R1-2508738
discussion
Modulation for 6GR air interface
From Huawei
Summary
Huawei presents a comprehensive technical case against adopting constellation shaping (both geometric and probabilistic) for 6G, documenting 73 observations and 13 proposals. The document argues that shaping gains observed in AWGN channels diminish or reverse in fading channels, while complexity (up to 100x LDPC decoding), throughput bottlenecks (~10x processing delay), and PAPR increases make shaping impractical; instead, Huawei proposes enhanced adaptive modulation and coding (E-AMC) which achieves up to 1.5dB gain with negligible additional complexity.
Position
Huawei presents a detailed technical case against introducing constellation shaping (geometric and probabilistic) in 6G, arguing that AWGN-optimized shaping parameters suffer substantial gain reduction or become losses in fading channels (e.g., CCDM loses 0.5dB in SISO and 0.8dB in rank-4 MIMO). They propose studying enhanced adaptive modulation and coding (E-AMC) as a superior alternative, demonstrating up to 1.5dB gain in fading conditions by jointly optimizing modulation order and code rate based on channel characteristics with almost no additional complexity. Huawei documents prohibitive complexity overheads: 2D-NUC demodulation is 14.4x LDPC decoding for 1024QAM, CCDM incurs ~10x processing delay over LDPC decoding, and reduced ML detection with 2D-NUC is 10-100x LDPC decoding complexity. They require that performance results in future 6G modulation studies must be reported together with transmitter/receiver complexity, latency impact, parallelism implementation, and storage requirements, and stress that RAN4 confirmation is needed for phase noise, EVM requirement, MPR/A-MPR under realistic PA models. Huawei also observes that both geometric and probabilistic shaping increase PAPR for DFT-s-OFDM, counteracting its power efficiency benefit.
Key proposals
- Proposal 1 (Sec: Modulation order in 6GR): Observations about the performance for higher order modulation should be made together with other aspects especially including the applicable scenarios, associated restrictions, and challenges, rather than observations solely on performance benefit. Full study should be performed before making decision on whether to introduce a higher modulation order for 6G.
- Proposal 2 (Sec: General principles for the study of joint coding and modulation): Apply the following rules for collecting results and for summarizing observations in the study of 6G modulation.
- Proposal 3 (Sec: General principles for the study of joint coding and modulation): The performance results should be reported together with other aspects in the agreement, including at least transmitter and receiver complexity, latency impact and parallelism implementation, and storage requirements.
- Proposal 5 (Sec: General principles for the study of joint coding and modulation): For fair comparison and consensus building, the performance gains concurrently with a transparent analysis of the corresponding transmitter and receiver complexity, storage overhead and latency impact shall be considered to draw observations.
- Proposal 7 (Sec: General principles for the study of joint coding and modulation): Adaptability of Modulation-Related Parameters with respect to the channel characteristic needs to be carefully studied and reported with respect to the feasibility and signalling overhead.
- Proposal 8 (Sec: Enhanced adaptive modulation and coding): Study enhanced adaptive modulation and coding (E-AMC) schemes to select the optimal MCS based on channel characteristics for performance improvement.
- Proposal 9 (Sec: PAPR/EVM impact): For shaping schemes, the factors including at least phase noise, EVM requirement, MPR or A-MPR increase under realistic PA model require RAN4 confirmation or inputs.
- Proposal 10 (Sec: Conclusion): Observations about the performance for higher order modulation should be made together with other aspects especially including the applicable scenarios, associated restrictions, and challenges, rather than observations solely on performance benefit. Full study should be performed before making decision on whether to introduce a higher modulation order for 6G.
- Proposal 11 (Sec: Conclusion): Apply the following rules for collecting results and for summarizing observations in the study of 6G modulation.
- Proposal 12 (Sec: Conclusion): The performance results should be reported together with other aspects in the agreement, including at least transmitter and receiver complexity, latency impact and parallelism implementation, and storage requirements.
- Proposal 13 (Sec: Conclusion): The template for collecting results should include columns of performance gains, transmitter and receiver complexity, storage overhead and latency impact.