R1-2508631
discussion
Waveform for 6GR air interface
From InterDigital
Summary
This InterDigital contribution to 3GPP RAN1 #123 proposes baseline waveforms for 6G Radio, advocating CP-OFDM only for downlink, CP-OFDM and DFT-s-OFDM for uplink with dynamic switching, and presents simulation results showing FDSS with spectrum extension provides up to 2.1 dB net gain over standard FDSS for UL DFT-s-OFDM PAPR reduction. The document contains 9 proposals and 4 observations across waveform selection, multi-layer DFT-s-OFDM evaluation methodology, and PAPR reduction techniques.
Position
InterDigital proposes restricting 6G downlink to CP-OFDM only, opposing any additional DL waveforms due to lack of PAPR benefits when frequency-domain multiplexing multiple UEs, scheduling restrictions from time-domain-only multiplexing, and large specification impact from creating two RATs. For uplink, they propose limiting waveforms to CP-OFDM and DFT-s-OFDM only, requiring dynamic waveform switching support from Day 1 for adaptive gNB selection based on channel conditions. They argue sensing waveforms belong in Agenda Item 11.14 rather than the communication waveform study in 11.3.1. For multi-layer DFT-s-OFDM evaluation, InterDigital requires gNB advanced MIMO receiver complexity comparison using ML or MMSE-SIC, sets multi-layer CP-OFDM with frequency selective precoding as the baseline, and mandates co-polarization UE antenna assumptions based on Rel-19 channel modeling findings that cross-polarized antennas are unrealistic for modern UE form factors. They present simulation results showing FDSS with spectrum extension achieves 0.7 to 2.1 dB net gain over FDSS alone for UL DFT-s-OFDM, with outer allocation gains exceeding inner allocation due to ACLR sensitivity at band edges.
Key proposals
- Proposal 1 (Sec 3): CP-OFDM is the only downlink waveform for 6GR; do not support additional DL waveforms
- Proposal 2 (Sec 3): CP-OFDM and DFT-s-OFDM are the only waveforms for uplink. Study enhancements for PAPR reduction for DFT-s-OFDM.
- Proposal 3 (Sec 3): Support dynamic waveform switching for the uplink for 6GR.
- Proposal 4 (Sec 3): Waveform for sensing is not covered in Agenda Item 11.3.1 and shall be studied separately in Agenda Item 11.14.
- Proposal 5 (Sec 4): Evaluation for multi-layer DFT-s-OFDM for UL should include gNB advanced MIMO receiver complexity (e.g., ML or MMSE-SIC).
- Proposal 6 (Sec 4): Baseline method for comparison of multi-layer DFT-s-OFDM for UL should be multi-layer CP-OFDM with frequency selective precoding
- Proposal 7 (Sec 4): MPR for multi-layer DFT-s-OFDM should be determined using link level simulation
- Proposal 8 (Sec 4): Co-polarization instead of cross-polarization should be assumed for UE antenna polarization when multi-layer DFT-s-OFDM is evaluated
- Proposal 9 (Sec 5.2): Study FDSS with spectrum extension as a potential candidate for uplink PAPR reduction for DFT-s-OFDM to support coverage enhancement for 6G