Tomlinson-Harashima Precoding-Aided Multi-Antenna Non-Orthogonal Multiple Access

TL;DR

This paper explores the use of Tomlinson-Harashima Precoding in multi-antenna NOMA systems, proposing novel beam design algorithms that outperform existing methods in mitigating interference and improving system performance.

Contribution

It introduces two new beam design algorithms for THP-aided MISO-NOMA, enhancing interference mitigation and system capacity over traditional approaches.

Findings

Proposed algorithms outperform existing methods in simulations.

THP effectively eliminates inter-cluster interference.

Enhanced beam design space improves weak user performance.

Abstract

In this paper, Tomlinson-Harashima Precoding (THP) is considered for multi-user multiple-input single-output (MU-MISO) non-orthogonal multiple access (NOMA) donwlink. Under the hierarchical structure in which multiple clusters each with two users are formed and served in the spatial domain and users in each cluster are served in the power domain, THP is applied to eliminate the inter-cluster interference (ICI) to the strong users and enlarge the dimension of the beam design space for mitigation of ICI to weak users as compared to conventional zero-forcing (ZF) inter-cluster beamforming. With the enlarged beam design space, two beam design algorithms for THP-aided MISO-NOMA are proposed. The first is a greedy sequential beam design with user scheduling, and the second is the joint beam redesign and power allocation. The two design problems lead to non-convex optimization problems. An efficient algorithm is proposed to solve the non-convex optimization problems based on successive convex approximation (SCA). Numerical results show that the proposed user scheduling and two beam design methods based on THP yield noticeable gain over existing methods.