R1-2509113
discussion
On modulation for 6G air interface
From Apple
Summary
This Apple contribution discusses 6G modulation design, presenting 4 Observations and 1 Proposal. It argues that higher-order QAM (4KQAM DL, 1KQAM UL) evaluation should depend on RAN4 progress due to RF impairment sensitivity, and provides preliminary simulation results comparing probability amplitude shaping (PAS) against uniform QAM across various MIMO configurations.
Position
Apple requires practical RF impairment modeling including phase noise, PA model, and IQ imbalance model for evaluating higher-order QAM. They propose that 4KQAM DL and 1KQAM UL evaluation in RAN1 should depend on RAN4 progress and request to avoid duplicate effort, noting that achieving necessary phase noise improvements for 1KQAM requires non-trivial RF power consumption increase without advanced baseband mitigation. They present a technical case that MIMO spatial layer increases using lower-order modulations provide a better trade-off between spectral efficiency and robustness than ultra-high modulation schemes. On modulation shaping, Apple presents preliminary evaluation results comparing Probability Amplitude Shaping (PAS) with CCDM against uniform QAM, showing performance varies significantly across MIMO configurations, with losses up to 2.2dB for 4x4 MIMO and gains up to 1.4dB for 4x6 MIMO.
Key proposals
- Observation 1 (Sec 2.1): Higher order QAM in DL and UL are sensitive to RF impairment. Practical RF impairment modeling including phase noise model, PA model and IQ imbalance model, are needed for the evaluation.
- Proposal 1 (Sec 2.1): To avoid duplicate effort, the evaluation of 4KQAM for DL and 1KQAM for UL should depend on RAN4 progress and request.
- Observation 2 (Sec 2.2.2): For one-layer 1x2 SIMO transmission over TDL-A channel, -0.7 to 0.4dB loss/gain is observed for different MCSs.
- Observation 3 (Sec 2.2.2): For two-layer MIMO transmission over TDL-A channel, -1.4dB to 0.5dB loss/gain is observed for different MCSs for 2x2 MIMO, while -1dB to 0.7dB gain was observed for 2x4 MIMO.
- Observation 4 (Sec 2.2.2): For four-layer MIMO transmission over TDL-A channel, -0.9dB to 2.2dB loss/gain is observed for different MCSs for 4x4 MIMO, while -1dB to 1.4dB gain was observed for 4x6 MIMO.