Low-Complexity Power Allocation in NOMA Systems With Imperfect SIC for Maximizing Weighted Sum-Rate

Xiaoming Wang,Qingmin Meng,Ruilu Chen,Youyun Xu

doi:10.1109/access.2019.2926757

Abstract

In this paper, we investigate the power allocation for maximizing weighted sum rate (WSR) in downlink multiple carriers non-orthogonal multiple access (MC-NOMA) systems with imperfect successive interference cancellation (SIC). We formulate the power allocation problem as a non-convex optimization problem with the total power constraint of all sub-channels while considering often-neglected issues of SIC error and power order constraints at users. First, we discuss that the optimization problem assuming receivers can perform perfect SIC, and we provide a concavity condition of the WSR maximization problem for the MC-NOMA system. When the concavity condition is not satisfied, a fractional quadratic transformation is used to overcome the difficulty of problem non-convexity. Based on the transformation, we propose an iterative power allocation algorithm. Then, we consider the SIC error and the power order constraints in the optimization problem and present a power allocation method with imperfect SIC. Moreover, for both the perfect and imperfect SIC, we derive some propositions of the optimal power allocation solution to the WSR maximization problem and propose a low-complexity power allocation algorithm based on these propositions. Finally, we provide a joint user scheduling and power allocation algorithm for maximizing the WSR. The simulation results illustrate that the proposed resource allocation methods have a better performance than the existing schemes.

Highlights

Non-multiple access (NOMA) has been recognized as a promising multiple access technique for the future wireless networks to meet the demands for high data-rates, low latency, and massive connectivity [1], [2]
We provide a concavity condition that should be satisfied by the weighting factors of users in multiple carriers non-orthogonal multiple access (MC-NOMA) systems
We first consider an ideal scenario assuming perfect successive interference cancelation (SIC) can be always realized at receivers. This ideal assumption is impractical, it is a basic assumption in most of the existing studies, in which we provide some insights for the design of MC-NOMA systems

Summary

Introduction

Non-multiple access (NOMA) has been recognized as a promising multiple access technique for the future wireless networks to meet the demands for high data-rates, low latency, and massive connectivity [1], [2]. By using the successive interference cancelation (SIC), NOMA can remove the co-channel interference among the users, to exploit the channel diversity more efficiently. Frequency resources, which is able to provide higher spectral efficiency and support more connections comparing with conventional orthogonal multiple access (OMA) techniques, such as orthogonal frequency division multiple access (OFDMA). The performance analyses of NOMA systems were given in [4]–[6].

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