R1-2600062
discussion
Discussion on 6G Uplink WUS and Operation
From FUTUREWEI
Summary
This document from Futurewei discusses UL WUS operation and design for 6G network energy saving, presenting 10 observations and 3 proposals. It argues for extending on-demand Sync Signal/SIB1 to standalone cells and any RRC state, and proposes a light Sync Signal design for UL WUS configuration.
Position
Futurewei proposes maximizing 6G network energy saving by supporting UL WUS in any RRC state and in standalone cells/carriers, removing the 5G NR constraints that limited on-demand SSB to SCell operation and on-demand SIB1 to cells with an assisting Cell A. They recommend adopting Rel-19 UL-WUS non-standalone operation as a baseline when a supporting cell is available, and propose a new light Sync Signal design with sequence-based structure to indicate UL WUS configuration, beam/Sync Signal index, and LSBs of SFN. They argue that preconfigured UL WUS configuration limits network flexibility in Sync Signal placement, and that MIB-based configuration fails to reduce initial access latency under long Sync Signal periodicity. They further propose UL WUS occasion definitions that account for coarse UE timing synchronization and support both window-based (for long preambles) and one-to-one association (for short preambles) depending on timing information availability.
Key proposals
- Proposal 1 (Sec 2): For network energy saving maximization, support of UL WUS with long Sync Signal periodicity in any RRC state and in single (standalone) cell/carrier scenarios may be considered for on-demand request of Sync Signal(s) and SIB1.
- Proposal 2 (Sec 3.1): Consider adoption of Rel-19 UL-WUS non-standalone operation for on-demand request of SIB1 when a supporting cell (Cell A) is available.
- Proposal 3 (Sec 3.3): Consider adoption of a light Sync Signal with sequence-based indication of UL-WUS configuration, beam/Sync Signal index, and/or LSBs of SFN, and UL WUS design based on limited number of sequences and UL WUS listening occasions.
- Observation 1 (Sec 2): In 5G NR network energy saving, on-demand SSB was limited to SCell operation and on-demand SIB1 was limited to an NES cell using UL WUS configuration acquired from an assisting cell (Cell A).
- Observation 2 (Sec 3.2): If UL WUS configuration is fully predefined/preconfigured at the UE, the network's flexibility in placing the Sync Signal within the carrier bandwidth may be very limited.
- Observation 3 (Sec 3.2): If UL WUS configuration is obtained using MIB in PBCH of a Sync Signal, then on-demand Sync Signal may not be helpful in reducing UE's initial access latency when longer Sync Signal default periodicity is considered for network energy saving.
- Observation 4 (Sec 3.2): Using a light Sync Signal design with sequence based structure for indicating UL WUS configuration can offer the network's flexibility in placing the Sync Signal within the carrier bandwidth while helping in reducing UE's initial access latency when longer Sync Signal default periodicity is considered for network energy saving.
- Observation 5 (Sec 3.3): UL WUS configuration may include indication of time and/or frequency resources as offsets at least w.r.t. light Sync Signal for TDD frame structures, and/or UL WUS preamble(s) type/format for limited coverage scenarios.
- Observation 6 (Sec 3.3): If timing information is not available in the light Sync Signal, the UL WUS transmission occasion(s) can be defined as a window for long UL WUS preamble(s) format(s) or with one-to-one association for short UL WUS preamble(s) format(s).
- Observation 7 (Sec 3.3): If timing information is available in the light Sync Signal, the UL WUS transmission occasion(s) can be defined with many/one-to-one association from the light Sync Signal index for short and/or long UL WUS preamble(s) format(s).
- Observation 8 (Sec 3.3): If timing information is available in the light Sync Signal, UE can acquire/notify the BS of the serving beam using limited number of UL WUS preamble(s)/occasion(s), and BS can save energy by limiting on-demand Sync Signal/SIB1 transmissions to a subset of the beams.
- Observation 9 (Sec 3.3): A simple UL WUS design based on limited number of OFDM sequences and/or UL WUS transmission occasions can allow the BS to use a low power radio in no/low load scenarios or outside Cell DRX.
- Observation 10 (Sec 3.3): Support of UE triggered on-demand sync signal(s) to speed up cell/frequency search may require UE's use of a single light Sync Signal detection and UL WUS occasion(s) design that accounts for potential UE's coarse timing synchronization.