Radio communication method, user terminal, and base station

Abstract

To provide a radio communication technique capable of suppressing power consumption.SOLUTION: A base station transmits a first control signal reporting a transmission of data, a second control signal relating to an inter-terminal communication and a data packet including the data to a plurality of terminals. The terminal demodulates the data packet on the basis of the first control signal and, in a case where the data packet is successfully demodulated, transmits a second data packet including the data which are successfully demodulated in a radio resource based on the second control signal to the other terminal. In a case where the demodulation of the data packet is failed, on the other hand, the terminal receives and demodulates the second data packet that the other terminal transmits in the radio resource based on the second control signal, and data obtained by the demodulation are defined as the data included in the data packet of which the demodulation is failed.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Cellular wireless communication systems were developed as systems that allow voice calls to be made while moving, regardless of the location of the telephone connected by a telephone line, and are now used not only for voice calls but also to access a wide variety of information and communication-based services.Furthermore, in addition to people using services via handheld terminals, their use is expanding into the industrial field, such as for remote control of various sensors and industrial machinery.

[0003] In a cellular wireless communication system, a base station is installed for each fixed service area, and a terminal communicates with the nearest base station. However, in places where it is difficult to install a base station due to cost or physical constraints, such as mountainous areas, on the sea, or inside an aircraft, a cellular wireless communication system has not been available. Therefore, in recent years, artificial satellites and high-altitude flying objects (hereinafter, in this disclosure, the term "satellite" is used to include artificial satellites and high-altitude flying objects) equipped with base station functions for a cellular wireless communication system have been developed. This will enable cellular wireless communication systems to be used anywhere on the planet. Although satellite-based communications have been around for some time, making them available as cellular wireless communications systems will make it possible to continue using the wide variety of services offered by cellular wireless communications systems developed using terrestrial base stations, making them highly useful. Satellite-based cellular wireless communications systems are also effective as emergency communications tools when terrestrial base stations become unusable due to disasters, etc.

[0004] Among the wide variety of services using cellular wireless communication systems, there are often communications that simultaneously deliver the same content to multiple terminals, such as receiving broadcasts, downloading popular content, and updating the terminals or the PCs and industrial equipment that use terminals as communication means. Communications to provide such services are more efficient when delivered via a communication channel set up for multiple specific or unspecified terminals (hereinafter referred to as a broadcast channel) rather than via a communication channel set up for each individual terminal (hereinafter referred to as an individual channel). Satellites, which can cover a wider area and provide communications to more terminals than terrestrial base stations, are highly suited to this type of communication.

[0005] In a cellular wireless communication system, a terminal connects to a base station and communicates with the base station under the control of the base station. Therefore, basically, there is no communication between terminals. However, the standard specifications for cellular wireless communication systems established by the 3rd Generation Partnership Project (3GPP (registered trademark)) state that , Release 12 and later standards established in 2013 support inter-device communication. The 3GPP standard specifications define two types of device-to-device communications: one in which a device is under the control of a base station and communicates with other devices using radio resources specified by the base station, and the other in which a device autonomously selects radio resources for device-to-device communications. The former minimizes the interference that device-to-device communications have on conventional communications between base stations and devices, while the latter enables device-to-device communications even in environments where communication with base stations is not possible. The Release 18 standard specifications in 2023 will support device-to-device communications using unlicensed frequency bands, and devices will use the CSMA-CA (Carrier Sense Multiple Access - Collision Avoidance) method to establish a connection before communicating with other devices. In this case, it is determined whether or not the frequency band for terminal-to-terminal communication is being used by another terminal, and if it is determined that the frequency band is not being used, terminal-to-terminal communication is performed.

[0006] Terminals that autonomously select radio resources in licensed frequency bands in accordance with the cellular radio communication system standards established by 3GPP for terminal-to-terminal communication select the radio resources to be used for transmission prior to transmission. A selection window, which is the range of selection, and a sensing window, which is the range of radio resources for monitoring radio wave usage status for that selection, are set. The terminal monitors control information for communications performed by other terminals within the sensing window and collects reservation information for the next radio resource to be used by the other terminals currently communicating. The terminal then selects a radio resource within the selection window that has no reservation information or that has reservation information by a terminal with weak signal strength, and transmits using that radio resource.

[0007] In wireless link design for cellular wireless communication systems, transmission power is controlled to the minimum necessary. The first reason is to reduce interference with communications using the same frequency. In cellular wireless communication systems, to efficiently utilize frequency resources, radio waves of the same frequency used in one area are repeatedly used in different areas. If the transmission power is higher than necessary, it will interfere with other communications using the same frequency and degrade the quality of those communications. For this reason, transmission power is controlled to the minimum necessary to ensure that each communication using the same frequency can be carried out with satisfactory quality. The second reason is to reduce power consumption in base stations or terminals. Needless to say, reducing the power consumption of wireless devices is a requirement for a low-carbon society. However, for terminals and satellite-mounted base stations, it is important to effectively utilize the limited power sources such as rechargeable batteries and solar cells.

[0008] The transmission power of a cellular wireless communication system is set so that the block error rate when a packet is received and decoded is, for example, 10 -1 This means that 9 / 10 of the received packets are correct. Always receive packets, with a 1 / 10 probability of receiving them incorrectly. For erroneous packets, the sender is asked to retransmit. This minimizes the total transmission power. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] M. H. C. Garcia et al., "A Tutorial on 5G NR V2X Communications," in IEEE Communications Surveys & Tutorials, vol. 23, no. 3, pp. 1972-2026, thirdquarter 2021, <URL: https: / / doi.org / 10.1109 / COMST.2021.<3057017> [Summary of the Invention] [Problems to be Solved by the Invention]

[0010] When transmitting data packets on a broadcast channel with multiple receiving terminals, it is conceivable to transmit with a transmission power such that all terminals satisfy a predetermined reception quality. However, in this method, the transmission power is adjusted so as to ensure sufficient signal strength for the terminal with the worst or assumed worst reception quality, resulting in an increase in the required transmission power. Also, even when multiple terminals receiving the broadcast channel have the same level of reception quality, i.e., the same level of block error rate, if the instantaneous noise and interference states are different for each terminal, reception errors will occur for different packets. If each terminal requests the base station, which is the transmission source, to retransmit different packets, the base station will retransmit more packets, leading to more power consumption.

[0011] One aspect of the present disclosure provides a wireless communication technology capable of suppressing power consumption. [Means for Solving the Problems]

[0012] One aspect of the present disclosure is a wireless communication method between a base station and a terminal, a first transmission step in which the base station transmits a first control signal notifying the transmission of data and a second control signal related to inter-terminal communication to the plurality of terminals; a second transmission step in which the base station transmits a data packet including the data to the plurality of terminals; a demodulation step in which the terminal demodulates the data packet based on the first control signal; an inter-terminal transmission step of transmitting, when the terminal has successfully demodulated the data packet, a second data packet including the successfully demodulated data to another terminal in a radio resource based on the second control signal; an inter-terminal reception step in which, when the terminal fails to demodulate the data packet, the terminal receives and demodulates the second data packet transmitted by another terminal in a radio resource based on the second control signal, and regards the demodulated data as the data included in the data packet that failed to be demodulated; A wireless communication method comprising:

[0013] Another aspect of the present disclosure is a receiving step of receiving, from a base station, a first control signal notifying transmission of data, a second control signal related to terminal-to-terminal communication, and a data packet including the data; a demodulation step of demodulating the data packet based on the first control signal; an inter-terminal transmission step of transmitting, when the demodulation of the data packet is successful, a second data packet including the successfully demodulated data to another terminal in a radio resource based on the second control signal; an inter-terminal reception step of receiving and demodulating the second data packet transmitted by another terminal in a radio resource based on the second control signal when demodulation of the data packet fails, and setting the demodulated data as the data included in the data packet that failed to be demodulated; The user terminal is provided with a processing unit that executes the above.

[0014] Yet another aspect of the present disclosure is A base station that transmits data to a plurality of terminals, transmitting a first control signal notifying the transmission of the data and a second control signal related to inter-terminal communication for transmitting and receiving the data between the plurality of terminals to the plurality of terminals; transmitting a data packet including the data to the plurality of terminals; The base station is characterized by the above. [Effects of the Invention]

[0015] According to the present disclosure, even if a terminal has deteriorated reception quality, it can receive data that has failed to be demodulated from other terminals with good reception conditions, thereby preventing an increase in transmission power required to restore a predetermined reception quality for a terminal whose reception quality has deteriorated or is assumed to have deteriorated. Also, since multiple terminals receiving the same data can each receive data that they failed to demodulate from a terminal that successfully demodulated it, the number of packets that the base station must retransmit is reduced. These aspects lead to a reduction in power consumption by the base station. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing the configuration of a wireless system according to an embodiment. [Figure 2] FIG. 2 is a functional block diagram of a user terminal and a base station according to the embodiment. [Figure 3] 6 is a flowchart of processing performed by a base station in the first embodiment. [Figure 4] 10 is a flowchart of processing performed by a user terminal according to the first embodiment. [Figure 5] 10 is a flowchart of a process performed by a base station in the second embodiment. [Figure 6] 13 is a flowchart of processing performed by a user terminal according to the fourth embodiment. [Figure 7] 13 is a flowchart of processing performed by a user terminal according to the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] (Embodiment 1) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The following embodiments are merely examples for the purpose of explanation, and the present disclosure is not limited to the configurations of the embodiments. For example, an example using mobile communication, particularly 5G standard cellular communication (mobile communication), will be described below, but the technology of the present disclosure may be applied to cellular communication other than the 5G standard, or wireless communication other than cellular communication.

[0018] FIG. 1 is a diagram showing the configuration of a wireless communication system according to this embodiment. The system includes multiple user terminals (User Equipment; UE) 10 and a base station 20. The user terminals 10 are devices with wireless communication capabilities, such as smartphone terminals, tablet terminals, personal computers (PCs), and IoT terminals. The base station 20 is installed, for example, on an artificial satellite or a high-altitude flying object, and performs communication with the user terminals 10. The base station 20 may have only the functionality of an RU (Radio Unit), or may have the functionality of a DU (Distributed Unit) or a CU (Central Unit) in addition to the RU. The base station 20 does not have to be installed in the air, such as on an artificial satellite or a high-altitude flying object, but may be installed on the ground.

[0019] FIG. 2 shows a functional block configuration of the user terminal 10 and the base station 20 according to this embodiment.

[0020] The radio unit 31 amplifies the radio signal, converts its frequency, extracts necessary frequency components, and modulates and demodulates it. The packet demodulator 32 demodulates the received packet and sends successfully demodulated packets to the packet disassembler, while also sending demodulation success / failure information to the radio protocol controller 36. The packet disassembler 33 separates the received data and control signal (received) from the successfully demodulated received packet. The received data is sent to the upper layer 34 as the content of the communication, and the control signal is sent to the radio protocol controller 36. The transmission data sent from the upper layer 34 and the control signal (transmitted) from the radio protocol controller 36 are assembled into a transmission packet by the packet assembler 35, which is then converted into a radio signal by the radio unit 31 and transmitted. The radio protocol controller 36 generates a control signal to be transmitted in accordance with standards and predetermined parameters, the success / failure of the demodulation of the received packet, the control signal in the received packet, etc., and controls the radio unit 31 so that the specified radio signal is transmitted and received using the specified radio resource.

[0021] The radio unit 31, packet demodulation unit 32, packet disassembly unit 33, packet assembly unit 35, and radio protocol control unit 36 ​​are each configured by a dedicated hardware circuit, but one circuit may have multiple functions. Also, any or all of the above functional units may be realized by a general-purpose processor executing a program.

[0022] 2 may have different detailed operations in the user terminal 10 and the base station 20, even if the functional blocks have the same name. Furthermore, functional blocks related to packet reception, such as the packet demodulator 32 and packet disassembler 33, are functional blocks necessary for the operation of both the base station 20 and the user terminal 10. However, since this embodiment describes transmission from the base station 20 to the user terminal 10, these functional blocks are necessary only for describing the user terminal 10 and are not necessary for describing the base station 20. In addition, functional blocks that are not directly necessary for describing the embodiment of the present invention in either the user terminal 10 or the base station 20, such as a power supply unit and a user interface unit, have been omitted.

[0023] Fig. 3 is a flowchart showing the flow of data transmission processing performed by the base station 20 in this embodiment. Note that the processing in Fig. 3 below is performed by the base station 20, and it is clear that the functional units (wireless protocol control unit 36, etc.) described below in relation to Fig. 3 are possessed by the base station 20, so repeated mention thereof will be omitted.

[0024] In step S101, data to be transmitted to a plurality of user terminals 10 is generated in an upper layer, and this data is notified to the wireless protocol control unit 36, thereby starting this process. Data transmission to multiple user terminals includes broadcast and multicast.

[0025] In step S102, the radio protocol control unit 36 ​​determines radio resources for transmitting packets containing data. The packets containing data are transmitted on a downlink data channel (PDSCH), and the radio protocol control unit 36 ​​determines frequency resource allocation and time resource scheduling in resource block units.

[0026] In step S103, the radio protocol control unit 36 ​​determines radio resources with which the terminals can perform terminal-to-terminal communication. Terminal-to-terminal communication is also called side link communication (SL communication), and the frequency resources and time resources to be used are determined by the base station 20. As will be described later, terminal-to-terminal communication in this embodiment is used to retransmit data transmitted from the base station 20 to the user terminal 10 between the terminals 10.

[0027] In step S104, the protocol control unit 36 ​​generates a control signal for notifying data transmission. In step S105, the protocol control unit 36 ​​generates a control signal notifying the wireless resources available for terminal-to-terminal communication. The control signal notifying the data transmission corresponds to a first control signal of the present invention, and the control signal notifying the wireless resources available for terminal-to-terminal communication corresponds to a second control signal of the present invention.

[0028] In step S106, the protocol control unit 36 ​​sends the control signals created in steps S104 and S105 to the packet assembling unit 35, and the packet assembling unit 35 generates a packet containing this control signal. Note that while it is assumed here that one packet is generated that includes a control signal notifying data transmission and a control signal related to terminal-to-terminal communication, two packets may be generated that each include these two control signals. These two control signals can be stored in a control signal field provided in the packet as a physical layer signal. The control signal related to terminal-to-terminal communication can also be stored in a data field in the packet as an upper layer message. The control information stored in the control signal field provided in the packet as a physical layer signal is sometimes called downlink control information (DCI). Furthermore, RRC messages and SIBs (System Information Blocks) are upper layer messages stored in the data area of ​​the packet. This is an example of sage.

[0029] In step S107, the packet assembly unit 35 receives the transmission data from the upper layer 34 and generates a packet including this transmission data. Note that the transmission data from the upper layer 34 may also be referred to as user data, and the packet including the transmission data may also be referred to as a user data packet.

[0030] In step S108, the radio unit 31 transmits the packet including the control information generated in step S106.

[0031] In step S109, the radio unit 31 transmits the packet including the transmission data in step S107.

[0032] In step S110, the wireless protocol control unit 36 ​​determines whether all the data generated in S101 has been transmitted, and if there is untransmitted data, the process returns to S102 and repeats the above processing until all the data has been transmitted.

[0033] FIG. 4 is a flow chart showing the flow of data reception processing performed by the user terminal 10 in this embodiment. 4. It is clear that the user terminal 10 performs the operations in the following process in FIG. 4, and the functional units (such as the wireless protocol control unit 36) described below in relation to FIG. 4 are possessed by the user terminal 10, and therefore, a detailed description thereof will be omitted.

[0034] In step S201, the user terminal 10 receives a packet including a control signal from the base station 20 via the radio unit 31. In step S202, the packet disassembly unit 33 disassembles the received packet and extracts the control signal notifying data transmission and the control signal related to terminal-to-terminal communication. The extracted control signals are passed to the radio protocol control unit 36.

[0035] In step S203, the radio unit 31 receives a packet including data transmitted from the base station 20 based on radio resource information included in a control signal notifying transmission of data. In step S204, the packet demodulation unit 32 demodulates the received packet. The packet demodulation unit 32 notifies the radio protocol control unit 36 ​​of demodulation success or failure information. In step S205, the radio protocol control unit 36 ​​determines whether the demodulation was successful, and if successful, the process proceeds to step S206, and if unsuccessful, the process proceeds to step S209.

[0036] If the demodulation is successful, in step S206, the radio protocol control unit 36 ​​generates a packet including the demodulated data using the packet assembly unit 35. This packet corresponds to the second data packet in the present invention. In step S207, the radio protocol control unit 36 ​​controls the radio unit 31 to transmit the generated packet using the radio resource specified by the control signal related to terminal-to-terminal communication extracted in step S202. Then, in step S208, the radio protocol control unit 36 ​​transfers the demodulated data to the upper layer 34.

[0037] If the demodulation fails, in step S209, the radio protocol control unit 36 ​​controls the radio unit 31 to receive the packet in the radio resource specified by the control signal related to the terminal-to-terminal communication extracted in step S202. In step S210, the packet demodulation unit 32 demodulates the packet (second data packet) received through the terminal-to-terminal communication and notifies the radio protocol control unit 36 ​​of success or failure of the demodulation. In step S211, the radio protocol control unit 36 ​​determines whether the demodulation was successful. If successful, the process proceeds to step S208, where the radio protocol control unit 36 ​​transfers the successfully demodulated data to the upper layer 34. That is, the user terminal 10 treats the data obtained by receiving and demodulating through the terminal-to-terminal communication as data included in the data packet that was received from the base station 20 and failed to be demodulated. On the other hand, if the demodulation fails, the process proceeds to step S212, where the radio protocol control unit 36 ​​reports the failure of the data reception to the upper layer 34. If a reception failure is reported, the upper layer 34 may treat the data as lost or may request a retransmission. If the unsuccessfully received data is part of a data string that has been error-corrected, and most of the remaining data has been successfully demodulated, the unsuccessfully demodulated data may be recovered by demodulating the error-correcting code. Even if there is data that has been unsuccessfully demodulated among packets received from the base station 20, the probability of recovery by decoding the error-correcting code increases if a certain amount of data obtained by demodulating packets received in terminal-to-terminal communications is added.

[0038] According to this embodiment, when a user terminal 10 fails to demodulate data from a base station 20, the user terminal 10 can obtain the data through terminal-to-terminal communication from another user terminal 10 that has successfully demodulated the data. Since the base station 20 can tolerate demodulation failures in the user terminal 10 to some extent, it is possible to set the transmission power low, and the number of packets that need to be retransmitted from the base station 20 decreases. This makes it possible to reduce the power consumption of the base station 20 and the consumption of communication resources.

[0039] (Embodiment 2) In the first embodiment, the base station 20 generates and transmits a packet including a control signal notifying data transmission and a control signal related to terminal-to-terminal communication every time a packet including data is transmitted. In the present embodiment, the base station 20 generates and transmits a packet including a control signal notifying data transmission and a control signal related to terminal-to-terminal communication prior to transmitting a series of packets including data.

[0040] The configurations of the user terminal 10 and the base station 20 in this embodiment are basically the same as those in the first embodiment, but the difference lies mainly in the content of the data transmission process of the base station 20. In the following, a description of the configurations that are the same as those in the first embodiment will be omitted, and the differences from the first embodiment will be mainly described.

[0041] 5 is a flowchart showing the flow of data transmission processing of the base station 20 in this embodiment. Prior to generating data to be transmitted to the terminals (S305), the base station 20 determines radio resources available for terminal-to-terminal communication, generates a control signal notifying the radio resources, and generates and transmits a packet including the control signal (S301 to S304). The radio resources determined here are determined and notified as periodically available radio resources. Periodic use of radio resources is defined as, for example, SPS (Semi Persistent Scheduling). The control signal notifying the radio resources may be a physical layer signal or a higher layer message such as an RRC message.

[0042] When data to be transmitted to a terminal is generated (S305-YES), the base station 20 determines the radio resource for transmitting the data, generates a control signal notifying the radio resource, and generates and transmits a packet including the control signal (S306-S307). The radio resource determined here is also determined and notified as a periodically available radio resource, as described above. This control signal may be a physical layer signal or a higher layer message such as an RRC message.

[0043] The base station 20 also generates a control signal notifying the start of data transmission, and transmits a packet including this control signal (S310-S311). The base station 20 then repeats the generation and transmission of packets including data until transmission of all data is complete (S312-S314). When transmission of all data is complete, the base station 20 generates a control signal notifying the end of data transmission, and transmits a packet including this control signal (S315-S316). The control signal notifying the start or end of data transmission may be a physical layer signal. However, if the content of the data to be transmitted is transmitted regularly, such as in a broadcast, transmission of this control signal may be omitted.

[0044] The flow of data reception processing performed by the user terminal 10 in this embodiment is basically the same as that in embodiment 1 (FIG. 4). However, among the processing flow shown in FIG. 4, the steps (S301 to S302) of receiving a packet containing a control signal and extracting a control signal notifying data transmission and a control signal related to terminal-to-terminal communication need only be performed once prior to receiving a series of packets containing data. Furthermore, because control signals notifying the start and end of data transmission are added, processing is added to extract the control signal and to control the start and end of data reception processing based on the control signal.

[0045] In this embodiment, as in the first embodiment, it is possible to reduce the amount of power consumed by the base station 20 and the amount of communication resources consumed.

[0046] (Embodiment 3) In this embodiment, the user terminal 10 performs inter-terminal communication of a packet including data that has been successfully demodulated. LBT (Listen Before Talk) is applied to transmissions in the above-mentioned embodiment. The configurations of the user terminal 10 and the base station 20 in this embodiment are basically the same as those in the first embodiment, except for the processing in step S207 in the flowchart of FIG. 4. In the following, a description of the configurations that are the same as those in the first embodiment will be omitted, and differences from the first embodiment will be mainly described. Note that this embodiment may be implemented in combination with the second embodiment.

[0047] 6 is a flowchart showing a transmission process by terminal-to-terminal communication in this embodiment. The user terminal 10 performs processing according to the flowchart in FIG. 4, and executes a transmission process (step S207) of terminal-to-terminal communication by the processing shown in the flowchart in FIG.

[0048] In this embodiment, the user terminal 10 receives a packet containing data transmitted from the base station, and if the packet is correctly demodulated, monitors the usage status of the radio resources available for terminal-to-terminal communication obtained from the control signal related to the terminal-to-terminal communication (S401). The time for monitoring the usage status of the radio resources may be set according to the CSMA-CA (Carrier Sense Multiple Access - Collision Avoidance) method or randomly in accordance therewith. Alternatively, the cellular radio In the case of communication between terminals in a licensed frequency band, autonomous radio resource selection may be performed in accordance with the standards for cellular radio communication.

[0049] The user terminal 10 monitors the usage status of the wireless resource to determine whether the wireless resource is available (S402), and if it determines that the wireless resource is available, transmits a packet including the successfully demodulated data (S403).

[0050] On the other hand, if it is determined that the wireless resources are in use, the user terminal 10 demodulates the packet (the packet received in S401) being transmitted by another terminal (a third terminal) in the terminal-to-terminal communication (S404). The user terminal 10 determines whether the received packet contains data obtained by demodulating the packet received from the base station, i.e., the same data as the data that was intended to be transmitted in the terminal-to-terminal communication (S405). If the same data is contained, the user terminal 10 cancels the transmission that was intended to be performed in the terminal-to-terminal communication (S408). If the packet received in the terminal-to-terminal communication does not contain the same data, the user terminal 10 determines whether a certain time has elapsed since receiving the data (S407). If the certain time has not elapsed, the user terminal 10 returns to step S401 and monitors the usage status of wireless resources available for the terminal-to-terminal communication. If the certain time has elapsed without the data that was intended to be transmitted being transmitted by another user terminal in the terminal-to-terminal communication and without there being any available wireless resources, the user terminal 10 cancels the transmission in the terminal-to-terminal communication (S408).

[0051] According to this embodiment, when there are multiple user terminals that have correctly demodulated data from packets received from a base station, collision of terminal-to-terminal communication packets caused by these user terminals simultaneously transmitting terminal-to-terminal communication packets can be avoided. Furthermore, since multiple user terminals will no longer transmit the same data, radio resources used for terminal-to-terminal communication can be used efficiently.

[0052] (Embodiment 4) In this embodiment, the base station 20 adds an identifier for identifying the data to a control signal notifying transmission of the data and transmits the control signal. Furthermore, the identifier may be added to a packet including the data. The data identifier may be included in a physical layer signal, for example, a DCI, and transmitted. This embodiment can be combined with any of the first to third embodiments. Below, an example in which this embodiment is combined with the third embodiment will be described, and differences from the third embodiment will be mainly described.

[0053] The user terminal 10 correctly demodulates the packet received from the base station 20 and obtains the data and its identifier, and when transmitting the data in terminal-to-terminal communication (S207), Before transmitting, the terminal receives and demodulates a packet transmitted by another terminal to obtain the data and its identifier (S404), and then determines whether the data contained in the packet transmitted by the other terminal is the same as the data it is about to transmit (S405) using the identifier.

[0054] If the user terminal 10 is unable to correctly demodulate a packet received from the base station 20, it can ascertain the identifier of the data that failed to be demodulated from the data identifier included in the control signal that notifies the transmission of the data. Therefore, if the identifier attached to the packet received in the inter-terminal communication matches the identifier attached to the control signal from the base station 20, the user terminal 10 transfers the data obtained in the inter-terminal communication to the upper layer 34 as correctly demodulated data.

[0055] According to this embodiment, it becomes possible to easily determine whether the data is identical (S405).

[0056] (Embodiment 5) In this embodiment, if a user terminal 10 fails to demodulate a packet transmitted from a base station, it transmits a demodulation failure notification via terminal-to-terminal communication, and if a user terminal 10 successfully demodulates the packet, it transmits the packet via terminal-to-terminal communication upon receiving the demodulation failure notification.

[0057] This embodiment is basically the same as embodiment 1, but differs from embodiment 1 in the operation of the user terminal 10. In the following, a description of the same configuration as embodiment 1 will be omitted, and differences from embodiment 1 will be mainly described. Note that this embodiment can also be implemented in combination with embodiments 2 to 4.

[0058] First, the process of receiving a packet transmitted by base station 20 and determining whether the data has been correctly demodulated is the same as that of embodiment 1 (steps S201 to S205 in FIG. 4). Fig. 7 is a flowchart explaining the process from step S205 onwards in this embodiment.

[0059] If the data transmitted from the base station is successfully demodulated (S205-YES), the user terminal 10 receives the packet in a radio resource available for terminal-to-terminal communication (S501) and determines whether information indicating that the data demodulation failed (herein referred to as a demodulation failure notification) has been sent from another user terminal (S502). If a demodulation failure notification has been received from another user terminal (S502-YES), the user terminal 10 generates a packet including the successfully demodulated data (S503) and transmits the packet in a radio resource available for terminal-to-terminal communication (S504). Note that, as in the third embodiment, this transmission process may be performed when the usage status of a radio resource available for terminal-to-terminal communication is monitored and it is determined that a packet including the data has not been transmitted to another terminal and that the radio resource is available. Furthermore, the method of the fourth embodiment may be used in combination. Regardless of whether or not a packet including the successfully demodulated data is transmitted in a radio resource available for terminal-to-terminal communication, the user terminal 10 transfers the successfully demodulated data to the upper layer 34.

[0060] If demodulation of a packet containing data received from the base station fails (S205-NO), the user terminal 10 transmits information indicating that demodulation of the data has failed (demodulation failure notification) in the radio resource available for terminal-to-terminal communication (S511). At this time, the usage status of the radio resource available for terminal-to-terminal communication may be monitored, and the demodulation failure notification may be transmitted if it is determined that a packet containing information indicating that demodulation of the data has failed has not been transmitted by another terminal and that the radio resource is available. Note that if an identifier for the data has been transmitted, the identifier for the data that has failed to be demodulated may be included in the demodulation failure notification. Good too.

[0061] Thereafter, the user terminal 10 receives the packet using radio resources available for terminal-to-terminal communication (S512) and demodulates the received packet (S513). If the demodulation of the packet received in the terminal-to-terminal communication is successful (S514-YES), the user terminal 10 transfers the successfully demodulated data to an upper layer (S515), and if demodulation is not successful (S514-NO), the user terminal 10 reports the failure of data reception to the upper layer (S516).

[0062] According to this embodiment, only data that has failed to be demodulated at any of the terminals is transmitted in terminal-to-terminal communication, which reduces the transmission processing at the user terminals and reduces the amount of radio resources consumed.

[0063] (Other variations) The above-described embodiment is merely an example, and the present disclosure can be modified and implemented as appropriate within the scope that does not deviate from the gist of the disclosure.

[0064] In the above embodiment, an example is shown in which 5G cellular communication (communication via a base station and sidelink communication) is used, but any standard of communication may be adopted as long as it is wide-area wireless communication via a base station or access point and direct communication between user terminals. Examples of wide-area wireless communication include wide-area wireless LAN (IEEE 802.11ah) and WiMax (IEEE 802.6). Examples of direct communication between user terminals include Wi-Fi Direct and Bluetooth (registered trademark).

[0065] The present disclosure can also be realized by providing a computer program implementing the functions described in the above embodiments to a computer, and having one or more processors in the computer read and execute the program. Such a computer program may be provided to the computer via a non-transitory computer-readable storage medium connectable to the computer's system bus or via a network. Non-transitory computer-readable storage media include, for example, any type of disk, such as a magnetic disk (e.g., a floppy disk, a hard disk drive (HDD), etc.), an optical disk (e.g., a CD-ROM, a DVD disk, a Blu-ray disk), a read-only memory (ROM), a random-access memory (RAM), an EPROM, an EEPROM, a magnetic card, a flash memory, an optical card, or any type of medium suitable for storing electronic instructions. [Explanation of symbols]

[0066] 10: User terminal, 20: Base station 31: Radio section, 32: Packet demodulation section, 33: Packet disassembly section 34: Upper layer, 35: Packet assembly unit, 36: Radio protocol control unit

Claims

1. A wireless communication method between a base station and a terminal, comprising: a first transmission step in which the base station transmits a first control signal notifying the plurality of terminals of a data transmission and a second control signal related to terminal-to-terminal communication to the plurality of terminals; a second transmission step in which the base station transmits a data packet including the data to the plurality of terminals; a demodulation step in which the terminal demodulates the data packet based on the first control signal; an inter-terminal transmission step of transmitting, when the terminal has successfully demodulated the data packet, a second data packet including the successfully demodulated data to another terminal in a radio resource based on the second control signal; an inter-terminal reception step in which, when the terminal fails to demodulate the data packet, the terminal receives and demodulates the second data packet transmitted by another terminal using a radio resource based on the second control signal, and regards the demodulated data as the data included in the data packet that failed to be demodulated; A wireless communication method comprising:

2. The terminal-to-terminal transmission step includes: the terminal monitoring a usage status of radio resources based on the second control signal; transmitting the second data packet by the terminal when the radio resources are available; The wireless communication method of claim 1 , comprising:

3. In the inter-terminal transmission step, when a third terminal transmits the data using the radio resource based on the second control signal, the terminal stops transmitting the second data packet.

3. The wireless communication method according to claim 2.

4. In the transmitting step, the base station adds an identifier of the data to one or both of the first control signal and the data packet and transmits the data; In the inter-terminal transmission step, the terminal adds an identifier of the data to the second data packet and transmits it, and determines whether the data has been transmitted by another terminal based on the identifier of the data included in the packet transmitted from the other terminal and the identifier of the first control signal or the data added to the data packet.

3. The wireless communication method according to claim 2.

5. The method further includes a step of transmitting, when the terminal fails to demodulate the data packet, a demodulation failure notification notifying that demodulation of the data packet has failed, using a radio resource based on the second control signal; In the inter-terminal transmission step, the terminal transmits the second data packet in response to receiving the demodulation failure notification from another terminal.

2. The wireless communication method according to claim 1.

6. In the transmitting step, the base station transmits the first control signal and the second control signal in the same packet.

2. The wireless communication method according to claim 1.

7. the first control signal and the second control signal are packetized as physical layer signals; 7. The wireless communication method according to claim 6.

8. In the transmitting step, the base station transmits the first control signal and the second control signal by including them in different packets.

2. The wireless communication method according to claim 1.

9. At least one of the first control signal and the second control signal periodically notifies available radio resources.

2. The wireless communication method according to claim 1.

10. At least one of the first control signal and the second control signal is included in an upper layer message.

10. The wireless communication method according to claim 9.

11. In the transmitting step, the base station transmits the first control signal, the second control signal, and the data packet to a plurality of terminals by broadcast or multicast.

2. The wireless communication method according to claim 1.

12. The base station is configured by an artificial satellite or an airborne vehicle.

2. The wireless communication method according to claim 1.

13. a receiving step of receiving, from a base station, a first control signal notifying transmission of data, a second control signal related to terminal-to-terminal communication, and a data packet including the data; a demodulation step of demodulating the data packet based on the first control signal; an inter-terminal transmission step of transmitting, when the demodulation of the data packet is successful, a second data packet including the successfully demodulated data to another terminal in a radio resource based on the second control signal; an inter-terminal reception step of receiving and demodulating the second data packet transmitted by another terminal in a radio resource based on the second control signal when demodulation of the data packet fails, and setting the demodulated data as the data included in the data packet that failed to be demodulated; A user terminal comprising a processing unit that executes the above.

14. The terminal-to-terminal transmission step includes: monitoring a usage status of radio resources based on the second control signal; transmitting the second data packet when the radio resource is available and no other terminal is transmitting the data; 14. The user terminal of claim 13, comprising:

15. If the data has been transmitted using the radio resource based on the second control signal in the inter-terminal transmission step, the transmission of the second data packet is stopped.

15. A user terminal according to claim 14.

16. an identifier of the data is added to the first control signal or the data packet; In the inter-terminal transmission step, an identifier of the data is added to the second data packet and transmitted, and a determination as to whether the data has been transmitted by another terminal is made based on an identifier of the data included in a packet transmitted from the other terminal and an identifier of the first control signal or the data added to the data packet.

15. A user terminal according to claim 14.

17. the processing unit further executes, when demodulation of the data packet fails, transmitting a demodulation failure notification, which notifies that demodulation of the data packet has failed, in a radio resource based on the second control signal; In the inter-terminal transmission step, the second data packet is transmitted in response to receiving the demodulation failure notification from another terminal.

17. A user terminal according to any one of claims 13 to 16.

18. an identifier of the data is added to the first control signal; The processing unit when demodulation of the data packet fails, an identifier of the data corresponding to the data packet that has failed to be demodulated is included in the demodulation failure notification, and a determination is made based on the identifier of the data whether or not data obtained by receiving and demodulating the second data packet transmitted by another terminal in a radio resource based on the second control signal is the data that has failed to be demodulated; In the inter-terminal transmission step, in response to receiving a demodulation failure notification including an identifier of the data from another terminal, data corresponding to the identifier of the data is included in the second data packet and transmitted.

18. A user terminal according to claim 17.

19. the first control signal and the second control signal are packetized as physical layer signals; 14. A user terminal according to claim 13.

20. At least one of the first control signal and the second control signal periodically notifies available radio resources and is included in an upper layer message.

14. A user terminal according to claim 13.

21. A base station that transmits data to a plurality of terminals, transmitting a first control signal notifying the transmission of the data and a second control signal related to inter-terminal communication for transmitting and receiving the data among the plurality of terminals to the plurality of terminals; transmitting a data packet including the data to the plurality of terminals; A base station characterized by:

22. adding an identifier of the data to the data packet and transmitting the data packet; 21. The base station of claim 20.

23. the first control signal and the second control signal are packetized as physical layer signals; 22. The base station of claim 21 .

24. At least one of the first control signal and the second control signal periodically notifies available radio resources and is included in an upper layer message.

22. The base station of claim 21 .

25. The base station is mounted on a satellite or an airborne vehicle.

22. The base station of claim 21 .

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