Non-orthogonal multiple-access based on superposition and three-index assignment in a Rayleigh fading channel

The throughput in wireless cells using orthogonal multiple-access schemes like OFDMA is limited due to the fact that a significant part of the approximately mutally orthogonal radio resources are for fairness reasons assigned to users with high pathloss channels and therefore used with only low spectral efficiency. In this paper we study a single-antenna multipleaccess scheme in a fading channel based on non-orthogonl superposition of the signals from at least two users on each of the mutually orthogonal radio resources and separation of the superimposed signals by non-linear multi-user detection based on successive interference cancellation. We propose a scheduling scheme based on solving a so-called three-index assignment problem. By pairing users with different path losses and assigning them in an optimal way to appropriate resources significant gains in cell throughput, cell-edge throughput and fairness are possible compared to the orthogonal (single-user per resource) case. The system performance with the proposed scheduling is significantly better than with random scheduling.