Abstract: Abstract： To solve the problem of high computational complexity in millimeter wave massive multiple-input multiple-output non-orthogonal multiple access （MIMO-NOMA） systems， a scheme of user clustering and power distribution is proposed to improve the spectral efficiency. Firstly， user clustering scheme based on cluster-head selection is improved， in which the threshold and the number of clusters are determined dynamically according to the real channel. The clustering result is more suitable for the actual situation， and users can get greater gain from the beams. Then power allocation is designed with the goal of maximizing the weighted sum of spectral efficiency and energy efficiency of the system and solved by an improved meta-heuristic algorithm. By introducing new vector components to Particle Swarm Optimization （PSO） algorithm and adding cosine perturbation， the algorithm can converge to the global optimal value more quickly. Sand Cat Swarm Optimization （SCSO） algorithm is integrated to make the algorithm more accurate. The simulation results show that compared with the existing algorithms， the spectral efficiency and energy efficiency of the proposed scheme are better than the traditional schemes， and it is more suitable for multi-user cases.

Key words: Key words： massive MIMO, non-orthogonal multiple access, user grouping, metaheuristic algorithm, power allocation