Abstract: In order to solve the problem of energy shortage and limited computing power of Internet of Things (IoT) nodes, In this paper, non-orthogonal Multiple Access (NOMA) technology is introduced into a backscatter communication (BackCom) assisted wireless powered mobile edge computing (MEC) network to construct a BackCom assisted wireless powered NOMA-MEC network.This network can not only take advantage of the combination of BackCom and active transmission, but also take advantage of the technical advantages of NOMA to further improve the spectrum efficiency of the network. In order to ensure the fairness of the computation bits at IoT nodes, based on the max-min criterion, this paper aims to maximize the computation bits at the worst IoT nodes. By jointly optimizing the energy harvesting time, backscattering time, backscattering coefficient, NOMA transmission time, NOMA transmit power, local computation frequency and local computation time of IoT nodes, a non-convex optimization problem is formulated to satisfy the constraints of energy causality and computation power. Then, the optimal local computation time of each node is obtained by proof by contradiction and substituted into the original problem. Then, the backscattering coefficient and backscattering time of IoT nodes are decoupled by means of the auxiliary variable method. As for the co-channel interference introduced by the NOMA technology, we replace the complex expression of the offloading bits with its low bound to achieve a more simple sub-problem and convert the sub-problem to a convex one by means of the variable substitution method. Finally, by optimizing the above sub-problem,we propose a corresponding iterative algorithm to achieve the optimal solution. The simulation results verify the fast convergence and accuracy of the proposed algorithm, and show that compared with the existing schemes, the proposed scheme can better guarantee the fairness of the computation bits among the IoT nodes in the investigated network.

Key words: BackCom, Wireless Powered Communication, NOMA, MEC, Fairness