Section: 5.14.1.1 SL Grant reception and SCI transmission
Content: In order to transmit on the SL-SCH the MAC entity must have at least one sidelink grant. Sidelink grants are selected as follows for sidelink communication: - if the MAC entity is configured to receive a single sidelink grant dynamically on the PDCCH and more data is available in STCH than can be transmitted in the current SC period, the MAC entity shall: - using the received sidelink grant determine the set of subframes in which transmission of SCI and transmission of first transport block occur according to clause 14.2.1 of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2]; - consider the received sidelink grant to be a configured sidelink grant occurring in those subframes starting at the beginning of the first available SC Period which starts at least 4 subframes after the subframe in which the sidelink grant was received, overwriting a previously configured sidelink grant occurring in the same SC period, if available; - clear the configured sidelink grant at the end of the corresponding SC Period; - else, if the MAC entity is configured by upper layers to receive multiple sidelink grants dynamically on the PDCCH and more data is available in STCH than can be transmitted in the current SC period, the MAC entity shall for each received sidelink grant: - using the received sidelink grant determine the set of subframes in which transmission of SCI and transmission of first transport block occur according to clause 14.2.1 of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2]; - consider the received sidelink grant to be a configured sidelink grant occurring in those subframes starting at the beginning of the first available SC Period which starts at least 4 subframes after the subframe in which the sidelink grant was received, overwriting a previously configured sidelink grant received in the same subframe number but in a different radio frame as this configured sidelink grant occurring in the same SC period, if available; - clear the configured sidelink grant at the end of the corresponding SC Period; - else, if the MAC entity is configured by upper layers to transmit using one or multiple pool(s) of resources as indicated in clause 5.10.4 of TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8] and more data is available in STCH than can be transmitted in the current SC period, the MAC entity shall for each sidelink grant to be selected: - if configured by upper layers to use a single pool of resources: - select that pool of resources for use; - else, if configured by upper layers to use multiple pools of resources: - select a pool of resources for use from the pools of resources configured by upper layers whose associated priority list includes the priority of the highest priority of the sidelink logical channel in the MAC PDU to be transmitted; NOTE 1: If more than one pool of resources has an associated priority list which includes the priority of the sidelink logical channel with the highest priority in the MAC PDU to be transmitted, it is left for UE implementation which one of those pools of resources to select. - randomly select the time and frequency resources for SL-SCH and SCI of a sidelink grant from the selected resource pool. The random function shall be such that each of the allowed selections (see TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2]) can be chosen with equal probability; - use the selected sidelink grant to determine the set of subframes in which transmission of SCI and transmission of first transport block occur according to clause 14.2.1 of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2]; - consider the selected sidelink grant to be a configured sidelink grant occurring in those subframes starting at the beginning of the first available SC Period which starts at least 4 subframes after the subframe in which the sidelink grant was selected; - clear the configured sidelink grant at the end of the corresponding SC Period; NOTE 2: Retransmissions on SL-SCH cannot occur after the configured sidelink grant has been cleared. NOTE 3: If the MAC entity is configured by upper layers to transmit using one or multiple pool(s) of resources as indicated in clause 5.10.4 of TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8], it is left for UE implementation how many sidelink grants to select within one SC period taking the number of sidelink processes into account. Sidelink grants are selected as follows for V2X sidelink communication: - if the MAC entity is configured to receive a sidelink grant dynamically on the PDCCH and data is available in STCH, the MAC entity shall for each carrier configured in sl-V2X-ConfigDedicated for which a sidelink grant has been dynamically received on the PDCCH for this TTI: - use the received sidelink grant to determine the number of HARQ retransmissions and the set of subframes in which transmission of SCI and SL-SCH occur according to clauses 14.2.1 and 14.1.1.4A of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2]; - consider the received sidelink grant to be a configured sidelink grant for the carrier; - if the MAC entity is configured by upper layers to receive a sidelink grant on the PDCCH addressed to SL Semi-Persistent Scheduling V-RNTI, the MAC entity shall for each SL SPS configuration and for each carrier configured in sl-V2X-ConfigDedicated for which a sidelink grant has been received on the PDCCH addressed to SL Semi-Persistent Scheduling V-RNTI either for this TTI or for this PDCCH occasion according to clause 3.1 of TS 38.321[ NR; Medium Access Control (MAC) protocol specification ]  [24]: - if PDCCH contents indicate SPS activation: - use the received sidelink grant to determine the number of HARQ retransmissions and the set of subframes in which transmission of SCI and SL-SCH occur according to clauses 14.2.1 and 14.1.1.4A of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2]; - consider the received sidelink grant to be a configured sidelink grant for the carrier. - if PDCCH contents indicate SPS release: - clear the corresponding configured sidelink grant for the carrier. - if the MAC entity is configured by upper layers to transmit using pool(s) of resources in one or multiple carriers as indicated in either clause 5.10.13.1 of TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8] or TS 38.331[ NR; Radio Resource Control (RRC); Protocol specification ]  [25] based on sensing, or partial sensing, or random selection only if upper layers indicates that transmissions of multiple MAC PDUs are allowed according to either clause 5.10.13.1a of TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8] or TS 38.331[ NR; Radio Resource Control (RRC); Protocol specification ]  [25], and the MAC entity selects to create a configured sidelink grant corresponding to transmissions of multiple MAC PDUs, and data is available in STCH associated with one or multiple carriers, the MAC entity shall for each Sidelink process configured for multiple transmissions: - if there is no configured sidelink grant associated with the Sidelink process on any carrier allowed for the STCH as indicated by upper layers, as specified in TS 24.386[ User Equipment (UE) to V2X control function; protocol aspects; Stage 3 ]  [15]: - trigger the TX carrier (re-)selection procedure as specified in clause 5.14.1.5; - else if there is a configured sidelink grant associated with the Sidelink process: - if SL_RESOURCE_RESELECTION_COUNTER = 0 and when SL_RESOURCE_RESELECTION_COUNTER was equal to 1 the MAC entity randomly selected, with equal probability, a value in the interval [0, 1] which is above the probability configured by upper layers in probResourceKeep; or - if neither transmission nor retransmission has been performed by the MAC entity on any resource indicated in the configured sidelink grant during the last second; or - if sl-ReselectAfter is configured and the number of consecutive unused transmission opportunities on resources indicated in the configured sidelink grant is equal to sl-ReselectAfter; or - if none of the configured sidelink grant(s) on the carrier(s) allowed for the STCH have radio resources available in this TTI to accommodate a RLC SDU according to clause 5.14.1.3.1 by using the maximum allowed MCS configured by upper layers in maxMCS-PSSCH and the MAC entity selects not to segment the RLC SDU; or NOTE 4: If none of the configured sidelink grant(s) on the carrier(s) allowed for the STCH have radio resources available in this TTI to accommodate the RLC SDU according to clause 5.14.1.3.1, it is left for UE implementation whether to perform segmentation or sidelink resource reselection. - if none of the configured sidelink grant(s) on the carrier(s) allowed for the STCH have radio resources available in this TTI, according to clause 5.14.1.3.1 to fulfil the latency requirement of the data in a sidelink logical channel according to the associated PPPP, and the MAC entity selects not to perform transmission(s) corresponding to a single MAC PDU; or NOTE 5: If the latency requirement is not met, it is left for UE implementation whether to perform transmission(s) corresponding to single MAC PDU or sidelink resource reselection. - if the pool of resources where the sidelink grant is configured for the Sidelink process, is reconfigured by upper layers: - trigger the TX carrier (re-)selection procedure as specified in clause 5.14.1.5; - clear the configured sidelink grant associated to the Sidelink process; - flush the HARQ buffer associated to the Sidelink process; - else if SL_RESOURCE_RESELECTION_COUNTER = 0 and when SL_RESOURCE_RESELECTION_COUNTER was equal to 1 the MAC entity randomly selected, with equal probability, a value in the interval [0, 1] which is less than or equal to the probability configured by upper layers in probResourceKeep: - clear the configured sidelink grant, if available; - randomly select, with equal probability, an integer value in the interval [5, 15] for the resource reservation interval higher than or equal to 100ms, in the interval [10, 30] for the resource reservation interval equal to 50ms or in the interval [25, 75] for the resource reservation interval equal to 20ms, and set SL_RESOURCE_RESELECTION_COUNTER to the selected value; - use the previously selected sidelink grant for the number of transmissions of the MAC PDUs determined in clause 14.1.1.4B of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2] with the resource reservation interval to determine the set of subframes in which transmissions of SCI and SL-SCH occur according to clauses 14.2.1 and 14.1.1.4B of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2]; - consider the selected sidelink grant to be a configured sidelink grant; - if the TX carrier (re-)selection procedure was triggered in above and one or more carriers have been (re-)selected in the Tx carrier (re-)selection according to clause 5.14.1.5: - determine the order of the (re-)selected carriers, according to the decreasing order based on the highest priority of logical channels which are allowed on each (re-)selected carrier, and perform the following for each Sidelink process on each (re-)selected carrier according to the order: - select one of the allowed values configured by upper layers in restrictResourceReservationPeriod and set the resource reservation interval by multiplying 100 with the selected value; NOTE 6: How the UE selects this value is up to UE implementation. - randomly select, with equal probability, an integer value in the interval [5, 15] for the resource reservation interval higher than or equal to 100ms, in the interval [10, 30] for the resource reservation interval equal to 50ms or in the interval [25, 75] for the resource reservation interval equal to 20ms, and set SL_RESOURCE_RESELECTION_COUNTER to the selected value; - select the number of HARQ retransmissions from the allowed numbers that are configured by upper layers in allowedRetxNumberPSSCH included in pssch-TxConfigList and, if configured by upper layers, overlapped in allowedRetxNumberPSSCH indicated in cbr-pssch-TxConfigList for the highest priority of the sidelink logical channel(s) allowed on the selected carrier and the CBR measured by lower layers according to TS 36.214[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer; Measurements ]  [6] if CBR measurement results are available or the corresponding defaultTxConfigIndex configured by upper layers if CBR measurement results are not available; - select an amount of frequency resources within the range that is configured by upper layers between minSubchannel-NumberPSSCH and maxSubchannel-NumberPSSCH included in pssch-TxConfigList and, if configured by upper layers, overlapped between minSubchannel-NumberPSSCH and maxSubchannel-NumberPSSCH indicated in cbr-pssch-TxConfigList for the highest priority of the sidelink logical channel(s) allowed on the selected carrier and the CBR measured by lower layers according to TS 36.214[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer; Measurements ]  [6] if CBR measurement results are available or the corresponding defaultTxConfigIndex configured by upper layers if CBR measurement results are not available; - randomly select the time and frequency resources for one transmission opportunity from the resources indicated by the physical layer according to clause 14.1.1.6 of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2], according to the amount of selected frequency resources. The selected time and frequency resources shall fulfil the physical layer requirements as specified in TS 36.101[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio transmission and reception ]  [10], and the random function shall be such that each of the allowed selections can be chosen with equal probability; - use the randomly selected resource to select a set of periodic resources spaced by the resource reservation interval for transmission opportunities of SCI and SL-SCH corresponding to the number of transmission opportunities of MAC PDUs determined in clause 14.1.1.4B of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2]; - if the number of HARQ retransmissions is equal to 1: - if there are available resources left in the resources indicated by the physical layer according to clause 14.1.1.6 of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2] that meet the conditions in clause 14.1.1.7 of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2] for more transmission opportunities: - randomly select the time and frequency resources for one transmission opportunity from the available resources, according to the amount of selected frequency resources. The selected time and frequency resources shall fulfil the physical layer requirements as specified in TS 36.101[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio transmission and reception ]  [10], and the random function shall be such that each of the allowed selections can be chosen with equal probability; - use the randomly selected resource to select a set of periodic resources spaced by the resource reservation interval for the other transmission opportunities of SCI and SL-SCH corresponding to the number of retransmission opportunities of the MAC PDUs determined in clause 14.1.1.4B of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2]; - consider the first set of transmission opportunities as the new transmission opportunities and the other set of transmission opportunities as the retransmission opportunities; - consider the set of new transmission opportunities and retransmission opportunities as the selected sidelink grant. - else: - consider the set as the selected sidelink grant; - use the selected sidelink grant to determine the set of subframes in which transmissions of SCI and SL-SCH occur according to clause 14.2.1 and 14.1.1.4B of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2]; - consider the selected sidelink grant to be a configured sidelink grant; - else, if the MAC entity is configured by upper layers to transmit using pool(s) of resources in one or multiple carriers as indicated in either clause 5.10.13.1 of TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8] or TS 38.331[ NR; Radio Resource Control (RRC); Protocol specification ]  [25], the MAC entity selects to create a configured sidelink grant corresponding to transmission(s) of a single MAC PDU, and data is available in STCH associated with one or multiple carriers, the MAC entity shall for a Sidelink process: - trigger the TX carrier (re-)selection procedure as specified in clause 5.14.1.5; - if one or more carriers have been (re-)selected in the Tx carrier (re-)selection according to clause 5.14.1.5: - determine the order of the (re-)selected carriers, according to the decreasing order based on the highest priority of logical channels which are allowed on each (re-)selected carrier, and perform the following for each Sidelink process on each (re-)selected carrier according to the order: - select the number of HARQ retransmissions from the allowed numbers that are configured by upper layers in allowedRetxNumberPSSCH included in pssch-TxConfigList and, if configured by upper layers, overlapped in allowedRetxNumberPSSCH indicated in cbr-pssch-TxConfigList for the highest priority of the sidelink logical channel(s) allowed on the selected carrier and the CBR measured by lower layers according to TS 36.214[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer; Measurements ]  [6] if CBR measurement results are available or the corresponding defaultTxConfigIndex configured by upper layers if CBR measurement results are not available; - select an amount of frequency resources within the range that is configured by upper layers between minSubchannel-NumberPSSCH and maxSubchannel-NumberPSSCH included in pssch-TxConfigList and, if configured by upper layers, overlapped between minSubchannel-NumberPSSCH and maxSubchannel-NumberPSSCH indicated in cbr-pssch-TxConfigList for the highest priority of the sidelink logical channel(s) allowed on the selected carrier and the CBR measured by lower layers according to TS 36.214[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer; Measurements ]  [6] if CBR measurement results are available or the corresponding defaultTxConfigIndex configured by upper layers if CBR measurement results are not available; - randomly select the time and frequency resources for one transmission opportunity of SCI and SL-SCH from the resources indicated by the physical layer according to clause 14.1.1.6 of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2] , according to the amount of selected frequency resources. The selected time and frequency resources shall fulfil the physical layer requirement as specified in TS 36.101[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio transmission and reception ]  [10], and the random function shall be such that each of the allowed selections can be chosen with equal probability; - if the number of HARQ retransmissions is equal to 1: - if there are available resources left in the resources indicated by the physical layer according to clause 14.1.1.6 of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2] that meet the conditions in subcause 14.1.1.7 of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2] for one more transmission opportunity: - randomly select the time and frequency resources for the other transmission opportunity of SCI and SL-SCH corresponding to additional transmission of the MAC PDU from the available resources, according to the amount of selected frequency resources. The selected time and frequency resources shall fulfil the physical layer requirements as specified in TS 36.101[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio transmission and reception ]  [10], and the random function shall be such that each of the allowed selections can be chosen with equal probability; - consider a transmission opportunity which comes first in time as the new transmission opportunity and a transmission opportunity which comes later in time as the retransmission opportunity; - consider both of the transmission opportunities as the selected sidelink grant; - else: - consider the transmission opportunity as the selected sidelink grant; - use the selected sidelink grant to determine the subframes in which transmission(s) of SCI and SL-SCH occur according to clause 14.2.1 and 14.1.1.4B of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2]; - consider the selected sidelink grant to be a configured sidelink grant. NOTE 7: For V2X sidelink communication, the UE should ensure the randomly selected time and frequency resources fulfill the latency requirement. NOTE 8: For V2X sidelink communication, when there is no overlapping between the chosen configuration(s) in pssch-TxConfigList and chosen configuration(s) indicated in cbr-pssch-TxConfigList, it is up to UE implementation whether the UE transmits and which transmitting parameters the UE uses between allowed configuration(s) indicated in pssch-TxConfigList and allowed configuration(s) indicated in cbr-pssch-TxConfigList. The MAC entity shall for each subframe: - for each configured sidelink grant occurring in this subframe: - if SL_RESOURCE_RESELECTION_COUNTER = 1 for the Sidelink process associated with the configured sidelink grant and the MAC entity randomly selected, with equal probability, a value in the interval [0, 1] which is above the probability configured by upper layers in probResourceKeep: - set the resource reservation interval for the configured sidelink grant equal to 0; - if the configured sidelink grant corresponds to transmission of SCI: - for V2X sidelink communication in UE autonomous resource selection: - consider the selected transmission format to be SL-V2X-TxProfile for the highest priority of the sidelink logical channel(s) in the MAC PDU (TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8]); - select a MCS which is, if configured, within the range that is configured by upper layers between minMCS-PSSCH and maxMCS-PSSCH included in pssch-TxConfigList associated with the selected transmission format and, if configured by upper layers, overlapped between minMCS-PSSCH and maxMCS-PSSCH indicated in cbr-pssch-TxConfigList associated with the selected transmission format for the highest priority of the sidelink logical channel(s) in the MAC PDU and the CBR measured by lower layers according to TS 36.214[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer; Measurements ]  [6] if CBR measurement results are available or the corresponding defaultTxConfigIndex configured by upper layers if CBR measurement results are not available; NOTE 9: MCS selection is up to UE implementation if the MCS or the corresponding range is not configured by upper layers. NOTE 10: For V2X sidelink communication, when there is no overlapping between the chosen configuration(s) included in pssch-TxConfigList and chosen configuration(s) indicated in cbr-pssch-TxConfigList, it is up to UE implementation whether the UE transmits and which transmitting parameters the UE uses between allowed configuration(s) indicated in pssch-TxConfigList and allowed configuration(s) indicated in cbr-pssch-TxConfigList. - for V2X sidelink communication in scheduled resource allocation: - consider the selected transmission format to be SL-V2X-TxProfile for the highest priority of the sidelink logical channel(s) in the MAC PDU (TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8]); - select a MCS which is associated with the selected transmission format unless it is configured by upper layer; - instruct the physical layer to transmit SCI corresponding to the configured sidelink grant; - for V2X sidelink communication, deliver the configured sidelink grant, the associated HARQ information and the value of the highest priority of the sidelink logical channel(s) in the MAC PDU to the Sidelink HARQ Entity for this subframe; - else if the configured sidelink grant corresponds to transmission of first transport block for sidelink communication: - deliver the configured sidelink grant and the associated HARQ information to the Sidelink HARQ Entity for this subframe. NOTE 11: If the MAC entity has multiple configured sidelink grants occurring in one subframe and if not all of them can be processed due to the single-cluster SC-FDM restriction, it is left for UE implementation which one of these to process according to the procedure above.