R1-2601826
discussion
Discussion on waveform and frame structure for ISAC
From Spreadtrum
Summary
This Spreadtrum/UNISOC contribution to 3GPP RAN1 #124bis discusses waveform and frame structure for 6G ISAC, presenting 13 proposals and 14 observations. The document argues for CP-OFDM and DFT-s-OFDM as baseline ISAC waveforms, proposes enhancements like extended CP/symbol duration and new SCS options for coverage improvement, and introduces the study of pulse waveforms, waveform characterization templates, and sensing performance metrics.
Position
Spreadtrum/UNISOC proposes CP-OFDM as the DL sensing waveform basis and both CP-OFDM and DFT-s-OFDM as UL sensing waveform bases, consistent with 5G NR communication waveform agreements. They propose studying OFDM-based waveform enhancements specifically targeting sensing coverage performance, including extended CP length, extended OFDM symbol duration, and larger/smaller SCS configurations, explicitly noting the inherent trade-off between SCS, range resolution, and velocity resolution. They propose studying the necessity and feasibility of pulse waveforms as an alternative for coverage enhancement, recommending OFDM-compatible generation methods to minimize specification impact, while arguing pulse waveforms are more naturally suited to monostatic sensing due to relaxed self-interference cancellation requirements. They recommend a structured waveform characterization template for comparative analysis and specify ambiguity function, PAPR, and OOBE/ACLR as key sensing performance metrics for evaluation, with contributions of waveform structure and sequence design to be separately analyzed.
Key proposals
- Proposal 1 (Sec 2.1): For DL sensing, CP-OFDM waveform as defined in 5G NR is supported as the basis. For UL sensing, CP-OFDM and DFT-s-OFDM waveforms as defined in 5G NR are supported as the basis, with other waveforms including DL DFT-s-OFDM not precluded for further study.
- Proposal 2 (Sec 2.2): OFDM-based waveform enhancement for ISAC can be considered to improve sensing coverage performance.
- Proposal 3 (Sec 2.2): At least the following enhancements for 6GR ISAC frame structure design should be studied: extended CP, extended OFDM symbol duration, larger/smaller SCS.
- Proposal 4 (Sec 2.3): The necessity and feasibility of pulse waveform for 6GR ISAC can be studied.
- Proposal 5 (Sec 2.4): For each proposed 6GR ISAC waveform, adopt a characterization table to collect waveform characterizations including name, description, applicable link direction, motivation/use case, key metrics, spec impact, MRSS compatibility, multiplexing/coexistence, and implementation impacts.
- Proposal 6 (Sec 2.5): At least the following performance metrics are recommended for 6GR ISAC waveform evaluation: ambiguity function, PAPR, OOBE/ACLR, with coordination with RAN4 needed.
- Proposal 7 (Sec 2.1): A unified waveform design is expected to support all agreed sensing use cases and sensing modes (presented as second Proposal 1 in original text).