Wireless communication system, base station, communication method, and non-transitory computer-readable storage medium

Abstract

A first base station of a wireless communication system includes a receiving unit that receives information indicating the number of terminals that should communicate via a relay device among terminals under a second base station, a control unit that calculates the total number of terminals that should communicate via the relay device as the sum of the number indicated by the received information and the number of terminals that should communicate via the relay device among one or more terminals under the first base station, and schedules a first communication between the first base station and the terminal via a plurality of reflecting elements of a first part of the relay device and a second communication between the second base station and the terminal via a plurality of reflecting elements of a second part of the relay device based on the total number, and a transmitting unit that transmits scheduling information for the second communication.

Description

[Technical field]

[0001] The present invention relates to a base station in a wireless communication system, a communication method, and a non-transitory computer-readable storage medium. [Background technology]

[0002] Reconfigurable Intelligent Surface (RIS) is an effective method to control the channel by appropriately adjusting the phase and amplitude of the electromagnetic signal. Various architectures and multiple access techniques have been proposed in recent research and experiments.

[0003] The use of RIS is being considered to extend the coverage of a cell. When a direct wave from a base station is blocked, the reception level of a radio signal from a user device located at the edge of a cell becomes lower than the reception level of a radio signal in line-of-sight communication.

[0004] In such cases, by combining the beamformed transmission waves transmitted from the base station and the reflected waves from the RIS, it is possible to increase the reception level of a user device located in a location where the direct waves from the base station are blocked by a building or the like. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] M. Hua, Q. Wu, DWK Ng, J. Zhao and L. Yang, “Intelligent Reflecting Surface-Aided Joint Processing Coordinated Multipoint Transmission,” in IEEE Transactions on Communications, vol. 69, no. 3, pp. 1650-1665, March 2021. [Non-Patent Document 2] B. Di, “Sharing the Surface: RIS-aided Distributed Mechanism Design for Hybrid Beamforming in Multi-cell Multi-user Networks,” IEEE INFOCOM 2021 - IEEE Conference on Computer Communications Workshops (INFOCOM WKSHPS), 2021, pp. 1-2, doi: 10.1109 / INFOCOMWKSHPS51825.2021.9484464. Summary of the Invention [Problem to be solved by the invention]

[0006] In a system consisting of multiple cells and multiple base stations, such as cellular communications, it is assumed that multiple radio base stations will share the same RIS (reflector) and perform beamforming toward user terminals under their own cell.

[0007] In such a system, competition for the same RIS is likely to occur.

[0008] The present invention has been made in consideration of the above-mentioned points, and has an object to provide a method for resolving contention for the same RIS while reducing the overhead of control information. [Means for solving the problem]

[0009] According to one aspect of the present invention,

[0010] A first base station;

[0011] A second base station;

[0012] a relay device including a plurality of reflective elements; and

[0013] A wireless communication system including a plurality of terminals,

[0014] a first communication area formed by the first base station overlaps with a second communication area formed by the second base station;

[0015] The first base station,

[0016] a first receiving unit that receives, from the second base station, information indicating a second number of terminals that should communicate via the relay device among one or more terminals under the second base station;

[0017] Calculating the sum of the second number indicated by the received information and a first number of terminals to communicate via the relay device among one or more terminals under the first base station as a total number of terminals to communicate via the relay device;

[0018] scheduling a first communication between each terminal that is to communicate via the relay device under the first base station and the first base station and a second communication between each terminal that is to communicate via the relay device under the second base station and the second base station, based on the total number and priorities set for the first base station and the second base station;

[0019] Among the plurality of reflecting elements included in the relay device, a plurality of reflecting elements in a first portion to be used for the first communication and a plurality of reflecting elements in a second portion to be used for the second communication are determined.

[0020] A first control unit;

[0021] a first transmitter configured to transmit scheduling information for the second communication and information indicative of a plurality of reflecting elements in the second portion to the second base station; Equipped with

[0022] The second base station,

[0023] a second transmission unit that transmits, to the first base station, information indicating the number of terminals that should communicate via the relay device among one or more terminals under the second base station;

[0024] a second receiver that receives scheduling information for the second communication and information indicative of a plurality of reflecting elements in the second portion from the first base station;

[0025] a second control unit that schedules the second communication using the plurality of reflecting elements in the second portion based on scheduling information of the second communication and information indicating the plurality of reflecting elements in the second portion; Equipped with A wireless communication system is provided. Effect of the Invention

[0026] According to an embodiment, a method for resolving contention for the same RIS is provided while reducing the overhead of control information. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. [Diagram 2] FIG. 2 is a diagram illustrating an example of a functional configuration of a base station. [Diagram 3] FIG. 2 is a diagram illustrating an example of a functional configuration of a terminal. [Figure 4] FIG. 1 is a diagram illustrating an example of the functional configuration of a Reconfigurable Intelligent Surface (RIS). [Diagram 5] FIG. 2 is a diagram showing an example of a plurality of elements included in a RIS. [Figure 6] A diagram showing an example of the hardware configuration of a base station, a terminal, and a RIS. [Figure 7] FIG. 1 illustrates an example in which multiple base stations share the same RIS. [Figure 8] FIG. 13 is a diagram showing an example of time resource allocation when sharing a RIS. [Figure 9] 11 is a flowchart illustrating an example of a processing procedure of the wireless communication system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Reconfigurable Intelligent Surface (RIS) is considered a method to effectively control the radio wave propagation channel by appropriately controlling the phase and amplitude of electromagnetic waves. According to recent research and experiments, various architectures and multiple access technologies have been found.

[0029] As an application of RIS, the method of multiple base stations sharing a single RIS is considered effective for improving communication efficiency. Since RIS is mainly implemented to improve the coverage of blocked areas, it is important to enable multiple base stations to share a single RIS. Although the method of arranging RIS for each base station is also considered, it is thought that interference and cost will increase in this method.

[0030] The application of RIS is developing together with existing technologies. Optimization of the transmission beamforming of base stations and the phase shift of each RIS based on the allocation of the transmission power of base stations has been studied. Also, for RIS-based beamforming, negotiation between base stations to obtain consensus between base stations without revealing information of terminals under the control of base stations has been proposed. That is, it is assumed that different base stations accessing RIS will perform a similar reflection response to terminals after obtaining consensus between base stations regarding RIS-based beamforming.

[0031] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an example of the configuration of a wireless communication system in the embodiment. As shown in FIG. 1, the wireless communication system includes a first base station 10A, a second base station 10B, a terminal 20, a Reconfigurable Intelligent Surface (RIS) 30, a network 40, and the like. The first base station 10A and the second base station 10B are connected to the network 40 by wire or wireless. The first base station 10A and the second base station 10B are connected to each other so that they can communicate with each other, for example, via an X2 interface. The first base station 10A and the RIS 30 are connected to each other so that they can communicate with each other, by wire or wireless. The second base station 10B and the RIS 30 are connected to each other so that they can communicate with each other, by wire or wireless. The RIS 30 may also be connected to the network 40 by wire or wireless. The first base station 10A, the second base station 10B, and the terminal 20 are all capable of transmitting and receiving signals by performing beamforming.

[0032] The first base station 10A is equipped with multiple antenna ports and can form beams in the vertical direction in addition to the horizontal direction. The first base station 10A can impart directionality to beams transmitted from multiple antenna ports by multiplying data supplied to each antenna port by a weighting factor of a precoding vector and adjusting the phase rotation amount (and / or amplitude) for each antenna port.

[0033] Similarly, the second base station 10B is equipped with multiple antenna ports and is capable of forming beams in the vertical direction in addition to the horizontal direction. The second base station 10B can impart directionality to beams transmitted from multiple antenna ports by multiplying the data supplied to each antenna port by the weighting of a precoding vector and adjusting the phase rotation amount (and / or amplitude) for each antenna port. The terminal 20 may also be equipped with multiple antenna ports and may be capable of forming beams in the vertical direction in addition to the horizontal direction.

[0034] The first base station 10A is a base station that forms a communication area outdoors or the like. The first base station 10A realizes high-speed wireless communication with the terminal 20 by transmitting and receiving radio waves in a frequency band used in a fifth generation mobile communication system (5G), for example. The second base station 10B is a base station that forms a communication area that overlaps with the communication area formed by the first base station 10A. Here, the overlap of the two communication areas may mean that the communication areas overlap almost completely, that one communication area is included in the other communication area, or that the two communication areas overlap partially. The second base station 10B realizes high-speed wireless communication with the terminal 20 by transmitting and receiving radio waves in a frequency band used in 5G, for example. The terminal 20 is a communication device such as a smartphone, a tablet terminal, or a personal computer (PC).

[0035] The first base station 10A can communicate with the terminal 20 directly or via the RIS 30 serving as a relay device. The second base station 10B can communicate with the terminal 20 directly or via the RIS 30 serving as a relay device.

[0036] The RIS 30 is connected to the first base station 10A by wire or wirelessly. The RIS 30 can relay a signal from the terminal 20 to the first base station 10A by changing the reflection direction of a carrier wave carrying the signal from the terminal 20 in accordance with the setting information from the first base station 10A. The RIS 30 can also relay a signal from the first base station 10A to the terminal 20 by changing the reflection direction of a carrier wave carrying the signal from the first base station 10A in accordance with the setting information from the first base station 10A.

[0037] In addition, the RIS 30 is connected to the second base station 10B either by wire or wirelessly. The RIS 30 can relay the signal from the terminal 20 to the second base station 10B by changing the reflection direction of the carrier wave on which the signal from the terminal 20 is carried according to the setting information from the second base station 10B. Also, the RIS 30 can relay the signal from the second base station 10B to the terminal 20 by changing the reflection direction of the carrier wave on which the signal from the second base station 10B is carried according to the setting information from the second base station 10B.

[0038] Note that when the RIS 30 is connected to the network 40 either by wire or wirelessly, the RIS 30 can relay the signal from the terminal 20 to the first base station 10A and / or the second base station 10B by changing the reflection direction of the carrier wave on which the signal from the terminal 20 is carried according to the setting information from the network 40. Also, the RIS 30 can relay the signal from the first base station 10A to the terminal 20 by changing the reflection direction of the carrier wave on which the signal from the first base station 10A is carried according to the setting information from the network 40. Also, the RIS 30 can relay the signal from the second base station 10B to the terminal 20 by changing the reflection direction of the carrier wave on which the signal from the second base station 10B is carried according to the setting information from the network 40.

[0039] In the example of FIG. 1, only one terminal 20 is shown. However, the number of terminals 20 is not limited to the example of FIG. 1, and more than one terminal 20 may be included. Also, in the example of FIG. 1, the first base station 10A and the second base station 10B are shown, but the number of base stations 10 is not limited to the example of FIG. 1, and more than two base stations 10 may be included. Also, in the example of FIG. 1, only one RIS 30 is shown, but the number of RIS 30s is not limited to the example of FIG. 1, and more than one RIS 30 may be included.

[0040] Fig. 2 is a diagram showing an example of the functional configuration of the first base station 10A and the second base station 10B. As shown in Fig. 2, both the first base station 10A and the second base station 10B have a transmitting unit 110, a receiving unit 120, and a control unit 130. The functional configuration shown in Fig. 2 is merely an example. The functional divisions and names of the functional units may be any names as long as they can execute the operations according to this embodiment.

[0041] The transmitter 110 creates a transmission signal from transmission data and transmits the transmission signal wirelessly. The receiver 120 wirelessly receives various signals and acquires a higher layer signal from the received physical layer signal. The receiver 120 also includes a measurement unit that measures the received signal and acquires the received power, etc.

[0042] The control unit 130 controls the base station (the first base station 10A or the second base station 10B). Note that the functions of the control unit 130 related to transmission may be included in the transmitting unit 110, and the functions of the control unit 130 related to reception may be included in the receiving unit 120.

[0043] Fig. 3 is a diagram showing an example of the functional configuration of the terminal 20. As shown in Fig. 3, the terminal 20 has a transmitting unit 210, a receiving unit 220, and a control unit 230. The functional configuration shown in Fig. 3 is merely an example. The functional divisions and names of the functional units may be any names as long as they can execute the operations according to the present embodiment.

[0044] The transmitter 210 includes a function of generating a signal to be transmitted to the base station (the first base station 10A and / or the second base station 10B) and wirelessly transmitting the signal. The receiver 220 includes a function of receiving various signals transmitted from the base station (the first base station 10A and / or the second base station 10B) and acquiring, for example, information of a higher layer from the received signal. The receiver 220 also includes a measurement unit that measures the received signal and acquires the received power, etc.

[0045] The control unit 230 controls the terminal 20. Note that the functions of the control unit 230 related to transmission may be included in the transmitting unit 210, and the functions of the control unit 230 related to reception may be included in the receiving unit 220.

[0046] Fig. 4 is a diagram showing an example of the functional configuration of RIS 30. As shown in Fig. 4, RIS 30 has a transmitting unit 310, a receiving unit 320, a control unit 330, and a plurality of elements 340. The functional configuration shown in Fig. 4 is merely an example. The functional divisions and names of the functional units may be any names as long as they can execute the operations according to this embodiment.

[0047] The transmitter 310 has a function of generating a signal to be transmitted to the base station (the first base station 10A and / or the second base station 10B) and transmitting the signal by wire and / or wirelessly. The receiver 320 has a function of receiving various signals transmitted from the base station (the first base station 10A and / or the second base station 10B) and acquiring, for example, information of a higher layer from the received signal.

[0048] The control unit 330 controls the RIS 30. The plurality of elements 340 have a function of changing the reflection direction of a carrier wave on which a signal from the terminal 20 and / or the base station (the first base station 10A and / or the second base station 10B) is carried. The control unit 330 has a function of controlling the reflection phase (or the reflection direction) of the reflected wave reflected by each of the plurality of elements 340 in response to, for example, an instruction signal from the first base station 10A and / or the second base station 10B. For example, the control unit 330 controls the reflection phase (or the reflection direction) of the reflected wave by controlling the impedance, the element interval, and / or the orientation of the reflection element of each of the plurality of elements 340. Note that the control unit 330 has a function of controlling the reflection phase (or the reflection direction) of the reflected wave reflected by the first portion (the first subset of the plurality of elements 340) among the plurality of elements 340 of the RIS 30 in response to an instruction signal from the first base station 10A. Further, the control unit 330 has a function of controlling the reflection phase (or the reflection direction) of the reflected wave reflected by the second portion (the second subset of the plurality of elements 340) among the plurality of elements 340 in response to an instruction signal from the second base station 10B (which may be the first base station 10A).

[0049] The elements 340 may be configured as a reflect array, for example. FIG. 5 is a diagram showing an example of the elements 340 as a reflect array. When the elements 340 are configured as a reflect array, for example, by changing the element interval between the elements 340, it is possible to change the reflection phase of the reflected wave and change the traveling direction of the reflected wave. The method of changing the reflection phase of the reflected wave is not limited to changing the element interval, and may be performed by changing the impedance of each element 340 among the elements 340. Additionally or alternatively, each element 340 among the elements 340 may include a reflecting element for changing the reflection direction of the incident wave, and the reflection direction of the reflected wave may be changed by changing the orientation of the reflecting element. For example, the reflecting element may include an actuator using Micro Electro Mechanical Systems (MEMS), and the reflection direction of the reflected wave may be controlled by controlling the voltage applied to the piezoelectric material forming the actuator.

[0050] 2 to 4 show functional unit blocks. These functional blocks (components) are realized by any combination of at least one of hardware and software. There are no particular limitations on the method of realizing each functional block. That is, each functional block may be realized by using one device that is physically or logically coupled, or may be realized by using two or more devices that are physically or logically separated and directly or indirectly connected (for example, by using wires, wirelessly, etc.) and these multiple devices.

[0051] For example, the first base station 10A, the second base station 10B, the terminal 20, and the RIS 30 may all function as a computer that performs processing according to this embodiment. FIG. 6 is a diagram showing an example of the hardware configuration of the first base station 10A, the second base station 10B, the terminal 20, and the RIS 30. Any of the first base station 10A, the second base station 10B, the terminal 20, and the RIS 30 may be physically configured as a computer device having a drive device 100, an auxiliary storage device 102, a memory device 103, a CPU 104, an interface device 105, and the like. The drive device 100, the auxiliary storage device 102, the memory device 103, the CPU 104, and the interface device 105, and the like, are each connected to each other by a bus B.

[0052] In the computer device, a program for implementing processing is provided by a recording medium 101 such as a CD-ROM. When the recording medium 101 storing the program is set in the drive device 100, the program is installed from the recording medium 101 to the auxiliary storage device 102 via the drive device 100. However, the program does not necessarily have to be installed from the recording medium 101, but may be downloaded from another computer via a network. The auxiliary storage device 102 stores the installed program as well as necessary files, data, etc.

[0053] When an instruction to start a program is received, the memory device 103 reads out the program from the auxiliary storage device 102 and stores it. The CPU 104 executes functions related to the computer device in accordance with the program stored in the memory device 103. The interface device 105 is used as an interface for connecting to a network.

[0054] FIG. 7 is a diagram showing an example in which a plurality of base stations share the same RIS. In the example of FIG. 7, the communication area formed by the first base station 10A overlaps with the communication area formed by the second base station 10B. In the example of FIG. 7, in a time interval t1 (a first time interval at a first time position), a first portion of the entire plurality of elements 340 of the RIS 30 is used by the first base station 10A. In addition, in a time interval t2 (a second time interval at a second time position), a second portion of the entire plurality of elements 340 of the RIS 30 (for example, the second portion may be a plurality of elements 340 other than the first portion of the entire plurality of elements 340 of the RIS 30) is used by the second base station 10B. Note that the time interval may be constituted by one or more radio frames in the time domain. The radio frame may include a plurality of subframes. The subframe may further be constituted by one or more slots in the time domain. The slot may be constituted by one or more symbols in the time domain. The time interval may be a time interval based on one radio frame, a time interval based on one subframe, a time interval based on one slot, or a time interval based on one symbol.

[0055] 7, in a time interval t1, a first portion of the elements 340 of the RIS 30 is used by the first base station 10A. Specifically, among the terminals 20_1 to 20_4 under the control of the first base station 10A, the terminals 20_1 and 20_2 communicate with the first base station 10A within line of sight.

[0056] On the other hand, the communication between the first base station 10A and the terminal 20_3 is non-line-of-sight communication. Also, the communication between the first base station 10A and the terminal 20_4 is non-line-of-sight communication.

[0057] In this case, for example, a first portion of the elements 340 of the RIS 30 relays communication between the first base station 10A and the terminal 20_3, thereby improving the quality of communication between the first base station 10A and the terminal 20_3. For example, the first base station 10A transmits a carrier wave of a signal to be transmitted to the terminal 20_3 toward the RIS 30 by controlling the directivity of a carrier wave beam. The first portion of the elements 340 of the RIS 30 controls the reflection phase (or reflection direction) of a reflected wave from the elements 340 of the first portion according to setting information transmitted from the first base station 10A, thereby transmitting the reflected wave toward the terminal 20_3, thereby improving the quality of communication between the first base station 10A and the terminal 20_3.

[0058] 7, when the RIS 30 is installed at a fixed position, the first base station 10A can apply a predetermined precoding matrix to multiple antenna ports to direct a carrier beam to the RIS 30. Also, the first base station 10A can apply a specific precoding matrix to multiple antenna ports to direct a carrier beam to a first portion of multiple elements 340 of the RIS 30.

[0059] Also, in the example of FIG. 7, for example, it is assumed that a first portion of the multiple elements 340 of the RIS 30 can select any one of direction 1, direction 2, ..., direction n as the reflection direction of a reflected wave. The first base station 10A instructs the RIS 30 to reflect a predetermined reference signal from the first base station 10A in the corresponding direction 1, direction 2, ..., direction n at time 1, time 2, ..., time n. The terminal 20_3 transmits the reception power value 1, reception power value 2, ..., reception power value n of the reference signal received at time 1, time 2, ..., time n to the first base station 10A as a measurement report. The first base station 10A that receives the measurement report from the terminal 20_3 may compare the reception power value 1, reception power value 2, ..., reception power value n of the reference signal received by the terminal 20_3 at time 1, time 2, ..., time n, and instruct the first portion of the multiple elements 340 of the RIS 30 to the direction corresponding to the maximum reception power value among these reception power values.

[0060] Thus, in the example of Figure 7, the first base station 10A can improve the quality of communication between the first base station 10A and the terminal 20_3 by directing the carrier beam from the first base station 10A toward a first portion of the multiple elements 340 of the RIS 30, and further by setting the reflection direction of the reflected wave from the first portion of the multiple elements 340 of the RIS 30 to a direction in which the received power at the terminal 20_3 is optimized.

[0061] Similarly, in the example of Figure 7, the quality of communication between the first base station 10A and the terminal 20_4 can be improved by relaying the communication between the first base station 10A and the terminal 20_4 by a first portion of the multiple elements 340 of the RIS 30.

[0062] 7, in a time interval t2, a second portion of the elements 340 of the RIS 30 (for example, the second portion may be a plurality of elements 340 other than the first portion of the elements 340 of the RIS 30) is used by the second base station 10B. Specifically, among the terminals 20_5 to 20_6 under the control of the second base station 10B, the terminal 20_5 communicates with the second base station 10B within line of sight.

[0063] In contrast to this, the communication between the second base station 10B and the terminal 20_6 is non-line-of-sight communication.

[0064] In the example of Figure 7, the quality of communication between the second base station 10B and the terminal 20_6 can be improved by relaying the communication between the second base station 10B and the terminal 20_6 by a second portion of the multiple elements 340 of the RIS 30.

[0065] In this manner, multiple base stations 10 may share the RIS 30 in a time-division manner. Also, for example, in the case of an orthogonal frequency-division multiplexing (OFDM) based communication system, multiple base stations 10 may share the RIS 30 based on time and frequency resource scheduling.

[0066] By sharing the RIS 30 based on time division or time and frequency resource scheduling, the terminal 20 can receive services without being interfered with by the RIS 30.

[0067] 7, in time interval t1, a first portion of the plurality of elements 340 of the RIS 30 is used by the first base station 10A, and in time interval t2, a second portion of the plurality of elements 340 of the RIS 30 is used by the second base station 10B. Below, an example of a method for defining time interval t1, a time position where time interval t1 is placed, the plurality of elements 340 of the first portion, time interval t2, a time position where time interval t2 is placed, and the plurality of elements 340 of the second portion in the example of FIG. 7 will be described.

[0068] The first base station 10A and the second base station 10B may determine time interval t1, the time position in which time interval t1 is placed, the multiple elements 340 of the first part, time interval t2, the time position in which time interval t2 is placed, and the multiple elements 340 of the second part based on the total number of terminals 20 using RIS 30, the number of terminals 20 using RIS 30 under the control of the first base station 10A, the number of terminals 20 using RIS 30 under the control of the second base station 10B, and the priority between the first base station 10A and the second base station 10B.

[0069] For example, the first base station 10A may calculate the total number of terminals 20 that should use the RIS 30 among the multiple terminals 20 under the first base station 10A based on the values ​​of reception quality reported from the multiple terminals 20 under the first base station 10A. The reception quality reported from the terminals 20 may be, for example, a Signal to Interference plus Noise Ratio (SINR). The first base station 10A may determine whether or not to use the RIS 30 for the terminal 20 by comparing a predetermined threshold value with the value of the SINR reported from the terminal 20. For example, when the value of the SINR reported from the terminal 20 is less than a predetermined threshold value, the first base station 10A may determine that the RIS 30 should be used for the terminal 20. Note that the reception quality reported from the terminal 20 is not limited to SINR. For example, Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), Received Signal Strength Indicator (RSSI), etc. may be used.

[0070] Similarly, the second base station 10B may calculate the total number of terminals 20 that should use RIS 30 among the multiple terminals 20 under the second base station 10B based on reception quality values ​​reported from the multiple terminals 20 under the second base station 10B.

[0071] For example, the first base station 10A and the second base station 10B may determine the time interval t1 and the time interval t2 by applying a proportional fairness method based on the total number of terminals 20 that should use the RIS 30 obtained as described above and the reported SINR value. For example, instead of the proportional fairness method, a max-min fairness method, a method based on α fairness, or the like may be used. In addition, the time position where the time interval t1 is placed and the time position where the time interval t2 is placed may be determined based on the priority between the first base station 10A and the second base station 10B. For example, when the priority set for the first base station 10A is higher than the priority set for the second base station 10B, in a predetermined time region, the time interval t1 may be placed forward in the time direction, and the time interval t2 may be placed after the time interval t1 in the time direction. Also, in time interval t1 (first time interval at first time position), a first portion of the elements 340 of the RIS 30 may be used by the first base station 10A, and in time interval t2 (second time interval at second time position), a second portion of the elements 340 of the RIS 30 may be used by the second base station 10B. In this case, the ratio R of the elements 340 of the first portion to the total number of the elements 340 of the RIS 30 may be determined based on a first number of terminals 20 that should use the RIS 30 among the terminals 20 under the first base station 10A and a second number of terminals 20 that should use the RIS 30 among the terminals 20 under the second base station 10B. For example, R may be (first number) / (first number+second number).

[0072] A more practical method can be considered as a method for determining the time interval t1, the time position where the time interval t1 is placed, the first part of the elements 340, the time interval t2, the time position where the time interval t2 is placed, and the second part of the elements 340. An example of a practical method will be described below.

[0073] FIG. 8 is a diagram showing an example of allocation of time resources to the first base station 10A and the second base station 10B when sharing the RIS 30 in the example of FIG. 7. In the example of FIG. 7, the first base station 10A is a master base station. The first base station 10A determines a first time interval (and a time position of the first time interval) during which the first base station 10A can access the RIS 30 and a second time interval (and a time position of the second time interval) during which the second base station 10B can access the RIS 30. The second base station 10B is a slave base station, and the second time interval during which the second base station 10B can access the RIS 30 is determined by the first base station 10A.

[0074] In the example of Fig. 7, among a plurality of terminals 20 (terminal 20_1, terminal 20_2, terminal 20_3, terminal 20_4) under the first base station 10A, terminal 20_3 and terminal 20_4 are terminals 20 that should use RIS 30. Also, among a plurality of terminals (terminal 20_5, terminal 20_6) under the second base station 10B, terminal 20_6 is terminal 20 that should use RIS 30. For convenience of explanation, terminals 20_1, 20_2, 20_3, 20_4, 20_5, and 20_6 are also referred to as U1, U2, U3, U4, U5, and U6, respectively.

[0075] The first base station 10A determines that the total number of terminals 20 that should use RIS30 among the multiple terminals 20 under the first base station 10A is 2 because U3 and U4 are terminals 20 that should use RIS30. The second base station 10B determines that the total number of terminals 20 that should use RIS30 among the multiple terminals 20 under the second base station 10B is 1 because U6 is terminal 20 that should use RIS30. The second base station 10B notifies the first base station 10A of information indicating that the total number of terminals 20 that should use RIS30 among the multiple terminals 20 under the second base station 10B is 1.

[0076] The first base station 10A determines that the total number of terminals 20 that should use the RIS 30 is 3. Based on the total number of terminals 20 that should use the RIS 30 and the priorities of the first base station 10A and the second base station 10B, the first base station 10A determines the time interval (and time position) in which the first base station 10A uses the RIS 30 and the time interval (and time position) in which the second base station 10B uses the RIS 30 in the predetermined time interval shown in FIG. 8. Specifically, the first base station 10A determines the time interval (and time position) in which the RIS 30 is used for U3 and U4 as shown in FIG. 8. Thereafter, the first base station 10A notifies the second base station 10B of information indicating the time interval t2 in which the second base station 10B can use the RIS 30 and the time position of the time interval t2. The second base station 10B determines the time interval in which the RIS 30 is used for U6 as shown in FIG. 8. In addition, in time interval t1 (first time interval at first time position), a first portion of the elements 340 of the RIS 30 is used by the first base station 10A, and in time interval t2 (second time interval at second time position), a second portion of the elements 340 of the RIS 30 is used by the second base station 10B. Here, the first base station 10A calculates the ratio R of the elements 340 of the first portion to the entire elements 340 of the RIS 30 as R=2 / 3 based on the first number (=2) of terminals 20 that should use the RIS 30 among the terminals 20 under the first base station 10A and the second number (=1) of terminals 20 that should use the RIS 30 among the terminals 20 under the second base station 10B. For example, the first base station 10A may assign serial numbers to all of the elements 340 of the RIS 30, and determine 2 / 3 of all of the elements 340 of the RIS 30 as the first part and the remaining part as the second part in ascending order of the serial numbers. Note that the method of determining the first part is not limited to ascending order of the serial numbers. For example, the method of determining the first part may be descending order of the serial numbers, or may be based on a method of dividing the elements 340 of the RIS 30 into a plurality of subsets in advance and assigning serial numbers to the subsets.

[0077] As shown in Fig. 8, the first base station 10A may perform scheduling for U1 and U2 in a time interval in which the first base station 10A does not use the RIS 30. The second base station 10B may perform scheduling for U5 in a time interval in which the second base station 10B does not use the RIS 30. In the example of Fig. 8, the first base station 10A may notify the RIS 30 in advance of setting information on reflection phase and amplitude for optimizing communication between the first base station 10A and U3 via a first part of the elements 340 of the RIS 30, setting information on reflection phase and amplitude for optimizing communication between the first base station 10A and U4 via the first part of the elements 340 of the RIS 30, and setting information on reflection phase and amplitude for optimizing communication between the second base station 10B and U6 via a second part of the elements 340 of the RIS 30. In addition, the RIS 30 may apply a reflection phase and amplitude setting for optimizing the communication between the first base station 10A and U3 via the first part of the elements 340 of the RIS 30 during communication between the first base station 10A and U3 shown in the example of FIG. 8 according to the scheduling information notified from the first base station 10A. Also, during communication between the first base station 10A and U4 shown in the example of FIG. 8, the RIS 30 may apply a reflection phase and amplitude setting for optimizing the communication between the first base station 10A and U4 via the first part of the elements 340 of the RIS 30. Also, during communication between the second base station 10B and U6 shown in the example of FIG. 8, the RIS 30 may apply a reflection phase and amplitude setting for optimizing the communication between the second base station 10B and U6 via the second part of the elements 340 of the RIS 30.

[0078] The example of FIG. 8 may be generalized as follows. Let r denote the RIS 30, j denote the base station 10, and u denote the terminal 20 that should use the RIS 30. Let B_{u, j}^r be the time interval of communication via the RIS 30(r) that is assigned by the base station 10(j) to the terminal 20(u). Here, if r is not zero, the communication between the base station 10(j) and the terminal 20(u) is relayed by the RIS 30(r). If r is zero, the communication between the base station 10(j) and the terminal 20(u) is not relayed by the RIS 30(r). Let N be the total number of the elements 340 of the RIS 30. Let η_{j}^{r} be the ratio of the number of elements 340 that can be assigned to the base station 10(j) by the RIS 30(r) to the total number of elements 340 of the RIS 30(r). Thus, N×η_{j}^{r} is the number of elements 340 available for allocation by RIS 30(r) to base station 10(j).

[0079] FIG. 9 is a flowchart illustrating an example of a processing procedure executed in the wireless communication system.

[0080] As a premise of the processing procedure of FIG. 9, the multiple terminals 20 are classified into normal terminals 20 and terminals 20 that should use the RIS 30. The classification may be performed by comparing the SINR value reported from each terminal 20 with a predetermined threshold. The first base station 10A is a master base station and determines resources (a first time interval, a first time position of the first time interval, and a first portion of the multiple elements 340 of the RIS 30) for the first base station 10A to use the RIS 30 and resources (a second time interval, a second time position of the second time interval, and a second portion of the multiple elements 340 of the RIS 30) for the second base station 10B to use the RIS 30. The second base station 10B is a slave base station and uses the second portion of the multiple elements 340 of the RIS 30 in the resources (the second time interval placed at the second time position) determined by the first base station 10A. Let u1 be a terminal 20 under the first base station 10A that should use the RIS 30. Let u2 be the terminal 20 under the second base station 10B that should use the RIS 30.

[0081] In the example of FIG. 9, in step S110, the first base station 10A receives information indicating the second number of terminals 20 that should use the RIS 30, among the terminals 20 under the control of the second base station 10B, from the second base station 10B.

[0082] In step S120, the first base station 10A performs scheduling for the terminals 20 that should use the RIS 30 among the terminals 20 under the first base station 10A and the terminals 20 that should use the RIS 30 among the terminals 20 under the second base station 10B, based on a first number of the terminals 20 that should use the RIS 30 among the terminals 20 under the first base station 10A and a second number of the terminals 20 that should use the RIS 30 among the terminals 20 under the second base station 10B. As a result of the scheduling, a first time interval during which the first base station 10A can access the RIS 30 and a second time interval during which the second base station 10B can access the RIS 30 are determined.

[0083] In step S130, the first base station 10A determines a first time position where the first time interval is placed and a second time position where the second time interval is placed, based on the priority between the first base station 10A and the second base station 10B. For example, when the priority set for the first base station 10A is higher than the priority set for the second base station 10B, the first time interval may be placed forward in the time direction and the second time interval may be placed backward in the time direction relative to the first time interval in a predetermined time region.

[0084] In step S140, the first base station 10A determines, based on a ratio between a first number of terminals 20 that should use RIS 30 among the terminals 20 under the first base station 10A and a second number of terminals 20 that should use RIS 30 among the terminals 20 under the second base station 10B, among the multiple elements 340 of RIS 30, a first portion of multiple elements 340 to be used by the first base station 10A and a second portion of multiple elements 340 to be used by the second base station 10B. For example, the first base station 10A may calculate the proportion R (which may be η_{10A}^{r}) of the multiple elements 340 of the first portion to the entire multiple elements 340 of the RIS 30 as R = (first number) / (first number + second number) based on a first number of terminals 20 that should use RIS 30 among the multiple terminals 20 under the first base station 10A and a second number of terminals 20 that should use RIS 30 among the multiple terminals 20 under the second base station 10B.

[0085] In step S140, the first base station 10A determines the first part of the elements 340 used by the first base station 10A and the second part of the elements 340 used by the second base station 10B based on the ratio between the first number of terminals 20 that should use the RIS 30 under the control of the first base station 10A and the second number of terminals 20 that should use the RIS 30 under the control of the second base station 10B, but the embodiment of the present invention is not limited to this example. For example, the first base station 10A may equally allocate the elements 340 of the RIS 30 based on the number of base stations 10 that share the RIS 30. For example, as shown in FIG. 7, when the first base station 10A and the second base station 10B share the RIS 30, half of the elements 340 of the RIS 30 may be allocated to the first base station 10A, and the remaining half of the elements 340 of the RIS 30 may be allocated to the second base station 10B.

[0086] In step S150, the first base station 10A transmits to the second base station 10B information indicating the second time interval, the second time position at which the second time interval is located (and / or scheduling information for terminals 20 under the control of the second base station 10B that should use the RIS 30), and information indicating the multiple elements 340 of the second part of the RIS 30 that the second base station 10B uses, among the multiple elements 340 of the RIS 30.

[0087] In step S160, the first base station 10A notifies the RIS 30 of the number of terminals 20 that should use the RIS 30 under the first base station 10A, and scheduling information for those terminals 20 (which may be information indicating the time slots that those terminals 20 should use).

[0088] In step S170, the second base station 10B notifies the RIS 30 of the number of terminals 20 that should use the RIS 30 under the second base station 10B, and scheduling information for those terminals 20 (which may be information indicating the time slots that those terminals 20 should use).

[0089] In step S180, the first base station 10A notifies the RIS 30 of reflection phase and amplitude setting information for optimizing communication between the first base station 10A and each terminal 20 under the first base station 10A via a first portion of the multiple elements 340 of the RIS 30.

[0090] In step S190, the second base station 10B notifies the RIS 30 of reflection phase and amplitude setting information for optimizing communication between the second base station 10B and each terminal 20 under the second base station 10B via a second portion of the multiple elements 340 of the RIS 30.

[0091] In step S200, the first base station 10A communicates with each terminal 20 under the first base station 10A (each terminal 20 that should use the RIS 30) via a first portion of the multiple elements 340 of the RIS 30 in accordance with the scheduling information.

[0092] In step S210, the second base station 10B communicates with each terminal 20 under the second base station 10B (each terminal 20 that should use the RIS 30) via a second portion of the multiple elements 340 of the RIS 30 in accordance with the scheduling information.

[0093] As described above, in the embodiment of the present invention, a technique for allocating a resource, that is, the utilization time of a Reconfigurable Intelligent Surface (RIS), in a wireless communication technique using a RIS is described.

[0094] In the embodiment of the present invention, a system consisting of multiple cells and multiple base stations, such as cellular communication, is assumed. It is also assumed that multiple wireless base stations share the same RIS and perform beamforming for user terminals in their own cells.

[0095] In such a system, it is conceivable that contention in the use of the RIS may occur. In the conventional method, for all RIS in the system, the weight matrices (corresponding to all terminals communicating) corresponding to the beams formed by the RIS must be exchanged between base stations for coordination. This method has the problem that the processing is complicated and it is not possible to completely avoid interference between reflectors.

[0096] Therefore, in the embodiment of the present invention, the RIS is divided into multiple fractions, and only information about terminals using the RIS is shared between the wireless base stations, and the wireless base stations calculate the fraction of the RIS that each wireless base station uses based on the shared information, thereby reducing the amount of control information to be transmitted and received.In addition, it is possible to completely avoid interference without causing contention for the use of the RIS. [Explanation of symbols]

[0097] 10A First base station 10B Second base station 20 Terminals 30 RIS 40 Network 110 Transmitter 120 Receiving unit 130 Control section 210 Transmitter 220 Receiving unit 230 Control Unit 310 Transmitter 320 Receiving unit 330 Control Unit 340 Elements 100 Drive device 101 Recording media 102 Auxiliary storage device 103 Memory device 104 CPU 105 Interface device B Bus

Claims

1. A wireless communication system including a first base station, a second base station, a relay device including a plurality of reflecting elements, and a plurality of terminals, wherein a first communication area formed by the first base station overlaps with a second communication area formed by the second base station, The first base station a first receiving unit that receives, from the second base station, information indicating a second number of terminals that should communicate via the relay device, among one or more terminals under the second base station; a first control unit that calculates a total number of terminals that should communicate via the relay device as the sum of the second number indicated by the received information and a first number of terminals that should communicate via the relay device among one or more terminals under the first base station, and schedules a first communication between each terminal that should communicate via the relay device under the first base station and the first base station and a second communication between each terminal that should communicate via the relay device under the second base station and the second base station based on the total number and priorities set for the first base station and the second base station, and determines a first portion of a plurality of reflecting elements to be used for the first communication and a second portion of a plurality of reflecting elements to be used for the second communication among a plurality of reflecting elements included in the relay device; a first transmitter configured to transmit scheduling information for the second communication and information indicative of a plurality of reflecting elements of the second portion to the second base station; Equipped with The second base station a second transmission unit that transmits, to the first base station, information indicating the number of terminals that should communicate via the relay device among one or more terminals under the second base station; a second receiver configured to receive from the first base station scheduling information for the second communication and information indicative of a plurality of reflecting elements in the second portion; a second control unit that schedules the second communication using the plurality of reflecting elements in the second portion based on scheduling information of the second communication and information indicating the plurality of reflecting elements in the second portion; Equipped with Wireless communication system.

2. The wireless communication system according to claim 1 , wherein the relay device is a Reconfigurable Intelligent Surface (RIS) that includes the plurality of reflecting elements and is capable of changing a traveling direction of a reflected wave.

3. the first control unit determines, based on a ratio between the first number and the second number, a plurality of reflecting elements in the first portion to be used for the first communication and a plurality of reflecting elements in the second portion to be used for the second communication, among a plurality of reflecting elements included in the relay device; 2. The wireless communication system according to claim 1.

4. the first control unit determines half of the plurality of reflecting elements included in the relay device as the plurality of reflecting elements of the first portion to be used for the first communication, and determines the remaining half of the plurality of reflecting elements included in the relay device as the plurality of reflecting elements of the second portion to be used for the second communication.

2. The wireless communication system according to claim 1.

5. A first base station in a wireless communication system including a first base station, a second base station, a relay device, and a plurality of terminals, wherein a first communication area formed by the first base station overlaps with a second communication area formed by the second base station, and the first base station: a receiving unit that receives, from the second base station, information indicating a second number of terminals that should communicate via the relay device, among one or more terminals under the second base station; a control unit that calculates a total number of terminals that should communicate via the relay device as the sum of the second number indicated by the received information and a first number of terminals that should communicate via the relay device among one or more terminals under the first base station, and schedules a first communication between each terminal that should communicate via the relay device under the first base station and the first base station and a second communication between each terminal that should communicate via the relay device under the second base station and the second base station based on the total number and priorities set for the first base station and the second base station, and determines a first portion of multiple reflecting elements to be used for the first communication and a second portion of multiple reflecting elements to be used for the second communication among a plurality of reflecting elements included in the relay device; a transmitter configured to transmit scheduling information for the second communication and information indicative of a plurality of reflecting elements of the second portion to the second base station; A base station comprising:

6. A communication method executed by a first base station in a wireless communication system including a first base station, a second base station, a relay device, and a plurality of terminals, wherein a first communication area formed by the first base station overlaps with a second communication area formed by the second base station, and the communication method includes: receiving, from the second base station, information indicating a second number of terminals that should communicate via the relay device, among one or more terminals under the second base station; calculating a total number of terminals to communicate via the relay device as a sum of the second number indicated by the received information and a first number of terminals to communicate via the relay device among one or more terminals under the first base station, and scheduling a first communication between each terminal under the first base station to communicate via the relay device and the first base station and a second communication between each terminal under the second base station to communicate via the relay device and the second base station based on the total number and priorities set for the first base station and the second base station, and determining a first portion of a plurality of reflecting elements to be used for the first communication and a second portion of a plurality of reflecting elements to be used for the second communication among a plurality of reflecting elements included in the relay device; transmitting scheduling information for the second communication and information indicative of a plurality of reflective elements in the second portion to the second base station; A communication method comprising:

7. A non-transitory computer-readable storage medium storing a program, the program being a wireless communication system including a first base station, a second base station, a relay device, and a plurality of terminals, the program being configured to, when executed by a first base station in the wireless communication system, cause the first base station to: receiving, from the second base station, information indicating a second number of terminals that should communicate via the relay device, among one or more terminals under the second base station; calculating a total number of terminals to communicate via the relay device as a sum of the second number indicated by the received information and a first number of terminals to communicate via the relay device among one or more terminals under the first base station, and scheduling a first communication between each terminal under the first base station to communicate via the relay device and the first base station and a second communication between each terminal under the second base station to communicate via the relay device and the second base station based on the total number and priorities set for the first base station and the second base station, and determining a first portion of a plurality of reflecting elements to be used for the first communication and a second portion of a plurality of reflecting elements to be used for the second communication among a plurality of reflecting elements included in the relay device; transmitting scheduling information for the second communication and information indicative of a plurality of reflective elements in the second portion to the second base station; A non-transitory computer-readable storage medium for causing the computer to execute

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