JP7787473B2 - Wireless communication device, communication system, wireless communication method, and program - Google Patents

Description

The present invention relates to wireless communication devices, communication systems, wireless communication methods, and program technologies.

Wireless systems such as 5G use high-frequency millimeter wave bands, and in future wireless systems such as 6G, it is expected that even higher frequency bands will be used to ensure wider bandwidths in order to achieve even higher speeds and capacities. High-frequency bands are known to have large propagation losses and tend to be highly directional, and distributed antenna systems are being considered to improve connectivity in covering communication areas (see Non-Patent Documents 1 and 2).

In a distributed antenna system, using multiple distributed antennas to perform SU-MIMO (Single User Multiple-Input Multiple-Output) or MU-MIMO (Multi-User MIMO) can improve frequency utilization efficiency and improve capacity and throughput. When performing MIMO, it is generally assumed that channel information (CSI: Channel State Information) between the distributed antenna and the terminal station (UE: User Equipment) is acquired to reduce inter-stream interference, and precoding is performed on the downlink and postcoding on the uplink at the base station (BS: Base Station).

Here, if the spatial correlation between antennas is high, it becomes difficult to separate the streams using precoding and postcoding, so it is necessary to reduce the number of streams (number of MIMO layers) that are transmitted and received simultaneously. In this way, rank adaptation, which controls the number of streams based on the reception conditions, is also used (see non-patent document 3). Rank adaptation increases the number of MIMO layers when channel conditions are good, based on the SINR and spatial correlation between antennas, and controls to use diversity when channel conditions are poor.

NTT Docomo, Inc., "Docomo 6G White Paper 4.0," November 2021 Uchida, Iwakuni, Kita, Onisawa, Kishiyama, Suyama, Nagata, and Asai, "Study on High-Frequency Band Distributed Antenna Systems for the 6G Era," IEICE Technical Report RCS2020-148, pp. 73-78, December 2020. T. Taoka, T. Nagata, T. Takeda, T. Kakishima, Y. Yu, and T. Kusume, "MIMO and Inter-Cell Cooperative Transmission and Reception Technology in LTE-Advanced," NTT DOCOMO Technical Journal, Vol. 18, No. 2, July 2010.

In a distributed antenna system, when a UE communicates by connecting to a single distributed antenna, if the link with the BS is severed due to obstruction caused by movement or changes in the surrounding environment, communication cannot continue until the link is reconnected. Furthermore, when switching the connected distributed antenna based on reception quality, there are concerns about an increase in control signals and processing associated with the switch, as well as an increase in the load of data transfer between distributed antennas via the BS.

Furthermore, when MIMO communication is performed using multiple antennas in a distributed antenna system, throughput will decrease if the link with one of the distributed antennas is cut off due to obstruction caused by movement or changes in the surrounding environment. In particular, if interference reduction is performed by precoding between antennas performing MIMO communication, this will also affect the demodulation of signals from other distributed antennas that are not obstructed, raising concerns about further degradation of throughput.

In consideration of the above circumstances, the present invention aims to provide technology that can improve communication continuity.

One aspect of the present invention is a wireless communication device comprising a prediction unit that predicts the communication quality with a counterpart device that communicates wirelessly via one or more antennas, and a control unit that reduces the number of streams that are simultaneously transmitted and received or sets the antenna for use in diversity communication for an antenna that is predicted by the prediction unit to have a degraded communication quality.

One aspect of the present invention is a communication system including one or more antennas and a wireless communication device that controls the antennas, wherein the wireless communication device is equipped with a prediction unit that predicts the communication quality with a counterpart device that communicates wirelessly via the antenna, and a control unit that, for an antenna predicted by the prediction unit to have a degraded communication quality, reduces the number of streams that are simultaneously transmitted and received or sets the antenna to be used for diversity communication.

One aspect of the present invention is a wireless communication method comprising a prediction step of predicting the communication quality with a counterpart device that communicates wirelessly via one or more antennas, and a control step of reducing the number of streams simultaneously transmitted and received or setting the antenna for use in diversity communication for an antenna predicted by the prediction step to have a degraded communication quality.

One aspect of the present invention is a program for causing a computer to execute a prediction step of predicting the communication quality with a counterpart device that communicates wirelessly via one or more antennas, and a control step of reducing the number of streams simultaneously transmitted and received or setting the antenna for use in diversity communication for an antenna predicted by the prediction step to have a degraded communication quality.

This invention makes it possible to improve communication continuity.

1 is a diagram illustrating an example of a communication system including a base station as a wireless communication device according to an embodiment of the present invention. FIG. 1 is a diagram illustrating an example of the configuration of a base station. FIG. 2 is a diagram illustrating an example of the configuration of a prediction unit. FIG. 2 is a diagram illustrating an example of the configuration of a prediction unit. 10 is a flowchart showing the flow of a multiple connection control process. 10 is a flowchart showing the flow of a predictive control process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings.
Fig. 1 is a diagram showing an example of a communication system 10 including a base station 100 as a wireless communication device according to this embodiment. The communication system 10 includes the base station 100, a plurality of antennas 200 (five in Fig. 1), and a UE (User Equipment) 300. As shown in Fig. 1, the communication system 10 is a communication system to which a distributed antenna system is applied. The UE 300 is a mobile terminal such as a smartphone used by a user.

Base station 100 supports MIMO (Multiple-Input Multiple-Output). Base station 100 also controls antennas 200 that are deployed extending from base station 100. Each distributed antenna 200 includes an RU (Radio Unit) function and supports beamforming by controlling the phase and/or amplitude of multiple elements to ensure gain in high frequency bands. UE 300 may also support beamforming. Base station 100 also has the function of predicting the future communication quality of connected UE 300.

Under normal control, the base station 100 performs downlink MIMO transmission by simultaneously transmitting multiple streams from multiple antennas 200. In addition to downlink, uplink MIMO transmission may also be performed by simultaneously receiving multiple streams from multiple antennas 200. The maximum number of streams that can be communicated simultaneously is determined by the maximum number of MIMO layers that the base station 100 can process, and all of the distributed antennas 200 may be used for communication simultaneously, or only some of the antennas 200 may be used.

Figure 2 is a diagram showing an example configuration of a base station 100. The base station 100 is composed of a control unit 110, a prediction unit 120, a transmission unit 130, a signal processing unit 140, a beam control unit 150, a transmission/reception unit 160, and a memory unit 170. The control unit 110 controls the entire base station 100 and the antennas 200. The control unit 110 controls, for example, the allocation of communication resources to opposing devices. Furthermore, for an antenna 200 for which the prediction unit 120 predicts that communication quality will deteriorate, the control unit 110 reduces the number of streams (i.e., the number of layers) to be simultaneously transmitted and received, or sets the antenna 200 to be used for diversity communication. In this specification, the number of streams and the number of layers are synonymous.

The prediction unit 120 predicts the communication quality with the UE 300. A method for predicting communication quality may be, for example, when the fluctuation range of the received power of the UE 300 within a certain period of time exceeds a set threshold, assuming obstruction around the UE 300, and predicting a decline in communication quality. Prediction methods may also be used, such as linear prediction based on communication quality records for each movement, or a method using machine learning, or a method using an external sensor such as a camera. The memory unit 170 stores various information required for prediction by the prediction unit 120. For example, the memory unit 170 stores feedback information from the UE 300 or values sensed by an external sensor.

The transmission unit 130 transmits signals between a higher-level device on the network and other wireless communication devices. The transmission unit 130 outputs received signals to the signal processing unit 140, and transmits signals input from the signal processing unit 140 to the higher-level device or other wireless communication devices. The signal processing unit 140 performs signal processing related to wireless communication. For example, the signal processing unit 140 performs signal processing on signals input from the transmission unit 130 and outputs the results to the beam control unit 150. The signal processing unit 140 also performs signal processing on signals input from the beam control unit 140 and outputs the results to the transmission unit 130. Furthermore, the signal processing unit 140 outputs feedback information received from the UE 300 to the control unit 110 and the memory unit 170. Note that when the prediction unit 120 performs prediction using values sensed by an external sensor, when the signal processing unit 140 receives the sensed values from the beam control unit 150, it outputs the sensed values to the memory unit 170.

The beam control unit 150 controls the beam formed by the antenna 200 using the transceiver unit 160 in accordance with the signal output from the signal processing unit 140. The beam control unit 150 outputs the signal output from the transceiver unit 160 to the signal processing unit 140. The transceiver unit 160 performs processing related to signals received by the antenna 200 and signals to be transmitted, in accordance with the control of the beam control unit 150. For example, the transceiver unit 160 performs beamforming that controls the phase and/or amplitude of the signal, and processing related to the transmission and reception of signals.

Note that the configuration of base station 100 is not limited to the configuration shown in Figure 2. For example, it may be configured in such a way that functional units such as signal processing units and beam control units are separated into devices, such as a CU (Central Unit), DU (Distributed Unit), and RU in 5G NR (New Radio).

An example configuration of the prediction unit 120 will be described. Figures 3 and 4 are diagrams showing an example configuration of the prediction unit 120. The prediction unit 120 in Figure 3 stores fluctuations in received power over a certain period of time for all antennas 200 connected to the UE 300 in the memory unit 170, predicts that an antenna 200 whose fluctuation range of received power exceeds a set threshold T is an antenna whose quality is expected to deteriorate, and outputs this to the control unit 110.

Figure 4 is a diagram showing an example configuration when the prediction unit 120 uses a machine learning model. For example, a machine learning model that has been pre-trained to identify antennas whose quality will deteriorate based on the position and direction of movement of the UE 300 is stored in the memory unit 170. Then, when the position and direction of movement of the UE 300 are input, the prediction unit 120 uses the stored machine learning model to output to the control unit 110 antennas whose quality is expected to deteriorate.

In either the configuration shown in Figure 3 or Figure 4, the control unit 110 sets the input antenna that is expected to deteriorate to either reduce the number of streams that are transmitted and received simultaneously or to use the antenna for diversity communication. This improves the continuity of communication.

Next, we will explain the feedback information received from UE300. First, base station 100 transmits a reference signal to UE300. UE300 feeds back to base station 100 the received signal strength, signal-to-noise power ratio, timestamp at the time of reception, timestamp at the time of transmission, CSI (Channel State Information), etc. from the received reference signal. In a cellular system, the feedback information includes CQI (Channel Quality Indicator), RI (Rank Indicator), PMI (Precoding Matrix Indicator), etc.

In addition, taking into account the possibility that the number of layers may be 1, UE 300 may also feed back PMI etc. corresponding to one layer. Based on this feedback information, base station 100 determines the number of transmission layers using rank adaptation that takes into account the received SINR and spatial correlation between antennas 200.

Next, we will explain how to improve connectivity. In this embodiment, in order to improve connectivity with the base station 100, the UE 300 is controlled by the base station 100 to connect to as many antennas 200 as possible, regardless of communication capacity or whether MIMO is applied. This control is sometimes referred to as "multiple connection control."

This multiple connection control may be classified into UEs 300 that apply the multiple connection control and those that do not. Furthermore, in multiple connection control, antennas 200 with high received power from a reference signal may be selected as the multiple antennas 200 to be connected to the UE 300. Alternatively, antennas 200 with low spatial correlation from CSI may be selected as the multiple antennas 200 to be connected, taking MIMO communication into consideration. Alternatively, antennas 200 with low correlation in the surrounding shielding environment may be selected as the multiple antennas 200 to be connected, taking connectivity into consideration. Specifically, for example, a pair of antennas 200 that maximizes the sum of the angular difference calculated from the direction of each distributed antenna with the UE 300 as the origin may be selected based on the location information of the UE 300 and the location information of each antenna 200. In either case, since the UE 300 connects to multiple antennas 200, the continuity of communication can be improved.

Figure 5 is a flowchart showing the flow of the multiple connection control process. The flowchart in Figure 5 shows an example of a process for selecting antennas with high received power. In Figure 5, the base station 100 transmits a reference signal to the UE 300 (step S101). The base station 100 acquires received power information from the UE 300 via the antenna 200 (step S102). The base station 100 sorts the acquired received power (step S103). The base station 100 instructs the UE 300 to communicate with multiple antennas 200, including the antenna 200 corresponding to the maximum received power among the sorted received powers (step S104), and terminates the multiple connection control process.

Next, we will explain the prediction control process using the prediction results by the prediction unit 120. Figure 6 is a flowchart showing the flow of the prediction control process. In Figure 6, the base station 100 transmits a reference signal to the UE 300 (step S201) and obtains the above-mentioned feedback information from the UE 300 (step S202).

The control unit 110 focuses on one antenna 200 out of the multiple antennas 200 and determines the number of layers M using rank adaptation that takes into account the received SINR and spatial correlation between antennas based on feedback information (step S203). The control unit 110 determines whether the number of layers M is 2 or greater (step S204). If the number of layers is 1 (step S204: NO), the number of layers for all antennas is set to 1 (step S213), and they are set to be used for diversity communication (step S214), and the process ends.

If the number of layers is two or more (step S204: YES), the control unit 110 assigns 0 to counter N (step S205). This counter N is a counter for counting antennas whose fluctuation range of received power is less than a set threshold T. The prediction unit 120 focuses on one antenna and determines whether the fluctuation range of received power of this antenna is greater than or equal to threshold T (step S206). If the fluctuation range of received power is greater than or equal to threshold T (step S206: YES), the process proceeds to step S208. If the fluctuation range of received power is less than threshold T (step S206: NO), the control unit 110 increments N by 1 (step S207).

The control unit 110 determines whether or not the process of determining whether the fluctuation range of the received power is equal to or greater than the threshold value T has been performed for all antennas (step S208). If the process has not been performed for all antennas (step S208: NO), the control unit 110 performs the process of step S206 for the antennas that have not been processed. If the process has been performed for all antennas (step S208: YES), the control unit 110 determines whether N is 0 or 1 (step S209). If N is 0 or 1 (step S209: YES), the control unit 110 proceeds to step S213 described above.

If N is neither 0 nor 1 (step S209: NO), the smaller of M and N is set to L (step S210). The control unit 110 sets the number of layers for all antennas to L (step S211), sets them to be used for MIMO (step S212), and terminates the process.

In the above process, the prediction unit 120 may predict whether the antenna 200 in question is an antenna expected to deteriorate, in addition to other indicators such as the received power value and the spatial correlation of the MIMO channel. After controlling the number of layers in this manner, wireless communication is performed between the base station 100 and each antenna 200 and the UE 300, thereby improving the continuity of communication.

The control unit 110 and the prediction unit 120 may be configured using a processor such as a CPU (Central Processing Unit) and memory. In this case, the control unit 110 and the prediction unit 120 function as the control unit 110 and the prediction unit 120 by the processor executing a program. Note that all or part of the functions of the control unit 110 and the prediction unit 120 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The above program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, and a semiconductor storage device (e.g., an SSD: Solid State Drive), as well as storage devices such as a hard disk or semiconductor storage device built into a computer system. The above program may be transmitted via a telecommunications line.

The above describes in detail an embodiment of the present invention with reference to the drawings, but the specific configuration is not limited to this embodiment and also includes designs that do not deviate from the gist of the present invention.

The present invention is applicable to wireless communication devices such as base stations that communicate wirelessly with UEs.

10 Communication system, 100 Base station, 110 Control unit, 120 Prediction unit, 130 Transmission unit, 140 Signal processing unit, 150 Beam control unit, 150 performs signal processing on the signal input from the beam control unit, 160 Transmitting/receiving unit, 170 Memory unit, 200 Antenna, 300 UE

Claims (8)

a prediction unit that predicts a communication quality with an opposite device that wirelessly communicates via a plurality of antennas , for each of the plurality of antennas ;
a control unit that sets an antenna, among the plurality of antennas, for which the prediction unit predicts that the communication quality will be degraded, to reduce the number of streams that are simultaneously transmitted and received or to use the antenna for diversity communication;
A wireless communication device comprising: The wireless communication device of claim 1, wherein the prediction unit predicts that communication quality will deteriorate if the fluctuation range of the received power detected by the opposite device within a certain period of time exceeds a predetermined threshold. The wireless communication device according to claim 1 , wherein the control unit controls the opposing device to perform wireless communication with the plurality of antennas. The wireless communication device according to claim 1 , wherein the control unit controls the opposing device to perform wireless communication with a plurality of antennas including an antenna corresponding to a maximum reception power among reception powers corresponding to the plurality of antennas. The wireless communication device according to claim 1, wherein the control unit determines the number of streams based on a CQI (Channel Quality Indicator), RI (Rank Indicator), or PMI (Precoding Matrix Indicator) fed back from the opposing device. A communication system including a plurality of antennas and a wireless communication device that controls the plurality of antennas,
The wireless communication device
a prediction unit that predicts a communication quality with an opposite device that wirelessly communicates via the plurality of antennas , for each of the plurality of antennas ;
a control unit that sets an antenna, among the plurality of antennas, for which the prediction unit predicts that the communication quality will be degraded, to reduce the number of streams that are simultaneously transmitted and received or to use the antenna for diversity communication;
A communication system comprising: a prediction step of predicting, for each of a plurality of antennas, a communication quality with an opposite device that wirelessly communicates via the plurality of antennas;
a control step of reducing the number of streams to be simultaneously transmitted and received or setting an antenna for which communication quality is predicted to deteriorate in the prediction step among the plurality of antennas to be used for diversity communication;
A wireless communication method comprising: On the computer,
a prediction step of predicting, for each of a plurality of antennas, a communication quality with an opposite device that wirelessly communicates via the plurality of antennas;
a control step of reducing the number of streams to be simultaneously transmitted and received or setting an antenna for which communication quality is predicted to deteriorate in the prediction step among the plurality of antennas to be used for diversity communication;
A program to execute.