A New Design of Hybrid SIC for Improving Transmission Robustness in Uplink NOMA

Conventionally, it was thought that outage probability error floors are unavoidable in uplink non-orthogonal multiple access (NOMA) regardless which type of successive interference cancellation (SIC) is adopted. However, a recent work breaks such myths by introducing the concept of hybrid SIC, which dynamically chooses the decoding order according to the users’ channel conditions and quality of service requirements. However, there is still a limitation in this existing work that the error floors can only be avoidable under a stringent condition on users’ target rates. To this end, this letter proposes a new hybrid SIC scheme by exploiting the benefit of power control, which guarantees no error floor without any conditions on users’ target rates.

I. Introduction

Non-Orthogonal multiple access (NOMA) technique has received extensive attention in the past few years, due to its superior spectral efficiency and capability for realizing massive connectivity [1]–[5]. The key idea of NOMA is to allow multiple users access to one channel resource block simultaneously, which is strictly prohibited in conventional orthogonal multiple access (OMA). However, due to the channel sharing among users, NOMA can potentially suffer severe inter-user interference. To suppress the impact of inter-user interference, the most widely used method is successive interference cancellation (SIC), where the users’ signals are decoded in a successive manner [6].