Research On Carrier Synchronization Technology Of Burst Signals In Satellite Communication

Satellite communication can provide universal service on a global scale.It is not affected by natural environments and natural disasters such as earthquakes and snowstorms.It has a wide international reach.In satellite communications,burst mode is often used for signal transmission.Burst signals have higher anti-interception and anti-interference capabilities than continuous signals.The reliability of the satellite communication system is mainly affected by the carrier synchronization module,and carrier acquisition is an important part of the synchronization module and is responsible for pulling the carrier frequency into the tracking loop bandwidth to facilitate the follow-up module to track the carrier.However,in the low-earth orbit satellite communication system,satellites and user terminals perform high-speed movement relative to the earth.The resulting Doppler Effect causes serious distortion of received signals,such as large frequency offset and time-varying frequency offset.So the process of carrier acquisition is more difficult.Therefore,how to carry out carrier acquisition of satellite burst signals is the focus of this study.Due to low satellite transmission power and small gains of the transmitting and receiving antennas,the carrier acquisition algorithm in satellite communication needs to adapt to a low signal-to-noise ratio.And the complexity of the algorithm should not be too high,otherwise it will cause overloaded resources on the satellite.Therefore,low signal-to-noise ratio and low complexity are two key factors that need to be considered in this thesis.In order to solve the above problems,this thesis will start from the following two aspects,and carry out research work on carrier acquisition of burst signals.In the static or low dynamic communication scenarios,the frequency offset is considered to be fixed during the observation time,and the received signal is considered as a complex sine signal.So carrier capturing only considers frequency offset.First,this thesis focuses on the traditional parameter estimation methods represented by Kay,L&W,Fitz,L&R,and M&M algorithms.The research shows that the above algorithms cannot be balanced among the estimation range,estimation accuracy,and SNR threshold.Therefore,this thesis proposes a NEW algorithm,which adopts the idea of joint estimation and achieves a large frequency offset acquisition at low SNR with higher estimation accuracy.In high-dynamic communication scenarios,the frequency offset exhibits time-varying characteristic in the observation time,and the received signal is considered as a complex LFM signal.Carrier capturing not only needs to capture the initial frequency offset,but also needs to capture the rate of frequency offset.First,this thesis focuses on the traditional parameter estimation methods represented by Delayed Autocorrelation,Discrete Chirp Fourier Transform and First-order Frequency Approximation Algorithm.Then for the problem that the Delayed Autocorrelation algorithm can’t realize the parameter estimation at low SNR,this thesis proposes a pilot-aided DFT time-varying frequency acquisition algorithm.The proposed algorithm can estimate the frequency offset and the rate of frequency offset for LFM signal based on two Fast Fourier Transform operations,and has a lower signal-to-noise ratio threshold.For the problem that First-order Frequency Approximation Algorithm has high computational complexity,this thesis proposes an approximation algorithm based on three division method.The algorithm optimizes the stepping,and removes the constraint relationship among the stepping and the estimation accuracy and the computational complexity in First-order Frequency Approximation Algorithm,and reduces the computational complexity of the system.