R1-2600033
discussion
On PRACH and RACH procedure
From Nokia
Summary
Nokia's Tdoc R1-2600033 presents 21 proposals and 9 observations on 6G PRACH and RACH procedure design. The document addresses sequence selection, capacity enhancement, preamble formats for new frequency ranges, configuration scenarios (MRSS, NTN, SBFD), RACH procedure simplification, and AI/ML-based beam prediction for initial access.
Position
Nokia proposes Zadoff-Chu sequences for 6G PRACH preamble due to CAZAC property and frequency offset robustness, and refrains from sequences lacking good cross-correlation under timing errors. They propose 4-step RACH as the sole baseline procedure, with Msg3-based identification as baseline and Msg1-based identification restricted to limited use cases. For the 7 GHz frequency range, they require short PRACH formats based on 30 kHz SCS (baseline from NR) and long PRACH formats based on 5 kHz SCS. They propose supporting PRACH and PUxCH overlapping to enhance RACH capacity through increased time-domain allocations. They propose studying AI/ML-based Spatial-Domain Beam Prediction (BM-Case1) for coverage extension and PRACH attempt reduction, and Temporal-Domain Beam Prediction (BM-Case2) for improving Msg2/3/4 transmission/reception in 4-step RACH.
Key proposals
- Proposal 1 (Sec 2.1): RAN1 should consider Zadoff-Chu sequence for PRACH preamble.
- Proposal 3 (Sec 2.2): If RACH capacity is to be further enhanced in 6GR compared to NR, 6GR to consider a simple design by increasing time domain allocations.
- Proposal 4 (Sec 2.3): 6GR PRACH preamble format to have a structure having a CP, one or multiple symbols consecutively (no CP in between) and a guard period when applicable.
- Proposal 8 (Sec 2.4.1): RAN1 to study further the RACH design under MRSS scenario and to consider separate/dedicated RACH resources as starting point.
- Proposal 10 (Sec 2.4.2): RAN1 to prioritize a unified design for TN and NTN where feasible.
- Proposal 11 (Sec 2.4.3): In 6GR, RA support in SBFD should be designed such that it does not increase the complexity of basic RA operation in TDD.
- Proposal 13 (Sec 2.4.4): Study the simplification of the group-based mapping (group of SSBs mapped to a group of ROs).
- Proposal 15 (Sec 2.4.5): Support mechanism for time adaptation, including the possibility of allowing new RACH transmission on UL resources.
- Proposal 16 (Sec 3): Avoid multiple options for RACH procedure in 6GR and support 4-step RACH as baseline.
- Proposal 17 (Sec 3): Consider Msg3 based identification as a baseline. Restrict use Msg1 based identification to limited use cases.
- Proposal 18 (Sec 3): Support for repetitions for all messages for RACH procedure, e.g. Msg1, Msg2, Msg3, Msg4.
- Proposal 19 (Sec 4): RAN1 should consider studying AI/ML in initial access and RA procedures by fully reusing AIML models evaluated for Rel19 AIML beam management use cases (BM-Case1: Spatial-Domain DL Tx Beam Prediction and BM-Case2: Temporal-Domain DL Tx Beam Prediction).
- Proposal 20 (Sec 4.1): Study the application of AI/ML-based Spatial-Domain Beam Prediction (BM-Case1) in initial access and RA procedures.
- Proposal 21 (Sec 4.2): Study the application of AI/ML-based Temporal-Domain Beam Prediction (BM-Case2) in initial access and RA procedures.