Power-Collision-Based 2-Shot Grant-Free NOMA with Cross-Slot SIC for mMTC

This paper proposes a retransmission or 2-shot method using the cross-slot SIC for the grant-free power-domain non-orthogonal multiple access (GF-NOMA) in the massive machine-type communications (mMTC). The proposed method allows only the users experiencing power collisions to retransmit their packets in a quasi-coordinated fashion by order of IDs of pilot sequences. Our second-shot mechanism enhances the impacts of cross-slot SIC to recover packet errors in the first transmission due to power collisions. Our simulation results highlight that the proposed method provides 32% higher throughput than the baseline method retransmitting all the error packets.