Comparative Analytical Study of SCMA Detection Methods for PA Nonlinearity Mitigation.

Elie Sfeir,Georges Kaddoum,Rangeet Mitra,Vimal Bhatia

doi:10.3390/s21248408

Abstract

Non-orthogonal multiple access (NOMA) has emerged as a promising technology that allows for multiplexing several users over limited time-frequency resources. Among existing NOMA methods, sparse code multiple access (SCMA) is especially attractive; not only for its coding gain using suitable codebook design methodologies, but also for the guarantee of optimal detection using message passing algorithm (MPA). Despite SCMA’s benefits, the bit error rate (BER) performance of SCMA systems is known to degrade due to nonlinear power amplifiers at the transmitter. To mitigate this degradation, two types of detectors have recently emerged, namely, the Bussgang-based approaches and the reproducing kernel Hilbert space (RKHS)-based approaches. This paper presents analytical results on the error-floor of the Bussgang-based MPA, and compares it with a universally optimal RKHS-based MPA using random Fourier features (RFF). Although the Bussgang-based MPA is computationally simpler, it attains a higher BER floor compared to its RKHS-based counterpart. This error floor and the BER’s performance gap are quantified analytically and validated via computer simulations.

Highlights

Methods for power amplifier (PA) NonlinearityApart from PD-Non-orthogonal multiple access (NOMA), specific code-domain NOMA-based approaches, like sparse code multiple access (SCMA) have recently been found to be promising [6,7,8,9], as they allow for potential coding/shaping gains through codebook design, and enable near-optimal detection using message passing algorithm (MPA). Besides, SCMA is known for its robustness to error propagation
LaCIME, Génie Electrique, École De Technologie Supérieure, Montréal, QC H3C1K3, Canada; Abstract: Non-orthogonal multiple access (NOMA) has emerged as a promising technology that allows for multiplexing several users over limited time-frequency resources
Contributions: In this paper, we present rigorous analytical studies and insights on the optimality of the Bussgang-based message passing algorithm (MPA) for downlink sparse code multiple access (SCMA) with power amplifier (PA) impairments

Summary

Methods for PA Nonlinearity

Apart from PD-NOMA, specific code-domain NOMA-based approaches, like sparse code multiple access (SCMA) have recently been found to be promising [6,7,8,9], as they allow for potential coding/shaping gains through codebook design, and enable near-optimal detection using MPAs. Besides, SCMA is known for its robustness to error propagation. BER floor compared to the universally optimal RFF-based MPA, and the analytical results are presented to quantify the BER floor. These results are validated using computer simulations under different fading distributions. The quantification of this error floor could potentially allow for switching between detection methods in hardware-constrained IIoT environments, where meeting a specific QoS constraint with minimal computations is of paramount importance

System Model

Bussgang Decomposition-Based MPA

1: Initialization

Simulations

Conclusions