5.Scheduling/HARQ NR Physical Layer Specifications in 5G
In NR, as in LTE, the downlink data channels and uplink data channels are scheduled based on the Downlink Control Information (DCI). The DCI is transmitted and received via the Physical Downlink Control Channel (PDCCH). As in LTE, it is Scheduling/HARQ NR Physical Layer Specifications in 5G.
possible to use the frequency domain resource assignment field included in DCI to allocate frequency- domain resources in resource block units. In addition, in NR, the DCI is also able to indicate the time- domain resources for data channel scheduling. Scheduling/HARQ NR Physical Layer Specifications in 5G.
The base station allocates a Physical Downlink Shared Channel (PDSCH) to the user equipment and uses PDCCH to transmit downlink control information for the PDSCH. The user equipment receives and demodulates the PDCCH, and receives the PDSCH based on this downlink control information in the PDCCH. After receiving the PDSCH, the user equipment sends a Hybrid Automatic Re-peat reQuest ACKnowledgment (HARQ-ACK) to feedback the results of decoding. HARQ-ACK is transmitted via the Physical Uplink Control Channel (PUCCH), as are Scheduling Requests (SR) and CSI. The PUCCH transmission timing and resources can also be indicated by the DCI in the same way as the data channel. Figure 5 shows an example of data and HARQ-ACK resource allocation.
In HARQ retransmissions, in addition to the method whereby the entire transport block as initially transmitted and received is retransmitted, another method called code-block-group-based retransmission is specified. In code-block-group-based retransmission, when a transport block consists of multiple code blocks, only the code block groups that contain errors are retransmitted instead of retransmitting the entire transport block.
In general, uplink data scheduling is followed by scheduling request procedure, in which the user equipment transmits an SR using configured SR resources (Figure 6 (a)). In this scheme, however,
there is an unavoidable delay due to the scheduling request step. Therefore, NR supports configured grants, whereby a Physical Uplink Shared Channel (PUSCH) resource is configured to a user equipment, and the user equipment can transmit a PUSCH with this allocated resource when uplink data traffic arrives without performing a scheduling request procedure (Fig. 6 (b)).