Section: 5.3.2.2 HARQ process
Content: For each TTI where a transmission takes place for the HARQ process, one or two (in case of downlink spatial multiplexing) TBs and the associated HARQ information are received from the HARQ entity. For each received TB and associated HARQ information, the HARQ process shall: - if the NDI, when provided, has been toggled compared to the value of the previous received transmission corresponding to this TB; or - if the HARQ process is equal to the broadcast process and if this is the first received transmission for the TB according to the system information schedule indicated by RRC; or - if this is the very first received transmission for this TB (i.e. there is no previous NDI for this TB): - consider this transmission to be a new transmission. - else: - consider this transmission to be a retransmission. The MAC entity then shall: - if this is a new transmission: - attempt to decode the received data. - else if this is a retransmission: - if the data for this TB has not yet been successfully decoded: - combine the received data with the data currently in the soft buffer for this TB and attempt to decode the combined data. - if the data which the MAC entity attempted to decode was successfully decoded for this TB; or - if the data for this TB was successfully decoded before: - if the HARQ process is equal to the broadcast process: - deliver the decoded MAC PDU to upper layers. - else if this is the first successful decoding of the data for this TB: - deliver the decoded MAC PDU to the disassembly and demultiplexing entity. - generate a positive acknowledgement (ACK) of the data in this TB. - else: - replace the data in the soft buffer for this TB with the data which the MAC entity attempted to decode. - generate a negative acknowledgement (NACK) of the data in this TB. - if the HARQ process is associated with a transmission indicated with a Temporary C-RNTI and the Contention Resolution is not yet successful (see clause 5.1.5); or - if the HARQ process is equal to the broadcast process; or - if the HARQ process is not associated with a transmission indicated with a PUR-RNTI and the timeAlignmentTimer, associated with the TAG containing the serving cell on which the HARQ feedback is to be transmitted, is stopped or expired; or - if the HARQ feedback is disabled for the corresponding HARQ process: - if harq-FeedbackEnablingforSPSactive is configured and the transmission is the first SPS PDSCH transmission after SPS activation: - indicate the generated positive or negative acknowledgement for this TB to the physical layer. - else: - do not indicate the generated positive or negative acknowledgement to the physical layer. - else: - indicate the generated positive or negative acknowledgement for this TB to the physical layer. The MAC entity shall ignore NDI received in all downlink assignments on PDCCH for its Temporary C-RNTI when determining if NDI on PDCCH for its C-RNTI has been toggled compared to the value in the previous transmission. NOTE 1: When the MAC entity is configured with more than one serving cell, UE behaviors for storing data to the soft buffer is specified in TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2]. NOTE 2: If the MAC entity receives a retransmission with a TB size different from the last valid TB size signalled for this TB, the UE behavior is left up to UE implementation.