Energy Efficiency Maximization of Backscatter-Assisted Wireless-Powered MEC With User Cooperation

The integrated backscatter communication (BackCom) and active communication (AC) scheme can improve wireless-powered mobile edge computing (WPMEC) system performance in general single-user and multi-user scenarios. However, there is little research in the cooperation-assisted WPMEC scenario. In this article, we consider a cooperation-assisted WPMEC system consisting of a source node (SN), a helper and a hybrid access point (HAP) integrated with MEC servers. An innovative user cooperation (UC) scheme with the integrated BackCom and AC is proposed to enhance the system performance. As a relay, the helper can help the SN to transmit its computing tasks due to the poor communication link between the SN and the HAP. To be specific, we aim at maximizing the user energy efficiency (EE) by jointly optimizing the backscatter reflection coefficient for BackCom, the transmission power for AC, the system time and task optimization allocation while considering the minimum computation bits requirement, the channel capacity and energy constraints. Based on a fractional program, we first transform the EE maximization problem into an equivalent one (non-convex problem) and then transform this non-convex problem into a convex problem by exploiting variable substitution and convex optimization. In addition, semi-closed form expressions of the optimal solution are deduced. An energy efficiency maximization algorithm is proposed to solve this convex problem. Simulation results demonstrate that the proposed scheme significantly improves the user EE than the existing schemes.