Patent Publication Number: US-2022225353-A1

Title: Sidelink data transmission method and device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is continuation application of PCT International Application No. PCT/CN2020/102992 filed on Jul. 20, 2020, which claims priority to Chinese Patent Application No. 201910691372.6 filed in China on Jul. 29, 2019, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present disclosure relate to the communications field, and in particular, to a sidelink data transmission method and a device. 
     BACKGROUND 
     Long Term Evolution (LTE) sidelink communication is performed based on broadcast. It can be used for basic safety-related communications of vehicle to everything (V2X), but it is not applicable to higher-level V2X services. A New Radio (NR) system supports more advanced designs of sidelink transmission, such as unicast, broadcast or groupcast, and the like, so as to support more comprehensive service types. 
     For a terminal device, a transport block size (TBS) needs to be calculated during a sidelink data transmission process. At present, in an NR system, how to accurately calculate a TBS for sidelink data transmission is a technical problem urgently need to be solved in the related art. 
     SUMMARY 
     According to a first aspect, a sidelink data transmission method is provided, where the method is performed by a terminal device and includes: 
     calculating a TBS based on a size of an allocated resource and a target resource overhead; and 
     transmitting sidelink data based on the calculated TBS. 
     According to a second aspect, a terminal device is provided and includes: 
     a TBS calculation module, configured to calculate a TBS based on a size of an allocated resource and a target resource overhead; 
     a transmission module, configured to transmit sidelink data based on the calculated TBS. 
     According to a third aspect, a terminal device is provided, where the terminal device includes a processor, a memory, and a computer program that is stored in the memory and that can run on the processor, and when the computer program is executed by the processor, steps of the sidelink data transmission method in the first aspect are implemented. 
     According to a fourth aspect, a computer-readable storage medium is provided, where the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, steps of the sidelink data transmission method in the first aspect are implemented. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings illustrated herein are provided to further understand this application and form a part of this application. The exemplary embodiments of this application and the descriptions thereof are used to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings: 
         FIG. 1  is a schematic flowchart of a sidelink data transmission method according to an embodiment of the present disclosure; 
         FIG. 2  is a schematic structural diagram of a terminal device according to an embodiment of the present disclosure; and 
         FIG. 3  is a schematic structural diagram of a terminal device according to another embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     To make the objectives, technical solutions, and advantages of this application clearer, the following clearly describes the technical solutions of this application with reference to the specific embodiments of this application and the corresponding accompanying drawings. Apparently, the described embodiments are merely some rather than all of the embodiments of this application. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of this application shall fall within the protection scope of this application. The term “and/or” in the embodiments of the present disclosure indicates at least one of a former one and a latter one. 
     It should be understood that, the technical solutions in the embodiments of the present disclosure may be applied to various communications systems, such as an LTE sidelink system, an NR sidelink system, or a subsequently evolved sidelink communications system. 
     In the embodiments of the present disclosure, a terminal device may include but is not limited to a mobile station (MS), a mobile terminal, a mobile telephone, user equipment (UE), a handset, portable equipment, a vehicle, and the like. The terminal device may communicate with one or more core networks by using a radio access network (RAN). For example, the terminal device may be a mobile phone (or referred to as a “cellular” phone), or a computer having a wireless communication function; or the terminal device may be a portable, pocket-sized, handheld, computer built-in, or in-vehicle mobile apparatus. 
     As shown in  FIG. 1 , the present disclosure provides a sidelink data transmission method  100 . The method may be performed by a terminal device, and includes steps S 102  and S 104 . 
     S 102 : Calculate a Transport Block Size (TBS) based on a size of an allocated resource and a target resource overhead. 
     Generally, a TBS mainly depends on a size of an allocated resource. Optionally, an allocated resource is composed of one or a plurality of resource blocks (RB). One RB occupies a plurality of symbols in time domain and a plurality of subcarriers in frequency domain. 
     In the embodiments of this specification, the target resource overhead may include at least one of the following: 
     a resource overhead of a physical sidelink control channel (PSCCH); 
     a resource overhead of a physical sidelink feedback channel (PSFCH); 
     a resource overhead of sidelink feedback control information (SFCI), where the SFCI may include at least one of a HARQ ACK/NACK and a channel state information report; 
     a resource overhead of a demodulation reference signal (DMRS); 
     a resource overhead of a phase-tracking reference signal (PTRS); 
     a resource overhead of a channel state information-reference signal (CSI-RS); 
     a resource overhead of automatic gain control (AGC); and 
     a resource overhead of a guard period (GP). 
     Optionally, the target resource overhead may include at least one of the resource overhead of the PSFCH and the resource overhead of the SFCI reused in the PSSCH, where the resource overhead of the SFCI herein includes a resource overhead for transmitting a CSI report, and the resource overhead of the PSFCH herein includes a resource overhead for transmitting a HARQ ACK/NACK. 
     For example, an upper layer configures an available resource for the PSFCH, and the terminal device obtains, based on information configured by the upper layer, a slot(s) for configuring the resource for the PSFCH. In a case that the terminal device has used the slot(s) to transmit the PSSCH, an overhead of the resource configured for the PSFCH is subtracted during calculation of the TBS. 
     It should be noted that, if the PSFCH is not in allocated symbols for the PSSCH, the resource overhead of the PSFCH does not need to be considered during calculation of the TBS. 
     In a specific example, in this step, the foregoing target resource overhead may be subtracted from the allocated resource during calculation of the TBS. 
     For example, during a process of calculating the TBS, a certain value is subtracted based on the size of the allocated resource. The value is related to the foregoing target resource overhead. During the subtraction calculation process, the subtrahend may be the foregoing allocated resource, or may be another value used during the calculation process. 
     For another example, in a process of calculating the TBS, a scale factor is multiplied based on the size of the allocated resource. The scale factor is related to the foregoing target resource overhead and greater than 0 and less than or equal to 1. During the multiplication calculation process, the multiplicand may be the foregoing allocated resource, or may be another value used during the calculation process. 
     S 104 : Transmit sidelink data based on the calculated TBS. 
     In this step, the sidelink data is transmitted based on the calculated TBS. Specifically, the sidelink data may be sent or received during the sidelink data transmission. 
     In this step, for a transmitting terminal device, the sidelink data may be sent by a transceiver based on the calculated TBS; and for a receiving terminal device, the sidelink data may be obtained through demodulation based on the calculated TBS. 
     According to the sidelink data transmission method provided in the present disclosure, a terminal device can calculate a TBS based on a size of an allocated resource and a target resource overhead, and transmitting sidelink data based on the calculated TBS. According to this embodiment of the present disclosure, the target resource overhead in the allocated resource is fully considered during calculation of a TBS, helping improve accuracy of the calculated TBS. 
     For the receiving terminal device, in this embodiment of the present disclosure, a case in which a transmission bit rate of a transmission block exceeds a bit rate allowed during demodulation can be avoided, a success rate of decoding is increased, and communication efficiency is improved. 
     Optionally, the target resource overhead mentioned in the foregoing embodiment may include the resource overhead of the PSCCH. The resource overhead of the PSCCH may be calculated based on configuration of the PSCCH. 
     Certainly, the foregoing target resource overhead may further include the resource overhead of the PSFCH, the resource overhead of the SFCI, or the like. For example, when the target resource overhead includes the resource overhead of the SFCI, during calculation of the TBS in step S 102 , the resource overhead of the SFCI can be determined based on indication of sidelink control information (SCI) and used to calculate the TBS. 
     Optionally, when the foregoing target resource overhead includes the resource overhead of the PSCCH, and before step S 102  is performed, the following steps may be further included: 
     (1) Calculate the resource overhead of the PSCCH based on a resource occupied by the PSCCH during blind detection; or 
     (2) Calculate a total resource overhead of the PSCCH based on a first resource overhead of a first PSCCH and a second resource overhead of a second PSCCH, where the total resource overhead may be specifically a sum of the first resource overhead and the second resource overhead, the first PSCCH may be predefined or may be configured or preconfigured by a network device, and the second PSCCH is indicated by the first PSCCH. 
     Optionally, the first PSCCH may explicitly or implicitly indicate the second PSCCH. 
     For example, the first PSCCH includes indication information, and the indication information indicates whether the second PSCCH is included and information such as a resource size or resource location of the second PSCCH, that is, explicit indication is used. 
     For another example, the first PSCCH may indicate a transmission type (for example, unicast, groupcast, or broadcast). If the transmission type is unicast/groupcast, it indicates that the second PSCCH exists, and the second resource overhead of the second PSCCH is determined based on a preconfigured resource size of the second PSCCH, that is, implicit indication is used. 
     Optionally, in parallel to the foregoing embodiments, when the sidelink data is retransmission sidelink data, a TBS for initial transmission of the sidelink data may be used as a TBS of the retransmission sidelink data, and retransmission of the sidelink data is performed based on the TBS for the initial transmission of the sidelink data. 
     For example, if a TB of the sidelink data meets 28≤I MCS ≤31, a size of the TB (TBS) is determined from the latest SCI for the same TB, where when I MCS  meets 28≤I MCS ≤31, the TBS is used for retransmission of the sidelink data; and when I MCS  meets 0≤I MCS ≤28, the TBS is used for initial transmission of the sidelink data. 
     Optionally, in the plurality of foregoing embodiments, the calculating a TBS based on a size of an allocated resource and a target resource overhead may include at least one of the following: 
     Manner (1): Subtract a first parameter from a quantity of allocated symbols to calculate a quantity of available resource elements (RE) in a physical resource block (PRB), and calculate the TBS based on the quantity of available REs in the PRB, where the allocated resource includes the quantity of allocated symbols. 
     Manner (2): Subtract a second parameter from a quantity of available REs in the allocated resource, and calculate the TBS based on an obtained value, where the quantity of available REs in the allocated resource is calculated based on the size of the allocated resource. In this manner, the quantity of available REs in the allocated resource may be calculated in the foregoing manner (1), or may be calculated in another manner. 
     Manner (3): Multiply a third parameter by the quantity of available REs in the allocated resource, and calculate the TBS based on an obtained value, where the quantity of available REs in the allocated resource is calculated based on the size of the allocated resource. In this manner, the quantity of available REs in the allocated resource may be calculated in the foregoing manner (1), or may be calculated in another manner. 
     Manner (4): Multiply a fourth parameter by a quantity of available PRBs in the allocated resource, and calculate the TBS based on an obtained value. 
     Manner (5): Multiply an information median by a fifth parameter, and calculate the TBS based on an obtained value, where the information median is calculated based on the size of the allocated resource. In this manner, the information median is calculated based on the quantity of available REs in the allocated resource. The quantity of available REs in the allocated resource may be calculated in the foregoing manners (2) and (3), or may be calculated in another manner. 
     The first parameter, the second parameter, the third parameter, the fourth parameter, and the fifth parameter are all related to the target resource overhead mentioned in the foregoing description, and the third parameter, the fourth parameter, and the fifth parameter are all greater than 0 and less than or equal to 1. 
     To describe the sidelink data transmission method provided in the present disclosure in detail, a calculation process of the TBS is described in detail below with reference to several specific embodiments. 
     Embodiment 1 
     1. Calculate a quantity of available REs in each PRB based on the following formula: 
         N′   RE   =N   sc   RB ·( N   symbol   sh   −N   oh_sym )− N   DMRS   PRB   −N   oh   PRB  
 
     where N′ RE  denotes a quantity of available REs in a PRB; N sc   RB  denotes a quantity of subcarriers in a PRB and is generally 12; N symbol   sh  an denotes a quantity of allocated symbols; N oh_sym  denotes a quantity of symbols related to the target resource overhead and corresponds to the first parameter in the foregoing description; N DMRS   PRB  denotes a resource overhead of a DMRS in a PRB; N oh   PRB  is a parameter predefined in a protocol, (pre)configured by a network device, configured by a terminal device, or obtained through negotiation or feedback. 
     (a) In this embodiment, optionally, N oh_sym =1. For example, N oh_sym  denotes a resource overhead of a GP and/or AGC. 
     Alternatively, optionally, a mapping relationship between numerology and N oh_sym  may be predefined as follows: 
     if a carrier frequency is FR1, and SCS=15 kHz, N oh_sym =1; 
     if the carrier frequency is FR1, and SCS=30 kHz, N oh_sym =2; 
     if the carrier frequency is FR1, and SCS=60 kHz, N oh_sym =2; 
     if the carrier frequency is FR2, and SCS=60 kHz, N oh_sym =1; or 
     if the carrier frequency is FR2, and SCS=120 kHz, N oh_sym =2. 
     (b) Optionally, an optional value of N oh   PRB  is 0, 6, 12, or 18. The terminal device may determine the resource overhead based on a transmission type. For example: 
     if the transmission type is broadcast transmission, N oh   PRB  is configured to be 0 by default; 
     if the transmission type is unicast transmission, the transmitting terminal device selects an overhead value of N oh   PRB  based on configuration; or 
     if the transmission type is multicast transmission, N oh   PRB  is configured to be 0 by default. 
     2. Calculate a quantity of available REs in all PRBs in the allocated resource based on the following formula: N RE =min(156,N′ RE )·n PRB . 
     where N RE  denotes the quantity of available REs in all PRBs in the allocated resource, for example, a quantity of available REs in all PRBs in a slot; and n  PRB  denotes a quantity of available PRBs. 
     3. Calculate an information median based on the following formula: N inf o =N RE ·R·Q m ·υ 
     where R denotes a bit rate, Q m  denotes a modulation order, and υ denotes a quantity of layers. 
     When N inf o ≤3824, the TBS is obtained through the following step 4. Otherwise, the TBS is obtained through the following step 5. 
     4. When the information median meets N inf o ≤3824, a quantized median 
     
       
         
           
             
               N 
               
                 inf 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 o 
               
               ′ 
             
             = 
             
               max 
               ⁡ 
               
                 ( 
                 
                   24 
                   , 
                   
                     
                       2 
                       n 
                     
                     · 
                     
                       ⌊ 
                       
                         
                           N 
                           
                             inf 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             o 
                           
                         
                         
                           2 
                           n 
                         
                       
                       ⌋ 
                     
                   
                 
                 ) 
               
             
           
         
       
     
     is obtained, where n=max(3,└log 2 (N inf o )┘−6); and then a last TBS that is not less than the quantized median N′ inf o  is found in the following Table 1. 
       5 . When the information median meets N inf o &gt;3824, the quantized median meets 
     
       
         
           
             
               
                 N 
                 
                   inf 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   o 
                 
                 ′ 
               
               = 
               
                 max 
                 ⁡ 
                 
                   ( 
                   
                     3840 
                     , 
                     
                       
                         2 
                         n 
                       
                       × 
                       
                         round 
                         ⁡ 
                         
                           ( 
                           
                             
                               
                                 N 
                                 
                                   inf 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   o 
                                 
                               
                               - 
                               24 
                             
                             
                               2 
                               n 
                             
                           
                           ) 
                         
                       
                     
                   
                   ) 
                 
               
             
             , 
           
         
       
     
     where n=└log 2 (N inf o −24)┘−5; and then the TBS is determined based on the quantized median N′ inf o . 
     In this embodiment, optionally, if the transmission type is unicast sidelink transmission, the transmitting terminal device may send SCI or sidelink radio resource control (SL-RRC), to indicate an overhead of N oh   PRB  to the receiving terminal device. 
     Optionally, the receiving terminal device determines the overhead of N oh   PRB  based on the transmission type, and calculates the TBS. Specifically, for example: 
     if the transmission type is broadcast transmission, N oh   PRB  is configured to be 0 by default; 
     if the transmission type is unicast transmission, the transmitting terminal device selects an overhead value based on configuration, and sends SCI/SL-RRC to indicate the overhead of N oh   PRB ; or 
     if the transmission type is multicast transmission, N oh   PRB  is configured to be 0 by default. 
     In Embodiment 1, during calculation of the TBS, N oh_sym  is subtracted from a quantity of allocated symbols to calculate a quantity of available REs in a PRB, and the TBS is subsequently calculated based on the obtained quantity of available REs. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 TBSs obtained when an information median meets N inf o  ≤ 3824 
               
            
           
           
               
               
               
            
               
                   
                 Index 
                 TBS 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 1 
                 24 
               
               
                   
                 2 
                 32 
               
               
                   
                 3 
                 40 
               
               
                   
                 4 
                 48 
               
               
                   
                 5 
                 56 
               
               
                   
                 6 
                 64 
               
               
                   
                 7 
                 72 
               
               
                   
                 8 
                 80 
               
               
                   
                 9 
                 88 
               
               
                   
                 10 
                 96 
               
               
                   
                 11 
                 104 
               
               
                   
                 12 
                 112 
               
               
                   
                 13 
                 120 
               
               
                   
                 14 
                 128 
               
               
                   
                 15 
                 136 
               
               
                   
                 16 
                 144 
               
               
                   
                 17 
                 152 
               
               
                   
                 18 
                 160 
               
               
                   
                 19 
                 168 
               
               
                   
                 20 
                 176 
               
               
                   
                 21 
                 184 
               
               
                   
                 22 
                 192 
               
               
                   
                 23 
                 208 
               
               
                   
                 24 
                 224 
               
               
                   
                 25 
                 240 
               
               
                   
                 25 
                 256 
               
               
                   
                 27 
                 272 
               
               
                   
                 2S 
                 288 
               
               
                   
                 29 
                 304 
               
               
                   
                 30 
                 320 
               
               
                   
                 31 
                 336 
               
               
                   
                 32 
                 352 
               
               
                   
                 33 
                 368 
               
               
                   
                 34 
                 384 
               
               
                   
                 35 
                 408 
               
               
                   
                 36 
                 432 
               
               
                   
                 37 
                 456 
               
               
                   
                 38 
                 480 
               
               
                   
                 39 
                 504 
               
               
                   
                 40 
                 528 
               
               
                   
                 41 
                 552 
               
               
                   
                 42 
                 576 
               
               
                   
                 43 
                 608 
               
               
                   
                 44 
                 640 
               
               
                   
                 45 
                 672 
               
               
                   
                 46 
                 704 
               
               
                   
                 47 
                 736 
               
               
                   
                 48 
                 768 
               
               
                   
                 49 
                 808 
               
               
                   
                 50 
                 848 
               
               
                   
                 51 
                 888 
               
               
                   
                 52 
                 928 
               
               
                   
                 53 
                 984 
               
               
                   
                 54 
                 1032 
               
               
                   
                 55 
                 1064 
               
               
                   
                 56 
                 1128 
               
               
                   
                 57 
                 1160 
               
               
                   
                 5S 
                 1192 
               
               
                   
                 59 
                 1224 
               
               
                   
                 60 
                 1256 
               
               
                   
                 61 
                 1288 
               
               
                   
                 62 
                 1320 
               
               
                   
                 63 
                 1352 
               
               
                   
                 64 
                 1416 
               
               
                   
                 65 
                 1480 
               
               
                   
                 66 
                 1544 
               
               
                   
                 67 
                 1608 
               
               
                   
                 68 
                 1672 
               
               
                   
                 69 
                 1736 
               
               
                   
                 70 
                 1800 
               
               
                   
                 71 
                 1864 
               
               
                   
                 72 
                 1928 
               
               
                   
                 73 
                 2024 
               
               
                   
                 74 
                 2088 
               
               
                   
                 75 
                 2152 
               
               
                   
                 76 
                 2216 
               
               
                   
                 77 
                 2280 
               
               
                   
                 78 
                 2408 
               
               
                   
                 79 
                 2472 
               
               
                   
                 80 
                 2536 
               
               
                   
                 81 
                 2600 
               
               
                   
                 82 
                 2664 
               
               
                   
                 83 
                 2728 
               
               
                   
                 84 
                 2792 
               
               
                   
                 85 
                 2856 
               
               
                   
                 86 
                 2976 
               
               
                   
                 87 
                 3104 
               
               
                   
                 88 
                 3240 
               
               
                   
                 89 
                 3368 
               
               
                   
                 90 
                 3496 
               
               
                   
                 91 
                 3624 
               
               
                   
                 92 
                 3752 
               
               
                   
                 93 
                 3824 
               
               
                   
                   
               
            
           
         
       
     
     Specifically, in step 2 to step 5 in Embodiment 1, a TBS calculation process for the Uu interface, for example, a TBS calculation process for the PUSCH, may be used. 
     Optionally, in Embodiment 1, N oh_sym  is related to at least one of feedback information configuration, PSCCH configuration, AGC configuration, PTRS configuration, CSI-RS configuration, a carrier frequency, numerology configuration, CSI configuration, and a transmission type. Alternatively, N oh_sym  is a value predefined in a protocol, (pre)configured by a network device or terminal device, obtained through negotiation by the terminal device, or fed back by the receiving terminal device to the transmitting terminal device. 
     Specifically, for example, in step 1 in Embodiment 1, a quantity of symbols for a GP may be subtracted from a quantity of allocated symbols for a PSSCH. The quantity of symbols for the GP may be one symbol or half a symbol. Optionally, a mapping relationship between numerology and a GP and/or AGC is defined as follows: 
     if a carrier frequency is FR1, and SCS=15 kHz, a resource overhead of the AGC is half a symbol, and an overhead of the GP is half a symbol; 
     if the carrier frequency is FR1, and SCS=30 kHz, the resource overhead of the AGC is one symbol, and the resource overhead of the GP is half a symbol; 
     if the carrier frequency is FR1, and SCS=60 kHz, the resource overhead of the AGC is one symbol, and the overhead of the GP is one symbol; 
     if the carrier frequency is FR2, and SCS=60 kHz, the resource overhead of the AGC is one symbol, and the overhead of the GP is half a symbol; or 
     if the carrier frequency is FR2, and SCS=120 kHz, the resource overhead of the AGC is one symbol, and the overhead of the GP is one symbol. 
     For another example, in step 1 in Embodiment 1, a quantity of symbols for the AGC may be subtracted from a quantity of allocated symbols for the PSSCH. The quantity of symbols for the AGC may be one symbol, half a symbol, or two symbols. For another example, based on configuration of the PSFCH, in a case that a resource for the PSFCH is configured in the allocated resource, in step 1 in Embodiment 1, a quantity of symbols for the PSFCH may be subtracted from the quantity of allocated symbols for the PSSCH. 
     For still another example, in step 1 in Embodiment 1, a certain symbol overhead may be subtracted from a quantity of symbols allocated for the PSSCH, and the symbol overhead is half a symbol or one symbol, and is used to indicate that a symbol overhead of at least one of the CSI-RS, PTRS, SFCI, CSI, and PSCCH is subtracted. The symbol overhead may be (pre)configured by a network device or configured by a terminal device. 
     It should be noted that, the foregoing description uses only one resource overhead as examples. Actually, N oh_sym  may be a sum of a plurality of resource (symbol) overheads, for example, N oh_sym  is a sum of symbol overheads of the AGC, the GP, and the like. 
     Embodiment 2 
     1. Calculate a quantity of available REs in each PRB based on the following formula: 
         N′   RE   =N   sc   RB ·( N   symbol   sh   −N   oh_sym )− N   DMRS   PRB   −N   oh   PRB  
 
     where N′ RE  denotes a quantity of available REs in a PRB; N sc   RB  denotes a quantity of subcarriers in a PRB and is generally 12; N symbol   sh  denotes a quantity of allocated symbols and may be specifically a quantity of allocated symbols in a slot for the PSSCH; N oh_sym  denotes a quantity of symbols related to the target resource overhead and corresponds to the first parameter in the foregoing description; N DMRS   PRB  denotes a resource overhead of a DMRS in a PRB; N oh   PRB  may be a parameter predefined in a protocol, (pre)configured by a network device, configured by a terminal device, or obtained through negotiation or feedback. 
     (a) In this embodiment, optionally, N oh_sym =1. For example, N oh_sym  denotes a symbol overhead of a GP and/or AGC. 
     Alternatively, optionally, a mapping relationship between numerology and a GP and/or AGC may be predefined as follows: 
     if a carrier frequency is FR1, and SCS=15 kHz, a resource overhead of the AGC is half a symbol, and an overhead of the GP is half a symbol; 
     if the carrier frequency is FR1, and SCS=30 kHz, the resource overhead of the AGC is one symbol, and the resource overhead of the GP is half a symbol; 
     if the carrier frequency is FR1, and SCS=60 kHz, the resource overhead of the AGC is one symbol, and the overhead of the GP is one symbol; 
     if the carrier frequency is FR2, and SCS=60 kHz, the resource overhead of the AGC is one symbol, and the overhead of the GP is half a symbol; or 
     if the carrier frequency is FR2, and SCS=120 kHz, the resource overhead of the AGC is one symbol, and the overhead of the GP is one symbol. 
     (b) In this embodiment, optionally, an optional value of N oh   PRB  is 0, 6, 12, or 18. The transmitting terminal device selects an overhead value of N oh   PRB  based on configuration. 
     2. Calculate a quantity of available REs in all PRBs in the allocated resource based on the following formula: N RE =min(156,N′ RE )·n PRB , where N RE  denotes the quantity of available REs in all PRBs, and n PRB  denotes a quantity of available PRBs. 
     3. This step is the same as steps 3, 4, and 5 in Embodiment 1. Specifically, in step 2 and subsequent steps in Embodiment 2, a TBS calculation process for the Uu interface, for example, a TBS calculation process for the PUSCH, may be used. 
     In Embodiment 2, optionally, the transmitting terminal device may send SCI/SL-RRC to indicate a value of N oh   PRB . In this way, the receiving terminal device obtains the value of N oh   PRB  to calculate the TBS. 
     According to Embodiment 2, during calculation of the TBS, N oh_sym  is subtracted from a quantity of allocated symbols to calculate a quantity of available symbols in a PRB; then a quantity of available REs is calculated based on the obtained quantity of available symbols and a frequency domain resource; and subsequently, the TBS is calculated based on the obtained quantity of available REs. 
     Embodiment 3 
     1. The receiving terminal device feeds back resource overheads of AGC and the like. For example, the resource overhead of the AGC is one symbol. 
     2. The transmitting terminal device determines N oh_sym =1 based on received feedback information and configuration information. 
     3. Calculate a quantity of available REs in each PRB based on the following formula: 
         N′   RE   =N   sc   RB ·( N   symbol   sh   −N   oh_sym )− N   DMRS   PRB   −N   oh   PRB  
 
     For meanings of the parameters in the formula, refer to step 1 in Embodiment 1. A difference lies in that, in this embodiment, N oh_sym  may be used to indicate resource overheads of at least one of the AGC, PSCCH, SFCI, DMRS, PTRS, CSI-RS, and GP. For example, N oh_sym  denotes the overheads of the GP and/or the AGC. In this embodiment, N oh_sym =1. 
     In this embodiment, an optional value of N oh   PRB  is 0, 6, 12, or 18. The transmitting terminal device selects an overhead value of N oh   PRB  based on configuration. 
     4. Calculate a quantity of available REs in all PRBs in the allocated resource based on the following formula: N RE =min(156,N′ RE )·n PRB . 
     For meanings of the parameters in the formula, refer to step 2 in Embodiment 1. 
     5. This step is the same as steps 3, 4, and 5 in Embodiment 1. Specifically, in step 4 and subsequent steps in this embodiment, a TBS calculation process for the Uu interface, for example, a TBS calculation process for the PUSCH, may be used. 
     According to Embodiment 3, during calculation of a TBS, N oh_sym  is subtracted from a quantity of allocated symbols to calculate a quantity of available REs in a PRB, and the TBS is subsequently calculated based on the obtained quantity of available REs. 
     In Embodiment 3, N oh_sym  is obtained based on feedback from the receiving terminal device. 
     Embodiment 4 
     1. Calculate a quantity of available REs in each PRB based on the following formula: 
         N′   RE   =N   sc   RB ·( N   symbol   sh   −N   oh_sym )− N   DMRS   PRB   −N   oh   PRB  
 
     For meanings of the parameters in the formula, refer to step 1 in Embodiment 1. 
     In this embodiment, optionally, N oh_sym =2. N oh_sym  may be used to indicate resource overheads of at least one of the AGC, PSCCH, SFCI, DMRS, PTRS, CSI-RS, and GP. Specifically, N oh_sym  in this embodiment is used to indicate the resource overhead of the GP and/or AGC and the resource overhead of the PSFCH. 
     Optionally, N oh_sym  may alternatively be determined based on configuration of the PSFCH. A relationship between a configuration relationship and N oh_sym  is predefined. For example, in a case that a resource for the PSFCH is configured in the allocated resource, N oh_sym =2; Otherwise, N oh_sym =1. 
     2. Calculate a quantity of available REs in all PRBs in the allocated resource based on the following formula: N RE =min(156,N′ RE )·n PRB . 
     For meanings of the parameters in the formula, refer to step 2 in Embodiment 1. 
     3. This step is the same as steps 3, 4, and 5 in Embodiment 1. Specifically, in step 2 and subsequent steps in this embodiment, a TBS calculation process for the Uu interface, for example, a TBS calculation process for the PUSCH, may be used. 
     Optionally, in this embodiment, if the PSFCH is not included in allocated symbols for the PSSCH, the overhead of the PSFCH does not need to be considered when N oh_sym  is determined. 
     Embodiment 5 
     1. Calculate a quantity of available REs in each PRB based on the following formula: 
     
       
      
       N′ 
       RE 
       =N 
       sc 
       RB 
       ·N 
       symbol 
       sh 
       −N 
       DMRS 
       PRB 
       −N 
       oh 
       PRB 
       −N  
      
     
     where N′ RE  denotes a quantity of available REs in a PRB; N sc   RB  denotes a quantity of subcarriers in a PRB and is generally 12; N symbol   sh  denotes a quantity of allocated symbols and may be specifically a quantity of allocated symbols for the PSSCH; N DMRS   PRB  denotes a resource overhead of a DMRS in a PRB; N oh   PRB  is a parameter predefined in a protocol, (pre)configured by a network device, configured by a terminal device, or obtained through negotiation or feedback; and N is a parameter related to the target resource overhead. 
     In this embodiment, optionally, N=12. For example, N denotes resource overheads of a GP and/or AGC. Alternatively, optionally, a mapping relationship between numerology and N may be predefined as follows: 
     if a carrier frequency is FR1, and SCS=15 kHz, N=12; 
     if the carrier frequency is FR1, and SCS=30 kHz, N=24; 
     if the carrier frequency is FR1, and SCS=60 kHz, N=24; 
     If the carrier frequency is FR2, and SCS=60 kHz, N=12; or 
     if the carrier frequency is FR2, and SCS=120 kHz, N=24. 
     2. Calculate a quantity of available REs in all PRBs in the allocated resource based on the following formula: N RE =min(156,N′ RE )·n PRB    
     For meanings of the parameters in the formula, refer to step 2 in Embodiment 1. 
     3. This step is the same as steps 3, 4, and 5 in Embodiment 1. Specifically, in step 2 and subsequent steps in this embodiment, a TBS calculation process for the Uu interface, for example, a TBS calculation process for the PUSCH, may be used. 
     In Embodiment 5, during calculation of a TBS, N is subtracted from a quantity of available REs in a PRB, and the TBS is subsequently calculated based on an obtained value. 
     Optionally, in Embodiment 5, N is related to at least one of feedback information configuration, PSCCH configuration, AGC configuration, PTRS configuration, CSI-RS configuration, a carrier frequency, numerology configuration, CSI configuration, and a transmission type. Alternatively, N is a value predefined in a protocol, configured by a network device or terminal device, obtained through negotiation by the terminal device, or fed back by the receiving terminal device to the transmitting terminal device. 
     For example, the network device preconfigures a mapping relationship between numerology and N or between N and a quantity of symbols for the AGC; and the terminal device obtains N based on the configured numerology or the configured quantity of symbols for the AGC, so as to calculate the quantity of available REs in each PRB. 
     Embodiment 6 
     1. Calculate a quantity of available REs in each PRB based on the following formula: 
     
       
      
       N′ 
       RE 
       =N 
       sc 
       RB 
       ·N 
       symbol 
       sh 
       −N 
       DMRS 
       PRB 
       −N 
       oh 
       PRB 
       −N  
      
     
     For meanings of the parameters in the formula, refer to step 1 in Embodiment 5. Certainly, the parameter N in Embodiment 5 is not included in the formula. 
     Optionally, N oh   PRB  in the formula includes an overhead of SCI. The overhead of the SCI may include overheads of SCI in two stages. The 1 st -stage SCI is carried in the PSCCH, and the 2 nd -stage SCI is carried in the PSSCH. 
     2. Calculate a quantity of available REs in all PRBs in the allocated resource based on the following formula: N RE =min(156,N′ RE )·n PRB −M 
     where N RE  denotes the quantity of available REs in all PRBs; n PRB  denotes a quantity of available PRBs, for example, a quantity of available PRBs in the allocated resource; and M is a parameter related to the target resource overhead. 
     Optionally, M=144. M is a value predefined in a protocol. 
     Optionally, M is calculated based on a resource configured for the SCI. 
     Optionally, M is obtained through negotiation by the terminal device. 
     Optionally, M is fed back by the receiving terminal device to the transmitting terminal device. 
     3. This step is the same as steps 3, 4, and 5 in Embodiment 1. Specifically, in step 3 and subsequent steps in this embodiment, a TBS calculation process for the Uu interface, for example, a TBS calculation process for the PUSCH, may be used. 
     According to Embodiment 6, during calculation of a TBS, considering that each PSSCH may include only one PSCCH (target resource overhead), M is subtracted from a quantity of available REs in all PRBs, and the TBS is subsequently calculated based on the obtained quantity of available REs. 
     Optionally, in Embodiment 6, M is related to at least one of feedback information configuration, PSCCH configuration, AGC configuration, PTRS configuration, CSI-RS configuration, a carrier frequency, numerology configuration, CSI configuration, and a transmission type. Alternatively, M is a value predefined in a protocol, configured by a network device or terminal device, obtained through negotiation by the terminal device, or fed back by the receiving terminal device to the transmitting terminal device. 
     For example, the network device preconfigures a mapping relationship between numerology and M or between M and a quantity of symbols for the AGC; and the terminal device obtains M based on the configured numerology or the configured quantity of symbols for the AGC, so as to calculate the quantity of available REs in all PRBs. 
     Embodiment 7 
     1. Calculate a quantity of available REs in each PRB based on the following formula: 
         N′   RE =( N   sc   RB   ·N   symbol   sh   −N   DMRS   PRB   −N   oh   PRB )*alpha_1 
     where N sc   RB  denotes a quantity of subcarriers in a PRB, N symbol   sh  denotes a size of the allocated resource, N DMRS   PRB  denotes a resource overhead of a DMRS in a PRB, N oh   PRB  is a parameter predefined in a protocol, (pre)configured by a network device, configured by a terminal device, obtained based on negotiation by the terminal device, or fed back by the receiving terminal device to the transmitting terminal device, alpha_1 is a parameter related to the target resource overhead, and 0&lt;alpha_1≤1. 
     2. Refer to steps 2, 3, 4, and 5 in Embodiment 1. Specifically, in step 2 and subsequent steps in this embodiment, a TBS calculation process for the Uu interface, for example, a TBS calculation process for the PUSCH, may be used. 
     According to Embodiment 7, during calculation of a TBS, a scale factor (corresponding to the third parameter in the foregoing description) is multiplied by a quantity of available REs in each PRB, and the TBS is subsequently calculated based on the obtained quantity of available REs. 
     Embodiment 8 
     1. Calculate a quantity of available REs in each PRB based on the following formula: 
     
       
      
       N′ 
       RE 
       =N 
       sc 
       RB 
       ·N 
       symbol 
       sh 
       −N 
       DMRS 
       PRB 
       −N 
       oh 
       PRB  
      
     
     where N′ RE  denotes a quantity of available REs in a PRB; N sc   RB  denotes a quantity of subcarriers in a PRB and is generally 12; N symbol   sh  denotes a quantity of allocated symbols and may be specifically a quantity of allocated symbols for the PSSCH; −N DMRS   PRB  denotes a resource overhead of a DMRS in a PRB; N oh   PRB  is a parameter predefined in a protocol, (pre)configured by a network device, configured by a terminal device, obtained through negotiation by the terminal device, or fed back by the receiving terminal device to the transmitting terminal device. 
     2. Calculate a quantity of available REs in all PRBs in the allocated resource based on the following formula: 
         N   RE =min(156, N′   RE )· n   PRB ·alpha_2
 
     where n PRB  denotes a quantity of allocated PRBs, alpha_2 is a parameter related to the target resource overhead, and 0&lt;alpha_2≤1. 
     3. This step is the same as steps 3, 4, and 5 in Embodiment 1. Specifically, in step 3 and subsequent steps in this embodiment, a TBS calculation process for the Uu interface, for example, a TBS calculation process for the PUSCH, may be used. 
     According to Embodiment 8, during calculation of a TBS, a scale factor (corresponding to the fourth parameter in the foregoing description) is multiplied by a quantity of available REs in all PRBs in the allocated resource, that is, the fourth parameter is multiplied by a quantity of allocated PRBs, and the TBS is subsequently calculated based on an obtained value. 
     Embodiment 9 
     1. Calculate a quantity of available REs in each PRB based on the following formula: 
     
       
      
       N′ 
       RE 
       =N 
       sc 
       RB 
       ·N 
       symbol 
       sh 
       −N 
       DMRS 
       PRB 
       −N 
       oh 
       PRB  
      
     
     For meanings of the parameters in the formula, refer to step 1 in Embodiment 8. 
     2. Calculate a quantity of available REs in all PRBs in the allocated resource based on the following formula: N RE =min(156,N′ RE )·n PRB    
     where N RE  denotes a quantity of available REs in all PRBs, and n PRB  denotes a quantity of available PRBs. 
     3. Calculate an information median based on the following formula: N info =N RE ·R·Q m ·ν·alpha_3 
     where R denotes a bit rate, Q m  denotes a modulation order, υ denotes a quantity of layers, alpha_3 is a parameter related to the target resource overhead, and 0&lt;alpha_3≤1. 
     4. Refer to steps 4 and 5 in Embodiment 1. In steps 1 and 2 as well as step 4 and subsequent steps in this embodiment, a TBS calculation process for the Uu interface, for example, a TBS calculation process for the PUSCH, may be used. 
     According to Embodiment 9, during calculation of a TBS, a scale factor (corresponding to the fifth parameter in the foregoing description) is multiplied by an information median, and the TBS is subsequently calculated based on an obtained value. 
     Embodiment 10 
     1. Calculate a quantity of available REs in each PRB based on the following formula: 
     
       
      
       N′ 
       RE 
       =N 
       sc 
       RB 
       ·N 
       symbol 
       sh 
       −N 
       DMRS 
       PRB 
       −N 
       oh 
       PRB  
      
     
     where N′ RE  denotes a quantity of available REs in a PRB; N sc   RB  denotes a quantity of subcarriers in a PRB and is generally 12; N symbol   sh  denotes a quantity of allocated symbols and may be specifically a quantity of allocated symbols for the PSSCH; N DMRS   PRB  denotes a resource overhead of a DMRS in a PRB; and N oh   PRB  is a parameter related to the target resource overhead, and the target resource overhead may be resource overheads of at least one of the AGC, PSCCH, SFCI, DMRS, PTRS, CSI-RS, and GP. 
     2. Refer to steps 2, 3, 4, and 5 in Embodiment 1. Specifically, in step 2 and subsequent steps in this embodiment, a TBS calculation process for the Uu interface, for example, a TBS calculation process for the PUSCH, may be used. 
     In Embodiment 10, during calculation of a TBS, N oh   PRB  (corresponding to the first parameter in the foregoing description) is subtracted from a quantity of available REs in each PRB, and the TBS is subsequently calculated based on the obtained quantity of available REs. 
     Optionally, N oh   PRB  is related to at least one of feedback information configuration, PSCCH configuration, AGC configuration, PTRS configuration, CSI-RS configuration, a carrier frequency, numerology configuration, CSI configuration, and a transmission type. Alternatively, N oh   PRB  is a value predefined in a protocol, configured by a network device or terminal device, obtained through negotiation by the terminal device, or fed back by the receiving terminal device to the transmitting terminal device. 
     For example, an optional value of N oh   PRB  is 12, 18, 24, or 30. Herein, rate matching for the GP is at least considered. 
     For another example, a relationship between feedback information and N oh   PRB  is predefined. If no feedback resource is configured, N oh   PRB  is N1; or if a feedback resource is configured, N oh   PRB  is N2. In this implementation, a value of N oh   PRB  may be obtained based on configuration of a feedback resource, so as to obtain a quantity of available REs. 
     It should be noted that, the TBS calculation methods described in Embodiment 1 to Embodiment 10 may be combined for use. For example, step 2 in Embodiment 1 may be replaced with step 2 in Embodiment 8. For another example, step 3 in Embodiment 1 may be replaced with step 3 in Embodiment 9. For still another example, referring to Embodiment 5, N may be further subtracted in the formula in step 1 in Embodiment 1. For still yet another example, referring to Embodiment 6, M may be further subtracted in the formula in step 2 in Embodiment 1. 
     It should also be noted that, in Embodiment 1 to Embodiment 10, parameters related to the target resource overhead, for example, N oh_sym  in Embodiment 1 to Embodiment 4, N in Embodiment 5, M in Embodiment 6, alpha_1 in Embodiment 7, alpha_2 in Embodiment 8, alpha_3 in Embodiment 9, and N oh   PRB  in Embodiment 10 may all be obtained in at least one of the following manners: 
     (1) predefined in a protocol; 
     (2) preconfigured by a network device; 
     (3) configured by a network device; 
     (4) configured based on a transmission type (for example, broadcast, groupcast, or unicast), where the transmission type may be indicated in SCI/DCI, or may be obtained based on a destination ID (for example, there is a mapping relationship between a destination ID and a transmission type). 
     (5) indicated by SCI or downlink control information (Downlink Control Information, DCI); 
     (6) negotiated through radio resource control RRC configuration between terminal devices; and 
     (7) obtained based on feedback information. 
     For example, the foregoing parameter (parameter related to the target resource overhead) is related to the transmission type. The terminal device may predefine or preconfigure a value of the parameter based on different transmission types and protocols; or there are different configuration methods for different transmission types: 
     if the transmission type is broadcast transmission, the target resource overhead is a predefined/preconfigured value; 
     if the transmission type is unicast transmission, the target resource overhead is a configurable value; 
     if the transmission type is groupcast transmission, the overhead of the AGC may be a default value or is configurable. 
     For another example, the foregoing parameter (parameter related to the target resource overhead) may be indicated in SCI, and/or may be obtained through negotiation based on RRC configuration of the terminal device or through feedback. Specifically, for example: 
     The transmitting terminal device sends indication information indicating whether a corresponding target resource overhead is to be subtracted and a size of the target resource overhead during calculation of a sidelink TBS. 
     An overhead set is configured through SL-RRC. It is indicated in SCI that the target resource overhead is a value in the set. 
     When the parameter is obtained based on feedback information, an indication of the target resource overhead is carried in the feedback information to indicate whether a corresponding target resource overhead is included and/or a size of the target resource overhead. 
     Optionally, during calculation of a TBS, at least one resource overheads of the PSCCH, DMRS, AGC, GP, SFCI (PSFCH, CSI), PTRS, and CSI-RS, namely the target resource overhead, may alternatively be obtained in at least one of the foregoing (seven) manners. 
     The sidelink data transmission method provided in the present disclosure is described in detail above with reference to  FIG. 1  and subsequent specific embodiments. The terminal device provided in the present disclosure is described in detail below with reference to  FIG. 2 . 
       FIG. 2  is a schematic structural diagram of a terminal device according to an embodiment of the present disclosure. As shown in  FIG. 2 , the terminal device  200  includes: 
     a TBS calculation module  202 , may be configured to calculate a TBS based on a size of an allocated resource and a target resource overhead; and 
     a transmission module  204 , may be configured to transmit sidelink data based on the calculated TBS. 
     The terminal device provided in the embodiments of this specification may be a terminal device that sends sidelink data, or may be a terminal device that receives sidelink data. Certainly, the two terminal devices may be one terminal device because one terminal device may perform both a step of sending sidelink data and a step of receiving sidelink data. 
     According to the terminal device provided in the embodiments of this specification, a TBS is calculated based on a size of an allocated resource and a target resource overhead; and sidelink data is transmitted based on the calculated TBS. According to this embodiment of the present disclosure, the target resource overhead in the allocated resource is fully considered during calculation of a TBS, helping improve accuracy of the calculated TBS. 
     For the receiving terminal device, in this embodiment of the present disclosure, a case in which a transmission bit rate of a transmission block exceeds a bit rate allowed during demodulation can be avoided, a success rate of decoding is increased, and communication efficiency is improved. 
     Optionally, as an embodiment, the target resource overhead includes at least one of the following: a resource overhead of a PSCCH; 
     a resource overhead of a PSFCH; 
     a resource overhead of SFCI; 
     a resource overhead of a DMRS; 
     a resource overhead of a PTRS; 
     a resource overhead of a CSI-RS; 
     a resource overhead of AGC; and 
     a resource overhead of a GP. 
     Optionally, as an embodiment, the TBS calculation module  202  may be configured to perform at least one of the following: 
     subtracting a first parameter from a quantity of allocated symbols to calculate a quantity of available REs, and calculating the TBS based on an obtained value; 
     subtracting a second parameter from a quantity of available REs in the allocated resource, and calculating the TBS based on an obtained value, where the quantity of available REs in the allocated resource is calculated based on the size of the allocated resource; multiplying a third parameter by the quantity of available REs in the allocated resource, and calculating the TBS based on an obtained value, where the quantity of available REs in the allocated resource is calculated based on the size of the allocated resource; multiplying a fourth parameter by a quantity of available physical resource blocks PRBs in the allocated resource, and calculating the TBS based on an obtained value; and 
     multiplying an information median by a fifth parameter, and calculating the TBS based on an obtained value, where the information median is calculated based on the size of the allocated resource, where 
     the first parameter, the second parameter, the third parameter, the fourth parameter, and the fifth parameter are related to the target resource overhead, and the third parameter, the fourth parameter, and the fifth parameter are all greater than 0 and less than or equal to 1. 
     Optionally, as an embodiment, the TBS calculation module  202  may be configured to calculate a quantity N′ RE  of available REs in a PRB on an allocated symbol based on the following formula, and calculate the TBS based on N′ RE : 
         N′   RE   =N   sc   RB ·( N   symbol   sh   −N   oh_sym )− N   DMRS   PRB   −N   oh   PRB  
 
     where N sc   RB  denotes a quantity of subcarriers in a PRB, N symbol   sh  denotes a quantity of allocated symbols, N oh_sym  denotes a quantity of symbols related to the target resource overhead, N DMRS   PRB  denotes a resource overhead of a DMRS in a PRB on an allocated symbol, and N oh   PRB  is a parameter predefined in a protocol, (pre)configured by a network device, or configured by a terminal device. 
     Optionally, as an embodiment, the TBS calculation module  202  may be configured to calculate a quantity N′ RE  of available REs in a PRB on an allocated symbol based on the following formula, and calculate the TBS based on N′ RE : 
     
       
      
       N′ 
       RE 
       =N 
       sc 
       RB 
       ·N 
       symbol 
       sh 
       −N 
       DMRS 
       PRB 
       −N 
       oh 
       PRB  
      
     
     where N sc   PRB  denotes a quantity of subcarriers in a PRB, N symbol   sh  denotes a quantity of allocated symbols, N DMRS   PRB  denotes a resource overhead of a DMRS in a PRB on an allocated symbol, and N oh   PRB  is a parameter related to the target resource overhead. 
     Optionally, as an embodiment, the TBS calculation module  202  may be configured to calculate a quantity N′ RE  of available REs in a PRB on an allocated symbol based on the following formula, and calculate the TBS based on N′ RE : 
     
       
      
       N′ 
       RE 
       =N 
       sc 
       RB 
       ·N 
       symbol 
       sh 
       −N 
       DMRS 
       PRB 
       −N 
       oh 
       PRB 
       −N  
      
     
     where N sc   RB  denotes a quantity of subcarriers in a PRB, N symbol   sh  denotes a quantity of allocated symbols, N DMRS   PRB  denotes a resource overhead of a DMRS in a PRB on an allocated symbol, N oh   PRB  is a parameter predefined in a protocol, (pre)configured by a network device, or configured by a terminal device, and N is a parameter related to the target resource overhead. 
     Optionally, as an embodiment, the TBS calculation module  202  may be configured to calculate a quantity N′ RE  of available REs in a PRB on an allocated symbol based on the size of the allocated resource, calculate a quantity N RE  of available REs in the allocated resource based on the following formula, and calculate the TBS based on N RE : 
         N   RE =min(156, N′   RE )· n   PRB   −M  
 
     where n PRB  denotes a quantity of available PRBs, and M is a parameter related to the target resource overhead. 
     Optionally, as an embodiment, the TBS calculation module  202  may be configured to calculate a quantity N′ RE  of available REs in a PRB on an allocated symbol based on the following formula, and calculate the TBS based on N′ RE : 
         N′   RE =( N   sc   RB   ·N   symbol   sh   −N   DMRS   PRB   −N   oh   PRB )*alpha_1 
     where N sc   RB  denotes a quantity of subcarriers in a PRB, N symbol   sh  denotes a quantity of allocated symbols, N DMRS   PRB  denotes a resource overhead of a DMRS in a PRB on an allocated symbol, N oh   PRB  is a parameter predefined in a protocol, (pre)configured by a network device, or configured by a terminal device, alpha_1 is a parameter related to the target resource overhead, and 0&lt;alpha_1≤1. 
     Optionally, as an embodiment, the TBS calculation module  202  may be configured to calculate a quantity N′ RE  of available REs in a PRB on an allocated symbol based on the size of the allocated resource, calculate a quantity N RE  of available REs in the allocated resource based on the following formula, and calculate the TBS based on N RE : 
         N   RE =min(156, N′   RE )· n   PRB ·alpha_2
 
     n PRB  denotes a quantity of allocated PRBs, alpha_2 is a parameter related to the target resource overhead, and 0&lt;alpha_2≤1. 
     Optionally, as an embodiment, the TBS calculation module  202  may be configured to calculate a quantity N RE  of available REs based on the size of the allocated resource, calculate an information median N inf o  based on the following formula, and calculate the TBS based on N inf o : 
         N   info   =N   RE   ·R·Q   m ·ν·alpha_3
 
     where N RE  denotes a quantity of available REs in the allocated resource, R denotes a bit rate, Q m  denotes a modulation order, υ denotes a quantity of layers, alpha_3 is a parameter related to the target resource overhead, and 0&lt;alpha_3≤1. 
     Optionally, as an embodiment, the target resource overhead includes the resource overhead of the PSCCH and is calculated based on configuration of the PSCCH. 
     Optionally, as an embodiment, the TBS calculation module  202  may be further configured to: 
     calculate the resource overhead of the PSCCH based on a resource occupied by the PSCCH during blind detection; or 
     calculate the resource overhead of the PSCCH based on a first resource overhead of a first PSCCH and a second resource overhead of a second PSCCH, where the first PSCCH is predefined or is configured or preconfigured by a network device, and the second PSCCH is indicated by using the first PSCCH. 
     Optionally, as an embodiment, the TBS calculation module  202  may be configured to calculate the TBS based on the size of the allocated resource and a parameter related to the target resource overhead, where the parameter is obtained in at least one of the following manners: 
     predefined in a protocol; 
     preconfigured by a network device; 
     configured by a network device; 
     configured based on a transmission type; 
     indicated by using sidelink control information SCI or downlink control information DCI; 
     negotiated through radio resource control RRC configuration between terminal devices; and 
     obtained based on feedback information. 
     Optionally, as an embodiment, the TBS calculation module  202  may also be configured to use a TBS for initial transmission of sidelink data as a TBS of retransmission sidelink data. 
     For the terminal device  200  provided in the present disclosure, reference may be made to the corresponding procedure of the method  100  provided in the present disclosure, and each unit/module in the terminal device  200  and the foregoing other operations and/or functions are used to implement the corresponding procedure of the method  100 , and a same or equivalent effect can be achieved. For brevity, details are not described herein again. 
       FIG. 3  is a structural block diagram of a terminal device according to another embodiment of the present disclosure. As shown in  FIG. 3 , the terminal device  300  includes: at least one processor  301 , a memory  302 , at least one network interface  304 , and a user interface  303 . All components of the terminal device  300  are coupled together by using the bus system  305 . It can be understood that the bus system  305  is configured to implement a connection and communication between these components. In addition to a data bus, the bus system  305  may include a power bus, a control bus, and a status signal bus. However, for clarity of description, various buses are marked as the bus system  305  in  FIG. 3 . 
     The user interface  303  may include a display, a keyboard, or a click device (for example, a mouse, a trackball (trackball), a touchpad, or a touchscreen). 
     It may be understood that the memory  302  in this embodiment of the present disclosure may be a volatile memory or a non-volatile memory, or may include both a volatile memory and a non-volatile memory. The nonvolatile memory may be a 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 (RAM), used as an external cache. By way of example rather than limitative description, many forms of RAMs are available, such as 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, DDRSDRAM), 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, DRRAM). The memory  302  of the system and the method described in the embodiments of the present disclosure is intended to include, but is not limited to, these and any other suitable types of memories. 
     In some implementations, the memory  302  stores the following element: an executable module or a data structure, a subset thereof, or an extended set thereof: an operating system  3021  and an application program  3022 . 
     The operating system  3021  includes various system programs, for example, a framework layer, a kernel library layer, and a driver layer, and is configured to implement various basic services and process hardware-based tasks. The application  3022  includes various applications, for example, a media player, and a browser, to implement various application services. A program for implementing the method in the embodiments of the present disclosure may be included in the application  3022 . 
     In this embodiment of the present disclosure, the terminal device  300  further includes a computer program that is stored in the memory  302  and that can run on the processor  301 , and when the computer program is executed by the processor  301 , the steps of the method  100  are implemented. 
     The method disclosed in the embodiments of the present disclosure may be applied to the processor  301  or implemented by the processor  301 . The processor  301  may be an integrated circuit chip having a signal processing capability. During implementation, the steps of the foregoing method may be completed by hardware integrated logic circuits in the processor  301  or instructions in a form of software. The foregoing processor  301  may be a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or another programmable logic component, a discrete gate or a transistor logic component, or a discrete hardware component. The processor  301  may implement or execute the methods, steps, and logic block diagrams disclosed in the embodiments of the present disclosure. The general-purpose processor may be a microprocessor or may be any conventional processor or the like. The steps of the method disclosed in the embodiments of the present disclosure may be directly performed by a hardware decoding processor or by a combination of hardware and software modules in the decoding processor. The software module may be located in a mature computer-readable storage medium in this field such as a random access memory, a flash memory, a read-only memory, a programmable read-only memory or an electrically erasable programmable memory, or a register. The computer-readable storage medium is located in the memory  302 , and the processor  301  reads information from the memory  302  and completes the steps of the foregoing method in combination with hardware of the processor  301 . Specifically, the computer-readable storage medium stores a computer program, and when the computer program is executed by the processor  301 , the steps of the foregoing embodiment of method  100  are performed. 
     It can be understood that those embodiments described in the embodiments of the present disclosure can be implemented with hardware, software, firmware, middleware, microcode, or a combination thereof. For hardware implementation, a processing unit may be implemented in one or more Application Specific Integrated Circuits (ASIC), digital signal processors (DSP), digital signal processing devices (DSP Device, DSPD), programmable logic devices (PLD), field-programmable gate arrays (FPGA), general purpose processors, controllers, microcontrollers, microprocessors, or other electronic units or a combination thereof used to perform the functions in the present disclosure. 
     For implementation with software, technologies described in the embodiments of the present disclosure may be implemented by executing functional modules (for example, a process and a function) in the embodiments of the present disclosure. Software code may be stored in a memory and executed by a processor. The memory may be implemented in the processor or outside the processor. 
     The terminal device  300  can implement each process implemented by the terminal device in the foregoing embodiments, and can achieve the same or equivalent technical effect. To avoid repetition, details are not described herein again. 
     The present disclosure further provides a computer-readable storage medium. The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the processes in the foregoing method embodiment  100  are implemented, and a same technical effect can be achieved. To avoid repetition, details are not described herein again. An example of the computer-readable storage medium includes a non-transitory computer-readable storage medium, for example, a read-only memory (ROM for short), a random access memory (RAM for short), a magnetic disk, an optical disc, or the like. 
     It should be noted that, in this specification, the terms “include”, “comprise”, or any of their variants are intended to cover a non-exclusive inclusion, so that a process, a method, an article, or an apparatus that includes a series of elements not only includes those elements but also includes other elements that are not expressly listed, or further includes elements inherent to such a process, method, article, or apparatus. In the absence of more restrictions, an element defined by the statement “including a . . . ” does not exclude another same element in a process, method, article, or apparatus that includes the element. 
     Based on the descriptions of the foregoing implementations, a person skilled in the art may clearly understand that the method in the foregoing embodiment may be implemented by software in addition to a necessary universal hardware platform or by hardware only. In most circumstances, the former is a preferred implementation. Based on such an understanding, the technical solutions of the present disclosure essentially or the part contributing to the related art may be implemented in a form of a software product. The computer software product is stored in a storage medium (such as a ROM/RAM, a magnetic disk, or an optical disc), and includes several instructions for instructing a terminal (which may be a mobile phone, a computer, a server, an air conditioner, a network device, or the like) to perform the methods described in the embodiments of the present disclosure. 
     The embodiments of the present disclosure are described above with reference to the accompanying drawings, but the present disclosure is not limited to the foregoing specific implementations. The foregoing specific implementations are merely exemplary instead of restrictive. Under enlightenment of the present disclosure, a person of ordinary skills in the art may make many forms without departing from the aims of the present disclosure and the protection scope of claims, all of which fall within the protection of the present disclosure.