A Comparative Study of User Pairing Techniques of MIMO-NOMA System in different channel models

In 6G wireless communication systems, Nonorthogonal multiple access (NOMA) can solve the problem of extra consumption power and bandwidth to enhance the spectral-efficiency (SE) of the system. Multiple-users can share the same bandwidth by using user pairing techniques (UPT) which superimposes their signals with different power levels. Multiple-input multiple-output (MIMO) NOMA system can be used to improve the performance of systems, especially for massive internet of things (IOT) devices where a large number of devices need to be connected with low latency and high energy efficiency. Therefore, MIMO NOMA system is a promising technology for 6G internet of things. In this paper, the performance of different UPT in power-domain downlink MIMO-NOMA system at multi-scattering channel (MSC) and the Rayleigh fading channel (RFC) is studied. It notices that the enhancement of UPT is obvious at lower signal to noise ratio (SNR) in MSC rather than RFC. The UPT is compared at several condition of MSC with different number of antenna MIMO. The improvement of using UPT decreases, when the number of antennas decrease and the number of scatters increase. So, we can reduce the complexity of selecting suitable type of UPT at rich scattering channel and at simple MIMONOMA systems.