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A novel multi-user grouping scheme for downlink non-orthogonal multiple access systems

Non-orthogonal multiple access (NOMA) is a promising technology for the fifth generation. However, the increasing number of multiplexed users brings two challenges. One is the computational complexity of existing grouping schemes increases rapidly. The other is the performance of multiplexed users deteriorates sharply. To deal with these challenges, we propose a novel multi-user grouping scheme with low-complexity to select several UEs for multiplexing. Moreover, a corresponding power allocation scheme is proposed to guarantee the performance of the multiplexed users. Simulation results show that the novel multi-user grouping scheme can reduce the computational complexity at the cost of user fairness in contrast to the full search method. Besides, the proposed power allocation scheme can improve the spectrum efficiency compared with the existing power allocation schemes in NOMA systems.