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 technology]

[0002] The fifth generation mobile communication system (5G (Above-6GHz)) uses a high frequency band called the millimeter wave band in addition to conventional frequency bands. Generally, radio waves in the high frequency band called Above-6, such as the 28GHz band that can be used for 5G and local 5G, have a large attenuation over distance, so long-distance transmission is achieved by using ultra-high gain beamforming transmission technology. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US 9,620,862 [Non-patent literature]

[0004] [Non-Patent Document 1] W. Tang et al., “Wireless Communications With Reconfigurable Intelligent Surface: Path Loss Modeling and Experimental Measurement,” in IEEE Transactions on Wireless Communications, vol. 20, no. 1, pp. 421-439, Jan. 2021. [Non-Patent Document 2] Y. Ramamoorthi and A. Kumar, "Dynamic Time Division Duplexing for Downlink / Uplink Decoupled Millimeter Wave-Based Cellular Networks," in IEEE Communications Letters, vol. 23, no. 8, pp. 1441-1445, Aug. 2019 [Non-Patent Document 3] S. Singh, X. Zhang, and JG Andrews, “Joint rate and SINR coverage analysis for decoupled uplink-downlink biased cell associations in HetNets,” IEEE Trans. Wireless Commun., vol. 14, no. 10, pp. 5360-5373, Oct. 2015. [Non-Patent Document 4] 3GPP, Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and NR; Multi-connectivity;, Tech. Rep. TR 37.740 v16.5.0, 2021. Summary of the Invention [Problem to be solved by the invention]

[0005] Here, we consider a situation in which downlink and uplink decoupling (DUDe) is applied to separate uplink (UL) and downlink (DL) in spaces where large obstructions move quasi-statically or dynamically, such as inside a factory or warehouse.

[0006] In this case, because radio waves in the high frequency bands described above tend to travel in a very straight line and are subject to significant loss due to obstructions, there is a need to improve the performance of uplink transmissions from terminals.

[0007] The present invention has been made in view of the above-mentioned points, and has an object to improve the performance of uplink transmission from a terminal. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided a terminal for communicating 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; and a processor that, when a first reception power of the first downlink signal at the terminal is greater than a second reception power of the second downlink signal at the terminal and a third reception power of the first uplink signal at the first base station is equal to or less than a fourth reception 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, in response to the receiving unit 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. Effect of the Invention

[0009] According to the embodiment, it is possible to improve the performance of uplink transmission from a terminal. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. [Diagram 2] FIG. 2 is a diagram illustrating an example of a functional configuration of a base station. [Diagram 3]FIG. 2 is a diagram illustrating an example of a functional configuration of a terminal. [Figure 4] FIG. 1 is a diagram illustrating an example of the functional configuration of a Reconfigurable Intelligent Surface (RIS). [Diagram 5] FIG. 2 is a diagram showing an example of a plurality of elements included in a RIS. [Figure 6] A diagram showing an example of the hardware configuration of a base station, a terminal, and a RIS. [Figure 7] FIG. 1 illustrates an example of UL-DL imbalance. [Figure 8] FIG. 13 is a diagram illustrating an example of a DUDe. [Figure 9] FIG. 13 is a diagram showing an example of applying RIS to the UL of DUDe. [Figure 10] FIG. 13 is a diagram showing an example of UL performance when RIS is applied to the UL of DUDe. [Figure 11] FIG. 13 is a diagram showing an example of applying RIS to the UL of DUDe. [Figure 12] 11 is a flowchart illustrating an example of a processing procedure of a wireless system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Reconfigurable Intelligent Surface (RIS) is an effective method to control the channel by appropriately adjusting the phase and amplitude of the electromagnetic signal. Various architectures and multiple access techniques have been proposed in recent research and experiments.

[0012] It is expected that future heterogeneous networks will use multi-connectivity, and it is important to consider that terminals (which may be user equipment) are connected to multiple transmission points (TPs). However, under such circumstances, there is a problem of transmission power imbalance caused by differences in the transmission power of multiple deployed base stations. One way to correct this is to split the uplink (UL) and downlink (DL) associations. This is called UL / DL split in the standard, and was later developed into the uplink and downlink separation method (DUDe).

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an example of the configuration of a wireless communication system in an embodiment. As shown in FIG. 1, the wireless communication system includes a macrocell base station 10A, a small cell base station 10B, a terminal 20, a Reconfigurable Intelligent Surface (RIS) 30, and a network 40. The macrocell base station 10A and the small cell base station 10B are connected to the network 40 by wire or wirelessly. The macrocell base station 10A and the small cell base station 10B are connected to each other so that they can communicate with each other, for example, via an X2 interface. The small cell base station 10B and the RIS 30 are connected to each other so that they can communicate with each other, 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 embodiment of the present invention is not limited to this example. For example, the RIS 30 may be connected to the macrocell base station 10A. The macrocell base station 10A, the small cell base station 10B, and the terminal 20 are all capable of transmitting and receiving signals by performing beamforming.

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

[0015] The terminal 20 can communicate with the macrocell base station 10A and the small cell base station 10B simultaneously by setting dual connectivity between the macrocell 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, it is assumed that the RIS 30 relays communication between the small cell base station 10B and the terminal 20, but the embodiment of the present invention is not limited to this example. For example, the RIS 30 may relay communication between the macrocell 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 a signal from the terminal 20 to the small cell base station 10B by changing the reflection direction of a carrier wave carrying the signal from the terminal 20 according to setting information from the small cell base station 10B.

[0017] 1 illustrates only one each of the macro cell base station 10A, the small cell base station 10B, the terminal 20, and the RIS 30, but the embodiment of the present invention is 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 RIS 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, each of the macro cell base station 10A and the small cell base station 10B has a transmitting unit 110, a receiving unit 120, and a control unit 130. The functional configuration shown in Fig. 2 is merely an example. The functional divisions and names of the functional units may be any names as long as they can execute the operations according to the present embodiment.

[0019] The transmitter 110 creates a transmission signal from transmission data and transmits the transmission signal wirelessly. The receiver 120 wirelessly receives various signals and acquires a higher layer signal from the received physical layer signal. The receiver 120 also includes a measurement unit that measures the received signal and acquires the received power, etc.

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

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

[0022] The transmitter 210 includes a function of generating a signal to be transmitted to the base station (macrocell base station 10A and / or small cell base station 10B) and transmitting the signal wirelessly. The receiver 220 includes a function of receiving various signals transmitted from the base station (macrocell base station 10A and / or small cell base station 10B) and acquiring, for example, information of a higher layer from the received signal. The receiver 220 also includes a measurement unit that measures the received signal and acquires the received power, etc.

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

[0024] Fig. 4 is a diagram showing an example of the functional configuration of RIS 30. As shown in Fig. 4, RIS 30 has a transmitting unit 310, a receiving unit 320, a control unit 330, and a plurality of elements 340. The functional configuration shown in Fig. 4 is merely an example. The functional divisions and names of the functional units may be any names as long as they can execute the operations according to this embodiment.

[0025] The transmitter 310 has a function of generating a signal to be transmitted to the base station (macrocell base station 10A and / or small cell base station 10B) and transmitting the signal by wire and / or wirelessly. The receiver 320 has a function of receiving various signals transmitted from the base station (macrocell base station 10A and / or small cell base station 10B) and acquiring, for example, information of a higher layer from the received signal.

[0026] The control unit 330 controls the RIS 30. The multiple elements 340 have a function of changing the reflection direction of a carrier wave carrying a signal from the terminal 20. The control unit 330 has a function of controlling the reflection phase (or reflection direction) of a reflected wave reflected by each element 340 of the multiple 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 orientation of the reflecting element of each element 340 of the multiple elements 340.

[0027] The elements 340 may be configured as a reflect array, for example. FIG. 5 is a diagram showing an example of the elements 340 as a reflect array. When the elements 340 are configured as a reflect array, for example, by changing the element interval between the elements 340, it is possible to change the reflection phase of the reflected wave and change the traveling direction of the reflected wave. The method of changing the reflection phase of the reflected wave is not limited to changing the element interval, and may be performed by changing the impedance of each element 340 among the elements 340. Additionally or alternatively, each element 340 among the elements 340 may include a reflecting element for changing the reflection direction of the incident wave, and the reflection direction of the reflected wave may be changed by changing the orientation of the reflecting element. For example, the reflecting element may include an actuator using Micro Electro Mechanical Systems (MEMS), and the reflection direction of the reflected wave may be controlled by controlling the voltage applied to the piezoelectric material forming the actuator.

[0028] 2 to 4 show functional unit blocks. These functional blocks (components) are realized by any combination of at least one of hardware and software. There are no particular limitations on the method of realizing each functional block. That is, each functional block may be realized by using one device that is physically or logically coupled, or may be realized by using two or more devices that are physically or logically separated and directly or indirectly connected (for example, by using wires, wirelessly, etc.) and these multiple devices.

[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 processing according to this embodiment. FIG. 6 is a diagram showing an example of a 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 among the macrocell base station 10A, the small cell base station 10B, the terminal 20, and the RIS 30 may be physically configured as a computer device having a drive device 100, an auxiliary storage device 102, a memory device 103, a CPU 104, an interface device 105, and the like. The drive device 100, the auxiliary storage device 102, the memory device 103, the CPU 104, and the interface device 105, and the like, are each connected to each other by a bus B.

[0030] In the computer device, a program for implementing processing is provided by a recording medium 101 such as a CD-ROM. When the recording medium 101 storing the program is set in the drive device 100, the program is installed from the recording medium 101 to the auxiliary storage device 102 via the drive device 100. However, the program does not necessarily have to be installed from the recording medium 101, but may be downloaded from another computer via a network. The auxiliary storage device 102 stores the installed program as well as necessary files, data, etc.

[0031] When an instruction to start a program is received, the memory device 103 reads out the program from the auxiliary storage device 102 and stores it. The CPU 104 executes functions related to the computer device in accordance with the program stored in the memory device 103. The interface device 105 is used as an interface for connecting to a network.

[0032] (UL-DL imbalance)

[0033] 7 is a diagram showing an example in which a terminal 20 is placed between a macro cell base station 10A and a 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, the reception power when the terminal 20 receives a downlink signal from the macrocell base station 10A is defined as reception power A. The power when the terminal 20 receives a downlink signal from the small cell base station 10B is defined as reception power B. The reception power when the macrocell base station 10A receives an uplink signal from the terminal 20 is defined as reception power C. The reception power when the small cell base station 10B receives an uplink signal from the terminal 20 is defined as reception 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, are possible.

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

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

[0038] State 3: When the received power A is less than the received power B and the received power C is less than the received power D, the state is set to state 3.

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

[0040] Furthermore, in state 1, the reception power C at which the macrocell base station 10A receives an uplink signal from the terminal 20 is equal to or greater than the reception power D at which the small cell base station 10B receives an uplink signal from the terminal 20. Therefore, in state 1, it is efficient for the terminal 20 to connect to the macrocell base station 10A via uplink.

[0041] That is, in the case of state 1, it is efficient for the terminal 20 to establish a connection with the macrocell base station 10A in both the uplink and the downlink.

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

[0043] Furthermore, in state 3, the reception power C at which the macrocell base station 10A receives an uplink signal from the terminal 20 is less than the reception power D at which the small cell base station 10B receives an uplink signal from the terminal 20. Therefore, in 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 state 3, it is efficient for the terminal 20 to connect to the small cell base station 10B in the uplink and downlink.

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

[0046] Furthermore, in state 2, the reception power C at which the macrocell base station 10A receives an uplink signal from the terminal 20 is less than the reception power D at which the small cell base station 10B receives an uplink signal from the terminal 20. Therefore, in 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 in which the received power from the macrocell base station 10A is large in the downlink and the received power from the small cell base station 10B is large in the uplink, as in state 2, is called UL-DL imbalance. In the case of UL-DL imbalance, Downlink and Uplink Decoupling (DUDe), which separates UL and DL, can be applied as a method of improving communication efficiency.

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

[0050] 8 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. 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 settings of the radio bearer.

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

[0052] 11, an incident wave from the terminal 20 is incident on the RIS 30 and is 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 communicates with the macro cell base station 10A and the small cell base station 10B by applying the DUDe method. In the example of FIG. 9, 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 an incident wave from the terminal 20, the RIS 30 controls the reflection direction of the reflected wave in response to an instruction signal from the small cell base station 10B. The RIS 30 may control the reflection direction of the reflected wave so that the reception power of the uplink signal from the terminal 20 (the reflected wave from the RIS 30) at the small cell base station 10B is optimized (maximized). Additionally or alternatively, the RIS 30 may optimize the uplink communication by switching the small cell base station 10B communicating with the terminal 20 to another small cell base station 10B by controlling the reflection direction of the reflected wave.

[0054] For example, assume that the RIS 30 can select any one of direction 1, direction 2, ..., direction n as the reflection direction of a reflected wave. The small cell base station 10B instructs the RIS 30 to reflect a predetermined reference signal from the terminal 20 in the corresponding direction 1, direction 2, ..., direction n at time 1, time 2, ..., time n. The small cell base station 10B may compare the received power value 1, received power value 2, ..., received power value n of the reference signal received at time 1, time 2, ..., time n, and instruct the RIS 30 on 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 placed near a small cell base station 10B in communication with a terminal 20. Assume that the small cell base station 10B and the other small cell base station 10B are capable of communicating with each other via an X2 interface. The small cell base station 10B in communication with the terminal 20 instructs the RIS 30 to reflect a predetermined reference signal from the terminal 20 in the corresponding directions 1, 2, ..., and n at times 1, 2, ..., and n. The small cell base station 10B compares received power value 1A, received power value 2A, ..., received power value nA of a reference signal received by the small cell base station 10B itself at time 1, time 2, ..., time n with received power value 1B, received power value 2B, ..., received power value nB of a reference signal received by another small cell base station 10B, and identifies the maximum received power value among received power value 1A, received power value 2A, ..., received power value nA and received power value 1B, received power value 2B, ..., received power value nB.

[0056] When the small cell base station 10B itself receives a reference signal corresponding to the specified maximum received power value, the small cell base station 10B may keep the communication destination with the terminal 20 at the small cell base station 10B and instruct the RIS 30 on the direction of the maximum received power value. When the small cell base station 10B receives a reference signal corresponding to the specified maximum received power value at another small cell base station 10B, the small cell base station 10B may instruct the RIS 30 on the direction of the maximum received power value and 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 embodiment of the present invention is 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 UL of DUDe. As described above, by relaying communication between the terminal 20 and the small cell base station 10B by the RIS 30 and controlling the reflection direction by the RIS 30 of the carrier wave carrying the signal from the terminal 20, 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, 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 compared to the example of Fig. 7.

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

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

[0060] In step S110, the macrocell base station 10A receives a measurement report from the terminal 20. The measurement report includes information indicating the received power value of a signal from a base station (including the macrocell base station 10A and the small cell base station 10B) located near the terminal 20.

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

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

[0063] 12, the macro cell base station 10A transmits a request for adding the small cell base station 10B (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 acknowledgement (SCBC Addition request acknowledgement) to the request for adding the small cell base station 10B.

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

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

[0066] 12, a random access procedure is executed between the terminal 20 and the small cell base station 10B. After uplink communication between the terminal 20 and the small cell base station 10B is set in step S310, the small cell base station 10B performs reconfiguration so that the uplink communication between the terminal 20 and the small cell base station 10B is relayed 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 decide to have the RIS 30 relay uplink communication with the terminal 20. Additionally, the small cell base station 10B may set configuration information including phase and timing information to be transmitted to the RIS 30 so that the received power at the small cell base station 10B of the signal from the terminal 20 reflected by the RIS 30 is optimized (maximized).

[0068] In step S340, the small cell base station 10B transmits configuration information including phase and timing information to the RIS 30. The RIS 30 may adjust the direction in which the carrier wave of the signal from the terminal 20 is reflected 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 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, it is possible to improve the overall communication rates of the DL and UL of the terminal 20. Therefore, it is possible to effectively increase the throughput of the wireless communication system. [Explanation of symbols]

[0071] 10A Macrocell base station 10B Small cell base station 20 Terminals 30 RIS 40 Network 110 Transmitter 120 Receiving unit 130 Control section 210 Transmitter 220 Receiving unit 230 Control Unit 310 Transmitter 320 Receiving unit 330 Control Unit 340 Elements 100 Drive device 101 Recording media 102 Auxiliary storage device 103 Memory device 104 CPU 105 Interface device B Bus

Claims

1. A terminal communicating with a first base station and a second base station, a receiver for receiving a first downlink signal from the first base station and a second downlink signal from the second base station; a transmitter for transmitting a first uplink signal to the first base station and a second uplink signal to the second base station; a processor that establishes a downlink connection with the first base station and an uplink connection with the second base station when a first reception power of the first downlink signal at the terminal is greater than a second reception power of the second downlink signal at the terminal and a third reception power of the first uplink signal at the first base station is equal to or less than a fourth reception power of the second uplink signal at the second base station; having In response to the receiving unit receiving the instruction signal from the second base station, the processor changes an uplink connection with the second base station to an uplink connection with the second base station via a relay device. Terminal.

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

3. The transmitter transmits a scheduling request for uplink transmission to the second base station; The receiving unit receives uplink transmission scheduling information including setting information of a phase or a transmission timing for the uplink transmission from the second base station. The terminal according to claim 1.

4. the transmitting unit transmits an uplink signal to the second base station via the relay device based on the scheduling information of the uplink transmission, the scheduling information including the setting information of the phase or the transmission timing received from the second base station; The terminal according to claim 3.

5. A communication method performed by a terminal communicating with a first base station and a second base station, 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 a first reception power of the first downlink signal at the terminal is greater than a second reception power of the second downlink signal at the terminal and a third reception power of the first uplink signal at the first base station is equal to or less than a fourth reception power of the second uplink signal at the second base station, establishing a downlink connection with the first base station and an uplink connection with the second base station; having the step of setting up the uplink includes changing an uplink connection with the second base station to an uplink connection with the second base station via a relay device in response to receiving an instruction signal from the second base station; Communication methods.

6. A wireless communication system including 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 transmitter for transmitting a first downlink signal to the terminal; a first receiving unit for receiving a first uplink signal from the terminal; having The second base station a second transmitter for transmitting a second downlink signal to the terminal; a second receiving unit for receiving a second uplink signal from the terminal; having The terminal includes: a receiver for receiving the first downlink signal from the first base station and the second downlink signal from the second base station; a transmitter for transmitting the first uplink signal to the first base station and the second uplink signal to the second base station; a processor that establishes a downlink connection with the first base station and an uplink connection with the second base station when a first reception power of the first downlink signal at the terminal is greater than a second reception power of the second downlink signal at the terminal and a third reception power of the first uplink signal at the first base station is equal to or less than a fourth reception power of the second uplink signal at the second base station; having In response to the receiving unit receiving the instruction signal from the second base station, the processor changes an uplink connection with the second base station to an uplink connection with the second base station via a relay device. Wireless communication system.

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