PDCCH
Physical Downlink Control Channel: carries Downlink Control Information (DCI) that schedules PDSCH/PUSCH resources, power control commands, and slot format indicators.
PDCCH is the channel that schedules everything else. It carries DCI — the instructions telling a UE where its downlink data sits, what resources to use for uplink, which MCS to apply, HARQ process numbers, power control, and more. No PDCCH decode, no data transfer, so its reliability and the UE's ability to find it are foundational.
The hard part is that the UE doesn't know in advance exactly where its DCI is, so it blind-decodes: it tries every candidate location at each aggregation level within its configured search spaces and checks the CRC, which is scrambled with the UE's RNTI. A successful CRC unscramble means "this one's for me." Aggregation levels (1, 2, 4, 8, 16 control channel elements) trade capacity for resilience — the network sends critical DCI at a high aggregation level so it survives a weak link, at the cost of more control resources. Each blind decode costs UE processing, so the number of candidates a UE must monitor is capped.
Frequently asked questions
- What's the difference between PDCCH and PDSCH?
- PDCCH carries control — the DCI that tells the UE where and how its data is scheduled. PDSCH carries the actual downlink payload: user data, SIBs, paging, RRC messages. The UE first decodes PDCCH to learn the scheduling, then uses that information to receive PDSCH. Control points to data; data carries the payload.
- What is blind decoding on PDCCH?
- The UE is not told the exact location of its DCI, so it attempts to decode every candidate position in its search spaces at each aggregation level and checks whether the CRC, scrambled with its own RNTI, unscrambles cleanly. A clean check means that DCI is addressed to it. It's called blind because the UE searches without knowing in advance where its message is.
Related terms
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