Priority-based Distributed Queuing Random Access Mechanism for mMTC/uRLLC Terminals Coexistence

For mMTC and uRLLC coexistence system, traditional random access techniques cannot meet the different requirements of the mixed traffic. To tackle this issue, in this paper, a novel priority based distributed queuing random access (PDQRA) mechanism is proposed for mMTC and uRLLC coexistence system. To meet the access delay requirement of uRLLC devices (UTDs), the preambles are divided into two groups. The first group is completely selected by partial UTDs, while the second group is shared by the mMTC devices (MTDs) and the rest of the UTDs. To evaluate the performance of the proposed mechanism, the access delay of devices is mathematically analyzed. Moreover, an optimization problem is formulated via jointly optimizing the preamble division ratio and selection probability of the preamble groups to minimize the access delay of MTDs while guaranteeing the delay requirement of the UTDs. Then, a low-complexity algorithm developed based on particle swarm optimization (PSO) is proposed to obtain the suboptimal solutions. Finally, numerical simulations are presented to verify the effectiveness of the proposed mechanism.