| With the advancement of mobile communication,from the first generation(1G)of mobile communication technology to achieve analog voice communication,to the fourth generation(4G)of mobile communication technology to achieve local high-speed internet access,and now the fifth generation(5G)of mobile communication technology achieves the interconnection of everything anytime and anywhere,high-speed,high-capacity,and low-latency services through millimeter wave(mm Wave).In this paper,it mainly focuses on improvement of spectrum efficiency under 5G.Compare to 4G,5G mainly uses high-frequency millimeter waves.And due to its shorter wavelength and the use of more antennas,it can better concentrate energy to target users.However,the more antennas there are,the narrower the beam width,and the beam can only be directed in one direction so that the number of users that can be served at the same time is limited.In order to further improve spectrum efficiency,the method to improve spectrum efficiency in this paper is to convert a single beam into multi beams so that it can serve multiple users more accurately and improve the fairness between users.This paper studys the characteristics of the millimeter wave channel,and then uses the extended Saleh-Valenzuela(SV)channel to model and studys the digital precoding design according to its characteristics at the same time.The approximate zero-forcing(ZF)digital precoding based on strong user and the approximate zero-forcing digital precoding based on singular value decomposition(SVD)equivalent channel are designed,and the performance advantage of the approximate zero-forcing digital precoding based on the strong user equivalent channel are verified through system simulations.It studies user grouping and several multi-beam methods,such as beam splitting,beam superposition,and weighted beam superposition that combines the advantages of the other two methods.Through the beam response gain and the system performance simulation simulations,it is verified that compared to other multi-beam methods,the beam superposition after the coefficient weighting,the weighted beam superposition,its performance is always best,under different power budget,regardless of channel conditions.Then it studies the power allocation method for mm Wave massive multiple input multiple output non-orthogonal multiple access(MIMO-NOMA),and then proposes a power allocation based on quality of service(Qo S),which improves the system rate on the basis of satisfying the Qo S of weak users.From the perspective of fairness and system performance,several multi-beam methods are verified and compared.After the new power allocation method based on Qo S is used,the performance and fairness of weighted beam superposition are both good. |
