Energy efficiency maximization for NOMA backscatter systems

Abstract

Non-orthogonal multiple access (NOMA) and backscatter communication are two emerging technologies for low-power communication. In this thesis, we consider a NOMA backscatter system, where signals from two backscatter devices are multiplexed on a frequency resource block using NOMA in each time slot. Our objective is to maximize the average energy efficiency by optimizing backscatter device pairing, reflection coefficients of backscatter devices, and the transmit power of the reader. We formulate the average energy efficiency maximization problem subject to the minimum circuit power requirements of the backscatter devices and the transmit power constraint of the reader. The formulated problem is nonconvex. To obtain a suboptimal solution for this problem, we use alternating optimization technique and decompose the problem into two subproblems. The subproblems are solved by using fractional programming, Dinkelbach’s algorithm, and successive convex approximation method. We further extend the average energy efficiency maximization problem formulation by considering the minimum data rate requirements of backscatter devices. Simulation results show that our proposed algorithm converges quickly to a suboptimal solution. Our proposed algorithm increases the average energy efficiency of the system by 20% and 8% when compared with the fixed device pairing scheme and genetic algorithm, respectively. In addition to the average energy efficiency as the objective, we also study maximizing the spectral efficiency of NOMA backscatter system. Simulation results show that backscatter system with NOMA achieves a spectral efficiency which is 65% higher than that of the orthogonal multiple access (OMA) scheme.