Basics of Downlink Control Information in 5G NR

How does a UE decode Downlink Control Information (DCI) in 5G NR?

Fig 1. DCI-to-PDCCH-to-CORESET mapping. Remember that PDCCH’s basic unit is CCE. CORESET’s basic unit is REG. Hence, PDCCH-to-CORESET mapping is actually CCE-to-REG mapping.

Downlink Control Information (DCI) carries information from gNB-to-UE such as info DL/UL resource scheduling, power control, modulation and coding schemes to decode a message, HARQ related aspects etc.

A DCI is carried as a payload within Physical Downlink Control Channel (PDCCH). PDCCH is itself wrapped inside something known as Control Set (CORESET). This article assumes that the reader has a basic understanding of the 5G NR channels. Otherwise, click here to learn more.

CORESETs are time-frequency resources where DCI is transmitted.

The actual DCI message passes through the chain as presented in Fig. 1 above before riding over the PDCCH over the air.

UE’s DCI Decoding Procedure

At the UE end, the following procedure takes place to read the control message.

1. The UE scans the CORESET to get PDCCH locations.
2. Within PDCCH UE can find DCI.
3. The UE performs RNTI unmasking and CRC decoding.
4. Successful CRC decoding means a UE knows if the message is intended for it or if there is an error in the DCI. Both purposes are…