between the functional blocks (e) shown in FIG.

The CU and DU are communicated and connected by an optical access network called MFH. In the conventional MFH, the time from the start of transfer of the radio signal to the completion of transfer is 250 μs or less. This is due to the fact that the hybrid ARP performed between the UE (wireless terminal) and the CU is performed at high speed. Specifically, it is necessary that the main signal is transferred within the delay request time provided for the low delay transfer of the ACK signal and the NAK signal.

The processing of the hybrid ARP is performed in the MAC layer. Therefore, even if the functions of the radio base station are separated among the five functional blocks of the radio base station (a) to (e) shown in FIG. 1, the CU-DU The transfer of radio signals between them should be completed within 250 microseconds.

The delay requirement in the MFH is rate-determined by the hybrid ARQ. FIG. 2 shows a transmission procedure for the downlink.
When the uplink data signal is transmitted from the UE on the uplink, the CU determines whether the reception of the uplink data signal is successful or unsuccessful during the processing time for three subframes. If the CU determines that the reception is successful, the CU sends an ACK signal back to the UE. If the CU determines that the failure has occurred, the CU sends a NAK signal back to the UE.

The UE must receive the ACK or NAK signal within 4 subframes of transmitting the uplink data signal. Here, the subframe represents an element constituting a wireless frame, and one wireless frame is composed of 10 subframes. For example, if the radio frame length is 10 μs, one subframe is 1 μs.

The downlink data transmission procedure is the same as the uplink data transmission procedure. Since the time from the reception of the ACK signal or the NAK signal to the retransmission is not standardized, it depends on the mounting method.

The above data transmission procedure is a data transmission procedure in the case of the frequency division duplex (FDD) method. The data transmission procedure in the case of the Time Division Duplex (TDD) system will be described below. FIG. 3 is a diagram showing the vertical link ratios of seven types of TDD schemes defined by 3GPP.

In FIG. 3, "D" represents a downlink signal and "U" represents an uplink signal. Further, in FIG. 3, “S” means that both the uplink and downlink signals and the guard interval are included.
For example, No. It is shown in FIG. 3 that the subframe of item No. 3 of No. 1 is an uplink data signal.

Regarding the uplink data transmission procedure, the basic operation is the same as that of the FDD method, but the reply timings of the ACK signal and the NAK signal are not all timings after 4 subframes. This is because, in the TDD method, the upper and lower links are switched in time, so that the subframe after 4 subframes is not always the subframe that can be transmitted.

FIG. 4 shows a list of reply timings of the ACK signal and the NAK signal. For example, in this list, No. When the CU receives the uplink data signal in the subframe of item No. 3 of No. 1, it is expressed that the CU may send back the ACK signal or the NAK signal within 6 subframes.
As shown in FIG. 4, the reply timing of the ACK signal and NAK is a value of 4 subframes or more.

FIG. 5 shows an uplink data transmission procedure in a time chart. The “process time in CU” shown in FIG. 5 is the time required for issuing the ACK signal and the NAK signal. After that, there is a waiting time until the transmission possible timing is reached.

Therefore, it is required to transfer the main signal within the delay request time of 250 microseconds provided for the low delay transfer of the ACK signal.
For example, when MFH is concentrated using a layer 2 bridge network (see Non-Patent Document 2) or TDM-PON (Time Division Multiplexing --Passive Optical Network), the number of radio base stations that can be concentrated is limited due to strict delay requirements. Will be done.

FIG. 6 shows a radio base station configuration that simplifies the radio base station configuration shown in FIG. It is assumed that the function separation point of the radio base station is one of the functional blocks from (b) to (d) shown in FIG.

FIG. 7 shows the configuration of the radio base station according to the first embodiment. The radio base station according to the first embodiment has DU1 and CU2, communicates and connects between DU1 and CU2 by a communication network (MFH) via a plurality of transfer devices, and flows a plurality of DU1s to CU2. It is a radio base station that transfers to.

The radio base station according to the first embodiment includes a channel separation unit 11 and a channel identifier assigning unit 12 in the DU 1. The channel separation unit 11 and the channel identifier assignment unit 12 are included in any of the Decoder, Demodulator, and Prefiltering shown in FIG. 1, but are described only as the channel separation unit 11 for the sake of simplicity. ..

The channel separation unit 11 separates the uplink radio signal transmitted from the UE 3 and propagating in the radio section into an uplink data signal and an uplink control signal (ACK signal or NAK signal). The channel separation unit 11 transfers the separated uplink data signal and uplink control signal to the channel identifier assigning unit 12.

The channel identifier assigning unit 12 acquires the uplink data signal and the uplink control signal separated by the channel separation unit 11. The channel identifier assigning unit 12 assigns an identifier that makes it possible to distinguish between the uplink data signal and the uplink control signal to the uplink data signal and the uplink control signal, respectively.

Further, the above identifier given to the uplink data signal and the uplink control signal can set the priority so that the uplink control signal is prioritized and transferred over the uplink data signal in the signal transfer from DU1 to CU2. It is composed.
The channel identifier assigning unit 12 transfers the uplink data signal and the uplink control signal to the CU 2 via the MFH according to different requirements for each identifier.

When the MFH detects congestion, the DU 1 transfers the uplink control signal to the CU 2 in preference to the uplink data signal according to the identifier assigned by the channel identifier assigning unit 12.

Hereinafter, an example of the operation of the radio base station will be described. FIG. 8 is a flowchart showing the operation of the radio base station. This flowchart starts when a radio signal is transmitted from the UE 3 to the DU 1.

First, the antenna unit (reception unit) included in the DU 1 receives the radio signal transmitted from the UE 3 and propagated in the radio section (step S1).
Next, the channel separation unit 11 separates the uplink radio signal received by the antenna unit (reception unit) into an uplink data signal and an uplink control signal (step S2).

Next, the channel identifier assigning unit 12 makes it possible to distinguish between the uplink data signal and the uplink control signal with respect to the uplink data signal and the uplink control signal separated by the channel separation unit 11, and in the transfer of the signal to the CU 2. An identifier that makes the priority identifiable is given (step S3).

Next, the channel identifier assigning unit 12 transfers the uplink data signal and the uplink control signal to the CU 2 via the MFH according to different requirements for each identifier assigned to the uplink data signal and the uplink control signal.
This completes the process shown in this flowchart.

<Second embodiment>
Hereinafter, a second embodiment of the present invention will be described.
The radio base station according to the first embodiment described above separates the radio signal received from the UE 3 into an uplink data signal and an uplink control signal at the uplink, and sets a priority for the uplink data signal and the uplink control signal. It was configured to transfer the uplink data signal and the uplink control signal from the DU1 to the CU2 according to the set priority by assigning a possible identifier.

Hereinafter, the radio base station according to the second embodiment has a configuration in which, in addition to the configuration of the radio base station according to the first embodiment described above, the downlink also performs the same processing as the uplink.

FIG. 9 shows the configuration of the radio base station according to the second embodiment. The radio base station according to the second embodiment has DU1 and CU2, communicates and connects between DU1 and CU2 by a communication network (MFH) via a plurality of transfer devices, and transfers the flow of CU2 to a plurality of DU1s. It is a radio base station that transfers to.

The radio base station according to the second embodiment includes a channel separation unit 21 and a channel identifier assigning unit 32 in the CU 2. The channel separation unit 21 and the channel identifier assignment unit 22 are included in any of the Decoder, Demodulator, and Prefiltering shown in FIG. 1, but are described only as the channel separation unit 21 for the sake of simplicity. ..

The channel separation unit 21 separates the downlink radio signal into a downlink data signal and a downlink control signal (ACK signal or NAK signal). The channel separation unit 21 transfers the separated downlink data signal and downlink control signal to the channel identifier assigning unit 22.

The channel identifier assigning unit 22 acquires the downlink data signal and the downlink control signal separated by the channel separation unit 21. The channel identifier assigning unit 22 assigns an identifier to the downlink data signal and the downlink control signal so that the downlink data signal and the downlink control signal can be distinguished from each other.

Further, the above identifier given to the downlink data signal and the downlink control signal can set the priority so that the downlink control signal is prioritized and transferred over the downlink data signal in the signal transfer from CU2 to DU1. It is composed.
The channel identifier assigning unit 22 transfers the downlink data signal and the downlink control signal to the DU1 via the MFH according to different requirements for each identifier.

When the MFH detects congestion, the CU 2 transfers the downlink control signal to the DU 1 in preference to the downlink data signal according to the identifier assigned by the channel identifier assigning unit 22.

As described above, the radio base station according to the first embodiment and the second embodiment of the present invention separates the radio signal into a data signal and a control signal, and gives priority to the data signal and the control signal. A settable identifier is assigned, and the data signal and the control signal are transferred via the MFH according to the set priority.

With the above configuration, the control signal (ACK signal or NAK signal) can be transferred with priority over the data signal by setting the priority. Therefore, the allowable delay of the data signal is observed while observing the delay request time. Time is extended.
As a result, according to the radio base station according to the first embodiment and the second embodiment of the present invention, for example, when the front hole is connected in multiple stages by a layer 2 switch, the optical overhang station in the C-RAN ( It is possible to increase the capacity of DU).

Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment and includes a design within a range that does not deviate from the gist of the present invention.

1 ... DU, 2 ... CU, 3 ... UE, 11 ... channel separator, 12 ... channel identifier assigning unit, 21 ... channel separator, 22 ... channel identifier assigning section

Claims (6)

It has an optical overhang station of a radio base station that adopts a time division duplex system and an aggregate station that aggregates the optical overhang stations, and communicates between the optical overhang station and the aggregate station via a plurality of transfer devices. A radio base station system that communicates and connects via a network and transfers the flow of a plurality of the optical overhanging stations to the centralized station.
The light overhanging station is
A receiver that receives a wireless signal transmitted from a wireless terminal and propagated in a wireless section,
A channel separation unit that separates the radio signal received by the reception unit into a data signal and a control signal,
The data signal and the control signal separated by the channel separation unit are given an identifier that makes it possible to identify the priority set to transfer the control signal with priority over the data signal . An identifier assigning unit that transfers the data signal and the control signal to the aggregation station via the communication network according to the priority.
Equipped with
The identifier assigning unit is a radio base station system that transfers the data signal within the delay request time provided for the low delay transfer of the control signal. The delay request time is a time when at least 4 subframes have elapsed from the control signal transmission time when the control signal subframe is transmitted from the identifier assigning unit to the aggregation station. The radio base station system according to claim 1, which is the time obtained by subtracting the time for 4 subframes from the time until the time when the optical overhanging station becomes able to receive the downlink control signal transmitted from the aggregation station. .. The centralized station
A downlink channel separator that separates the downlink radio signal to be transferred to the optical overhang station into a downlink data signal and a downlink control signal.
A downlink identifier that makes it possible to distinguish the downlink data signal and the downlink control signal from the downlink data signal and the downlink control signal separated by the downlink channel separation unit, and to identify the priority in transfer. A downlink identifier assigning unit that assigns and transfers the downlink data signal and the downlink control signal to the optical overhang station via the communication network according to the downlink identifier.
The radio base station system according to claim 1 or 2. According to any one of claims 1 to 3, the optical overhanging station transfers the control signal to the aggregation station in preference to the data signal according to the identifier assigned by the identifier assigning unit. The radio base station system described. The radio base station system according to claim 3, wherein the aggregate station transfers the downlink control signal to the optical overhang station in preference to the downlink data signal according to the downlink identifier assigned by the downlink identifier assigning unit. .. It has an optical overhang station of a radio base station that adopts a time-divided duplex system and an aggregate station that aggregates the optical overhang stations, and communicates between the optical overhang station and the aggregate station via a plurality of transfer devices. It is a communication method by a computer of a wireless base station system that communicates and connects by a network and transfers the flow of a plurality of the optical overhanging stations to the centralized station.
A reception step that receives a radio signal transmitted from a wireless terminal and propagated in a wireless section,
A channel separation step for separating the radio signal received by the reception step into a data signal and a control signal, and
The data signal and the control signal separated by the channel separation step are given an identifier that makes it possible to identify the priority set to transfer the control signal in preference to the data signal . An identifier assignment step of transferring the data signal and the control signal from the optical overhanging station to the aggregation station via the communication network according to the priority.
In the identifier assignment step, the step of transferring the data signal within the delay request time provided for the low delay transfer of the control signal, and the step of transferring the data signal.
Communication method with.

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