NR DCIs &​ CORESETs

 

• PDCCH stands for Physical Downlink Control Channel​
• It is a standalone physical channel that carries control information in the form of DCI.

PDCCH basic concept 

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.

 

 

 

PDCCH Aggregation Level

• AL used by the UE depends on the radio conditions, ensuring a more efficient use of PDCCH resources.​
• Please note that Dynamic AL can be used only in UE-Specific Search Spaces with C-RNTI. For common transmission scheduling like paging or SIBs, only static AL can be used.

 

• 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

• 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.

Non-interleaved vs. interleaved CORESET

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.​