- PDCCH stands for Physical Downlink Control Channel
- It is a standalone physical channel that carries control information in the form of DCI.
By listening to the PDCCH, the UE is able to know the below conditions and perform actions accordingly: -
- Where & when it has to transmit data on PUSCH
- Where & when it has to receive data on PDSCH
Location of PDCCH
Based upon the access technology, the PDCCH is located into different locations for FDD and TDD.
- In TDD, PDCCH is in the first one or two OFDM symbols of all DL Slots
- In FDD, PDCCH is in the first two or three OFDM symbols of all DL Slots.
PDCCH building blocks
- PDCCH is made up of so-called Enhanced Control Channel Elements (CCE)
- Each CCE consists of 6 Resource-Element Groups (REG)
- 1 REG = 1 resource block during one OFDM symbol (12 REs)
- 1 RE = 1 subcarrier on 1 OFDM symbol
- PDCCH uses an aggregation of several consecutive enhanced control channel elements (CCEs), which defines the size of the PDCCH in frequency domain.
- Aggregation Level (AL) defines the number of CCEs which will be used for Downlink Control Information (DCI) transmission.
- Higher AL keeps PDCCH transmission on high robustness level, suitable for cells where coverage has the highest priority.
- But higher AL consumes more CCEs which could be used by other UEs in this slot, reducing the cell capacity.
- AL configuration should provide a balance between the PDCCH coverage and resource availability in a single slot.
- CORESET stands for Control Resource Set
- CORESET is a set of frequency resources over a given duration.
- Size of the CORESET tells how many CCEs are available to send DCI and are defined by the number of PRBs and symbols occupied by the CORESET.
- CORESET=PDCCH Occasion
- The number and position of PDCCH occasions (CORESET occurrences) within the slot (and slots over System Frame Structure) is defined by search spaces.
- CORESET might be either common or dedicated, same as the search spaces.
- 3GPP allows configuring up to 3 CORESETs per downlink bandwidth part, but currently Nokia supports configuration of two: CORESET0 and CORESET>0 per BWP.
https://www.nrexplained.com/pdcchmod
Note:-
As per 3GPP Coreset0 is always interleaved (regBundleSize = 6, interleaverSize = 2), whereas CORESET>0 might be not-interleaved (regBundleSize = 6) or interleaved (regBundleSize = 2,interleaverSize = 3)
CORESET 0
It is also referred as Type 0 CORESET
It is a fundamental CORESET for both NSA and SA
It is configured to UE by using a pointer included in the MIB or in the RRC Reconfiguration message
The configuration index points to a row within a look-up table standardized by 3GPP
It is used by Search Spaces belonging to both the Initial and Dedicated Bandwidth Parts
CORESET0 is a specific use case of Common Coreset, where SIB 1 message is broadcasted.
