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5G NR UE Search Space Types: Type0, Type0A, Type1, Type2, Type3

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This document outlines the different types of search spaces in 5G New Radio (NR) for User Equipment (UE), specifically focusing on Type0, Type0A, Type1, Type2, and Type3 search spaces. It also covers UE-specific search space sets as defined in the 5G NR standards. We’ll also look at the fields within the Search Space Information Element (IE) used by the Radio Resource Control (RRC) layer.

Introduction to Search Spaces

  • Think of it as similar to the search space concept in LTE.
  • The search space represents the area within the downlink frame where the Physical Downlink Control Channel (PDCCH) might be transmitted.
  • The UE monitors this area to find the PDCCH, which carries important data known as Downlink Control Information (DCI).
  • There are two main categories of search spaces: common and UE-specific.

The following table summarizes the different types of search spaces in 5G NR.

5G NR Search Space Types

Search Space TypeDescription
Type0A PDCCH common search space set configured by searchSpaceZero in the MasterInformationBlock (MIB) or by searchSpaceSIB1 in PDCCH-ConfigCommon for a DCI format with a CRC scrambled by a System Information Radio Network Temporary Identifier (SI-RNTI) on the primary cell.
Type0AA PDCCH common search space set configured by searchSpace-OSI in PDCCH-ConfigCommon for a DCI format with a CRC scrambled by a SI-RNTI on the primary cell.
Type1A PDCCH common search space set configured by ra-SearchSpace in PDCCH-ConfigCommon for a DCI format with a CRC scrambled by a Random Access RNTI (RA-RNTI) or a Temporary C-RNTI (TC-RNTI) on the primary cell.
Type2A PDCCH common search space set configured by pagingSearchSpace in PDCCH-ConfigCommon for a DCI format with a CRC scrambled by a Paging RNTI (P-RNTI) on the primary cell.
Type3A PDCCH common search space set configured by SearchSpace in PDCCH-Config with searchSpaceType = common for DCI formats with a CRC scrambled by INT-RNTI, SFI-RNTI, TPC-PUSCH-RNTI, TPC-PUCCH-RNTI, or TPC-SRS-RNTI. Additionally, only for the primary cell, it can be used for C-RNTI or CS-RNTI(s).
UE-specific search spaceThis set is configured by SearchSpace in PDCCH-Config with searchSpaceType = ue-Specific for DCI formats with CRC scrambled by C-RNTI or CS-RNTI(s).

Search Space Information Element (IE)

  • The following illustrates the structure and various fields used within the RRC Search Space Information Element (IE).
  • This IE dictates how and where the UE should search for PDCCH candidates.
  • Each search space is linked to a specific ControlResourceSet.

search space IE1

search space IE2

References

  • 3GPP TS 38.213
  • 3GPP TS 38.331