Control device, terminal device, control method, and program for transmission power control in a cell-free massive MIMO system composed of a plurality of antennas

Abstract

To appropriately control the transmission power of a terminal device in a cell-free massive MIMO system including a large number of antennas.SOLUTION: A control device in a wireless communication system that provides a communication service to a terminal device via some of a large number of antennas notifies the terminal device of information that allows the terminal device to identify a wireless signal to be measured to be used when the terminal device performs transmission power control from among wireless signals transmitted from the large number of respective antennas.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a transmission power control technique in a cell-free massive MIMO system composed of a large number of antennas.

Background Art

[0002] A cell-free massive MIMO system that arranges a large number of antennas at high density and communicates with a terminal device using a part of the large number of antennas has been studied. In this cell-free massive MIMO system, by selecting the antennas used for each terminal device, a virtual cell is configured for each terminal device, and the terminal device will generally exist at the center of its virtual cell. According to such a technique, the terminal device can obtain uniform communication quality regardless of its position.

[0003] When a large number of terminal devices transmit signals in parallel, it is important to appropriately set the transmission power of the signals from the terminal devices in order to suppress the mutual interference of the signals from these multiple terminal devices. Non-Patent Document 1 describes such transmission power control. Transmission power control includes an open-loop type of control in which the terminal device autonomously determines the target transmission power based on the measurement result of the radio quality (for example, reference signal received power (RSRP)) of the radio signal transmitted from the base station device at the terminal device and performs transmission power control, and a closed-loop type of control in which the transmission power control is performed according to an instruction from the base station device.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the open-loop transmission power control in a conventional system, transmission power control is performed based on the radio quality between a terminal device and one of the base station devices (cells) to which the terminal device is connected. On the other hand, in a cell-free massive MIMO system, since there is no defined cell to which the terminal device is explicitly connected, the conventional transmission power control cannot be directly applied.

Means for Solving the Problem

[0006] The present invention provides a transmission power control technique in a cell-free massive MIMO system composed of a large number of antennas.

[0007] A control device according to an aspect of the present invention is a control device in a wireless communication system that provides communication services to a terminal device via a part of a large number of antennas, and includes notification means for notifying the terminal device of information that enables identification of a radio signal to be measured, which is to be used by the terminal device when performing transmission power control, from among the radio signals transmitted from each of the large number of antennas. are geographically dispersed and arranged at high density, and the plurality of antennas

[0008] A terminal device according to an aspect of the present invention is a terminal device that receives communication services via a part of a large number of antennas, and includes receiving means for receiving, from a control device, information that enables identification of a radio signal to be measured, which is to be used by the terminal device when performing transmission power control, from among the radio signals transmitted from each of the large number of antennas, and control means for measuring the radio quality of the radio signal to be measured identified based on the information and controlling the transmission power based on the radio quality. are geographically dispersed and arranged at high density, and the plurality of antennas

Advantages of the Invention

[0009] According to the present invention, the transmission power of a terminal device in a cell-free massive MIMO system composed of a large number of antennas can be appropriately controlled.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of the features described in the embodiments are essential for the invention. Two or more of the plurality of features described in the embodiments may be arbitrarily combined. Also, the same or similar configurations are given the same reference numerals, and duplicate descriptions are omitted.

[0012] (System Configuration) Fig. 1 shows a configuration example of the wireless communication system according to the present embodiment. As shown in Fig. 1, in the wireless communication system according to the present embodiment, a large number of antennas 111 to 112 are arranged at high density over a wide geographical area, and these antennas 111 to 112 are each connected to control devices 101 to 102 such as base station devices via, for example, optical fibers. In the present embodiment, they are referred to as antennas 111 to 112, but in addition to antennas, they can be transmission / reception devices having communication functions capable of executing respective processes of physical layers and upper layers. Note that one transmission / reception device may include only one antenna or may include a plurality of antennas. The control devices 101 to 102 are connected to the terminal device 121 via at least one antenna to perform communication. In Fig. 1, only a small number of control devices 101 to 102 and terminal device 121 are shown for simplicity of explanation, but these devices can naturally exist in larger numbers than shown in Fig. 1.

[0013] The terminal device 121 communicates by connecting to at least one of the control devices 101 to 102 via a part of the antennas 111 to 112 existing in the vicinity. The control devices 101 to 102 communicate with the terminal device 121 using at least a part of the antennas connected to their own devices in a state where a connection with the terminal device 121 is established. As a result, one or more of the control devices 101 to 102 constitute a virtual area centered on the terminal device 121, and a high-quality and highly stable communication service can be provided regardless of the position of the terminal device 121. Note that a part of the numerous antennas for constituting the virtual area here may be called a user-centric cluster, and is simply called a "cluster" in the present embodiment. The cluster is configured, for example, by connecting to the antenna with the best radio quality when the terminal device 121 starts communication, and selecting, as the antenna that provides a communication service to the terminal device 121, an antenna that is not performing communication in the resource block available to the terminal device 121 in the situation where the terminal device 121 should communicate. Note that when the antenna is a transmission / reception device having, for example, a control function of a higher layer, for example, the control devices 101 to 102 inquire about the resource usage status of each transmission / reception device, and a transmission / reception device that is not using the resource to be used can be selected as the transmission / reception device that provides a communication service to the terminal device 121. Note that the configuration of the cluster is not limited to this, and the selection of the antenna to be used can be performed by an algorithm appropriately selected by the network operator.

[0014] Here, the terminal device 121 determines the transmission power when transmitting a signal based on the downlink transmitted from the antennas 111 to 112. However, in a system such as that shown in FIG. 1, since there is no conventional "cell" as a connection destination, it is not clear on what basis the terminal device 121 executes transmission power control. For this reason, the present embodiment provides a procedure for the terminal device 121 to perform transmission power control in a system such as that shown in FIG. 1.

[0015] In this embodiment, the terminal device 121 measures the radio quality of a radio signal to be measured, for example, from some of the antennas forming a cluster, and performs transmission power control based on the radio quality. The radio quality is, for example, the reference signal received power (RSRP), but is not limited thereto, and may be any radio quality capable of specifying propagation loss, such as the signal-to-noise ratio (SNR), for example. Here, the terminal device 121 can obtain the received power of a plurality of radio signals to be measured, and use the total received power, average received power, minimum received power, maximum received power, or the median of the received power distribution as an index to perform transmission power control. Note that the median of the received power distribution may be a predetermined percentile value of the received power (for example, 10th percentile value or 90th percentile value).

[0016] The terminal device 121 can, for example, specify the total amount of propagation loss between the antennas forming the cluster based on the total received power of the radio signal to be measured, and perform transmission power control to compensate for the propagation loss. Also, the terminal device 121 can determine the transmission power between one antenna based on the propagation loss corresponding to the average received power, minimum received power, maximum received power, or the median of the received power distribution of the radio signal to be measured, and multiply the determined transmission power by a constant corresponding to the number of antennas to determine the total transmission power.

[0017] In this embodiment, the control devices 101 to 102 can notify the terminal device 121 of information that enables the identification of the radio signal to be measured to be used when the terminal device 121 performs transmission power control via an antenna capable of communicating with the terminal device 121.

[0018] For example, the wireless signal is configured to be able to identify from which of a number of antennas it was transmitted, and the control devices 101 to 102 can notify the terminal device 121 of information identifying some of the antennas that provide the communication service. For example, the reference signals transmitted by each antenna are transmitted using mutually orthogonal resources such as frequency, time, and code, and the terminal device 121 may be notified of the resources used for transmitting the reference signal to be measured. Also, the wireless signal transmitted from each antenna may include information capable of identifying the transmitting antenna. The terminal device 121 can measure the wireless quality of the wireless signal transmitted from some of the antennas that provide the communication service to its own device based on the notified information, and can perform transmission power control. For example, the terminal device 121 can identify the RSRP based on the reference signal transmitted from each antenna, identify the propagation loss based on the RSRP, and perform transmission power control. Also, the terminal device 121 may perform transmission power control using the above-described indicators.

[0019] At this time, the control devices 101 to 102 may notify the terminal device 121 of information specifying which of the above-described indicators should be used, for example. Also, the control devices 101 to 102 may collect the propagation path estimation error (estimation error of propagation loss) for each antenna based on, for example, the communication performance, hold the statistical value thereof, and notify the terminal device 121 of the information of the statistical value. Note that the propagation path estimation error may be collected for each area where the terminal device 121 exists or for the entire area where the antennas under the control device are arranged, and the statistical value may be held. When the terminal device 121 acquires this information, it can perform transmission power control using the propagation path estimation error as an offset value. For example, the power obtained by adding the offset value to the transmission power value corresponding to the estimated value of the propagation loss may be determined as the transmission power actually used.

[0020] Also, when the control devices 101 to 102 use, for example, the minimum reception power or the maximum reception power of the radio signal of the measurement target for transmission power control by the terminal device 121, the control devices 101 to 102 may further notify information regarding the antenna that transmitted the radio signal of the minimum reception power or the maximum transmission power. According to this, the terminal device 121 can specify, for example, whether the minimum reception power is obtained as a result of receiving a radio signal from an antenna at a position far from the own device, or whether the minimum reception power is instantaneously obtained due to, for example, a shielding object or the like. Further, the terminal device 121 can execute transmission power control more appropriately by acquiring, for example, the setting information at the time of transmission of the radio signal at the antenna that is the transmission source of the radio signal of the maximum reception power or the minimum reception power. Note that even when other indicators are used, information that enables specification of which antenna transmitted what kind of radio signal may be notified to the terminal device 121.

[0021] Note that it is also conceivable that it is not possible to specify from which of a number of antennas a radio signal is transmitted. In this case, the control devices 101 to 102 may notify the terminal device 121 of, for example, the number of antennas constituting a cluster that provides a communication service to the terminal device 121. In this case, the terminal device 121 can measure, for example, the radio quality of the specified number of radio signals among the received radio signals and execute transmission power control based on the radio quality. The terminal device 121 can execute transmission power control based on, for example, the radio quality of the number of radio signals notified from the ones with better radio quality. According to this, the terminal device 121 can reduce the probability of considering radio signals from antennas that do not belong to the cluster by measuring a number of radio signals exceeding the number of antennas belonging to the cluster that provides a communication service to the terminal device 121.

[0022] In addition, the control devices 101 to 102 can notify the terminal device 121 of information regarding the reference value of the radio quality. Then, the terminal device 121 can perform transmission power control based on the radio quality of a radio signal that can obtain a radio quality exceeding the reference value. It is assumed that the radio signal from the antenna belonging to the cluster that provides the communication service to the terminal device 121 has a sufficiently good radio quality. Therefore, by specifying the reference value of the radio quality, the probability that the terminal device 121 can selectively use the radio quality of the radio signal from the antenna belonging to the cluster to perform transmission power control can be improved. Note that the information regarding the reference value of the radio quality may be specified as a relative reference value with respect to any of the measured radio qualities, for example, in the range of 20 dB from the value of the best radio quality.

[0023] Note that even when the terminal device 121 cannot identify from which of a number of antennas the signal was transmitted, for example, it can identify the RSRP based on the radio signal determined to be used for transmission power control as described above, and identify the propagation loss based on the RSRP, and perform transmission power control. Also, the terminal device 121 may perform transmission power control using an index as described above. At this time, the control devices 101 to 102 may notify the terminal device 121 of information specifying which of the above-described indexes should be used, for example.

[0024] Note that the above-described control devices 101 to 102 may be provided in each of the antennas 111 to 112. For example, when the antennas 111 to 112 are transceiver devices capable of executing communication processing of the physical layer and the upper layer, in the transceiver device, the above-described processing may be executed by the control devices 101 to 102. That is, the control devices 101 to 102 may be included in the transceiver devices corresponding to the antennas 111 to 112, respectively, and may be distributed and arranged. In that case, each of the transceiver devices can exchange information with each other and execute transmission and reception of information for selection of transceiver devices constituting a cluster. In this case, the terminal device 121 can receive the above-described information notification from one of the transceiver devices forming a cluster corresponding to the own device, for example, from the transceiver device to which the terminal device 121 first connects before forming the cluster of the terminal device 121.

[0025] (Device Configuration) Subsequently, the configurations of the above-described control devices 101 to 102 and the terminal device 121 will be described. FIG. 2 shows a hardware configuration example of the control devices 101 to 102 and the terminal device 121. In one example, the control devices 101 to 102 and the terminal device 121 include a processor 201, a ROM 202, a RAM 203, a storage device 204, and a communication circuit 205. In the control devices 101 to 102 and the terminal device 121, for example, a computer-readable program for realizing each function of each device as described above recorded in any of the ROM 202, the RAM 203, and the storage device 204 is executed by the processor 201. Note that the processor 201 may be replaced by one or more processors such as an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a DSP (Digital Signal Processor). The control devices 101 to 102 and the terminal device 121 control the communication circuit 205 by the processor 201, for example, to perform communication with other devices. Note that FIG. 2 shows a schematic diagram in which the control device has one communication circuit 205, but the present invention is not limited thereto.

[0026] FIG. 3 shows a functional configuration example of the control devices 101 to 102. The functions shown in FIG. 3 are realized, for example, when the processors 201 of the control devices 101 to 102 execute programs stored in the ROM 202, the RAM 203, and the storage device 204. Note that the control devices 101 to 102 may have hardware corresponding to at least any of the functions described later. Note that FIG. 3 selectively shows the functional units particularly related to the present embodiment among the functions of the control devices 101 to 102, and the control devices 101 to 102 naturally have functions for forming a user-centric cluster and communicating with the terminal device 121. As a function thereof, the control devices 101 to 102 have a measurement target information notification unit 301. Further, the control devices 101 to 102 may optionally have an index information notification unit 302.

[0027] The measurement target information notification unit 301 notifies the terminal device 121 of information that can identify the wireless signal to be measured, which should be used by the terminal device 121 when performing transmission power control, from among the wireless signals transmitted from each of a number of antennas. Note that, as described above, when the wireless signal is configured to be able to identify from which of the number of antennas it is transmitted, the information may include information for identifying some of the antennas used when providing a communication service to the terminal device 121. For example, the reference signals transmitted from each antenna are transmitted using wireless resources such as orthogonal frequencies, times, and codes, and the information may include information specifying the wireless resources. Further, each antenna may be assigned a separate identifier, and the identifier may be included in the wireless signal and transmitted. Further, the information may be information indicating the number of antennas used when providing a communication service to the terminal device 121. Further, the information may include information regarding a reference value of wireless quality. The index information notification unit 302 notifies the terminal device 121 of information indicating an index regarding the wireless quality of the wireless signal to be measured, which should be used by the terminal device 121 as a reference for transmission power control. Here, the index may include the total received power, the average received power, the minimum received power, the maximum received power, or the median value of the received power distribution of the wireless signal to be measured.

[0028] Fig. 4 shows a functional configuration example of the terminal device 121. The functions shown in Fig. 4 are realized, for example, when the processor 201 of the terminal device 121 executes programs stored in the ROM 202, the RAM 203, and the storage device 204. Note that the terminal device 121 may have hardware corresponding to at least any of the functions described later. Note that Fig. 4 selectively shows the functional parts particularly relevant to the present embodiment among the functions of the terminal device 121, and the terminal device 121 naturally has functions as a general terminal device. The terminal device 121 has, as its functions, a measurement target information receiving unit 401 and a transmission power control unit 402. Further, the terminal device 121 may optionally have an index information receiving unit 403.

[0029] The measurement target information receiving unit 401 receives information that can identify a wireless signal of a measurement target to be used when the terminal device 121 performs transmission power control, which is transmitted from the control devices 101 to 102 by the above-described measurement target information notification unit 301. When the measurement target information receiving unit 401 receives information that identifies a part of the antennas used when providing a communication service to the terminal device 121, for example, the transmission power control unit 402 measures the radio quality of the wireless signal transmitted from that part of the antennas, estimates the propagation loss, determines the transmission power to compensate for the propagation loss, and executes control of an amplifier or the like. Also, when it is not possible to identify the transmission source of the wireless signal, the transmission power control unit 402 can estimate the radio quality of the wireless signal without identifying from which antenna it was transmitted and execute transmission power control. When the measurement target information receiving unit 401 receives information indicating the number of antennas used when providing a communication service to the terminal device 121, for example, the transmission power control unit 402 can execute transmission power control based on the radio quality of the number specified by the information from the higher measured radio quality of the wireless signal. Further, when the measurement target information receiving unit 401 receives information regarding the reference value of the radio quality, the transmission power control unit 402 can execute transmission power control based on the radio quality exceeding the reference value. Note that the reference value may be information that can identify a second value obtained by subtracting the reference value from a first value of the best radio quality, for example, and the transmission power control unit 402 can execute transmission power control based on the radio quality exceeding the second value. The index information receiving unit 403 receives information indicating an index regarding the radio quality of a wireless signal of a measurement target to be used as a reference for transmission power control by the terminal device 121 from the control devices 101 to 102 by the index information notification unit 302. Here, the index may include the total received power, average received power, minimum received power, maximum received power, or the median value of the distribution of the received power of the wireless signal of the measurement target.

[0030] (Flow of processing) An example of the flow of processing executed in the wireless communication system will be described with reference to FIG. 5. Since the details of the processing are as described above, here, only an overview of the flow of processing will be given.

[0031] In this process, first, information that enables identification of a radio signal to be measured, which should be used by the terminal device 121 when performing transmission power control, is notified from any one of the control devices 101 to 102 to the terminal device 121 via any one of the antennas 111 to 112 (S501). Also, if necessary, information indicating an index related to the radio quality of the radio signal to be measured, which should be used by the terminal device 121 as a reference for transmission power control, may be notified to the terminal device 121 from any one of the control devices 101 to 102 via any one of the antennas 111 to 112 (S502). Note that the antennas and control devices used for the information notification in S501 and the antennas and control devices used for the information notification in S502 may be different or the same.

[0032] After that, for example, radio signals such as reference signals are transmitted from each antenna (S503). The terminal device 121 identifies the measurement target from the received radio signals based on the information obtained in S501 (S504), and measures the radio quality of the measurement target (S505). Then, the terminal device 121 controls the transmission power based on the radio quality measured in S505 and, for example, the index information obtained in S502 (S506). Thereby, the propagation loss is compensated, and the transmission power is set so that the received power at each antenna becomes the target power.

[0033] With the above configuration, according to this embodiment, the transmission power of the terminal device in a cell-free massive MIMO system composed of a large number of antennas can be appropriately controlled. Therefore, it becomes possible to contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, "Build resilient infrastructure, promote sustainable industrialization, and foster innovation."

[0034] The invention is not limited to the above-described embodiment, and various modifications and changes are possible within the scope of the gist of the invention.

Claims

1. A control device in a wireless communication system that provides communication services to a terminal device via a part of a plurality of antennas that are geographically dispersed and arranged at high density, the control device having notification means for notifying the terminal device of information that enables identification of a wireless signal to be measured from among the wireless signals transmitted from each of the plurality of antennas, the wireless signal being used by the terminal device when performing transmission power control.

2. The wireless signal is configured to be able to identify from which of the plurality of antennas it was sent, The information includes information for identifying the part of the plurality of antennas used when providing communication services to the terminal device, and the control device according to claim 1 is characterized in that.

3. The information includes information indicating the number of the part of the plurality of antennas used when providing communication services to the terminal device, and the control device according to claim 1 is characterized in that.

4. The information includes information regarding a reference value of wireless quality, The terminal device uses, as the wireless signal to be measured, a wireless signal that obtains a wireless quality exceeding the reference value among the wireless signals transmitted from the plurality of antennas, and the control device according to claim 1 is characterized in that.

5. The notification means further notifies the terminal device of information indicating an index regarding the wireless quality of the wireless signal to be measured that the terminal device should use as a reference for the transmission power control, and the control device according to any one of claims 1 to 4 is characterized in that.

6. The index includes the total received power, average received power, minimum received power, maximum received power, or median of the received power distribution of the wireless signal to be measured, and the control device according to claim 5 is characterized in that.

7. A terminal device that receives communication services via a part of a plurality of antennas that are geographically dispersed and arranged at high density, the terminal device having: Receiving means for receiving from a control device information that enables identification of a wireless signal to be measured from among the wireless signals transmitted from each of the plurality of antennas, the wireless signal being used by the terminal device when performing transmission power control; Control means for measuring the wireless quality of the wireless signal to be measured identified based on the information and controlling the transmission power based on the wireless quality; The terminal device is characterized by having.

8. The wireless signal is configured to be able to identify from which of the multiple antennas it was transmitted. The information includes information identifying a part of the multiple antennas used when providing a communication service to the terminal device. The control means measures the wireless quality of the wireless signal transmitted from the part of the multiple antennas indicated by the information, and controls the transmission power based on the wireless quality. The terminal device according to claim 7, characterized in that.

9. The information includes information indicating the number of the part of the multiple antennas used when providing a communication service to the terminal device. The control means measures the wireless quality of the wireless signals of the number indicated by the information, and controls the transmission power based on the wireless quality. The terminal device according to claim 7, characterized in that.

10. The information includes information regarding a reference value of wireless quality. The control means controls the transmission power based on the wireless quality of the wireless signal that can obtain a wireless quality exceeding the reference value among the wireless signals transmitted from the multiple antennas. The terminal device according to claim 7, characterized in that.

11. The receiving means further receives from the control device information indicating an index regarding the wireless quality of the wireless signal to be measured, which the terminal device should use as a reference for the transmission power control. The control means controls the transmission power based on the wireless quality of the wireless signal to be measured identified based on the information and the index. The terminal device according to any one of claims 7 to 10, characterized in that.

12. The index includes the total received power, average received power, minimum received power, maximum received power, or median of the distribution of received power of the wireless signal to be measured. The terminal device according to claim 11, characterized in that.

13. A control method executed by a control device in a wireless communication system in which multiple antennas are geographically dispersed and arranged at high density, and a communication service is provided to a terminal device through a part of the multiple antennas, the method comprising: notifying the terminal device of information that enables identification of a wireless signal to be measured, which the terminal device should use when performing transmission power control, from among the wireless signals transmitted from each of the multiple antennas. A control method characterized by that.

14. A control method executed by a terminal device that receives communication services via some of a plurality of antennas that are geographically dispersed and arranged at high density, the method comprising: receiving, from a control device, information that enables identification of a radio signal to be measured, among radio signals transmitted from each of the plurality of antennas, for use when the terminal device performs transmission power control; measuring the radio quality of the radio signal to be measured identified based on the information, and controlling the transmission power based on the radio quality; The control method is characterized by including the above.

15. A program for causing a computer provided in a control device in a wireless communication system that provides communication services to a terminal device via some of a plurality of antennas that are geographically dispersed and arranged at high density to notify the terminal device of information that enables identification of a radio signal to be measured, among radio signals transmitted from each of the plurality of antennas, for use when the terminal device performs transmission power control.

16. In a computer provided in a terminal device that receives communication services via some of a plurality of antennas that are geographically dispersed and arranged at high density, causing the computer to receive, from a control device, information that enables identification of a radio signal to be measured, among radio signals transmitted from each of the plurality of antennas, for use when the terminal device performs transmission power control; measuring the radio quality of the radio signal to be measured identified based on the information, and causing the transmission power to be controlled based on the radio quality; A program for the above.

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