Limited search sphere decoder and adaptive detector for NOMA with SU-MIMO

Non-orthogonal multiple access (NOMA), which improves spectrum efficiency and system throughput, is one of the promising radio access techniques for 5G. In this paper, NOMA is combined with spatial multiplexing multiple-input multiple-output (MIMO) technology for enhanced spectral efficiency. In multi-stream MIMO signaling, we considered stronger far user's MIMO signal when detecting the near user's MIMO signal. To lower computational complexity, we proposed a limited sphere decoder search method. In addition, an adaptive NOMA-MIMO detector, which switched between detecting methods according to MCS, power factor and SNR, was also presented.