Double-Threshold-Based Massive Random Access Protocol for Heterogeneous MTC Networks

In this paper, we consider the uplink transmission of a heterogeneous MTC network with massive number of delay-insensitive terminals and URLLC terminals coexistence, and propose a novel double-threshold-based massive random access (DT-MRA) protocol. On the one hand, the proposed DT-MRA protocol allows partial delay-insensitive terminals temporarily preempting URLLC spectrum channels to alleviate the traffic overload, via adaptively tuning access control parameters including ACB factor and traffic offloading factor. On the other hand, a grant-free access mechanism with packet repetition is applied to support the stringent QoS requirements of URLLC. Then, we formulate an optimization problem to maximize the access throughput of delay-insensitive terminals, while satisfying the QoS requirements of each URLLC terminal. Based on the statistical traffic load information, an optimal access control strategy is also developed to solve this optimization problem. Simulation results validate the theoretical analyses and demonstrate the effectiveness of our proposed DT-MRA protocol, in terms of improving access throughput.