5G/NR - Type 1 PDCCH Common Search Space  

 

 

 

Type 2 PDCCH Common Search Space

Type2-PDCCH CSS is a common search space specifically allocated for paging. It is configured by the network via the pagingSearchSpace parameter in PDCCH-ConfigCommon on the primary cell (PCell) of the UE’s master cell group.

Type2-PDCCH CSS is the dedicated search space for paging in 5G NR. By configuring the pagingSearchSpace parameter, the network instructs UEs to monitor for paging messages in a specific CORESET region at defined monitoring occasions, ensuring that UEs can be reached efficiently when they are not in active data transmission.

NOTE : For formal description of this type of search space, refer to 38.213-10.1

Purpose and Usage

Type2-PDCCH CSS serves as the dedicated common search space for paging. Its primary role is to carry paging-related downlink control information (DCI) with CRC scrambled by the P-RNTI (Paging-RNTI). In other words, when the network needs to inform a UE in RRC Idle or RRC Inactive states about incoming data or system reconfiguration, it broadcasts paging messages using this CSS. Because every UE in the cell potentially needs to monitor paging, the Type2-PDCCH CSS ensures a standardized way of broadcasting those messages across all UEs.

  • Type2-PDCCH CSS is specifically designated for paging.
  • It carries DCI with CRC scrambled by the P-RNTI, enabling paging messages to reach UEs in RRC Idle or Inactive states.
  • Because paging is broadcast to all UEs, this common search space ensures a standardized mechanism for distributing paging notices.

Configuration

The network enables Type2-PDCCH CSS through the pagingSearchSpace parameter in PDCCH-ConfigCommon. This parameter specifies how many PDCCH candidates a UE should monitor for paging, along with the monitoring occasions and aggregation levels. If the UE is not signaled any pagingSearchSpace setting (for instance, if it is omitted), the UE does not monitor for paging DCI in that bandwidth part. The pagingSearchSpace thus explicitly instructs the UE where and when in the core resource set (CORESET) it should decode for paging messages.

  • The network activates Type2-PDCCH CSS through the pagingSearchSpace parameter in PDCCH-ConfigCommon.
  • This parameter defines the monitoring periodicity, offset, and PDCCH candidates (including aggregation levels) to be used for paging detection.
  • If the UE does not receive any pagingSearchSpace configuration, it does not monitor for paging DCI in that bandwidth part.

Interaction With Other Search Spaces

Because Type2-PDCCH CSS is reserved for P-RNTI paging messages, it operates independently from other CSS types—Type0-PDCCH CSS (system information), Type1-PDCCH CSS (random access), and Type3-PDCCH CSS (various common RNTIs such as TPC or INT). UEs typically monitor paging alongside any other configured search spaces, but paging messages remain confined to the Type2-PDCCH CSS. In other words, while the UE may also be monitoring Type0 for SI or Type1 for random-access responses, it looks specifically to the Type2-PDCCH CSS for paging DCI.

  • Paging in Type2-PDCCH CSS is independent of other CSS types—e.g., Type0 for system information, Type1 for random access, and Type3 for TPC or INT-related RNTIs.
  • UEs may monitor multiple CSSs concurrently, but paging always appears in Type2-PDCCH CSS (scrambled by the P-RNTI).
  • No overlap in RNTI usage occurs with other CSS sets, thus preventing confusion or collisions in control information

Reference