Optimal scheduling for full duplex wireless powered communication networks

According to recent Ericsson mobility report, 24.6 billion sensor nodes are expected to be installed by 2025. Increasing the lifetime of this massive battery-powered installation, efficient spectrum utilization and strict delay requirements are the major challenges. Low power transceivers with energy harvesting capability, intelligent medium access protocol and full-duplex (FD) communication can overcome these challenges. Therefore, we investigate a FD wireless powered communication network (WPCN), in which a hybrid access point transmits wireless energy by using radio frequency signals and users harvest this energy to transmit information. We consider minimum length scheduling problem (MLSP) and sum throughput maximization problem (STMP) subject to traffic demand, energy causality and maximum transmit power of the users for a continuous rate (CR), discrete rate (DR) and constant transmission rate models. The novel formulated optimization problems are non-convex and combinatorial in nature, thus, difficult to solve for the global optimum. As a solution strategy, we demonstrate that the power control problems (PCPs) and scheduling problems can be solved separately in the optimal solution. For CR-MLSP, we optimally solve the PCP by evaluating Karush-Kuhn-Tucker conditions. For the scheduling, we introduce a penalty function allowing reformulation of problem as a sum penalty minimization problem. Based on the characteristics of the penalty function and optimality analysis, we propose two polynomial-time heuristic algorithms and a reduced-complexity exact algorithm employing smart pruning techniques. Next, many WPCNs are expected to use low-power transceivers with finite discrete configurations, we consider a novel DR-MLSP, where users select a rate from a finite set of discrete-rate levels. We optimally solve the PCP by using the optimality conditions of minimum length scheduling (MLS) slot, which is defined as a slot of minimum transmission completion time while starting transmission at any time after the decision time. Then, for scheduling, we classify the problem based on whether the MLS slots of the users overlap over time. We present the optimal algorithm for non-overlapping slot scenario based on the allocation of MLS slots, and a polynomial-time heuristic algorithm for overlapping scenario by allocating the transmission slot to the user with earliest MLS slot. Besides, we consider a multi-cell WPCN with concurrent transmission of users for constant and continuous rate models. We solve the PCPs by proposing optimal algorithms based on the evaluation of Perron-Frobenius conditions and usage of bisection method for constant and continuous rate models, respectively. Then, the solutions of PCPs are used to solve the scheduling problems. For the constant rate scheduling problem, we propose a heuristic algorithm which aims at maximizing the allowable interference on each user within a concurrently transmitting set. For the CR scheduling problem, we define a penalty function representing the advantage of concurrent transmission over individual transmission of those users. Then, following the optimality analysis and demonstration of the equivalence between MLSP and minimization of the sum of penalties, we propose a heuristic algorithm which allocates the users concurrently to minimize the sum penalties over the schedule. Furthermore, we consider an on-off transmission scheme for a single hop and relay-based WPCN, in which users either transmit at constant power or remain silent. For single hop problem, we propose a polynomial-time optimal scheduling algorithm. For relay-based system, following an optimality analysis, we propose a heuristic algorithm that performs very close to the optimal solution. Finally, for the CR-STMP, the PCP is proven to be convex and solved optimally. For scheduling, based on the derived optimality conditions, we propose a fast heuristic algorithm, which performs very close-to-optimal solution. Then, we characterize a novel optimization framework for DR-STMP to determine the rate adaptation and transmission schedule. We investigate the characteristics of the solution and propose a polynomial time heuristic algorithm for rate adaptation and scheduling problem.