Base station and communication method

Abstract

The present invention is a base station that allows communication from a wireless communication terminal to the base station without accepting allocation of wireless resources when a communication request is generated. The base station performs the following processing: a process of receiving wireless signals with encoded data coming from multiple wireless communication terminals; a second process of obtaining a first signal from a first wireless communication terminal among the multiple wireless communication terminals in which at least one of the amplitude and phase is adjusted from the received wireless signal, and generating a replica of the wireless signal coming from the first wireless communication terminal before at least one of the amplitude and phase is adjusted; a third process of extracting a signal from the received wireless signal in which the replica of the incoming wireless signal is removed; and repeating the first process to the third process in sequence.

Description

Technical Field

[0001] The present invention relates to wireless communications. Background Art

[0002] There is an increasing demand for terminals that can connect to public networks such as the Internet to be used in a controllable manner, and low latency communications for accessing public networks are sought. On the other hand, multiple-input multiple-output (MIMO) will be used in the future. MIMO is a technology in which a base station and a terminal communicate with each other using multiple antennas in the same frequency band. In addition, in MIMO, the technology related to simultaneous communication with multiple terminals is called multi-user MIMO. It is predicted that the number of terminals accessing public networks will increase in the future, and there is an urgency for uplink lines.

[0003] However, in wireless communication, which is one of the communications for accessing a public network, a communication procedure called Configured Grant (CG) is specified. As a communication procedure that does not depend on CG, Dynamic grant is exemplified. In Dynamic grant, when a terminal sends data to a base station, it sends a scheduling request (Scheduling Request, SR) to the base station. Then, the base station specifies the wireless resources that can be used for the data transmission to the terminal through downlink control information (Downlink Control Information, DCI) and approves the transmission. Then, the terminal accepts the transmission approval and sends data to the base station through the specified wireless resources.

[0004] In contrast, in CG, the base station sends transmission parameters such as physical resources that can be used in data transmission to the terminal device in advance. Furthermore, the base station sends the approval start, approval end, etc. of data transmission based on the CG access. However, sometimes the transmission parameters of physical resources and the like are sent at the same time as the approval start. As a result, the terminal can immediately use the specified physical resources to send data to the base station without sending an SR and without receiving a DCI. In this way, in CG-based communication, the terminal can send data to the base station without negotiating with the base station. Therefore, CG is expected to be a technology for achieving low-latency communication.

[0005] Prior art literature

[0006] Non-patent literature

[0007] Non-patent document 1: “NR physical layer specifications in 5G” NTT DOCOMO Technology Journal Vol. 26 No. 3 (Nov. 2018).

[0008] However, due to CG, the number of terminals (N) transmitting to the base station at the same time increases. The state in which the number of terminals (N) transmitting at the same time is greater than the number of receiving antennas M of the base station is called overloaded MIMO. The purpose of an embodiment of the present invention is to suppress the degradation of communication quality in a situation where overloaded MIMO is likely to occur. Summary of the invention

[0009] The embodiment of the present invention is exemplified by the following base station. This base station is a base station that allows the allocation of the wireless resources based on the communication from the wireless communication terminal to the base station without accepting the allocation request of the wireless resources when a communication request is generated from multiple wireless communication terminals to the base station, and does not set an upper limit on the number of terminals that can be connected at the same time.

[0010] This base station has a control unit, which performs the following processing: a process of receiving modulated wireless signals arriving from the multiple wireless communication terminals; a first process of obtaining a first signal in which at least one of the amplitude and phase of a first wireless communication terminal among the multiple wireless communication terminals is adjusted from the received wireless signal, and obtaining first data demodulated according to the first signal; a second process of generating a replica of the wireless signal arriving from the first wireless communication terminal before at least one of the amplitude and phase is adjusted based on the first signal or the first data; a third process of extracting a signal from the received wireless signal without the replica of the arriving wireless signal; and for the extracted signal, using one of the second wireless communication terminals among the multiple wireless communication terminals without the first wireless communication terminal as the first wireless communication terminal, and repeating the first process to the third process in sequence.

[0011] Effects of the Invention

[0012] According to this base station, it is possible to suppress degradation of communication quality in a situation where MIMO overload is likely to occur. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a diagram illustrating the configuration of a wireless communication system according to this embodiment.

[0014] Figure 2 This is a diagram illustrating the hardware configuration of a base station according to this embodiment.

[0015] Figure 3 is a block diagram illustrating the structure of a terminal.

[0016] Figure 4 is a block diagram illustrating the structure of a base station.

[0017] Figure 5 It is a flowchart illustrating CG-based processing of a base station.

[0018] Figure 6 It is a flowchart illustrating the steps of CG-based reception processing in a base station and a terminal.

[0019] Figure 7 This is a table illustrating the conditions of the simulation.

[0020] Figure 8 This is a diagram illustrating the difference in message bit error rate depending on whether SIC is applied or not in a simulation.

[0021] Fig. 9 This is a diagram illustrating the difference in message bit error rate depending on the presence or absence of transmit diversity in addition to the application of SIC in the simulation. DETAILED DESCRIPTION

[0022] Figure 1 1 is a diagram illustrating the structure of a wireless communication system according to the present embodiment. The wireless communication system includes a base station 1, and a plurality of terminals 2-1, 2-2, ..., 2-N that communicate with the base station 1 by wireless. The terminals 2-1 and the like are collectively referred to as terminals 2. In the present embodiment, an overloaded MIMO wireless communication system is illustrated in which the number of terminals N in multi-user MIMO is greater than the number of receiving antennas M in the base station 1. The terminals 2 can be referred to as wireless communication terminals.

[0023] When MIMO is overloaded, the communication quality deteriorates. The reason is that when MIMO is overloaded, multi-user MIMO cannot eliminate all interference signals. In the future, due to the Internet of Things (IoT), it is predicted that the number of terminals accessing the network will further increase. Therefore, the number of terminals that can set CG is reduced. As a result, the number of terminals that can perform low-latency communication is limited. Therefore, in this embodiment, a communication system that can suppress the degradation of communication quality even in the state of overloaded MIMO is illustrated.

[0024] This embodiment discloses a base station 1 that allows the allocation of the wireless resources based on the wireless resource allocation request not to be accepted when a communication request is generated from multiple wireless communication terminals to the base station 1, and does not set an upper limit on the number of terminals that can be connected simultaneously. However, this embodiment also discloses a communication method performed by the base station 1. Here, when a communication request is generated from multiple wireless communication terminals to the base station 1, the allocation of the wireless resources based on the wireless resource allocation request is not accepted, and an example of allowing the communication based on the wireless communication terminal to the base station 1 is CG-based communication.

[0025] The base station 1 includes a control unit that receives modulated wireless signals arriving from a plurality of wireless communication terminals. The control unit further executes the following first to third processes. Here, the incoming wireless signal refers to a received signal before being received by the base station 1.

[0026] Here, in the first process, the control unit obtains a first signal in which at least one of the amplitude and the phase of the first wireless communication terminal among the plurality of wireless communication terminals is adjusted from the received wireless signal, and obtains first data demodulated based on the first signal. The first signal in which at least one of the amplitude and the phase is adjusted refers to, for example, a signal in which wireless signals from wireless communication terminals other than the first wireless communication terminal are suppressed and wireless signals from the first wireless communication terminal are retained as much as possible.

[0027] In the second process, the control unit generates a replica of the wireless signal received from the first wireless communication terminal before at least one of the amplitude and phase is adjusted based on the first signal or the first data. That is, the control unit generates a signal simulating the wireless signal received from the first wireless communication terminal before being received.

[0028] In the third process, the control unit extracts a signal from the received wireless signal without the replica of the incoming wireless signal. The signal from the received wireless signal without the replica of the incoming wireless signal can be called a residual signal. In short, the control unit extracts the wireless signal from the wireless communication terminal other than the first wireless communication terminal.

[0029] Then, the control unit performs a process of, for the extracted signal, using one of the second wireless communication terminals of the plurality of wireless communication terminals except for the first wireless communication terminal as the first wireless communication terminal, and repeating the first process to the third process in sequence. In this way,

[0030] (1) When communication requests are generated from a plurality of wireless communication terminals to the base station 1, allocation of wireless resources is not requested.

[0031] (2) Not accepting the allocation of the wireless resources based on the allocation request.

[0032] In this process, even if the number of wireless communication terminals communicating simultaneously exceeds the permissible limit, such as the number of receiving antennas of the base station 1, the signals of the wireless communication terminals can be well separated.

[0033] The first processing includes diversity processing, which obtains the wireless signal from the first wireless communication terminal through at least one of multiple different arrival paths and different arrival times. Through the combination of the first to third processing and diversity processing, the signals of multiple wireless communication terminals are well separated.

[0034] The control unit may repeat the first to third processes when allowing communication between the wireless communication terminal and the base station 1 in a manner that the wireless resources are not allocated to at least one of the plurality of wireless communication terminals. When communication between the wireless communication terminal and the base station 1 is allowed without allocating wireless resources, the number of wireless communication terminals that simultaneously communicate with the base station 1 is likely to exceed the permissible limit. In the communication between the wireless communication terminals exceeding the permissible limit and the base station 1, repeating the first to third processes is effective.

[0035] In the base station 1, when performing communication without allocating wireless resources to at least one of the plurality of wireless communication terminals, the base station 1 does not set an upper limit on the number of terminals set when setting the number of wireless terminals that can simultaneously transmit wireless signals. Even in the absence of such an upper limit, the base station 1 can suppress an increase in a message bit error rate and receive signals from a plurality of wireless communication terminals.

[0036] The control unit generates a replica of the incoming wireless signal by performing coding, modulation processing, transmission diversity processing, and processing that reflects the state of the transmission path between the plurality of wireless communication terminals and the base station 1 on the first data. When the first data that has been coded, modulated, etc. in the first wireless communication terminal is well demodulated, decoded, etc., the control unit can generate a replica of the incoming wireless signal with high accuracy using the first data that has been demodulated, decoded, etc. The reason for this is that in wireless signals that have arrived from a number of wireless communication terminals exceeding the permissible limit, the signal-to-interference-to-noise ratio may be low.

[0037] Figure 2 The diagram exemplifies the hardware configuration of the base station 1 according to the present embodiment. The base station 1 includes a processor 11 , a memory 12 , an internal interface 13 , a network interface 14 for communicating with other base stations and the like, and a wireless processing device 15 .

[0038] The processor 11 is also referred to as a central processing unit (CPU) or a microprocessor unit (MPU). The processor 11 is not limited to a single processor and may be a multi-processor structure. In addition, a single physical CPU connected with a single socket may also have a multi-core structure. In addition, the processor 11 may include a computing device of various circuit structures such as a digital signal processor (DSP) and a graphics processing unit (GPU). In addition, the processor 11 may cooperate with an integrated circuit (IC), other digital circuits or analog circuits. 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 11 may also be referred to, for example, as a microcontroller (MCU), a SoC (system on chip), a system LSI, a chipset, etc.

[0039] The memory 12 stores instruction sequences (computer programs) executed by the processor 11 or data processed by the processor 11. The processor 11 and the memory 12 are also called a baseband unit (BBU). The internal interface 13 is a circuit that connects various peripheral devices to the processor 11. The baseband unit can also be called a control unit.

[0040] The network interface 14 is a communication device used by 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 based on optical communication.

[0041] The wireless processing device 15 includes a transceiver for sending wireless signals and a receiver for receiving wireless signals, and is connected to the antennas ANT-B1, ..., ANT-BM. The wireless processing device 15 can have N systems of transceivers and receivers, and the number of each transceiver and receiver is the same as the number of antennas. The wireless processing device 15 is called a remote radio head (RRH), and can be configured to be connected to the baseband device through a wired network based on optical communication and remotely set. In addition, it can also be a structure in which multiple remote radio heads are connected to one baseband device. In addition, the network connecting the baseband device and the remote radio head is also called fronthaul.

[0042] Figure 3 is a block diagram illustrating the structure of the terminal 2. Figure 3, a wireless resource block and a channel matrix H of a wireless channel are illustrated together with the structure of the terminal 2. The wireless resource block refers to a portion divided by the frequency and time axis of a subcarrier (subcarrier) assigned to the terminal 2. In addition, the channel matrix H is a matrix representing the amplitude and phase variation of the transmission path between each antenna ANT1, ANT2, etc. of the terminal 2 and the receiving antennas ANT-B1 to ANT-BM of the base station 1. By multiplying the transmission signal vector of each antenna ANT1, ANT2, etc. of the terminal 2 on the transmitting side by the channel matrix H, it is possible to obtain an estimated value of the reception signal vector in the receiving antennas ANT-B1 to ANT-BM of the base station 1.

[0043] exist Figure 3 In FIG. 1 , a plurality of terminals 2-1, ..., 2-N are illustrated. In addition, the detailed structure of the terminal 2 is illustrated by the terminal 2-1. Figure 3 In the embodiment, each terminal 2 has a pair of antennas ANT1, ANT2, ... ANT2N-1, ANT2N. In the following description, when the antennas of each terminal 2 are collectively referred to, they are simply described as antennas ANT. However, in this embodiment, the number of antennas of each terminal 2 is not limited to two.

[0044] Terminal 2 is also called user equipment (UE). In addition, terminal 2 has a processor, a memory, a wireless processing device, an antenna ANT, etc. The processor, memory, wireless processing device and Figure 2 The processor 11, memory 12, and wireless processing device 15 described in the embodiment are the same. However, in the terminal 2, the processor, memory, and wireless processing device are usually accommodated in one housing. The processor of the terminal 2 executes wireless communication processing including each processing of the encoding unit 206, the modulation unit 207, and the transmission diversity processing unit 208 through the instruction sequence (computer program) loaded executable in the memory.

[0045] The coding unit 206 performs error correction coding on the data sent from the terminal 2. The error correction code can be a soft decision code or a hard decision code, and there is no limitation on the type of coding. The modulation unit 207 performs digital modulation on the error correction coded data. Examples of digital modulation methods include quadrature amplitude modulation (QAM), phase shift keying (PSK), frequency shift keying (FSK), etc.

[0046] The transmission diversity processing unit 208 separates the digitally modulated signal into a plurality of signals to form branches of transmission diversity, and radiates the signals from the plurality of antennas ANT via the wireless processing device. Figure 3In the example, the transmit diversity processing unit 208 of each terminal 2 separates the transmission path through two antennas to form a branch of transmit diversity. However, in the present embodiment, the processing of the transmit diversity processing unit 208 is not limited to diversity based on multiple antennas. For example, in the case where the terminal 2 has a single antenna, the diversity processing 20 can also use polarization diversity, time diversity, frequency diversity, etc. In the present embodiment, it is not limited to diversity processing, as long as various types of diversity are used. That is, in the present embodiment, the processing based on the transmit diversity processing unit 208 can be called an example of diversity processing of obtaining a wireless signal from a wireless communication terminal through at least one of multiple different arrival paths and different arrival times.

[0047] Figure 4 1 is a block diagram illustrating the configuration of the base station 1. The base station 1 includes a replica removal unit 101, a diversity reception and equalization processing unit 102, a demodulation unit 103, a decoding unit 104, and a replica generation unit 105. In addition, the replica generation unit 105 includes a coding unit 106, a modulation unit 107, a transmission diversity processing unit 108, and a channel matrix multiplication unit 109. Figure 2 The illustrated processor 11 executes each process of the replica removal unit 101, the diversity reception and equalization processing unit 102, the demodulation unit 103, the decoding unit 104, the replica generation unit 105, the encoding unit 106, the modulation unit 107, the transmission diversity processing unit 108 and the channel matrix multiplication unit 109 through an instruction sequence (computer program) executablely loaded in the memory 12.

[0048] exist Figure 4 In FIG. 1 , the structure of the base station 1 and the channel matrix H are illustrated. The structure of the channel matrix H is Figure 3 The channel matrix H is a matrix representing the amplitude and phase variations of the transmission path between the antennas ANT1, ANT2, etc. of the terminal 2 and the antennas ANT-B1 to ANT-BM of the base station 1. The channel matrix H is determined by receiving the reference signal (Reference Signal, RS) sent from the antennas ANT2K-1, ANT2K (K=1, ..., N) of each terminal 2 by each antenna ANT-B1, ..., ANT-BM. The same is true when the number of antennas of each terminal 2 is different. In short, the variation corresponding to the transfer function of the transmission path is calculated by sending and receiving the reference signal between each antenna ANTK on the transmitting side and each antenna ANT-BK on the receiving side.

[0049] In the communication system of the present embodiment, RS is transmitted in the same resource block as that used in CG. However, RS may be transmitted in a resource block different from that used in CG. In the present embodiment, RS is transmitted in the same resource block as that used in CG, so that RS from each transmitting antenna ANT of each terminal 2 is orthogonal between multiple terminals 2 so that RS do not interfere with each other. As a method for making RS orthogonal, a method of non-overlapping in time (TDMA), a method of staggered frequency (FDMA), orthogonality based on code (CDMA), etc. can be exemplified. In the present embodiment, CDMA is used, for example. As the code used by RS, the base station 1 assigns different codes to each terminal 2 when setting CG. RS is attached before and after the data (DS: data signal) sent from the terminal 2. Since RS is orthogonal, the base station 1 can separate the signals of RS and measure the channel matrix H even in the overloaded MIMO state. In the present embodiment, the base station 1 always measures the latest channel matrix H for explanation.

[0050] In this embodiment, in the antennas ANT-B1 to ANT-BM, wireless signals in repeated resource blocks transmitted simultaneously from N terminals 2, which are greater than the number of antennas M, are received (overload MIMO). In each antenna ANT-B1 to ANT-BM, signals from multiple terminals 2 interfere with each other. Moreover, in the state of overload MIMO, the effect of transmit diversity is not produced. Here, in the base station 1 of this embodiment, the processor 11 repeatedly performs successive interference cancellation (SIC), which sequentially performs minimum mean square error (MMSE) equalization and removal of interference replicas of the transmitted signal.

[0051] In SIC, the processor 11 first calculates the received signals s1 and s2 from the transmission branches 1 and 2 (the antennas ANT-1 and ANT-2 of the terminal 2-1) by MMSE equalization. Then, the processor 11 generates interference replicas r1(i), r2(i), (i=1, ..., M) from the transmission branches 1 and 2 (transmission antennas ANT-1 and ANT-2) corresponding to the received signals s1 and s2. The interference replicas r1(i) and r2(i) are estimated values ​​of the received signals from the transmission branches 1 and 2 (transmission antennas ANT-1 and ANT-2) before MMSE equalization received by the receiving antenna ANT-Bi.

[0052] Then, the processor 11 removes interference replicas r1(i), r2(i), (i=1, ..., M) from the received signals on the antennas ANT-B1 to ANT-BM. As a result, the processor 11 can obtain received signals that are not affected by the transmitted signals from the transmission branches 1 and 2 (transmitting antennas ANT-1 and ANT-2) in the antennas ANT-B1 to ANT-BM. Hereinafter, the SIC process is repeatedly performed on the transmission branches 2j-1 and 2j (transmitting antennas ANT-2j-1 and ANT-2j of the terminal 2-j), (j=2, ..., N) in sequence. That is, in loop j, the same process is repeated for the received signals from the terminal 2-1 to the terminal 2-j-1 without the transmitted signals. Through the control of the processor 11 in this way, the received signals from the antennas ANT1, ANT2, ..., ANT2N-1, and ANT2N of the terminal 2 are calculated in sequence for the wireless signals received by overload MIMO.

[0053] The replica removal unit 101 subtracts interference replicas r1(1), r2(2) to r2j-3(i), r2j-2(i), (i=1, ..., M) of the terminal 2-1 to the terminal 2-j-1 from each received signal s(i), (i=1, ..., M) received in the receiving antennas ANT-B1 to ANT-BM in the j-th SIC cycle. The processing based on the replica removal unit 101 can be called the third processing of extracting a signal from which a replica of the incoming wireless signal is removed from the received wireless signal.

[0054] The diversity reception and equalization processing unit 102 suppresses interference other than the terminal 2-j (transmitting antennas ANT-2j-1, ANT-2j) of interest by the MMSE method. Then, the diversity reception and equalization processing unit 102 obtains the reception signal from the terminal 2-j of interest (transmitting antennas ANT-2j-1, ANT-2j) through each receiving antenna ANT-B1 to ANT-BM. That is, the diversity reception and equalization processing unit 102 obtains the reception signal from the terminal 2-j of interest (transmitting antennas ANT-2j-1, ANT-2j) based on the channel matrix H and its Hermitian transposed matrix H H , the MMSE weight matrix W is calculated by the following formula (1). I is the identity matrix with M rows and M columns.

[0055] W=H H {HH H +NI} -1 ; (Formula 1)

[0056] Then, the diversity reception and equalization processing unit 102 multiplies each reception signal s(i), (i=1, ..., M) received at the reception antennas ANT-B1 to ANT-BM by the MMSE weight matrix W. Thus, the diversity reception and equalization processing unit 102 performs equalization processing that suppresses interference from other transmission antennas for the signals from the transmission antennas ANT-2j-1 and ANT-2j of each terminal 2-j. In the j-th cycle of each SIC, the diversity reception and equalization processing unit 102 obtains the terminal 2 with the strongest signal (good signal) among the terminals 2 other than the terminals 2-1 to the terminal 2-j-1 that have been removed in the first to j-1 cycles according to the calculation result of (Formula 1). Then, the diversity reception and equalization processing unit 102 determines the terminal 2-j selected in the j-th cycle. Then, the diversity reception and equalization processing unit 102 performs the reception processing of the transmit diversity using a plurality of branches from the determined one terminal 2-j. Therefore, the diversity reception and equalization processing unit 102 selects the terminal 2 with the strongest signal (good signal) in any branch as the terminal 2 with the strongest signal. The process of calculating the signal from the terminal 2 with the strongest signal by MMSE equalization can be called the process of obtaining the first signal with at least one of the amplitude and phase adjusted from the first wireless communication terminal among the plurality of wireless communication terminals.

[0057] The demodulation unit 103 generates a bit sequence based on the received signal obtained by the diversity reception and equalization processing unit 102. The decoding unit 104 decodes the error correction code based on the bit sequence obtained by the demodulation unit 103 and obtains data. The processing from the diversity reception and equalization processing unit 102 to the demodulation unit 103 can be called a first processing of obtaining a first signal in which at least one of the amplitude and the phase is adjusted from a first wireless communication terminal among a plurality of wireless communication terminals and obtaining first data demodulated based on the first signal.

[0058] The replica generation unit 105 generates interference replicas that are transmitted from the antennas ANT2j-1 and ANT2j of the terminal 2 and received by the receiving antennas ANT-B1 to ANT-BM, based on the decoded signal from the terminal 2.

[0059] That is, the coding unit 106 performs error correction coding again on the data transmitted from the terminal 2 and decoded. The modulation unit 107 performs digital modulation on the error correction coded data. The transmission diversity processing unit 108 performs the same transmission diversity processing as the terminal 2. The channel matrix multiplication unit 109 multiplies the transmission signal transmitted from each transmission branch of the terminal 2 by the channel matrix. Through this multiplication, interference replicas received in the receiving antennas ANT-B1 to ANT-BM are generated. The data decoded by the decoding unit 104 can be referred to as the first data decoded according to the first signal. Therefore, it can be said that the replica generation unit 105 generates a replica of the incoming wireless signal by performing coding, modulation processing, transmission diversity processing and processing reflecting the state of the transmission path between the plurality of wireless communication terminals and the base station 1 on the first data. The processing based on the replica generation unit 105 can be referred to as the second processing of generating a replica of the incoming wireless signal.

[0060] Figure 5 This is a flowchart illustrating the CG-based processing of the base station 1. In this processing, the processor 11 approves the CG to the terminal 2 when connecting with the terminal 2, and specifies a different RS (Reference Signal) (R1) for each resource and terminal used in the CG. Here, when connected means, for example, when the connection is established between the terminal 2 and the base station 1 through a step called signaling, or when the initial setting is performed.

[0061] Next, the processor 11 implements the setting (R2) for receiving the SIC cycle in the base station 1. In the SIC cycle, for example, in order to confirm the RS received from the terminal 2 and identify the terminal 2, the processor 11 stores the relationship between the RS specified for the terminal 2 and the identification information of the terminal 2 in the memory 12. In addition, the processor 11 determines the number of SIC cycles and stores it in the memory 12. In addition, in the present embodiment, in the processing of R2, in the base station 1, when at least one of the multiple terminals 2 communicates in a manner in which no wireless resources are allocated, an upper limit on the number of terminals that can simultaneously send wireless signals is not set.

[0062] Next, the processor 11 receives a signal from the terminal 2 through the CG (R3). In addition, as the signal from the terminal 2 is received, the processor 11 appropriately responds to the response (ACK, NACK) from the base station 1. Then, when the base station 1 releases the connection with the terminal 2, the processor 11 releases the setting of the CG (R4) and ends the processing. According to the above processing, when the base station 1 approves the CG to the terminal 2, the processor 11 implements the setting for receiving the SIC cycle in the base station 1. Therefore, it can be said that the processor 11 executes the SIC cycle when allowing communication based on multiple terminals 2 and the base station 1 in a manner that does not allocate the wireless resources to at least one of the multiple wireless communication terminals.

[0063] Figure 6 This is an example of the reception processing based on CG between the base station 1 and the terminal 2 ( Figure 5 Flowchart of the steps of R3). In this process, the processor 11 obtains the received signal (S1) of the overload MIMO received by the receiving antennas ANT-B1 to ANT-BM and the wireless processing device 15. Next, the processor 11 obtains the signal (S2) sent from the terminal 2-1 of the branch with the strongest (good) signal by the MMSE method. The terminal 2-1 transmits a signal by transmitting diversity, so the processor 11 obtains the modulated carrier signal sent from the terminal 2-1 according to the multiple transmitting branches. The processor 11 performs the processing of S2 as a diversity receiving and equalization processing unit 102. The processing of S2 can be referred to as the processing of obtaining a first signal with an amplitude or phase adjusted from a first wireless communication terminal among multiple wireless communication terminals from the received wireless signal. In addition, the terminal 2-1 with the branch with the strongest (good) signal can be referred to as the first wireless communication terminal. In addition, obtaining a signal sent from the terminal 2-1 of the branch with the strongest (good) signal by the MMSE method can be referred to as an example of obtaining a first signal with an amplitude or phase adjusted from a first wireless communication terminal among multiple wireless communication terminals.

[0064] Next, the processor 11 performs digital demodulation processing (S3) based on the signal obtained in the process of S2. That is, a bit sequence is extracted from the modulated carrier signal as a baseband signal. The processor 11 performs the process of S3 as a demodulator 103. Next, the processor 11 decodes the data from the error correction coded signal as the baseband signal demodulated in the process of S3 (S4). The processor 11 performs the process of S4 as a decoder 104. Through the processes of S2 to S4, the data encoded, modulated, and carried by the modulated carrier in the terminal 2 is demodulated and decoded according to the received signal. Therefore, the processes of S2 to S4 can be called the first process.

[0065] Next, the processor 11 generates an interference replica from the transmission branch (transmission antenna) of the terminal 2-1 (S5). The processor 11 performs the process of S5 as the replica generation unit 105. The process of S5 can be called the second process. The interference replica can be called a copy of the incoming wireless signal.

[0066] Next, the processor 11 removes interference replicas (S6) from the received signals received by the receiving antennas ANT-B1 to ANT-BM and by the wireless processing device 15. The processing of S6 can be referred to as the third processing. In addition, the signal from which the interference replicas are removed from the received signal can be referred to as a residual signal. In addition, the processing of S6 to S9 is repeated until the signals of all terminals 2-j (j=1, ..., N) are separated. Therefore, in the processing S6 in the loop j in which the signal of the terminal 2-j is separated, the interference replicas corresponding to the terminals 2-1 to the terminal 2-j-1 are removed from the received signal. In the following, it is assumed that the processor 11 is processing the jth loop.

[0067] Next, the processor 11 separates the transmission signal from the terminal 2-j and performs diversity processing. Then, the processor 11 performs demodulation (S8) and decoding (S9). Then, the processor 11 determines whether there are any unseparated terminals 2 remaining (S10). In the case where there are unseparated terminals 2 remaining (Yes), the processor 11 returns the processing to S5. On the other hand, in the case where all the terminals 2 are processed and there are no unseparated terminals 2 remaining (No), the processor 11 ends the processing.

[0068] pass Figures 7 to 9 , illustrating simulation results based on the processing of this embodiment. Figure 7 The simulation conditions are illustrated as follows. The simulation was performed when the number of simultaneous transmitting terminals was 3 to 6 (each terminal 2 had two transmitting antennas) and when the number of simultaneous transmitting terminals was 5 to 10 (each terminal 2 had four transmitting antennas).

[0069] The transmission data size is 80 bits. The error correction code is Turbo code (coding rate 1 / 3). The modulation method is single carrier QPSK. The transmission path is assumed to be 1-path Rayleigh fading with a maximum Doppler frequency of 0 Hz. In addition, the signal-to-noise power ratio of the transmission path is assumed to be 30 dB.

[0070] exist Figure 8 The difference in message bit error rate based on whether SIC is applied or not in the simulation is illustrated. Figure 8 The curves in the figure are all examples without transmit diversity. Figure 8 In the figure, the horizontal axis is the number of terminals and the vertical axis is the message bit error rate. Figure 8 In the figure, the filled triangle mark indicates the case where the number of receiving antennas is 2 and SIC is not implemented, and the filled circle mark indicates the case where the number of receiving antennas is 2 and SIC is implemented. When SIC is not implemented, when the number of transmitting terminals is 3 and exceeds the number of receiving antennas 2, the message bit error rate deteriorates to a value exceeding 0.5. On the other hand, when SIC is implemented, the message bit error rate can be suppressed to about 0.1 even when the number of transmitting terminals is 3 and exceeds the number of receiving antennas 2.

[0071] In addition, Figure 8 In the figure, the blank triangle mark indicates the case where the number of receiving antennas is 4 and SIC is not implemented, and the blank circle mark indicates the case where the number of receiving antennas is 4 and SIC is implemented. When SIC is not implemented, when the number of transmitting terminals is 5 and the number of receiving antennas exceeds 4, the message bit error rate deteriorates to a value exceeding 0.2. On the other hand, when SIC is implemented, the message bit error rate can be suppressed to less than 0.01 even when the number of transmitting terminals is 5 and the number of receiving antennas exceeds 4.

[0072] Fig. 9 The difference in message bit error rate based on whether transmit diversity is applied in addition to SIC in the simulation is illustrated. Fig. 9 SIC is implemented in each of the graphs. Fig. 9 In the figure, the solid circle mark indicates the case where the number of receiving antennas is 2 and transmit diversity is not performed, and the solid square mark indicates the case where the number of receiving antennas is 2 and transmit diversity is performed. By implementing transmit diversity together with SIC, the message bit error rate can be improved. For example, even if the number of transmitting terminals is 3 and exceeds the number of receiving antennas by 2, the message bit error rate can be suppressed to about 0.01.

[0073] In addition, Fig. 9 In the figure, the hollow circle indicates the case where the number of receiving antennas is 4 and transmit diversity is not implemented, and the hollow quadrilateral indicates the case where the number of receiving antennas is 4 and transmit diversity is implemented. By implementing transmit diversity together with SIC, the message bit error rate can be improved. For example, even when the number of transmitting terminals is 6, the message bit error rate can be suppressed to about 0.001. In addition, even when the number of transmitting terminals is 7, the message bit error rate can be suppressed to about 0.01.

[0074] As described above, according to the communication system of this embodiment, in overloaded MIMO, by separating the signals from each terminal 2 through SIC, the message error rate can be suppressed, and efficient wireless communication can be achieved. In addition, according to the communication system of this embodiment, in overloaded MIMO, by using transmit diversity together with SIC, the message error rate can be further suppressed. That is, in this embodiment, in the base station 1, when communicating without allocating wireless resources to at least one of the multiple terminals 2, no upper limit is set for the number of terminals that can simultaneously send wireless signals. Even in such a case where there is no upper limit, the base station 1 separates the signals from the multiple terminals 2, and efficient and reliable wireless communication is achieved.

[0075] Therefore, in IoT, when CG is implemented and multiple terminals 2 communicate with base station 1 in a number exceeding the number of receiving antennas of the base station, base station 1 implements SIC to suppress the message error rate and achieve efficient and reliable wireless communication. In addition, base station 1 further achieves efficient and reliable wireless communication by using transmit diversity together with SIC. That is, in this embodiment, when base station 1 allocates CG resources to terminal 2 and allows CG, by executing SIC processing, it is foreseeable that the reliability of communication in CG and the efficiency of communication brought about by the suppression of message error rate can be improved.

[0076] Furthermore, in the present embodiment, since the interference replica is generated based on the error-corrected data, the base station 1 can generate the interference replica with high accuracy and feed it back even in a state where the signal-to-noise ratio SINR is low due to an overloaded MIMO state.

[0077] Description of Reference Numerals

[0078] 1 base station;

[0079] 2 Terminal;

[0080] 11 Processor;

[0081] 12 Memory;

[0082] 13 Internal interfaces;

[0083] 14 Network interface;

[0084] 15. Wireless processing device;

[0085] 101 Duplicate Removal Department;

[0086] 102 Diversity and equalization processing unit;

[0087] 103 Demodulation Department;

[0088] 104 Decoding Department;

[0089] 105 copy generation department;

[0090] 106 Coding Department;

[0091] 107 Modulation Department;

[0092] 108 transmit diversity processing unit;

[0093] 109 Channel Processing Unit;

[0094] ANT antenna.

Claims

1. A base station that, when a communication request is generated from a plurality of wireless communication terminals each having a plurality of transmission branches to the base station, does not accept the allocation of the wireless resource based on the wireless resource allocation request, allows the communication based on the wireless communication terminal to the base station, and does not set an upper limit on the number of terminals that can be connected simultaneously, the base station comprising a control unit that performs the following processing: receiving a plurality of modulated wireless signals corresponding to the transmission branches from the plurality of wireless communication terminals; Determine a branch of the best wireless signal from the plurality of wireless signals corresponding to the transmission branches received from the plurality of wireless communication terminals, obtain a first signal whose amplitude and phase are adjusted based on the plurality of transmission branches from a first wireless communication terminal having the branch of the best wireless signal among the plurality of wireless communication terminals, and obtain a first process of first data demodulated according to the first signal; a second process of generating, based on the first signal or the first data, a replica of the wireless signal corresponding to the plurality of transmission branches arriving from the first wireless communication terminal before at least one of the amplitude and the phase is adjusted; A third process of extracting a signal from which a replica of the incoming wireless signal is removed from the received wireless signal; For the extracted signal, one of the second wireless communication terminals excluding the first wireless communication terminal among the plurality of wireless communication terminals is used as the first wireless communication terminal, and the first to third processes are sequentially repeated.

2. The base station according to claim 1, wherein: The first processing includes diversity processing for obtaining a wireless signal from the first wireless communication terminal through at least one of a plurality of different arrival paths and different arrival times.

3. The base station according to claim 1, wherein: The control unit executes a process of repeating the first process to the third process when allowing communication between at least one of the plurality of wireless communication terminals and the base station so that communication is performed without allocating the wireless resource to at least one of the plurality of wireless communication terminals.

4. The base station according to any one of claims 1 to 3, wherein: In the base station, when communicating without allocating the wireless resource to at least one of the plurality of wireless communication terminals, an upper limit on the number of terminals set when setting the number of wireless terminals capable of simultaneously transmitting wireless signals is not set.

5. The base station according to any one of claims 1 to 3, wherein: The control unit generates a replica of the incoming wireless signal by performing coding, modulation processing, transmit diversity processing, and processing reflecting a state of a transmission path between the plurality of wireless communication terminals and the base station on the first data.

6. A communication method, wherein when a request for communication is generated from a plurality of wireless communication terminals each having a plurality of transmission branches to a base station, allocation of the wireless resource based on the wireless resource allocation request is not accepted, communication based on the wireless communication terminal to the base station is permitted, and an upper limit is not set on the number of terminals that can be connected simultaneously, the communication method performing the following processing: receiving a plurality of modulated wireless signals corresponding to the transmission branches from the plurality of wireless communication terminals; Determine a branch of the best wireless signal from the plurality of wireless signals corresponding to the transmission branches received from the plurality of wireless communication terminals, obtain a first signal whose amplitude and phase are adjusted based on the plurality of transmission branches from a first wireless communication terminal having the branch of the best wireless signal among the plurality of wireless communication terminals, and obtain a first process of first data demodulated according to the first signal; a second process of generating, based on the first signal or the first data, a replica of the wireless signal corresponding to the plurality of transmission branches arriving from the first wireless communication terminal before at least one of the amplitude and the phase is adjusted; A third process of extracting a signal from which a replica of the incoming wireless signal is removed from the received wireless signal; For the extracted signal, one of the second wireless communication terminals excluding the first wireless communication terminal among the plurality of wireless communication terminals is used as the first wireless communication terminal, and the first to third processes are sequentially repeated.

7. The communication method according to claim 6, wherein: The first processing includes diversity processing for obtaining a wireless signal from the first wireless communication terminal through at least one of a plurality of different arrival paths and different arrival times.

8. The communication method according to claim 6, wherein: When communication between at least one of the plurality of wireless communication terminals and the base station is permitted in such a manner that communication is performed without allocating the wireless resource to at least one of the plurality of wireless communication terminals, a process of repeating the first process to the third process is performed.

9. The communication method according to any one of claims 6 to 8, wherein: In the communication method, when communicating without allocating the wireless resource to at least one of the plurality of wireless communication terminals, the base station does not set an upper limit on the number of terminals set when setting the number of wireless terminals that can simultaneously transmit wireless signals.

10. The communication method according to any one of claims 6 to 8, wherein: A replica of the incoming wireless signal is generated by performing coding, modulation processing, transmit diversity processing, and processing reflecting the state of a transmission path between the plurality of wireless communication terminals and the base station on the first data.

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