Research And Implementation On Baseband Synchronization Techniques Of Ground Station For Spread Spectrum Measurement And Control

Measurement and control technology is one of the key technologies to maintain the normal operation of aerospace systems,where ranging and speed measurements are an important parts.In existing measurement schemes,the incoherent pseudo-code measuremen,which is currently the most efficient measurement and control program based on telemetry signals,can fully provide the limited on-board transmission power to the telemetry link,and effectively increase the signal-to-noise ratio of the telemetry signal,and improve the transmission efficiency of the telemetry data,by inserting the ranging information into the telemetry frame to transmit together.In the spread spectrum measurement and control system,the ranging accuracy depends on the measurement accuracy of the pseudo-code phase,while the velocity measurement accuracy depends on the measurement accuracy of the Doppler frequency offset.In order to improve the measuring accuracy of the spread spectrum measurement and control system,the baseband technology of the ground station,including the pseudocode synchronization and carrier synchronization technology of the ground station receiver,focused on the main research contents are as follows:(1) To solve the mismatch between the code length and the number of FFT points in the parallel code phase capture algorithm,the preprocessing methods of direct zeropadded and double-length zero-padded are studied.The simulation results show that the acquisition performance of the double-length zero-padded method is better than that of the direct zero-padded one,where the obtained pseudo-code correlation peak has no change with the shift of the code phase,and the probability of capture is high even in a low signal-to-noise ratio environment.To solve the problem of long frequency search time in the parallel code phase capture method,a peak comparison search strategy and a frequency compression capture method are designed.The former can determine the correct search direction of the frequency offset by comparing the magnitude of the two peaks before and after the shift,which changes monotonously with the Doppler frequency offset.And the latter can decrease the number of searches of frequency units by compressing adjacent subcarrier frequencies The simulation results show that the acquisition time of the two methods is shortened by more than half,which is more conducive to the realization of the parallel code phase method in the Doppler frequency offset environment.(2) To solve the problem of scallop loss in the correlation peak of the partial matched filter-fast Fourier transform(PMF-FFT)capture method with Doppler frequency offset,the windowing method and the zero-filling method are studied.The simulation results show that the loss of scallops using the two pretreatment methods is significantly decreased,where the peak losses are reduced from the original 0.35 to 0.05 and 0.06,respectively.To solve the problem of long phase-search time of the PMF-FFT acquisition method,a pseudo-code phase compression acquisition method is designed.The simulation results show that the improved PMF-FFT algorithm adopts this method to reduce the acquisition time significantly,which is more conducive to the acquisition in the long code environment.(3) To solve the accuracy of the pseudo-code tracking loop,the basic structure of the non-coherent delay-locked loop is studied.The simulation results show that the incoherent delay-locked loop has high tracking accuracy and large dynamic range,which is suitable for high-precision aerospace measurement and control systems.According to the problem of the dynamic change of the working environment of the carrier tracking loop,the dual-loop carrier tracking method of the frequency-locked loop assisted by the phase-locked loop is studied.The simulation results show that the double-loop tracking method has good tracking performance and large dynamic stress tolerance(4) According to the index requirements of the ground station of the measurement and control system,a set of baseband schemes for the transmitter and receiver are designed.Where the receiver and transmitter of the ground station are completed.The hardware simulation and actual results show that the synchronization algorithm has good performance and can successfully meet the technical indicators.