Joint power and subcarrier allocation for SWIPT in cognitive relay system

Abstract In this paper, we study power and subcarrier allocation in decode-and-forward (DF) cognitive relay network based on orthogonal frequency division multiple access (OFDMA) technology, in which power splitting (PS) is used for the secondary users (SUs) supporting simultaneous wireless information and the power transfer (SWIPT). We attempt to maximize the energy efficiency (EE) of the secondary system subject to the constraints of minimum system rate, maximum transmission power and minimum harvested energy. The optimal power allocation (OPA) algorithm is proposed to determine the optimal solution of relay transmission power, power splitting ratio and subcarrier allocation. To tackle the original non-convex optimization problem, the Dinkelbach method is used for fractional programming and the problem is decomposed into two solvable sub-problems. The Lagrangian dual algorithm is utilized to determine the optimal transmission power and the power splitting ratio. The Hungarian algorithm is then introduced to determine the optimal subcarrier allocation. Compared with some existing algorithms, the simulation results show that the proposed OPA scheme is able to achieve higher energy efficiency when certain communication quality is required.