Sparse Code Multiple Access (SCMA) is an enabling code-domain non-orthogonal multiple access (NOMA)scheme for massive connectivity and ultra low-latency in future machine-type communication networks. As an evolved variant of code division multiple access (CDMA), multiple users in SCMA are separated by assigning distinctive codebooks which display certain sparsity. At an SCMA receiver, efficient multiuser detection is carried out by employing the message passing algorithm (MPA) which exploits the sparsity of codebooks to achieve error rate performance approaching to that of the maximum likelihood receiver. Despite numerous research efforts on SCMA in recent years, a comprehensive and in-depth tutorial to SCMA is missing, to the best of our knowledge. To fill this gap and to stimulate more forthcoming research, we introduce the principles of SCMA encoding, codebook design, and MPA based decoding in a self-contained manner for layman researchers and engineers.

翻译：简单代码多重存取(SCMA)是未来机器型通信网络大规模连通和超低纬度的辅助代码-域域域非横向多存取(NOMA)方法。作为代码分多重存取(CDMA)的演进变异,SCMA的多个用户通过指定显示某些宽度的独特代码手册而分离。在SCMA接收器中,高效的多用户检测是通过利用信息传递算法(MPA)进行,该算法利用代码库的广度实现误差率性能接近最大可能性接收者。尽管近年来在SCMA方面做了许多研究,但根据我们的知识,缺少对SCMA的全面和深入的辅导。为了填补这一空白,并激励更近期的研究,我们引入了SCMA编码、代码设计以及以自成一体的方式为外行研究人员和工程师解码的MPA原则。