Sparse code multiple access (SCMA) is a promising multiuser communication technique for the enabling of future massive machine-type networks. Unlike existing codebook design schemes assuming uniform power allocation, we present a novel class of SCMA codebooks which display power imbalance among different users for downlink transmission. Based on the Star-QAM mother constellation structure and with the aid of genetic algorithm, we optimize the minimum Euclidean distance (MED) and the minimum product distance (MPD) of the proposed codebooks. Numerical simulation results show that our proposed codebooks lead to significantly improved error rate performances over Gaussian channels and Rayleigh fading channels.

翻译：简单代码多重存取(SCMA)是一种有前途的多用户通信技术,可以促进未来的大型机器型网络。 与现有的代码手册设计方案不同,我们提出了一套新型的代码手册,其中显示不同用户在下行传输方面的力量不平衡。 根据Star-QAM母星座结构,并在遗传算法的帮助下,我们优化了拟议代码手册中最小的Euclidean距离(MED)和最低产品距离(MPD ) 。 数字模拟结果表明,我们提议的代码手册大大改进了高斯河和雷利河道的错误率性能。