R1-2601808
discussion
Discussion on 6GR PRACH and RACH procedure
From Spreadtrum
Spreadtrum's prior position on
10.5.1.2
at
RAN1#124
· AI-synthesized, paraphrased
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Proposes a unified and integrated PRACH/RACH framework from 6G Day-1 to avoid fragmentation observed in NR Releases 16-20, requiring natively supporting random access in SBFD symbols rather than maintaining separate SBFD and non-SBFD procedures. Specifically opposes the separate RO-to-SSB mapping configurations and independent power control parameters currently used for SBFD RO in NR. Proposes 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. Supports 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. Proposes 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.
Summary
Spreadtrum presents 2 observations and 17 proposals on 6G PRACH and RACH procedure design, arguing that NR features introduced after Rel-16 have seen limited deployment and advocating for a unified random access framework with all necessary features integrated from 6G Day-1.
Position
Spreadtrum proposes that all necessary PRACH features be integrated into a unified random access framework from 6GR Day-1, citing limited commercial deployment of post-Rel-16 NR features as justification. They propose studying PRACH capacity increases via RO configuration and SBFD rather than increasing the number of preambles per RO beyond 64. For preamble sequences, they prefer reusing NR ZC sequences and require a structured gap analysis process before considering any new sequence designs. They propose a joint configuration for coverage level determination across all random-access-related channels and a joint coverage request from the UE. They support native integration of SBFD into the random access procedure to avoid separate configurations, power control, and RO-to-SSB mapping for SBFD and non-SBFD ROs.
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 2.2.1): Study 6GR PRACH capacity for eMBB (400MHz, AI token traffic), massive IoT/LPWA (up to 10⁶ devices/km²), NTN/TN integration, and only necessary preamble partitioning.
- Proposal 4 (Sec 2.2.2): Design 6GR coverage features day1 by identifying bottleneck DL/UL channels, using NR coverage features as starting point, with coverage features applicable to all device types.
- Proposal 6 (Sec 2.2.3): Reuse NR ZC sequence for 6GR preamble to avoid unnecessary research efforts.
- Proposal 9 (Sec 2.2.4): Adopt NR short and long preamble formats as starting point; strive for a small set of necessary preamble formats.
- Proposal 11 (Sec 2.2.5): Study same or separate SSB-RO mapping rules for PRACH repetition, and separate or joint SSB-RO mapping for SBFD RO and non-SBFD RO.
- Proposal 13 (Sec 2.2.6): Jointly consider SBFD-specific power control together with non-SBFD power control in 6GR day 1.
- Proposal 14 (Sec 2.3): Support NR 4-step RACH as baseline for 6GR; FFS on 2-step RACH with fallback mechanism.
- Proposal 15 (Sec 2.3.1): Study native support of random access procedure in SBFD symbols to establish an integrated random access mechanism maximizing uplink gains.
- Proposal 16 (Sec 2.3.2): Study multi-carrier RACH procedures for 6GR initial access.
- Proposal 17 (Sec 2.3.3): Study PRACH resource adaptation in time, frequency, and spatial domains, including multi-cell/carrier/TRP deployments from 6GR day1.