Resource allocation for discrete rate multi-cell energy constrained communication networks

Radio frequency energy harvesting is a promising technique to extend the lifetime of wireless powered communication networks (WPCNs) due to its controllability. In this paper, we consider a novel discrete rate based multi-cell WPCN, where multiple hybrid access points (HAPs) transmit energy to the users and users harvest this energy for the information transmission by using a transmission rate selected from a finite set of discrete rate levels. We formulate an optimization problem to minimize the schedule length through optimal rate allocation and scheduling of the users while considering the traffic demand, energy causality and interference constraints. The problem is mixed integer non-linear programming problem. Initially, we investigate the problem for non-simultaneous and simultaneous transmission considering both predetermined and variable transmission rates. We propose optimal and heuristic algorithms for all these categories by using optimality analysis, Perron-Frobenius conditions and iterative improvement of the total schedule length. Then, for the general problem, we propose heuristic algorithm based on the maximization of the number of concurrently transmitting users within each time slot by considering the maximum allowed interference level of the users. Via extensive simulations, we demonstrate significant improvement in schedule length through rate selection and proper scheduling of concurrently transmitting users.