Research On Sparse Code Multiple Access Technology In Satellite Communications

The rapid development of terrestrial mobile communication systems makes the interconnection of all things no longer a wish.At present,there are more and more researches on the fifth generation(5G)communication technology,and the commercialization of 5G is also developing rapidly.However,the terrestrial mobile communication systems still have problems that cannot be solved by themselves,such as long-distance transmission,global coverage and other problems.These problems need to be solved by satellite systems.Therefore,satellite communication is also a hot research topic in the communication field in recent years.On the contrary,due to the limited power and bandwidth,and the delay caused by the extremely long transmission distance between satellites in communication,the satellite-terrestrial 5G integration system still has many chanllenges to face.In order to increase the capacity and the spectrum utilization efficiency of satellite communication systems,and enable it to better integrate with terrestrial 5G technology,we consider to applicate sparse code multiple access(SCMA)technology in satellite communication scenarios.This dissertation proposes a low-complexity detection method that optimizes resource allocation for geostationary earth orbit(GEO)satellite communication scenarios.The algorithm is divided into two steps.Firstly,the codebook allocation algorithm based on maximum matching is adopted in satellite SCMA system with the idea of "0-1" problem.The channel state information is used to change the corresponding order of codebook and channel to improve the system's performance with lower bit error rate(BER).Secondly,on the basis of the traditional message passing algorithm(MPA)and Max-Log-MPA algorithm,we reduce the complexity of multi-user detection algorithm by adopting threshold limits to meet the requirements of satellite users.Simulation shows that this process can effectively reduce the complexity of the system while not causing more performance loss of bit error rate.In the GEO satellite communication scenario,this dissertation aims to design a low peak to average power ratio(PAPR)system using SCMA technology.Under the guidance of the probabilistically shaped SCMA codebook design method,the I,II,and III low PAPR SCMA codebooks are designed,and their specific codebooks and multidimensional constellation diagrams are given.Simulation compares the six performance parameters of PAPR,minimum Euclidean distance,bit error rate,average power,number of non-coincident constellation points,and detection complexity of these three and traditional SCMA codebooks.This provides references for different application scenarios.Finally,this dissertation discusses the application of SCMA technology in satellite secure communications.By regarding the channel phase as the physical layer secure communication secret key,we incorporate it into the SCMA codebook design.The Euclidean distance of the ideal receiving vector is defined as the distance spectrum.By maximizing the minimum distance spectrum,we find the SCMA security codebook with lower bit error rate.When using the codebook for secure communication,we try not to deteriorate the system performance.