Martingales-Based Energy-Efficient D-ALOHA Algorithms for MTC Networks With Delay-Insensitive/URLLC Terminals Co-Existence

One of the key features in machine type communications (MTCs), especially for MTCs embracing ultrareliable and low latency communications (URLLCs), is the short packet transmission with finite block-length. Both feature of short packet transmissions and requirement on supporting low latency communications or URLLCs pose challenges to radio access design for MTC networks in fifth generation. In this paper, for the MTC networks with delay-insensitive/URLLC terminals co-existence scenarios, we propose the energy-efficient differentiated ALOHA (D-ALOHA) random access algorithms, which simultaneously achieve energy efficient and satisfy the requirements of URLLC in a distributed mode. First, we abstract a service model of an MTC terminal with joint consideration of the achievable rate for short packet transmissions, the truncated channel inverse scheme, and the D-ALOHA scheme. Based on the formulated service model, then we derive the martingale parameters of service process for each terminal, and analyze the delay-bound violation probability of a terminal via the optimum stopping theory for martingales. The martingales-based delay analysis is verified via simulations. Finally, we formulate our energy-efficient D-ALOHA algorithm as an energy efficiency maximization problem with martingales-based statistical delayquality of service constraints, and the resultant optimization problem is solved by the invasive weed optimization-differential evolution (IWO-DE) algorithm. Furthermore, we propose a suboptimal but low-complexity energy-efficient D-ALOHA scheme, which neglects the distance difference of delay-insensitive terminals, such that the same access probability is imposed on these terminals for reducing the computational complexity of IWO-DE. Simulation results demonstrate that the energy efficiency performance of our D-ALOHA algorithms is favorite, and our D-ALOHA can achieve URLLCs in case of short duration of a slot.