Research On Key Techniques Of GEO Satellite Emergency Communication System

The field of satellite communication has been developed so far,and its application has popularized in many industries,which also brought convenience to people's lives.The satellite emergency communication system,which can work in the harsh environment,is widely used in military and emergency rescue and other fields.Nowadays,many countries compete to develop satellite communications,and the past L band are now in the tense situation of band resources.In this scenario,the C_N band goes back to the public view,and the GEO satellite emergency communication system works in the C_N band also has important research value and significance.In the design of a satellite communication system,many key techniques need to be overcome.This thesis demonstrates a scheme about GEO satellite emergency communication system,and mainly researches,analyzes and simulates the C_N band compatible signal design and LDPC decoding algorithm in the scheme.The main research results of this thesis are as follows:1.A scheme of GEO satellite emergency communication system operating in C_Nband is proposed.The forward link of the system includes navigation and communication modes,and the reverse link is the communication mode.According to the different working modes of the system,a structure about navigation message frame and the communication data frame is designed.The 64-ary LDPC and binary LDPC encoding and decoding is adopted respectively.In the design of the system compatibility signal,signal design scheme based on band-stop filtering and BPSK with raised cosine pulse filter are proposed.Because the front and reverse links of the system select a different spread code length,different receiver acquisition schemes are designed respectively.In the decoding algorithm of system,the EMS decoding is used in the navigation message frame,and the MS-CNM-BP decoding algorithm is adopted in the communication data frame.2.For the C_N band where the system works,because its adjacent band is the radio astronomy and microwave landing system,the signal of system may have an impact on the systems working on the adjacent band.In accordance with the international organization ITU's regulations on compatibility,the system uses BPSK modulated signals for compatibility simulation,and two methods of band-stop filtering in the radio astronomy band and raised cosine shaping method are proposed to solve the system signal compatibility requirements.3.In the research on the system LDPC decoding algorithm,for the communication data frame and navigation message frame structure designed for the system,binary and 64-ary LDPC decoding algorithms are used respectively.For the binary decoding algorithm,a Mini-Sum and Check Node Matching decoding algorithm based on Belief Propagation is proposed(MS-CNM-BP).When this decoding algorithm updates the check node iteratively,it can be updated differently according to the number of nodes connected to the check node,which makes up the problem of excessively high node update estimation in Mini-Sum algorithm.Moreover,it's performance is close to that of Log-BP decoding,and its decoding complexity is approximately equivalent to that of MS,OMS,and NMS.Comparing to Log-BP,the complexity has been decreased significantly.For q-ary LDPC decoding,this thesis simulates the FFT-QSPA and EMS algorithms.The simulation results show that although the EMS algorithm loss 0.1d B performance with FFT-QSPA,its complexity reduced to a lower level,fromO(q log₂^q)toO(n _mq),which is suitable for navigation message decoding.