Wireless communication method, terminal device, and control device

Abstract

Provided is a wireless communication method that is performed by a wireless communication system comprising a plurality of terminal devices and a base station. In the wireless communication method, a plurality of pieces of first propagation path information relating to a link between a plurality of terminal devices are estimated, a plurality of pieces of second propagation path information relating to a link between each of the plurality of terminal devices and the base station are estimated, the number of terminal devices required to satisfy a desired throughput from among the plurality of terminal devices is determined and each of these is designated as a relay terminal on the basis of the plurality of pieces of first propagation path information and the plurality of pieces of second propagation path information that have been estimated, and communication with the base station is performed via each designated relay terminal.　

Description

Wireless communication method, terminal device, and control device

[0001] The present invention relates to a wireless communication method, a terminal device, and a control device.

[0002] In recent years, the use of millimeter waves has been widely studied to increase the speed and capacity of wireless communications. However, millimeter waves (28 GHz and above) have a high degree of directivity and are subject to significant attenuation due to atmospheric moisture and other factors. Therefore, they are more susceptible to obstructions than lower frequency bands such as Sub-6 (less than 6 GHz). As a result, blockages are more likely to occur between base stations and terminal devices. Therefore, in order to mitigate this problem, relay transmission using a relay station, which is installed between the base station and the terminal device, has been proposed (see, for example, Non-Patent Document 1).

[0003] Y. Yu, and W. Zhang, “A Relaying Scheme based on diagonalization for multi-relay symmetric MIMO communication networks,” IEEE Commun, Lett., vol.21, no.8, Aug. 2017.

[0004] However, in order to achieve efficient transmission from the viewpoint of power saving, it is necessary to determine an appropriate relay route that can improve throughput. However, with conventional methods, it has sometimes been impossible to determine an appropriate relay route that can improve throughput.

[0005] In view of the above circumstances, an object of the present invention is to provide a technique capable of improving throughput in a system in which a plurality of relay terminals are installed between a base station and a terminal device.

[0006] One aspect of the present invention is a wireless communication method performed by a wireless communication system having a plurality of terminal devices and a base station, which estimates a plurality of first propagation path information regarding links between the plurality of terminal devices, estimates a plurality of second propagation path information regarding links between each of the plurality of terminal devices and the base station, determines as relay terminals from among the plurality of terminal devices a number of terminal devices required to satisfy a desired throughput based on the estimated plurality of first propagation path information and the estimated plurality of second propagation path information, and communicates with the base station via each determined relay terminal.

[0007] One aspect of the present invention is a terminal device in a wireless communication system comprising a plurality of terminal devices and a base station, the terminal device comprising: a quality information acquisition unit that estimates a plurality of first propagation path information regarding links between other terminal devices and second propagation path information regarding links between the terminal device and the base station; and a relay function unit that transmits frequency-multiplexed transmission target data to each of a number of relay terminals required to satisfy a desired throughput from among the plurality of terminal devices determined based on the estimated plurality of first propagation path information and the second propagation path information, and communicates with the base station via each relay terminal.

[0008] One aspect of the present invention is a control device in a wireless communication system comprising a plurality of terminal devices, a base station, and a control device that controls the plurality of terminal devices, the control device comprising: an acquisition unit that acquires a plurality of first propagation path information regarding links between the plurality of terminal devices and a plurality of second propagation path information regarding links between each of the plurality of terminal devices and the base station; a relay terminal determination unit that determines, based on the acquired plurality of first propagation path information and the acquired plurality of second propagation path information, as relay terminals a number of terminal devices from the plurality of terminal devices that are required to satisfy a desired throughput; a terminal device to be the target of data transmission or reception, and a communication unit that notifies information regarding the relay route to each determined relay terminal.

[0009] According to the present invention, it is possible to improve the throughput in a system in which a plurality of relay terminals are installed between a base station and a terminal device.

[0010] Fig. 1 is a diagram showing an example of the configuration of a wireless communication system in the present invention. Fig. 2 is a diagram showing an example of the configuration of a terminal device in an embodiment. Fig. 3 is a diagram showing an example of the configuration of a control device in an embodiment. Fig. 4 is a diagram showing an example of frequency resource allocation in an embodiment. Fig. 5 is a diagram showing an example of frequency resource and spatial resource allocation in an embodiment. Fig. 6 is a sequence diagram showing the flow of pre-processing performed by a wireless communication system in an embodiment. Fig. 7 is a sequence diagram showing the flow of relay processing performed by a wireless communication system in an embodiment. Fig. 8 is a flowchart showing the flow of relay path determination processing performed by a control device in an embodiment.

[0011] An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a diagram showing an example of the configuration of a wireless communication system 100 according to the present invention. The wireless communication system 100 includes a base station 10, a plurality of terminal devices 20, and a control device 30. Note that in the present invention, any number of terminal devices 20 may be used as long as there is more than one. In the following description, an example in which there are four terminal devices 20 will be described.

[0012] The base station 10 is a base station in a RAN (Radio Access Network). The base station 10 communicates within the RAN with a terminal device 20 (hereinafter referred to as a "transmitting terminal") among a plurality of terminal devices 20 that wants to transmit data to the base station 10 (hereinafter referred to as "transmitted data"), either directly or via one or more terminal devices 20. The base station 10 communicates within the RAN with a terminal device 20 (hereinafter referred to as a "receiving terminal") among the plurality of terminal devices 20 that is the destination of the requested data, either directly or via one or more terminal devices 20. Thus, the transmitting terminal and the receiving terminal include terminal devices 20 that transmit and receive data directly to and from the base station 10, and terminal devices 20 that transmit and receive data to and from the base station 10 via other terminal devices 20. In the following description, for ease of understanding, a terminal device 20 that relays data between the base station 10 and a terminal device 20 operating as a transmitting terminal or a receiving terminal may be referred to as a relay terminal.

[0013] A terminal device 20 forms a group with one or more other terminal devices 20. The terminal devices 20 belonging to each group form a wireless PAN (Personal Area Network) link between the terminal devices 20 belonging to the same group, thereby forming a wireless PAN network. A wireless PAN is a network formed between terminals located in close proximity, and is a network that uses less power than a RAN. FIG. 1 shows an example in which the wireless communication system 100 has one group G1, and the group G1 contains four terminal devices 20-1 to 20-4. Note that while FIG. 1 shows one group, the wireless communication system 100 may also have multiple groups. Furthermore, one group is also provided with a control device 30.

[0014] The terminal device 20 estimates propagation path information indicating the state of the propagation path between the terminal device 20 and the base station 10 and between the terminal device 20 and other terminal devices 20 belonging to the same group. The propagation path information is, for example, received power, a channel quality indicator (CQI), etc. Note that the propagation path information may be other information as long as it is information that can identify the state of the propagation path between the terminal device 20 and the base station 10 and between the terminal device 20 and other terminal devices 20 belonging to the same group. In the following explanation, an example will be given in which the propagation path information is CQI. Each terminal device 20 notifies the control device 30 of the estimated propagation path information.

[0015] The terminal device 20 estimates propagation path information between the terminal device 20 and the base station 10 by using a sounding signal transmitted from the base station 10. The terminal device 20 estimates propagation path information between the terminal device 20 and another terminal device 20 by transmitting and receiving a sounding signal to and from the other terminal device 20.

[0016] The terminal device 20 operates as either a transmitting terminal, a receiving terminal, or a relay terminal. A transmitting terminal is a terminal device 20 that transmits a transmission signal including data to be transmitted to the base station 10 directly or via a relay terminal. A receiving terminal is a terminal device 20 that is the destination of data transmitted from the base station 10 and receives the transmission signal from the base station 10 directly or via a relay terminal. A relay terminal is a terminal device 20 that relays between the base station 10 and a terminal device 20 operating as a transmitting terminal or a receiving terminal.

[0017] The control device 30 is a device that controls the entire wireless communication system 100. The control device 30 determines a relay route for transmitting and receiving data between, for example, a transmitting terminal or a receiving terminal and the base station 10. More specifically, the control device 30 determines which terminal device 20 should be used as a relay terminal for the relay route for transmitting and receiving data between the transmitting terminal and the base station 10. The control device 30 determines one or more terminal devices 20 from among the multiple terminal devices 20 to be relay terminals.

[0018] 2 is a diagram showing an example of the configuration of the terminal device 20 according to the embodiment. The terminal device 20 includes a RAN communication unit 21, a PAN communication unit 22, a control unit 23, a user function unit 24, and a relay function unit 25.

[0019] The RAN communication unit 21 is a wireless interface for the RAN. The RAN communication unit 21 communicates with the base station 10. The RAN communication unit 21 converts, for example, a transmission signal output from the relay function unit 25 into an appropriate frequency band and transmits the signal to the base station 10. The RAN communication unit 21 receives, for example, a transmission signal transmitted from the base station 10. The RAN communication unit 21 receives, for example, a sounding signal transmitted from the base station 10. The RAN communication unit 21 converts the received radio frequency band signal into a low frequency band for signal processing.

[0020] The PAN communication unit 22 is a wireless interface for the PAN. The PAN communication unit 22 communicates with other terminal devices 20 in the group and with the control device 30. The PAN communication unit 22 transmits, for example, a transmission signal output from the user function unit 24 or a sounding signal output from the control unit 23 to the terminal devices 20 in the group. Furthermore, the PAN communication unit 22 transmits a notification signal to the control device 30 in the group and receives a relay route notification transmitted from the control device 30.

[0021] The notification signal is a signal for notifying information to the control device 30. The notification signal includes, for example, at least one of a transmission relay request or a reception relay request, wireless quality information, remaining battery capacity, and transmission capability (for example, a link quality table including the number of antennas, bandwidth, frequency band, and transmission capacity per power consumption). The wireless quality information includes, for example, either propagation path information or received power information obtained with each terminal device 20, or propagation path information or received power information obtained with the base station 10. The transmission relay request is a signal for requesting relay of a transmission signal transmitted by a transmitting terminal. The reception relay request is a signal for requesting relay of a signal addressed to a receiving terminal.

[0022] A transmission relay request and a reception relay request are issued when the amount of data to be transmitted exceeds the rate achievable when transmitting directly to the base station 10, and when the amount of data to be received exceeds the rate achievable when receiving directly from the base station 10, respectively.

[0023] The relay route notification is a notification for notifying the relay route, and includes, for example, information such as quality information, remaining battery charge and transmission capacity, information indicating the relay route, and bandwidth information allocated to each terminal device 20 operating as a relay terminal, etc. The information indicating the relay route represents information for identifying the terminal device 20 determined as the relay route for the data to be transmitted (for example, identification information of the terminal device 20, address information of the terminal device 20, etc.).

[0024] The control unit 23 controls the entire terminal device 20. The control unit 23 is configured using one or more processors such as a CPU (Central Processing Unit) and one or more memories. The control unit 23 realizes the functions of a quality information acquisition unit 231, a notification unit 232, an acquisition unit 233, and an operation control unit 234 by the one or more processors executing programs. Furthermore, the control unit 23 includes a storage unit 235.

[0025] The quality information acquisition unit 231 acquires quality information between its own device and another terminal device 20 and between its own device and the base station 10. The quality information acquisition unit 231 acquires quality information between its own device and the base station 10, for example, by receiving a sounding signal transmitted from the base station 10 via the RAN communication unit 21. The quality information acquisition unit 231 acquires quality information between its own device and another terminal device 20, for example, by receiving a sounding signal transmitted from the other terminal device 20 via the PAN communication unit 22.

[0026] The notifying unit 232 notifies the surrounding terminal devices 20 of the sounding signal at a predetermined timing via the PAN communication unit 22. Furthermore, the notifying unit 232 notifies the control device 30 of the quality information obtained by the quality information acquiring unit 231, the remaining battery charge of the own device, the transmission capacity, and other information. Furthermore, the notifying unit 232 notifies the control device 30 of a transmission relay request or a reception relay request.

[0027] The acquisition unit 233 acquires the relay route notification transmitted from the control device 30. As a result, the acquisition unit 233 acquires information such as quality information, remaining battery capacity, and transmission capacity of the terminal device 20 operating as a relay terminal included in the relay route notification, information indicating the relay route, and bandwidth information.

[0028] The operation control unit 234 sets the operation mode of the own device. Specifically, the operation control unit 234 sets the operation mode of the own device to operate in either a transmission / reception mode or a relay mode. The operation control unit 234 sets the operation mode of the own device to the transmission / reception mode when the requested throughput is equal to or greater than the throughput achievable with the capabilities of the own device, or when it is desired to request data. The operation control unit 234 sets the operation mode of the own device to the relay mode in accordance with control from the control device 30.

[0029] The transmission / reception mode is a mode for transmitting desired data to the base station 10 or receiving data requested from the base station 10. The relay mode is a mode for operating the terminal device 20 as a relay terminal. In the relay mode, the terminal device 20 relays at least a part of a transmission signal transmitted from another terminal device 20 to the base station 10 as the destination, and relays at least a part of a transmission signal transmitted from the base station 10 to the terminal device 20 as the destination.

[0030] The storage unit 235 stores various types of information acquired by the acquisition unit 233. The storage unit 235 is, for example, a memory.

[0031] The user function unit 24 is a function unit that functions when the operation mode of the terminal device 20 is a transmission / reception mode. The user function unit 24 is composed of a transmission processing unit 241 and a reception processing unit 242. The transmission processing unit 241 performs transmission processing for transmitting signals to other terminal devices 20. The reception processing unit 242 performs reception processing for receiving signals transmitted from other terminal devices 20.

[0032] The transmission processing unit 241 includes a transmission signal processing unit 243 and a frequency multiplexing unit 244. The transmission signal processing unit 243 divides the transmission data for transmission to each relay terminal. For example, the transmission signal processing unit 243 divides the transmission data by a division number corresponding to the determined number of relay terminals. The frequency multiplexing unit 244 converts each transmission data divided by the transmission signal processing unit 243 into a transmission signal for each relay terminal and multiplexes the signals in the frequency direction.

[0033] The reception processing unit 242 includes a frequency separation unit 245 and a reception signal processing unit 246. The frequency separation unit 245 separates the signals transmitted from each relay terminal in the frequency direction. The reception signal processing unit 246 demodulates each signal separated in the frequency direction by the frequency separation unit 245 and rearranges the signals into an appropriate data sequence.

[0034] The relay function unit 25 is a function unit that functions when the operation mode of the terminal device 20 is in relay mode. The relay function unit 25 is composed of a reception processing unit 251 and a transmission processing unit 252. The reception processing unit 251 performs reception processing for receiving a signal transmitted from the transmitting terminal or base station 10. The transmission processing unit 252 performs transmission processing for transmitting a signal to the receiving terminal or base station 10.

[0035] The reception processing unit 251 includes a data extraction unit 253 and a demodulation unit 254. The data extraction unit 253 extracts signals in a frequency band relayed by the device itself from signals received via the RAN communication unit 21 or the PAN communication unit 22. For example, during uplink transmission, the data extraction unit 253 extracts signals in a frequency band relayed by the device itself from signals received from the transmitting terminal via the PAN communication unit 22. The frequency band relayed by the device itself can be identified based on band information stored in the storage unit 235.

[0036] For example, during downlink transmission, the data extraction unit 253 extracts signals in the frequency band relayed by the device itself from signals received from the base station 10 via the RAN communication unit 21. Uplink transmission is signal transmission in the direction from the transmitting terminal to the base station 10, and downlink transmission is signal transmission in the direction from the base station 10 to the receiving terminal. The demodulation unit 254 demodulates data using the signals extracted by the data extraction unit 253.

[0037] The transmission processing unit 252 includes a modulation unit 255 and a multiplexing method conversion unit 256. The modulation unit 255 modulates the data demodulated by the demodulation unit 254. The modulation unit 255, for example, modulates the data demodulated by the demodulation unit 254 into a form to be transmitted to the base station 10. The modulation unit 255, for example, modulates the data demodulated by the demodulation unit 254 into a form to be transmitted to the receiving terminal.

[0038] The multiplexing method conversion unit 256 is provided when the terminal device 20 uses MIMO (Multi-input-Multi-output) between the base station 10. Therefore, when the terminal device 20 does not use MIMO between the base station 10, the terminal device 20 does not need to be provided with the multiplexing method conversion unit 256. The multiplexing method conversion unit 256 performs spatial multiplexing processing.

[0039] 3 is a diagram showing an example of the configuration of the control device 30 in the embodiment. The control device 30 includes a communication unit 31, a control unit 32, and a storage unit 33. The communication unit 31 communicates with each terminal device 20.

[0040] The control unit 32 controls the entire control device 30. The control unit 32 is configured using one or more processors such as a CPU and one or more memories. The control unit 32 realizes the functions of an acquisition unit 321, a throughput acquisition unit 322, and a relay terminal determination unit 323 by the one or more processors executing programs.

[0041] The acquisition unit 321 acquires at least one of a transmission relay request, wireless quality information, remaining battery capacity, or transmission capacity included in a notification signal transmitted from each terminal device 20. The acquisition unit 321 stores the acquired wireless quality information, remaining battery capacity, and transmission capacity information in the storage unit 33 in association with identification information of the terminal device 20 that is the transmission source.

[0042] When the acquisition unit 321 acquires a transmission relay request, the throughput acquisition unit 322 acquires the throughput of the link between the terminal devices 20 (between the transmitting terminal and the relay terminal, or between the receiving terminal and the relay terminal) and the throughput of the link between the relay terminal and the base station 10, based on the quality information stored in the storage unit 33 and the throughput estimation table stored in the storage unit 33. The throughput estimation table is a table used to estimate the throughput of the link between the terminal devices 20 and the throughput of the link between the relay terminal and the base station 10.

[0043] The throughput estimation table is a table in which channel quality indicators (CQIs) are associated with throughput values. Therefore, the throughput acquisition unit 322 can refer to the throughput estimation table to acquire the throughput corresponding to each CQI included in each piece of quality information stored in the storage unit 33.

[0044] The relay terminal determination unit 323 determines one or more relay terminals from among the plurality of terminal devices 20 based on the throughput values ​​calculated by the throughput acquisition unit 322 .

[0045] The storage unit 33 stores wireless quality information, remaining battery charge, and transmission capacity information associated with the identification information of the terminal device 20, as well as a throughput estimation table. The storage unit 33 is configured using a storage device such as a magnetic storage device or a semiconductor storage device.

[0046] Next, we will explain the general flow of the present invention. In uplink transmission, a transmitting terminal transmits data to be transmitted to each relay terminal belonging to the same group as the base station 10 using a wideband signal. Each relay terminal extracts data that has been previously allocated to it within the transmission capacity of its own device from the received data to be transmitted and transmits it to the base station 10. At this time, the transmission bandwidth is set to W ｔ , the bandwidth relayed by each relay terminal is W ｎ (n=1,...,N, where N is the number of relay terminals), then W ｔ ≦Σ ｎ W ｎ By selecting N so that N satisfies the above condition, all transmission data that the transmitting terminal wishes to transmit can be relayed to the base station 10. The line from the relay terminal to the base station 10 may also use spatial multiplexing using MIMO.

[0047] In downlink transmission, the receiving terminal divides a data request it wishes to receive and notifies each relay terminal. Each relay terminal notifies the base station 10 of the data request it wishes to receive. Each relay terminal converts the data received from the base station 10 into the frequency band notified by the control device 30 and transmits it to the receiving terminal.

[0048] Fig. 4 is a diagram showing an example of frequency resource allocation in an embodiment, and Fig. 5 is a diagram showing an example of frequency resource and spatial resource allocation in an embodiment. Fig. 4 shows an example of frequency allocation when a transmission signal is transmitted from a transmitting terminal to a relay terminal, and Fig. 5 shows an example of frequency allocation when a transmission signal is relayed from each relay terminal to a base station 10. In Fig. 4, W ｔ represents the transmission bandwidth, and W １ ~W ３ represents the bandwidth relayed by each relay terminal. As shown in Figure 4, when a transmission signal is transmitted from a transmitting terminal to a relay terminal, the transmitting terminal arranges the transmission signals to be transmitted to each relay terminal in the frequency direction and transmits them to each relay terminal as a wideband signal.

[0049] 5, when transmitting a transmission signal from each relay terminal to the base station 10, each relay terminal transmits the transmission signal to the base station 10 in a lower frequency band. The transmission signals transmitted from each relay terminal can be separated by spatial separation in the base station 10. In this way, the link between the transmitting terminal and each relay terminal has a wider bandwidth than the link between each relay terminal and the base station 10.

[0050] 6 is a sequence diagram showing the flow of pre-processing performed by the wireless communication system 100 according to the embodiment. In FIG. 6, an example in which the number of terminal devices 20 is four (N=4) will be described, but for convenience of the drawing, the illustration of terminal devices 20-2 and 20-3 will be omitted. The terminal devices 20-2 and 20-3 will be described as performing the same processing as the terminal device 20-4.

[0051] The communication unit 31 of the base station 10 transmits a sounding signal (step S101). The sounding signal transmitted by the base station 10 is received by, for example, the terminal devices 20-1 to 20-4. The quality information acquisition unit 231-1 of the terminal device 20-1 estimates propagation path information between the base station 10 and the base station 10 based on the received sounding signal (step S102). The quality information acquisition unit 231-4 of the terminal device 20-4 estimates propagation path information between the base station 10 and the base station 10 based on the received sounding signal (step S103).

[0052] Each terminal device 20 associates information for identifying the estimated propagation path information (hereinafter referred to as "transmission path identification information") with the estimated propagation path information and notifies the control device 30 using a PAN or the like (step S104). The transmission path identification information is information for identifying whether the transmission path information is information obtained through a link between devices, and is, for example, identification information of each device (for example, identification information of the terminal device 20 and identification information of the base station 10).

[0053] The communication unit 31 of the control device 30 receives the propagation path information notified from each terminal device 20. The acquisition unit 321 stores the propagation path information received by the communication unit 31 in the storage unit 33 in association with the identification information of the terminal device 20 that is the sender. As a result, the storage unit 33 stores the propagation path information between the base station 10 and the terminal device 20-1, the propagation path information between the base station 10 and the terminal device 20-2, the propagation path information between the base station 10 and the terminal device 20-3, and the propagation path information between the base station 10 and the terminal device 20-4.

[0054] The broadcasting unit 232 of each terminal device 20 broadcasts a sounding signal at a predetermined timing (step S105). The sounding signal broadcast by each terminal device 20 is received by the other terminal devices 20. For example, the sounding signal broadcast by terminal device 20-1 is received by terminal devices 20-2 to 20-4. For example, the sounding signal broadcast by terminal device 20-4 is received by terminal devices 20-1 to 20-3.

[0055] The quality information acquisition unit 231-1 of the terminal device 20-1 estimates propagation path information between the terminal device 20-1 and the other terminal device 20 based on the received sounding signal (step S106). For example, the quality information acquisition unit 231-1 estimates propagation path information between the terminal device 20-2 based on the sounding signal transmitted by the terminal device 20-2. For example, the quality information acquisition unit 231-1 estimates propagation path information between the terminal device 20-3 based on the sounding signal transmitted by the terminal device 20-3. For example, the quality information acquisition unit 231-1 estimates propagation path information between the terminal device 20-4 based on the sounding signal transmitted by the terminal device 20-4.

[0056] The quality information acquisition unit 231-4 of the terminal device 20-4 estimates propagation path information between the terminal device 20-4 and the other terminal device 20 based on the received sounding signal (step S107). For example, the quality information acquisition unit 231-4 estimates propagation path information between the terminal device 20-1 based on the sounding signal transmitted by the terminal device 20-1. For example, the quality information acquisition unit 231-4 estimates propagation path information between the terminal device 20-2 based on the sounding signal transmitted by the terminal device 20-2. For example, the quality information acquisition unit 231-4 estimates propagation path information between the terminal device 20-3 based on the sounding signal transmitted by the terminal device 20-3.

[0057] Each terminal device 20 associates transmission path identification information (e.g., identification information of each terminal device 20) with the estimated propagation path information and notifies the control device 30 using a PAN or the like (step S108). The communication unit 31 of the control device 30 receives the propagation path information notified from each terminal device 20. The acquisition unit 321 stores the propagation path information received by the communication unit 31 in the storage unit 33 in association with the identification information of the terminal device 20 that is the sender. As a result, the storage unit 33 stores the propagation path information between the terminal devices 20-1 to 20-4.

[0058] Fig. 7 is a sequence diagram showing the flow of relay processing performed by the wireless communication system 100 in the embodiment. Fig. 7 explains the flow of relay processing during uplink transmission. In Fig. 7, an example is explained in which the number of terminal devices 20 is four (N = 4), but for convenience of the drawing, the illustration of terminal devices 20-2 and 20-3 is omitted. The terminal devices 20-2 and 20-3 will be explained as performing the same processing as terminal device 20-4.

[0059] When the requested throughput exceeds the throughput achievable with the capabilities of the terminal device 20-1, the operation control unit 234-1 sets the operation mode of the terminal device 20-1 to the transmission / reception mode. The notification unit 232-1 then notifies the control device 30 of a notification signal including a transmission relay request (step S201). Hereinafter, the terminal device 20-1 is referred to as the transmitting terminal that wishes to transmit the transmission target data. The communication unit 31 of the control device 30 receives the notification signal transmitted from the transmitting terminal (terminal device 20-1).

[0060] The control unit 32 of the control device 30 executes a relay route determination process based on the received transmission signal (step S202). The relay route determination process is a process for determining a relay terminal from among a plurality of terminal devices 20. In the relay route determination process for uplink transmission, a relay terminal is determined from among the terminal devices 20 other than the transmitting terminal (hereinafter referred to as "relay candidate terminals"). Specific processing of the relay route determination process will be described with reference to FIG. 8. Here, it is assumed that terminal devices 20-2 to 20-4 have been determined as relay terminals.

[0061] The relay terminal determination unit 323 of the control device 30 transmits a relay route notification to the transmitting terminal and the terminal devices 20-2 to 20-4, which are relay terminals, via the communication unit 31 (step S203). The transmitting terminal and the terminal devices 20-2 to 20-4 receive the relay route notification transmitted from the control device 30. The operation control unit 234 of the terminal devices 20-2 to 20-4 determines that the terminal devices have been determined as relay terminals based on the information indicating the relay route included in the received relay route notification. Thereafter, the operation control unit 234 of the terminal devices 20-2 to 20-4 sets the operation mode of the terminal devices to relay mode.

[0062] The transmitting terminal performs transmission processing of the data to be transmitted based on the relay route notification transmitted from the control device 30 (step S204). Specifically, the transmission signal processing unit 243 of the transmitting terminal divides the data to be transmitted for transmission to the terminal devices 20-2 to 20-4, which are relay terminals. For example, the transmission signal processing unit 243 divides the data to be transmitted into three parts. The transmission signal processing unit 243 may divide the data to be transmitted equally, or may divide it according to the transmission capacity of each relay terminal. The transmission signal processing unit 243 outputs each divided piece of transmission data to the frequency multiplexing unit 244.

[0063] The frequency multiplexing unit 244 converts each transmission data divided by the transmission signal processing unit 243 into a transmission signal for each relay terminal and multiplexes the signals in the frequency direction. The frequency multiplexing unit 244 transmits the multiplexed transmission signal to the terminal devices 20-2 to 20-4 via the PAN communication unit 22 (step S204).

[0064] The PAN communication units 22-2 to 22-4 of the terminal devices 20-2 to 20-4 receive transmission signals transmitted from the transmitting terminal. The PAN communication units 22-2 to 22-4 output the received transmission signals to the relay function units 25-2 to 25-4. The relay function units 25-2 to 25-4 perform relay processing of the data to be transmitted based on the transmission signals output from the PAN communication units 22-2 to 22-4 (step S205). Since the relay function units 25-2 to 25-4 perform similar processing, the following description will be given taking the relay function unit 25-4 as an example.

[0065] Specifically, the data extraction unit 253-4 of the relay function unit 25-4 identifies, from among the transmission signals, signals of a frequency band that the device itself will relay, based on the band information stored in the storage unit 235. The data extraction unit 253-4 extracts signals of the identified frequency band from the transmission signals. The data extraction unit 253-4 outputs the extracted signals to the demodulation unit 254-4. The demodulation unit 254-4 demodulates the data using the signals output from the data extraction unit 253-4. The demodulation unit 254-4 outputs the demodulated data to the modulation unit 255-4.

[0066] The modulation unit 255-4 modulates the data output from the demodulation unit 254-4 into a form for transmission to the base station 10. The modulation unit 255-4 outputs the modulated data to the RAN communication unit 21-4. The RAN communication unit 21-4 converts the modulated data output from the modulation unit 255-4 into an appropriate frequency band for transmission to the base station 10, thereby generating a transmission signal. The RAN communication unit 21-4 transmits the generated transmission signal to the base station 10 by radio.

[0067] When the terminal device 20-4 performs spatial multiplexing communication using MIMO with the base station 10, the modulation unit 255-4 outputs the modulated data to the multiplexing method conversion unit 256-4. The multiplexing method conversion unit 256-4 branches the modulated data output from the modulation unit 255-4 for spatial multiplexing and outputs the branched data to the RAN communication unit 21-4. The RAN communication unit 21-4 converts each piece of modulated data branched by the multiplexing method conversion unit 256-4 into an appropriate frequency band for transmission to the base station 10, thereby generating a plurality of transmission signals. The RAN communication unit 21-4 transmits the generated plurality of transmission signals to the base station 10 wirelessly using MIMO.

[0068] As described above, each of terminal devices 20-2 to 20-4, which are relay terminals, extracts a signal in the frequency band that the terminal device should relay from the transmission signal, and transmits a transmission signal generated based on the extracted signal to base station 10. At this time, terminal devices 20-2 to 20-4 transmit transmission signals at the same frequency to base station 10. Base station 10 receives the transmission signals transmitted from terminal devices 20-2 to 20-4 (step S206).

[0069] 8 is a flowchart showing the flow of a relay route determination process performed by the control device 30 in this embodiment. Here, as an example, a method will be described in which terminal devices are added to the relay terminals in order of the best propagation path conditions based on propagation path information (CQI).

[0070] The throughput acquisition unit 322 of the control device 30 estimates the throughput between the transmitting terminal and each relay candidate terminal (step S301). Specifically, the throughput acquisition unit 322 first acquires propagation path information between the transmitting terminal and each relay candidate terminal from among a plurality of pieces of propagation path information stored in the storage unit 33. At this time, the throughput acquisition unit 322 may acquire propagation path information in which identification information of the transmitting terminal and identification information of each relay candidate terminal are associated as transmission path identification information.

[0071] As a result, for example, the throughput acquisition unit 322 acquires propagation path information between the transmitting terminal (terminal device 20-1) and terminal device 20-2, propagation path information between the transmitting terminal (terminal device 20-1) and terminal device 20-3, and propagation path information between the transmitting terminal (terminal device 20-1) and terminal device 20-4. The throughput acquisition unit 322 estimates the throughput between the transmitting terminal and each relay candidate terminal using each piece of acquired propagation path information. For example, the control device 30 refers to a throughput estimation table and estimates the throughput of the link between the terminals for each relay candidate terminal based on propagation path information (e.g., CQI) between the transmitting terminal and each relay candidate terminal.

[0072] As described above, the throughput estimation table associates a channel quality index (CQI) with a throughput value. Therefore, the throughput acquisition unit 322 refers to the throughput estimation table and estimates the throughput value associated with the acquired propagation path information (e.g., CQI) between the transmitting terminal (terminal device 20-1) and the relay terminal (terminal device 20-2) as the throughput between the transmitting terminal and the relay terminal (terminal device 20-2).

[0073] Similarly, the throughput acquisition unit 322 refers to the throughput estimation table and estimates the throughput value associated with the acquired propagation path information (e.g., CQI) between the transmitting terminal (terminal device 20-1) and the relay terminal (terminal device 20-3) as the throughput between the transmitting terminal and the relay terminal (terminal device 20-3).The throughput acquisition unit 322 refers to the throughput estimation table and estimates the throughput value associated with the acquired propagation path information (e.g., CQI) between the transmitting terminal (terminal device 20-1) and the relay terminal (terminal device 20-4) as the throughput between the transmitting terminal and the relay terminal (terminal device 20-4).

[0074] Next, the throughput acquisition unit 322 estimates the throughput between the transmitting terminal and the base station 10 and between each relay candidate terminal and the base station 10 (step S302). Specifically, the throughput acquisition unit 322 first acquires propagation path information between the transmitting terminal and the base station 10 and propagation path information between each relay candidate terminal and the base station 10 from the plurality of pieces of propagation path information stored in the storage unit 33. At this time, the throughput acquisition unit 322 may acquire propagation path information in which identification information of the transmitting terminal and identification information of the base station 10 are associated as propagation path identification information, and propagation path information in which identification information of each relay candidate terminal and identification information of the base station 10 are associated as propagation path identification information.

[0075] As a result, for example, the throughput acquisition unit 322 acquires propagation path information between the transmitting terminal (terminal device 20-1) and the base station 10, propagation path information between the base station 10 and the relay candidate terminal (terminal device 20-2), propagation path information between the base station 10 and the relay candidate terminal (terminal device 20-3), and propagation path information between the base station 10 and the relay candidate terminal (terminal device 20-4).

[0076] The throughput acquisition unit 322 uses the acquired propagation path information to estimate the throughput between the transmitting terminal and the base station 10 and between each relay candidate terminal and the base station 10. For example, the control device 30 refers to a throughput estimation table and estimates the throughput of the link between the transmitting terminal and the base station 10 based on the propagation path information (e.g., CQI) between the transmitting terminal and the base station 10. Furthermore, the control device 30 refers to the throughput estimation table and estimates the throughput of the link between each relay candidate terminal and the base station 10 for each relay candidate terminal based on the propagation path information (e.g., CQI) between each relay candidate terminal and the base station 10.

[0077] Specifically, the throughput acquisition unit 322 refers to the throughput estimation table and estimates the throughput value associated with the acquired propagation path information (e.g., CQI) between the transmitting terminal (terminal device 20-1) and the base station 10 as the throughput between the transmitting terminal and the base station 10. Similarly, the throughput acquisition unit 322 refers to the throughput estimation table and estimates the throughput value associated with the acquired propagation path information (e.g., CQI) between the relay candidate terminal (terminal device 20-2) and the base station 10 as the throughput between the relay candidate terminal (terminal device 20-2) and the base station 10.

[0078] The throughput acquisition unit 322 refers to the throughput estimation table and estimates the throughput value associated with the acquired propagation path information (e.g., CQI) between the relay candidate terminal (terminal device 20-3) and the base station 10 as the throughput between the relay candidate terminal (terminal device 20-3) and the base station 10. The throughput acquisition unit 322 refers to the throughput estimation table and estimates the throughput value associated with the acquired propagation path information (e.g., CQI) between the relay candidate terminal (terminal device 20-4) and the base station 10 as the throughput between the relay candidate terminal (terminal device 20-4) and the base station 10.

[0079] The throughput acquisition unit 322 outputs each estimated throughput value to the relay terminal determination unit 323. Using each throughput value output from the throughput acquisition unit 322, the relay terminal determination unit 323 calculates the achievable throughput of the transmitting terminal and n (for example, n=4) relay candidate terminals as R Ｕｎ , the achievable throughput between the transmitting terminal and the base station 10 is R ＵＢ , n (for example, n=4) relay candidate terminals and the base station 10. ｎＢ (Step S303). The relay terminal determination unit 323 sorts the indices of the relay candidate terminals in descending order of the throughput of the relay link (Step S304). Here, the descending index is set as l(i) (i=1, . . . , N).

[0080] The relay terminal determination unit 323 assigns 1 to the constant M (step S305). The control device 30 calculates the throughput R when the relay candidate terminals with index numbers 1 to M are set as relay terminals based on the following formula (1) (step S306).

[0081]

[0082] At the start of the process, M=1, so the relay terminal determination unit 323 calculates the throughput R when the relay candidate terminals with the first index number are selected as relay terminals based on the above formula (1). After that, the relay terminal determination unit 323 checks whether the calculated throughput R is equal to the required throughput R. ｔｈThe control device 30 determines whether the calculated throughput R is greater than the required throughput R (step S307). ｔｈ If it is determined that the value is equal to or less than the predetermined value (step S307-NO), the relay terminal determination unit 323 adds 1 to the value of the constant M. Thereafter, the relay terminal determination unit 323 executes the process of step S306.

[0083] For example, when M=2, the relay terminal determination unit 323 calculates the throughput R when each of the relay candidate terminals with the first to second index numbers is selected as a relay terminal based on the above formula (1). Furthermore, when M=3, the relay terminal determination unit 323 calculates the throughput R when each of the relay candidate terminals with the first to third index numbers is selected as a relay terminal based on the above formula (1). In this way, the control device 30 calculates the throughput R when the throughput R is greater than the required throughput R ｔｈ A relay terminal is determined from among the relay candidate terminals until the number of relay terminals exceeds the limit.

[0084] In the process of step S304, the relay links are sorted in descending order of throughput, so the smaller the index number (for example, the closer the index number is to 1), the higher the throughput. Therefore, the relay terminal determination unit 323 determines relay candidate terminals as relay terminals in descending order of throughput.

[0085] In the process of step S307, the relay terminal determination unit 323 determines whether the calculated throughput R is equal to the required throughput R ｔｈ If it is determined that the length is greater than the predetermined length (YES in step S307), the relay terminal determination unit 323 ends the addition of the relay terminal (step S309). Thereafter, the relay terminal determination unit 323 determines a transmission frame length t1 between the transmitting terminal and each of the determined relay terminals, and a transmission frame length t2 between each of the determined relay terminals and the base station 10 based on the following equation (2) (step S310).

[0086]

[0087] The relay terminal determination unit 323 notifies each determined relay terminal and transmitting terminal of the destination and transmission frame length (step S311). Here, the uplink and downlink relay routes may be calculated separately, or the uplink route may be set as the downlink route as is. The downlink route may be determined first, and the same route may be used for the uplink.

[0088] In the wireless communication system 100 configured as described above, each terminal device 20 estimates propagation path information regarding the link between the terminal device 20 and the other terminal devices 20, and each terminal device 20 estimates propagation path information regarding the link between the terminal device 20 and the base station 10. The control device 30 determines, based on the estimated propagation path information, as many terminal devices 20 as necessary to achieve a desired throughput from among the multiple terminal devices 20 as relay terminals. The terminal device 20 operating as a transmitting terminal then communicates with the base station 10 via the determined relay terminals. In this manner, the control device 30 determines relay terminals by increasing the number of relay terminals until the desired throughput is achieved. Therefore, the terminal device 20 operating as a transmitting terminal transmits data to the base station 10 via as many relay terminals as possible to achieve the desired throughput. This makes it possible to improve throughput in a system in which multiple relay terminals are installed between the base station 10 and the terminal device 20.

[0089] Furthermore, in the wireless communication system 100, the control device 30 adds the terminal devices 20 as candidates for relay terminals in descending order of throughput between each of the terminal devices 20 and the base station 10, calculates the throughput during relaying, and ends the addition of the relay terminal when the calculated throughput satisfies the desired throughput. In this way, the control device 30 determines the terminal device 20 with the highest throughput during relaying as the relay terminal. This enables efficient relaying.

[0090] (Variation 1) In the above example, uplink transmission has been mainly described, but the present invention can also be applied to downlink transmission. When applying the present invention to downlink transmission, the pre-processing shown in FIG. 6 and the relay path determination processing shown in FIG. 8 are the same as those in the above-described embodiment. However, the downlink propagation path information is used. Note that, assuming that there is a correlation between the uplink and downlink propagation path information, the uplink propagation path information may be used as is. In FIG. 7, in the processing of step S201, the terminal device 20 (e.g., terminal device 20-1) operating as a receiving terminal that desires to acquire data transmits a reception relay request, rather than a transmission relay request, to the control device 30. This triggers the control device 30 to execute the processing of step S202. Then, in downlink transmission, the base station 10 divides the data that the receiving terminal desires to receive and notifies each relay terminal. Each relay terminal notifies the base station 10 of a request for the data that it desires to receive. Each relay terminal converts the data received from the base station 10 into the frequency band broadcast by the control device 30 and transmits it to the receiving terminal.

[0091] (Variation 2) In the above-described embodiment, a configuration has been described in which a relay terminal is determined based on propagation path information between terminal devices 20 and propagation path information between each terminal device 20 and the base station 10. The method for determining a relay terminal is not limited to the above-described method. For example, a method for determining a relay terminal may be performed using a method aimed at low-power relaying. When implementing a method aimed at low-power relaying, the relay terminal determination unit 323 uses information on the remaining battery capacity of each terminal device 20 in addition to the propagation path information between the terminal devices 20 and the propagation path information between each terminal device 20 and the base station 10. Specifically, the relay terminal determination unit 323 calculates a metric based on information on the remaining battery capacity of each of the multiple terminal devices 20, the propagation path information between the terminal devices 20, and the propagation path information between each terminal device 20 and the base station 10. Next, the relay terminal determination unit 323 adds candidates for relay terminals in descending order of metric and calculates the throughput during relaying based on the above formula (1). Then, the relay terminal determination unit 323 stops adding relay terminals when the calculated throughput satisfies the desired throughput. By determining the relay terminal in this manner, the terminal device 20 with the largest remaining battery power can be preferentially determined as the relay terminal.

[0092] (Variation 3) The control device 30 may be implemented in any of the terminal devices 20. In such a configuration, at least one of the terminal devices 20 further includes each functional unit included in the control device 30. The terminal device 20 having the control device 30 implemented therein performs the same processing as the processing performed by the control device 30. The terminal device 20 having the control device 30 implemented therein may exclude or include itself from the selection of relay terminals in the relay route determination processing.

[0093] In this case, the terminal device 20 equipped with the control device 30 acquires the propagation path information notified from the other terminal device 20. This process is executed by the acquisition unit 321. The propagation path information notified from the other terminal device 20 includes a plurality of pieces of propagation path information relating to links between the plurality of terminal devices 20 and propagation path information relating to links between the other terminal device 20 and the base station 10. As a result, the terminal device 20 equipped with the control device 30 holds each piece of propagation path information acquired by the other terminal device 20 in addition to each piece of propagation path information acquired by the terminal device itself.

[0094] The terminal device 20 having the control device 30 implemented therein determines, based on the plurality of pieces of propagation path information it holds, as relay terminals the number of terminal devices 20 required to satisfy the desired throughput. This process is executed by the relay terminal determination unit 323. Then, the terminal device 20 having the control device 30 implemented therein transmits a relay route notification to the terminal device 20 that is the target of data transmission or reception and to each of the determined relay terminals. This process is executed by the PAN communication unit 22.

[0095] Some of the functions of the terminal device 20 described above may be implemented by a computer. In this case, a program for implementing these functions may be recorded on a computer-readable recording medium, and the program may be loaded into a computer system and executed. Note that the term "computer system" here includes hardware such as an operating system (OS) and peripheral devices. Furthermore, the term "computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, read-only memories (ROMs), and CD-ROMs, as well as storage devices such as hard disks built into computer systems.

[0096] Furthermore, the term "computer-readable recording medium" may include a medium that dynamically stores a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, or a medium that stores a program for a certain period of time, such as a volatile memory within a computer system that serves as a server or client in such a case. The program may also be one that realizes part of the above-mentioned functions, or one that can realize the above-mentioned functions in combination with a program already stored in the computer system, or one that can be realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0097] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0098] The present invention is applicable to wireless access networks.

[0099] DESCRIPTION OF SYMBOLS 10... base station, 20, 20-1 to 20-4... terminal device, 21... RAN communication unit, 22... PAN communication unit, 23... control unit, 24... user function unit, 25... relay function unit, 30... control device, 31... communication unit, 32... control unit, 33... storage unit, 231... quality information acquisition unit, 232... reporting unit, 233... acquisition unit, 234... operation control unit, 235... storage unit, 241, 252... transmission processing unit, 242, 251... reception processing unit, 243... transmission signal processing unit, 244... frequency multiplexing unit, 245... frequency separation unit, 246... reception signal processing unit, 253... data extraction unit, 254... demodulation unit, 255... modulation unit, 256... multiplexing method conversion unit, 321... acquisition unit, 322... throughput acquisition unit 323...Relay terminal determination unit

Claims

1. A wireless communication method performed by a wireless communication system having a plurality of terminal devices and a base station, comprising: estimating a plurality of first propagation path information regarding links between the plurality of terminal devices; estimating a plurality of second propagation path information regarding links between each of the plurality of terminal devices and the base station; determining, based on the estimated plurality of first propagation path information and the estimated plurality of second propagation path information, a number of terminal devices required to satisfy a desired throughput from among the plurality of terminal devices as relay terminals; and communicating with the base station via each determined relay terminal.

2. The wireless communication method according to claim 1, further comprising the steps of: adding the plurality of terminal devices as candidates for relay terminals in descending order of throughput between the respective terminal devices and the base station, calculating the throughput during relaying; and terminating the addition of the relay terminal when the calculated throughput satisfies the desired throughput.

3. The wireless communication method according to claim 1, further comprising: acquiring information on remaining battery charge of each of the plurality of terminal devices; adding the plurality of terminal devices as candidates for relay terminals in descending order of metric calculated based on the information on remaining battery charge of each of the plurality of terminal devices, the plurality of first propagation path information, and the plurality of second propagation path information, thereby calculating a throughput during relaying; and terminating the addition of the relay terminal when the calculated throughput satisfies the desired throughput.

4. A wireless communication method according to any one of claims 1 to 3, further comprising using the plurality of first propagation path information and the plurality of second propagation path information to determine a ratio of frame lengths of links between a terminal device to be transmitted or received from data and each relay terminal, and links between each relay terminal and the base station, so as to maximize throughput during relaying.

5. A wireless communication method according to any one of claims 1 to 3, wherein the terminal device transmits data to be transmitted to each relay terminal by frequency multiplexing, and each relay terminal extracts data to be transmitted by itself from the data to be transmitted received from the terminal device and transmits the data to the base station using a lower frequency band.

6. A terminal device in a wireless communication system having a plurality of terminal devices and a base station, comprising: a quality information acquisition unit that estimates a plurality of first propagation path information regarding links between other terminal devices and a second propagation path information regarding links between the terminal device and the base station; and a relay function unit that transmits frequency-multiplexed transmission target data to each of a number of relay terminals required to satisfy a desired throughput from among the plurality of terminal devices determined based on the estimated plurality of first propagation path information and the second propagation path information, and communicates with the base station via each relay terminal.

7. A terminal device as described in claim 6, further comprising: an acquisition unit that acquires from the other terminal devices a plurality of first propagation path information regarding links between a plurality of terminal devices and a second propagation path information regarding links between the other terminal devices and the base station; a relay terminal determination unit that determines, from the plurality of terminal devices, a number of terminal devices required to satisfy a desired throughput as relay terminals based on the plurality of first propagation path information and the second propagation path information estimated by the quality information acquisition unit and the plurality of first propagation path information and the plurality of second propagation path information acquired by the acquisition unit; and a communication unit that notifies a terminal device to be the target of data transmission or reception and each determined relay terminal of information regarding the relay route.

8. A control device in a wireless communication system comprising a plurality of terminal devices, a base station, and a control device for controlling the plurality of terminal devices, the control device comprising: an acquisition unit for acquiring a plurality of first propagation path information relating to links between the plurality of terminal devices and a plurality of second propagation path information relating to links between each of the plurality of terminal devices and the base station; a relay terminal determination unit for determining, as relay terminals, a number of terminal devices required to satisfy a desired throughput from the plurality of terminal devices based on the acquired plurality of first propagation path information and the acquired plurality of second propagation path information; and a communication unit for notifying a terminal device to be a target for transmitting or receiving data and each determined relay terminal of information regarding the relay route.

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