User Clustering And Power Allocation In Massive MIMO-NOMA System

Communication is going on all the time and communication technology is improving day by day,the data traffic of wireless broadband communication services has exploded.The shortage of spectrum resources has become an urgent problem for 5G/6G communication systems.Massive Multiple-Input Multiple-Output(MIMO)antenna technology and a new generation of multiple access technology,non-orthogonal multiple access(Non-Orthogonal Multiple Access,NOMA)technologies have become effective technologies to improve spectrum efficiency and increase system capacity.With the increase in the number of access users,how to suppress mutual interference between users,reasonably allocate resources and control hardware costs has become a hotspot in the current massive MIMO-NOMA wireless communication system.Under the premise of ensuring the quality of user communication,this paper has carried out research on how to clustering and allocate power resources.The details are as follows:1)A low-complexity clustering algorithm is proposed to be applied to the downlink of massive MIMO-NOMA system.The chord distance is used as a criterion to measure the channel correlation,and the user with lower channel correlation is selected as the head user for each beam to suppress inter-beam interference,and the remaining users are allocated to each beam.The channel of the selected head user is used as the equivalent channel and the hybrid precoding technology is used to design the analog precoding and digital precoding.The proposed algorithm combined with hybrid precoding technology can effectively suppress inter-beam interference,increase the number of users that can be accommodated in the beam,and improve the spectrum efficiency of the system under the premise of using a small number of RF chains.2)Aiming at maximizing spectrum efficiency,a low-complexity power allocation algorithm is proposed.Using Lagrange's theorem,the original problem is transformed into a dual problem,and the optimal dual value and the optimal power value are obtained by solving.In the algorithm for solving the optimal dual value,the complexity of each iteration is reduced,thereby reducing the complexity of the entire algorithm.3)Aiming at the problem that the rate maximization scheme will cause the weak user rate to be lost.A power allocation algorithm that max-min the sum rate of the system,which is proposed to improve communication fairness.The objective function is nonlinear due to interference between the beams and within the beams.By rewriting the nonlinear constraints,the original objective function is converted into a linear problem.Then the optimal value and power value are obtained through the less complex dichotomy.The simulation results show that although the communication rate of the system is lost compared with the rate-maximizing scheme,the minimum rate of the system is effectively increased to ensure the rate performance of weak users,thereby improving the fairness of communication.