A Novel Grant-Free Random Access Scheme for mMTC

Grant-free (GF) random access is a promising technique to support massive machine-type communication (mMTC) systems. Due to the conflicts, the performance is degraded. The repeated transmission of packets reduces the probability of conflict. In this paper, we propose a novel GF random access scheme with retransmissions. An optimal preamble allocation method is proposed to determine the size of the retransmission preamble pool. Numerical simulations are performed to validate the theoretical analysis. The proposed scheme adapts to various mMTC scenarios.