Communication system and communication method

Abstract

To improve quality of a result of MIMO demodulation.SOLUTION: A communication system for performing MIMO transmission between a base station and a plurality of terminals includes: a plurality of Helper terminals; a plurality of Detection terminals for outputting a decoded bit sequence and a residual error coefficient, respectively; and a destination terminal that has a function similar to the Detection terminals and, on the basis of respective decoded bit sequences and residual error coefficients acquired from the plurality of Detection terminals and the own terminal, performs selection on the received decoded bit sequences together with the minimum residual error coefficient. The destination terminal includes: a residual error determination unit for determining whether or not the respective residual error coefficients are lower than a determination threshold; and a transmission unit that when it is determined by the residual error determination unit that no residual error coefficients lower than the determination threshold exist, transmits a command for role changing from a role of the Detection terminal to the Helper terminal to a predetermined Detection terminal determined using a predetermined reference.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a technology for performing terminal-cooperative MIMO communication in a communication system in which MIMO transmission is performed between a base station and multiple communication terminals, in which multiple communication terminals cooperate with each other. [Background technology]

[0002] In recent years, MIMO transmission, which uses multiple antennas to perform spatial division multiplexing over the same wireless channel, has been adopted in various communication systems, including 5G and Wi-Fi, as a technology to increase capacity in communication systems.

[0003] Furthermore, in the past, in a communication system that performs terminal-linked MIMO communication, a communication has been proposed that combines what is called a Helper terminal that transfers a received signal waveform to a Detection terminal (determination terminal), and a Detection terminal that performs MIMO demodulation and determination processing using its own received signal and the received signal waveform from the Helper terminal (see Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Error Control on Mobile Station Sides in Collaborative Multiple-Input Multiple-Output Systems:IEEE Digital Object Identifier 10.1109 / ACCESS.2022.3156604Received January 11, 2022, accepted February 19, 2022, date of publication March 3, 2022, date of current version March 11, 2022. Summary of the Invention [Problem to be solved by the invention]

[0005] However, since the role of each terminal group was assigned fixedly, there was no method provided to further utilize the received signal waveform held by the detection terminal to improve the quality of the MIMO demodulation results when there was a large residual error after MIMO demodulation and decision processing.

[0006] The present invention has been made in view of the above circumstances, and has an object to improve the quality of the results of MIMO demodulation. [Means for solving the problem]

[0007] In order to achieve the above object, the present disclosure provides a communication system for performing MIMO transmission between a base station and a plurality of terminals, the communication system comprising: a plurality of Helper terminals that transmit signals received from the base station; a plurality of Detection terminals that perform MIMO decoding processing based on signals received from the plurality of Helper terminals and signals received from the base station, thereby outputting decoded bit strings and residual error coefficients, respectively; and a destination terminal that selects the decoded bit string received with the smallest residual error coefficient based on the decoded bit strings and residual error coefficients obtained from the plurality of Detection terminals and its own terminal having similar functions to the Detection terminal, wherein the destination terminal has a residual error determination unit that determines whether each residual error coefficient is below a determination threshold, and a transmission unit that, when the residual error determination unit determines that there is no residual error coefficient that is below the determination threshold, transmits an instruction to a predetermined Detection terminal determined according to a predetermined criterion to change its role from that of the Detection terminal to that of the Helper terminal. [Effects of the Invention]

[0008] As described above, the present disclosure provides an advantage in that it is possible to improve the quality of the results of MIMO demodulation. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an overall configuration diagram of a communication system according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating the electrical hardware configuration of each communication terminal and a base station. [Figure 3] FIG. 2 is a functional configuration diagram of each communication terminal. [Figure 4] FIG. 2 is a sequence diagram for explaining processing of the communication system according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] A communication system 10 according to an embodiment will be described below with reference to the drawings. The communication system 10 according to the embodiment is not limited to a specific system. For example, the communication system 10 according to the embodiment may be a wireless LAN, a system such as LTE (Long Term Evolution) or 5G (fifth generation mobile communication system), or a system other than these.

[0011] [Overall configuration of communication system] First, an overall configuration diagram of a communication system 10 will be described with reference to Fig. 1. Fig. 1 is an overall configuration diagram of a communication system according to an embodiment. As shown in Fig. 1, the communication system 10 includes a base station BS (hereinafter referred to as "BS") and a plurality of communication terminals (also simply referred to as "terminals") under the control of the BS.

[0012] The BS is equipped with multiple antennas and has the function of transmitting multiple streams of MIMO (Multi-Input Multi-Output) signals according to the number of antennas. Each of the communication terminals h1, h2, ..., hm; d1, d2, ..., dm (hereinafter, the communication terminals will be collectively referred to as "communication terminal MS") is equipped with one antenna, and the communication terminals MS cooperate with each other via wireless communication, and can transmit and receive signals to and from each other. FIG. 1 shows an example in which multiple communication terminals MS receive MIMO signals from the BS, thereby implementing terminal cooperation MIMO reception. Also, in FIG. 1, cooperation communication between the communication terminals MS is shown as Collaboration links. Note that the communication terminal MS may be equipped with multiple antennas.

[0013] The communication terminals MS are classified into either a Helper terminal group H including Helper terminals h1, h2, ..., hm, or Detection terminals D including Detection terminals d1, d2, ..., dm. The Helper terminals h1, h2, ..., hm are collectively referred to as "Helper terminal h." The Detection terminals d1, d2, ..., dm are collectively referred to as "Detection terminal d."

[0014] Helper terminal h relays the signal received from the BS to Detection terminal d, and Detection terminal d performs MIMO decoding processing (including demodulation processing) based on the signal received from the BS and the relayed signal from Helper terminal h.

[0015] Furthermore, among the multiple communication terminals MS (Helper terminal h, Detection terminal d), one or more destination terminals to which the wireless signal transmitted by the BS is addressed are included. In FIG. 1, as an example, one Detection terminal d1 also serves as destination terminal 30.

[0016] The Detection terminal d relays the results of the MIMO demodulation process (decoded bit string, residual interference coefficients β) to the destination terminal 30, and the destination terminal 30 acquires the decoded bit string based on the relayed MIMO demodulation process result. If the destination terminal 30 is also a Detection terminal d, the destination terminal 30 acquires the final decoded bit string using the results of its own MIMO demodulation process and the results of MIMO demodulation process received from other Detection terminals d.

[0017] Note that the multiple communication terminals MS in this embodiment may have the same configuration, or may have different configurations depending on the roles of the Helper terminal h, the Detection terminal d, and the destination terminal 30. When the multiple communication terminals MS have the same configuration, the processing differs depending on the roles.

[0018] [Hardware configuration] 2 is a diagram showing the electrical hardware configuration of each communication terminal and BS. As shown in Fig. 2, the communication terminal MS has a processor 1001, a memory 1002, an auxiliary storage device 1003, an input / output device 1004, and a transmission / reception unit 1005, which are connected by a bus 1010.

[0019] For example, a program that realizes the operation of the communication terminal MS is stored in the auxiliary storage device 1003. The program may also be stored in the auxiliary storage device 1003 from a computer-readable recording medium or from a server on a network via the network.

[0020] When the communication terminal MS is operating, the program is loaded into memory 1002, and processor 1001 reads and executes the program from memory 1002. For example, processor 1001 executes the above-mentioned MIMO decoding process, decoding result selection process, etc. Input / output device 1004 performs, for example, input and output of data.

[0021] Note that since the electrical hardware configuration of the BS is the same as that of the communication terminal MS, the description thereof is omitted.

[0022] 〔Functional Configuration of Communication Terminal〕 Subsequently, the functional configuration of the communication terminal will be described using FIG. 3. FIG. 3 is a diagram showing the functional configuration of the communication terminal. In FIG. 3, functional configuration examples (outline configuration examples) of the Helper terminal h, the Detection terminal d, and the destination terminal 30 are shown. FIG. 3 shows an example in which the destination terminal 30 also serves as the Detection terminal d.

[0023] <Functional Configuration of Helper Terminal> As shown in FIG. 3, the Helper terminal h includes a signal reception unit 11 and a signal transmission unit 19. The signal reception unit 11 receives the signal transmitted from the BS, and the signal transmission unit 19 transmits the signal by broadcast. Note that the transmission is not limited to broadcast. For example, it may be multicast.

[0024] <Functional Configuration of Detection Terminal> The Detection terminal d includes a signal reception unit 21, a decoding processing unit 22, a data transmission unit 23, a data reception unit 24, and a signal transmission unit 29. The signal reception unit 21 receives the signal broadcast from one or more Helper terminals h and the signal transmitted from the BS. The decoding processing unit 22 performs MIMO decoding processing on the signal received by the signal reception unit 21 and outputs data (decoded bit sequence) and a residual error coefficient β. The data transmission unit 23 transmits the data (decoded bit sequence) and the residual error coefficient β obtained by the decoding processing unit 22 to the destination terminal 30. This “transmission” includes a process in which the Detection function unit 30d in the destination terminal 30 that also serves as the Detection terminal d notifies the decoding result calculation unit 35 of the data (decoded bit sequence) and the residual error coefficient β. The data reception unit 24 receives a request for information on the decoded bit sequence (Detected Bit Sequence(s)) and the residual error coefficient β from the destination terminal 30. [[ID=E20]]

[0025] The signal receiving unit 21 also has the same function as the signal receiving unit 11 of the Helper terminal h. The signal transmitting unit 29 also has the same function as the signal transmitting unit 19 of the Helper terminal h.

[0026] <Functional configuration of destination terminal> The destination terminal 30 includes a detection function unit 30 d, a decoding result calculation unit 35 , an output unit 36 ​​, and a residual error determination unit 37 .

[0027] The Detection function unit 30d has the same functional configuration as the Detection terminal d. That is, the Detection function unit 30d has a signal receiving unit 21, a decoding processing unit 22, a data transmitting unit 23, a data receiving unit 24, and a signal transmitting unit 29. The data receiving unit 24 in the Detection function unit 30d receives data (decoded bit strings) and residual error coefficients β from one or more Detection terminals d.

[0028] The decoding result calculation unit 35 calculates (selects) the final decoding result based on multiple sets of data (decoded bit strings) and residual error coefficients β that are relayed from the decoding processing unit 22 via the data transmission unit 23 in a Detection terminal d other than the destination terminal 30, received by the data receiving unit 24 in the Detection function unit 30d of the destination terminal 30, and acquired from the data transmission unit 23, as well as sets of data (decoded bit strings) and residual error coefficients β that are directly acquired in the Detection function unit 30d from the decoding processing unit 22 via the data transmission unit 23.

[0029] The output unit 36 ​​outputs the data selected by the decoding result calculation unit 35 .

[0030] The residual error determination unit 37 determines whether the residual error coefficient β exceeds a determination threshold. This determination threshold is set to a constant value in advance. However, the residual error determination unit 37 may change the threshold for each residual error determination (processing block) described below according to a reliability target or the like that is assumed to be necessary depending on the communication content.

[0031] <Example of transmission flow for device-cooperative MIMO> An example of a terminal cooperation MIMI transmission flow executed by the communication system 10 will be described along the procedure shown in Fig. 4. Fig. 4 is a sequence diagram for explaining the processing of the communication system according to the embodiment.

[0032] S11: The BS transmits a signal (MIMO signal) to the communication terminal MS. For example, if the BS has four antennas, the BS transmits four streams of data (packets) as MIMO signals, and the signal receiving unit 11 of each communication terminal MS receives the signal transmitted from the BS.

[0033] S12: The signal transmission unit 19 of each Helper terminal h relays (waveform forwards) the signal that the terminal (own station) has received from the BS to each Detection terminal d. In this case, the signal transmission unit 19 of each Helper terminal h broadcasts the signal received from the BS.

[0034] Furthermore, the signal transmission unit 19 of each Helper terminal h broadcasts signals at different timings. In the example of Fig. 4, Helper terminal h1 transmits a signal first, Helper terminal h2 transmits a signal next, and so on, until Helper terminal hm transmits a signal last. This allows the receiving side to identify which Helper terminal h broadcasted the received signal (and whether the signal was received from the BS) based on the difference in reception timing.

[0035] S13: In each Detection terminal d, the decoding processing unit 22 performs MIMO decoding processing (detection processing) on ​​the signal relayed and transmitted by the signal receiving unit 21 from each Helper terminal h and the signal received by the signal receiving unit 21 from the BS, and obtains the decoded bit sequence (Detected Bit Sequence(s)) and residual error coefficient β, which are the decoding results. Examples of the MIMO decoding processing and the residual error coefficient β are disclosed in Reference 1. <Reference 1> Taromaru, Hokuto, et al. "Error control on mobile station sides in collaborative multiple-input multiple-output systems." IEEE Access 10 (2022): 26493-26500. S14: In each Detection terminal d, as an error control process, in response to a request from the destination terminal 30 received by the data receiving unit 24, the data transmitting unit 23 relays (transmits) information on the decoded bit string and the residual error coefficient β to the destination terminal 30. In the example shown in FIG. 4, since the Detection terminal d1 is the destination terminal 30, the data receiving unit 24 in the Detection function unit 30d of the destination terminal 30 receives information on the decoded bit string and the residual error coefficient β from each of the Detection terminals d2, ..., dm. Note that the destination terminal 30 performs MIMO demodulation processing as the Detection terminal d1, and therefore acquires the decoded bit string and the residual error coefficient β.

[0036] S15: The decoding result calculation unit 35 of the destination terminal 30 selects the decoded bit string received with the smallest residual error coefficient for each processing block based on the decoded bit strings and the residual error coefficients acquired from multiple Detection terminals d other than the destination terminal 30 and its own terminal (destination terminal 30) having the same function as Detection terminal d. Then, the output unit 36 ​​outputs the final decoding result (selected data). Note that the selection of the decoded bit string may be performed for each processing block, for each decoded stream, or for the entire decoded bit string. For example, when video data of a certain length is received as the decoded bit string, the entire decoded bit string is the decoded bit string corresponding to the video data of that length.

[0037] Here, a processing block is a bit string that is a unit for decoding processing by Detection terminal d. Here, as an example, a case will be described in which there are four BS antennas, three Detection terminals d, and Detection terminal dm is Detection terminal d3.

[0038] The data of stream sa, data of stream sb, data of stream sc, and data of stream sd acquired by the Detection terminal d1 (destination terminal 30) itself will be referred to as processing block data b1. The destination terminal 30 receives the data of stream sa, data of stream sb, data of stream sc, and data of stream sd as one processing block of data from the Detection terminal d2. These will be collectively referred to as processing block data b2. Furthermore, the Detection terminal d1 (destination terminal 30) receives the data of stream sa, data of stream sb, data of stream sc, and data of stream sd as one processing block of data from the Detection terminal d3. These will be collectively referred to as processing block data b3.

[0039] S16: The residual error determination unit 37 determines whether each residual error coefficient β is below a determination threshold (for example, 0.10) to determine whether there are no residual error coefficients β below the determination threshold (all residual error coefficients β are equal to or greater than the determination threshold). If there is one or more residual error coefficients β below the determination threshold, the decoding result calculation unit 35 selects the processing block data with the smallest residual error coefficient β below the determination threshold as the final decoding result. For example, if the residual error coefficient β of the processing block data b1 is 0.01, the residual error coefficient β of the processing block data b2 is 1.11, and the residual error coefficient β of the processing block data b3 is 0.05, the processing block data b1 is selected as the final decoding result.

[0040] S17: On the other hand, if the residual error determination unit 37 determines that there is no residual error coefficient β below the determination threshold, the data transmission unit 23 of the Detection function unit 30d transmits a role change instruction to a predetermined Detection terminal d determined by a "predetermined criterion," such as a predetermined order or random selection, from among the transmission sources of the residual error coefficient β. For example, if the residual error coefficient β of the processing block data b1 is 0.11, the residual error coefficient β of the processing block data b2 is 1.11, and the residual error coefficient β of the processing block data b3 is 0.15, the data transmission unit 23 of the Detection function unit 30d transmits a role change instruction from a Detection terminal to a Helper terminal to the Detection terminal d2. As a result, the predetermined Detection terminal d2 changes its role from a Detection terminal to a Helper terminal based on the role change instruction.

[0041] Note that, as the number of Helper terminals increases, the number of propagation paths increases and the accuracy of MIMO transmission improves, so it is expected that the residual error coefficient β of each processing block data will be improved (its value will decrease) in the next processing (processing S21) and onwards. As a result, when processing similar to processing S16 is performed again in processing S21 and onwards, if there is one or more residual error coefficients β that are below the decision threshold, the decoding result calculation unit 35 selects the processing block data with the smallest residual error coefficient β that are below the decision threshold as the final decoding result.

[0042] On the other hand, even if the residual error coefficient β is improved, when processing similar to process S16 is performed again from process S21 onwards, if there is no residual error coefficient β below the judgment threshold, the data transmission unit 23 of the detection function unit 30d transmits a role change instruction to the other (remaining) predetermined detection terminals d determined by the "predetermined standard." For example, if the residual error coefficient β of the processing block data b1 is 0.11 and the residual error coefficient β of the processing block data b3 is 0.13, the data transmission unit 23 of the detection function unit 30d transmits an instruction to the detection terminal d3 to change its role from a detection terminal to a helper terminal. As a result, the predetermined detection terminal d3 changes its role from a detection terminal to a helper terminal based on the role change instruction. Note that the role change from a detection terminal to a helper terminal can be repeated until a predetermined minimum number of detection terminals is reached. The minimum number of terminals is, for example, 1 or 0.

[0043] Then, after the BS transmits a signal (MIMO signal) to the communication terminal MS (see S21), the predetermined Detection terminal d2, as a Helper terminal hn, relays the signal that it received from the BS to each Detection terminal d (except for Detection terminal d2) (see S22). Note that if the residual error determination unit 37 determines that there is no residual error coefficient β that exceeds the determination threshold, the data transmission unit 23 of the Detection function unit 30d does not transmit an instruction to change roles.

[0044] [Major Effects of the Embodiments] As described above, Helper terminal h relays signals received from the BS to other Detection terminals d by broadcast communication. The multiple Detection terminals d each perform MIMO decoding processing and aggregate the results to destination terminal 30. Destination terminal 30 selects the optimal data. This reduces the amount of information that needs to be relayed between communication terminals, while improving the reception characteristics in the terminal-cooperative MIMO transmission scheme.

[0045] Furthermore, if the residual error after MIMO demodulation and decision processing is larger than the decision threshold, the destination terminal 30 can improve the quality of the MIMO demodulation result by further utilizing the received signal waveform of the detection terminal d.

[0046] 〔supplement〕 "Computer-readable recording media" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Furthermore, "computer-readable recording media" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs over networks like the Internet or telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within a computer system that serves as a server or client. Furthermore, the program may be a program that implements part of the aforementioned functions, or may be a program that can realize the aforementioned functions in combination with a program already stored in the computer system, or may be implemented using hardware such as a programmable logic device (PLD) or field programmable gate array (FPGA). [Explanation of symbols]

[0047] 10. Communication Systems 30 Destination terminal 21 Signal receiving unit 22 Decryption processing unit 23 Data transmission unit (an example of a transmission unit) 24 Data receiving unit (an example of a receiving unit) 29 Signal transmitter 30d Detection function section 35 Decoding result calculation unit 36 Output section 37 Residual error determination section

Claims

1. A communication system that performs MIMO transmission between a base station and a plurality of terminals, a plurality of helper terminals that transmit signals received from the base station; a plurality of detection terminals that perform MIMO decoding processing based on signals received from the plurality of helper terminals and signals received from the base station, and output decoded bit strings and residual error coefficients, respectively; a destination terminal that selects a decoded bit string received with a minimum residual error coefficient based on the decoded bit strings and residual error coefficients acquired from the plurality of detection terminals and its own terminal having the same function as the detection terminal; and The destination terminal: a residual error determination unit that determines whether each residual error coefficient is below a determination threshold; a transmitter that transmits, when the residual error determination unit determines that there is no residual error coefficient that is below the determination threshold, an instruction to change the role of the Detection terminal to the Helper terminal, to a predetermined Detection terminal determined by a predetermined criterion; A communication system having:

2. The communication system according to claim 1 , wherein the residual error determination unit changes the determination threshold in accordance with a reliability target assumed to be required depending on the content of communication.

3. The communication system according to claim 1 or 2, wherein the predetermined detection terminal changes its role from that of the detection terminal to that of the helper terminal based on the instruction.

4. A communication method executed by a communication system that performs MIMO transmission between a base station and a plurality of terminals, The communication system includes: a plurality of helper terminals that transmit signals received from the base station; a plurality of detection terminals that perform MIMO decoding processing based on signals received from the plurality of helper terminals and signals received from the base station, and output decoded bit strings and residual error coefficients, respectively; a destination terminal that selects a decoded bit string received with a minimum residual error coefficient based on the decoded bit strings and residual error coefficients acquired from the plurality of detection terminals and its own terminal having the same function as the detection terminal; and The destination terminal: a residual error determination process for determining whether each residual error coefficient is below a determination threshold; a transmission process of transmitting, to a predetermined detection terminal determined by a predetermined criterion, an instruction to change the role of the detection terminal to the helper terminal when the residual error determination process determines that there is no residual error coefficient that is below the determination threshold; A communication method that performs

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