Paging Early Indication with Paging Subgrouping

Description

PEIPS is a power-saving feature introduced in 3GPP Release 17 for 5G New Radio (NR). It operates by dividing UEs in a paging occasion into multiple subgroups. Before the full paging message is transmitted, the network sends a Paging Early Indication (PEI) signal in a specific PEI occasion. This PEI is a compact, low-complexity signal that indicates whether a paging message for a particular subgroup will follow in the subsequent paging occasion. The UE, configured with a specific subgroup ID, only needs to monitor the PEI for its subgroup. If the PEI indicates 'paging present' for its subgroup, the UE then wakes up its main receiver to decode the full Paging Downlink Control Information (DCI) and the paging message on the Physical Downlink Shared Channel (PDSCH). If the PEI indicates 'no paging' for its subgroup, the UE can immediately return to a deep sleep state, skipping the more power-intensive decoding of the full paging channel. The architecture involves coordination between the Access and Mobility Management Function (AMF) in the core network, which initiates paging, and the gNB in the RAN, which schedules and transmits the PEI and paging messages. The subgroup assignment is typically derived from the UE's 5G-S-TMSI, ensuring a deterministic mapping. This mechanism is crucial for managing paging load and is specified across RAN and core network protocols, including NGAP (38.413), XnAP (38.423), F1AP (38.473), and the NAS protocol (24.501).

Purpose & Motivation

PEIPS was created to address the critical challenge of power consumption for User Equipment (UE), especially for massive Machine-Type Communication (mMTC) devices and always-on mobile phones. In previous 5G releases, a UE in RRC_IDLE or RRC_INACTIVE state had to periodically wake up to monitor full paging occasions, which involves decoding the PDCCH for DCI format 1_0 scrambled with the P-RNTI. This process consumes significant battery power, even when no paging message is intended for that UE. The problem is exacerbated with the growth of IoT, where devices may need to operate for years on a single battery charge. PEIPS solves this by introducing a two-step filtering process. The lightweight PEI signal acts as a 'wake-up signal' only for a subset of UEs. This dramatically reduces the number of times a UE must fully activate its high-power radio components. The motivation stems from the industry's push for extreme energy efficiency in 5G-Advanced and beyond, enabling new use cases for low-power sensors and wearables while improving the battery life of smartphones. It directly tackles a key limitation of the legacy paging procedure where energy was wasted on decoding irrelevant paging information.