A Tutorial on Decoding Techniques of Sparse Code Multiple Access

Abstract

Sparse Code Multiple Access (SCMA) is a disruptive code-domain non-orthogonal multiple access (NOMA) scheme to enable future massive machine-type communication networks. As an evolved variant of code division multiple access (CDMA), multiple users in SCMA are separated by assigning distinctive sparse codebooks (CBs). Efficient multiuser detection is carried out at the receiver by employing the message passing algorithm (MPA) that exploits the sparsity of CBs to achieve error performance approaching to that of the maximum likelihood receiver. In spite of numerous research efforts in recent years, a comprehensive one-stop tutorial of SCMA covering the background, the basic principles, and new advances, is still missing, to the best of our knowledge. To fill this gap and to stimulate more forthcoming research, we provide a holistic introduction to the principles of SCMA encoding, CB design, and MPA based decoding in a self-contained manner. As an ambitious paper aiming to push the limits of SCMA, we present a survey of advanced decoding techniques with brief algorithmic descriptions as well as several promising directions.

Asynchronous multiuser detection for sparse code multiple access with unknown delays: A compressed sensing approach

“…The linear model (7) captures the behavior of the asynchronous SCMA system on RE k over a transmission frame as a noisy sum of delayed signals. Our goal is to use this model to estimate the delays d j for the users sharing RE k. However, in (7), the unknown delays are represented by the structure of the symbol matrix, namely, by the number of zeros that precede the first nonzero symbol in each column. Thus, in its current form, the linear model is composed of an unknown matrix multiplied by a known vector.…”

“…Thus, many works have focused on developing SCMA decoding schemes with decreased complexity. A recent and thorough survey discussing these methods, among other aspects of SCMA, is provided by Rebhi et al 6 Additionally, another recent survey focusing specifically on decoding methods for SCMA is provided by Chaturvedi et al 7 Here, we outline some notable schemes that are considered in finer detail in the aforementioned surveys.…”

Constellation Partitioning-Based Scma Codebook Design

“…The standard of using orthogonal resources has seen a shift due to new technology, such as the Internet of Things (IoT), massive machine type communication (mMTC), ultra-reliable, and low latency communication (URLLC). The 5G networks require the ability to serve a massive amount of connections, with the Third Generation Partnership Project (3GPP) setting diverse requirements arising from identified problem areas, such as latency and throughput [1][2][3][4]. These requirements have prompted the research of non-orthogonal multiple access (NOMA) techniques instead of the traditional orthogonal multiple access (OMA) methods in [4][5][6].…”

CG-SCMA Codebook Design Based on Maximized Euclidian Distance

“…The message passing algorithm (MPA), making use of the sparsity of CBs to produce error-free performance approaching the maximum potential of the receiver, is used at the receiver to perform efficient multiuser identification. To the best of our knowledge, despite multiple research initiatives undertaken in recent years, a thorough tutorial of SCMA covering the background, its fundamental concepts and new advancements, is still to be revealed [3].…”