WO2024024075A1

WO2024024075A1 - Radio communication system, relay device, communication method, and non-transitory computer readable storage medium

Info

Publication number: WO2024024075A1
Application number: PCT/JP2022/029259
Authority: WO
Inventors: Yoghitha RAMAMOORTHI; Riku OMIYA; Masashi Iwabuchi; Tomoaki Ogawa; Yasushi Takatori
Original assignee: Nippon Telegraph And Telephone Corporation
Priority date: 2022-07-29
Filing date: 2022-07-29
Publication date: 2024-02-01

Abstract

A relay device of a radio communication system includes a controller that determines a first number of terminals to communicate via the relay device under control of a first base station and a second number of terminals to communicate via the relay device under control of a second base station, and that determines a first portion of a plurality of reflection elements to be used by the first base station and a second portion of the plurality of reflection elements to be used by the second base station, based on a ratio of the first number to the second number; and a transmitter that transmits information indicating the first portion to the first base station, and that transmits information indicating the second portion to the second base station.

Description

RADIO COMMUNICATION SYSTEM, RELAY DEVICE, COMMUNICATION METHOD, AND NON-TRANSITORY COMPUTER READABLE STORAGE MEDIUM

The present invention relates to a relay device, a communication method, and a non-transitory computer readable storage medium in a radio communication system.

A Reconfigurable Intelligent Surface (RIS) has been considered as an effective way to control a channel by properly tuning a phase and amplitude of an electromagnetic signal. Recent studies and experiments have proposed various architectures and multiple access techniques.

The use of RIS for cell coverage extension is under consideration. When a direct wave from a base station is blocked, a reception level of a radio signal at a user terminal located at an edge of a cell is lower than a reception level of a radio signal in a case of line-of-sight communication.

In such a case, the combination of the beam-formed transmission waves transmitted from the base station and the reflected waves from the RIS can increase the reception level of the user terminal located at a location where the direct waves from the base station are blocked by a building or the like.

[NPL 1] M. Hua, Q. Wu, D. W. K. 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.
[NPL 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.

In a system including multiple cells and multiple base stations, such as a system for cellular communications, it is assumed that multiple radio base stations share the same RIS (reflector) to perform beam forming for the user terminals under control of their own cells.

In such a system, contention for the same RIS may occur.

The present invention has been achieved in view of the above-described point, and an object is to provide a method of solving the contention for the same RIS while reducing an overhead of control information.

According to an aspect of the present invention, there is provided a radio communication system including
a first base station;
a second base station;
a relay device including a plurality of reflection elements; and
a plurality of terminals,
　　wherein a first communication area formed by the first base station overlaps a second communication area formed by the second base station,
wherein the relay device includes
a receiver that receives, from the first base station, values of received quality reported from a plurality of terminals under control of the first base station, and that receives, from the second base station, values of received quality reported from a plurality of terminals under control of the second base station;

a controller that determines a first number of one of more terminals to communicate via the relay device under control of the first base station and a second number of one or more terminals to communicate via the relay device under control of the second base station based on the values of received quality, and that determines a first portion of the plurality of reflection elements to be used by the first base station and a second portion of the plurality of reflection elements to be used by the second base station, from among the plurality of reflection elements included in the relay device, based on a ratio of the first number to the second number; and

a transmitter that transmits, to the first base station, information indicating the first portion of the plurality of reflection elements of the relay device, and that transmits, to the second base station, information indicating the second portion of the plurality of reflection elements of the relay device.

According to an embodiment, a method is provided that solves contention for the same RIS while reducing an overhead of control information.

Figure 1 is a diagram illustrating an example of a configuration of a radio communication system. Figure 2 is a diagram illustrating an example of a functional configuration of a base station. Figure 3 is a diagram illustrating an example of a functional configuration of a terminal. Figure 4 is a diagram illustrating an example of a functional configuration of a Reconfigurable Intelligent Surface (RIS). Figure 5 is a diagram illustrating an example of a plurality of elements included in the RIS. Figure 6 is a diagram illustrating an example of a hardware configuration of each of the base station, the terminal, and the RIS. Figure 7 is a diagram illustrating an example of a case where multiple base stations share the same RIS. Figure 8 is a diagram illustrating an example of a resource allocation when the RIS is shared. Figure 9 is a flowchart illustrating an example of a procedure in the radio communication system. Figure 10 is a flowchart illustrating an example of a procedure executed by the terminal in the radio communication system.

A Reconfigurable Intelligent Surface (RIS) has been considered as a way of effectively controlling a propagation channel of radio waves by appropriately controlling a phase and amplitude of the radio waves. Recent studies and experiments have found various architectures and multiple access techniques.

As an application of the RIS, a method in which multiple base stations share a single RIS is considered effective for the efficiency of communication. Since the RIS is implemented primarily to enhance coverage of a blocked region, it is important to ensure that multiple base stations can share a single RIS. One possible approach would be to place an RIS on a per base station basis. However, in this method, interference and cost increase.

The applications of RIS are evolving with existing technologies. Optimization of the transmission beam forming and the phase shift of each RIS based on the assignment of the transmit power by the base station has been studied. Furthermore, for RIS-based beam forming, negotiation between base stations has been proposed in order to reach consensus between the base stations without revealing the information of terminals under control of the base station. Namely, it is assumed that the different base stations that have accessed the RIS make similar reflective responses for the terminal after reaching the consensus between the base stations on the RIS-based beam forming.

In the following, the embodiments of the present invention are described with reference to the drawings. Fig. 1 is a diagram illustrating an example of a configuration of a radio communication system according to an embodiment. As illustrated in Fig. 1, the radio 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 radio. The first base station 10A and the second base station 10B are connected, for example, via an X2 interface, so that the first base station 10A and the second base station 10B can communicate with each other. The first base station 10A and the RIS 30 are connected by wire or radio, so that the first base station 10A and the RIS 30 can communicate with each other. The second base station 10B and the RIS 30 are connected by wire or radio, so that the second base station 10B and the RIS 30 can communicate with each other. The RIS 30 may also be connected to the network 40 by wire or radio. The first base station 10A, the second base station 10B, and the terminal 20 are capable of transmitting and receiving signals by applying beam forming.

Note that multiple antenna ports are installed in the first base station 10A, so that the first base station 10A can form a beam in the vertical direction in addition to the horizontal direction. The first base station 10A can adjust a phase rotation (and/or amplitude) on a per antenna port basis by applying weight of a precoding vector to data supplied to the antenna port, so that a beam transmitted from the multiple antenna port can have directivity.

Similarly, multiple antenna ports are installed in the second base station 10B, so that the second base station 10B can form a beam in the vertical direction in addition to the horizontal direction. The second base station 10B can adjust a phase rotation (and/or amplitude) on a per antenna port basis by applying weight of a precoding vector to data supplied to the antenna port, so that a beam transmitted from the multiple antenna port can have directivity. Here, the terminal 20 may also include multiple antenna ports, so that the terminal can form a beam in the vertical direction in addition to the horizontal direction.

The first base station 10A is a base station that forms a communication area in an outdoor area or the like. The first base station 10A provides high-speed radio communication with the terminal 20, for example, by transmitting and receiving radio waves in a frequency band used in the fifth generation mobile communication system (5G). The second base station 10B is a base station that forms a communication area overlapping with a communication area formed by the first base station 10A. Here, when two communication areas overlap each other, the communication areas may overlap almost completely, one of the communication areas may be included in the other communication area, or a portion of the two communication areas may overlap each other. The second base station 10B provides high-speed radio communication with the terminal 20, for example, by transmitting and receiving radio waves in the frequency band used in the 5G. The terminal 20 is, for example, a communication device, such as a smartphone, a tablet terminal, or a Personal Computer (PC).

The first base station 10A can communicate with the terminal 20 directly or through the RIS 30 as the relay device. The second base station 10B can communicate with the terminal 20 directly or through the RIS 30 as the relay device.

The RIS 30 is connected to the first base station 10A by wire or radio. 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 on which the signal from the terminal 20 is carried in accordance with configuration information from the first base station 10A. Furthermore, the RIS 30 can relay a signal from the first base station 10A to the terminal 20 by changing the reflection direction of a carrier wave on which the signal from the first base station 10A is carried in accordance with configuration information from the first base station 10A.

The RIS 30 is connected to the second base station 10B by wire or radio. The RIS 30 can relay a signal from the terminal 20 to the second base station 10B by changing the reflection direction of a carrier wave on which the signal from the terminal 20 is carried in accordance with configuration information from the second base station 10B. Furthermore, the RIS 30 can relay a signal from the second base station 10B to the terminal 20 by changing the reflection direction of a carrier wave on which the signal from the second base station 10B is carried in accordance with configuration information from the second base station 10B.

When the RIS 30 is connected to the network 40 by wired or wireless communication, the RIS 30 may relay a 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 in accordance with configuration information from the network 40. The RIS 30 may relay a 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 in accordance with configuration information from the network 40. The RIS 30 may relay a 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 in accordance with configuration information from the network 40.

In the example of Fig. 1, only one terminal 20 is illustrated. However, the number of the terminals 20 is not limited to that of the example of Fig. 1, and may include more than one terminal 20. Furthermore, in the example of Fig. 1, the first base station 10A and the second base station 10B are illustrated. However, the number of the base stations 10 is not limited to that of the example in Fig. 1, and more than two base stations 10 may be included. Furthermore, in the example of Fig. 1, only one RIS 30 is illustrated. However, the number of the RISs 30 is not limited to that of the example of Fig. 1, and more than one RIS 30 may be included.

Fig. 2 is a diagram illustrating an example of a functional configuration of each of the first base station 10A and the second base station 10B. As illustrated in Fig. 2, each of the first base station 10A and the second base station 10B includes a transmitter 110; a receiver 120; and a controller 130. The functional configuration illustrated in Fig. 2 is only an example. The functional division and the names of the functional units may be any division and any names, provided that an operation according to the embodiments can be executed.

The transmitter 110 creates a transmission signal from transmission data and wirelessly transmits the transmission signal. The receiver 120 receives various signals wirelessly and obtains higher layer signals from the received physical layer signals. The receiver 120 includes a measuring unit that measures a received signal and obtains received power.

The controller 130 controls the base station (the first base station 10A or the second base station 10B). The function of the controller 130 related to transmission may be included in the transmitter 110, and the function of the controller 130 related to reception may be included in the receiver 120.

Fig. 3 is a diagram illustrating an example of a functional configuration of the terminal 20. As illustrated in Fig. 3, the terminal 20 includes a transmitter 210, a receiver 220, and a controller 230. The functional configuration illustrated in Fig. 3 is only an example. The functional division and the names of the functional units may be any division and any names, provided that an operation according to the embodiments can be executed.

The transmitter 210 includes a function for creating a signal to be transmitted to a base station (the first base station 10A and/or the second base station 10B) and transmitting the signal wirelessly. The receiver 220 includes a function for receiving various signals transmitted from a base station (the first base station 10A and/or the second base station 10B) and obtaining, for example, information of a higher layer from the received signals. The receiver 220 includes a measuring unit that measures a received signal and obtains received power.

The controller 230 controls the terminal 20. The function of the controller 230 related to transmission may be included in the transmitter 210, and the function of the controller 230 related to reception may be included in the receiver 220.

Fig. 4 is a diagram illustrating an example of a functional configuration of the RIS 30. As illustrated in Fig. 4, the RIS 30 includes a transmitter 310, a receiver 320, a controller 330, and a plurality of elements 340. The functional configuration illustrated in Fig. 4 is only an example. The functional division and the names of the functional units may be any division and any names, provided that an operation according to the embodiments can be executed.

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

The controller 330 controls the RIS 30. The plurality of elements 340 includes a function for changing a reflection direction of a carrier wave by 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 controller 330 has a function to control a reflection phase (or a reflection direction) of a wave reflected by each element 340 of the plurality of elements 340 in response to an indication signal from the first base station 10A and/or the second base station 10B. For example, the controller 330 controls a reflection phase (or a reflection direction) of a reflected wave by controlling impedance, spacing, and/or an orientation of each element 340 of the plurality of elements 340. Note that the controller 330 has a function to control a reflection phase (or a reflection direction) of a wave reflected by a first portion of the plurality of elements 340 of the RIS 30 (which includes a first subset of the plurality of elements 340), in response to an indication signal from the first base station 10A. Furthermore, the controller 330 has a function to control a reflection phase (or a reflection direction) of a wave reflected by a second portion of the plurality of elements 340 of the RIS 30 (which includes a second subset of the plurality of elements 340), in response to an indication signal from the second base station 10B (which may be the first base station 10A).

The plurality of elements 340 may be configured, for example, as a reflect array. Fig. 5 is a diagram illustrating an example of the plurality of elements 340 as a reflect array. When the plurality of elements 340 are configured as a reflect array, for example, a travelling direction of a reflected wave can be changed by changing a reflection phase of the reflected wave by changing element spacing of the plurality of elements 340. Note that the method of changing the reflection phase of the reflected wave is not limited to changing the element spacing, and the reflection phase of the reflected wave can be changed by changing the impedance of each element 340 of the plurality of elements 340. Additionally or alternatively, a reflection direction of a reflected wave may be changed by including, in each element 340 of the plurality of elements 340, a reflection element for changing the reflection direction of an incident wave, and by changing an orientation of the reflection element. For example, the reflection element may include an actuator utilizing Micro Electro Mechanical Systems (MEMS), and a reflection direction of a reflected wave may be controlled by controlling a voltage applied to a piezoelectric material forming the actuator.

Figs. 2-4 illustrate blocks of functional units. These functional blocks (components) are implemented by any combination of hardware and/or software. The implementation method of each functional block is not particularly limited. That is, each functional block may be implemented by using a single device that is physically or logically combined, these devices may be implemented by directly or indirectly connecting (e.g., by using wire or radio) two or more devices that are physically or logically separated.

For example, each of the first base station 10A, the second base station 10B, the terminal 20, and the RIS 30 may function as a computer for executing a process according to the embodiments. Fig. 6 is a diagram illustrating an example of the hardware configuration of each of the first base station 10A, the second base station 10B, the terminal 20, and the RIS 30. Each device 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, the interface device 105, and the like are mutually connected by a bus B.

In a computer device, a program for implementing processing is provided by a recording medium 101, such as a compact disc read-only memory (CD-ROM). When the recording medium 101 storing a program is set in the drive device 100, the program is installed in the auxiliary storage device 102 from the recording medium 101 through the drive device 100. However, the installation of the program need not be performed by using the recording medium 101, and the program may be downloaded from another computer via a network. The auxiliary storage device 102 stores the installed program and stores necessary files, data, and the like.

The memory device 103 reads out a program from the auxiliary storage device 102 and stores the program when an instruction to start a program is issued. The CPU 104 executes the function of the computer device according to the program stored in the memory device 103. The interface device 105 is used as an interface for connecting to a network.

Fig. 7 is a diagram illustrating an example in which multiple base stations share the same RIS. In the example of Fig. 7, the communication area formed by the first base station 10A overlaps the communication area formed by the second base station 10B. In the example of Figure 7, at time interval t1 (which may be a first time interval at a first time position), the first portion of the plurality of elements 340 of the RIS 30 is used by the first base station 10A. Furthermore, at time interval t2 (which may be a second time interval at a second time position), the second portion of the 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 plurality of elements 340 of the RIS 30) is used by the second base station 10B. Note that a time interval may be formed of one or more radio frames in a time domain. A radio frame may include multiple subframes. In the time domain, a subframe may be formed of one or more slots. In the time domain, a slot may be formed of one or more symbols. A time interval may be a time interval in units of one radio frame, a time interval in units of one subframe, a time interval in units of one slot, or a time interval in units of one symbol.

In the example of Fig. 7, at time interval t1, the first portion of the plurality of elements 340 of the RIS 30 is used by the first base station 10A. Specifically, from among terminals 20_1 through 20_4 under control of the first base station 10A, the terminal 20_1 and the terminal 20_2 are performing line-of-sight communication with the first base station 10A.

In contrast, the communication between the first base station 10A and the terminal 20_3 is non-line-of-sight communication. Furthermore, the communication between the first base station 10A and the terminal 20_4 is non-line-of-sight communication.

In this case, the quality of communication between the first base station 10A and the terminal 20_3 can be enhanced, for example, by relaying the communication between the first base station 10A and the terminal 20_3 by using the first portion of the plurality of elements 340 of the RIS 30. For example, the first base station 10A transmits carrier waves of a signal to be transmitted to the terminal 20_3 toward the RIS 30 by controlling directivity of a beam of the carrier waves. The first portion of the plurality of elements of the RIS 30 controls a reflection phase (or a reflection direction) of reflected waves from the first portion of the plurality of elements 340 in accordance with configuration information transmitted from the first base station 10A, so that the reflected waves are transmitted toward the terminal 20_3. In this manner, the first portion of the plurality of elements 340 of the RIS 30 can enhance the quality of communication between the first base station 10A and the terminal 20_3.

When the RIS 30 is installed in a fixed position, as in the example of Fig. 7, the first base station 10A can direct the beam of the carrier waves toward the RIS 30 by applying a predetermined precoding matrix to the plurality of antenna ports. Furthermore, the first base station 10A can direct the beam of the carrier waves toward the first portion of the plurality of elements 340 of the RIS 30 by applying a specific precoding matrix to the plurality of antenna ports.

In the example of Fig. 7, for example, suppose that the first portion of the plurality of elements 340 of the RIS 30 can select one of a direction 1, a direction 2, ..., and a direction n, as the reflection direction. The first base station 10A instructs the RIS 30 to reflect a predetermined reference signal from the first base station 10A in the direction 1, the direction 2, ..., and the direction n, at timing 1, timing 2, ... , and timing n, respectively. The terminal 20_3 transmits, to the first base station 10A, a received power value 1, a received power value 2, ... , and a received power value n of the reference signal received at the timing 1, the timing 2, ... , and the timing n, respectively, as a measurement report. The first base station 10A that receives the measurement report from the terminal 20_3 compares the received power value 1, the received power value 2, ... , and the received power value n of the reference signal received by the terminal 20_3 at the timing 1, the timing 2, ... , and the timing n, respectively, and the first base station 10A may indicate, to the first portion of the plurality of elements 340 of the RIS 30, a direction corresponding to the maximum received power value from among these received power values.

As described above, in the example of Fig. 7, the first base station 10A can enhance the quality of the communication between the first base station 10A and the terminal 20_3 by directing the beam of the carrier waves from the first base station 10A toward the first portion of the plurality of elements 340 of the RIS 30, and setting the reflection direction of the reflected waves from the first portion of the plurality of elements 340 of the RIS 30 to the direction in which the received power at the terminal 20_3 is optimized.

Similarly, in the example of Fig. 7, quality of communication between the first base station 10A and the terminal 20_4 can be enhanced by relaying the communication between the first base station 10A and the terminal 20_4 by using the first portion of the plurality of elements 340 of the RIS 30.

In the example of Fig. 7, at the time interval t2, the second portion of the plurality of elements 340 of the RIS 30 (for example, the second portion may be a plurality of elements 340 other then the first portion from among the plurality of elements 340 of the RIS 30) is used by the second base station 10B. Specifically, of the terminals 20_5 and 20_6 under control of the second base station 10B, the terminal 20_5 performs line-of-sight communication with the second base station 10B.

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

In the example of Fig. 7, quality of the communication between the second base station 10B and the terminal 20_6 can be enhanced by relaying the communication between the second base station 10B and the terminal 20_6 by using the second portion of the plurality of elements 340 of the RIS 30.

As described above, the multiple base stations 10 may share the RIS 30 based on time division. Furthermore, for example, in a case of an orthogonal frequency-division multiplexing (OFDM) based communication system, the multiple base stations 10 may share the RIS 30 based on scheduling of time and frequency resources.

By sharing the RIS 30 based on time division or scheduling of time and frequency resources, the terminal 20 can be provided with services without interference from the RIS 30.

In the example of Fig. 7, at the time interval t1, the first portion of the plurality of elements 340 of the RIS 30 is used by the first base station 10A, and at the time interval t2, the second portion of the plurality of elements 340 of the RIS 30 is used by the second base station 10B. In the following, an example of a method of determining the time interval t1, a time position at which the time interval t1 is allocated, the first portion of the plurality of elements 340, the time interval t2, a time position at which the time interval t2 is allocated, and the second portion of the plurality of elements 340 in the example of Fig. 7 is described.

The first base station 10A and the second base station 10B may determine the time interval t1, the time position at which the time interval t1 is allocated, the first portion of the plurality of elements 340, the time interval t2, the time position at which the time interval t2 is allocated, and the second portion of the plurality of elements 340, based on the total number of the terminals 20 that should use the RIS 30, the number of the terminals 20 that should use the RIS 30 under control of the first base station 10A, the number of the terminals 20 that should use the RIS 30 under control of the second base station 10B, and priority levels of the first base station 10A and the second base station 10B.

For example, the first base station 10A may transmit values of received quality reported from the plurality of terminals 20 under control of the first base station 10A to the RIS 30, and the RIS 30 may calculate the total number of terminals 20 that should use the RIS 30 from among the plurality of terminals 20 under control of the first base station 10A, based on the reported values of received quality. As the received quality reported from the terminal 20, for example, a Signal to Interference plus Noise Radio (SINR) may be used. The RIS 30 may determine whether the RIS 30 should be used for the terminal 20 by comparing a predetermined threshold value with a value of SINR reported from the terminal 20. For example, if the value of SINR reported by the terminal 20 is less than the predetermined threshold value, the RIS 30 may determine that the RIS 30 should be used for the terminal 20. Note that the received quality reported from the terminal 20 is not limited to the SINR. For example, Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), Received Signal Strength Indicator (RSSI), or the like may be used.

Similarly, the second base station 10B may transmit values of received quality reported from the plurality of terminals 20 under control of the second base station 10B to the RIS 30, and the RIS30 may calculate the total number of terminals 20 that should use the RIS 30 from among the plurality of terminals 20 under control of the second base station 10B, based on the reported values of received quality.

For example, the RIS30 may apply a proportional fairness method to determine the time interval t1 and the time interval t2 based on the total number of terminals 20 that should use the RIS 30 obtained as described above and the reported SINR values. For example, instead of the proportional fairness method, the max-min fairness method, the method based on α-fairness, or the like may be used. Furthermore, based on the priority levels between the first base station 10A and the second base station 10B, the time position at which the time interval t1 is allocated and the time position at which the time interval t2 is allocated may be determined. For example, if the priority level assigned to the first base station 10A is higher than the priority level assigned to the second base station 10B, the time interval t1 may be allocated at a front side in the time direction in a predetermined time domain, and the time interval t2 may be allocated after the time interval t1 in the time direction in the predetermined time domain. Furthermore, in the time interval t1 (the first time interval at the first time position), the first portion of the plurality of elements 340 of the RIS 30 may be used by the first base station 10A, and, in the time interval t2 (the second time interval at the second time position), the second portion of the plurality of elements 340 of the RIS 30 may be used by the second base station 10B. In this case, the ratio R of the first portion of the plurality of elements 340 to the entire plurality of elements 340 of the RIS 30 may be determined based on the first number of the terminals 20 that should use the RIS 30 from among the plurality of terminals 20 under control of the first base station 10A and the second number of the terminals 20 that should use the RIS 30 from among the plurality of terminals 20 under control of the second base station 10B. For example, R = (the first number)/(the first number + the second number).

A more practical method for determining the time interval t1, the time position at which the time interval t1 is allocated, the first portion of the plurality of elements 340, the time interval t2, the time position at which the time interval t2 is allocated, and the second portion of the plurality of elements 340 can be considered. In the following, an example of a practical method is described.

Fig. 8 is a diagram illustrating an example of an allocation of time resources to the first base station 10A and the second base station 10B when the RIS 30 is shared in the example of Fig. 7. The RIS 30 determines the first time interval (and the time position of the first time interval) at which the first base station 10A can access the RIS 30 and the second time interval (and the time position of the second time interval) at which the second base station 10B can access the RIS 30.

In the example illustrated in Fig. 7, from among the plurality of terminals 20 under control of the first base station 10A (the terminal 20_1, the terminal 20_2, the terminal 20_3, and the terminal 20_4), the terminal 20_3 and the terminal 20_4 are the terminals 20 that should use the RIS 30. Furthermore, from among the plurality of terminals under control of the second base station 10B (the terminal 20_5 and the terminal 20_6), the terminal 20_6 is the terminal 20 that should use the RIS 30. In the following, for convenience of the description, the terminal 20_1, the terminal 20_2, the terminal 20_3, the terminal 20_4, the terminal 20_5, and the terminal 20_6 may also be denoted as U1, U2, U3, U4, U5, and U6, respectively.

Since U3 and U4 are the terminals 20 that should use the RIS 30, the RIS 30 determines that the total number of the terminals 20 that should use the RIS 30 from among the plurality of terminals 20 under control of the first base station 10A is two. Since U6 is the terminal that should use the RIS 30, the RIS 30 determines that the total number of the terminals 20 that should use the RIS 30 from among the plurality of terminals 20 under control of the second base station 10B is one.

The RIS 30 determines that the total number of the terminals 20 that should use the RIS 30 is three. The RIS 30 determines a time interval (and a time position) at which the first base station 10A uses the RIS 30 and a time interval (and a time position) at which the second base station 10B uses the RIS 30 in the predetermined time interval illustrated in Fig. 8, based on the total number of the terminals 20 that should use the RIS 30 and the priority levels of the first base station 10A and the second base station 10B. Specifically, the RIS 30 determines, for U3 and U4, time intervals (and time positions) at which the RIS 30 is used, as illustrated in Fig. 8. The RIS 30 determines, for U6, a time interval (and a time position) at which the RIS 30 is used, as illustrated in Fig. 8. Furthermore, in the time interval t1 (the first time interval at the first time position), the first portion of the plurality of elements 340 of the RIS 30 is used by the first base station 10A, and, in the time interval t2 (the second time interval at the second time position), the second portion of the plurality of elements 340 of the RIS 30 is used by the second base station 10B. Here, based on the first number (= 2) of the terminals 20 that should use the RIS 30 from among the plurality of terminals 20 under control of the first base station 10A and the second number (= 1) of the terminals 20 that should use the RIS 30 from among the plurality of terminals 20 under control of the second base station 10B, the RIS 30 calculates the ratio R of the first portion of the plurality of elements 340 to the entire plurality of elements 340 of the RIS 30 to be 2/3. For example, the RIS 30 may assign serial numbers to the entire plurality of elements 340 of the RIS 30, and the first base station 10A may determine that 2/3 of the entire plurality of elements 340 of the RIS as the first portion and the rest as the second portion in accordance with ascending order of the serial numbers. Note that the method for determining the first portion is not limited to the ascending order of the serial numbers. For example, the method of determining the first portion may be based on the descending order of the serial numbers, or based on a method in which the plurality of elements 340 of the RIS 30 is divided into a plurality of subsets and serial numbers are assigned to the subsets.

As illustrated in Fig. 8, the first base station 10A may schedule U1 and U2 at time intervals at which the first base station 10A does not use the RIS 30. The second base station 10B may also schedule U5 at a time interval at which the second base station 10B does not use the RIS 30. Note that, in the example of Fig. 8, the first base station 10A may transmit, in advance to the RIS 30, configuration information on the reflection phase and amplitude for optimizing the communication between the first base station 10A and U3 via the first portion of the plurality of elements 340 of the RIS 30, and configuration information on the reflection phase and amplitude for optimizing the communication between the first base station 10A and U4 via the first portion of the plurality of elements 340 of the RIS 30. The second base station 10B may transmit, in advance to the RIS 30, configuration information on the reflection phase and amplitude for optimizing the communication between the second base station 10B and U6 via the second portion of the plurality of elements 340 of the RIS 30. Based on this, the RIS 30 may apply the configuration of the reflection phase and amplitude for optimizing the communication between the first base station 10A and U3 via the first portion of the plurality of elements 340 of the RIS 30, during the communication between the first base station 10A and U3 illustrated in the example of Fig. 8. Furthermore, during the communication between the first base station 10A and U4 illustrated in the example of Fig. 8, the RIS 30 may apply the configuration of the reflection phase and amplitude for optimizing the communication between the first base station 10A and U4 via the first portion of the plurality of elements 340 of the RIS 30. Furthermore, during the communication between the second base station 10B and U6 illustrated in the example of Fig. 8, the RIS 30 may apply the configuration of the reflection phase and amplitude for optimizing the communication between the second base station 10B and U6 via the second portion of the plurality of elements 340 of the RIS 30.

The example of Fig. 8 may be generalized as follows. The RIS 30 is denoted by r, the base station 10 is denoted by j, and the terminal 20 that should use the RIS 30 is denoted by u. B_{u, j}^r is the time interval of the communication via the RIS 30(r) that is allocated to the terminal 20(u) by the base station 10(j). Here, if r is not equal to 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). N is defined to be the total number of the plurality of elements 340 of the RIS 30. η_{j}^{r} is defined to be the ratio of the number of a plurality of elements 340 that can be assigned to the base station 10(j) by the RIS 30(r) to the total number of the plurality of elements 340 of the RIS 30. Accordingly, N × η_{j}^{r} is the number of the elements 340 that can be assigned to the base station 10(j) by the RIS 30(r).

Fig. 9 is a flowchart illustrating an example of a processing procedure performed in the radio communication system.

As an assumption for the processing procedure of Fig. 9, the plurality of terminals 20 is classified into normal terminals 20 and terminals 20 that should use the RIS 30. Classification may be performed by comparing the SINR value reported from each terminal 20 to a predetermined threshold value. The RIS 30 determines a resource (the first time interval, the first time position of the first time interval, and the first portion of the plurality of elements 340 of the RIS 30) for the first base station 10A to use the RIS 30 and a resource (the second time interval, the second time position of the second time interval, and the second portion of the plurality of elements 340 of the RIS 30) for the second base station 10B to use the RIS 30.

In the example of Fig. 9, at step S110, the first base station 10A transmits values of received quality reported from the plurality of terminals 20 under control of the first base station 10A to the RIS 30 together with identifiers of the plurality of terminals 20. In this case, the first base station 10A may determine the first number of terminals 20 that should use the RIS 30 from among the terminals 20 under control of the first base station 10A by comparing the values of the received quality reported from the plurality of terminals 20 under control of the first base station 10A with a predetermined threshold value.

At step S120, the second base station 10B transmits values of received quality reported from the plurality of terminals 20 under control of the second base station 10B to the RIS 30 together with identifiers of the plurality of terminals 20. In this case, the second base station 10B may determine the second number of terminals 20 that should use the RIS 30 from among the terminals 20 under control of the second base station 10B by comparing the values of the received quality reported from the plurality of terminals 20 under control of the second base station 10B with a predetermined threshold value.
　　At step S130, the RIS 30 determines the first number of terminals 20 that should use the RIS 30 from among the terminals 20 under control of the first base station 10A by comparing the values of the received quality reported from the plurality of terminals 20 under control of the first base station 10A with a predetermined threshold value. Furthermore, the RIS 30 determines the second number of terminals 20 that should use the RIS 30 from among the terminals 20 under control of the second base station 10B by comparing the values of the received quality reported from the plurality of terminals 20 under control of the second base station 10B with a predetermined threshold value. The RIS 30 schedules one or more terminals 20 that should use the RIS 30 from among the terminal 20 under control of the first base station 10A and the one or more terminals 20 that should use the RIS 30 from among the terminal 20 under control of the second base station 10B, based on the first number of the one or more terminals 20 that should use the RIS 30 from among the terminals 20 under control of the first base station 10A and the second number of the one or more terminals 20 that should use the RIS from among the plurality of terminals 20 under control of the second base station 10B. As a result of scheduling, the first time interval at which the first base station 10A can access the RIS 30 and the second time interval at which the second base station 10B can access the RIS 30 are determined.

Furthermore, at step S130, the RIS 30 determines a first time position at which the first time interval is to be allocated and a second time position at which the second time interval is to be allocated based on the priority levels between the first base station 10A and the second base station 10B. For example, if the priority level assigned to the first base station 10A is higher than the priority level assigned to the second base station 10B, the first time interval may be allocated at a front side in the time direction in a predetermined time domain, and the second time interval may be allocated after the first time interval in the time direction in the predetermined time domain.

Furthermore, at step S130, the RIS 30 determines the first portion of the plurality of elements 340 to be used by the first base station 10A and the second portion of the plurality of elements 340 to be used by the second base station 10B from among the plurality of elements 340 of the RIS 30, based on the ratio of the first number of the one or more terminals 20 that should use the RIS 30 from among the terminals 20 under control of the first base station 10 to the second number of the one or more terminals 20 that should use the RIS 30 from among the terminals 20 under control of the second base station 10B. For example, based on the first number of the one or more terminals 20 that should use the RIS 30 from among the plurality of terminals 20 under control of the first base station 10A and the second number of the one or more terminals 20 that should use the RIS 30 from among the plurality of terminals under control of the second base station 10B, the RIS 30 may calculate the ratio R (which may be η_{10A}^r) of the first portion of the plurality of elements 340 to the entire plurality of elements 340 of the RIS 30 as R = (the first number)/(the first number + the second number).

Furthermore, at step 130, the RIS 30 transmits, to the first base station 10A, information indicating the first time interval, the first time position at which the first time interval is to be allocated (and/or scheduling information of the one or more terminals 20 that should use the RIS 30 from among the terminals 20 under control of the first base station 10A (which may be information indicating one or more time slots to be used by the one or more terminals 20)), and information indicating the first portion of the plurality of elements 340 to be used by the first base station 10A from among the plurality of elements 340 of the RIS 30. Additionally, at step 130, the RIS 30 transmits, to the second base station 10B, information indicating the second time interval, the second time position at which the second time interval is to be allocated (and/or scheduling information of the one or more terminals 20 that should use the RIS 30 from among the terminals 20 under control of the second base station 10B (which may be information indicating one or more time slots to be used by the one or more terminals 20)), and information indicating the second portion of the plurality of elements 340 to be used by the second base station 10B from among the plurality of elements 340 of the RIS 30.

Note that, at step S130, the RIS 30 determines the first portion of the plurality of elements 340 to be used by the first base station 10A and the second portion of the plurality of elements 340 to be used by the second base station 10B based on the radio of the first number of the one or more terminals 20 that should use the RIS 30 from among the plurality of terminals 20 under control of the first base station 10A to the second number of the one or more terminals 20 that should use the RIS 30 from among the plurality of terminals under control of the second base station 10B. However, the embodiments of the present invention are not limited to this example. For example, the RIS 30 may evenly allocate the plurality of elements 340 of the RIS 30 based on the number of the base stations 10 that share the RIS 30. For example, as illustrated in Fig. 7, when the first base station 10A and the second base station 10B share the RIS 30, a half of the plurality of elements 340 of the RIS 30 may be allocated to the first base station 10A, and the other half of the plurality of elements 340 of the RIS 30 may be allocated to the second base station 10B.

At step S140, the first base station 10A transmits, to the RIS 30, configuration information of the reflection phase and amplitude for optimizing the communication between the first base station 10A and each terminal 20 under control of the first base station 10A via the first portion of the plurality of elements 340 of the RIS 30.

At step S150, the second base station 10B transmits, to the RIS 30, configuration information of the reflection phase and amplitude for optimizing the communication between the second base station 10B and each terminal 20 under control of the second base station 10B via the second portion of the plurality of elements 340 of the RIS 30.

At step S160, the first base station 10A communicates with each terminal 20 (each terminal 20 that should use the RIS 30) under control of the first base station 10A via the first portion of the plurality of elements 340 of the RIS 30, in accordance with the scheduling information.

At step S170, the second base station 10B communicates with each terminal 20 (each terminal 20 that should use the RIS 30) under control of the second base station 10B via the second portion of the plurality of elements 340 of the RIS 30, in accordance with the scheduling information.

Next, an example of a procedure executed by the terminal 20 under control of the first base station 10A is described with reference to Fig. 10. Note that, in the example of Fig. 10, it is assumed that multiple antenna ports are installed in the terminal 20, so that the terminal 20 can direct a beam in multiple directions.

At step S210, the terminal 20 transmits, to the first base station 10A, information indicating a first received power value of a first signal received from the first base station 10A, as a measurement report. The first base station 10A receives the measurement report and compares the first received power value with a first threshold value.

If the first received power value is greater than or equal to the first threshold value, the first base station 10A determines to continue the communication with the terminal 20, as it is. That is, the first base station 10A determines that the communication between the first base station 10A and the terminal 20 is not relayed by the RIS 30.

If the first received power value is less than the first threshold value, the first base station 10A causes the terminal 20 to report information indicating a second power value of a second signal from the second base station 10B.

If the second received power value is greater than or equal to the first threshold value, the first base station 10A may transmit a handover command to the terminal 20 to cause the terminal 20 to hand over to the second base station 10B.

In step S220, if the second received power value is less than the first threshold value, the first base station 10A determines to communicate with the terminal 20 via the RIS 30. Namely, the first base station 10A determines that the communication between the first base station 10A and the terminal 20 is relayed by the RIS 30.

At step S230, the first base station 10A determines the first portion of the plurality of elements 340 to be used by the first base station 10A and the second portion of the plurality of elements 340 to be used by the second base station 10B from among the plurality of elements 340 of the RIS 30, based on the ratio of the first number of the one or more terminals 20 that should use the RIS 30 from among the terminals 20 under control of the first base station 10 to the second number of the one or more terminals 20 that should use the RIS 30 from among the terminals 20 under control of the second base station 10B.

At step S240, the first base station 10A transmits a predetermined reference signal to the first portion of the plurality of elements 340 of the RIS 30 and indicates, to the first portion of the plurality of elements 340 of the RSI 30, a direction in which the received power at the terminal 20 is maximized, based on a measurement report received from the terminal 20. For example, the first base station 10A instructs the first portion of the plurality of elements 340 of the RIS 30 to reflect a predetermined reference signal from the first base station 10A in a direction 1, a direction 2, ..., and a direction n, at timing 1, timing 2, ... , and timing n, respectively. The terminal 20 transmits, to the first base station 10A, a received power value 1, a received power value 2, ... , and a received power value n of the reference signal received at the timing 1, the timing 2, ... , and the timing n, respectively, as a measurement report. The first base station 10A that receives the measurement report from the terminal 20 compares the received power value 1, the received power value 2, ... , and the received power value n of the reference signal received by the terminal 20 at the timing 1, the timing 2, ... , and the timing n, respectively, and the first base station 10A may indicate, to the first portion of the plurality of elements 340 of the RIS 30, a direction corresponding to the maximum received power value from among these received power values.

At step S250, the first base station 10A indicates, to the terminal 20, to transmit a predetermined uplink reference signal (which may be a Sounding Reference Signal (SRS)) in a direction 1, a direction 2, ..., and in a direction n, at timing 1, timing 2, ..., and timing n, respectively. For example, in response to receiving the indication from the first base station 10A, the terminal 20 may transmit an uplink reference signal at the timing 1 while applying a precoding vector V1 corresponding to the direction 1 to the uplink reference signal (the uplink reference signal may include information indicating the precoding vector V1). Similarly, the terminal 20 may transmit an uplink reference signal at the timing 2 while applying a precoding vector V2 corresponding to the direction 2 to the uplink reference signal (the uplink reference signal may include information indicating the precoding vector V2). Similarly, the terminal 20 may transmit an uplink reference signal at the timing n while applying a precoding vector Vn corresponding to the direction n to the uplink reference signal (the uplink reference signal may include information indicating the precoding vector Vn).

At step S260, the first base station 10A compares a received power value 1, a received power value 2, ... , and a received power value n of the predetermined uplink reference signals received at the timing 1, the timing 2, ... , and the timing n, respectively, and the first base station 10A identifies a direction corresponding to the maximum received power value from among these received power values. For example, the first base station 10A may identify the precoding vector V1 applied by the terminal 20A at the timing t1 based on the information included in the uplink reference signal received from the terminal 20A at the timing t1. Similarly, the first base station 10A may identify the precoding vector V2 applied by the terminal 20A at the timing t2 based on the information included in the uplink reference signal received from the terminal 20A at the timing t2. Similarly, the first base station 10A may identify the precoding vector Vn applied by the terminal 20A at the timing tn based on the information included in the uplink reference signal received from the terminal 20A at the timing tn. Subsequently, the first base station 10A compares the received power value 1, the received power value 2, ... , and the received power value n of the uplink reference signals received at the timing 1, the timing 2, ... , and the timing n, respectively, and the first base station 10A may identify a precoding vector corresponding to the maximum received power value from among these received power values.

At step S270, the first base station 10A schedules the communication between the first base station 10A and the terminal 20, and determines a time interval (which may be a time slot) and a time position (which may be a time position of the time slot) used for the communication between the first base station 10A and the terminal 20.

At step S280, the first base station 10A transmits, to the terminal 20, scheduling information including information indicating the direction determined at step S260 and information indicating the time interval and the time position of the time interval determined at step S270. For example, the first base station 10A may include information indicating the time slot and the time position of the time slot for communication between the first base station 10A and the terminal 20 in the scheduling information. Furthermore, the first base station 10A may transmit, to the terminal 20, a notification of the precoding vector corresponding to the maximum received power value from among the received power values of the uplink reference signals, as the information indicating the direction determined at step S260.

At step S290, the first base station 10A and the terminal 20 communicate with each other through the first portion of the plurality of elements 340 of the RIS 30 based on the scheduling information. For example, the first base station 10A and the terminal 20 may communicate via the first portion of the plurality of elements of the RIS 30 in the time slot located at the time position notified based on the information indicating the time slot and the time position of the time slot transmitted to the terminal 20 from the first base station 10A at step S280. Furthermore, when the terminal 20 is to transmit an uplink signal to the first base station 10A via the first portion of the plurality of elements 340 of the RIS 30 in the time slot located at the time position notified by the first base station 10A, the terminal 20 may transmit the uplink signal while applying the precoding vector indicated by the scheduling information received from the first base station 10A at step S280.

In the example of Fig. 10, at step S220 and step S230, the first base station 10A determines that the communication between the first base station 10A and the terminal 20 is to be relayed by the RIS 30, and the first base station 10A determines the first portion of the plurality of elements 340 of the RIS 30 to be used by the first base station 10A and the second portion of the plurality of elements 340 of the RIS 30 to be used by the second base station 10B. However, the embodiments are not limited to this example. For example, by the process similar to the process of step S130 of Fig. 9, the RIS 30 may determine that the communication between the first base station 10A and the terminal 20 is to be relayed by the RIS 30, and the RIS 30 may determine the first portion of the plurality of elements 340 of the RIS 30 to be used by the first base station 10A and the second portion of the plurality of elements 340 of the RIS 30 to be used by the second base station 10B.

As described above, in the embodiments of the present invention, the technique is described for allocating resources that are time intervals for using the RIS in the radio communication technology using the Reconfigurable Intelligent Surface (RIS).

In the embodiments of the present invention, a system including multiple cells and multiple base stations, such as the system for cellular communication, is assumed. Furthermore, it is assumed that the multiple radio base stations share the same RIS, and each of the multiple radio base stations performs beam forming toward the user terminal under control of the own cell.

In such a system, it is expected that contention for using the RIS occurs. In a method according to related art, coordination is required for all the RISs in the system by exchanging the weight matrices (corresponding to all the communicating terminals) corresponding to the beams formed by the RISs between the base stations. In this method, processing is complicated and interference between the reflectors cannot be completely avoided.

Accordingly, in the embodiments of the present invention, the RIS is divided into fractions, only the information on the terminals that should use the RIS is shared between the radio base stations, and the control information to be transmitted and received is reduced by calculating, by the radio base station, the fractions of the RIS to be used by the respective base stations based on the shared information. Furthermore, it is also possible to completely avoid interference without causing contention for using the RIS.

10A　　first base station
10B　　second base station
20　　terminal
30　　RIS
40　　network
110　　transmitter
120　　receiver
130　　controller
210　　transmitter
220　　receiver
230　　controller
310　　transmitter
320　　receiver
330　　controller
340　　element
100　　drive device
101　　recording medium
102　　storage device
103　　memory device
104　　CPU
105　　Interface device
B　　Bus

Claims

　　　　A radio communication system comprising:
　　　　a first base station;
　　　　a second base station;
　　　　a relay device including a plurality of reflection elements; and
　　　　a plurality of terminals,
　　　　wherein a first communication area formed by the first base station overlaps a second communication area formed by the second base station,
　　　　wherein the relay device includes
　　　　a receiver that receives, from the first base station, values of received quality reported from a plurality of terminals under control of the first base station, and that receives, from the second base station, values of received quality reported from a plurality of terminals under control of the second base station;
　　　　a controller that determines a first number of one of more terminals to communicate via the relay device under control of the first base station and a second number of one or more terminals to communicate via the relay device under control of the second base station based on the values of received quality, and that determines a first portion of the plurality of reflection elements to be used by the first base station and a second portion of the plurality of reflection elements to be used by the second base station, from among the plurality of reflection elements included in the relay device, based on a ratio of the first number to the second number; and
　　　　a transmitter that transmits, to the first base station, information indicating the first portion of the plurality of reflection elements of the relay device, and that transmits, to the second base station, information indicating the second portion of the plurality of reflection elements of the relay device.
　　　　The radio communication system according to claim 1, wherein the relay device is a Reconfigurable Intelligent Surface (RIS) including the plurality of reflection elements, the RIS being capable of changing a traveling direction of a reflection wave.
　　　　The radio communication system according to claim 1, wherein the controller determines a first time interval in which the first base station uses the relay device and a second time interval in which the second base station uses the relay device, based on the values of received quality and priority levels between the first base station and the second base station.
　　　　A relay device of a radio communication system including a first base station, a second base station, the relay device including a plurality of reflection elements, and a plurality of terminals, wherein a first communication area formed by the first base station overlaps a second communication area formed by the second base station, the relay device comprising:
　　　　a receiver that receives, from the first base station, values of received quality reported from a plurality of terminals under control of the first base station, and that receives, from the second base station, values of received quality reported from a plurality of terminals under control of the second base station;
　　　　a controller that determines a first number of one of more terminals to communicate via the relay device under control of the first base station and a second number of one or more terminals to communicate via the relay device under control of the second base station based on the values of received quality, and that determines a first portion of the plurality of reflection elements to be used by the first base station and a second portion of the plurality of reflection elements to be used by the second base station, from among the plurality of reflection elements included in the relay device, based on a ratio of the first number to the second number; and
　　　　a transmitter that transmits, to the first base station, information indicating the first portion of the plurality of reflection elements of the relay device, and that transmits, to the second base station, information indicating the second portion of the plurality of reflection elements of the relay device.
　　　　A communication method executed by a relay device of a radio communication system including a first base station, a second base station, the relay device including a plurality of reflection elements, and a plurality of terminals, wherein a first communication area formed by the first base station overlaps a second communication area formed by the second base station, the communication method comprising:
　　　　receiving, from the first base station, values of received quality reported from a plurality of terminals under control of the first base station, and receiving, from the second base station, values of received quality reported from a plurality of terminals under control of the second base station;
　　　　determining a first number of one of more terminals to communicate via the relay device under control of the first base station and a second number of one or more terminals to communicate via the relay device under control of the second base station based on the values of received quality, and determining a first portion of the plurality of reflection elements to be used by the first base station and a second portion of the plurality of reflection elements to be used by the second base station, from among the plurality of reflection elements included in the relay device, based on a ratio of the first number to the second number; and
　　　　transmitting, to the first base station, information indicating the first portion of the plurality of reflection elements of the relay device, and transmitting, to the second base station, information indicating the second portion of the plurality of reflection elements of the relay device.
　　　　A non-transitory computer readable storage medium that stores a program, which, when executed by a relay device of a radio communication system including a first base station, a second base station, the relay device including a plurality of reflection elements, and a plurality of terminals, wherein a first communication area formed by the first base station overlaps a second communication area formed by the second base station, causing the relay device to execute
　　　　receiving, from the first base station, values of received quality reported from a plurality of terminals under control of the first base station, and receiving, from the second base station, values of received quality reported from a plurality of terminals under control of the second base station;
　　　　determining a first number of one of more terminals to communicate via the relay device under control of the first base station and a second number of one or more terminals to communicate via the relay device under control of the second base station based on the values of received quality, and determining a first portion of the plurality of reflection elements to be used by the first base station and a second portion of the plurality of reflection elements to be used by the second base station, from among the plurality of reflection elements included in the relay device, based on a ratio of the first number to the second number; and
　　　　transmitting, to the first base station, information indicating the first portion of the plurality of reflection elements of the relay device, and transmitting, to the second base station, information indicating the second portion of the plurality of reflection elements of the relay device.