Energy-Delay Tradeoff in Device-Assisted NOMA MEC Systems: A Matching-Based Algorithm

This paper develops a multi-helper non-orthogonal multiple access (NOMA)-enabled mobile edge computing (MEC) system, in order to support massive connectivity. To achieve a tradeoff between the energy consumption and delay, we introduce a novel performance metric, called energy-delay tradeoff, which is defined as the weighted sum of energy consumption and delay. The joint optimization of helper clustering, power allocation and task assignment is formulated as a mixed integer nonlinear programming problem with the aim of minimizing the energy-delay tradeoff. The formulated problem with coupled and 0-1 variables belongs to the NP-hard problem, which cannot be directly solved within polynomial time. To efficiently solve such a challenging problem, we first decouple it into a power allocation and task assignment (PATA) subproblem. Then, with the solution obtained from the PATA subproblem, we equivalently reformulate the original problem as a discrete helper clustering (DHC) problem. For the PATA subproblem, a successive convex approximation (SCA)-based algorithm is proposed. Then, based on the solution obtained from the PATA subproblem, we design a low-complexity matching-based clustering (MBC) algorithm to solve the DHC problem. Simulation results are provided to demonstrate the effectiveness of our proposed algorithm in the compromise of energy consumption and delay.