Section: 5.3.2.1 HARQ Entity
Content: There is one HARQ entity at the MAC entity for each Serving Cell which maintains a number of parallel HARQ processes. Each HARQ process is associated with a HARQ process identifier. The HARQ entity directs HARQ information and associated TBs received on the DL-SCH to the corresponding HARQ processes (see clause 5.3.2.2). The number of DL HARQ processes per HARQ entity is specified in TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2], clause 7. When the physical layer is configured for downlink spatial multiplexing, as specified in TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [2], one or two TBs are expected per TTI and they are associated with the same HARQ process. Otherwise, one TB is expected per TTI. For NB-IoT UEs or BL UEs or UEs in enhanced coverage, the parameter DL_REPETITION_NUMBER provides the number of transmissions repeated in a bundle. For each bundle, DL_REPETITION_NUMBER is set to a value provided by lower layers. Within a bundle, after the initial (re)transmission, DL_REPETITION_NUMBER-1 HARQ retransmissions follow. The HARQ feedback is transmitted for the bundle and a downlink assignment corresponding to a new transmission or a retransmission of the bundle is received after the last repetition of the bundle. A retransmission of a bundle is also a bundle. HARQ feedback may be disabled per HARQ process by configuring downlinkHARQ-FeedbackDisabled and/or by indication from lower layers. If the MAC entity is configured with blindSlotSubslotPDSCH-Repetitions or blindSubframePDSCH-Repetitions on a serving cell (TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8]), the parameter DL_REPETITION_NUMBER provides the number of transmissions repeated in a bundle for a downlink assignment received on that serving cell. For each bundle, DL_REPETITION_NUMBER and the redundancy version for each transmission within a bundle are set to values provided by lower layers. Within a bundle, after the initial (re-)transmission, DL_REPETITION_NUMBER-1 HARQ retransmissions follow. The HARQ feedback is sent only one time for the bundle and after the last transmission of the bundle. In addition to the broadcast HARQ process, NB-IoT has one or two DL HARQ processes. The MAC entity shall: - If a downlink assignment has been indicated for this TTI; or - If this TTI is for a retransmission within a bundle: - allocate the TB(s) received from the physical layer and the associated HARQ information to the HARQ process indicated by the associated HARQ information. - If a downlink assignment has been indicated for the broadcast HARQ process: - allocate the received TB to the broadcast HARQ process. NOTE: In case of BCCH and BR-BCCH a dedicated broadcast HARQ process is used.