Hybrid SIC-Aided Hybrid NOMA: A New Approach for Improving Energy Efficiency

Hybrid non-orthogonal multiple access (NOMA), which organically combines pure NOMA and conventional OMA, has recently received significant attention to be a promising multiple access framework for future wireless communication networks. However, most of the literatures on hybrid NOMA only consider fixed order of successive interference cancellation (SIC), namely FSIC, for the NOMA transmission phase of hybrid NOMA, resulting in limited performance. Differently, this paper aims to reveal the potential of applying hybrid SIC (HSIC) to improve the energy efficiency of hybrid NOMA. Specifically, a HSIC aided hybrid NOMA scheme is proposed, which can be treated as a simple add-on to the legacy orthogonal multiple access (OMA) based network. The proposed scheme offers some users (termed “opportunistic users”) to have more chances to transmit by transparently sharing legacy users’ time slots. For a fair comparison, a power reducing coefficient $\beta $ is introduced to ensure that the energy consumption of the proposed scheme is less than conventional OMA. Given $\beta $ , the probability for the event that the achievable rate of the proposed HSIC aided hybrid NOMA scheme cannot outperform its OMA counterpart is obtained in closed-form, by considering impact of user pairing. Furthermore, asymptotic analysis shows that the aforementioned probability can approach zero in the high SNR regime under some given conditions, which are compositely determined by the users’ transmit powers, primary user’s target data rate and $\beta $ , indicating that the energy efficiency of the proposed scheme is almost surely higher than that of OMA for these given conditions. Numerical results are presented to verify the analysis and also demonstrate the benefit of applying HSIC compared to FSIC.

I. Introduction

Multiple access techniques plays a vital role in each generation wireless communication networks. However, most of existing networks adopt orthogonal multiple access (OMA) techniques. OMA techniques can well mitigate inter-user interferences, but has limited performance in terms of throughput and connectivity. Under this background, non-orthogonal multiple access (NOMA) techniques has recently received significant research interest [1], [2], [3]. For example, International Mobile Telecommunications (IMT)-2030 Framework issued by the International Telecommunication Union (ITU) has recognized NOMA as a crucial component for 6G [4]. The advantage of NOMA compared to OMA is that channel resources are encouraged to be shared among users, which may result in higher rate and larger connectivity. Besides, it has been shown by the literature that NOMA is compatible with many advancing techniques such as integrated sensing and communications (ISAC) [5], fluid antenna systems (FAS) [6], reconfigurable intelligent surface (RIS) networks [7], [8], semantic communications [9], non-terrestrial networks (NTN) [10] and so on.