Section: 5.14.1.2.1 Sidelink HARQ Entity
Content: The MAC entity is configured by upper layers to transmit using pool(s) of resources on one or multiple carriers as indicated in clause 5.10.13.1 of TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8]. For each carrier, there is one Sidelink HARQ Entity at the MAC entity for transmission on SL-SCH, which maintains a number of parallel Sidelink processes. For sidelink communication, the number of transmitting Sidelink processes associated with the Sidelink HARQ Entity is defined in TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8]. For V2X sidelink communication, the maximum number of transmitting Sidelink processes associated with each Sidelink HARQ Entity is 8. A sidelink process may be configured for transmissions of multiple MAC PDUs. For transmissions of multiple MAC PDUs, the maximum number of transmitting Sidelink processes associated with each Sidelink HARQ Entity is 2. A delivered and configured sidelink grant and its associated HARQ information are associated with a Sidelink process. For each subframe of the SL-SCH and each Sidelink process, the Sidelink HARQ Entity shall: - if a sidelink grant corresponding to a new transmission opportunity has been indicated for this Sidelink process and there is SL data, for sidelink logical channels of ProSe destination associated with this sidelink grant, available for transmission: - obtain the MAC PDU from the "Multiplexing and assembly" entity; - deliver the MAC PDU and the sidelink grant and the HARQ information to this Sidelink process; - instruct this Sidelink process to trigger a new transmission. - else, if this subframe corresponds to retransmission opportunity for this Sidelink process: - instruct this Sidelink process to trigger a retransmission. NOTE: The resources for retransmission opportunities are specified in clause 14.2.1 of TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2] unless specified in clause 5.14.1.1.