PROBE: Reactive MCS Adaptation from Summarized HARQ Feedback for NR Sidelink Groupcast

초록

Featured Application An MCS adaptation rule for NR sidelink groupcast that operates on the summarized HARQ acknowledgment alone, requires no channel state information, and requires no modification to the sidelink standard.Abstract NR sidelink groupcast provides no group channel-quality report, yet one modulation and coding scheme (MCS) must serve every member. We propose PROBE, a reactive MCS adaptation scheme that operates directly on the summarized HARQ outcome. PROBE increases the MCS index by one after a group ACK and retreats by D after a group NACK. We show that, away from the index boundaries, this update has a zero-drift group-NACK probability = 1/(D + 1), which gives the retreat parameter a direct operating-point interpretation and provides a principled basis for selecting it from group-level feedback. We characterize BLER for MCS 0-28 with an NR SL-SCH coding chain and use the resulting curves throughout the evaluation. Across the evaluated group sizes, topologies, and transmission periods, PROBE remains within 1.26% of the per-condition best fixed retreat and improves goodput over the conventional 10%-target reference by 1.09-15.50 percentage points. PROBE also outperforms a feedback-matched discounted Thompson-sampling learner across the evaluated steady-state conditions. These results show that a constant-complexity controller driven only by summarized HARQ feedback can adapt the groupcast MCS without CSI or changes to the NR sidelink framework.

키워드