Research On Nonlinear Precoding Technology Of Multi-beam Satellite Communication System

With the increasing demand for high-speed and high-capacity communication,high-throughput satellite communication system is becoming the focus of future research.In this development trend,there are two kinds of satellite communication systems that can improve the system throughput:the first is the multi beam satellite communication system that can provide high satellite resource utilization and high equivalent omni-directional radiation power;the second is the satellite diversity virtual MIMO communication system that can improve the system throughput.In addition,the performance of multi beam satellite communication system integrating the above two communication systems can be further improved.However,there are three problems in the application of multi beam satellite communication system:the first problem is that there are serious inter beam interference within the satellite and inter beam interference between satellites;the second problem is that Linear Precoding algorithm is not suitable for multi beam satellite system because of unstable power allocation or increasing terminal complexity The third problem is that the system is lack of inter beam interference suppression technology based on nonlinear precoding algorithm.In view of the above problems,the main work and innovation of this thesis are as follows:1.There are serious inter beam interference and inter beam interference in multiple multi beam satellite communication systems.In order to quantify the inter beam interference,this thesis calculates the inter beam interference according to the antenna mode,satellite position and terminal position of multi beam antenna and terminal antenna,constructs the multi satellite inter beam interference channel matrix and simulates the degradation degree of inter beam interference to the system performance based on different frequency multiplexing schemes.The results show that inter beam interference will seriously deteriorate the system performance,and determine the necessity of inter beam interference suppression technology.2.When using nonlinear precoding algorithm to suppress inter beam interference in multiple multi beam satellite communication systems,it is necessary to avoid the disadvantage of high channel correlation between terminals,and the existing terminal grouping algorithm has high computational complexity and poor performance.In this thesis,a terminal grouping algorithm based on gain correlation between adjacent beams is proposed.The initial terminal in the group can be confirmed without calculating the channel vector modulus of the terminal.By using the unique extremum characteristic of gain correlation function between adjacent beams,the terminals with close relative positions in different beams are grouped.Nonlinear precoding is used to realize space division multiplexing in the group,and frequency division is used between groups Reuse.The results show that the algorithm has very low computational complexity and 2dB performance gain.3.Tomlinson Harashima precoding(THP),as a kind of nonlinear precoding,has become the research goal of this thesis because of its excellent power stability and the complexity and performance of equalization.However,the order of data stream will affect the performance of THP,and the limitation of the number of antennas equipped with the terminal makes the existing data stream sorting algorithms have poor performance when applied to satellite communication systems.Therefore,this thesis proposes an iterative optimized th precoding algorithm for multiple multi beam satellite communication systems,designs a variety of transmission modes,uses iterative structure and selection strategy to obtain the best transmission mode,optimizes the data stream order and carries out th precoding.The algorithm improves the system performance at the expense of complexity.The results show that the algorithm has 4dB performance gain.4.In order to comprehensively evaluate the system performance of the inter beam interference suppression technology based on the nonlinear precoding algorithm proposed in this thesis,a co simulation platform is built and the co simulation of the proposed algorithm is carried out.The results show that the joint algorithm has 6dB performance gain.