CG-SCMA Codebook Design Based on Maximized Euclidian Distance, Journal of Telecommunications and Information Technology, 2023, nr 1

Sparse code multiple access (SCMA) is a multi-dimensional codebook based on a class of non-orthogonal multiple access (NOMA) technologies enabling the delivery of non-orthogonal resource elements to numerous users in 5G wireless communications without increasing complexity. This paper proposes a computer-generated sparse code multiple access (CG-SCMA) technique, where the minimum Euclidian distance (MED) of a star 16-point quadrature amplitude modulation is maximized by CG-SCMA, thus creating a complex SCMA codebook based on optimizing the difference between the first and other radiuses over rotated constellations. To specify the most suitable values for this constellation, it is divided into four sub-constellations using trellis coded modulation (TCM) in an effort to optimize MED. The new codebook has four sub-constellations with MED values of 3.85, 2.26, 2.26, and 3.85, respectively. Application of the message passing algorithm (MPA) ensures low complexity of the decoding proces

Design Low Complexity SCMA Codebook Using Arnold’s Cat Map, Journal of Telecommunications and Information Technology, 2022, nr 4

In 5G wireless communications, sparse code multiple access (SCMA) – 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 constellation’s initial dimension. The first dimension is then rotated to produce other dimensions. Additionally, interleaving is employed for even dimensions to enhance fading channel performance. Arnold’s 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

Journal of Telecommunications and Information Technology

kwartalni

Rotation matrices for signal space diversity analysis and MC-CDMA versus SCMA performance and complexity comparison

Orientadores: Celso de Almeida, Henry Ramiro Carvajal MoraTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: A crescente necessidade por sistemas de comunicação sem fio que apresentem maior eficiência espectral e confiabilidade, tem norteado os estudos e as propostas tecnológicas futuras das comunicações. Temáticas como eficiência espectral, múltiplo acesso e algoritmos de detecção de sinais são muito importantes e fazem parte dos estudos propostos pelo 3GPP (Third Generation Partnership Project), para elaboração da quinta geração de sistemas móveis, 5G. Nesse sentido, a fim de colaborar com o futuro das comunicações, uma das vertentes desta tese apresenta contribuições na área de diversidade espacial de sinais (SSD - Signal Space Diversity), técnica essa que permite o aumento da ordem de diversidade do sistema, sem impactar na eficiência espectral do mesmo. A técnica SSD trabalha com constelações rotacionadas. Uma nova métrica de avaliação, denominada métrica K, será usada neste trabalho para a obtenção de parâmetros de rotação ótimos. Em uma das abordagens, serão propostas e avaliadas novas estruturas matriciais de rotação multidimensional. Uma comparação de desempenho, em termos da taxa de erro de bit (BER - Bit Error Rate) média destas matrizes propostas, com estruturas de rotação comumente encontradas na literatura será realizada. Em outra avaliação, por meio de simulação computacional, os parâmetros de rotação ótimos de matrizes de rotação ortogonais em cenários com um único usuário serão obtidos usando a métrica K. Os resultados mostram que os ângulos de rotação ótimos obtidos neste trabalho, apresentam melhor desempenho que os ângulos de rotação encontrados por meio da distância produto mínima (MPD - Minimum Distance Product), métrica essa comumente usada na literatura. Além disso, os resultados apontam que os ângulos de rotação ótimos variam de acordo com as configurações do sistema, sendo que, neste trabalho são avaliados diferentes ordens de modulação QAM, número de dimensões e quantidade de antenas usadas na recepção. Será também realizada uma análise em cenário multiusuário, com o objetivo de verificar o impacto no desempenho devido ao uso de diferentes parâmetros de rotação em cada um dos usuários. Expressões analíticas para auxiliar nessa avaliação serão apresentadas. Será verificado se os parâmetros de rotação encontrados para os cenários com um único usuário, podem ser utilizados por todos os usuários no cenário multiusuário, sem prejuízo de desempenho. Outra contribuição desta tese se refere à comparação realizada entre as técnicas de múltiplo acesso MC-CDMA (Multicarrier Code Division Multiple Access) e SCMA (Sparse Code Multiple Access), usando seus respectivos detectores multiusuários, MU-MLD (Multiuser Maximum Likelihood Detector) implementado via detecção esférica (SD - Sphere Detector) e MPA (Message Passing Algorithm). Nessa análise comparativa serão apresentadas curvas da BER média em função da razão sinal-ruído (SNR - Signal to Noise Ratio) em canais com desvanecimento. Esses resultados serão obtidos por meio de simulações de Monte Carlo. Serão também apresentados os resultados de complexidade dos detectores multiusuário, em termos do número de operações matemáticas, obtidos por meio de expressões analíticas e simulações. Nessas análises será considerado o enlace reverso de sistemas celulares sobrecarregados, ou seja, quando o número de usuários alocados no sistema é maior do que o número de recursos físicos disponíveis. Os resultados mostram que, em mesmas condições de eficiência espectral e sem o uso de códigos corretores de erros, a técnica MC-CDMA apresenta um melhor desempenho em relação à técnica SCMA e que o decodificador SD é menos complexo que o detector MPAAbstract: The growing necessity for wireless communication systems with greater spectral efficiency and reliability has been guiding the future communication technological proposals. Spectral efficiency, multiple access techniques and signal detection algorithms compose part of the 3GPP (Third Generation Partnership Project) research for the fifth generation of mobile communication systems, 5G. In order to cooperate with the communication development, this thesis presents contributions in the signal spatial diversity (SSD) area, technique that allows to increase the system diversity order without impact its spectral efficiency. The SSD technique uses rotated constellations. Thus, a new metric, named metric K, is used in this thesis in order to obtain the optimum rotation parameters for SSD systems. In addition, new multidimensional rotation matrices are proposed and evaluated in this work. A performance comparison, in terms of the mean bit error rate (BER), of these proposed rotation matrices with others rotation matrices commonly found in the literature is done. Employing the metric K, the optimum rotation parameters used in matrices are obtained by simulation, considering single user scenarios. The results show that the optimum rotation parameters obtained in this work present better performance compared to the rotation parameters obtained by the minimum product distance (MPD) metric, commonly used in the literature. Our analysis evidences that the optimum rotation parameters vary according to the system parameters, that is, the M-QAM modulation order, the number of dimensions and the number of antennas used at the receiver. Another analysis is done for a multiuser scenario. In this case, the performance impact due to the use of different rotation parameters for each user is evaluated. Matrix expressions to emulate the received signals in a multiuser scenario are also presented. Due to the high complexity to obtain the optimum rotation parameters for a multiuser scenario, we also evaluate if the single user optimum rotation parameters can be used by all the users in the multiuser scenario. Another thesis contribution is related to multicarrier code division multiple access (MC-CDMA) and sparse code multiple access (SCMA). Specifically, a performance comparison is carried out considering their respective multiuser detectors, that is the multiuser maximum likelihood detector (MU-MLD) implemented via sphere decoder (SD) for MC-CDMA and the message passing algorithm (MPA) for SCMA. The performance results are shown in terms of mean BER as a function of the signal to noise ratio (SNR) in fading channels, and they are obtained via Monte Carlo simulations. In addition, the multiuser detectors complexity, in terms of the mean number of mathematical operations, is obtained by simulation and also by analytics expressions. In these analysis, an overloaded uplink mobile system is considered, that is, the number of simultaneous active users is greater than the number of available physical resources. The results show that, in the same spectral efficiency conditions, the MC-CDMA technique presents better performance than SCMA technique and the SD multiuser decoder is less complex than the MPA detectorDoutoradoTelecomunicações e TelemáticaDoutora em Engenharia Elétric

Optimized SCMA Codebook Design by QAM Constellation Segmentation With Maximized MED

An optimized design of a sparse code multiple access (SCMA) codebook for uplink wireless communications is presented by dividing an optimized 16-point round quadrature amplitude modulation (QAM) into several subsets. The main goal of the scheme is to maximize the minimum Euclidean distance and thus reduces the collisions of the information bits on the resources. The final SCMA codebook is obtained with the mapping matrix, which indicates the sub-constellations generating by dividing the mother QAM constellation. Simulation results show that, in a Nakagami fading channel, the optimized SCMA scheme by the proposed design method achieves significantly performance gains approximately 1.0, 1.4, 2.5, 3.5, and 4.0 dB at bit error rate of $10^{-4}$ , respectively, when compared with those of an undivided 16-QAM constellation, a trellis code modulation (TCM) division, an original SCMA codebooks, a low-density signature (LDS), and an irregular LDS (IrLDS) schemes. In addition, at the signal-to-noise ratio ranging from 0 to 10 dB, the constellation constrained capacity of the scheme by the proposed method achieves more gains over those of the original SCMA, TCM, the undivided star-QAM, the LDS, and the IrLDS schemes. Thus, it can be combined with the grant-free random access mechanism to obtain rapid and low-cost access in next-generation wireless packet services and other applications