R1-2601823
discussion
Discussion on NTN specific requirements and design for GNSS based operation
From Spreadtrum
Spreadtrum's prior position on
10.7.1
at
RAN1#124
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Proposes reusing 5G NTN legacy solutions as the starting point for UL frequency synchronization and UL timing advance maintenance. Requires a unified TN/NTN design for cell search procedure, coverage features, HARQ process number/HARQ-ACK feedback disable, maximum SSB index count (Lmax), and cell DTX/DRX mechanism. Proposes studying longer SSB periodicity (160ms or larger values) for NTN with limited simultaneously active beams, and proposes studying OCC-based UL capacity increase with OCC schemes, OCC length, and specific UL channels (PRACH, Msg3, CG-based SDT) in NTN first, applying conclusions to TN. Proposes studying TN energy-saving technologies first, then adapting results to NTN considering time/frequency synchronization, timing relationship, and beam hopping. Supports FDD and HD-FDD for 6G day-1 NTN.
Summary
Spreadtrum presents 12 proposals and 2 observations on 6G NTN design for GNSS-based operation, covering time-frequency synchronization, timing relationships, capacity improvements, beam management, and energy efficiency with a strong emphasis on unified TN/NTN designs.
Position
Spreadtrum proposes reusing 5G NTN solutions extensively, with GNSS-based operation as the baseline mechanism for UL time-frequency synchronization and 5GA NR NTN GNSS resilience outcomes as the starting point for GNSS-degraded and GNSS-free/GNSS-less operation. They prefer Option 1 for scheduling offsets, reusing the k_offset concept from NR. They propose studying longer SSB periodicity up to 160ms or larger values for initial access, and cell DTX/DRX mechanisms for beam hopping. They emphasize unified TN/NTN designs for cell search procedure, maximum SSB index count (Lmax), and energy-saving technologies, with the latter to be studied in TN first then adapted to NTN. They oppose TDD for NTN, supporting only FDD and HD-FDD in 6GR day-1 due to large and variable guard times in satellite scenarios.
Key proposals
- Observation 1 (Sec 2.1): For DL synchronization, robust DL initial synchronization performance can be achieved by 6GR sync signals (e.g., SSB) and no pre-compensation is needed on the network side.
- Proposal 1 (Sec 2.2): GNSS-based operation should be baseline mechanism for UL time-frequency synchronization and a unified design for GNSS-based, GNSS-degraded and GNSS-free/GNSS-less operation should be studied.
- Proposal 3 (Sec 3): On scheduling offsets, Option 1 can be supported and the legacy solution in 5G NTN can be reused.
- Proposal 4 (Sec 4.1): For 6GR NTN, larger HARQ process number and HARQ-ACK feedback disable can be considered for avoid reduction in peak data rates.
- Proposal 5 (Sec 4.2): For 6GR NTN, increasing UL capacity through OCC can be studied with aspects including OCC schemes, OCC length, UL channel(s) applied OCC (e.g., PRACH, Msg3, CG based SDT).
- Proposal 6 (Sec 6): Cell search procedure should be unified design for TN and NTN, which should be uniformly discussed in initial access section.
- Proposal 7 (Sec 7): Considering satellite with limited number of simultaneously active beams, longer periodicity (e.g., 160ms or larger values) of sync signal(s) for initial access in 6GR NTN can be studied.
- Proposal 8 (Sec 7): On beam hopping in NTN, cell DTX/DRX mechanism can be considered for RRC idle/inactive mode and RRC connected mode, which can be unified design for NTN and TN.
- Proposal 9 (Sec 7): On the maximum number of SSB indexes (i.e., Lmax), unified design for NTN and TN should be considered and it should be uniformly discussed in initial access section.
- Proposal 10 (Sec 8): Study signaling overhead in aspect of mobility management, scheduling, etc.
- Proposal 11 (Sec 9): Support FDD and HD-FDD in 6GR day-1.
- Proposal 12 (Sec 10): Energy-saving technologies (for UE and/or network) can be studied in the TN first, then adapted to NTN considering time/frequency synchronization, timing relationship, and beam hopping.