20 research outputs found
Multi-Dimensional Codebooks for Multiple Access Schemes
The sparse code multiple access (SCMA) scheme directly maps the incoming bits of several sources (users/streams) to complex multi-dimensional codewords selected from a specific predefined sparse codebook set. The codewords of all sources are then superimposed and exchanged. The shaping gain of the multi-dimensional constellation of SCMA leads to a better system performance. The decoderâs objective will be to separate the superimposed sparse codewords. Most existing works on SCMA decoders employ message passing algorithm (MPA) or one of its variations, or a combination of MPA and other methods. The system architecture is highlighted and its basic principles are presented. Then, an overview of main multi-dimensional constellations for SCMA systems will be provided. Afterwards, we will focus on how the SCMA codebooks are decoded and how their performance is evaluated and compared
A Tutorial on Decoding Techniques of Sparse Code Multiple Access
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
Design Low Complexity SCMA Codebook Using Arnoldâs Cat Map, Journal of Telecommunications and Information Technology, 2022, nr 4
In 5G wireless communications, sparse code multiple access (SCMA) â a multi-dimensional codebook based on a specific category of the non-orthogonal multiple access (NOMA) technique - enables many users to share non-orthogonal resource components with a low level of detection complexity. The multi-dimensional SCMA (MD-SCMA) codebook design presented in this study is based on the constellation rotation and interleaving method. Initially, a subset of the lattice Z 2 is used to form the mother constellationâs initial dimension. The first dimension is then rotated to produce other dimensions. Additionally, interleaving is employed for even dimensions to enhance fading channel performance. Arnoldâs chaotic cat map is proposed as the interleaving method to reduce computational complexity. Performance of the SCMA codebook based on interleaving is evaluated by comparing it with selected codebooks for SCMA multiplexing. The metrics used for performance evaluation purposes include bit error rate (BER), peak to average power ratio (PAPR), and minimum Euclidean distance (MED), as well as complexity. The results demonstrate that the suggested codebook with chaotic interleaving offers performance that is equivalent to that of the conventional codebook based on interleaving. It is characterized by lower MED and higher BER compared to computer-generated and 16-star QAM codebook design approaches, but its complexity is lower than that of the conventional codebook based on interleaving
Implementation of New Multiple Access Technique Encoder for 5G Wireless Telecomunication Networks
RĂSUMĂ Les exigences de la connectivitĂ© mobile massive de diffĂ©rents appareils et de diverses applications dĂ©terminent les besoins des prochaines gĂ©nĂ©rations de technologies mobiles (5G) afin de surmonter les demandes futures. L'expansion significative de la connectivitĂ© et de la densitĂ© du trafic caractĂ©risent les besoins de la cinquiĂšme gĂ©nĂ©ration de rĂ©seaux mobiles. Par consĂ©quent, pour la 5G, il est nĂ©cessaire d'avoir une densitĂ© de connectivitĂ© beaucoup plus Ă©levĂ©e et une plus grande
portée de mobilité, un débit beaucoup plus élevé et une latence beaucoup plus faible. En raison de l'exigence d'une connectivité massive, de nombreuses nouvelles technologies
doivent ĂȘtre amĂ©liorĂ©es: le codage des canaux, la technique d'accĂšs multiple, la modulation et la diversitĂ©, etc. Par consĂ©quent, compte tenu de l'environnement 5G, surcoĂ»t de signalisation et de la latence devrait ĂȘtre pris en compte [1]. En outre, l'application de la virtualisation des accĂšs sans fil (WAV) devrait Ă©galement ĂȘtre considĂ©rĂ©e et, par consĂ©quent, il est Ă©galement nĂ©cessaire de concevoir la plate-forme matĂ©rielle prenant en charge les nouvelles normes pour la mise en Ćuvre des Ă©metteurs-rĂ©cepteurs virtuels. L'une des nouvelles technologies possibles pour la 5G est l'accĂšs multiple pour amĂ©liorer
le débit. Par conséquent, au lieu d'OFDMA utilisé dans la norme LTE (4G), l'application d'une nouvelle technique d'accÚs multiple appelée Sparse Code Multiple Access (SCMA) est investiguée dans cette dissertation. SCMA est une nouvelle technique d'accÚs multiple non orthogonale du
domaine fréquentiel proposée pour améliorer l'efficacité spectrale de l'accÚs radio sans fil [2]. L'encodage SCMA est l'un des algorithmes les plus simples dans les techniques d'accÚs multiple qui offre l'opportunité d'expérimenter des méthodes génériques de mise en oeuvre. En outre, la nouvelle méthode d'accÚs multiple est supposée fournir un débit plus élevé. Le choix du codage
SCMA avec moins de complexitĂ© pourrait ĂȘtre une approche appropriĂ©e. La cible fixĂ©e pour cette recherche Ă©tait d'atteindre un dĂ©bit dâencodage de plus de 1 Gbps pour le codeur SCMA. Les implĂ©mentations de codage SCMA ont Ă©tĂ© effectuĂ©es Ă la fois en logiciel et en matĂ©riel
pour permettre de les comparer. Les implémentations logicielles ont été développées avec le langage de programmation C. Parmi plusieurs conceptions, la performance a été améliorée en utilisant différentes méthodes pour augmenter le parallélisme, diminuer la complexité de calcul et par conséquent le temps de traitement.----------ABSTRACT The demands of massive mobile connectivity of different devices and diverse applications
at the same time set requirments for next generations of mobile technology (5G). The significant expansion of connectivity and traffic density characterize the requirements of fifth generation mobile. Therefore, in 5G, there is a need to have much higher connectivity density, higher mobility ranges, much higher throughput, and much lower latency. In pursuance of the requirement of massive connectivity, numerous technologies must be
improved: channel coding, multiple access technique, modulation and diversity, etc. For instance,
with 5G, the cost of signaling overhead and latency should be taken into account [1]. Besides, applying wireless access virtualization (WAV) should be considered and there is also a need to have effective implementations supporting novel virtual transceiver. One of the possible new technologies for 5G is exploiting multiple access techniques to improve throughput. Therefore, instead of OFDMA in LTE (4G), applying a new multiple access
technique called Sparse Code Multiple Access (SCMA) is an approach considered in this dissertation. SCMA is a new frequency domain non-orthogonal multiple access technique proposed to improve spectral efficiency of wireless radio access [2]. SCMA encoding is one of the simplest
multiple access technique that offers an opportunity to experiment generic implementation methods. In addition, the new multiple access method is supposed to provide higher throughput, thus choosing SCMA encoding with less complexity could be an appropriate approach. The target
with SCMA was to achieve an encoding throughput of more that 1Gbps. SCMA encoding implementations were done both in software and hardware to allow comparing them. The software implementations were developed with the C programing language. Among several designs, the performance was improved by using different methods to increase
parallelism, decrease the computational complexity and consequently the processing time. The best achieved results with software implementations offer a 3.59 Gbps throughput, which is 3.5 times more that the target. For hardware implementation, high level synthesis was experimented. In order to do that, the C based functions and testbenches which were developed for software implementations, were
used as inputs to Vivado HLS
Sparse or Dense: A Comparative Study of Code-Domain NOMA Systems
This paper is focused on code-domain non-orthogonal multiple access (CD-NOMA), which is an emerging paradigm to support massive connectivity for future machine-type wireless networks. We take a comparative approach to study two types of overloaded CD-NOMA, i.e., sparse code multiple access (SCMA) and dense code multiple access (DCMA), which are distinctive from each other in terms of their codebooks having sparsity or not. By analysing their individual diversity orders (DO) in Rayleigh fading channels, it is found that DCMA can be designed with the aid of generalized sphere decoder (i.e., a nonlinear multiuser detector) to enjoy full DO which is equal to the maximum number of resource nodes in the system. This is in contrast to SCMA whose error rate suffers from limited DO equal to the codebook sparsity (i.e., the effective number of resource nodes occupied by each user). We conduct theoretical analysis for the codebook design criteria and propose to use generalized sphere decoder for DCMA detection. We numerically evaluate two types of multiple access schemes under â4 Ă 6â (i.e., six users communicate over four subcarriers) and â5 Ă 10â NOMA settings and reveal that DCMA gives rise to significantly improved error rate performance in Rayleigh fading channels, whilst having decoding complexity comparable to that of SCMA