Conclusions and Future Research Directions for NOMA

This chapter is to conclude the book and also provide discussions for promising future research directions. Particularly, in this book, various important topics about multiple access techniques, including the fundamental limits of these multiple access techniques and their applications to practical communication systems, have been discussed. Since multiple access techniques for 5G wireless networks and beyond are still emerging research topics, there are still plenty of open problems. In particular, it is not clear how these multiple access techniques can be efficiently used together with conventional multiple access techniques, advanced physical layer technologies, as well as other communication systems other than cellular networks, and these challenges will be discussed in detail in this chapter.