Base station and communication method

Abstract

To prevent a deterioration in communication quality in a situation in which overloaded MIMO easily occurs.SOLUTION: A base station does not receive allocation of wireless resources at the occurrence of a communication request and permits communication with the base station performed by a wireless communication terminal. The base station executes receiving wireless signals arriving from a plurality of wireless communication terminals and in which data is coded, acquiring, from the received wireless signals, a first signal in which at least one of the amplitude and the phase is adjusted from a first wireless communication terminal of the plurality of wireless communication terminals, second processing of generating a replication of a wireless signal arriving from the first wireless communication terminal before at least one of the amplitude and the phase is adjusted, third processing of extracting signals other than the replication of the arriving wireless signal from the received wireless signals, and processing of sequentially repeating first processing through the third processing.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] There is an increasing need to use terminals that can connect to public networks such as the Internet for control, and there is a demand for low latency in communications accessing public networks. Meanwhile, Multiple Input Multiple Output (MIMO) will be used in the future. MIMO is a technology in which a base station and a terminal communicate in the same frequency band using multiple antennas. In addition, in MIMO, a technology in which multiple terminals 2 are involved in communication at the same time is called multi-user MIMO. The number of terminals accessing public networks is expected to increase in the future, raising concerns about congestion on upstream lines.

[0003] In wireless communication, which is one type of communication for accessing a public network, a communication procedure called Configured Grant (CG) is defined. An example of a communication procedure that does not rely on CG is Dynamic Grant. In Dynamic Grant, a terminal sends data to a base station by The terminal transmits a scheduling request (SR) to the base station. The base station then assigns the radio resources that can be used for data transmission to the terminal using downlink control information (DCI) and grants permission for transmission. The terminal then receives permission to transmit and transmits data to the base station using the designated radio resources.

[0004] In contrast, in CG, the base station device transmits transmission parameters that specify the physical resources that can be used for data transmission in advance to the terminal device. Furthermore, the base station device transmits permission start, permission end, etc. for data transmission for access by CG. However, there are cases where the transmission parameters for physical resources, etc. and permission start are transmitted at the same time. This allows the terminal to immediately use the specified physical resources and transmit data to the base station without transmitting an SR and without receiving a DCI. In this way, in CG communications, terminals can send data to base stations without negotiating with them. For this reason, CG is expected to be a technology that will realize low-latency communications. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] "NR Physical Layer Specifications for 5G" NTT DOCOMO Technical Journal Vol. 26 No. 3 (Nov. 2018) Summary of the Invention [Problem to be solved by the invention]

[0006] However, CG increases the number of terminals (N) that transmit to the base station at the same time. A state in which the number of terminals (N) transmitting at the same time is greater than the number of receiving antennas M of a base station is called overloaded MIMO. An object of the disclosed embodiments is to suppress deterioration of communication quality in a situation in which overloaded MIMO is likely to occur. [Means for solving the problem]

[0007] The disclosed embodiments are exemplified by the following base station, which allows a plurality of wireless communication terminals to communicate with the base station when the terminals make a request for communication with the base station without receiving wireless resources based on a request for wireless resource allocation, and does not set an upper limit on the number of terminals that can be connected simultaneously.

[0008] The base station receives modulated radio signals arriving from the plurality of radio communication terminals, and identifies a first radio communication terminal among the plurality of radio communication terminals from the received radio signals. a first process of acquiring a first signal in which at least one of the amplitude and phase has been adjusted from the first wireless communication terminal and acquiring first data to be demodulated from the first signal; and a first process of acquiring first data to be demodulated from the first wireless communication terminal before at least one of the amplitude and phase has been adjusted based on the first signal or the first data. a second process for generating a replica of the incoming radio signal from the received radio signal; a third process for extracting a signal excluding copies of the wireless signal; and repeating the first to third processes in sequence, with one of the second wireless communication terminals excluding the first wireless communication terminal as the first wireless communication terminal. and a control unit that executes the process. [Effects of the Invention]

[0009] This base station can suppress deterioration of communication quality in situations where overloaded MIMO is likely to occur. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a wireless communication system according to this embodiment. [Figure 2] FIG. 2 is a diagram illustrating a hardware configuration of the base station 1 according to the present embodiment. [Figure 3] FIG. 3 is a block diagram illustrating the configuration of a terminal. [Figure 4] FIG. 4 is a block diagram illustrating the configuration of a base station. [Figure 5] FIG. 5 is a flowchart illustrating processing by the CG of the base station. [Figure 6] FIG. 6 is a flowchart illustrating a procedure of reception processing by CG between a base station and a terminal. [Figure 7] FIG. 7 is a table illustrating the conditions of the simulation. [Figure 8] FIG. 8 is a diagram illustrating the difference in packet error rate between the cases where SIC is applied and not applied in a simulation. [Figure 9] FIG. 9 is a diagram illustrating the difference in packet error rate between the application of SIC and the presence or absence of transmit diversity in a simulation. DETAILED DESCRIPTION OF THE INVENTION

[0011] 1 is a diagram illustrating a configuration of a wireless communication system according to this embodiment. The system includes a base station 1 and a plurality of terminals 2-1, 2-2, . . . , 2-N that communicate wirelessly with the base station 1. The terminals 2-1, 2-2, . . . , 2-N are also collectively referred to as terminals 2. In this embodiment, An example of such a system is an overloaded MIMO wireless communication system in which the number of terminals N is greater than the number of receiving antennas M at the base station in a multi-user MIMO system. Terminal 2 can be referred to as a wireless communication terminal.

[0012] Overloaded MIMO leads to a deterioration in communication quality. This is because overloaded MIMO makes it impossible for multi-user MIMO to remove all interfering signals. In the future, the number of terminals accessing the network is expected to increase further due to the Internet of Things (IoT). Therefore, it is considered that the number of terminals that can set CG will decrease. As a result, the number of terminals that can perform low-latency communication will be limited. Therefore, in this embodiment, a communication system that can suppress the deterioration of communication quality even in an overloaded MIMO state will be exemplified.

[0013] This embodiment discloses a base station that, when a communication request is issued from a plurality of wireless communication terminals to the base station, allows the wireless communication terminals to communicate with the base station without receiving wireless resources based on a wireless resource allocation request, 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 executed by this base station. Here, an example of communication by the wireless communication terminals to the base station that, when a communication request is issued from a plurality of wireless communication terminals to the base station, does not receive wireless resources based on a wireless resource allocation request is communication by CG.

[0014] The base station has a control unit that receives modulated radio signals arriving from a plurality of wireless communication terminals. Furthermore, the control unit executes the following first to third processes. Here, the arriving radio signals are received signals before being received by the base station.

[0015] Here, in the first processing, the control unit acquires, from the received wireless signals, a first signal in which at least one of the amplitude and phase from a first wireless communication terminal of the plurality of wireless communication terminals has been adjusted, and acquires first data to be demodulated from the first signal. The first signal in which at least one of the amplitude and phase has been adjusted is, for example, a first signal in which wireless signals arriving from wireless communication terminals other than the first wireless communication terminal have been suppressed and the wireless signal arriving from the first wireless communication terminal has been left as much as possible. This refers to a signal.

[0016] In the second processing, the control unit calculates the amplitude and phase based on the first signal or the first data. At least one of the signals is a replica of the radio signal coming from the first radio communication terminal before being adjusted. That is, the control unit generates a radio signal that arrives from the first radio communication terminal and is not yet received. A signal that simulates the signal is generated.

[0017] In the third process, the control unit removes copies of the incoming radio signal from the received radio signal. The signal obtained by removing the replica of the incoming radio signal from the received radio signal can be called a residual signal. The radio signal coming from the receiving terminal is extracted.

[0018] The control unit then selects the first of the plurality of wireless communication terminals for the extracted signal. The first to third processes are repeated in order, with one of the second wireless communication terminals excluding the first wireless communication terminal being set as the first wireless communication terminal. (1) When a communication request is made from a plurality of wireless communication terminals to a base station, no request is made for allocation of wireless resources. (2) Not receiving the allocation of the radio resources based on the allocation request. The radio signals transmitted from multiple wireless communication terminals are separated into signals for each wireless communication terminal. In this process, even if the number of wireless communication terminals communicating simultaneously exceeds an allowable limit, for example, the number of receiving antennas of a base station, the signals for each wireless communication terminal are well separated.

[0019] The first processing includes diversity processing for obtaining the radio signal from the first wireless communication terminal through at least one of a plurality of different arrival paths and different arrival times. By combining the first to third processing with the diversity processing, the signals from the plurality of wireless communication terminals are effectively separated.

[0020] The control unit allocates the radio resource to at least one of the plurality of radio communication terminals. When the wireless communication terminal is allowed to communicate with the base station in a manner that allows communication without The process of repeating the steps from the first to the third steps is performed. When a wireless communication terminal is allowed to communicate with a base station, the number of wireless communication terminals simultaneously communicating with the base station tends to exceed the allowable limit. In such communications between a base station and a number of wireless communication terminals exceeding the allowable limit, repeating the first to third processes is effective.

[0021] A base station does not allocate radio resources to at least one of a plurality of wireless communication terminals. In this system, the base station does not set an upper limit on the number of wireless terminals to which it can simultaneously transmit wireless signals. Even without such an upper limit, the base station can receive signals from multiple wireless communication terminals while suppressing an increase in the packet error rate.

[0022] The control unit performs encoding, modulation processing, transmission diversity processing, and A replica of the incoming radio signal is generated by performing processing that reflects the state of the transmission path between the plurality of wireless communication terminals and the base station. If the first data that has been demodulated, decoded, etc. is properly demodulated, decoded, etc., the control unit By using the first data thus obtained, a replica of the incoming radio signal can be generated with high accuracy. This is possible because the signal-to-noise ratio may be low in radio signals arriving from a number of radio communication terminals exceeding the allowable limit.

[0023] FIG. 2 is a diagram illustrating a hardware configuration of the base station 1 according to the present embodiment. It has 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 radio processing unit 15.

[0024] The processor 11 is also called a Central Processing Unit (CPU) or a Microprocessor Unit (MPU). The processor 11 is not limited to a single processor, but may have a multi-processor configuration. In addition, a single physical CPU connected to a single socket may have a multi-core configuration. Furthermore, the processor 11 may include an arithmetic unit with various circuit configurations, such as a Digital Signal Processor (DSP) or a Graphics Processing Unit (GPU). The processor 11 may also be integrated with an integrated circuit (IC), other digital circuits, or analog circuits. The integrated circuit may be an LSI, an Application Specific Integrated Circuit (ASIC), a processor, or the like. The processor 11 may include, for example, a programmable logic device (PLD). The PLD may include, for example, a field-programmable gate array (FPGA). Microcontrollers (MCU), SoC (System-on-a-chip), system LSI, chipsets, etc. It can be anything that is called.

[0025] The memory 12 stores a sequence of instructions (computer program) to be executed by the processor 11, or data to be processed by the processor 11. The processor 11 and the memory 12 are sometimes called a baseband unit (BBU). The internal interface 13 connects various peripheral devices to the processor. It is a circuit connected to the processor 11. The baseband device can also be called a control unit.

[0026] The network interface 14 connects the base station 1 to 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.

[0027] The wireless processing device 15 includes a transceiver for transmitting wireless signals and a receiver for receiving wireless signals, and is connected to antennas ANT-B1, ..., ANT-BM. The wireless processing device 15 may have N systems of transceivers and receivers, the same number as the number of antennas. The baseband device is called a remote radio head (RRH) and is connected to a wired network by optical communication. It is also possible to configure the baseband equipment so that it is installed remotely by connecting it with a network. A network that connects the baseband device and the remote radio heads may also be called a fronthaul.

[0028] 3 is a block diagram illustrating the configuration of the terminal 2. In FIG. 3, the configuration of the terminal 2 is illustrated, along with radio resource blocks and a channel matrix H of radio channels. The blocks are divided into subcarrier frequencies assigned to terminal 2 and time axes. The channel matrix H is a matrix that indicates the amount of fluctuation in amplitude and phase of the transmission path between each antenna ANT1, ANT2, etc. of terminal 2 and the receiving antennas ANT-B1 to ANT-BM of the base station. By multiplying the transmission signal vector of each antenna ANT1, ANT2, etc. of terminal 2 on the transmitting side by the channel matrix H, it is possible to obtain an estimate of the received signal vector at the receiving antennas ANT-B1 to ANT-BM of the base station.

[0029] In FIG. 3, a plurality of terminals 2-1, . . . , 2-N are illustrated. The detailed configuration of terminal 2 is as follows: , is exemplified by terminal 2-1. In FIG. 3, 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 will be simply referred to as antenna ANT. However, in this embodiment, when the number of antennas of each terminal 2 is two, It is not limited to:

[0030] The terminal 2 is also called User Equipment (UE). The terminal 2 has a processor, a memory, a radio processing device, an antenna ANT, etc. The processor, memory, and radio processing device of the terminal 2 are similar to the processor 11, memory 12, and radio processing device 15 described in FIG. 2. However, in the terminal 2, the processor, memory, and radio processing device are usually housed in one housing. The processor of the terminal 2 executes radio communication processing including the processing of an encoding unit 206, a modulation unit 207, and a transmit diversity processing unit 208, by an instruction sequence (computer program) that is executable and deployed in the memory. Execute.

[0031] The encoding unit 206 performs error correction encoding on the data transmitted from the terminal 2. The error correction encoding may be soft decision encoding or hard decision encoding, and there is no limitation on the type of encoding. The encoded data is digitally modulated using a method such as Quadrature Amplitude Modulation (QAM), Phase Shift Keying (PSK), or Frequency Shift Keying (FSK).

[0032] The transmit diversity processing unit 208 separates the digitally modulated signal into multiple signals and transmits them as a diversity signal. The signal is radiated from multiple antennas ANT via a radio processing unit. In the example of Fig. 3, the transmit diversity processing unit 208 of each terminal 2 separates the transmission path using two antennas and forms a transmit diversity branch. However, in this embodiment, the processing by the transmit diversity processing unit 208 is not limited to diversity using multiple antennas. For example, if terminal 2 has a single antenna, the diversity processing 20 Wave diversity, time diversity, frequency diversity, etc. may be adopted. In this embodiment, there is no limitation on the diversity processing, and various types of diversity may be adopted. That is, in this embodiment, the processing by the transmission diversity processing unit 208 is This can be considered an example of diversity processing in which radio signals are obtained through at least one of a plurality of different arrival paths and different arrival times.

[0033] 4 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. The replica generation unit 105 also includes an encoding unit 106, a transmission diversity processing unit 108, and a channel The processor 11 illustrated in FIG. 2 executes a replica elimination unit 101, a diversity reception unit 102, and a multiplication unit 109 by using an instruction sequence (computer program) that is loaded in an executable manner in the memory 12. and an equalization processing unit 102, a demodulation unit 103, a decoding unit 104, a replica generation unit 105, an encoding unit 106, a transmission delay unit 107, a The diversity processing unit 108 and the channel matrix multiplication unit 109 perform their respective processes.

[0034] 4 illustrates the configuration of the base station 1 and the channel matrix H. The configuration of the channel matrix H is the same as that in FIG. 3. The channel matrix H is a matrix of the antennas ANT1, ANT2, etc. of the terminal 2 and the is a matrix showing the amplitude and phase fluctuations of the transmission path between the antennas ANT-B1 to ANT-B M of the station. The channel matrix H is the matrix of the signals transmitted from the antennas 2K-1, 2K (K=1, . . . , N) of each terminal 2. It is determined by receiving a Reference Signal (RS) at each antenna ANT-B1, ..., ANT-BM. The same applies when the number of antennas at each terminal 2 is different from 2. In short, the amount of variation corresponding to the transfer function of the transmission path is determined by the reference signal transmitted and received between each antenna ANTK on the transmitting side and each antenna ANT-BK on the receiving side.

[0035] In the communication system of this embodiment, the RS is transmitted in the same resource block as the resource block used in the CG. However, the RS may be transmitted in a resource block different from the resource block used in the CG. In this embodiment, the RS is transmitted in the same resource block as the resource block used for the CG, so that the RSs of multiple terminals 2 do not interfere with each other. The RSs from the respective transmitting antennas ANT of each terminal 2 are orthogonal to prevent overlapping. Examples of methods for orthogonalizing the RSs include a method of preventing overlapping in time (TDMA), a method of shifting frequencies (FDMA), and orthogonalization by code (CDMA). In this embodiment, for example, CDMA is adopted. When the base station 1 sets the CG, it assigns different codes to each terminal 2 as the codes used for the RSs. The RSs are used to transmit data (DS: data signal) transmitted from the terminal 2. Since RSs are orthogonal, base station 1 can transmit RSs even in an overloaded MIMO environment. The base station 1 can separate these signals and measure the channel matrix H. In this embodiment, the base station 1 will be described assuming that it has always measured the latest channel matrix H.

[0036] In this embodiment, antennas ANT-B1 to ANT-BM receive radio signals in overlapping resource blocks simultaneously transmitted from N terminals 2, which is greater than the number of antennas M (overlap). Each of the antennas ANT-B1 to ANT-BM receives signals from multiple terminals 2. Furthermore, in an overloaded MIMO state, the effect of transmit diversity is not achieved. Therefore, in the base station 1 of this embodiment, the processor 11 performs MMSE equalization and A serial canceller (SIC) that sequentially removes interference replicas is repeatedly executed.

[0037] In the SIC, the processor 11 first performs the signal processing on the transmitting branches 1 and 2 (antennas ANT-1 and ANT-2 of the terminal 2-1). ) by MMSE equalization. Next, the processor 11 calculates interference replicas r1(i), r2(i), r3(i), r4(i), r5(i), r6(i), r7(i), r8(i), r9(i), r10(i), r11, r12, r13, r14, r15, r16, r17, r18, r19, r19, r20, r21, r22, r23, r24, r25, r26, r27, r28, r29 ...8, r29, r29, r30, r31, r3 r2(i), (i = 1, , M), where interference replicas r1(i), r2(i) are estimates of the received signals from transmit branches 1 and 2 (transmit antennas ANT-1 and ANT-2) before MMSE equalization, received at receive antenna ANT-Bi.

[0038] Then, the processor 11 removes the interference replicas r1(i), r2(i), (i=1, . . . , M) from the received signals at the antennas ANT-B1 to ANT-BM. The antennas ANT-B1 to ANT-BM can acquire received signals that are not affected by the transmission signals from the transmission branches 2j-1 and 2j (transmission antennas ANT-1 and ANT-2). The SIC process is repeatedly executed for each of the receiving antennas ANT-2j-1, ANT-2j, (j=2, . . . , N). That is, in loop j, the transmission signals from the terminals 2-1 to 2-j-1 are removed. By such control of the processor 11, received signals from the antennas ANT1, ANT2, ..., ANT2N-1, ANT2N of each terminal 2 are sequentially obtained for the wireless signals received by overloaded MIMO.

[0039] The replica removal unit 101 removes the respective signals received by the receiving antennas ANT-B1 to ANT-BM. In the i-th SIC loop, interference replicas r1(1), r2(2) through r2j-3(i), r2j-2(i), (i=1, . . . , M) of terminals 2-1 through 2-j-1 are subtracted from the received signal s(i), (i=1, . . . , M). The process by the duplicate removal unit 101 is to remove duplicates of the incoming radio signal from the received radio signal. This can be considered the third process, which extracts the missing signals.

[0040] The diversity receiving and equalization processing unit 102 suppresses interference other than that of the terminal 2-j of interest (transmitting antennas ANT-2j-1, ANT-2j) by the MMSE method. The diversity receiving and equalization processing unit 102 then acquires received signals from the terminal 2-j of interest (transmitting antennas ANT-2j-1, ANT-2j) at each of the receiving antennas ANT-B1 to ANT-BM. That is, the diversity receiving and equalization processing unit 102 obtains a channel matrix H and its Hermitian transpose matrix H H Therefore, by the following formula (1), , calculate the MMSE weight matrix W, where I is an identity matrix with M rows and M columns.

[0041] W=H H {HH H + NI} -1 ; (Formula 1) The diversity reception and equalization processing unit 102 receives the signals from the receiving antennas ANT-B1 to ANT-BM. Each received signal s(i) (i=1, ,M) is multiplied by the MMSE weight matrix W. As a result, the diversity receiving and equalization processing unit 102 performs equalization processing on the signals from the transmitting antennas ANT-2j-1 and ANT-2j of each terminal 2-j, suppressing interference from other transmitting antennas. In the j-th loop of each SIC, the diversity receiving and equalization processing unit 102 obtains the terminal 2 with the strongest signal (good signal) from among the terminals 2 other than terminals 2-1 to 2-j-1 that have already been canceled in the 1st to j-1th loops, from the calculation result of (Equation 1). Then, the diversity receiving and equalization processing unit 102 determines the terminal 2-j to be selected in the j-th loop. Then, the diversity reception and equalization processing unit 102 receives a plurality of broadcasts from the determined terminal 2-j. Therefore, the diversity reception and equalization processing unit 102 determines whether one of the branches is the strongest for the terminal 2 with the strongest signal. The terminal 2 with the strongest signal (good signal) is selected. The process of obtaining the signal from the terminal 2 with the strongest signal by MMSE equalization is carried out by using the signal from the first wireless communication terminal among the plurality of wireless communication terminals. This can be said to be a process of obtaining a first signal in which at least one of the width and phase has been adjusted.

[0042] The demodulation unit 103 generates a bit string from the received signal obtained by the diversity reception and equalization processing unit 102. The decoding unit 104 decodes the error correction code from the bit string obtained by the demodulation unit 103 to obtain data. The processing by the diversity reception and equalization processing unit 102 to the demodulation unit 103 is performed when at least one of the amplitude and phase from a first wireless communication terminal among a plurality of wireless communication terminals is adjusted. This can be said to be a first process of obtaining a demodulated first signal and obtaining first data demodulated from the first signal.

[0043] The replica generation unit 105 generates interference replicas 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 signals from the terminal 2. Generate.

[0044] That is, the encoding unit 106 performs error correction encoding again on the data transmitted from the terminal 2 and decoded. The demodulation unit 107 digitally modulates the error correction encoded data. The channel matrix multiplication unit 109 multiplies the transmit signals that have been subjected to transmit diversity processing and transmitted from each transmit branch of the terminal 2 by a channel matrix. This multiplication generates interference replicas that are received at the receive antennas ANT-B1 to ANT-BM. The data decoded by the decoding unit 104 can be said to be first data decoded from the first signal. Therefore, the replica generation unit 105 generates a code for the first data. It can be said that a replica of the incoming radio signal is generated by performing multiplication, modulation processing, transmission diversity processing, and processing that reflects the state of the transmission path between the multiple radio communication terminals and the base station. The processing by replica generation unit 105 can be said to be a second processing that generates a replica of the incoming radio signal.

[0045] FIG. 5 is a flowchart illustrating processing by the CG of the base station 1. In this processing, the processor 11 grants CG to the terminal 2 when connecting with the terminal 2, and also designates resources to be used in the CG and a different RS (Reference Signal) for each terminal (R1). Here, "when connecting" refers to, for example, when the terminal 2 and the base station establish a connection by a procedure called signaling, or when the terminal 2 and the base station establish a connection for the first time. An example is when the initial setting is performed.

[0046] Next, the processor 11 performs settings for receiving the SIC loop in the base station 1 (R2). In the SIC loop, for example, the processor 11 checks the RS received from the terminal 2 and identifies the terminal 2. Therefore, the relationship between the RS assigned to the terminal 2 and the identification information of the terminal 2 is stored in the memory 12. The processor 11 also determines the number of SIC loops and stores the number in the memory 12. In the process of R2, the base station 1 allocates wireless resources to at least one of the multiple terminals 2. When a communication method is used without assigning a wireless resource, the number of terminals that can simultaneously transmit wireless signals is There is no upper limit.

[0047] Next, the processor 11 receives a signal from the terminal 2 by CG (R3). Upon receiving the signal from the terminal 2, the processor 11 returns a response (ACK, NACK) from the base station 1 as appropriate. Then, when the base station 1 releases the connection with the terminal 2, the processor 11 cancels the CG setting (R4) and ends the processing. According to the above processing, when the base station 1 permits the terminal 2 to use CG, the processor 11 performs settings for receiving the SIC loop within the base station 1. Therefore, the processor 11 does not allocate the wireless resource to at least one of the multiple wireless communication terminals. When a plurality of terminals 2 are allowed to communicate with the base station 1, it can be said that a SIC loop is executed. do.

[0048] FIG. 6 is a flowchart illustrating the procedure of reception processing (R3 in FIG. 5) by CG with terminal 2 in base station 1. In this processing, processor 11 acquires overloaded MIMO reception signals received by receiving antennas ANT-B1 to ANT-BM and radio processing device 15 (S1). Next, processor 11 acquires a signal transmitted from terminal 2-1 having the branch with the strongest (best) signal by the MMSE method (S2). Since terminal 2-1 transmits a signal by transmit diversity, processor 11 acquires a modulated carrier signal transmitted from terminal 2-1 based on multiple transmit branches. Processor 11 performs the processing of S2 as diversity reception and equalization processing unit 102. The process of S2 is to determine, from the received wireless signal, the first wireless communication terminal among the plurality of wireless communication terminals. This can be said to be a process of acquiring a first signal from a terminal whose amplitude or phase has been adjusted. The terminal 2-1 having the good signal branch can be called the first wireless communication terminal. In addition, by the MMSE method, obtaining the signal transmitted from the terminal 2-1 having the strongest (best) signal branch is possible by using the amplitude or can be said to be an example of obtaining a first signal whose phase has been adjusted.

[0049] Next, the processor 11 performs digital demodulation processing based on the signal obtained in the processing of S2 (S3). That is, a bit string is extracted as a baseband signal from the modulated carrier signal. The processor 11 performs the processing of S3 as the demodulation unit 103. Next, the processor 11 extracts data from the error correction coded signal, which is the baseband signal demodulated in the processing of S3. The processor 11, as the decoding unit 104, executes the process of S4. The processing involves encoding and demodulating the received signal at terminal 2 and converting it into data carried on a modulated carrier. Therefore, the processing from S2 to S4 can be called the first processing.

[0050] Next, the processor 11 generates an interference replica from the transmission branch (transmission antenna) of the terminal 2-1 (S5). The processor 11 executes the process of S5 as the replica generation unit 105. The process of S5 can be called the second process. The interference replica is a copy of the incoming wireless signal. It can be said that.

[0051] Next, the processor 11 removes the interference replicas from the signals received by the receiving antennas ANT-B1 to ANT-BM and the radio processing device 15 (S6). The process of S6 can be called the third process. Furthermore, the signal from which the interference replica has been removed from the received signal can be called the residual signal. Note that the processes from S6 to S9 are repeated until the signals of all terminals 2-j (j=1,...,N) are separated. Therefore, in processing S6 in loop j that separates the signal from terminal 2-j, interference replicas corresponding to terminals 2-1 through 2-j-1 are removed from the received signal. Hereinafter, it is assumed that processor 11 is currently processing the j-th loop.

[0052] Next, the processor 11 separates the transmission signal from the terminal 2-j and performs diversity processing. Then, the processor 11 executes demodulation (S8) and decoding (S9). Then, the processor 11 determines whether or not there are any unseparated terminals 2 remaining (S10). If there are any unseparated terminals 2 remaining, If the answer is YES, the processor 11 returns the process to S5. On the other hand, if all the terminals 2 have been processed and there are no unseparated terminals 2 remaining (NO), the processor 11 ends the process.

[0053] 7 to 9 show examples of simulation results obtained by the processing of this embodiment. The simulation conditions are as follows: This simulation is performed for a case where the number of simultaneous transmitting terminals is 3 to 6 (two transmitting antennas for each terminal), and a case where the number of simultaneous transmitting terminals is 5 to 10 (five transmitting antennas for each terminal). The experiment was conducted for the case of four transmitting antennas at terminal 2.

[0054] 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 one-path Rayleigh fading with a maximum Doppler frequency of 0 Hz. The signal-to-noise power ratio of the transmission path is also assumed to be 30 dB.

[0055] Figure 8 illustrates the difference in packet error rate depending on whether SIC is applied or not in a simulation. Each graph in Figure 8 is an example without transmit diversity. In Figure 8, the horizontal axis is the number of terminals and the vertical axis is the packet error rate. Also, in Figure 8, the filled triangle marks indicate The solid circle indicates the case where the number of receiving antennas is two and SIC is not implemented, and the solid circle indicates the case where the number of receiving antennas is two and SIC is implemented. When SIC is not implemented, the number of transmitting terminals becomes three, and when the number of receiving antennas exceeds two, the packet error rate deteriorates to a value exceeding 0.5. On the other hand, when SIC is implemented, even when the number of transmitting terminals is three and the number of receiving antennas exceeds two, the packet error rate It can be seen that the error rate can be suppressed to about 0.1.

[0056] In addition, the open triangle mark in Fig. 8 indicates the case where the number of receiving antennas is four and SIC is not implemented. The white circle marks indicate the case where SIC is performed with four receiving antennas. If SIC is not implemented, the number of transmitting terminals will be 5, and if the number of receiving antennas exceeds 4, the packet error rate will deteriorate to a value exceeding 0.2. It can be seen that even when the number of tenners exceeds 4, the packet error rate can be suppressed to less than 0.01.

[0057] Figure 9 illustrates the difference in packet error rate between the application of SIC and the presence or absence of transmit diversity in a simulation. That is, in each graph in Figure 9, SIC is implemented. Furthermore, in Figure 9, the solid circle marks represent the case where the number of receive antennas is two and transmit diversity is not implemented, and the solid square marks represent the case where the number of receive antennas is two and transmit diversity is not implemented. This is the case when transmit diversity is implemented. By implementing transmit diversity together with SIC, For example, if the number of transmitting terminals is 3 and the number of receiving terminals is 1, the packet error rate can be improved. It can be seen that even when the number of antennas exceeds two, the packet error rate can be suppressed to about 0.01.

[0058] Furthermore, in FIG. 9, the open circle marks indicate the case where the number of receiving antennas is four and transmit diversity is not implemented, and the open square marks indicate the case where the number of receiving antennas is four and transmit diversity is implemented. By implementing transmit diversity together with SIC, the packet For example, even when the number of transmitting terminals is six, the packet error rate is It can be seen that the packet rate can be suppressed to about 0.001. It can be seen that the error rate can be suppressed to about 0.01.

[0059] As described above, according to the communication system of this embodiment, in overloaded MIMO, SIC By separating the signals from each terminal 2, the packet error rate is reduced and the efficiency is improved. Furthermore, according to the communication system of this embodiment, in overloaded MIMO, by using transmit diversity together with SIC, packet errors can be further reduced. That is, in this embodiment, when the base station 1 communicates with at least one of the multiple terminals 2 without allocating radio resources to the terminals 2, the base station 1 simultaneously transmits radio signals to the terminals 2. There should be no limit on the number of devices that can be used. The station 1 separates signals from multiple terminals 2, enabling efficient and reliable wireless communication.

[0060] Therefore, in IoT, when CG is implemented and a large number of terminals 2 communicate with base station 1 in excess of the number of receiving antennas of the base station, base station 1 can suppress the packet error rate by implementing SIC. Therefore, efficient and reliable wireless communication is realized. Furthermore, when the base station 1 uses transmit diversity together with SIC, even more efficient and reliable wireless communication is realized. That is, in this embodiment, when the base station 1 allocates CG resources to the terminal 2 and allows the CG, it executes SIC processing, thereby improving the reliability of communication in the CG and reducing packet errors. It is expected that communication efficiency will be improved by reducing the rate.

[0061] In addition, in this embodiment, since an interference replica is generated based on the data after error correction, even in a state where the signal-to-interference-and-noise ratio (SINR) is low due to an overloaded MIMO state, the base station 1 can accurately Interference replicas can be generated and fed back. [Explanation of symbols]

[0062] 1 base station 2. Devices 11 processors 12 Memory 13 Internal Interface 14 Network Interface 15 Radio processing unit 101 Replica Removal Section 102 Diversity and equalization processing section 103 Demodulation section 104 Decoding unit 105 Replica Generation Unit 106 Encoding section 107 Modulation section 108 Transmission diversity processing unit 109 Channel Processing Unit ANT antenna

Claims

1. A base station that allows communication from a plurality of wireless communication terminals, each having a plurality of transmission branches, to the base station without receiving allocation of wireless resources based on a wireless resource allocation request when a communication request is made from the wireless communication terminals to the base station, and does not set an upper limit on the number of terminals that can be connected simultaneously, receiving a plurality of incoming modulated radio signals corresponding to the plurality of transmit branches from each of the plurality of wireless communication terminals; a first process of acquiring, from the received wireless signal, first signals in which at least one of amplitude and phase is adjusted based on a plurality of transmission branches from each of the plurality of wireless communication terminals, and acquiring first data demodulated from the first signal transmitted from a first wireless communication terminal having a transmission branch of the best wireless signal among the first signals; a second process of generating replicas of radio signals corresponding to a plurality of transmission branches arriving from the first radio communication terminal before at least one of the amplitude and the phase is adjusted, based on the first signal or the first data; a third process of extracting a signal from the received wireless signal, excluding copies of the incoming wireless signal; a control unit that executes a process of repeating the first process to the third process for the extracted signal, sequentially selecting one of the second wireless communication terminals among the plurality of wireless communication terminals, excluding the first wireless communication terminal, as the first wireless communication terminal.

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

3. The control unit executes a process of repeating the first process to the third process when at least one of the plurality of wireless communication terminals is allowed to communicate with the base station in a manner of communication without allocating the wireless resource to at least one of the plurality of wireless communication terminals. The base station of claim 1 .

4. 4. The base station according to claim 1, wherein when the base station communicates without allocating the wireless resources to at least one of the plurality of wireless communication terminals, no upper limit is set on the number of terminals to be set when setting the number of wireless terminals that can simultaneously transmit wireless signals.

5. The base station according to any one of claims 1 to 4, wherein the control unit generates a replica of the incoming radio signal by performing encoding, modulation processing, transmission diversity processing, and processing that reflects the state of a transmission path between the plurality of wireless communication terminals and the base station on the first data.

6. A communication method in which, when a request for communication is made from a plurality of wireless communication terminals each having a plurality of transmission branches to a base station, the wireless communication terminals are allowed to communicate with the base station without receiving allocation of the wireless resources based on a request for allocation of the wireless resources, and no upper limit is set on the number of terminals that can be connected simultaneously, receiving a plurality of incoming modulated radio signals corresponding to the plurality of transmit branches from each of the plurality of wireless communication terminals; a first process of acquiring, from the received wireless signal, first signals in which at least one of amplitude and phase is adjusted based on a plurality of transmission branches from each of the plurality of wireless communication terminals, and acquiring first data demodulated from the first signal transmitted from a first wireless communication terminal having a transmission branch of the best wireless signal among the first signals; a second process of generating replicas of radio signals corresponding to a plurality of transmission branches arriving from the first radio communication terminal before at least one of the amplitude and the phase is adjusted, based on the first signal or the first data; a third process of extracting a signal from the received wireless signal, excluding copies of the incoming wireless signal; a process of repeating the first process to the third process sequentially for the extracted signal, with one of the second wireless communication terminals among the plurality of wireless communication terminals excluding the first wireless communication terminal as the first wireless communication terminal.

7. 7. The communication method according to claim 6, wherein the first processing includes diversity processing for obtaining the radio 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 at least one of the plurality of wireless communication terminals is allowed to communicate with the base station in a manner of communication without allocating the wireless resources to at least one of the plurality of wireless communication terminals, a process of repeating the first process to the third process is executed.

9. 9. The communication method according to claim 6, wherein when the communication method is a method of communicating without allocating the radio resources to at least one of the plurality of radio communication terminals, the base station does not set an upper limit on the number of terminals to be set when setting the number of radio terminals to which radio signals can be simultaneously transmitted.

10. 10. The communication method according to claim 6, wherein a replica of the incoming radio signal is generated by performing encoding, modulation processing, transmission diversity processing, and processing that reflects 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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