Research On Channel Quality Estimation And Adaptive Soft Demodulation Of High Throughput Low Orbit Satellite Communication

A low-orbit satellite communication system has the advantages of small transmission delay,short construction period and low investment cost,and has become an important way to realize communication globalization,commercialization and broadbandization.After years of development of the satellite communication system since the 1960s,communication frequency resources of low bands,such as the C band and the L band,have become increasingly tight,which has become a major problem restricting construction of a low-orbit satellite constellation system.High in working frequency and wide in available bandwidth,the Ka band has gradually been applied to the low-orbit satellite communication system and has become a current research hotspot.Since the Ka-band low-orbit satellite is low in running orbit and the frequency wavelength is close to the radius of rainwater,serious rain attenuation exists,and the adaptive coding and modulation technology can avoid a waste of system resources.In order to improve a data transmission rate and a frequency resource utilization rate,a low-density parity-check?LDPC?coding mode and a high-order modulation scheme can be adopted.Therefore,the DVB-S2X standard adopts the adaptive coding and modulation technology and introduces a higher-order modulation scheme.Channel quality estimation is an important part in an adaptive coding and modulation system,and a corresponding coding and modulation mode needs to be selected according to a current channel state.In this paper,the principle of signal-to-noise ratio?SNR?estimation is analyzed and studied,and an SNR estimation algorithm suitable for the Ka-band low-orbit satellite communication system is provided.The LDPC coding mode and the high-order modulation scheme for the satellite communication system are computationally complex and difficult to implement.In order to solve these problems,this paper improves the soft demodulation algorithm of high-order modulation scheme16 Amplitude Phase Shift Keying?16APSK?,and proposes a soft demodulation algorithm to reduce the computational complexity.The main content of the paper is summarized as follows:1.The communication channel characteristics of the Ka-band low-orbit satellite communication system and the working principle and composition of the adaptive modulation and demodulation communication system are analyzed.2.The characteristics of a 16APSK constellation map,the principle of modulation and demodulation,a hard demodulation algorithm,a soft demodulation log likelihood ratio?LLR?algorithm and a soft demodulation Max-log-MAP algorithm in the DVB-S2X standard are analyzed.According to the characteristics of the 16APSK constellation map,soft demodulation optimization algorithms are proposed for the4+12APSK constellation map and the 8+8APSK constellation map respectively.Through a simulation analysis and a calculation complexity comparison,the advantages and disadvantages of simplified soft demodulation algorithms and a performance improvement situation are analyzed.3.The basic principles and application scopes of the traditional SNR estimation algorithms ML algorithm,M₂M₄ algorithm,Split-Symbol Moments Estimator?SSME?algorithm and Signal-to-Variation Ratio?SVR?algorithm are analyzed.The estimation effects of the four algorithms in the Binary Phase Shift Keying?BPSK?modulation scheme are simulated and compared.The SNR estimation simulations of the SSME algorithm in Quadrature Phase Shift Keying?QPSK?,8PSK,16APSK and 32APSK modulation schemes are completed.The SNR estimation method suitable for the Ka-band low-orbit satellite communication system is provided,and the performance is significantly improved.