PDCCH Search Space refers to the area in the downlink resource grid where PDCCH may be carried. UE performs blind decoding throughout these search space trying to find PDCCH data (i.e, DCI).
UE has to try to decode PDCCH/DCI using (CCE Index, Aggregation Level, RNTI) based on trial and error method.
There are two types of search space called “UE-specific search space” and “Common Search Space“.
UE Specific Search Space is dedicated for each specific UE and informed to UE via RRC signaling message. It means UE need to complete RRC establishment to get the information about UE-specific search space.
Common Search Space is the specific search space that every UE need to search for the signals for every UE(e.g, PDCCH for SIB) or signaling message that is applied to every UE before dedicated channel is established for a specific UE(e.g, PDCCH used during RACH process and for Paging).
Important IEs:
1)searchSpaceId
2)controlResourceSetId
3)monitoringSlotPeriodicityAndOffset
4)monitoringSymbolsWithinSlot
5)nrofCandidates
6)searchSpaceType
7)common
8)dci-Format0-0-AndFormat1-0
9)dci-Format2-0
10)nrofCandidates-SFI
11)dci-Format2-1
12)dci-Format2-2
13)dci-Format2-3
14)ue-Specific