A Special CORESET : CORESET 0
These are configured by RRC. It is a special type of CORESET which is called CORESET 0. It is the one transmitting PDCCH for SIB1 scheduling. It cannot be specified by RRC since it should be used before any RRC is transmitted. It implies that CORESET0 should be configured by some predefined process and pre-defined parameters.
The network can define common control regions and UE-specific control regions. The number of CORESET is limited to 3 per BWP (bandwidth part) including both common and UE specific CORESET.
Search space: Each Search space is a set of control channel elements at a different aggregation level. It tells how many candidates are there to decode at different aggregation levels. There is a mapping between CORESET and search space. It is the space where UE attempts blind decoding. Different aggregation levels are there to mitigate the situation when UE is under bad coverage.
- The motivation of BWP: In most cases, NR would operate in very wideband and there wouldn’t be any issues for the high-end UEs to handle the full operating band. There is also a need for the mechanism so that narrowband UE can operate. So BWP is no parameters are defining fraction of the spectrum that a UE only needs to care about. It is defined for both UL/DL.
- Default BWP: DL BWP to be used upon expiry of the BWP inactivity time. When this field is absent then UE uses Initial BWP as the default BWP.