Patent Publication Number: US-2022217702-A1

Title: Information transmission method and apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2019/108320, filed on Sep. 26, 2019, the disclosures of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This application relates to the field of communication technologies, and in particular, to an information transmission method and an apparatus. 
     BACKGROUND 
     In a network of a long term evolution (long term evolution, LTE) technology proposed in the 3rd generation partnership project (the 3rd generation partnership project, 3GPP), an Internet of vehicles technology for vehicle-to-everything (vehicle-to-everything, V2X) communication is proposed. The V2X communication is communication between a vehicle and everything outside the vehicle, and includes vehicle-to-vehicle (vehicle-to-vehicle, V2V) communication, vehicle-to-pedestrian (vehicle-to-pedestrian, V2P) communication, vehicle-to-infrastructure (vehicle-to-infrastructure, V2I) communication, and vehicle-to-network (vehicle-to-network, V2N) communication. 
     With development of a V2X communication technology, more and more terminal devices use the V2X communication technology for communication. For example, during a resource scheduling process shown in  FIG. 1 , when performing resource transmission on a sidelink (sidelink, SL), a terminal device may first perform resource sensing in a sensing window, and then select an idle resource in a selection window for resource transmission. 
     Therefore, a person skilled in the art works on a problem of how to perform information transmission when a terminal device interacts with a terminal device. 
     SUMMARY 
     Embodiments of this application provide an information transmission method and an apparatus, and may be applied to a communication system, for example, vehicle-to-everything (vehicle-to-everything, V2X) communication, long term evolution-vehicle (long term evolution-vehicle, LTE-V), Internet of vehicles, machine type communication (machine type communication, MTC), Internet of things (internet of things, IoT), long term evolution-machine (long term evolution-machine, LTE-M), or machine-to-machine (machine-to-machine, M2M) communication, to resolve a problem of information transmission between terminal devices in a contention-based scheduling mode. 
     According to a first aspect, an embodiment of this application provides an information transmission method, including: a first terminal device sends first sidelink control information SCI to a second terminal device, where the first SCI includes information about a first subchannel set, the first subchannel set is an available subchannel set sensed by the first terminal device on a sidelink SL, and the first SCI does not include modulation and coding scheme (modulation and coding scheme, MCS) information. 
     In this embodiment of this application, the first SCI does not include the MCS information. This can both reduce signaling overheads of the first terminal device, and improve efficiency of demodulating the first SCI by the second terminal device. 
     In a possible implementation, the first SCI includes a first field and a second field; the first field is used to indicate transmit end information of data transmitted on the SL, or the first field is a format identifier of the first SCI; and the second field is used to indicate priority information of the data. 
     In a possible implementation, the method further includes: the first terminal device receives second SCI sent by the second terminal device, where the second SCI includes information about a second subchannel set, the second subchannel set is an available subchannel set sensed by the second terminal device on the SL, and the second SCI does not include MCS information. 
     In a possible implementation, a payload of the second SCI is the same as a payload of the first SCI. 
     In a possible implementation, the second SCI includes a third field and a fourth field; 
     the third field is used to indicate receive end information of the data transmitted on the SL, or the third field is a format identifier of the second SCI; and the fourth field is used to indicate at least one of channel state information CSI, feedback information, or a reserved bit. 
     In a possible implementation, a format of the first SCI and a format of the second SCI are configured by using same higher layer signaling. 
     In this embodiment of this application, the payload (payload) of the first SCI is the same as the payload of the second SCI, and the first SCI and the second SCI are configured by using the same higher layer signaling. This avoids separately configuring two pieces of SCI by using two pieces of signaling, and reduces signaling overheads. 
     In a possible implementation, the method further includes: the first terminal device determines a target subchannel set based on the first subchannel set and the second subchannel set; and sends the data to the second terminal device by using the target subchannel set. 
     In this embodiment of this application, the first terminal device sends the information about the first subchannel set to the second terminal device, and the second terminal device sends the information about the second subchannel set to the first terminal device, so that the first terminal device and the second terminal device can clearly learn of the available subchannel set sensed by each other. Therefore, the terminal device learns more of the available subchannel set sensed by the other, further determines the target subchannel set more accurately, and improves efficiency of determining the target subchannel set. 
     In a possible implementation, the target subchannel set is an intersection between the first subchannel set and the second subchannel set. 
     In this embodiment of this application, the target subchannel set is an intersection between the first subchannel set and the second subchannel set. In other words, both the first terminal device and the second terminal device may transmit data information and/or control information by using the target subchannel set. This avoids a case in which the first terminal device or the second terminal device cannot receive the data information and/or the control information, and improves reliability of information transmission. 
     In a possible implementation, the method further includes: the first terminal device sends third SCI to the second terminal device, where the third SCI includes scheduling information of the data transmitted on the SL. 
     In a possible implementation, the third SCI further includes information used to indicate a feedback subchannel set, and the feedback subchannel set is at least included in the first subchannel set. 
     According to a second aspect, an embodiment of this application provides an information transmission method, including: before sensing whether a subchannel set is available, determining a scheduling mode, where the scheduling mode includes a first mode or a second mode; sensing an available subchannel set; and when the scheduling mode is the first mode, sensing the available subchannel set by using a first threshold; or when the scheduling mode is the second mode, sensing the available subchannel set by using a second threshold, where the first threshold is less than the second threshold. 
     In this embodiment of this application, sensing, in the first mode, may be performed by a terminal device, and the terminal device reports the available subchannel set to a network device. Therefore, a requirement of an energy threshold of the available subchannel set reported in the first mode may be stricter, to ensure that data transmitted by using the reported available subchannel set does not collide. Sensing, in the second mode, may be performed by both a terminal device  1  and a terminal device  2 . Therefore, an energy threshold of the available subchannel set is defined to be larger. This can ensure that the terminal device can use the available subchannel set, avoid collision, and improve resource utilization. 
     In a possible implementation, the first threshold and the second threshold are predefined, or the first threshold and the second threshold are configured by the network device by using signaling. 
     According to a third aspect, an embodiment of this application provides an information transmission method, including: a second terminal device receives first SCI sent by a first terminal device, where the first SCI includes information about a first subchannel set, the first subchannel set is an available subchannel set sensed by the first terminal device on a sidelink SL, and the first SCI does not include modulation and coding scheme MCS information; and sends second SCI to the first terminal device, where the second SCI includes information about a second subchannel set, the second subchannel set is an available subchannel set sensed by the second terminal device on the SL, and the second SCI does not include MCS information. 
     In a possible implementation, the first SCI includes a first field and a second field; the first field is used to indicate transmit end information of data transmitted on the SL, the first field is a format identifier of the first SCI, or the first field is indication information of a reference signal for measurement on the SL; and the second field is used to indicate priority information of the data. 
     In a possible implementation, the second SCI includes a third field and a fourth field; the third field is used to indicate receive end information of the data transmitted on the SL, or the third field is a format identifier of the second SCI; and the fourth field is used to indicate at least one of channel state information CSI, feedback information, or a reserved bit. 
     In a possible implementation, a payload of the second SCI is the same as a payload of the first SCI. 
     In a possible implementation, a format of the first SCI and a format of the second SCI are configured by using same higher layer signaling. 
     In a possible implementation, the method further includes: the second terminal device receives the data sent by the first terminal device by using a target subchannel set, where the target subchannel set is an intersection between the first subchannel set and the second subchannel set. 
     In a possible implementation, the method further includes: the second terminal device receives third SCI sent by the first terminal device, where the third SCI includes scheduling information of the data transmitted on the SL. 
     In a possible implementation, the third SCI further includes information used to indicate a feedback subchannel set, and the feedback subchannel set is at least included in the first subchannel set. 
     According to a fourth aspect, an embodiment of this application provides a communication apparatus. The communication apparatus is a first terminal device, and includes a processing unit, a receiving unit, and a sending unit. The processing unit is configured to perform the corresponding method in the first aspect or the second aspect, the receiving unit is configured to perform the corresponding method in the first aspect or the second aspect, and the sending unit is configured to perform the corresponding method in the first aspect or the second aspect. 
     According to a fifth aspect, an embodiment of this application provides a communication apparatus. The communication apparatus is a second terminal device, and includes a receiving unit and a sending unit. The receiving unit is configured to perform the corresponding method in the third aspect, and the sending unit is configured to perform the corresponding method in the third aspect. 
     In a possible implementation, the communication apparatus further includes a processing unit. For example, the processing unit may be configured to sense a second subchannel set. 
     It should be noted that the second terminal device may also be configured to perform the method in the second aspect. For example, the processing unit may be configured to perform the corresponding method in the second aspect. 
     According to a sixth aspect, an embodiment of this application provides a communication apparatus, including a processor and a memory. The memory is configured to store computer-executable instructions, and the processor is configured to execute the computer-executable instructions stored in the memory, to enable the communication apparatus to perform the corresponding method in the first aspect or the second aspect. 
     According to a seventh aspect, an embodiment of this application provides a communication apparatus, including a processor and an interface circuit. The interface circuit is configured to receive code instructions and transmit the code instructions to the processor, and the processor runs the code instructions, to perform the corresponding method in the first aspect or the second aspect. 
     According to an eighth aspect, an embodiment of this application provides a communication apparatus, including a processor and a memory. The memory is configured to store computer-executable instructions, and the processor is configured to execute the computer-executable instructions stored in the memory, to enable the communication apparatus to perform the corresponding method in the third aspect. 
     According to a ninth aspect, an embodiment of this application provides a communication apparatus, including a processor and an interface circuit. The interface circuit is configured to receive code instructions and transmit the code instructions to the processor, and the processor runs the code instructions, to perform the corresponding method in the third aspect. 
     According to a tenth aspect, an embodiment of this application provides a communication system, including a first terminal device and a second terminal device. The first terminal device may be configured to perform the method in the first aspect, and the second terminal device may be configured to perform the method in the third aspect. 
     In a possible implementation, the first terminal device may alternatively be configured to perform the method in the second aspect, and the second terminal device may alternatively be configured to perform the method in the second aspect. 
     According to an eleventh aspect, an embodiment of this application provides a readable storage medium. The readable storage medium is configured to store instructions, and when the instructions are executed, the method in the first aspect or the second aspect is implemented. 
     In a possible implementation, the readable storage medium may include a computer-readable storage medium. 
     According to a twelfth aspect, an embodiment of this application provides a readable storage medium. The readable storage medium is configured to store instructions, and when the instructions are executed, the method in the third aspect is implemented. 
     In a possible implementation, the readable storage medium may include a computer-readable storage medium. 
     According to a thirteenth aspect, an embodiment of this application provides a computer program product including instructions. When the instructions are executed, the method in the first aspect or the second aspect is implemented. 
     According to a fourteenth aspect, an embodiment of this application provides a computer program product including instructions. When the instructions are executed, the method in the third aspect is implemented. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic flowchart of a resource scheduling process according to an embodiment of this application; 
         FIG. 2  is a schematic diagram of a communication system according to an embodiment of this application; 
         FIG. 3 a    is a schematic diagram of a sidelink communication scenario according to an embodiment of this application; 
         FIG. 3 b    is a schematic diagram of a sidelink communication scenario according to an embodiment of this application; 
         FIG. 3 c    is a schematic diagram of a sidelink communication scenario according to an embodiment of this application; 
         FIG. 3 d    is a schematic diagram of a sidelink communication scenario according to an embodiment of this application; 
         FIG. 3 e    is a schematic diagram of a sidelink communication scenario according to an embodiment of this application; 
         FIG. 3 f    is a schematic diagram of a sidelink communication scenario according to an embodiment of this application; 
         FIG. 3 g    is a schematic diagram of a sidelink communication scenario according to an embodiment of this application; 
         FIG. 4  is a schematic diagram of a frame structure according to an embodiment of this application; 
         FIG. 5  is a schematic diagram of a structure of first SCI and a structure of second SCI according to an embodiment of this application; 
         FIG. 6  is a schematic flowchart of an information transmission method according to an embodiment of this application; 
         FIG. 7  is a schematic diagram of a method for sending first SCI according to an embodiment of this application; 
         FIG. 8  is a schematic diagram of a method for sending first SCI according to an embodiment of this application; 
         FIG. 9  is a schematic diagram of a structure of third SCI according to an embodiment of this application; 
         FIG. 10 a    is a schematic flowchart of an information transmission method according to an embodiment of this application; 
         FIG. 10 b    is a schematic flowchart of a resource scheduling process according to an embodiment of this application; 
         FIG. 11  is a schematic diagram of a structure of a communication apparatus according to an embodiment of this application; 
         FIG. 12  is a schematic diagram of a structure of a communication apparatus according to an embodiment of this application; 
         FIG. 13  is a schematic diagram of a structure of a terminal device according to an embodiment of this application; 
         FIG. 14  is a schematic diagram of a structure of a terminal device according to an embodiment of this application; and 
         FIG. 15  is a schematic diagram of a structure of a communication apparatus according to an embodiment of this application. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes embodiments of this application with reference to the accompanying drawings in embodiments of this application. 
     In the specification, claims, and accompanying drawings of this application, the terms “first”, “second”, and so on are intended to distinguish between different objects but do not indicate a particular order. In addition, the terms “including”, “having”, and any other variant thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but optionally further includes an unlisted step or unit, or optionally further includes another inherent step or unit of the process, method, product, or device. 
     It should be understood that in this application, “at least one (item)” means one or more, “a plurality of” means two or more, and “at least two (items)” means two, three, or more. The term “and/or” is used to describe an association relationship between associated objects, and indicates that three relationships may exist. For example, “A and/or B” may indicate the following three cases: Only A exists, only B exists, and both A and B exist, where A and B may be singular or plural. The character “I” usually indicates an “or” relationship between the associated objects. “At least one of the following items (pieces)” or a similar expression thereof indicates any combination of these items, including a single item (piece) or any combination of a plurality of items (pieces). For example, at least one (piece) of a, b, or c may represent: a, b, c, a and b, a and c, b and c, or a, b, and c, where a, b, and c may be singular or plural. 
     A communication system used in this application may be understood as a wireless cellular communication system, or may be understood as a wireless communication system based on a cellular network architecture, for example, a 5th generation (5th generation, 5G) mobile communication system and a next generation mobile communication system.  FIG. 2  is a schematic diagram of a communication system according to an embodiment of this application. The solutions in this application are applicable to the communication system. The communication system may include at least one network device, and only one network device is shown, for example, a next generation NodeB (the next generation NodeB, gNB) in the figure. The communication system may further include one or more terminal devices connected to the network device, for example, a terminal device  1  and a terminal device  2  in the figure. 
     The network device may be a device that can communicate with the terminal device. The network device may be any device that has a wireless transceiver function, and includes but is not limited to a base station. For example, the base station may be a gNB, or a base station in a future communication system. Optionally, the network device may alternatively be an access node, a wireless relay node, a wireless backhaul node, or the like in a wireless local area network (wireless fidelity, Wi-Fi) system. Optionally, the network device may alternatively be a radio controller in a cloud radio access network (cloud radio access network, CRAN) scenario. Optionally, the network device may alternatively be a wearable device, a vehicle-mounted device, or the like. Optionally, the network device may alternatively be a small station, a transmission node (transmission reference point, TRP), or the like. Certainly, this application is not limited thereto. 
     The terminal device may also be referred to as user equipment (user equipment, UE), a terminal, or the like. The terminal device is a device having a wireless transceiver function. The terminal device may be deployed on land, and includes an indoor device, an outdoor device, a handheld device, a wearable device, or a vehicle-mounted device; or may be deployed on a water surface, for example, on a ship; or may be deployed in the air, for example, on an airplane, a balloon, or a satellite. The terminal device may be a mobile phone (mobile phone), a tablet computer (Pad), a computer having a wireless transceiver function, a virtual reality (virtual reality, VR) terminal device, an augmented reality (augmented reality, AR) terminal device, a wireless terminal in industrial control (industrial control), a wireless terminal in self-driving (self-driving), a wireless terminal in remote medical (remote medical), a wireless terminal in a smart grid (smart grid), a wireless terminal in transportation safety (transportation safety), a wireless terminal in a smart city (smart city), a wireless terminal in a smart home (smart home), or the like. 
     It may be understood that, in the communication system shown in  FIG. 2 , the terminal device  1  may alternatively communicate with the terminal device  2  by using a device-to-device (device-to-device, D2D) technology or a vehicle-to-everything (vehicle-to-everything, V2X) communication technology. 
     It should be noted that the communication system in  FIG. 1  may be applied to a communication scenario in another embodiment of this application. Details are not described herein. For example, the terminal device  1  and the terminal device  2  may be configured to perform an information transmission method embodiment shown in  FIG. 6  or  FIG. 10 a   . 
     The following uses the terminal device  1  and the terminal device  2  in NR-V2X as an example to specifically describe a communication scenario of a corresponding information transmission method provided in embodiments of this application. 
       FIG. 3 a    to  FIG. 3 g    are schematic diagrams of sidelink (sidelink) (which may also be referred to as a direct link) communication scenarios according to embodiments of this application. 
     In the scenario shown in  FIG. 3 a   , both the terminal device  1  and the terminal device  2  are outside a coverage area of a cell. 
     In the scenario shown in  FIG. 3 b   , the terminal device  1  is in a coverage area of a cell, and the terminal device  2  is outside the coverage area of the cell. 
     In the scenario shown in  FIG. 3 c   , both the terminal device  1  and the terminal device  2  are in a coverage area of a same cell, and in a same public land mobile network (public land mobile network, PLMN), for example, a PLMN  1 . 
     In the scenario shown in  FIG. 3 d   , both the terminal device  1  and the terminal device  2  are in a same PLMN, for example, a PLMN  1 , but in coverage areas of different cells. 
     In the scenario shown in  FIG. 3 e   , the terminal device  1  and the terminal device  2  are in different PLMNs and different cells, and the terminal device  1  and the terminal device  2  are in a common coverage area of two cells. For example, the terminal device  1  is in a PLMN  1 , and the terminal device  2  is in a PLMN  2 . 
     In the scenario shown in  FIG. 3 f   , the terminal device  1  and the terminal device  2  are in different PLMNs and different cells, the terminal device  1  is in a common coverage area of two cells, and the terminal device  2  is in a coverage area of a serving cell. 
     In the scenario shown in  FIG. 3 g   , the terminal device  1  and the terminal device  2  are in different PLMNs and different cells, and the terminal device  1  and the terminal device  2  are in coverage areas of respective serving cells. 
     It may be understood that the foregoing scenarios are applicable to vehicle-to-everything (vehicle-to-everything, V2X), which may also be referred to as V2X. For a specific application scenario, for example, the D2D technology may be applied to a neighborhood-based social application. For example, data between adjacent terminal devices is transmitted by using the D2D technology, for example, content sharing and interactive games. The D2D technology may further resolve communication interruption, in a rescue, caused by a natural disaster. For example, in the rescue scenario, wireless communication can still be established between two adjacent terminal devices by using the D2D technology. For another example, information such as a commodity discount promotion, a movie preview, and the like may be pushed to a user by using the D2D technology. A scenario to which the D2D technology is applied is not uniquely limited in this embodiment of this application. 
       FIG. 4  is a schematic diagram of a frame structure according to an embodiment of this application. In N2R, frame structures may be classified into four types, respectively shown in  4   a  to  4   d  in  FIG. 4 . A sidelink data channel such as a physical sidelink shared channel (physical sidelink shared channel, PSSCH) and a sidelink control channel such as a physical sidelink control channel (physical sidelink control channel, PSCCH) overlap in time domain but do not overlap in frequency domain, overlap in frequency domain but do not overlap in time domain, and overlap in time domain and frequency domain. 
     For example, in V2X communication (or in M2M communication, LTE-V communication, or the like), when a resource is transmitted on a sidelink (sidelink, SL), two modes are usually included, namely, a network device-based scheduling mode, which is usually referred to as a mode  1 , and a contention-based scheduling mode, which is usually referred to as a mode  2 . 
     For example, in  FIG. 1 , in a scheduling process of the mode  2 , the terminal device may perform resource sensing in a sensing (sensing) window, and then select an idle resource in a selection window for resource transmission. Alternatively, the terminal device may perform sensing on a resource by using listen before talk (listen before talk, LBT). When the LBT succeeds, a resource that is successfully sensed may be used for resource transmission. When the LBT fails, an available resource needs to be sensed again. In this case, an embodiment of this application provides an information transmission method, to further improve a contention-based resource scheduling process. 
     Before the information transmission method provided in embodiments of this application is described, the following describes terms in embodiments of this application in detail. 
     Listen before talk (listen before talk, LBT) is also referred to as listen before talk, and is a carrier sense multiple access (carrier sense multiple access, CSMA) technology. An LBT mechanism can avoid a conflict when an unlicensed spectrum resource is used. 
     With a sharp increase of wireless data service volumes, a licensed spectrum may not meet a spectrum requirement of communication. Preemption of an unlicensed spectrum for information transmission may improve a data throughput in a wireless communication network, and can better meet a user requirement. Based on this, the 3rd generation partnership project (3rd generation partnership project, 3GPP) introduces licensed assisted access (license assisted access, LAA) and enhanced licensed assisted access (enhanced LAA, eLAA) technologies in release  13  (release  13 ) and release  14  (release  14 ) respectively. To be specific, an LTE/LTE-A system is deployed on an unlicensed spectrum in a non-standalone manner, and usage of an unlicensed spectrum resource is maximized with assistance by a licensed spectrum. 
     Usually, a communication apparatus (including the foregoing network device and terminal device) in the communication system deployed on the unlicensed spectrum uses a radio resource in a contention-based manner. In other words, before sending a signal, the communication apparatus first listens whether the unlicensed spectrum is idle. For example, a busy/idle state of a channel is determined based on a value of received power on the unlicensed spectrum. If the received power is less than or equal to a specific threshold, it is considered that the channel in the unlicensed spectrum is in the idle state, and the signal may be sent on the unlicensed spectrum; otherwise, the signal is not sent. The listen before send mechanism is called an LBT mechanism. In other words, to enable a plurality of unlicensed frequency band devices to fairly use unlicensed frequency band channels, and avoid mutual interference between the unlicensed frequency band devices, currently, the LBT mechanism is used to listen whether a channel is idle. When it is listened that an unlicensed frequency band channel is occupied, it indicates that the LBT fails, and a signal is not sent. Only when it is listened that an unlicensed frequency band channel is idle, it indicates that the LBT succeeds, and the communication apparatus sends a signal. 
     If the LBT succeeds, it indicates that a sending device obtains an available channel through contention. Therefore, after the LBT succeeds, the sending device may send a channel occupancy signal to another peripheral device. The channel occupancy signal may be referred to as a channel reservation (reservation) signal or a channel utilization (utilization) signal in different embodiments. The channel occupancy signal is used to indicate, to another device, transmission duration, namely, channel occupancy duration that needs to be occupied by the sending device on the channel obtained through contention, to avoid collision caused because the another device transmits data on the channel. This improves communication reliability and communication efficiency. The sending device is the foregoing communication apparatus that can perform the LBT, and may be a terminal device. Specifically, if a device that initiates an LBT procedure is a terminal device, the sending device is a terminal device. 
     The channel occupancy duration may be measured in a unit of microseconds (μs), a unit of orthogonal frequency division multiplexing (orthogonal frequency division multiplexing, OFDM) symbols, a unit of slots (slot), a unit of mini-slots (mini-slot), or the like. A subcarrier spacing corresponding to the foregoing OFDM symbol or slot may be a subcarrier spacing predefined in a standard, or may be the same as a subcarrier spacing of the channel occupancy signal. 
     The following describes sidelink control information (sidelink control information, SCI) in embodiments of this application. 
     In the D2D/V2X technology, SCI may include a modulation and coding scheme (modulation and coding scheme, MCS), data scheduling information, and the like. In embodiments of this application, the SCI in this format may be referred to as SCIB (third SCI). 
     However, embodiments of this application provide SCI in another format. For example, the SCI in the another format is referred to as SCIA, and the SCIA may further be classified into SCIA  1  (first SCI) and SCIA  2  (second SCI). The following describes the SCIA by using the first SCI and the second SCI as an example. 
       FIG. 5  shows content carried in the first SCI and the second SCI respectively. It may be understood that a payload (payload) of the first SCI is the same as a payload of the second SCI. In addition, a format of the first SCI and/or a format of the second SCI are configured by same higher layer signaling. In other words, a location of a field in the first SCI, or a location and a meaning of a field in the first SCI are configured for the terminal device by using the higher layer signaling. A location of a field in the second SCI, or a location and a meaning of a field in the second SCI are configured for the terminal device by using the higher layer signaling. The location of the field in the first SCI and the location of the field in the second SCI, or the location and the meaning of the field in the first SCI and the location and the meaning of the field in the second SCI are configured for the terminal device by using the same higher layer signaling. In other words, a location of each field configured by the higher layer signaling, or a location and a meaning of each field configured by the higher layer signaling are applicable to both the first SCI and the second SCI. 
     As shown in  FIG. 5 , a first field is used to indicate transmit end information of data transmitted on an SL, and a third field is used to indicate receive end information of the data transmitted on the SL. The data may be data sent by the terminal device  1  to the terminal device  2 . The terminal device  1  is a data transmit end, and the terminal device  2  is a data receive end. In other words, the first field and the third field are used to indicate a transmission direction of the data. Alternatively, the first field may indicate transmit end information of the data, and the third field may indicate receive end information of the data. The transmit end information of the data may be understood as that a transmit end of the data transmitted on a PSSCH from the terminal device  1  to the terminal device  2  is the terminal device  1 . The receive end information of the data may be understood as that a receive end of the data transmitted on the PSSCH from the terminal device  1  to the terminal device  2  is the terminal device  2 . For example, the first field and the third field may each be one bit. For example, 1 or 0 may be used to respectively identify a transmit (transmission, Tx) terminal device such as the terminal device  1  and a receive (reception, Rx) terminal device such as the terminal device  2 . For example, when the first field is  1 , it may indicate that the transmit terminal device is the terminal device  1 . In this case, the third field is 0, and it indicates that the receive terminal device is the terminal device  2 . It may be understood that an indication manner of the first field and the third field may alternatively be another manner. For example, the first field and the third field may each be two bits, and 11 or 00 is used to respectively indicate a transmit terminal device and a receive terminal device. The foregoing examples are not limited in this embodiment of this application. In this embodiment of this application, a first field of the first SCI and a third field of the second SCI are used as an example. The third field of the second SCI may alternatively be replaced with a first field of the second SCI. 
     Optionally, the first field and the third field may alternatively be a format identifier of the first SCI and a format identifier of the second SCI respectively. For example, the format identifier of the first field may be A 1 , and may indicate that the first SCI is from the transmit end of the data. The format identifier of the third field is A 2 , and may indicate that the second SCI is from the receive end of the data (the receive end is relative to the transmit end of the data). This embodiment of this application uses format identifiers A 1  and A 2  as an example. The format identifier A 1  may alternatively be replaced with a format identifier X (or Tx), the format identifier A 2  may alternatively be replaced with a format identifier Y (or Rx), and the like. For example, X may be an integer, and Y may also be an integer. For example, X may be a letter, and Y may also be a letter. For example, X may be a combination of an integer and a letter, and Y may also be a combination of an integer and a letter. 
     Optionally, the first SCI and the second SCI may each include a field used to indicate information about an available subchannel set. The available subchannel set may be an idle subchannel set sensed by the transmit terminal device or the receive terminal device, or the available subchannel set may be an available subchannel set sensed by the transmit terminal device or the receive terminal device. In other words, a field of an available subchannel shown in  FIG. 5  may be used to carry the available subchannel set sensed by the transmit terminal device or the receive terminal device. For example, an available subchannel set determined by the transmit terminal device is a subchannel  1  to a subchannel  5  and a subchannel  7  to a subchannel  9 . In this case, the subchannel  1  to the subchannel  5  and the subchannel  7  to the subchannel  9  may be padded in fields corresponding to available subchannels. It may be understood that the subchannel  1  to the subchannel  5  and the subchannel  7  to the subchannel  9  are indexes of a plurality of subchannels included in the available subchannel set. For example, the available subchannel set may be a set index indicator, a subchannel index indicator, or a bitmap. 
     In this embodiment of this application, N physical resource blocks (physical resource block, PRB) may be grouped into one subchannel, and the N PRBs may be continuous PRBs, discontinuous PRBs, or the like. This is not limited in this embodiment of this application. Herein, N is a positive integer. For example, N =12, and one physical subchannel is a time-frequency two-dimensional structure including 12 subcarriers and one slot, where one slot may be 14 orthogonal frequency division multiplexing (orthogonal frequency division multiplexing, OFDM) symbols or 13 OFDM symbols. In addition, N may be any defined positive integer, and may be one slot, one mini-slot, or M symbols in time domain, where M is a positive integer greater than or equal to 1 and less than or equal to 14. For another example, N may be any integer less than or equal to 12. It may be understood that the continuous PRBs may be uninterrupted PRBs from a PRB (M) to a PRB (N), where M is less than N, and M and N are positive integers. Specifically, during sidelink transmission, the available subchannels may be used to transmit data information between the terminal device  1  and the terminal device  2 , and/or the available subchannels may be used to transmit control information, or the like. 
     Specifically, a method for sensing whether a subchannel is available is as follows: For example, the terminal device may sense, based on signal energy received on the subchannel or signal energy sensed/listened on the subchannel, whether the subchannel is available. The signal energy includes any one of a received signal strength indication (received signal strength indication, RSSI), reference signal received power (reference signal received power, RSRP), or a signal to interference plus noise ratio (signal to interference plus noise ratio, SINR). For example, when sensing the subchannel  1 , the terminal device may first interpret, from sensed control information sent by a surrounding terminal device, quality of service (quality of service, QoS) information included in the control information; compare QoS information of to-be-transmitted data of the terminal device and the sensed QoS information of to-be-transmitted data on the subchannel  1 ; determine a threshold based on the foregoing QoS information; and if signal energy received on the subchannel meets the corresponding threshold, determine that the subchannel  1  is available; otherwise, determine that the subchannel  1  is unavailable. The QoS information included in the control information is QoS information of to-be-sent data of a surrounding terminal device. Meeting the corresponding threshold may be understood as that the sensed signal energy is less than or equal to the threshold. The sensed signal energy may be determined based on any one or more of the RSSI, the RSRP, or the SINR, or may be determined based on signal strength of sensed SCI, signal strength of a sensed PSSCH, or the like. This is not limited in this embodiment of this application. That the signal energy received on the subchannel is the signal strength of the sensed PSSCH may specifically be: sensing the PSSCH that is obtained from the SCI and that uses the subchannel, to obtain the signal strength of the PSSCH that uses the subchannel It may be understood that the QoS information in this application may also be referred to as QoS level information, service priority information, or the like. A specific name of the QoS information is not limited in this embodiment of this application. The QoS information includes at least one of a ProSe per-packet priority (ProSe per-packet priority, PPPP), N quality indexes (quality index, QI), or another related parameter used to indicate QoS. It may be understood that the threshold is a threshold determined based on QoS information of a sensing terminal device and QoS information of a sensed terminal device, and the threshold may be preconfigured, or configured by the network device for the terminal device by using RRC signaling. 
     In this embodiment of this application, sensing a subchannel, receiving a subchannel, or listening a subchannel may be interchanged. Further, the foregoing method for sensing whether a subchannel is available may further be applied to a subchannel set. For example, sensed signal energy of all subchannels included in the subchannel set is averaged. In other words, a linear average value or a weighted average value of the sensed signal energy of all the subchannels included in the subchannel set is considered as final sensed signal energy of the subchannel set. 
     For example, when the subchannel set includes the subchannel  1 , the subchannel  3 , and the subchannel  5 , sensed signal energy of the three subchannels is averaged, to obtain an average value. 
     Optionally, the first SCI and the second SCI may further include a field used to indicate a channel occupancy indicator (channel utilization indicator, CUI). The CUI may be used to indicate duration in which the transmit terminal device or the receive terminal device is to occupy the available subchannel. Alternatively, the CUI may indicate duration in which another terminal device needs to reserve the available subchannel for the transmit terminal device or the receive terminal device. For example, the duration indicated by the CUI may be any duration obtained through division based on a unit of a time domain resource. In this embodiment of this application, the unit of the time domain resource may be a combination of any one or more of an orthogonal frequency division multiplexing (orthogonal frequency division multiplexing, OFDM) symbol, a mini-slot, or a slot (slot). For example, the CUI may indicate 10 slots (slot), 5 slots, or the like. It may be understood that the CUI may be a continuous time period, a discontinuous time period, or the like. This is not limited in this embodiment of this application. 
     It should be noted that the available subchannel set may include one or more subchannels. In other words, the first SCI may include information about one or more subchannels. This is not limited in this embodiment of this application. When the first SCI includes information about a plurality of subchannels, the plurality of subchannels may be a plurality of continuous subchannels, a plurality of discontinuous subchannels, or the like. This is not limited in this embodiment of this application. It may be understood that the second SCI may alternatively indicate information about one or more subchannels. Details are not described herein again. 
     It may be understood that when available subchannel sets separately sensed by the transmit terminal device and the receive terminal device have a common available subchannel set, the transmit terminal device may transmit control information and/or data information by using the sensed common available subchannel set. Having a common available sub-channel set includes: the available subchannel set sensed by the transmit terminal device is the same as the available subchannel set sensed by the receive terminal device, or there is an overlapping (overlap) part (namely, an intersection) between the available subchannel set sensed by the transmit terminal device and the available subchannel set sensed by the receive terminal device. However, when the available subchannel sets separately sensed by the transmit terminal device and the receive terminal device are completely different, that is, there is no intersection between the available subchannel set sensed by the transmit terminal device and the available subchannel set sensed by the receive terminal device, the transmit terminal device may transmit the control information and/or the data information by using the available subchannel set sensed by the receive terminal device. 
     Optionally, the first SCI and the second SCI may further include feature (feature) fields, namely, a second field and a fourth field. The feature field of the transmit terminal device, namely, the second field, may be used to indicate priority information of the data. The first SCI indicates the priority information of the data. Therefore, when sensing the available subchannel included in the first SCI of the transmit terminal device, another terminal device determines, based on the priority information of the data, whether the available subchannel can be preempted or whether to avoid using the available subchannel The feature domain of the receive terminal device may be used to indicate channel state information (channel state information, CSI). The CSI may be understood as a channel state of a subchannel set sensed by the receive terminal device. The transmit terminal device may learn, by using the CSI, a channel state when the receive terminal device receives information, so that the transmit terminal device can use a corresponding MCS or the like during scheduling and transmission of data information on a sidelink. Optionally, the feature domain of the receive terminal device may be a reserved bit. For example, if the feature domain of the receive terminal device is not activated, that is, the receive terminal device cannot feed back a channel state, the feature domain of the receive terminal device may be a reserved bit. In this case, the receive terminal device may indicate, by using radio resource control (radio resource control, RRC) signaling or dynamic signaling, that the CSI is not activated. Optionally, when the dynamic signaling is used to indicate that the CSI is not activated, the dynamic signaling may be SCIB (third SCI), downlink control information (downlink control information, DCI), SCIA, or the like. This is not limited in this embodiment of this application. 
     Optionally, the first field may be indication information of a reference signal for measurement on the SL. The indication information of the reference signal for measurement on the SL may be an index of the reference signal for measuring the CSI on the SL, activation information of the reference signal for measuring the CSI on the SL, or activation information used to measure the CSI on the SL. The activation information may also be referred to as enabling information. Optionally, the third field may be CSI, and the fourth field may be used to indicate a reserved bit (which is also referred to as a reserved field) or feedback information. In this application, the feedback information included in the second SCI is feedback information for the first SCI, that is, whether a feedback (ACK/NACK) of the first SCI is correctly received. 
     It may be understood that the foregoing SCIA does not include scheduling information such as an MCS. In this embodiment of this application, the MCS is a modulation and coding scheme (modulation and coding scheme). In this application, the MCS is used in a general sense, that is, in different control information, the MCS may be different values. 
     Optionally, because the first SCI and the second SCI may not include an MCS, that is, the first SCI and the second SCI are different from the third SCI, a subchannel set (including one or more subchannels) used for transmitting the first SCI and the second SCI may be defined to be located in specific search space. In other words, the subchannel set used by the transmit terminal device to send the first SCI may be one or more subchannels in the specific search space. For example, the subchannel set in which a control channel element (control channel element, CCE)/control resource set (control resource set, CORSET) used by the transmit terminal device to send the first SCI is located may be a subchannel set x in the specific search space, where the subchannel set x includes one or more subchannels. 
     It should be noted that a sequence of fields, domains, or information included in the first SCI and the second SCI is merely an example, and should not be construed as a limitation on this embodiment of this application. 
     Then, the following describes the information transmission method in embodiments of this application by using an example in which the transmit terminal device is the terminal device  1 , the receive terminal device is the terminal device  2 , the SCIA corresponding to the terminal device  1  is the first SCI, and the SCIA corresponding to the terminal device  2  is the second SCI. However, during actual application, the terminal device  1  may interact with the terminal device  2 , a terminal device  3 , a terminal device  4 , and the like. The terminal device  2  may interact with the terminal device  1 , the terminal device  3 , the terminal device  4 , a terminal device  5 , and the like. Therefore, the following example should not be construed as a limitation on this application. 
       FIG. 6  is a schematic diagram of a scenario of an information transmission method according to an embodiment of this application. The information transmission method includes the following steps. 
       601 : A terminal device  1  senses and determines an available subchannel set. For example, the determined available subchannel set is referred to as a first subchannel set, and the first subchannel set includes one or more subchannels. 
     In this embodiment of this application, that the terminal device  1  senses an available subchannel may also be referred to as that the terminal device  1  listens an available subchannel For a method for sensing the available subchannel set by the terminal device  1 , refer to the method for sensing the available subchannel or the available subchannel set by the transmit terminal device or the receive terminal device in the foregoing embodiments. Details are not described herein again. 
       602 : The terminal device  1  sends first SCI to a terminal device  2 . 
     The field used to indicate the information about the available subchannel set in the first SCI shown in  FIG. 5  includes information about the first subchannel set. For example, the field may include an index (index) of the first subchannel set, where the index may also be referred to as an identifier or the like. For another example, the field may include an index (index) forming subchannels of the first subchannel set, where the index may also be referred to as an identifier or the like. For another example, the field may include a bitmap (bitmap) including subchannels, namely, a bitmap in which bits corresponding to the subchannels of the first subchannel set are marked as  1 . 
       603 : The terminal device  2  senses and determines an available subchannel set. For example, the determined available subchannel set is referred to as a second subchannel set, and the second subchannel set includes one or more subchannels. 
     The terminal device  2  may sense and determine the available subchannel set after receiving the first SCI or before receiving the first SCI. In other words, step  603  may be performed after step  601 , before step  601 , or the like. This is not limited in this embodiment of this application. 
       604 : The terminal device  2  sends second SCI to the terminal device  1 . 
     The field used to indicate the information about the available subchannel set in the second SCI shown in  FIG. 5  may include information about the second subchannel set. In other words, the field used to indicate the available subchannel set in the second SCI may indicate the second subchannel set. 
     It may be understood that for specific content of the first SCI and the second SCI, refer to the foregoing embodiments. The field used to indicate the information about the available subchannel set in the second SCI includes the information about the second subchannel set. For example, the field may include an index (index) of the second subchannel set, where the index may also be referred to as an identifier or the like. For another example, the field may include an index (index) forming subchannels of the second subchannel set, where the index may also be referred to as an identifier or the like. For another example, the field may include a bitmap (bitmap) including subchannels, namely, a bitmap in which bits corresponding to the subchannels of the second subchannel set are marked as  1 . 
     Optionally, the first SCI and the second SCI may be sent in search space by using examples shown in  FIG. 7  and  FIG. 8 . As shown in  FIG. 7 , SCI occupies one slot (slot) in time domain and is arranged adjacent to each other sequentially. Alternatively, as shown in  FIG. 8 , SCI occupies several symbols, less than one slot, in time domain and is arranged adjacent to each other sequentially in time domain and frequency domain. 
     In this embodiment of this application, for data sent from the terminal device  1  to the terminal device  2 , the first SCI and the second SCI have a sequence relationship in time domain. In other words, time at which the terminal device  1  sends the first SCI is earlier than time at which the terminal device  2  sends the second SCI. For different data service pairs or data service groups, the first SCI and the second SCI have no sequence relationship in time domain In other words, if the terminal device  1  sends data to the terminal device  2 , and a terminal device  3  sends data to a terminal device  4 , the first SCI sent by the terminal device  1  and the second SCI sent by the terminal device  4  have no sequence relationship in time domain. In other words, time at which the terminal device  1  sends the first SCI may be earlier than time at which the terminal device  4  sends the second SCI, time at which the terminal device  4  sends the second SCI is earlier than time at which the terminal device  1  sends the first SCI, or time at which the terminal device  4  sends the second SCI may be the same as time at which the terminal device  1  sends the first SCI. 
       605 : The terminal device  1  receives the second SCI from the terminal device  2 , and determines a target subchannel set. 
     In this embodiment of this application, the target subchannel set may be a subchannel set determined based on an intersection between the first subchannel set and the second subchannel set, or a subchannel set determined based on the second subchannel set. For specific description of the target subchannel set, refer to the foregoing embodiments. Details are not described herein again. 
       606 : The terminal device  1  sends third SCI to the terminal device  2  by using the target subchannel set, and sends sidelink data to the terminal device  2 . 
       FIG. 9  is a schematic diagram of a format of the third SCI according to an embodiment of this application. The third SCI may include a combination of at least one or more of an MCS, a scheduling subchannel set (including one or more subchannels), a PPPP, and a CUI, and may further include indication information for a feedback resource. The scheduling subchannel set may be understood as a subchannel set used to schedule data, and the indication information for the feedback resource may be understood as a resource used to transmit feedback information. Specifically, the resource used to transmit the feedback information may be subchannel set information (which may be referred to as a feedback subchannel set) used to transmit the feedback information, or physical resource block (physical resource block, PRB)/resource element (resource element, RE) information used to transmit the feedback information. For example, the subchannel set information used to transmit the feedback information may be indicated by a subchannel (which is referred to as a feedback subchannel) used to transmit the feedback information, or may be identified by an offset relative to a subchannel used to transmit data information. For example, the PRB/RE information may be indicated as a PRB/RE index in a subchannel. Alternatively, the PRB/RE information may be indicated only as a PRB/RE index. In this embodiment of this application, the PPPP is merely an example, and the PPPP may alternatively be replaced with any QoS information. For example, the QoS information may alternatively be a QoS index, for example, N QoS indexes (N QI), where N is a positive integer. 
     Optionally, the feedback subchannel set may be a subchannel set determined based on the intersection between the first subchannel set and the second subchannel set, or a subchannel set determined based on the first subchannel set. In other words, the feedback subchannel set is at least included in the first subchannel set. After receiving the data on the SL, the terminal device  2  needs to feed back whether the data is correctly received. Therefore, the feedback information may be fed back by using the feedback subchannel set. Further, to enable the terminal device  1  to receive the feedback information, the feedback subchannel set is at least included in the first subchannel set. 
     In this application, the feedback information is HARQ information on the sidelink, namely, SL ACK/NACK information. The HARQ information on the sidelink is usually carried on a physical sidelink feedback channel (physical sidelink feedback channel, PSFCH). 
       607 : The terminal device  2  receives the third SCI from the terminal device  1 , and sends physical sidelink feedback information to the terminal device  1 . 
     In this embodiment of this application, the PSFCH is transmitted to the terminal device  1  based on the resource, indicated by the third SCI, used to transmit the feedback information. 
     It should be noted that if there is a requirement of a sending moment for sending SCI, or there is a requirement of aligning a slot boundary for sending SCI, before sending SCI by using any selected subchannel set used to send the SCI, padding (padding) needs to be performed on the selected subchannel set. That there is a requirement of the sending moment for sending the SCI, or there is a requirement of aligning the slot boundary for sending the SCI may be understood as: 
     the moment for sending the SCI needs to be located at a start point of a first symbol of the slot, or a start point of an N th  symbol (N is greater than or equal to 1 and less than or equal to 14). Specifically, padding (padding) may be performed by using a sequence (sequence), where the sequence may be preamble code (preamble code) or a sounding reference signal (sounding reference signal, SRS). It should be noted that the SCI shown in the paragraph may be the first SCI or the second SCI. 
     In this embodiment of this application, the terminal device  1  and the terminal device  2  may sense SCI of a same size. In other words, a payload (payload) of the first SCI sent by the terminal device  1  is the same as a payload of the second SCI sent by the terminal device  2 . In addition, fields at a same location of the first SCI and the second SCI have different meanings. 
     This meets a requirement of the terminal device  1  for sending QoS, and meets a requirement of the terminal device  2  for sending CSI. The same payload reduces sensing complexity, and corresponding requirements are met based on requirements of a transmit end and a receive end, to reduce overheads. 
       FIG. 10 a    is a schematic flowchart of an information transmission method according to an embodiment of this application. The information transmission method may be applied to a first terminal device, a second terminal device, and the like. A terminal device that performs the information transmission method is not limited in this embodiment of this application. The following directly uses a terminal device as an example for description. As shown in  FIG. 10 a   , the information transmission method includes the following steps. 
       1001 : A terminal device determines a scheduling mode, where the scheduling mode includes a first mode or a second mode. 
     In this embodiment of this application, the first mode is a network device-based scheduling mode (namely, a mode  1 ), and the second mode is a contention-based scheduling mode (mode  2 ). For specific description of the mode  2 , refer to the foregoing embodiments. Details are not described herein again. 
       FIG. 10 b    is a flowchart in which a terminal device  1  interacts with a network device and the terminal device  1  interacts with a terminal device  2  in the mode  1 . When the terminal device  1  needs to send data, the terminal device  1  may send an SR to the network device, and the network device delivers downlink control information (downlink control information, DCI). The DCI may be used to indicate a transmission resource used to transmit a buffer state report (buffer state report, BSR) (which may also be referred to as a buffer state report) of an amount of to-be-transmitted data on an SL. Then, the terminal device  1  sends the BSR to the network device by using the indicated transmission resource used to transmit the BSR of the amount of the to-be-transmitted data on the SL, and the network device delivers DCI again, where the DCI is used to indicate the transmission resource used to transmit the to-be-transmitted data on the SL. The transmission resource used to transmit the to-be-transmitted data on the SL is usually indicated by using a subchannel, and the transmission resource usually includes at least one of a resource used for a physical sidelink control channel (physical sidelink control channel, PSCCH) and a physical sidelink shared channel (physical sidelink shared channel, PSSCH). Further, the terminal device  1  may communicate with the terminal device  2  about control information on the PSCCH, and/or communicate with the terminal device  2  about data information on the PSSCH. It may be understood that the method shown in  FIG. 10 b    is merely an example, and should not be construed as a limitation on this embodiment of this application. 
       1002 : The terminal device senses and determines an available subchannel set. 
     In this embodiment of this application, for different scheduling modes, the terminal device senses the available subchannel set based on different determining thresholds. For example, the first mode corresponds to a first threshold, the second mode corresponds to a second threshold, and the first threshold is less than the second threshold. That the first mode corresponds to the first threshold may be understood as: when performing sidelink data transmission in the first mode, the terminal device may sense, based on whether sensed signal energy is less than or equal to the first threshold, whether a subchannel set is available. That the second mode corresponds to the second threshold may be understood as: when performing sidelink data transmission in the second mode, the terminal device may sense, based on whether sensed signal energy is less than or equal to the second threshold, whether a subchannel set is available. 
     Specifically, for example, the terminal device may sense, based on signal energy received on a subchannel or signal energy sensed on a subchannel, whether a subchannel is available. For example, when sensing a subchannel  1 , the terminal device may first interpret, from sensed control information sent by a surrounding terminal device, quality of service (quality of service, QoS) information included in the control information; compare QoS information of to-be-transmitted data of the terminal device and the sensed QoS information of to-be-transmitted data on the subchannel  1 ; determine the first threshold (or the second threshold) based on the foregoing QoS information; and if signal energy received on the subchannel  1  meets the corresponding threshold, determine that the subchannel  1  is available; otherwise, determine that the subchannel  1  is unavailable. The QoS information included in the control information is QoS information of to-be-sent data of a surrounding terminal device. Meeting the corresponding threshold may be understood as that the sensed signal energy is less than or equal to the first threshold (or the second threshold). The sensed signal energy may be determined based on any one or more of the RSSI, the RSRP, or the SINR, or may be determined based on signal strength of sensed SCI, signal strength of a sensed PSSCH, or the like. This is not limited in this embodiment of this application. It may be understood that the QoS information in this application may also be referred to as QoS level information, service priority information, or the like. A specific name of the QoS information is not limited in this embodiment of this application. The QoS information includes at least one of a ProSe per-packet priority (ProSe per-packet priority, PPPP), N quality indexes (quality index, QI), or another related parameter used to indicate QoS. It may be understood that the first threshold and/or the second threshold is a threshold determined based on QoS information of a sensing terminal device and QoS information of a sensed terminal device, and the threshold may be preconfigured, or configured by the network device for the terminal device by using RRC signaling. 
     It may be understood that after sensing and determining the available subchannel set, the terminal device may perform a related operation based on the available subchannel set, for example, may report the available subchannel set to the network device, or may notify another terminal device of the available subchannel set (for example, perform the method shown in  FIG. 6 ). The related operation performed by the terminal device based on the available subchannel set is not limited in this embodiment of this application. 
     In this embodiment of this application, sensing, in the first mode, may be performed only by the terminal device, and the terminal device reports the available subchannel set to the network device. Therefore, a requirement of an energy threshold of the available subchannel set reported in the first mode may be stricter, to ensure that data transmitted by using the reported available subchannel set does not collide. Sensing, in the second mode, may be performed by both the terminal device  1  and the terminal device  2 . Therefore, an energy threshold of the available subchannel set is defined to be larger. This can ensure that the terminal device can use the available subchannel set, avoid collision, and improve resource utilization. 
     Finally, a communication apparatus provided in this embodiment of this application is described in detail. 
       FIG. 11  is a schematic diagram of a structure of a communication apparatus according to an embodiment of this application. The communication apparatus is configured to perform the information transmission method described in embodiments of this application. As shown in  FIG. 11 , the communication apparatus includes: 
     a sending unit  1101 , configured to send first sidelink control information SCI to a second terminal device, where 
     the first SCI includes information about a first subchannel set, the first subchannel set is an available subchannel set sensed by the first terminal device on a sidelink SL, and the first SCI does not include modulation and coding scheme MCS information. 
     In a possible implementation, the first SCI includes a first field and a second field; the first field is used to indicate transmit end information of data transmitted on the SL, or the first field is a format identifier of the first SCI; and the second field is used to indicate priority information of the data. 
     In a possible implementation, the communication apparatus further includes: 
     a receiving unit  1102 , configured to receive second SCI sent by the second terminal device, where the second SCI includes information about a second subchannel set, the second subchannel set is an available subchannel set sensed by the second terminal device on the SL, and the second SCI does not include MCS information. 
     In a possible implementation, a payload of the second SCI is the same as a payload of the first SCI. 
     In a possible implementation, the second SCI includes a third field and a fourth field; the third field is used to indicate receive end information of the data transmitted on the SL, or the third field is a format identifier of the second SCI; and the fourth field is used to indicate at least one of channel state information CSI, feedback information, or a reserved bit. 
     In a possible implementation, a format of the first SCI and a format of the second SCI are configured by using same higher layer signaling. 
     In a possible implementation, the communication apparatus further includes: 
     a processing unit  1103 , configured to determine a target subchannel set based on the first subchannel set and the second subchannel set. 
     The sending unit  1101  is further configured to send the data to the second terminal device by using the target subchannel set. 
     In a possible implementation, the target subchannel set is an intersection between the first subchannel set and the second subchannel set. 
     In a possible implementation, the sending unit  1101  is further configured to send third SCI to the second terminal device, where the third SCI includes scheduling information of the data transmitted on the SL. 
     In a possible implementation, the third SCI further includes information used to indicate a feedback subchannel set, and the feedback subchannel set is at least included in the first subchannel set. 
     Optionally, the communication apparatus shown in  FIG. 11  may further be configured to perform the following operations. 
     The processing unit  1103  may be configured to determine a scheduling mode, where the scheduling mode includes a first mode or a second mode. 
     The processing unit  1103  may further be configured to: sense an available subchannel set; when the scheduling mode is the first mode, sense the available subchannel set based on a first threshold; and when the scheduling mode is the second mode, sense the available subchannel set based on a second threshold, where the first threshold is less than the second threshold. 
     In a possible implementation, the first threshold and the second threshold are predefined, or the first threshold and the second threshold are configured by the network device by using signaling. 
     In this embodiment of this application, when the communication apparatus is a terminal device or a component that implements the foregoing functions in a terminal device, the processing unit  1103  may be one or more processors, the sending unit  1101  may be a transmitter, and the receiving unit  1102  may be a receiver. Alternatively, the sending unit  1101  and the receiving unit  1102  are integrated into one component, for example, a transceiver. For example, the transceiver may send the first sidelink control information SCI to the second terminal device, and send the data to the second terminal device by using the target subchannel set. For another example, the transceiver may receive the second SCI sent by the second terminal device. 
     When the foregoing communication apparatus is a chip, the processing unit  1103  may be one or more processors, the sending unit  1101  may be an output interface, and the receiving unit  1102  may be an input interface. Alternatively, the sending unit  1101  and the receiving unit  1102  are integrated into one unit, for example, an input/output interface. 
     It may be understood that for implementation of each unit shown in  FIG. 11 , refer to corresponding description of the method embodiment shown in  FIG. 6 , or corresponding description of the method embodiment shown in  FIG. 10   a.    
       FIG. 12  is a schematic diagram of a structure of a communication apparatus according to an embodiment of this application. The communication apparatus is configured to perform the information transmission method described in embodiments of this application. As shown in  FIG. 12 , the communication apparatus includes: 
     a receiving unit  1201 , configured to receive first SCI sent by a first terminal device, where the first SCI includes information about a first subchannel set, the first subchannel set is an available subchannel set sensed by the first terminal device on a sidelink SL, and the first SCI does not include modulation and coding scheme MCS information; and 
     a sending unit  1202 , configured to send second SCI to the first terminal device, where the second SCI includes information about a second subchannel set, the second subchannel set is an available subchannel set sensed by the second terminal device on the SL, and the second SCI does not include MCS information. 
     In a possible implementation, the first SCI includes a first field and a second field; the first field is used to indicate transmit end information of data transmitted on the SL, or the first field is a format identifier of the first SCI; and the second field is used to indicate priority information of the data. 
     In a possible implementation, the second SCI includes a third field and a fourth field; the third field is used to indicate receive end information of the data transmitted on the SL, or the third field is a format identifier of the second SCI; and the fourth field is used to indicate at least one of channel state information CSI, feedback information, or a reserved bit. 
     In a possible implementation, a payload of the second SCI is the same as a payload of the first SCI. 
     In a possible implementation, a format of the first SCI and a format of the second SCI are configured by using same higher layer signaling. 
     In a possible implementation, the receiving unit  1201  is further configured to receive the data sent by the first terminal device by using a target subchannel set, where the target subchannel set is an intersection between the first subchannel set and the second subchannel set. 
     In a possible implementation, the receiving unit  1201  is further configured to receive third SCI sent by the first terminal device, where the third SCI includes scheduling information of the data transmitted on the SL. 
     In a possible implementation, the third SCI further includes information used to indicate a feedback subchannel set, and the feedback subchannel set is at least included in the first subchannel set. 
     In this embodiment of this application, when the communication apparatus is a terminal device or a component that implements the foregoing functions in a terminal device, the sending unit  1202  may be a transmitter, and the receiving unit  1201  may be a receiver. Alternatively, the sending unit  1202  and the receiving unit  1201  are integrated into one component, for example, a transceiver. For example, the transceiver may receive the first SCI sent by the first terminal device, and may further send the second SCI to the first terminal device. It may be understood that the communication apparatus may further include a processor. For example, the processor may sense the second subchannel set. This is not limited in this embodiment of this application. 
     When the foregoing communication apparatus is a chip, the sending unit  1202  may be an output interface, and the receiving unit  1201  may be an input interface. Alternatively, the sending unit  1202  and the receiving unit  1201  are integrated into one unit, for example, an input/output interface. It may be understood that the communication apparatus may further include a processor. 
     It may be understood that for implementation of each unit shown in  FIG. 12 , refer to corresponding description of the method embodiment shown in  FIG. 6 , or corresponding description of the method embodiment shown in  FIG. 10   a.    
       FIG. 13  is a schematic diagram of a structure of a terminal device  1300  according to an embodiment of this application. The terminal device may perform an operation of the first terminal device (the terminal device  1 ) in the method shown in  FIG. 6 , or an operation of the communication apparatus shown in  FIG. 11 . Alternatively, the terminal device may be configured to perform an operation of the second terminal device (the terminal device  2 ) in the method shown in  FIG. 6 , or an operation of the communication apparatus shown in  FIG. 12 . The terminal device may alternatively be configured to perform the method shown in  FIG. 10   a.    
     For ease of description,  FIG. 13  shows only main components of the terminal device. As shown in  FIG. 13 , the terminal device  1300  includes a processor, a memory, a radio frequency circuit, an antenna, and an input/output apparatus. The processor is mainly configured to: process a communication protocol and communication data, control the entire terminal device, execute a software program, and process data of the software program, for example, support the terminal device in performing the procedure described in  FIG. 6  or  FIG. 10 a   . The memory is mainly configured to store the software program and the data. The radio frequency circuit is mainly configured to: convert a baseband signal and a radio frequency signal, and process the radio frequency signal. The antenna panel is mainly configured to send and receive a radio frequency signal in an electromagnetic wave form. The terminal device  1300  may further include an input/output apparatus, for example, a touchscreen, a display screen, or a keyboard. The input/output apparatus is mainly configured to: receive data entered by a user, and output data to the user. It should be noted that some types of terminal devices may not have an input/output apparatus. 
     After the terminal device is powered on, the processor may read a software program in a storage unit, explain and execute an instruction of the software program, and process data of the software program. When data needs to be sent in a wireless manner, after performing baseband processing on to-be-sent data, the processor outputs a baseband signal to the radio frequency circuit. After performing radio frequency processing on the baseband signal, the radio frequency circuit sends a radio frequency signal through an antenna in a form of an electromagnetic wave. When data is sent to the terminal device, the radio frequency circuit receives the radio frequency signal through the antenna, converts the radio frequency signal into a baseband signal, and outputs the baseband signal to the processor. The processor converts the baseband signal into data and processes the data. 
     A person skilled in the art may understand that, for ease of description,  FIG. 13  shows only one memory and one processor. In an actual terminal device, there may be a plurality of processors and a plurality of memories. The memory may also be referred to as a storage medium, a storage device, or the like. This is not limited in embodiments of this application. 
     In an optional implementation, the processor may include a baseband processor and a central processing unit (central processing unit, CPU). The baseband processor is mainly configured to process a communication protocol and communication data. The CPU is mainly configured to: control the entire terminal device, execute a software program, and process data of the software program. Optionally, the processor may alternatively be a network processor (network processor, NP) or a combination of a CPU and an NP. The processor may further include a hardware chip. The hardware chip may be an application-specific integrated circuit (application-specific integrated circuit, ASIC), a programmable logic device (programmable logic device, PLD), or a combination thereof. The PLD may be a complex programmable logic device (complex programmable logic device, CPLD), a field-programmable gate array (field-programmable gate array, FPGA), generic array logic (generic array logic, GAL), or any combination thereof. A memory may include a volatile memory or a non-volatile memory, or may include both a volatile memory and a non-volatile memory. The non-volatile memory may be a read-only memory (read-only memory, ROM), a programmable read-only memory (programmable ROM, PROM), an erasable programmable read-only memory (erasable PROM, EPROM), an electrically erasable programmable read-only memory (electrically EPROM, EEPROM), or a flash memory. The volatile memory may be a random access memory (random access memory, RAM) that is used as an external cache. Through example but not limitative description, many forms of RAMs may be used, for example, a static random access memory (static RAM, SRAM), a dynamic random access memory (dynamic RAM, DRAM), a synchronous dynamic random access memory (synchronous DRAM, SDRAM), a double data rate synchronous dynamic random access memory (double data rate SDRAM, DDR SDRAM), an enhanced synchronous dynamic random access memory (enhanced SDRAM, ESDRAM), a synchlink dynamic random access memory (synchlink DRAM, SLDRAM), and a direct rambus random access memory (direct rambus RAM, DR RAM). 
     For example, in this embodiment of this application, the antenna and the radio frequency circuit that have receiving and sending functions may be considered as a transceiver unit  1301  in the terminal device  1300 , and the processor having a processing function may be considered as a processing unit  1302  in the terminal device  1300 . 
     As shown in  FIG. 13 , the terminal device  1300  may include the transceiver unit  1301  and the processing unit  1302 . The transceiver unit may also be referred to as a transceiver, a transceiver machine, a transceiver apparatus, or the like. Optionally, a component that is in the transceiver unit  1301  and that is configured to implement a receiving function may be considered as a receiving unit, and a component that is in the transceiver unit  1301  and that is configured to implement a sending function may be considered as a sending unit. In other words, the transceiver unit  1301  includes the receiving unit and the sending unit. For example, the receiving unit may also be referred to as a receiver machine, a receiver, a receiver circuit, or the like, and the sending unit may be referred to as a transmitter machine, a transmitter, a transmitter circuit, or the like. 
     In some embodiments, the transceiver unit  1301  and the processing unit  1302  may be integrated into one component, or may be separated into different components. In addition, the processor and the memory may be integrated into one component, or may be separated into different components. 
     It may be understood that the transceiver unit  1301  may be configured to perform sending and receiving operations of the terminal device  1  in the foregoing method embodiments, and the processing unit  1302  is configured to perform another operation, other than the sending and receiving operations, of the terminal device  1  in the foregoing method embodiments. 
     For example, the transceiver unit  1301  may be configured to perform the sending and receiving operations in  602 ,  604 , and  606  in  FIG. 6 , and the processing unit  1302  may be configured to perform the operations in  601 ,  603 , and  604  in  FIG. 6 , and may further be configured to perform operations in  1001  and  1002  in  FIG. 10   a.    
     It may be understood that for an implementation of the terminal device in this embodiment of this application, refer to the foregoing embodiments. Details are not described herein again. 
     For the terminal device in this embodiment of this application, refer to a device shown in  FIG. 14 . In  FIG. 14 , the terminal device includes a processor  1410 , a data sending processor  1420 , and a data receiving processor  1430 . The processing unit  1103  in the foregoing embodiment may be the processor  1410  in  FIG. 14 , and implements a corresponding function. For another example, the sending unit  1101  in the foregoing embodiment may be the data sending processor  1420  in  FIG. 14 , and the receiving unit  1102  may be the data receiving processor  1430  in  FIG. 14 . Although  FIG. 14  shows a channel encoder and a channel decoder, it may be understood that the modules are merely examples, and do not constitute a limitation on this embodiment. 
       FIG. 15  shows another form of an embodiment of this application. A processing apparatus  1500  includes modules such as a modulation subsystem, a central processing subsystem, and a peripheral subsystem. The communication apparatus in this embodiment of this application may be used as the modulation subsystem in the processing apparatus. Specifically, the modulation subsystem may include a processor  1503  and an interface  1504 . The processor  1503  completes a function of the processing unit  1103 , and the interface  1504  completes a function of the sending unit  1101  and/or a function of the receiving unit  1102 . In another variation, the modulation subsystem includes a memory  1506 , a processor  1503 , and a program that is stored in the memory  1506  and that can be run on the processor. When executing the program, the processor  1503  implements the method of the terminal device  1  in the foregoing method embodiment. It should be noted that the memory  1506  may be nonvolatile or volatile. The memory  1506  may be located in the modulation subsystem, or may be located in the processing apparatus  1500 , provided that the memory  1506  can be connected to the processor  1503 . 
     An embodiment of this application further provides a computer-readable storage medium, storing instructions. When the instructions are executed, the method of the terminal device  1  in the foregoing method embodiment is performed. 
     An embodiment of this application further provides a computer program product including instructions. When the instructions are executed, the method of the terminal device  1  in the foregoing method embodiment is performed. 
     An embodiment of this application further provides a computer-readable storage medium, storing instructions. When the instructions are executed, the method of the terminal device  2  in the foregoing method embodiment is performed. 
     An embodiment of this application further provides a computer program product including instructions. When the instructions are executed, the method of the terminal device  2  in the foregoing method embodiment is performed. 
     A person of ordinary skill in the art may understand that all or some of the procedures of the methods in the foregoing embodiments may be implemented by a computer program indicating related hardware. The program may be stored in a computer-readable storage medium. When the program is executed, the procedures of the methods in the foregoing embodiments may be performed. The foregoing storage medium includes: any medium that can store program code, such as a ROM or a random access memory (RAM for short), a magnetic disk or an optical disc.