| With the continuous development of aerospace industry,the aerospace tracking,telemetry and command(TT&C)system also needs to be upgraded simultaneously according to the number increase of satellites,In the low-orbit satellite TT&C system,in order to increase the number of satellites served by one ground station at the same time,the satellite needs to report its own state and location information to the ground by short burst spread spectrum signals.Therefore,the ground station receivers need to have capability for acquiring and tracking the short burst signals.In satellite TT&C system,the synchronization module is an important part of baseband signal processing,and carrier tracking is one of the key technologies to achieve precise synchronization.Because of the features of the short burst signal,the signal acquisition and carrier lock process must be completed within a very short symbol length to complete the signal demodulation correctly.However,the low-orbit satellite’s characteristics and constraints make its signal have a large Doppler frequency deviation and Doppler change rate with low SNR when entering the receiver.As the result,the receiver need longer lock time and lower tracking accuracy.Under this condition,the thesis mainly studies the method and realization of the accurate tracking of the carrier frequency and phase of the burst short signal with low SNR and high dynamics.First,this article studies the traditional carrier synchronization algorithm.Based on the analysis of the characteristics of the current short burst spread spectrum signal,the dynamics of the signal entering the carrier tracking module are explained in combination with the receiver parameters.The basic principles,advantages and disadvantages of three existing high dynamic carrier tracking algorithms are analyzed,and the tracking performance of these algorithms for current short burst spread spectrum signals is simulated.The simulation results show that none of the above three algorithms can achieve loop lock within the specified symbol length and obtain satisfactory demodulation results for this burst short signal.Secondly,by analyzing the limitations of the traditional high dynamic carrier tracking algorithm and the advantages of the open-loop carrier synchronization algorithm in fast frequency offset estimation,combining the characteristics of the short burst communication system and its applicable environment,a carrier frequency parameter estimation aided third-order phase-locked loop algorithm can effectively improve the system carrier tracking performance.And by adding storage modules to complete the signal iteration,the improved algorithm reducing the length of the signal pilot sequence required on this basis.Through simulation analysis,the improved algorithm can meet the system index requirements in terms of tracking success rate and tracking accuracy.Finally,the FPGA design of burst signal carrier tracking algorithm based on hardware platform is studied,the structure and function of each module involved in the algorithm are explained,and Modelsim is used to simulate the output of each module.The actual performance of the algorithm is tested in the communication system.The test results show that the burst signal carrier tracking technology proposed in this paper can meet the expected index requirements. |
