Research On Uplink Non-Orthogonal Multiple Access Technology For Low-Orbit Satellite Mobile Communication

The low-orbit satellite mobile communication system has the characteristics of wide coverage,not affected by weather and natural disasters,safe and efficient,etc.It has become an important part of the future global communication network.With the development of 5G technology,the low-orbit satellite Internet of Things has also received more and more attention.The integration of satellites and 5G is an inevitable trend in the construction of the future ”Internet of Everything” world.Aiming at the problem of large-scale terminal access in the satellite Internet of Things system,this paper studies the receiving end detection method of Sparse Code Multiple Access(SCMA)technology based on the satellite mobile communication system,and has achieved the following results.First,the satellite Io T system and its channel model are briefly described.The system composition and business characteristics of the low-orbit satellite Internet of Things are given,and the technical requirements for multiple access under the satellite Internet of Things are analyzed.The link transmission characteristics in satellite mobile communication systems are introduced,and the channel models are given,including the AWGN model and the Lutz model.Next,the receiver algorithm of the satellite uplink SCMA system is studied.The system model of the upstream SCMA system is studied,the codebook design guidelines are briefly introduced,and then the detection algorithm at the receiving end is studied.Aiming at the problem that the optimal performance detection algorithm MAP is too complex,a sub-optimal performance message passing algorithm(MPA)is studied.To further reduce the complexity,the Log-MPA algorithm,Max-Log-MPA,is proposed from the perspective of reducing the amount of calculation The algorithm and the improved Max-Log-MPA algorithm are compared by analyzing the complexity of each algorithm.Finally,simulation verification shows that the improved Max-Log-MPA algorithm can achieve a balance between performance and complexity.Finally,the receiver detection algorithm of the satellite multi-antenna SCMA system is studied.Combining MIMO technology and SCMA technology,a satellite uplink MIMO-SCMA system model is established,and its expansion factor graph model is analyzed,focusing on the research of receiving end detection technology.On the one hand,first consider combining the MIMO linear filtering technology with the MPA detection algorithm of the SCMA system.The joint detection algorithm can reduce the exponential complexity to linearity;The algorithm uses QR decomposition to convert the fully connected factor graph into a subgraph with a lower number of edges for transmitting messages,thereby reducing the complexity of multi-antenna MPA.Based on the QR-MPA algorithm,a dynamic node selection scheme D-QR-MPA is further proposed to filter out the user nodes that have converged and no longer participate in subsequent iterations,thereby further reducing the complexity.Finally,the simulation verifies that the proposed D-QR-MPA algorithm can reduce the complexity and ensure the detection performance.