Energy-Efficient Resource Allocation for Downlink Non-Orthogonal Multiple Access Network

Non-orthogonal multiple access (NOMA) is a promising technique for the fifth generation mobile communication due to its high spectral efficiency. By applying superposition coding and successive interference cancellation techniques at the receiver, multiple users can be multiplexed on the same subchannel in NOMA systems. Previous works focus on subchannel assignment and power allocation to achieve the maximization of sum rate; however, the energy-efficient resource allocation problem has not been well studied for NOMA systems. In this paper, we aim to optimize subchannel assignment and power allocation to maximize the energy efficiency for the downlink NOMA network. Assuming perfect knowledge of the channel state information at base station, we propose a low-complexity suboptimal algorithm, which includes energy-efficient subchannel assignment and power proportional factors determination for subchannel multiplexed users. We also propose a novel power allocation across subchannels to further maximize energy efficiency. Since both optimization problems are non-convex, difference of convex programming is used to transform and approximate the original non-convex problems to convex optimization problems. Solutions to the resulting optimization problems can be obtained by solving the convex sub-problems iteratively. Simulation results show that the NOMA system equipped with the proposed algorithms yields much better sum rate and energy efficiency performance than the conventional orthogonal frequency division multiple access scheme.

I. Introduction

In the fourth generation mobile communication systems such as long-term evolution (LTE) and LTE-Advanced [1], orthogonal frequency division multiple access (OFDMA) has been widely adopted to achieve higher data rate. The demand for mobile traffic data volume is expected to be 500-1,000 times larger in 2020 than that in 2010 [2]. To further meet overwhelming requirement of data rates, various new techniques have been proposed in recent years, and these techniques include massive multiple-input multiple output (MIMO) [3], millimeter wave communications [4], LTE-U [5], C-RAN [6], SON [7] and non-orthogonal multiple access (NOMA) [8]. Among them, NOMA takes advantage of spectrum efficiency by allowing multiple users to occupy the same subchannel, which is different from the resource allocation in OFDM systems [9]–[11]. By applying successive interference cancellation (SIC) in NOMA systems, superposition coded signal can be correctly decoded and demodulated at the receiver [12]–[15]. Therefore, NOMA has been well considered as a promising candidate for the next generation mobile communication systems.