R1-2600027
discussion
On remaining aspects of waveform for 6GR
From Nokia
Summary
Nokia's R1-2600027 presents 18 proposals and 15 observations on 6G waveform, arguing for 5G NR CP-OFDM/DFT-s-OFDM as baseline with targeted enhancements while strongly deprioritizing DL DFT-s-OFDM and Zak-OTFS studies due to technical limitations and complexity concerns.
Position
Nokia proposes CP-OFDM and DFT-s-OFDM as defined in 5G NR as the supported baseline communication waveforms for 6G downlink and uplink respectively, with CP-OFDM for all layers and DFT-s-OFDM restricted to single-layer UL. They present a technical case against DL DFT-s-OFDM, arguing its PAPR advantage is neutralized by transparent PAPR reduction techniques already in deployed base stations, while introducing significant limitations including contiguous frequency allocation requirements, reduced SU/MU-MIMO precoding flexibility, and multi-RAT/MRSS incompatibility in FR1. They oppose studying Zak-OTFS, presenting simulation evidence that CP-OFDM outperforms it with realistic channel estimation and asserting its claimed benefits apply only to atypical propagation conditions. For UL coverage enhancement, they support FDSS and FDSS-SE with transparent filtering, propose PC2 high power class as baseline, and require DWS via DCI from the first 6G release.
Key proposals
- Proposal 1 (Sec 2.1): CP-OFDM waveform as defined in 5G NR is supported for communications in 6G downlink, with enhancements/modifications studied as potential additions and DFT-s-OFDM or other OFDM-based waveforms studied as potential additional waveforms.
- Proposal 2 (Sec 2.1): CP-OFDM and DFT-s-OFDM waveforms as defined in 5G NR are supported for communications in 6G uplink, with enhancements/modifications studied as potential additions and other OFDM-based waveforms not precluded.
- Proposal 3 (Sec 2.3.1): RAN1 to deprioritize DFT-s-OFDM study for DL due to comparable PAPR to CP-OFDM with transparent reduction techniques, no meaningful NES or coverage gain, higher baseband complexity, link performance degradation, and significant design limitations.
- Proposal 4 (Sec 2.3.2): RAN1 to deprioritize studying Zak-OTFS because CP-OFDM outperforms it with realistic assumptions and channel estimation, it provides benefit mainly in atypical propagation conditions, and introduces major system change and additional complexity.
- Proposal 8 (Sec 2.4): Frequency Domain Spectrum shaping (FDSS) and FDSS with spectrum extension (FDSS-SE) are supported in 6G Radio.
- Proposal 11 (Sec 2.4): Dynamic waveform switching using DCI is introduced to 6G in the first release.
- Proposal 14 (Sec 2.5): RAN1 to consider baseline reference scenario for multi-layer waveforms study including 5G NR UL MIMO codebooks, CP-OFDM for all layers & DFT-s-OFDM for single layer, fully coherent UE capability, DWS rel-18 enabled, and at least rel-16 full power mode(s).
- Proposal 15 (Sec 2.5): For multi-layer DFT-s-OFDM study, RAN1 to consider cell average throughput gain/loss and cell edge throughput (5%-percentile) gain/loss relative to 5G NR baseline reference.
- Proposal 17 (Sec 2.5.2): Support CP-OFDM in uplink for all number of layers and all UE coherence capabilities, at least for non-power limited UEs where DFT-s-OFDM potential power gain cannot be exploited.
- Proposal 18 (Sec 2.5.2): Support DFT-s-OFDM in uplink for single layer transmission due to its advantage for power limited UEs; potential for more than 1 layer needs further justification.
- Proposal 5 (Sec 2.4): Proposed low PAPR methods are compared using net gains and assuming similar spectral efficiency and bandwidth for each compared method and used baseline.
- Proposal 7 (Sec 2.4): Transparent filtering approach (receiver does not need to be aware of the used filter parameters) is assumed for FDSS and FDSS-SE in 6G Radio.
- Proposal 9 (Sec 2.4): High power class should be the baseline for 6G due to significant enhancement in coverage.
- Proposal 10 (Sec 2.4): Power boosting features such as the ones specified in NR should be part of the baseline for 6G.
- Proposal 13 (Sec 2.5): Low PAPR waveform study for multi-layers UL transmission in 6G needs to consider at least fully coherent and partially coherent UEs.