Next-Generation Multiple Access Based on NOMA With Power Level Modulation

To cope with the explosive traffic growth expected in next-generation wireless networks, it is necessary to design next-generation multiple access techniques that can provide higher spectral efficiency as well as larger-scale connectivity. As a promising candidate, power-domain non-orthogonal multiple access (NOMA) has been widely studied. In conventional power-domain NOMA, multiple users are multiplexed in the same time and frequency band with different preset power levels, which, however, may limit the spectral efficiency under practical finite alphabet inputs. Inspired by the concept of spatial modulation, we propose to solve this problem by encoding extra information bits into the power levels, and exploiting different signal constellations to help the receiver distinguish between them. To convey this idea, termed power selection (PS)-NOMA, clearly, we consider a simple downlink two-user NOMA system with finite input constellations. Assuming maximum-likelihood detection, we derive closed-form approximate bit error rate (BER) expressions for both users. Moreover, the two-user achievable rate region is also characterized. Simulation results verify the analysis and show that the proposed PS-NOMA can outperform conventional NOMA in terms of BER and achievable rate.

I. Introduction

Future wireless networks, such as beyond fifth-generation (B5G) or sixth-generation (6G) networks, are expected to support extremely high data rates and numerous users or nodes with various applications and services [1]. However, the conventional orthogonal access (OMA) schemes used in the previous wireless generations cannot meet these unprecedented demands, limiting the improvement of the overall spectral efficiency (SE). Against the background, non-orthogonal multiple access (NOMA) was proposed, which allows numerous users to share the same resource (e.g., a time/frequency resource block) and separate the users in power or code domains at the expense of additional receiver complexity [2]–[4]. In power-domain NOMA, users are typically multiplexed with different power levels by using superposition coding at the transmitter and are distinguished through successive interference cancellation (SIC) at the receiver [5]–[7]. Compared with OMA, NOMA has higher significant system throughput and greater fairness [8]–[11]. Due to these advantages, NOMA has been recognized as a key technology by the third-generation partnership project (3GPP) for future wireless networks [12].