R1-2509110
discussion
Waveforms for 6GR air interface
From Apple
Summary
This Apple contribution presents 8 proposals and 6 observations across waveform design for 6G, focusing on low-PAPR enhancements to DFT-s-OFDM, opposition to DL DFT-s-OFDM, and multi-layer DFT-s-OFDM evaluation methodology.
Position
Apple proposes studying UL π/2-BPSK DFT-S-OFDM with GMSK approximation filters to achieve near constant envelope waveforms for coverage enhancement, demonstrating through Net Gain evaluations that GMSK approximation filters consistently outperform legacy 3-tap FDSS filters under ACLR 31 and ACLR 37 constraints. They require revisiting the PA model from R4-164542 and RF requirements to enable a high-power boost feature targeting 33 dBm output power similar to GSM handheld devices, and propose sending a liaison statement to RAN4 to evaluate maximum power boost and Tx power gain for sub-1dB PAPR waveforms. They oppose DFT-S-OFDM in the DL, presenting a technical case against it due to specification impact, separate handling of physical channels and signals, and unresolved multiplexing challenges. They support using Net Gain as the evaluation metric for multi-layer DFT-S-OFDM with 4G LTE 2-layer non-coherent precoding as baseline.
Key proposals
- Proposal 1 (Section 2.1): Details the motivations of Low PAPR waveforms for 6G in a table covering coverage enhancement, energy efficiency, and PA non-linearity mitigation for uplink.
- Proposal 2 (Section 2.2): To evaluate MPR or power gain, PA model and RF requirement should be revisited to support power boost feature in 6G, noting the existing PA model from R4-164542 may be insufficient.
- Proposal 3 (Section 2.3): Study UL π/2-BPSK DFT-S-OFDM with support for FDSS, FDSS-SE and GMSK approximation filters to reach near constant envelope waveform using transparent and non-transparent schemes.
- Proposal 4 (Section 2.4.2): Consider near constant envelope waveform and potential impact to RAN4 for example in terms of amount of power boost and associated RF requirement.
- Proposal 5 (Section 2.4.2): Study Transparent/non-Transparent scheme with the GMSK approximation filter to approximate constant envelope waveform with π/2-BPSK and DFT-S-OFDM for uplink coverage enhancement.
- Proposal 6 (Section 2.4.2): Send LS to RAN4, to inform RAN4 that near constant envelope waveform shall be considered for 6G, and request RAN4 to evaluate the PA model, RF requirements, maximum power boost, and Tx power gain of a near constant envelope (sub-1dB) waveforms.
- Proposal 7 (Section 3): Do not support DFT-S-OFDM in the DL, citing large specification impact, separate handling of physical channels and signals, multiplexing challenges, and unresolved use case clarification.
- Proposal 8 (Section 4): Use the Net Gain as Evaluation Metric for Multi-Layer DFT-S-OFDM, with baseline scheme being 2-layer DFT-S-OFDM with non-coherent precoding from 4G LTE.