文档介绍：munications Magazine ? September 2015 74 0163-6804/15/$ ? 2015 IEEE Linglong Dai, Bichai Wang, and Zhaocheng Wang are with Tsinghua University. Yifei Yuan is with ZTE Corporation. Shuangfeng Han and Chih-Lin I are with China Mobile Research Institute. This work was supported in part by the Interna- tional Science & Tech- nology Cooperation Program of China (Grant No. 2015DFG12760), the National Natural Science Foundation of China (Grant Nos. 61571270 and 61201185), and the Beijing Natural Science Foundation (Grant No. 4142027).. 1 Note that “NOMA” is also used by NTT DoCo- Mo to refer to NOMA via power domain multi- plexing. I NTRODUCTION In the history of munications from the first generation (1G) to 4G, the multiple access scheme has been the key technology to distinguish different wireless systems. It is well known that frequency-division multiple access (FDMA) for 1G, time-division multiple access (TDMA) mostly for 2G, code-division multiple access (CDMA) for 3G, and orthogonal frequen- cy-division multiple access (OFDMA) for 4G are primarily orthogonal multiple access (OMA) schemes. In these conventional multiple access schemes, different users are allocated to orthog- onal resources in either the time, frequency, or code domain in order to avoid or alleviate inter- user interference. In this way, multiplexing gain can be achieved with plexity. However, the fast growt