Sparse Code Multiple Access (SCMA) is a multi-dimensional codebook based on a class of Non-Orthogonal Multiple Access (NOMA) to provide many users through non-orthogonal resource elements without detection complexity in 5G wireless communications. The codebook design is one of the main criteria in SCMA downlink systems. This paper proposes an efficient SCMA joint codebook design and assignment model to reduce the detection complexity and maximize the Minimum Euclidean Distance (MED) in Rayleigh fading channels. Initially, we express codebook assignment, which is allotted to group the highest priority subcarriers and then assign to the specific user using k-medoid clustering algorithm and codebook design (i.e., sparse mapping matrix and factor graph constellation design). The obtained mapping matrix with a factor graph uses four ring 32-Quadrature Amplitude Modulation (QAM) features of SCMA that carefully design the mother constellation points for each codebook. In particular, the 32-QAM mother constellation points are obtained for each codebook by phase rotation. In this manner, the codebook is designed without any detection complexity. Further, the Message Passing Algorithm (MPA) is used to reduce the multi-user interference in the receiver side. The experimental results depicts that the proposed SCMA codebook approach achieves low Bit Error Rate (BER) and High Spectral Efficiency (SE) performance comparing with existing known designs in Rayleigh channels.

稀疏代码多路访问（SCMA）是基于一类非正交多路访问（NOMA）的多维码本，可通过非正交资源元素为许多用户提供5G无线通信中的检测复杂性。码本设计是SCMA下行链路系统中的主要标准之一。本文提出了一种有效的SCMA联合码本设计和分配模型，以降低检测复杂度并最大化瑞利衰落信道中的最小欧几里得距离（MED）。最初，我们表示码本分配，分配给高优先级子载波分组，然后使用k-medoid聚类算法和码本设计（即稀疏映射矩阵和因子图星座设计）分配给特定用户。获得的带有因子图的映射矩阵使用SCMA的四个环32正交幅度调制（QAM）功能，这些功能为每个密码本精心设计了母星座点。特别地，通过相位旋转为每个码本获得32-QAM母星座点。以这种方式，码本被设计成没有任何检测复杂性。此外，消息传递算法（MPA）用于减少接收方的多用户干扰。实验结果表明，与瑞利信道中的现有已知设计相比，所提出的SCMA码本方法实现了低误码率（BER）和高频谱效率（SE）性能。通过相位旋转为每个码本获得32-QAM母星座点。以这种方式，码本被设计成没有任何检测复杂性。此外，消息传递算法（MPA）用于减少接收方的多用户干扰。实验结果表明，与瑞利信道中的现有已知设计相比，所提出的SCMA码本方法实现了低误码率（BER）和高频谱效率（SE）性能。通过相位旋转为每个码本获得32-QAM母星座点。以这种方式，码本被设计成没有任何检测复杂性。此外，消息传递算法（MPA）用于减少接收方的多用户干扰。实验结果表明，与瑞利信道中的现有已知设计相比，所提出的SCMA码本方法实现了低误码率（BER）和高频谱效率（SE）性能。