Joint Power Control and Routing in Multihop D2D Assisted Cellular Systems

This paper considers a cellular system with multihop device-to-device (D2D) communications to extend the coverage of a cell, for user equipment (UEs) experiencing service outage. The D2D system we consider is an inband underlay system. The target is to perform power control and routing to minimize the expended UE energy while satisfying the signal-to-noise-ratio (SNR) requirements on the downlink connections on every pre-allocated resource block (RB), signal-to-interference-plus-noise-ratio (SINR) requirements for every D2D sidelink connection on every pre-allocated RB, and a maximum allowable interference at the base-station (BS) receiver on all uplink frame RBs. An optimization problem is formulated that turns out to be a mixed integer non-linear program. We propose the generalized Benders decomposition which breaks down the formulation to a master sub-problem, an auxiliary sub-problem and a feasibility sub-problem. In this paper, we focus on finding efficient solution methods for the auxiliary sub-problem that is necessary for generating under-estimators to one of two types of Benders' cuts. These cut-off infeasible power allocations in a relaxed version of the master problem, and tighten the lower bounds on the optimal objective function value. Simulations are conducted to show how multihop D2D routing improves the cell coverage, by reducing the probability of service outage. The simulation results also show the effect of the requirements of SNR, SINR and interference at the BS on the expended UE energy.