Terminal, Communication Method, and Wireless Communication System

Abstract

1. A terminal comprising: a receiving unit that receives a first downlink signal from a first base station and a second downlink signal from a second base station; a transmitting unit that transmits a first uplink signal to the first base station and a second uplink signal to the second base station; and a processor that, when UL-DL imbalance is detected, establishes a downlink connection with the first base station and an uplink connection with the second base station, wherein, in response to receiving an instruction signal from the second base station, the processor changes the uplink connection with the second base station to an uplink connection with the second base station via a relay device.

Description

Technical Field

[0001] The present invention relates to a terminal and a communication method in a wireless communication system.

Background Art

[0002] In the fifth-generation mobile communication system (5G (Above-6GHz)), in addition to the conventional frequency bands, a high-frequency band called the millimeter-wave band is used. Generally, radio waves in the high-frequency band called Above-6 such as the 28GHz band available in 5G and Local 5G have large distance attenuation, so long-distance transmission is realized by using an ultra-high-gain beamforming transmission technology.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

[0005] Here, assume a situation where a downlink and uplink decoupling (DUDe) method that separates the uplink (UL) and downlink (DL) is applied in a space such as a factory or a warehouse where large obstacles move quasi-statically or dynamically.

[0006] In this case, radio waves in the high-frequency band as described above have high directivity and a large loss due to obstacles, so an improvement in the performance of uplink transmission from the terminal is required.

[0007] The present invention has been made in view of the above points, and an object thereof is to improve the performance of uplink transmission from a terminal.

Means for Solving the Problems

[0008] According to one aspect of the present invention, there is provided a terminal that communicates with a first base station and a second base station, the terminal including a receiving unit that receives a first downlink signal from the first base station and a second downlink signal from the second base station, a transmitting unit that transmits a first uplink signal to the first base station and a second uplink signal to the second base station, and a processor that, when a first received power of the first downlink signal at the terminal is greater than a second received power of the second downlink signal at the terminal and a third received power of the first uplink signal at the first base station is less than or equal to a fourth received power of the second uplink signal at the second base station, establishes a downlink connection with the first base station and an uplink connection with the second base station. The processor changes the uplink connection with the second base station to an uplink connection with the second base station via a relay device in response to the receiving unit receiving an instruction signal from the second base station. Shi 、 The relay device includes a plurality of reflecting elements and is a Reconfigurable Intelligent Surface (RIS) capable of changing the propagation direction of reflected waves. The second base station transmits configuration information including phase and timing information to the relay device. The transmitting unit transmits an uplink signal to the second base station via the relay device based on information received from the second base station and specifying time and frequency resources for transmitting to the second base station via the relay device. A terminal is provided.

Advantages of the Invention

[0009] According to the embodiment, the performance of uplink transmission from the terminal can be improved.

Brief Description of the Drawings

[0010]

Figure 1

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Modes for Carrying Out the Invention

[0011] A Reconfigurable Intelligent Surface (RIS) is an effective method for controlling a channel by appropriately adjusting the phase and amplitude of an electromagnetic signal. In recent research and experiments, various architectures and multiple access technologies have been proposed.

[0012] In future heterogeneous networks, multi-connectivity is considered to be used, and it is important to consider that a terminal (which may be a user device) is connected to a plurality of transmission points (TPs). However, in such a situation, there is a problem that an imbalance in transmission power occurs due to differences in the transmission power of a plurality of arranged base stations. As a method for correcting this, there is a method of dividing the association between the uplink (UL) and the downlink (DL). This is called UL / DL splitting in the standard and has been developed later as the uplink / downlink separation method (DUDe).

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration example of a wireless communication system in an embodiment. As shown in FIG. 1, the wireless communication system includes a macro cell base station 10A, a small cell base station 10B, a terminal 20, a Reconfigurable Intelligent Surface (RIS) 30, a network 40, and the like. The macro cell base station 10A and the small cell base station 10B are connected to the network 40 by wire or wirelessly. The macro cell base station 10A and the small cell base station 10B are communicably connected via, for example, an X2 interface. The small cell base station 10B and the RIS 30 are communicably connected by wire or wirelessly. In the example of FIG. 1, it is assumed that the RIS 30 is connected to the small cell base station 10B, but the embodiments of the present invention are not limited to this example. For example, the RIS 30 may be connected to the macro cell base station 10A. The macro cell base station 10A, the small cell base station 10B, and the terminal 20 can all perform beamforming to transmit and receive signals.

[0014] The macro cell base station 10A is a base station that forms a wide communication area outdoors or the like. The macro cell base station 10A may also be called a high-power base station or the like. The macro cell base station 10A realizes high-speed and high-capacity wireless communication with the terminal 20 by transmitting and receiving radio waves in a high-frequency band used in, for example, the fifth-generation mobile communication system (5G). The small cell base station 10B is a base station that forms a narrow communication area indoors or the like. The small cell base station 10B may also be called a low-power base station or the like. The small cell base station 10B realizes high-speed wireless communication with the terminal 20 by transmitting and receiving radio waves in a high-frequency band used in 5G, for example. The terminal 20 is a communication device such as a smartphone, a tablet terminal, or a PC (Personal Computer), for example.

[0015] The terminal 20 can communicate with the macro cell base station 10A and the small cell base station 10B simultaneously by setting dual connectivity between the macro cell base station 10A and the small cell base station 10B. When communicating with the terminal 20, the small cell base station 10B can communicate via the RIS 30 as a relay device. In the example of FIG. 1, the RIS 30 is assumed to relay the communication between the small cell base station 10B and the terminal 20, but the embodiments of the present invention are not limited to this example. For example, the RIS 30 may relay the communication between the macro cell base station 10A and the terminal 20.

[0016] The RIS 30 is connected to the small cell base station 10B (or may be connected to the macro cell base station 10A) by wire or wirelessly. The RIS 30 can relay the signal from the terminal 20 to the small cell 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 small cell base station 10B.

[0017] Although only one macro cell base station 10A, small cell base station 10B, terminal 20, and RIS 30 are shown in Fig. 1, the embodiments of the present invention are not limited to this example. The wireless communication system may include one or more macro cell base stations 10A, one or more small cell base stations 10B, one or more terminals 20, and one or more RISs 30.

[0018] Fig. 2 is a diagram showing an example of the functional configuration of the macro cell base station 10A and the small cell base station 10B. As shown in Fig. 2, both the macro cell base station 10A and the small cell base station 10B have a transmission unit 110, a reception unit 120, and a control unit 130. The functional configuration shown in Fig. 2 is merely an example. Any functional division and name of the functional units may be used as long as the operations according to the present embodiment can be executed.

[0019] The transmission unit 110 creates a transmission signal from the transmission data and wirelessly transmits the transmission signal. The reception unit 120 wirelessly receives various signals and acquires signals of higher layers from the received physical layer signals. The reception unit 120 also includes a measurement unit that measures the received signals to acquire received power and the like.

[0020] The control unit 130 controls the base station (macro cell base station 10A or small cell base station 10B). Note that the functions of the control unit 130 related to transmission may be included in the transmission unit 110, and the functions of the control unit 130 related to reception may be included in the reception unit 120.

[0021] 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 transmission unit 210, a reception unit 220, and a control unit 230. The functional configuration shown in Fig. 3 is merely an example. Any functional division and name of the functional units may be used as long as the operations according to the present embodiment can be executed.

[0022] The transmission unit 210 includes a function of generating a signal to be transmitted to the base station (macro cell base station 10A and / or small cell base station 10B) side and wirelessly transmitting the signal. The reception unit 220 includes a function of receiving various signals transmitted from the base station (macro cell base station 10A and / or small cell base station 10B) and obtaining information of a higher layer, for example, from the received signals. The reception unit 220 also includes a measurement unit that measures the received signal to obtain the received power and the like.

[0023] The control unit 230 controls the terminal 20. Note that the function of the control unit 230 related to transmission may be included in the transmission unit 210, and the function of the control unit 230 related to reception may be included in the reception unit 220.

[0024] FIG. 4 is a diagram showing an example of the functional configuration of the RIS 30. As shown in FIG. 4, the RIS 30 includes a transmission unit 310, a reception unit 320, a control unit 330, and a plurality of elements 340. The functional configuration shown in FIG. 4 is merely an example. Any functional classification and name of the functional units may be used as long as the operations according to the present embodiment can be executed.

[0025] The transmission unit 310 includes a function of generating a signal to be transmitted to the base station (macro cell base station 10A and / or small cell base station 10B) side and transmitting the signal by wire and / or wirelessly. The reception unit 320 includes a function of receiving various signals transmitted from the base station (macro cell base station 10A and / or small cell base station 10B) and obtaining information of a higher layer, for example, from the received signals.

[0026] The control unit 330 controls the RIS 30. The plurality of elements 340 have a function of changing the reflection direction of the carrier wave on which the signal from the terminal 20 is carried. The control unit 330 has a function of controlling the reflection phase (or 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 small cell base station 10B. For example, the control unit 330 controls the reflection phase (or reflection direction) of the reflected wave by controlling the impedance, element spacing, and / or the orientation of the reflection elements of each of the plurality of elements 340.

[0027] Note that the plurality of elements 340 may be configured as, for example, a reflectarray. FIG. 5 is a diagram showing an example of the plurality of elements 340 as a reflectarray. When the plurality of elements 340 are configured as a reflectarray, for example, by changing the element spacing between the plurality of elements 340, it is possible to change the reflection phase of the reflected wave and change the propagation direction of the reflected wave. Note that the method of changing the reflection phase of the reflected wave is not limited to changing the element spacing, and may be performed by changing the impedance of each of the plurality of elements 340. Additionally or alternatively, the reflection direction of the reflected wave may be changed by changing the orientation of the reflection elements including reflection elements for changing the reflection direction of the incident wave for each of the plurality of elements 340. For example, the reflection 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.

[0028] Figures 2 to 4 show the functional unit blocks. These functional blocks (components) are realized by any combination of at least one of hardware and software. The realization method of each functional block is not particularly limited. That is, each functional block may be realized using one physically or logically combined device, or two or more physically or logically separated devices may be directly or indirectly (for example, using wired, wireless, etc.) connected and realized using these multiple devices.

[0029] For example, the macrocell base station 10A, the small cell base station 10B, the terminal 20, and the RIS 30 may all function as a computer that performs the processing according to this embodiment. FIG. 6 is a diagram showing an example of the hardware configuration of the macrocell base station 10A, the small cell base station 10B, the terminal 20, and the RIS 30. Any of the devices of the macrocell base station 10A, the small cell base station 10B, the terminal 20, and the RIS 30 may physically be 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 are mutually connected by a bus B.

[0030] In the computer device, the program for realizing the 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 installation of the program does not necessarily have to be performed from the recording medium 101, and it may be downloaded from another computer via a network. The auxiliary storage device 102 stores the installed program and also stores necessary files, data, and the like.

[0031] When there is an instruction to start a program, the memory device 103 reads and stores the program from the auxiliary storage device 102. The CPU 104 executes functions related to 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.

[0032] (UL-DL imbalance)

[0033] FIG. 7 is a diagram showing an example in which the terminal 20 is arranged between the macro cell base station 10A and the small cell base station 10B. It is assumed that the terminal 20 moves on a straight line connecting the macro cell base station 10A and the small cell base station 10B.

[0034] In this case, let the received power when the terminal 20 receives the downlink signal from the macro cell base station 10A be the received power A. Let the power when the terminal 20 receives the downlink signal from the small cell base station 10B be the received power B. Let the received power when the macro cell base station 10A receives the uplink signal from the terminal 20 be the received power C. Let the received power when the small cell base station 10B receives the uplink signal from the terminal 20 be the received power D.

[0035] When the terminal 20 moves from a position close to the macro cell base station 10A to the small cell base station 10B, the following three states, state 1 to state 3, can be considered.

[0036] State 1: A state where the received power A is greater than or equal to the received power B and the received power C is greater than or equal to the received power D.

[0037] State 2: A state where the received power A is greater than or equal to the received power B and the received power C is less than the received power D.

[0038] State 3: A state where the received power A is less than the received power B and the received power C is less than the received power D.

[0039] In the case of state 1, the received power A at which the terminal 20 receives the downlink signal from the macro cell base station 10A is equal to or greater than the received power B at which the terminal 20 receives the downlink signal from the small cell base station 10B. Therefore, in the case of state 1, it is efficient for the terminal 20 to connect to the macro cell base station 10A in the downlink.

[0040] Also, in the case of state 1, the received power C at which the macro cell base station 10A receives the uplink signal from the terminal 20 is equal to or greater than the received power D at which the small cell base station 10B receives the uplink signal from the terminal 20. Therefore, in the case of state 1, it is efficient for the terminal 20 to connect to the macro cell base station 10A in the uplink.

[0041] That is, in the case of state 1, it is efficient for the terminal 20 to connect to the macro cell base station 10A in both the uplink and the downlink.

[0042] In the case of state 3, the received power A at which the terminal 20 receives the downlink signal from the macro cell base station 10A is less than the received power B at which the terminal 20 receives the downlink signal from the small cell base station 10B. Therefore, in the case of state 3, it is efficient for the terminal 20 to connect to the small cell base station 10B in the downlink.

[0043] Also, in the case of state 3, the received power C at which the macro cell base station 10A receives the uplink signal from the terminal 20 is less than the received power D at which the small cell base station 10B receives the uplink signal from the terminal 20. Therefore, in the case of state 3, it is efficient for the terminal 20 to connect to the small cell base station 10B in the uplink.

[0044] That is, in the case of state 3, it is efficient for the terminal 20 to connect to the small cell base station 10B in both the uplink and the downlink.

[0045] In the case of state 2, the received power A at which the terminal 20 receives the downlink signal from the macro cell base station 10A is equal to or greater than the received power B at which the terminal 20 receives the downlink signal from the small cell base station 10B. Therefore, in the case of state 2, it is efficient for the terminal 20 to connect to the macro cell base station 10A in the downlink.

[0046] Also, in the case of state 2, the received power C at which the macro cell base station 10A receives the uplink signal from the terminal 20 is less than the received power D at which the small cell base station 10B receives the uplink signal from the terminal 20. Therefore, in the case of state 2, it is efficient for the terminal 20 to connect to the small cell base station 10B in the uplink.

[0047] (DUDe)

[0048] A state where the received power from the macro cell base station 10A is large in the downlink and the received power at the small cell base station 10B is large in the uplink as in state 2 is called UL-DL imbalance (UL-DL imbalance). As a method for improving the communication efficiency in the case of UL-DL imbalance, Downlink and Uplink Decoupling (uplink and downlink separation method: DUDe) that separates UL and DL can be applied.

[0049] DUDe is a method for improving throughput by independently selecting the downlink transmission source base station and the uplink transmission destination base station in a network where multiple types of base stations exist.

[0050] FIG. 8 is a diagram showing an example in which the terminal 20 communicates with the macro cell base station 10A and the small cell base station 10B by applying the DUDe method. For example, the terminal 20 may apply the DUDe method to communicate with the macro cell base station 10A and the small cell base station 10B by setting dual connectivity between the macro cell base station 10A and the small cell base station 10B and then changing the setting of the radio bearer.

[0051] Here, assume a situation where DUDe is applied in a space such as a factory or a warehouse where a large shield moves quasi-statically or dynamically. For example, as shown in FIG. 11, assume that a shield is placed between the terminal 20 and the small cell base station 10B, and line-of-sight communication becomes impossible. Also, assume that the RIS 30 is arranged on the ceiling and there are no shields between the terminal 20 and the RIS 30, and between the RIS 30 and the small cell base station 10B.

[0052] In the example of FIG. 11, the incident wave from the terminal 20 is incident on the RIS 30 and reflected by the RIS 30. In this case, by adjusting the traveling direction of the reflected wave by the RIS 30, it is possible to optimize (maximize) the received power of the uplink signal from the terminal 20 at the small cell base station 10B. Additionally or alternatively, by changing the traveling direction of the reflected wave by the RIS 30, it is possible to switch the small cell base station 10B communicating with the terminal 20 to another small cell base station 10B.

[0053] FIG. 9 is a diagram showing an example in which the terminal 20 applies the DUDe method to communicate with the macro cell base station 10A and the small cell base station 10B. In the example of FIG. 9, the uplink communication between the terminal 20 and the small cell base station 10B is relayed by the RIS 30. In the example of FIG. 9, as shown in FIG. 11, when the RIS 30 reflects the incident wave from the terminal 20, the RIS 30 controls the reflection direction of the reflected wave according to the instruction signal from the small cell base station 10B. The RIS 30 may control the reflection direction of the reflected wave so that the received power of the uplink signal (reflected wave from the RIS 30) from the terminal 20 at the small cell base station 10B is optimized (maximized). Additionally or alternatively, the RIS 30 may optimize the uplink communication by controlling the reflection direction of the reflected wave to switch the small cell base station 10B communicating with the terminal 20 to another small cell base station 10B.

[0054] For example, assume that RIS 30 can select any one of directions 1, 2, …, n as the reflection direction of the reflected wave. The small cell base station 10B instructs RIS 30 to reflect a predetermined reference signal from the terminal 20 in the corresponding directions 1, 2, …, n at times 1, 2, …, n. The small cell base station 10B compares the received power values 1, 2, …, n of the reference signals received at times 1, 2, …, n, and may instruct RIS 30 as to the direction corresponding to the maximum received power value among these received power values.

[0055] As another example, assume that another small cell base station 10B is arranged in the vicinity of the small cell base station 10B that is communicating with the terminal 20. Assume that the small cell base station 10B and another small cell base station 10B can communicate via the X2 interface. The small cell base station 10B that is communicating with the terminal 20 instructs RIS 30 to reflect a predetermined reference signal from the terminal 20 in the corresponding directions 1, 2, …, n at times 1, 2, …, n. The small cell base station 10B compares the received power values 1A, 2A, …, nA of the reference signals received by the small cell base station 10B itself at times 1, 2, …, n with the received power values 1B, 2B, …, nB of the reference signals received by another small cell base station 10B, and identifies the maximum received power value among the received power values 1A, 2A, …, nA and the received power values 1B, 2B, …, nB.

[0056] When the small cell base station 10B receives a reference signal corresponding to the specified maximum received power value at the small cell base station 10B itself, the communication destination with the terminal 20 may remain the small cell base station 10B, and the direction with respect to the maximum received power value may be indicated to the RIS 30. When another small cell base station 10B receives a reference signal corresponding to the specified maximum received power value, the small cell base station 10B may indicate the direction with respect to the maximum received power value to the RIS 30 and also instruct the terminal 20 to change the communication destination of the terminal 20 to another small cell base station 10B. In the above example, it is assumed that two small cell base stations 10B are arranged near the terminal 20, but the embodiments of the present invention are not limited to this example. For example, three or more small cell base stations 10B may be arranged near the terminal 20.

[0057] FIG. 10 is a diagram showing an example of UL performance when RIS is applied to the UL of DUDe. As described above, the communication between the terminal 20 and the small cell base station 10B is relayed by the RIS 30, and at this time, by controlling the reflection direction of the carrier wave carrying the signal from the terminal 20 by the RIS 30, it is possible to optimize (maximize) the received power of the uplink signal from the terminal 20 at the small cell base station 10B. In the example of FIG. 10, compared with the example of FIG. 7, the received power of the uplink signal from the terminal 20 at the small cell base station 10B is higher in the case of UL-DL imbalance.

[0058] As described above, when RIS is applied to the UL of DUDe, the terminal 20 can always be connected to an optimal base station in both the uplink and the downlink. In particular, in an environment with a lot of shielding, it is possible to offload UL traffic to an optimal small cell base station 10B near the terminal 20. It is possible to improve the overall communication speed of the DL and UL of the terminal 20 placed in a shielding environment (and an area where UL-DL imbalance occurs) and effectively increase the throughput of the system. Note that the received power may be calculated based on the path loss in free space.

[0059] FIG. 12 is a flowchart for explaining an example of a processing procedure executed in a wireless communication system.

[0060] In step S110, the macro cell base station 10A receives a measurement report from the terminal 20. The measurement report includes information indicating the received power values of signals from base stations (including the macro cell base station 10A and the small cell base station 10B) placed in the vicinity of the terminal 20.

[0061] In step S120, communication between the macro cell base station 10A and the terminal 20 is set up. In step S130, the macro cell base station 10A schedules downlink communication for the terminal 20.

[0062] If it is shown in the measurement report received by the macro cell base station 10A in step S110 that the received power value from the small cell base station 10B is greater than a predetermined threshold, the macro cell base station 10A determines to set up uplink communication between the terminal 20 and the small cell base station 10B. In step S140, the macro cell base station 10A notifies the terminal 20 that uplink communication between the terminal 20 and the small cell base station 10B will be set up.

[0063] Next, in step S210 of FIG. 12, the macro cell base station 10A transmits a Small Cell base station (SCBS) addition request to the small cell base station 10B. In step S220, the small cell base station 10B transmits an SCBC Addition request acknowledgement as a positive response to the Small Cell base station addition request.

[0064] In step S220, in response to receiving an affirmative response to the request for addition of the small cell base station 10B, the macro cell base station 10A transmits, in step S230, Radio Resource Control (RRC) Connection reconfiguration for UL, which is configuration information for changing the uplink communication setting of the terminal 20, to the terminal 20.

[0065] In step S230, in response to receiving RRC Connection reconfiguration for UL, in step S240, the terminal 20 transmits RRC Connection reconfiguration complete for UL to the macro cell base station 10A. In step S240, in response to receiving RRC Connection reconfiguration complete for UL, in step S250, the macro cell base station 10A transmits SCBS Reconfiguration complete to the small cell base station 10B.

[0066] Next, in step S310 of FIG. 12, a random access procedure is executed between the terminal 20 and the small cell base station 10B. After the uplink communication between the terminal 20 and the small cell base station 10B is configured in step S310, the small cell base station 10B performs a reconfiguration for relaying the uplink communication between the terminal 20 and the small cell base station 10B by the RIS 30.

[0067] In step S320, the terminal 20 transmits an uplink scheduling request to the small cell base station 10B. In step S330, the small cell base station 10B performs scheduling for the terminal 20. In this case, the small cell base station 10B may determine to relay the uplink communication with the terminal 20 to the RIS 30. Additionally, the small cell base station 10B may set the configuration information including the phase and timing information to be transmitted to the RIS 30 so that the received power of the signal from the terminal 20 reflected by the RIS 30 is optimized (maximized) at the small cell base station 10B.

[0068] In step S340, the small cell base station 10B transmits the configuration information including the phase and timing information to the RIS 30. The RIS 30 may adjust the direction of reflecting the carrier wave of the signal from the terminal 20 based on the received phase and timing information. In step S350, the small cell base station 10B transmits a UL scheduling grant to the terminal 20. At this time, the small cell base station 10B may transmit the UL scheduling grant to the terminal 20 via the RIS 30. The UL scheduling grant may include information specifying the resources (time and frequency domain resources) for transmitting the signal from the terminal 20 to the small cell base station 10B via the RIS 30.

[0069] Thereafter, in step S360, the terminal 20 performs UL transmission to the RIS 30, and in step S370, the RIS 30 relays the UL transmission from the terminal 20 to the small cell base station 10B.

[0070] As described above, according to the embodiment, by applying the RIS 30 to the UL of the DUDe, the overall communication rate of the DL and UL of the terminal 20 can be improved. Therefore, the throughput of the wireless communication system can be effectively increased.

Description of Reference Numerals

[0071] 10A Macro cell base station 10B Small Cell Base Station 20 Terminal 30 RIS 40 Network 110 Transmitter 120 Receiver 130 Control Unit 210 Transmitter 220 Receiver 230 Control Unit 310 Transmitter 320 Receiver 330 Control Unit 340 Element 100 Drive Device 101 Recording Medium 102 Auxiliary Storage Device 103 Memory Device 104 CPU 105 Interface Device B Bus

Claims

1. A terminal that communicates with a first base station and a second base station, comprising: a receiving unit that receives a first downlink signal from the first base station and a second downlink signal from the second base station; a transmitting unit that transmits a first uplink signal to the first base station and a second uplink signal to the second base station; a processor that, when a first received power of the first downlink signal at the terminal is greater than a second received power of the second downlink signal at the terminal and a third received power of the first uplink signal at the first base station is less than or equal to a fourth received power of the second uplink signal at the second base station, establishes a downlink connection with the first base station and an uplink connection with the second base station; and in response to the receiving unit receiving an indication signal from the second base station, the processor changes the uplink connection with the second base station to an uplink connection with the second base station via a relay device; the relay device is a Reconfigurable Intelligent Surface (RIS) including a plurality of reflecting elements and capable of changing a traveling direction of a reflected wave; the second base station transmits configuration information including phase and timing information to the relay device; the transmitting unit transmits an uplink signal to the second base station via the relay device based on information received from the second base station and designating time and frequency resources for transmitting to the second base station via the relay device; a terminal.

2. The transmitting unit transmits a scheduling request for uplink transmission to the second base station, and the receiving unit receives uplink transmission scheduling information from the second base station. The terminal according to Claim 1.

3. A communication method executed by a terminal that communicates with a first base station and a second base station, the method comprising: receiving a first downlink signal from the first base station and a second downlink signal from the second base station; transmitting a first uplink signal to the first base station and a second uplink signal to the second base station; When the first received power of the first downlink signal at the terminal is greater than the second received power of the second downlink signal at the terminal, and the third received power of the first uplink signal at the first base station is less than or equal to the fourth received power of the second uplink signal at the second base station, a step of establishing a downlink connection with the first base station and an uplink connection with the second base station; having; The step of performing the uplink setting, in response to receiving an instruction signal from the second base station, changes the uplink connection with the second base station to an uplink connection with the second base station via a relay device; The relay device includes a plurality of reflecting elements and is a Reconfigurable Intelligent Surface (RIS) capable of changing the propagation direction of reflected waves; The second base station transmits configuration information including phase and timing information to the relay device; The terminal transmits an uplink signal to the second base station via the relay device based on information received from the second base station and specifying time and frequency resources for transmission to the second base station via the relay device; Communication method.

4. A wireless communication system comprising a first base station, a second base station, a relay device, and a terminal that communicates with the first base station and the second base station, The first base station, A first transmission unit that transmits a first downlink signal to the terminal; A first reception unit that receives a first uplink signal from the terminal; having; The second base station, A second transmission unit that transmits a second downlink signal to the terminal; A second reception unit that receives a second uplink signal from the terminal; having; The terminal, A reception unit that receives the first downlink signal from the first base station and the second downlink signal from the second base station; A transmission unit that transmits the first uplink signal to the first base station and the second uplink signal to the second base station; A processor that, when the first received power of the first downlink signal at the terminal is greater than the second received power of the second downlink signal at the terminal and the third received power of the first uplink signal at the first base station is less than or equal to the fourth received power of the second uplink signal at the second base station, establishes a downlink connection with the first base station and an uplink connection with the second base station, having, in response to the receiving unit receiving an instruction signal from the second base station, the processor changes the uplink connection with the second base station to an uplink connection with the second base station via a relay device, wherein the relay device includes a plurality of reflection elements and is a Reconfigurable Intelligent Surface (RIS) capable of changing the propagation direction of reflected waves, the second base station transmits configuration information including phase and timing information to the relay device, the transmitting unit transmits an uplink signal to the second base station via the relay device based on information received from the second base station and specifying time and frequency resources for transmission to the second base station via the relay device, a wireless communication system.

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