The increasing need for high data-rate transmissions over time- or frequency-selective fading channels has drawn attention to modulation schemes with high spectral efficiency such as QAM. With the aim of increasing the “diversity order” of the signal

Being an effective non-orthogonal multiple access (NOMA) technique, sparse code multiple access (SCMA) is promising for future wireless communication. Compared with orthogonal techniques, SCMA enjoys higher overloading tolerance and lower complexity

稀疏码多址 (SCMA) 是最近设计的一种扩展技术，其中 QAM 符号被映射到不同的 OFDMA 音调。基于码本的映射可以看作是一种扩频编码过程，其中整形增益有助于提高频谱效率并增强系统性能。本文基于 SCMA 编码方案，提出了一种联合多用户检测 (MUD) 和信道解码方法，应用了“turbo 原理”。与传统的分离检测和解码方案相比，turbo检测性能更好，增益更高，复杂度适中。在此之上，提出了一种改进方法，即在迭代之前修改外在信息。改进是基于信息的可靠性，保持可靠的信息并减少不可靠的信息。具体