Research On 5G-Oriented Nonlinear Precoding And Non-Orthogonal Multiple Access Technology

Facing the requirements of high spectrum efficiency,high system capacity,and massive connections in the fifth generation(5G)systems,both nonlinear precoding technology and non-orthogonal multiple access(NOMA)have high practical value.In 5G systems,it is necessary to maximize the use of airspace freedom to improve spectrum efficiency.Therefore,nonlinear precoding has promising application prospects.While making full use of spatial dimensional resources,NOMA can greatly increase the number of user access and spectrum efficiency by superimposing multi-user information on the same time-frequency resources.This paper takes Tomlinson Harashima Precoding(THP)in non-linear precoding technology and Sparse Code Multiple Access(SCMA)in NOMA technology with Multiple Input and Multiple Output(MIMO)structure as the main research objects,respectively,and proposes a variety of schemes for performance improvement or reducing complexity.All of these schemes have been analyzed and simulated.Firstly,the principle of traditional linear precoding and non-linear precoding techniques have been deeply studied.The implementation of linear precoding is simple,but the system performance is limited by channel conditions and noise,etc.The performance of non-linear precoding is better than linear precoding,but the higher complexity and the performance that needs to be improved have become the bottlenecks of practical applications.The thesis proposes three improved schemes based on THP precoding technology.Partially-modulo THP scheme effectively avoids certain modulo loss while reducing complexity.The new THP scheduling scheme amplifies the performance advantage of THP precoding while ensuring schedule fairness.The THP schemes assisted with codebook(THP-CB)technology reduces the amount of information feedback,and also improves system performance by reducing power loss.Secondly,the thesis investigates NOMA technologies and explain their principles.Besides,the principle of SCMA and the MIMO-SCMA structure with improvement scheme are introduced.And all of these algorithms have been analyzed and simulated.Finally,in this paper,three improved schemes with MIMO-SCMA structure have been proposed.In MPA-P scheme,the detection algorithm under the MIMO-SCMA structure has been improved.What's more,The advantages of the SCMA-ZF scheme combining Zero Force(ZF)precoding and MIMO-SCMA system in data rate and complexity have been introduced.Based on this technique,performance gain is obtained by replacing ZF technique with some improved nonlinear precoding schemes.