Description
The Paging Early Indication RNTI (PEI-RNTI) is a Radio Network Temporary Identifier in the 5G NR physical layer, specifically designed for the Paging Early Indication (PEI) feature. An RNTI is essentially a number used to scramble and identify control channel messages intended for a specific UE or group of UEs. The PEI-RNTI is a group identifier, meaning a single PEI-RNTI value is shared by a configured set of UEs monitoring the same Paging Early Indication-Occasion (PEI-O). The gNB uses this PEI-RNTI to scramble the Cyclic Redundancy Check (CRC) bits of the Downlink Control Information (DCI) format that conveys the PEI signal.
Operationally, when a gNB needs to alert a group of UEs that paging messages will follow, it generates a DCI on the PDCCH during the PEI-O. This DCI is scrambled with the PEI-RNTI known to the target UE group. Each UE in that group, upon waking at its PEI-O, attempts to blindly decode PDCCH candidates using its assigned PEI-RNTI. The process is highly efficient: the UE only needs to perform a CRC check with the PEI-RNTI. If the CRC check passes, the DCI is successfully decoded, and the payload (a simple indicator) informs the UE to monitor the subsequent Paging Occasion. If no DCI with the matching PEI-RNTI is detected, the UE interprets this as a 'negative' PEI and returns to sleep.
The PEI-RNTI is a critical component that enables the group-based addressing required for efficient PEI signaling. Without such a shared identifier, the network would need to signal to each UE individually, negating the power-saving benefits. The value of the PEI-RNTI is derived from parameters provided to the UE during configuration, such as via System Information Block (SIB) or dedicated RRC signaling. Its use is confined to the physical and MAC layers for the specific purpose of PEI detection. This mechanism exemplifies the layered approach to power saving in 5G, where a minimal physical layer signal, efficiently addressed via a group RNTI, gates the more energy-intensive higher-layer paging procedure.
Purpose & Motivation
The PEI-RNTI was created to solve the problem of efficiently and reliably addressing multiple UEs with a single, low-overhead wake-up signal within the Paging Early Indication framework. Prior to this feature, paging was addressed using the P-RNTI, which alerted all UEs in a paging occasion to decode a subsequent paging message, but did not provide an early, low-power filtering step. The need for a dedicated identifier arose from the design goal of the PEI: to be an ultra-low-power signal that a UE can detect with minimal processing.
Using a shared group RNTI is a proven, efficient method in cellular systems for multicast control signaling. The PEI-RNTI enables this for the PEI, allowing one compact DCI message to serve an entire group of UEs simultaneously. This design minimizes control channel overhead and UE processing complexity compared to individual signaling. It was motivated by the stringent power consumption targets for 5G, especially for IoT. The PEI-RNTI provides the necessary addressing mechanism that makes the two-step paging process (PEI check followed by potential PO decode) feasible and power-efficient, directly contributing to extended battery life for devices that are paged infrequently.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (17 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the PEI-RNTI was not newly introduced; the provided Change Request titles and grounding context contain no mention of the PEI-RNTI, its function, or any related paging early indication procedures. The technical details from the context exclusively cover other RNTI types, MAC functions, and Random Access resource selection procedures.
In Release 16, the PEI-RNTI function was not introduced or modified; the provided Change Request titles and grounding context exclusively detail corrections to procedures involving other RNTI types like TC-RNTI, C-RNTI, and DCP, primarily concerning MAC layer prioritization, uplink grant handling in RAR, and resource overlapping for random access. The technical details from the context, such as Msg3, UL-SCH, and the selection of Random Access resources, pertain to existing MAC and RRC procedures but contain no information on a new PEI-RNTI feature for this release.
- Correction on prioritization between DCP and RAR to C-RNTI for CFRA BFR – Option 2 TS 38.321CR0794
- Corrections to SUL field in SRS Spatial Relation Indication MAC CE TS 38.321CR0890
- Correction on resource overlapping with grants addressed to TC-RNTI TS 38.321CR0927
- Correction for Uplink Grant Received in RAR and Addressed to Temporary C-RNTI TS 38.321CR1026
- Correction to 38.321 on priority handling of the UL grant addressed to TC-RNTI TS 38.321CR1145
- Correction of RV indication TS 38.321CR1207
In Release 17, the PEI-RNTI was newly introduced as a dedicated Radio Network Temporary Identifier to support the Paging Early Indication function. This allows the network to address UEs with a specific identifier to signal an upcoming paging occasion, enabling more efficient discontinuous reception (DRX). The UE monitors for this specific RNTI to determine if it needs to fully wake up to receive a subsequent paging message, thereby reducing power consumption.
- Introduction of PEI-RNTI TS 38.321CR1262
In Release 18, the PEI-RNTI function was not introduced or modified; the provided Change Request titles and grounding context from the 3GPP specifications contain no mention of PEI-RNTI, its procedures, or any related paging early indication enhancements. The listed corrections and clarifications for this release focus on other areas such as TCI state indication, power ramping, and PDCCH-order triggered random access. Therefore, based solely on the given materials, there were no new developments for PEI-RNTI in Release 18.
- Introduction of Cross-RRH TCI state switch indication for high speed train TS 38.321CR1706
- Correction on Power Ramping for early TA TS 38.321CR2111
- Clarification on PDCCH order triggered early RACH TS 38.321CR2115
- Correction on use of recommended of IAB-MT beam indication TS 38.321CR1902
- CR on TCI state indication of CORESET#0 TS 38.321CR1995
In Release 19, the PEI-RNTI function was not specifically mentioned as a new feature within the provided grounding context or the listed Change Request titles. The available details focus on MAC layer procedures, such as corrections for RO type indication in enhanced LTM MAC CEs and the selection of Random Access resources for various features including Msg1 repetition, RedCap, and eRedCap. Therefore, based solely on the provided materials, no new developments for PEI-RNTI in Release 19 can be described.
- Correction for RO type indication in (enhanced) LTM MAC CE TS 38.321CR2138
Explore further
Broader topics and technologies where PEI-RNTI plays a role.
Defining Specifications
3GPP specifications that define or reference PEI-RNTI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 38.321 vj00 | NR MAC Protocol Specification | Rel-19 |