Communication system, base station, terminal, and communication method

Abstract

To improve the communication efficiency of a terminal that communicates in an environment with relatively high propagation loss in a wireless communication network using non-orthogonal multiple access.SOLUTION: In a communication system, a plurality of terminals are connected to a base station by non-orthogonal multiple access. The plurality of terminals in the communication system include a relay terminal that relays uplink communication data to the base station and a relayed terminal that transmits uplink communication data to the base station via the relay terminal. The relay terminal transmits, to the base station, superimposed data obtained, by superimposing the uplink communication data from the relayed terminal on uplink communication data based on a communication request generated in the relay terminal.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a communication system, a base station, a terminal, and a communication method. [Background technology]

[0002] There is a demand for wireless access technology that can achieve both low latency and multiple connections. Among these, there is hope for the use of technology that relaxes the orthogonality of wireless signals in order to increase the number of terminals that can connect to a base station. This technology is called Non-Orthogonal Multiple Access (NORMA). In a wireless network, there may be cases where propagation loss between at least some of the terminals that can connect to a base station and the base station becomes relatively high. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] 3GPP TR 38.830, Study on NR coverage enhancements (Release 17), December 2020 [Non-patent document 2] Moriyama, et al. “Experimental Evaluation of a Novel Up-Link NOMA System for IoT Communication Equipping Repetition Transmission and Receive Diversity” IEICE TRANS. COMMUN. Aug. 2019 Vol.E102-B, No.8. p.1467-1476 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the embodiments of the present disclosure is to improve the communication efficiency of a terminal that communicates in an environment with relatively high propagation loss in a wireless communication network using non-orthogonal multiple access. [Means for solving the problem]

[0005] One aspect of the disclosed embodiment is exemplified by a communication system, a base station, a wireless terminal, and a communication method. In the communication system, multiple terminals are non-orthogonally multiple-accessed to a base station. In the communication system, the multiple terminals include a relay terminal that relays uplink communication data to the base station and a relayed terminal that transmits uplink communication data to the base station via the relay terminal. The relay terminal transmits superimposed data, which is obtained by superimposing uplink communication data from the relayed terminal on uplink communication data based on a communication request generated by the relay terminal, to the base station. However, other aspects of the disclosed embodiment are also exemplified by a base station included in the communication system. Other aspects of the disclosed embodiment are also exemplified by a terminal included in the communication system. Furthermore, other aspects of the disclosed embodiment are also exemplified by a method in a base station or a method in a terminal included in the communication system. [Effects of the Invention]

[0006] According to this information processing device, it is possible to improve the communication efficiency of a terminal that communicates in an environment with relatively high propagation loss in a wireless communication network using non-orthogonal multiple access. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram illustrating a communication system according to the first embodiment. [Figure 2] FIG. 2 is a diagram illustrating a hardware configuration of a base station. [Figure 3] FIG. 3 is a diagram illustrating the relay process performed by the relay station. [Figure 4] FIG. 4 is a diagram illustrating the effect of using a relay station. [Figure 5]FIG. 5 is a diagram illustrating an example of data flow on the uplink and downlink between the base station and the terminal. [Figure 6] FIG. 6 is a diagram illustrating a first communication method including a relayed station and a relay station. [Figure 7] FIG. 7 is a diagram illustrating a second communication method from a relayed station to a relay station. [Figure 8] FIG. 8 is a block diagram of the processing of a terminal other than a relay station. [Figure 9] FIG. 9 is a block diagram of the process of a relay station that does not perform non-orthogonal multiple access with a relayed station. [Figure 10] FIG. 10 is a block diagram of the base station processing. [Figure 11] FIG. 11 is a block diagram of the process of a relay station that performs non-orthogonal multiple access with a relayed station. [Figure 12] FIG. 12 is a flowchart illustrating a control procedure of the base station. [Figure 13] FIG. 13 is a diagram illustrating the selection of relay station candidates and relayed station candidates, the measurement of path loss between relay station candidates and relayed station candidates, and the selection process of relay stations and relayed stations. [Figure 14] FIG. 14 shows an example of a process for selecting candidates for a relay station and a candidate for a relayed station. [Figure 15] FIG. 15 shows a first example of a process for setting a propagation loss between a relay station and a relayed station. [Figure 16] FIG. 16 shows a second example of the process for setting the path loss between the relay station and the relayed station. [Figure 17] FIG. 17 is a diagram illustrating an example of setting of transmission power by a base station in transmission from a relayed station to a relay station. [Figure 18] FIG. 18 is a diagram illustrating an example of setting of transmission power by the base station in transmission from each terminal to the base station. [Figure 19] FIG. 19 is a diagram illustrating a method for updating the transmission power at the relay station. [Figure 20] FIG. 20 is a diagram illustrating a transmission power setting process for a relay station by a base station when the relay station has finished transmitting data on its own uplink line. [Figure 21] FIG. 21 is a diagram illustrating the processing of the base station when data transmission on the uplink of any of the relayed stations relayed by the relay station is completed. [Figure 22] FIG. 22 is a diagram illustrating an example of data flow on the uplink and downlink between the base station and the terminal in the second embodiment. [Figure 23] FIG. 23 is a diagram illustrating a method for searching for a relayed station. DETAILED DESCRIPTION OF THE INVENTION

[0008] A communication system, a base station, a terminal, and a communication method according to this embodiment will be described below with reference to the drawings. In this communication system, multiple terminals are connected to the base station via non-orthogonal multiple access. The multiple terminals include a relay terminal that relays uplink communication data from terminals other than the terminal itself to the base station, and a relayed terminal that transmits uplink communication data to the base station via the relay terminal. The relay terminal then transmits superimposed data, which is obtained by superimposing the uplink communication data from the relayed terminal on the uplink communication data based on a communication request generated by the relay terminal, to the base station.

[0009] First Embodiment (System Configuration) 1 is a diagram illustrating a communication system 100 according to the first embodiment. The communication system 100 includes a base station 1 and devices A, B, C, etc. that access a wireless network RN provided by the base station 1 for communication.

[0010] The wireless network RN is a communication network called, for example, Long Term Evolution (LTE), 5th Generation Mobile Communication System (5G), 6th Generation Mobile Communication System (6G), etc. The device A, etc., for example, Device A is a terminal that accesses N. Device A is a mobile phone, a smartphone, an in-vehicle communication device, etc. Other applications include communication devices mounted on drones, machine tools, various sensors, etc.

[0011] Devices A and the like are connected to base station 1 via non-orthogonal multiple access in wireless network RN. For example, uplink communication data from multiple devices, such as devices A, B, and C, are transmitted in a redundant manner on physical resources defined by time and frequency. However, there is a difference in reception power at base station 1 between the multiple devices' respective redundantly transmitted uplink communication data, exceeding a certain limit. That is, it can be said that FIG. 1 illustrates a communication system 100 in which multiple terminals are connected to a base station via non-orthogonal multiple access.

[0012] The base station 1 repeatedly performs successive interference canceller (SIC) processing on the uplink communication data that is received in duplicate by non-orthogonal multiple access. In this way, the base station 1 separates the uplink communication data from each of the multiple devices A, B, C, etc. In the example of FIG. In this example, base station 1 receives uplink communication data from multiple devices A, B, C, etc. in the same frequency region and in the same time slot. However, it is assumed that the received power of the signal received from device A is the largest, the received power of the signal received from device B is the second largest, and the received power of the signal received from device C is the smallest.

[0013] First, base station 1 measures the signal from device A, which has the highest received power, by Minimum Mean Square Error (MSE). The base station 1 performs equalization processing such as the MMSE (Multi-mode Signal-to-Noise Ratio) standard. Furthermore, the base station 1 demodulates and decodes the received data from the equalized signal. The base station 1 generates a replica of the signal from the device A received by the receiving antenna based on the demodulated and decoded received data from the device A. The base station 1 obtains the uplink communication data received in duplicate from the devices B, C, etc. excluding the device A by subtracting the replica from the above-mentioned redundantly transmitted uplink communication data. The base station 1 repeats this processing to separate the uplink communication data from each of the multiple devices A, B, C, etc. In the following embodiment, the multiple devices A, B, C, etc. are referred to as terminals 2. In the following embodiment, the multiple devices A, B, C, etc. are referred to as terminals 2-1, 2-2, 2-3, etc. In addition, when the terminals 2-1, etc. are collectively referred to as terminals 2, they are referred to as terminals 2. The number of terminals 2 is not limited to three.

[0014] 2 is a diagram illustrating a hardware configuration of the base station 1 according to the present embodiment. The base station 1 includes a processor 101, a memory 102, an internal interface 103, a network interface 104 for communicating with other base stations, and a wireless processing device 105.

[0015] The processor 101 is also called a Central Processing Unit (CPU) or a Microprocessor Unit (MPU). The processor 101 is not limited to a single processor, but may have a multi-processor configuration. The processor 101 may also have a multi-core configuration where a single physical CPU connected via a single socket is used. Furthermore, the processor 101 may be various other processors such as a Digital Signal Processor (DSP) or a Graphics Processing Unit (GPU). The processor 101 may include an arithmetic unit having various circuit configurations. The processor 101 may also cooperate with an integrated circuit (IC), other digital circuit, or analog circuit. The integrated circuit may include an LSI, an application specific integrated circuit (ASIC), or a programmable logic device (PLD). The PLD may include, for example, a field-programmable gate array (FPGA). Therefore, the processor 101 may be, for example, a microcontroller (MCU), a system-on-a-chip (SoC), a system LSI, It may also be called a chipset.

[0016] The memory 102 stores a sequence of instructions (computer program) executed by the processor 101, or data processed by the processor 101. The processor 101 and the memory 102 are sometimes called a baseband unit (BBU). The internal interface 103 is a circuit that connects various peripheral devices to the processor 101.

[0017] The network interface 104 is a communication device that enables the base station 1 to access a network to which other base stations are connected. The network to which other base stations are connected is also called a backhaul. The backhaul is, for example, a wired network using optical communication.

[0018] The radio processing device 105 includes a transmitter for transmitting radio signals and a receiver for receiving radio signals, and is connected to an antenna. The number of antennas, transmitters, and receivers in the radio processing device 105 is not limited to one. The radio processing device 105 may have N systems of these. The radio processing device 105 is called a remote radio head (RRH), and may be configured to be installed remotely by connecting to the baseband device via a wired network using optical communication, for example. Alternatively, multiple remote radio heads may be connected to one baseband device. The network connecting the baseband device and the remote radio heads is also called a fronthaul.

[0019] The hardware configuration of the terminal 2 has similar components to those of the base station 1 in Fig. 2. That is, the terminal 2 has a processor 101, a memory 102, an internal interface 103, and a wireless processing device 105. Since the hardware configuration of the terminal 2 is the same as that in Fig. 2, a description thereof will be omitted. However, in the terminal 2, the network interface 104 is not for connecting to a network to which other base stations are connected. For example, the terminal 2 may use a wireless local area network (LAN), Bluetooth, etc. to connect to devices other than the base station 1. (registered trademark), Bluetooth (registered trademark) Low Energy (BLE), or the like.

[0020] (Terminal relay function) Fig. 3 is a diagram illustrating the relay process by the relay station 2R. Here, it is assumed that terminals 2-1 to 2-5 are connected to the wireless network RN of the base station 1. The bar graph illustrated in graph G1 in the upper left of Fig. 2 illustrates the received power at the base station 1 relative to the noise floor (or noise level) of terminals 2-1 to 2-5. However, even between terminals 2-1 to 2-5, received signals from other terminals 2 act as interference signals for each received signal.

[0021] In graph G1, terminals 2-1 and 2-2 show a high signal-to-interference ratio (SIR) relative to interference signals from other terminals such as terminal 2-4. Naturally, terminals 2-1 and 2-2 also show a high signal-to-noise ratio (SNR) relative to the noise floor. On the other hand, the terminals 2-4 and 2-5 have only a low SNR relative to the noise floor. It can be assumed that the terminals 2-4 and 2-5 are in an environment with a large path loss (propagation loss), for example, at the cell edge of the wireless network RN or inside a tunnel.

[0022] On the other hand, graph G2 in the upper right illustrates, for example, the received power of signals received at terminal 2-3 from terminals 2-4 and 2-5. At base station 1, the transmitted signals from terminals 2-4 and 2-5 have only a low SNR, but at terminal 2-3, they have a certain degree of SNR.

[0023] In this embodiment, an attempt is made to improve transmission efficiency in such a communication environment. To this end, the communication system 100 uses a terminal 2-3 or the like in Fig. 3, which is not considered to be in an environment with a large path loss (propagation loss), as a relay station 2R (also called a relay terminal). That is, the communication system 100 selects a relay station 2R from a plurality of terminals 2, and performs transmission via the selected relay station 2R. Among the terminals 2 that communicate with the base station 1, the terminal 2 that communicates with the base station 1 via the relay station 2R is called a relayed station 2S. The relayed station 2S is also called a relayed terminal.

[0024] In this embodiment, the relay station 2R superimposes the transmission signal of the relayed station 2S on its own transmission signal (the transmission signal for which a transmission request has been issued by the relay station 2R) and transmits the superimposed signal. In this case, the relay station 2R reduces the transmission power of its own transmission signal by a predetermined limit ΔP and superimposes the transmission signal of the relayed station 2S on its own transmission signal. If there are multiple relayed stations 2S to be relayed, the relay station 2R sequentially reduces the transmission power by ΔP and superimposes the transmission signal of each relayed station 2S on its own transmission signal. By relaying in this manner, the base station 1 can receive received signals from terminals 2-4 and 2-5 in addition to received signals from terminals 2-1, 2-2, and 2-3. That is, as shown in graph G3 in FIG. 2, the base station 1 can ensure SIR between multiple terminals 2 using non-orthogonal multiple access and communicate with each terminal 2 with a sufficient SNR. Furthermore, the relaying in this embodiment allows relaying without changing the codeword length.

[0025] FIG. 4 is a diagram illustrating the effect of using a relay station 2R. In a wireless communication environment where the SNR is insufficient, a continuous transmission is performed in which the same signal (e.g., a packet) is repeatedly transmitted from a transmitting station to a receiving station. For example, the transmitting station repeatedly transmits the same signal in multiple time slots. This improves the SNR of the communication system 100. However, the more the number of continuous transmissions, the lower the transmission efficiency.

[0026] Figure 4 is a diagram comparing the number of time slots (number of consecutive transmissions) when the relay station 2R is not used and the number of time slots (number of relays and number of consecutive transmissions) when the relay station 2R is used. Both of these numbers of time slots can be obtained by simulation.

[0027] In both graphs in Figure 4, the horizontal axis represents the terminal ID (also called user ID) of terminal 2. The vertical axis is the number of time slots required for continuous transmission of one communication data. In the graph, the black circle is the minimum value of the number of continuous transmissions obtained in the simulation, the white circle is the maximum value, and the triangle mark is the average value. Of the two graphs in Figure 4, the left side shows the simulation results when there is no relay station, and the right side shows the simulation results when there is a relay station.

[0028] In the simulation of Figure 4, a sufficient SNR is set for terminal 2 with user IDs 1 to 4. In addition, terminal 2 with user IDs 5 and 6 is the same as terminals 2-4 and 2-5 in Figure 3. It is assumed that the relay station 2R is located at the edge of the cell, and a low SNR is set. As can be seen from the figure, the number of required time slots to achieve a desired SNR is significantly reduced by employing the relay station 2R.

[0029] FIG. 5 is a diagram illustrating an example of data flow on the uplink and downlink between a base station 1 and a terminal 2. The uplink is also called an uplink channel. The downlink is also called a downlink channel. FIG. 5 is a diagram illustrating a system in which a server collects data from sensors and the like. This system has a server connected to the base station 1, and sensors connected to a terminal station 2N, a relay station 2R, a relayed station 2S, and the like.

[0030] 5, the configurations of the base station 1, terminal station 2N, etc. are illustrated in a simplified manner. In Fig. 5, the radio equipment of the base station 1 and the radio equipment of the terminal station 2N, etc. correspond to the radio processing device 105 in Fig. 2. Also, the control device of the base station 1 and the control device of the terminal station 2N, etc. correspond to the processor 101 and memory 102 in Fig. 2. In this system, a sensor, etc. transmits information to a server connected to the base station 1 by a network via the terminal station 2N, relay station 2R, relayed station 2S, etc., via the base station 1.

[0031] The terminal station 2N is one of the terminals 2 that operates as both a relay station 2R and a relayed station 2S. A relay station 2R refers to a terminal 2 that relays uplink data of a relayed station 2S to the base station 1. A relayed station 2S refers to a terminal 2 whose uplink data to the base station 1 is relayed by a relay station 2R. In FIG. 5, the total number of terminals 2 is K, the number of relay stations 2R is Kr, the number of relayed stations 2S is Ks, and the number of terminal stations 2N is K-Kr-Ks.

[0032] 5 illustrates a case where the relayed station 2S is located within the cell of the base station 1, and communication is possible between the relayed station 2S and the base station 1 via an uplink control channel and a downlink control channel (also referred to as a control line) at least without relaying. Meanwhile, data on the uplink data channel (also referred to as a data line) transmitted from the relayed station 2S is once received by the relay station 2R. Then, the relay station 2R superimposes the transmission signal of the uplink data channel data received from the relayed station 2S on the transmission signal of the uplink data channel data generated by itself, and transmits the superimposed signal to the base station 1. Also, the terminal station N transmits the transmission signal of the uplink data channel data generated by itself to the base station 1 as usual.

[0033] 5, the physical resources defined by frequency and time are overlapped and used by multiple terminals 2. However, the base station 1 allocates at least one time slot to an uplink data channel from the relayed station 2S to the relay station 2R.

[0034] When relaying the signal of the uplink data channel of the relayed station 2S, the relay station 2R superimposes its own transmission signal on the transmission signal of the relayed station and transmits it. This is the same for the data signal and the reference signal. The reference signal x transmitted from the relay station 2R is RS,relay is expressed by the following formula: It is possible.

[0035]

number

[0036]

number

[0037] FIG. 6 is a diagram illustrating a first communication method including a relayed station 2S, a relay station 2R, and a base station 1 (BS). In FIG. 6, uplink data from the relayed station 2S to the relay station 2R is transmitted individually without non-orthogonal multiple access. FIG. 6 illustrates the allocation of time slots in this case. In FIG. 6, RS indicates the transmission of a reference signal, and DS indicates the transmission of a data signal. Furthermore, the numbers N->M shown before and after the arrows illustrate transmission from terminal 2-N to terminal 2-M. Furthermore, the numbers N and M in this case are terminal IDs. Furthermore, in FIG. 6, the "Uplink (Relay)" column illustrates the allocation of uplink transmission data from the relayed station 2S to the relay station 2R. Therefore, RS4->3 illustrates the transmission of a reference signal from terminal 2-4, which is the relayed station 2S, to terminal 2-3, which is the relay station 2R. DS4->3 illustrates the transmission of a data signal from terminal 2-4, which is the relayed station 2S, to terminal 2-3, which is the relay station 2R. In the example of Fig. 6, in the allocation of transmission data on the uplink from the relayed station 2S to the relay station 2R, one set of relayed station 2S and relay station 2R is allocated to one time slot, and there is no overlap.

[0038] On the other hand, in Figure 6, "uplink" illustrates transmission from relay station 2R to base station 1. In this case, the transmission of reference signals or data signals from multiple terminals 2-1, 2-2, and 2-3 to base station 1 is assigned to the same time slot in an overlapping manner. In Figure 6, RS1-3->BS indicates that the transmission of reference signals from terminals 2-1, 2-2, and 2-3 to base station 1 is performed in the same time slot. Also, DS1-3->BS indicates that the transmission of data signals from terminals 2-1, 2-2, and 2-3 to base station 1 is performed in the same time slot. In other words, multiple terminals 2-1, 2-2, 2-3, etc. perform non-orthogonal multiple access with base station 1.

[0039] FIG. 7 illustrates a second communication method from a relayed station 2S to a relay station 2R. In FIG. 7, the communication method from the relay station 2R to the base station 1 (BS) is the same as that in FIG. 6. In the second communication method, the allocation of uplinks from the relayed station 2S to the relay station 2R overlaps among multiple terminals 2. That is, the relayed station 2S performs non-orthogonal multiple access with the relay station 2R. In FIG. 7, data transmission of reference signals and data signals from terminals 2-4 and 2-5, which are relayed stations 2S, to terminal 2-3, which is relay station 2R, overlaps in the same time slot. In this case, the relay station 2R separates the non-orthogonally multiple-accessed received signals from the multiple relayed stations 2S using SIC. Then, the relay station 2R allocates a predetermined transmission power to the separated received signals from the multiple relayed stations 2S, superimposes them on transmission data generated by the relay station, and transmits them to the base station 1. The configuration in FIG. 7 can be considered an example of relay processing by a relay terminal that performs non-orthogonal multiple access with the multiple relayed terminals.

[0040] 8 is a block diagram of processing of a terminal 2 (terminal station 2N or relayed station 2S) other than the relay station 2R. A processor 101 of the relay station 2R executes processing as each component of FIG. 8 using a computer program executablely loaded in a memory 102. Processing by such a computer program is similar to that in FIGS. 9 to 11. As shown in FIG. 8, the terminal 2 operating as the terminal station 2N or relayed station 2S has an RS (reference signal) processing unit 21, a DS (data signal) processing unit 22, a reception processing unit 23, and an antenna 24.

[0041] The RS processing unit 21 generates a reference signal and transmits it to the base station 1 from the antenna 24. The RS processing unit 21 includes, for example, a sequence generation unit 211, an amplitude adjustment unit 212, and a cyclic prefix (CP) insertion unit 213. The sequence generation unit 211 generates, for example, a Zadoff-C A signal sequence is generated using an orthogonal sequence such as a hu sequence. The signal sequence generated by the sequence generation unit 211 is a sequence common to multiple terminals 2 that transmit simultaneously. Therefore, if this signal sequence is used as is, the reference signals of multiple terminals 2 will interfere with each other, so each terminal 2 uses a different signal sequence. Therefore, each terminal 2 cyclically shifts the signal sequence according to the terminal 2, thereby shifting the starting point of the signal sequence by a predetermined number of samples. Since the starting point of the signal sequence differs for each terminal 2, the reference signal used for each terminal 2 is The series will be different.

[0042] The amplitude adjustment unit 212 adjusts the amplitude of the reference signal to transmit it at the transmission power instructed by the base station 1. The base station 1 instructs each terminal 2 on its transmission power so that a predetermined power difference occurs between the received powers from each terminal 2. The CP insertion unit 213 sets a signal section called a cyclic prefix in each reference signal. This suppresses interference between reference signals due to signal delays.

[0043] The DS processing unit 22 has a Cyclic Redundancy Check (CRC) encoding unit 221, an error correction encoding unit 222, a modulation unit 223, an amplitude adjustment unit 224, and a CP insertion unit 225. The CRC encoding unit 221 adds a CRC error detection code to the data transmitted from the terminal 2. The error correction encoding unit 222 further performs error correction encoding on the data. The error correction code may be a block code or a convolutional code, and there is no limitation on the type of encoding. The modulation unit 223 modulates the error correction encoded data. The modulation is, for example, digital modulation, and there is no limitation on the modulation method. The modulation method is, for example, Quadrature Amplitude Modulation (QAM). Modulation (QAM), Phase Shift Keying (PSK), etc. The processing of the insertion unit 225 is similar to the processing of the amplitude adjustment unit 212 and the CP insertion unit 213 of the RS processing unit 21. The RS processing unit 21 and the DS processing unit 22 are connected to the antenna 24 by the switch SW1, for example, in a time-division manner. That is, the switch SW1 multiplexes the signal from the RS processing unit 21 and the signal from the DS processing unit 22. The function of the switch SW2 and the switches SW3 to SW8 shown in Figures 9 to 11 can also be said to be signal multiplexing.

[0044] The reception processing unit 23 has a CP removal unit 231, a propagation path estimation unit 232, a CP removal unit 233, a demodulation unit 234, an error correction decoding unit 235, and an error detection unit 236. A radio signal received by the antenna 24 is connected to the CP removal unit 231 or the CP removal unit 233 by a switch SW2, for example, in a time-division manner.

[0045] The CP removal unit 231 and the propagation path estimation unit 232 process a reference signal from the received signal received by the antenna 24. The CP removal unit 231 removes the CP from the reference signal. The propagation path estimation unit 232 calculates a propagation path estimate for the propagation path from the base station 1 to the terminal 2 based on the reference signal from which the CP has been removed. The propagation path estimate can be said to be the amount of fluctuation in the amplitude and phase of the radio signal on the propagation path from each base station 1 to the antenna 24 of the terminal 2.

[0046] The CP removal unit 233 through the error detection unit 236 process the data signal from the received signal. The CP removal unit 233 removes the CP from the data signal received by the antenna 24. The demodulation unit 234 demodulates the transmitted data based on the data signal from which the CP has been removed. The error correction decoding unit 235 performs error correction decoding on the demodulated data. The error detection unit 236 performs error detection on the decoded data using, for example, CRC.

[0047] In this embodiment, if the propagation loss to the base station 1 is greater than a certain threshold, the terminal 2 becomes a candidate for a relayed station and is selected as the relayed station 2S by the base station 1. The relayed station 2S transmits uplink data (also referred to as uplink communication data) to the base station 1 via the relay station 2R.

[0048] Fig. 9 is a block diagram of the process of a relay station 2RA that does not perform non-orthogonal multiple access with the relayed station 2S. Therefore, in Fig. 8, the relay station 2RA does not perform SIC process. In other words, the relay station 2R in Fig. 9 is not premised on receiving data from multiple relayed stations 2S in the same slot.

[0049] 9, relay station 2RA has RS processing section 21A, DS processing section 22A, reception processing section 23, switches SW3 and SW4, and antenna 24. Of these, the functions of reception processing section 23, switch SW4, and antenna 24 are similar to those of reception processing section 23, switch SW2, and antenna 24 in FIG. 8, and therefore description thereof will be omitted.

[0050] The RS processing unit 21A has, for example, a plurality of sequences, each of which is made up of a sequence generator 211 and an amplitude adjuster 212. A signal combiner 214 and a CP inserter 213 are connected downstream of these sequences. A first sequence of the plurality of sequences generates a reference signal for the local station and outputs it to the signal combiner 214. One or more second sequences are provided, which generate reference signals for one or more relayed stations and output them to the signal combiner 214. The signal combiner 214 adds the reference signals generated from the first and second sequences on the time axis and outputs the result to the CP inserter 225. The CP inserter 213 sets a cyclic prefix to the reference signal from the plurality of sequences combined by the signal combiner 214. The signal with the set cyclic prefix is then handed over by the switch SW3 to the transmitter of the radio processing device 105 (FIG. 2) and transmitted from the antenna 24 to the base station 1.

[0051] In this way, the reference signal from the multiple series combined by the signal combining unit 214 passes through the propagation path from the antenna 24 to the base station 1 and reaches the base station 1. The communication system 100 of this embodiment transmits a different reference signal for each relayed station 2S using the second series so that the base station 1 can identify the relayed station 2S. As a result, even when the reference signal is relayed by the relay station 2RA, the base station 1 determines from which relayed station 2S it is receiving the signal and how many terminals 2 it is receiving the signal from. In other words, even if the reference signal is transmitted from the relay station 2RA, the base station 1 can use the reference signal to identify the relay station 2RA and the relayed station 2S.

[0052] The DS processing unit 22A has, for example, multiple sequences, each including a CRC encoding unit 221, an error correction encoding unit 222, a modulation unit 223, and an amplitude adjustment unit 224. A signal combining unit 226 and a CP insertion unit 225 are connected downstream of these sequences. A first sequence among the multiple sequences generates a data signal for the local station and outputs it to the signal combining unit 226. One or more second sequences are provided, which process data signals from one or more relayed stations 2S and output them to the signal combining unit 226. The signal combining unit 226 adds the data signals from the first and second sequences on the time axis and outputs the result to the CP insertion unit 225. The CP insertion unit 225 sets a cyclic prefix to the data signal from the multiple sequences combined by the signal combining unit 226. The data signal with the set cyclic prefix is then handed over by the switch SW3 to the transceiver of the radio processing device 105 (FIG. 2) and transmitted to the base station 1 from the antenna 24.

[0053] In this way, the data signal from the multiple streams combined by the signal combiner 226 travels through a propagation path from the antenna 24 to the base station 1 and reaches the base station 1. The data signal from the multiple streams combined by the signal combiner 226 can be considered an example of superimposed data in which uplink communication data from the relayed terminal is superimposed on uplink communication data based on a communication request generated by the relay terminal 2R. In other words, the relay station 2RA in FIG. 9 can be considered an example of a relay terminal that relays uplink communication data to the base station 1. In other words, as an example of a relay terminal, the relay station 2RA transmits superimposed data in which uplink communication data from the relayed terminal is superimposed on uplink communication data based on a communication request generated by the relay station 2RA to the base station 1.

[0054] 10 is a block diagram of the processing of the base station 1. As shown in FIG. 10, the base station 1 includes an RS processing unit 11, a DS processing unit 12, a reception processing unit 13, switches SW5 and SW6, and an antenna 1. 8. RS processing unit 11 has, for example, a sequence generation unit 111 and a CP insertion unit 113. Sequence generation unit 111 and CP insertion unit 113 of RS processing unit 11 are similar to sequence generation unit 211 and CP insertion unit 213 of terminal 2 shown in FIG. 8. That is, although RS processing unit 11 of base station 1 does not have amplitude adjustment unit 212, its processing is similar to that of RS processing unit 21 of terminal 2, and therefore description thereof will be omitted.

[0055] The DS processing unit 12 has a CRC encoding unit 121, an error correction encoding unit 122, a modulation unit 123, and a CP insertion unit 125. The CRC encoding unit 121, the error correction encoding unit 122, the modulation unit 123, and the CP insertion unit 125 are similar to the error correction encoding unit 222, the modulation unit 223, and the CP insertion unit 225 of the terminal 2 illustrated in Fig. 8. That is, although the DS processing unit 12 of the base station 1 does not have an amplitude adjustment unit 224, its processing is similar to that of the DS processing unit 22 of the terminal 2, and therefore its description will be omitted. Furthermore, the processing of the switch SW5 is similar to that of the switch SW1 in Fig. 8, and therefore its description will be omitted.

[0056] The reception processing unit 13 includes a CP removal unit 131, a channel estimation unit 132, a CP removal unit 133, a demodulation unit 134, an error correction decoding unit 135, an error detection unit 136, a replica creation unit 137, and a replica removal unit 138. Furthermore, a radio signal received by the antenna 14 is connected to the CP removal unit 131 or the CP removal unit 133 by a switch SW6, for example, in a time-division manner. The CP removal unit 131, the channel estimation unit 132, and the CP removal unit 133 are similar to the CP removal unit 231, the channel estimation unit 232, and the CP removal unit 233 of the terminal 2 in FIG. 8. Meanwhile, the demodulation unit 134, the error correction decoding unit 135, the error detection unit 136, the replica creation unit 137, and the replica removal unit 138 of the base station 1 form a SIC loop that executes the SIC algorithm. That is, the reception processing unit 13 of the base station 1 differs from the terminal 2 in FIG. 8 in that it includes the replica creation unit 137 and the replica removal unit 138.

[0057] The demodulator 134 performs equalization processing on the received signal received by the antenna 14, and extracts the received signal from each terminal 2. That is, the demodulator 134 extracts and demodulates the received signal from a specific terminal 2 by equalization processing using the propagation path estimate value between each terminal 2 generated by the propagation path estimation unit 132. In the equalization processing, the received signal from the corresponding terminal 2 is extracted using the propagation path estimate value between each terminal 2, and received signals from other wireless terminals are suppressed.

[0058] The processing of the error correction decoder 135 and the error detector 136 is the same as that of the error correction decoder 235 and the error detector 236 of the terminal 2 in Fig. 8. The replica generator 137 generates a replica of the received signal from the terminal 2 using the propagation path estimation value generated by the propagation path estimator 132 based on the demodulated and decoded data. The replica is a simulated signal that simulates the maximum power received signal received by the antenna 14. In other words, the replica is a modulated signal that arrives at the antenna 14 from one terminal 2 and simulates the signal with the highest signal-to-interference-plus-noise ratio (SINR). This is what happened.

[0059] The replica removal unit 138 removes the replica created by the replica creation unit 137 from the radio signal received by the antenna 14. As a result, in the example of Fig. 10, the SIC loop removes the simulation signal equivalent to the modulated signal with maximum power from the received radio signal. As shown in Fig. 10, the signal from which the simulation signal equivalent to the modulated signal with maximum power has been removed by the SIC loop is returned to the SIC loop again. The reception processing unit 13 executes the SIC loop to sort the received signals in descending order of the signal with the highest signal-to-interference-plus-noise ratio (SINR), as shown in the upper part of FIG. 10 or FIG. 1. That is, the reception processing unit 13 separates the reception signals transmitted from each terminal 2 from the reception signals transmitted from a plurality of terminals 2 by non-orthogonal multiple access. The reception processing unit 13 separates the reception signals transmitted from each terminal 2 from the reception signals transmitted by the non-orthogonal multiple access from the plurality of terminals 2. The SIC loop is repeated until the received signal from each terminal 2 is demodulated. In this way, the reception processing unit 13 demodulates the received signal from each terminal 2 from a signal in which received signals from a plurality of terminals 2 are mixed. The processing of the reception processing unit 13 is an example of the control unit of the base station receiving superimposed data in which uplink communication data from the relayed terminal is superimposed on uplink communication data based on a communication request generated by the relay terminal from the relay terminal.

[0060] FIG. 11 is a block diagram of the processing of relay station 2RB that performs non-orthogonal multiple access with relayed station 2S. Therefore, relay station 2RB performs SIC processing. As shown in FIG. 11, relay station 2RB has RS processing unit 21A, DS processing unit 22A, reception processing unit 23A, switches SW7 and SW8, and antenna 24. Among these, RS processing unit 21A, DS processing unit 22A, and switch SW7 have the same configuration as RS processing unit 21A, DS processing unit 22A, and SW3 in FIG. 9, and therefore their description will be omitted. Note that relay station 2RB in FIG. 11 can also be considered an example of a relay terminal that relays uplink communication data to base station 1. Furthermore, the processing of relay station 2RB in FIG. 11 is also an example of transmitting superimposed data, in which uplink communication data from the relayed terminal is superimposed on uplink communication data based on a communication request generated by the relay terminal, to base station 1.

[0061] The reception processing unit 23A has a CP removal unit 231, a propagation path estimation unit 232, a CP removal unit 233, a demodulation unit 234, an error correction decoding unit 235, an error detection unit 236, a replica creation unit 237, and a replica removal unit 238. A radio signal received by the antenna 24 is connected to the CP removal unit 231 or the CP removal unit 233 by a switch SW8, for example, in a time-division manner.

[0062] Of these, CP removal unit 231, channel estimation unit 232, and CP removal unit 233 have the same configuration as terminal 2 in Fig. 8, and therefore description thereof will be omitted. Meanwhile, reception processing unit 23A executes an SIC loop, similar to base station 1 in Fig. 10, using demodulation unit 234, error correction decoding unit 235, error detection unit 236, replica creation unit 237, and replica removal unit 238. That is, relay station 2RB performs non-orthogonal multiple access with multiple relayed stations 2S. Then, relay station 2RB demodulates the received signals from each of the multiple relayed stations 2S from a radio signal in which received signals from the multiple relayed stations 2S are mixed. That is, the configuration of relay station 2R in Fig. 11 can be said to be an example of a relay terminal that performs non-orthogonal multiple access with the multiple relayed terminals.

[0063] (Processing flow) 12 is a flowchart illustrating a control procedure of the base station 1. The processor 101 of the base station 1 executes the following process using a computer program executablely loaded in the memory 102. In the following description, the maximum transmit power that can be set to the terminal 2 is denoted as Pmax,UE. Furthermore, the propagation loss threshold serving as the criterion for selecting a candidate relay station 2R is denoted as Lth,0, and the propagation loss threshold serving as the criterion for selecting a candidate relayed station 2S is denoted as Lth,1. Here, Lth,0 is a value smaller than Lth,1. Furthermore, the relay gain threshold for determining a pair of the relay station 2R and the relayed station 2S from the combination of the candidate relay station 2R and the candidate relayed station 2S is denoted as Δ. Furthermore, in non-orthogonal multiple access, the power difference set between the received powers received by the base station 1 from each terminal 2 is denoted as ΔP.

[0064] In the processing of this embodiment, the base station 1 calculates the propagation loss L of the path from each terminal 2 to the base station 1 from the reference signal transmitted from each terminal 2. k (S1) where k is the The terminal ID of the terminal 2-k is a value in the range of 1 to K. However, the base station 1 calculates the propagation loss L k may be measured and the results obtained from each terminal 2-k.

[0065] Next, the base station 1 selects candidates for the relay station 2R and the relayed station 2S, and calculates the propagation loss L r,s The process then measures the received signal strength and selects the relay station 2R and the relayed station 2S (S2). Details of S2 will be described later with reference to FIG. Then, the base station 1 sets the transmission power Pk of each terminal 2-k (each terminal ID is k=1 to K) (S3).

[0066] FIG. 13 shows the selection of candidates for the relay station 2R and the relayed station 2S, and the propagation loss L r,s 10 is a diagram illustrating the measurement of the relay station 2R and the relayed station 2S selection process.

[0067] In this process, the base station 1 first calculates the propagation loss L from the terminal 2-k (terminal ID: k) to the base station 1. k If the propagation loss L is smaller than the threshold Lth,0, the terminal 2-k is set as a candidate for the relay station 2R. k is greater than the threshold Lth,1, terminal 2-k is selected as a candidate for relayed station 2S (S21). The processing of S21 can be considered an example of the control unit of base station 1 acquiring the propagation loss of the propagation path between each of multiple terminals 2, and designating terminal 2 whose propagation loss of the propagation path is less than a first reference value as a candidate for relay terminal. The processing of S21 can also be considered an example of base station 1 designating terminal 2 whose propagation loss of the propagation path is equal to or greater than a second reference value that is greater than the first reference value as a candidate for relayed terminal. The threshold Lth,0 is an example of a first reference value, and the threshold Lth,1 is an example of a second reference value.

[0068] Next, the base station 1 calculates the propagation loss L of the path from the terminal 2-s to the base station 1 via the terminal 2-r as the relay station 2R for the terminal 2-r (terminal ID: r) as a relay station candidate and the terminal 2-s (terminal ID: s) as a relayed station candidate. r、s Then, the base station 1 issues an instruction to measure the propagation loss L via the terminal 2-r, which is a candidate for a relay station, as the relay station 2R (S22). r、s However, the propagation loss L sIt is then determined whether the propagation loss L r、s is the propagation loss L s If the improvement is equal to or greater than the relay gain threshold ΔdB, the base station 1 selects the terminal 2-r as the relay station 2R and the terminal 2-s as the relayed station 2S (S23). However, if multiple terminals 2-r meet this criterion (the propagation loss L via the relay station 2R), r、s is the propagation loss L without relay station 2R s If the first propagation loss is improved by a third reference value or more (improvement of the relay gain threshold ΔdB or more compared to the second propagation loss), the base station 1 selects the terminal 2-r with the greatest propagation loss reduction effect as the relay station 2R. The process of S23 can be considered an example of the control unit of the base station 1 selecting a relay terminal and a relayed terminal from the relay terminal candidates and the relayed terminal candidates. The process of S23 is also an example of the control unit of the base station 1 calculating a first propagation loss when the relayed terminal candidate communicates with the base station 1 after being relayed by the relay terminal candidate. The process of S23 is also an example of the control unit of the base station 1 calculating a second propagation loss when the relayed terminal candidate communicates with the base station 1 without being relayed by the relay terminal candidate. In the process of S23, the control unit of the base station 1 selects the relayed terminal candidate and the relay terminal candidate as the relayed terminal and the relay terminal, respectively, if the first propagation loss is improved by a third reference value or more compared to the second propagation loss. The relay gain threshold ΔdB is also an example of the third reference value.

[0069] Next, the base station 1 calculates the propagation loss L r The required power difference ΔP is added to the value of the propagation loss L of the relay station 2S. s However, if there are multiple relayed stations, the propagation loss L between the relayed station 2S and the relay station 2R is updated. r,s18. In other words, the base station 1 sets values calculated by the base station 1 with a difference of ΔP in ascending order of the relayed station 2S, rather than actual measured values, as the propagation loss of the path from the relayed station 2S to the base station 1. Then, the base station 1 uses the set values in the transmission power setting process for each terminal 2 (including the terminal station 2N, relay station 2R, and relayed station 2S) in FIG. 18. By using such set values as the propagation loss of the path from the relayed station 2S to the base station 1, the base station 1 can set transmission power for all terminals 2 (including the terminal station 2N, relay station 2R, and relayed station 2S) using the same procedure.

[0070] FIG. 14 shows an example of the process (S21 to S23 in FIG. 13) for selecting candidates for the relay station 2R and the relayed station 2S. In the example of FIG. 14, one relay station 2R and two relayed stations 2S are selected. In each graph in FIG. 14, the horizontal axis represents the terminal ID of terminal 2, and the vertical axis represents an example of the measured value of the propagation loss. Graph G11 in FIG. 14 shows the propagation loss L of the path from each terminal 2-k (terminal ID: k=1 to 5) to the base station 1. k (k=1 to 5) is shown as an example.

[0071] As shown in graph G11, the propagation losses L1, L2, and L3 of terminals 2-1, 2-2, and 2-3 are as follows: The propagation loss is less than the propagation loss threshold Lth,0. Therefore, the base station 1 -3 is a candidate for the relay station 2R. On the other hand, the path losses L4 and L5 of the terminals 2-4 and 2-5 are values that exceed the path loss threshold Lth,1. Therefore, the base station 1 selects the terminals 2-4 and 2-5 as candidates for the relayed station 2S.

[0072] Graph G12 shows the data of the uplink of terminals 2-4 and 2-5 with terminal 2-1 as relay station 2R. The propagation loss when relaying the r=1,s In the following, the propagation loss L r=i,s=j Simply, L i,j Comparing graphs G11 and G12, the propagation loss L when the uplink data from terminal 2-4 is relayed by terminal 2-1 is1,4 is worse than the propagation loss L4 without relay. Also, when the uplink from terminal 2-5 is relayed by terminal 2-1, the propagation loss L 1,5 is the propagation loss L5 without relays However, the degree of the decrease, that is, the degree of improvement, does not reach the relay gain threshold ΔdB. Therefore, the base station 1 does not adopt the combination in which the terminal 2-1 is a candidate for the relay station 2R and the terminals 2-4 and 2-5 are candidates for the relayed station 2S.

[0073] Graph G13 shows the propagation loss L when terminal 2-2 is used as relay station 2R to relay data from the uplinks of terminals 2-4 and 2-5. r=2,s By comparing the graphs G11 and G13, it can be seen that the propagation loss L 2,4 is reduced by more than the relay gain threshold ΔdB compared to the propagation loss L4 without relaying, and is improved. On the other hand, when the uplink data from terminal 2-5 is relayed by terminal 2-2, the propagation loss L 2,5 is almost the same as the propagation loss L5 without relaying. In other words, the degree of reduction, i.e., the degree of improvement, does not reach the relay gain threshold ΔdB. Therefore, the base station 1 only adopts the combination in which the terminal 2-2 is a candidate for the relay station 2R and the terminal 2-4 is a candidate for the relayed station 2S. On the other hand, the base station 1 does not adopt the combination in which the terminal 2-2 is a candidate for the relay station 2R and the terminal 2-5 is a candidate for the relayed station 2S.

[0074] Graph G14 shows the propagation loss L when terminal 2-3 is used as relay station 2R to relay the uplinks of terminals 2-4 and 2-5. r=3,s By comparing the graphs G11 and G14, the propagation loss L 3,4 is reduced by more than the relay gain threshold ΔdB compared to the propagation loss L4 without relaying, and is improved. 3,5Therefore, the base station 1 selects the terminal 2-3 as a candidate for the relay station 2R, and adopts both the combination of the terminal 2-4 and the terminal 2-5 as candidates for the relayed station 2S.

[0075] Here, the propagation loss L 2,4 and propagation loss L 3,4 The two have a reduction effect greater than the relay gain threshold ΔdB and satisfy the condition for the propagation loss reduction effect. 3,4 The propagation loss L 2,4 Therefore, in this embodiment, for example, the base station 1 reduces the propagation loss L 3,4 In this case, the terminal 2-3 is selected as the relay station 2R, and the terminal 2-4 is selected as the relayed station 2S. In this case, there is one relay station (terminal 2-4), and the relayed station S is relayed to two stations (terminals 2-4 and 2-5) by one relay station 2R.

[0076] 15 shows a first example of the process (S24 in FIG. 13) of setting the propagation loss between the relay station 2R and the relayed station 2S. In the first example, the relay station 2R selects one station and the relayed station 2S selects two stations. In this case, the base station 1 uses the propagation loss L r The value obtained by adding the required power difference ΔP to the terminal 2-4, which is the first relayed station 2S, is set to the terminal 2-4. Furthermore, since there is a terminal 2-5, which is the second relayed station 2S, the base station 1 sets the propagation loss L r,4 , L r,5 Integer multiples of ΔP are assigned in ascending order. r,4 =L3+ΔP, L r,5 =L3+2ΔP. Here, the required power difference ΔP is an example of the fourth reference value. Also, Fig. 15 shows an example in which, when a relay terminal relays uplink communication data from a relayed terminal, the relayed terminal transmits the uplink communication data from the relayed terminal to the base station with transmission power that is lower by at least the fourth reference value than the transmission power used when transmitting the uplink communication data generated by the relay terminal.

[0077] Fig. 16 shows a second example of the process (S24 in Fig. 13) for setting the propagation loss between the relay station 2R and the relayed station 2S. In the second example, two relay stations 2R are selected, and one relayed station 2S is selected for each relay station 2R. This is the case, for example, when the propagation loss L 2,4 L 3,4 In this case, the base station 1 sets the value obtained by adding the required power difference ΔP to the propagation loss L2 of the terminal 2-2, which is the first relay station 2R, to the terminal 2-4, which is the relayed station 2S. Similarly, the base station 1 sets the value obtained by adding the required power difference ΔP to the propagation loss L3 of the terminal 2-3, which is the second relay station 2R, to the terminal 2-5, which is the relayed station 2S. Therefore, L 2,4 =L2+ΔP, L 3,5 16 also shows an example in which, when a relay terminal relays uplink communication data from a relayed terminal, the relayed terminal transmits the uplink communication data from the relayed terminal to a base station with transmission power that is smaller by at least the fourth reference value than the transmission power when transmitting the uplink communication data generated by the relay terminal.

[0078] 17 is a diagram illustrating the setting of transmission power Pk for transmission from relayed station 2S to relay station 2R, during the process (S3 in FIG. 12) in which base station 1 sets transmission power Pk for terminal 2-k. Base station 1 repeats the process a number of times equal to Kr, the number of relay stations 2R (S37). In FIG. 17, the index indicating relay station 2R is i.

[0079] In this process, the base station 1 determines whether the currently processing relay station 2R (index i) receives simultaneous transmissions from multiple relayed stations 2S. Simultaneous transmission refers to transmission using non-orthogonal multiple access, in which multiple relayed stations 2S transmit uplink data in the same time slot.

[0080] If the determination in S31 is simultaneous transmission, the base station 1 sets the maximum transmission power of the terminal 2 to Pmax,UE for the first relayed station 2S (index j=1) among the multiple relayed stations 2S (index j) (S34). r(i),s(i,j)=Pmax,UE. In addition, the base station 1 sets a value obtained by subtracting the required power difference ΔP from the transmission power of the previous relayed station 2S (index j-1) for the second and subsequent relayed stations 2S (index j-1) after adjusting the difference in propagation loss from each relayed station 2S to the relay station 2R (S35). That is, P r(i),s(i,j) =P r(i),s(i,j-1) -L r(i),s(i,j-1) +L r(i),s(i,j) Set to -ΔP, where P r(i),s(i,j-1) is the transmission power of the previously set relay station 2S. r(i),s(i,j-1) +L r(i),s(i,j) is the propagation loss L used in the transmission power of the relay station 2S set one step previously. r(i)),s(i,j-1) is temporarily canceled, and the path loss L from the currently processed relay station 2S (index j) to the relay station is calculated. r(i),s(i,j) The transmission power P r(i),s(i,j) By this process, the relay station 2S (index i) calculates the propagation loss L r(i),s(i,j) Since the received power is reduced by the difference of ΔP, the received power from each relay station 2S (index j) is reduced by the difference of ΔP. P r(i),s(i,j) is set so as not to exceed the maximum transmit power Pmax,UE.

[0081] The base station 1 repeats the process from S32 to S35 as many times as the number of relayed stations Kr,s (S3 6) where Kr,s is the number of relayed stations 2S relayed by the currently processing relay station 2R. Also, if the determination in S31 is individual, that is, one relay station 2R is connected to only one relayed station 2S at a time to receive uplink data. In this case (N in S31), the base station 1 sets the transmission power of the relayed station 2S to the maximum transmission power Pmax,UE (S38). The base station 1 repeats the above process for the number Kr of relay stations 2R (S37), and then ends the process.

[0082] 18 is a diagram illustrating the setting of transmission power Pk from each terminal 2-k to the base station 1, during the process (S3 in FIG. 12) in which the base station 1 sets transmission power Pk for the terminal 2-k. However, during this process, it is assumed that data on the uplink transmission line for the relayed station 2S has reached the relay station 2R. Therefore, for the uplink data of the relayed station 2S, the relay station 2R sets the transmission power for the uplink data of the relayed station 2S to be superimposed on the uplink data of the relay station 2R itself.

[0083] In this process, the base station 1 sets the maximum transmission power Pmax,UE for the first terminal 2-1 (when k=1 in S3A) (S3B). Furthermore, for the second and subsequent terminals 2-k, the base station 1 determines whether the terminal 2-k is a relayed station 2S (S3C). If the terminal 2-k is not a relayed station 2S (N in S3C), the base station 1 sets a value obtained by subtracting the required power difference ΔP from the transmission power of the previous terminal 2-k-1 after adjusting for the difference in propagation loss from each terminal 2-k to the base station 1 (S3D). That is, P k =P k-1 -L k-1 + L k Set to -ΔP, where P k-1 is the transmission power of terminal 2-k-1 set one time previously. - L k-1 + L k is the transmission power of terminal 2-k-1, which was set one time ago. Propagation loss L used in force k-1 is temporarily canceled, and the path loss L k is a term to be added to the transmission power Pk. By this processing, the base station 1 calculates the propagation loss L k Since the terminals 2-k receive the signals with reduced reception power, a difference of ΔP occurs in the reception power from each terminal 2-k.

[0084] On the other hand, if the terminal 2-k is determined to be a relayed station 2S in the determination of S3C (Y in S3C), the base station 1 sets a value obtained by adjusting the difference in propagation loss from each terminal 2-k to the base station 1 from the transmission power of the previous terminal 2-k-1 (S3E). In this case, the required power difference ΔP is not subtracted as in S3D. That is, P k =P k-1 -L k-1 + L k Set to As mentioned above, - L k-1 + L k is the transmission of the previously set terminal 2-k-1. Propagation loss L used in power k-1 is temporarily canceled, and the path loss L k The transmission power P k is a term to be added to

[0085] However, for the relayed station 2S, the base station 1 calculates the propagation loss Ls of the relayed station 2S as the propagation loss Ls of the relayed station 2R by the process of S24 in FIG. r In addition, when there are multiple relayed stations 2S, the base station 1 calculates the propagation loss L s is an integer multiple of ΔP (the propagation loss L between the relayed station s and the relay station r) r,s However, in reality, when data on the uplink of the relayed station 2S is relayed by the relay station 2R, the propagation loss L sis determined by the propagation loss between the relay station 2R and the base station 1. Therefore, the base station 1 sets a value obtained by adjusting the propagation loss difference from each terminal 2-k to the base station 1 from the transmission power of the previous terminal 2-k-1 according to S3E. As a result, the received power at the base station 1 relayed by the relay station 2R will have a transmission power difference of ΔP between the relay station 2S and the first relayed station, and between the relayed stations 2S. As a result, the relay station 2R relays the uplink transmission data from the relayed station 2S with a transmission power difference of ΔP. In other words, the processing of S3E is carried out so that when the relay terminal relays uplink communication data from the relayed terminal, the relayed terminal will receive the uplink communication data at a transmission power that is at least the fourth reference value lower than the transmission power when transmitting the uplink communication data generated by the relay terminal. This is an example of transmitting uplink communication data from the relay terminal to the base station 1. The process of S3E is also an example of the control unit of the base station 1 instructing the relay terminal to use transmission power that is smaller by a fourth reference value. The base station 1 repeats the processes of S3A to S3E the same number of times as the number K of all terminals 2 (S3F).

[0086] In the process of FIG. 18, the propagation loss of the relayed station 2S (or multiple stations) relayed by the relay station 2R is calculated as the propagation loss L r In other words, the base station 1 may use the received power P r Set the transmission power to P r +L r When the relay station 2R is set to the first relayed station 2S, the transmission power P r +L r -ΔP. This allows the base station 1 to set the received power P r Similarly, the base station 1 can receive the second relayed station 2S at this relay station 2S with a reception power P r -2ΔP so that base station 1 can receive the transmission power P r +L r Generally, the base station 1 sets the transmission power P for the s-th relayed station 2S at this relay station 2S so that the base station 1 can receive the signal with the reception power Pr-sΔP.r +L r -sΔP is set. Here, L r is the propagation loss of the path from relay station 2R to base station 1.

[0087] The propagation loss of the relayed station 2S, where the base station 1 is relayed by the relay station 2R, is determined as follows: r When (fixed value) is used, the determination of S3C and the processing of S3E are not required in Fig. 18. In this case, the base station 1 can set the transmission power for all terminals 2, including the normal terminal 2 that does not perform relaying, the relay station 2R, and the relayed station 2S, by the processing of S3D.

[0088] That is, when data from the terminal 2-k, which is the relayed station 2S, is relayed by the relay station 2R, the propagation loss L k corresponds to the propagation path from the relay station 2R to the base station 1, and is the same value regardless of the relayed station 2S. That is, for the relayed station 2S that is relayed by the relay station 2R, by using the propagation loss from the relay station 2R to the base station 1, the transmission power Pk can be set by the process of S3D in FIG. 18, just like other terminals 2.

[0089] FIG. 19 is a diagram illustrating a method for updating transmission power in a relay station 2R. When the relay station 2R finishes transmitting its own data, if data transmission from a relayed station 2S remains uncompleted, the process of FIG. 19 is executed. In this case, the base station 1 instructs the relay station 2R to set its transmission power. In accordance with the instruction from the base station 1, the relay station 2R updates the transmission power of the relayed station 2S with the highest transmission power to that of the relay station 2S. That is, the relay station 2R updates the transmission power from that relay station 2S to the base station 1 to the maximum power. Furthermore, if there are other relayed stations 2S for which transmission has not yet been completed, the transmission power of the other relayed stations 2S is also updated to increase its transmission power.

[0090] 19, graph G14 illustrates the received power of base station 1 before relay station 2R finishes transmitting its own data. Ideally, at base station 1, terminal 2-3, which is relay station 2R, and terminals 2-4 and 2-5, which are relayed stations 2S, receive the transmitted power with a power difference of ΔP. For example, if the received powers of terminals 2-3, 2-4, and 2-5 at base station 1 are P3, P4, and P5, respectively, then P3 - P4 = P4 - P5 = ΔP.

[0091] 19, graph G5 illustrates the received power of base station 1 after relay station 2R has finished transmitting its own data. In this case, base station 1 instructs relay station 2R to increase the transmission power of terminals 2-4 and 2-5 by ΔP. That is, relay station 2R increases the transmission power of uplink data from terminals 2-4 and 2-5, which are relayed station 2S, so that the received powers from terminals 2-4 and 2-5 at base station 1 become P4=P3 and P5=P4, respectively.

[0092] FIG. 20 is a diagram illustrating a process of setting the transmission power for the relay station 2R by the base station 1 when the relay station 2R has finished transmitting data on its own uplink. Here, for example, it is assumed that the number of continuous transmissions N is initially set in the relay station 2R. However, there is a case where the relay station 2R finishes transmitting data on its own uplink before the initially set number of continuous transmissions N is executed. FIG. 20 illustrates a process of setting the transmission power for the relay station 2R by the base station 1 in such a case. In FIG. 20, each of the multiple relay stations 2R is represented by relay station 2R(i). i is an index of the number of relay stations and ranges from 1 to the number of relay stations. Furthermore, each of the multiple relayed stations 2S relayed by the relay station 2R(i) is represented by relayed station 2S(i,j). j is an index of the relayed station and ranges from 1 to the number of relayed stations Kr,s.

[0093] In this process, the base station 1 determines whether the relay station 2R(i) has completed uplink data transmission to all relayed stations S(i,:) (S41). Here, a colon (:) indicates all relayed stations 2S. If the relay station 2R(i) has completed uplink data transmission to all relayed stations S(i,:) (Y in S41), the base station 1 ends the process of FIG. 21.

[0094] On the other hand, if the uplink data transmission of all the relayed stations S(i,:) has not been completed (N in S41), the base station 1 identifies the relayed station 2S(i,1) with the highest uplink transmission power among the relayed stations 2S(i,j). Then, the base station 1 sets the uplink transmission power of the identified relayed station 2S(i,1) to the uplink transmission power P of the relay station 2R(i). r(i) (S42, S43, S44). In addition, the base station 1 sets the uplink transmission power to P s(i,j) Each of these is the next higher transmission power P s(i,j-1) The base station 1 repeats the processes of S43 and S44 the number of times Kr,s is the number of relayed stations relayed by the relay station 2R(i) (S46), increasing the transmission power of each relayed station 2S(i,j) by one step at a time. After that, when the uplink data transmission of any relayed station 2S(i,j) is completed, the base station 1 may increase the transmission power of the relayed station 2S(i,j+1) or lower by one step at a time. The process of FIG. 20 is an example of a process performed when the transmission of uplink communication data generated by the relay terminal is completed before the relay terminal completes relaying the uplink communication data of the relayed terminal. The process of S45 is an example of increasing the transmission power when the relay terminal transmits uplink communication data of the relayed terminal. The process of S45 is also an example of increasing the transmission power when the control unit of the base station 1 transmits uplink communication data of the relayed terminal.

[0095] By this process, when the relay station 2R completes its own uplink data transmission, the base station 1 increases the transmission power of the relayed station 2S, reducing the transmission error rate and enabling efficient data relay. Furthermore, even when the uplink data transmission of any relayed station 2S(i,j) has finished, the base station 1 increases the transmission power of the lower relayed station 2S(i,j+1) and below, reducing the transmission error rate and enabling efficient data relay. If the relay station 2R completes its own uplink data transmission before the initially set number of consecutive transmissions N, instead of the process of FIG. 20, the base station 1 may continue transmitting data to the relay station 2R for the initial number of consecutive transmissions N.

[0096] FIG. 21 is a diagram illustrating the processing of the base station 1 when data transmission on the uplink of any relayed station S(i,j) relayed by the relay station 2R(i) is completed. In this processing, the base station 1 determines whether or not there is a relayed station S(i,j+1) next to the relayed station S(i,j) whose data transmission has been completed. That is, the base station 1 determines whether or not the relayed station S(i,j) whose data transmission has been completed is the Kr, sth, last relayed station 2S (S47, S48). Then, if there is a next relayed station S(i,j+1) (N in S48), the base station 1 The base station 1 increases the transmission power of the next relayed station 2S(i,j+1) and the following relayed stations by one step at a time (S49). FIG. 21 shows an example of processing performed when relaying of uplink communication data of one of a plurality of relayed terminals relayed by the relay terminal is completed. The processing of S49 is an example of the relay terminal increasing the transmission power for relaying uplink communication data of the relayed terminal that has a lower transmission power set than that of the relayed terminal that has completed relaying. The processing of S49 is also an example of the control unit of the base station 1 instructing the relay terminal to increase the transmission power for relaying uplink communication data of the relayed terminal that has a lower transmission power set than that of the relayed terminal that has completed relaying. If the next relayed station S(i,j+1) does not exist (Y in S48), the base station 1 ends the processing.

[0097] (Effects of the embodiment) As described above, according to the present embodiment, a communication system 100 in which multiple terminals 2 are non-orthogonally multiplexed to a base station 1 includes a terminal 2 operating as a relay station 2R and a terminal 2 operating as a relayed station 2S. The relay station 2R transmits superimposed data, which is obtained by superimposing uplink communication data from the relayed station 2S on uplink communication data based on a communication request generated by the relay station 2R, to the base station 1. This enables efficient reception by the base station 1 even when the received signal directly received by the base station 1 from the relayed station 2S has a low SNR. In other words, by relaying the received signal from the relayed station 2S by the relay station 2R, the base station 1 can receive the signal from the relayed station 2S with a received power that is lower than that of the relay station 2R by a predetermined value ΔP. As a result, the SNR of the received signal from the relayed station 2S can be effectively increased, thereby improving the transmission error rate. Therefore, in this communication system 100, even if the relayed station 2S is in an environment with large path loss (propagation loss), such as at the cell edge of the wireless network RN or inside a tunnel, uplink data can be transmitted to the base station 1 efficiently.

[0098] In this embodiment, the base station 1 selects such a relay station 2R and a relayed station 2S. That is, in this embodiment, the base station 1, which can grasp the state of the received power from the terminal 2, can appropriately select the relay station 2R and the relayed station 2S.

[0099] In this embodiment, the base station 1 calculates the propagation loss L from the terminal 2-k (terminal ID: k) to the base station 1. k If the propagation loss L is smaller than the threshold Lth,0, the terminal 2-k (ID: k) is set as a candidate for the relay station 2R. k is greater than the threshold Lth,1, the terminal 2-k (ID: k) is selected as a candidate for the relayed station 2S. k From the above, it is possible to select the most desirable candidates for the relay station 2R and the relayed station 2S.

[0100] In addition, the base station 1 calculates the propagation loss L via the terminal 2-r, which is a candidate for the relay station 2R. r、s However, the propagation loss without relay station is L sIt is then determined whether the propagation loss L r、s is the propagation loss L s If the propagation loss is greater than or equal to the relay gain threshold ΔdB, the base station 1 selects the terminal 2-r as the relay station 2R and the terminal 2-s as the relayed station 2S. Therefore, the base station 1 can identify candidates for the relay station 2R and the relayed station 2S whose propagation loss will be improved by relaying, and select the relay station 2R and the relayed station 2S.

[0101] In this embodiment, the relay station 2R is capable of non-orthogonal multiple access with a plurality of relayed stations 2S. That is, in this communication system 100, the relay station 2R can relay signals to a plurality of relayed stations 2S in simultaneous communication.

[0102] In this embodiment, the base station 1 controls the relay station 2R to transmit a signal with a transmission power P so that the signal can be received at the base station 1 with a reception power Pr. r +L r When the setting is made, the transmission power P r +L r -ΔP. As a result, the base station 1 sets the received power P r -ΔP at the base station 1. Generally, the base station 1 receives the For the sth relay station 2S, the transmission power P is set so that the base station 1 can receive the signal with the reception power Pr-sΔP. r +L r -sΔP can be set. That is, the base station 1 instructs the relay station 2R to use a power when relaying uplink communication data from the relayed station 2S that is smaller by the fourth reference value ΔP than the power when transmitting uplink communication data generated by the relay terminal. Therefore, the base station 1 sets a power difference of the fourth reference value ΔP between the received power of the relay station 2R from its own station and the received power from the relayed station 2S relayed by the relay station 2R, thereby enabling relaying in non-orthogonal multiple access. Furthermore, even when the relay station 2S relays the power of uplink lines from multiple relayed stations 2S, a power difference of the fourth reference value ΔP is set in stages, enabling relaying in non-orthogonal multiple access.

[0103] Furthermore, when the relay station 2R finishes transmitting data on its own uplink, the base station 1 instructs the relay station 2R to set the uplink transmission power of the relayed station 2S having the largest uplink transmission power among the relayed stations 2S as the uplink transmission power P r Therefore, in this communication system 100, when the relay station 2R completes data transmission on its own uplink, it increases the transmission power of the relayed station 2S, thereby reducing the transmission error rate and enabling efficient data relay.

[0104] Furthermore, when the relay station 2R completes uplink data transmission to any of the relayed stations 2S(i,j), the base station 1 issues the same instruction as above. That is, the base station 1 may instruct the relay station 2S(i) to increase the transmission power of the relayed stations 2S(i,j+1) and below, which have lower transmission power than the relayed station 2S(i,j) that has completed transmission, by one step at a time. Therefore, in the present communication system 100, when the uplink data transmission of any of the relayed stations 2S(i,j) is completed, the transmission power of the uplink relay of the relayed station 2S(i,j+1), which is set to a lower transmission power and is relaying data, is increased. This allows the present communication system 100 to reduce the transmission error rate of the relayed station 2S(i,j+1) and efficiently relay data.

[0105] (Variation) In FIG. 13, the base station 1 calculates the propagation loss L r、s However, the propagation loss L s It is determined whether the relay gain is greater than or equal to the relay gain threshold ΔdB. Instead of such a determination, if the base station 1 can collect location information of the terminal 2, it may set the relayed distance D. That is, by setting the relayed distance D, the base station 1 can select the relay station 2R and the relayed station 2S based on the relayed station candidate 2-s that is present within the radius D from the location of the terminal 2-r that is a relay station candidate.

[0106] Second Embodiment A communication system 100 according to the second embodiment will be described below with reference to FIGS. 22 and 23. The first embodiment described a process in which a relay station 2R relays uplink data of a relayed station 2S in a non-orthogonal multiple access communication system 100 in which a relayed station 2S exists within a cell of a base station 1. In this embodiment, a communication system 100 in which a relay station 2R relays data is described, with a terminal 2 not existing within a cell of a base station 1 as the relayed station 2S. The configuration and operation of the second embodiment are the same as those of the first embodiment, except that at least some of the relayed stations 2S do not exist within a cell of a base station 1. Therefore, the same components as those in the first embodiment are denoted by the same reference numerals, and their description will be omitted. The process of the communication system 100 according to the present embodiment does not conflict with the process of the first embodiment, and can be executed in combination with the process of the first embodiment.

[0107] Fig. 22 is a diagram illustrating an example of data flow of the uplink and downlink between the base station 1 and the terminal 2 in the second embodiment. In Fig. 22, since the relayed station 2S is not present in the cell of the base station 1, communications via the uplink control channel and the downlink control channel as well as the uplink data channel are relayed by the relay station 2R.

[0108] Therefore, in this embodiment, as in the first embodiment, physical resources defined by frequency and time are used overlappingly. The base station 1 allocates at least one time slot to a downlink control channel from the relay station 2R to the relayed station 2S. The base station 1 also allocates at least one time slot to an uplink control channel from the relayed station 2S to the relay station 2R.

[0109] FIG. 23 is a diagram illustrating a method for searching for a relayed station 2S. In this process, first, the base station 1 transmits a message to each terminal 2 inviting a terminal 2 that wishes to operate as a relay station 2R (S51). Then, the terminal 2 that wishes to operate as a relay station 2R transmits a response to the base station 1. If the terminal 2 already has the terminal ID of the relayed station 2S to be relayed, the terminal 2 also notifies the base station 1 of the terminal ID (S52). Note that the terminal 2 may obtain the terminal ID of the relayed station 2S to be relayed via another communication method or the like. Here, the other communication method is, for example, a local communication method between a plurality of terminals 2. The local communication method may be, for example, a wireless LAN, Bluetooth (registered trademark), Bluetooth (registered trademark) Low Energy (BL E), 5G sidelink communications, etc. When a terminal 2 that is a candidate for a relay station 2R is about to search for a relayed station 2S, the base station 1 instructs the terminal 2 that is a candidate for the relay station 2R of the frequency and time slot to be used in searching for a terminal 2 located outside the cell (S53). The terminal 2 that is a candidate for the relay station 2R transmits a notification signal inviting a relayed station 2S at the specified frequency and time in order to search for a terminal 2 that is outside the cell and will become a relayed station 2S (S54).

[0110] A terminal 2-s desiring to become a relayed station 2S transmits a response to the notification signal from a terminal 2-r that is a candidate for a relay station 2R together with its own terminal ID (referred to as a relayed station ID) (S55). Having obtained the terminal ID of the terminal 2-s desiring to become a relayed station 2S, the candidate terminal 2-r for a relay station 2R replies to the base station 1 with the relayed station ID and its received signal strength (S56).

[0111] The base station 1 registers the relayed station ID. If there are multiple overlapping candidates for the relayed station 2S among the candidate terminals 2-r of multiple relay stations 2R, the base station 1 leaves only the candidate terminal 2-r of the relay station 2R with the higher received signal strength (S57). After that, when the base station 1 sends control information to the relayed station 2S, it transmits the frequency and slot for the relay control CH together with the control information to the corresponding relay station 2R (S58).

[0112] Through the above processing, the relay station 2R can relay the downlink control channel, the uplink control channel, and the uplink data channel to the terminal 2 outside the cell. The configuration in Fig. 22 and the processing in Fig. 23 are an example in which the relayed terminal includes a terminal 2 located outside the cell provided by the base station 1. The configuration in Fig. 22 and the processing in Fig. 23 are also an example in which the control unit of the base station 1 causes the relay terminal to search for a terminal located outside the cell provided by the base station and relay communication data from the terminal that has been found.

[0113] <Other embodiments> The above-described embodiment is merely an example, and the present disclosure may be modified as appropriate within the scope of the present disclosure. Furthermore, the processes and means described in the present disclosure may be freely combined and implemented as long as no technical contradiction occurs.

[0114] Furthermore, a process described as being performed by one device may be shared and executed by multiple devices. Alternatively, a process described as being performed by different devices may be executed by a single device. In a computer system, the hardware configuration that realizes each function can be flexibly changed. [Explanation of symbols]

[0115] 1 base station 2. Terminal 2N terminal station 2R, 2RA, 2RB relay station 2S Relay station 11 processors 12 Memory 15 Radio processing unit 11, 21, 21A RS processing section 12, 22, 22A DS processing section 13, 23, 23A Receiving processing section

Claims

1. A communication system in which a plurality of terminals are connected to a base station via non-orthogonal multiple access, the plurality of terminals include a relay terminal that relays uplink communication data to the base station and a relayed terminal that transmits uplink communication data to the base station via the relay terminal; the relay terminal transmits superimposed data, which is obtained by superimposing the upstream communication data from the relayed terminal on the upstream communication data based on the communication request generated by the relay terminal, to the base station; a communication system in which the base station acquires propagation losses of propagation paths between the base station and each of the plurality of terminals, selects a terminal whose propagation loss of the propagation path is less than a first reference value as a candidate for the relay terminal, and selects a terminal whose propagation loss of the propagation path is equal to or greater than a second reference value that is greater than the first reference value as a candidate for the relayed terminal, and selects the relay terminal and the relayed terminal from the candidates for the relay terminal and the candidates for the relayed terminal.

2. 2. The communication system of claim 1, wherein the base station selects the candidate relayed terminal and the candidate relay terminal as the candidate relayed terminal and the candidate relay terminal when the propagation loss when the candidate relayed terminal communicates with the base station after being relayed by the candidate relay terminal is improved by a third reference value or more compared to the propagation loss when the candidate relayed terminal communicates with the base station without being relayed by the candidate relay terminal.

3. 3. The communication system according to claim 1, wherein the relay terminal performs non-orthogonal multiple access with a plurality of the relayed terminals.

4. A communication system in which a plurality of terminals are connected to a base station via non-orthogonal multiple access, the plurality of terminals include a relay terminal that relays uplink communication data to the base station and a relayed terminal that transmits uplink communication data to the base station via the relay terminal; the relay terminal transmits superimposed data, which is obtained by superimposing the upstream communication data from the relayed terminal on the upstream communication data based on the communication request generated by the relay terminal, to the base station; When relaying the upstream communication data from the relayed terminal, the relay terminal increases the transmission power by at least a fourth reference value from the transmission power when transmitting the upstream communication data generated by the relay terminal. A communication system in which upstream communication data from the relayed terminal is transmitted to the base station with low transmission power.

5. A communication system as described in claim 4, wherein the relay terminal increases the transmission power when transmitting the upstream communication data of the relayed terminal if the transmission of the upstream communication data generated by the relay terminal is completed before the relay of the upstream communication data of the relayed terminal is completed.

6. A communication system as described in claim 4 or 5, wherein when relaying of upstream communication data of any of the multiple relayed terminals relayed by the relay terminal is completed, the relay terminal increases the transmission power for relaying the upstream communication data of the relayed terminal, which has a lower transmission power set than the relayed terminal for which relaying has been completed.

7. The communication system according to claim 1 , wherein the relayed terminal includes a terminal located outside a cell provided by a base station.

8. A base station to which a plurality of terminals are connected via non-orthogonal multiple access, selecting, from the plurality of terminals, a relay terminal that relays uplink communication data to the base station and a relayed terminal that transmits uplink communication data to the base station via the relay terminal; receiving, from the relay terminal, superimposed data in which upstream communication data from the relayed terminal is superimposed on upstream communication data based on a communication request generated by the relay terminal; The control unit acquires the propagation loss of the propagation path between each of the plurality of terminals, and selects a terminal whose propagation loss of the propagation path is less than a first reference value as a candidate for the relay terminal, and a terminal whose propagation loss of the propagation path is equal to or greater than a second reference value that is greater than the first reference value as a candidate for the relayed terminal, and selects the relay terminal and the relayed terminal from the candidates for the relay terminal and the candidates for the relayed terminal.

9. The base station according to claim 8, wherein the control unit selects the candidate relayed terminal and the candidate relay terminal as the candidate relayed terminal and the candidate relay terminal when the propagation loss when the candidate relayed terminal communicates with the base station after being relayed by the candidate relay terminal is improved by a third reference value or more compared to the propagation loss when the candidate relayed terminal communicates with the base station without being relayed by the candidate relay terminal.

10. A base station to which a plurality of terminals are connected in non-orthogonal multiple access, comprising: selecting, from the plurality of terminals, a relay terminal that relays uplink communication data to the base station and a relayed terminal that transmits uplink communication data to the base station via the relay terminal; receiving, from the relay terminal, superimposed data in which upstream communication data from the relayed terminal is superimposed on upstream communication data based on a communication request generated by the relay terminal; The control unit is a base station that instructs the relay terminal to use a transmission power when relaying uplink communication data from the relayed terminal that is at least a fourth reference value lower than the transmission power when transmitting uplink communication data generated by the relay terminal.

11. The base station according to claim 10, wherein the control unit increases the transmission power when transmitting the uplink communication data of the relayed terminal to the relay terminal when the transmission of the uplink communication data generated by the relay terminal is completed before the relaying of the uplink communication data of the relayed terminal is completed.

12. When relaying of upstream communication data of any of the relayed terminals relayed by the relay terminal is completed, the control unit instructs the relay terminal to relay upstream communication data of the relayed terminal to which a lower transmission power is set than that of the relayed terminal for which relaying has been completed.

12. The base station according to claim 10, wherein the transmission power is increased in

13. A base station to which a plurality of terminals are connected in non-orthogonal multiple access, comprising: selecting, from the plurality of terminals, a relay terminal that relays uplink communication data to the base station and a relayed terminal that transmits uplink communication data to the base station via the relay terminal; receiving, from the relay terminal, superimposed data in which upstream communication data from the relayed terminal is superimposed on upstream communication data based on a communication request generated by the relay terminal; The control unit causes the relay terminal to search for a terminal located outside a cell provided by the base station and relay communication data from the terminal that has been found.

14. A terminal in a communication system in which a plurality of terminals are non-orthogonally multiple-accessed to a base station, the terminal communicates with the base station as a relay terminal that relays uplink communication data to the base station or as a relayed terminal that transmits uplink communication data to the base station via the relay terminal; When communicating as the relay terminal, transmitting superimposed data obtained by superimposing uplink communication data from the relayed terminal on uplink communication data based on a communication request generated by the relay terminal to the base station; a control unit that executes the The control unit is a terminal that increases the transmission power when transmitting the upstream communication data of the relayed terminal if the transmission of the upstream communication data generated by the relay terminal is completed before the relaying of the upstream communication data of the relayed terminal is completed.

15. A communication method for a base station in which a plurality of terminals are non-orthogonally multiple-accessed to the base station, comprising: selecting, from the plurality of terminals, a relay terminal that relays uplink communication data to the base station and a relayed terminal that transmits uplink communication data to the base station via the relay terminal; receiving superimposed data obtained by superimposing upstream communication data from the relayed terminal on upstream communication data based on a communication request generated by the relay terminal; a communication method comprising: acquiring propagation losses of propagation paths between each of the plurality of terminals; designating a terminal whose propagation loss of the propagation path is less than a first reference value as a candidate for the relay terminal; designating a terminal whose propagation loss of the propagation path is equal to or greater than a second reference value that is greater than the first reference value as a candidate for the relayed terminal; and selecting the relay terminal and the relayed terminal from the candidates for the relay terminal and the candidates for the relayed terminal.

16. The communication method of claim 15, further comprising selecting the candidate relay terminal and the candidate relay terminal as the candidate relay terminal and the relay terminal when the propagation loss when the candidate relay terminal communicates with the base station after being relayed by the candidate relay terminal is improved by a third reference value or more compared to the propagation loss when the candidate relay terminal communicates with the base station without being relayed by the candidate relay terminal.

17. A communication method for a plurality of terminals in which the terminals are non-orthogonally multiple-accessed to a base station, the method comprising: The terminal communicates with the base station as a relay terminal that relays uplink communication data to the base station or as a relayed terminal that transmits uplink communication data to the base station via the relay terminal; When communicating as the relay terminal, transmitting superimposed data obtained by superimposing upstream communication data from the relayed terminal on upstream communication data based on a communication request generated by the relay terminal to the base station; When the transmission of the upstream communication data generated by the relay terminal is completed before the relay of the upstream communication data of the relayed terminal is completed, increasing the transmission power when transmitting the upstream communication data of the relayed terminal; A communication method comprising:

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