Research On Multi-user Detection And Scheduling Technology In Multibeam Satellite Communication System

Satellite communications play an irreplaceable role in emergency communications,communications in areas not covered by terrestrial cellular,and communications in air and offshore areas.At the same time,the emergence of 5G networks and the introduction of a satellite-ground integrated architecture will greatly change the role of satellite communications in the near future.The continued demand for higher rates and higher system throughput has driven the development of high-throughput satellites.One of its key technologies is the Multibeam transmission technology.By using spot beams,the antenna gain can be greatly increased to support small satellite user terminals.At the same time,frequency reuse can be performed between different spot beams,which improves the utilization rate of the frequency band and increases the system capacity.But at the same time,using the same frequency band in adjacent beams also brings serious inter-beam interference problems,also known as Co-Channel Interference(CCI).Users at the edge of the beam are affected by the most severe CCI,resulting in greatly reduced achievable transmission performance.This thsis aims to study the multi-user detection and user scheduling of multi-beam satellite systems under full frequency multiplexing.This thesis first studies the structure of the multi-beam satellite communication system and its equivalent MIMO system model,and then analyzes the characteristics of the three satellite MIMO transmission schemes.Based on the characteristics of multi-beam MIMO,the link model of the multi-beam satellite communication system is analyzed,and the relevant channel model is given.Secondly,the multi-user satellite reverse link multi-user detection algorithm is studied.First,the system model of the multi-beam satellite reverse link is briefly introduced,and several traditional multi-user detection algorithms are analyzed and simulated.Then the concept of factor graph model and confidence propagation are introduced,and the factor graph model according to the channel characteristics of the multi-beam satellite reverse link is established.Then the corresponding standard belief propagation multi-user detection algorithm is discussed for the model,and the message design and message update criteria in the algorithm are explained.Based on the standard belief propagation algorithm,the idea of screening edges in the factor graph model is analyzed,and a low-complexity BP-MIMO detection algorithm based on single-side,partial-edge and mixed-edge message transmission is proposed.And in some sides,it is further divided into two schemes: fixed number of sides and adaptive adjustment of the number of sides by channel conditions.The simulation results show that the BP detection algorithm based on edge selection proposed in this thesis can achieve higher detection performance with low complexity,and a compromise between complexity and performance.Finally,the forward link precoding and user scheduling problems in the multi-beam satellite communication system are studied.First,the system model of the high-throughput satellite forward link is briefly introduced.Then ZF precoding is used to eliminate the multiuser interference problem in the forward link,and the optimal precoding matrix is designed under the constraints of total power and single antenna power from the fairness of transmission rate.On the basis of completing the precoding design,further study the user group scheduling scheme,the scheduling algorithm mainly considers two factors,one is to meet the business needs of each user,and the other is the transmission efficiency after group scheduling.In the algorithm,the channel correlation degree with a low calculation amount is substituted for the precoding SINR as a measure of the grouping scheme,and a low complexity grouping scheme is designed.Finally,the performance of the user group scheduling scheme proposed in this thesis is simulated to verify its feasibility.