R1-2600113
discussion
Discussion on 6GR PRACH and RACH procedure
From Spreadtrum
Summary
This document contains 15 proposals and 3 observations from Spreadtrum on 6G PRACH and RACH procedure design, advocating for a unified Day-1 framework that integrates NR features as baseline while natively supporting SBFD and addressing capacity, coverage, and multi-carrier enhancements.
Position
Spreadtrum proposes a unified and integrated PRACH/RACH framework from 6GR Day-1 to avoid the fragmentation and compatibility issues observed in NR Releases 16-20, where enhanced coverage features achieved limited commercial deployment. They require natively supporting random access in SBFD symbols rather than maintaining separate SBFD and non-SBFD procedures as in NR, specifically opposing the separate RO-to-SSB mapping configurations and independent power control parameters currently used for SBFD RO. They propose studying a joint coverage configuration and joint coverage request from UE spanning all related channels during random access, replacing NR's per-channel independent RSRP threshold configuration. They support reusing NR ZC sequences, NR short and long preamble formats, and NR SSB-RO association patterns as baselines, while proposing further study on RO-SSB mapping rules for PRACH repetition and SBFD/non-SBFD joint mapping. They propose removing the NR dependency where MSG3 and MSG4 HARQ-ACK PUCCH scheduling in SBFD symbols is conditional on MSG1 transmission via SBFD, advocating full independent scheduling.
Key proposals
- Proposal 1 (Sec 2.1): All necessary PRACH features should be identified and integrated into a unified random access framework from 6GR Day-1.
- Proposal 2 (Sec 2.2.2): To design the coverage features during initial access and random access, identify bottleneck DL and UL channels for diverse device types, use NR coverage features as starting point, and FFS coverage features applicable to all device types.
- Proposal 4 (Sec 2.2.3): For 6GR, random access procedure in SBFD symbols should be studied to be natively supported to establish an integrated random access mechanism to maximize uplink gains.
- Proposal 5 (Sec 2.2.4): NR ZC sequence can be reused for 6GR preamble sequence to avoid unnecessary research efforts.
- Proposal 6 (Sec 2.2.5): Support same and different SCS between 6GR PRACH and other channels/signals for a given band.
- Proposal 8 (Sec 2.2.6): NR one-to-one, one-to-more, and more-to-one SSB-RO associations are adopted as the baseline for 6GR.
- Proposal 9 (Sec 2.2.6): Besides legacy NR RO-SSB mapping, further study same or separate RO-SSB mapping rule for PRACH repetition, and separate or joint RO-SSB mapping for SBFD RO and non-SBFD RO.
- Proposal 10 (Sec 2.2.7): For PRACH power control in 6GR, legacy NR open-loop power control including power ramping can be a starting point.
- Proposal 11 (Sec 2.2.7): SBFD specific power control should be jointly considered together with non-SBFD power control in 6GR day 1.
- Proposal 12 (Sec 2.3): NR 4-step RACH should be supported as the baseline for 6GR; FFS 2-step RACH procedures with fallback mechanism.
- Proposal 13 (Sec 2.3): RACH procedure enhancement can be studied in 6GR day1, e.g., the scheduling of MSG3 and MSG4 HARQ-ACK PUCCH in SBFD symbols is independent of transmission of MSG1 via SBFD.
- Proposal 14 (Sec 2.3.1): Multi-carrier RACH procedures should be studied for 6GR initial access.
- Proposal 15 (Sec 2.3.2): Based on lessons from NR, PRACH resource adaptation should be studied in 6GR day1 covering time domain, frequency domain, spatial domain, deployments (single cell/carrier, multi cells/carriers/TRPs), and combinations.
- Proposal 3 (Sec 2.2.2): RAN1 can study a joint configuration to determine coverage level for all related channels during random access, and a joint coverage request from UE for all channels for 6GR.
- Proposal 7 (Sec 2.2.5): NR short and long preamble formats are adopted as a baseline for 6GR.