5G PDCCH 5G PDSCH

5G PDCCH and 5G PDSCH

5G PDCCH is used to carry Downlink Control Information (DCI), and following types of DCI are supported in NR.

*  PDSCH assignments to convey TB(s) to a certain UE, including time/frequency-domain resource information

*  PUSCH grants for a certain UE to transmit a TB, including time/frequency-domain resource information

*  Slot format indication, where how each of symbols within a slot is indicated

*  Pre-emption indication, which is used to inform UEs that there is no DL transmission on the informed time/frequency-domain resources

*  UL transmit power control (TPC)

*  Each device monitors a number of PDCCHs, typically once per slot although it is possible to configure more frequent monitoring to support traffic requiring very low latency. Upon detection of a valid PDCCH, the device follows downlink control information contained in the PDCCH, e.g., the scheduling decision so that the device receives PDSCH (or transmits PUSCH) accordingly.

*  The PDCCHs are transmitted in one or more control resource sets (CORESETs). A CORESET spans overdone, two or three OFDM symbol(s) in time domain and over a configurable bandwidth in the frequency domain. This is needed in order to handle devices with different bandwidth capabilities and also beneficial from a forward-compatibility perspective. One control channel element (CCE) is defined as 6 resource element groups (REGs), where 1 REG is composed of 12 resource elements (REs). In a CORESET, a PDCCH with DM-RS can be mapped on one or more CCEs as shown in Figure. Different number of CCEs (aggregation level) provides different coding rate for the control channels.

There are different formats for DCI transmitted on a PDCCH as shown in DCI Table. A UE monitors one or more PDCCH candidates for DCI with CRC scrambled by a certain RNTI in PDCCH common search space (CSS) set and/or UE-specific search space (USS) set. DCI format is distinguished by the PDCCH payload size and the RNTI scrambling the CRC.

General description of NR PDCCH

NR DCI formats

DCI format	RNTI	Notes
DCI format 0_0	RA-RNTI, TC-RNTI, C-RNTI, CS-RNTI	Monitored on CSS or USS Scheduling PUSCH
DCI format 0_1	C-RNTI, CS-RNTI	Monitored in USS Scheduling PUSCH
DCI format 1_0	SI-RNTI, RA-RNTI, P-RNTI, C-RNTI, CS-RNTI	Monitored in CSS or USS Scheduling PDSCH
DCI format 1_1	C-RNTI, CS-RNTI	Monitored in USS Scheduling PDSCH
DCI format 2_0	SFI-RNTI	Monitored in CSS Indicating slot format for slot(s)
DCI format 2_1	INT-RNTI	Monitored in CSS Indicating pre-emption of DL resource
DCI format 2_2	TPC-PUSCH-RNTI, TPC-PUCCH-RNTI	Monitored in CSS Group-TPC command for PUSCH/PUCCH
DCI format 2_3	TPC-SRS-RNTI	Monitored in CSS Group-command for SRS

PDSCH is used to transmit one or two transport blocks (TBs). A DCI in a PDCCH can assign a PDSCH transmission with DM-RS (and other RS if any). The PDSCH is decoded based on the information in the PDCCH, for example, time/frequency-domain resource, modulation, and layer. PDSCH transmissions are processed with durations from 2 to 14 symbols. The number of layers for PDSCH transmissions is 8. HARQ feedback/retransmission is supported for PDSCH transmissions as mentioned in HARQ Post.