Beyond Equal-Power Sparse NOMA: Two User Classes and Closed-Form Bounds on the Achievable Region.

Benjamin M Zaidel,Ori Shental,Shlomo Shamai (Shitz)

doi:10.3390/e24020227

Abstract

Non-orthogonal multiple access (NOMA) is a promising technology for future beyond-5G wireless networks, whose fundamental information-theoretic limits are yet to be fully explored. Considering regular sparse code-domain NOMA (with a fixed and finite number of orthogonal resources allocated to any designated user and vice versa), this paper extends previous results by the authors to a setting comprising two classes of users with different power constraints. Explicit rigorous closed-form analytical inner and outer bounds on the achievable rate (total class throughput) region in the large-system limit are derived and comparatively investigated in extreme-SNR regimes. The inner bound is based on the conditional vector entropy power inequality (EPI), while the outer bound relies on a recent strengthened version of the EPI. Valuable insights are provided into the potential performance gains of regular sparse NOMA in practically oriented settings, comprising, e.g., a combination of low-complexity devices and broadband users with higher transmit power capabilities, or combinations of cell-edge and cell-center users. The conditions for superior performance over dense code-domain NOMA (taking the form of randomly spread code-division multiple access), as well as a relatively small gap to the ultimate performance limits, are identified. The proposed bounds are also applicable for the analysis of interference networks, e.g., Wyner-type cellular models.

Highlights

Non-orthogonal multiple access (NOMA) is a key enabler in the design of future overloaded beyond-5G communication systems with many more designated users than available physical resources, precluding the conventional orthogonal multiple access (OMA) paradigm [1,2,3,4]
Potentially facilitates enhanced spectral efficiency with practical receiver implementation based on sparsity exploiting iterative message passing algorithms (MPAs), to the ones empowering the efficient decoding of low-density parity-check (LDPC) codes
The focus here is on overloaded settings (β1, β2 > 1), corresponding to use cases where NOMA is of particular interest, while noting that the bounds generally apply to underloaded regimes

Summary

Introduction

Non-orthogonal multiple access (NOMA) is a key enabler in the design of future overloaded beyond-5G communication systems with many more designated users than available physical resources, precluding the conventional orthogonal multiple access (OMA) paradigm [1,2,3,4] (see [5] for a very recent technology review). The main potential appeal of NOMA over OMA stems from either supporting more simultaneous users or, in lieu, facilitating higher user throughputs when orthogonality is practically unsustainable. Power-domain NOMA essentially relies on direct superposition of the transmitted signals, successive interference cancellation (SIC) at the receivers and appropriate power allocation to different users in order to achieve desired performance objectives [1,2,6,7]. Under the code-domain NOMA paradigm, the users’ signals are distinguished by different spreading signatures chosen to facilitate efficient multiuser detection (MUD) at the receivers (see, e.g., [2,8]). Relying on sparse spreading signatures, sparse NOMA potentially facilitates enhanced spectral efficiency with practical receiver implementation based on sparsity exploiting iterative message passing algorithms (MPAs), to the ones empowering the efficient decoding of low-density parity-check (LDPC) codes. Different designs of sparse spreading signatures and their impact on MUD error-rate performance are discussed, e.g., in [11,13,14] and references therein

Objectives

Results

Conclusion