Non orthogonal Multi User Superposition and Shared Access
This chapter addresses major technology aspects of non orthogonal multi user superposition transmission and shared access. The chapter describes key techniques: low density spreading (LDS) sparse code multiple access (SCMA) multi user shared access (MUSA) and pattern defined multiple access (PDMA) together with simulation results. For spectral efficiency improvement purposes, a macro coverage scenario is the suitable deployment environment for non orthogonal multi user transmission/access. Deploying non orthogonal multi user schemes in a macro setting can help to get both benefits of both of the technologies that will play an important role in significantly boosting the system capacity. The multiple access mechanism in the uplink of IS 95, code division multiple access (CDMA)2000 and Universal Mobile Terrestrial Services (UMTS) is indeed non orthogonal. One of the key scenarios for downlink non orthogonal multi user transmission is mobile broadband (MBB) in which the target is to maximize the downlink system capacity. Roughly, the schemes can be divided into two groups: direct superposition without Gray mapping restriction and superposition with Gray mapping.