High Dynamic Positioning Satellite Receivers Spread Spectrum Signal Synchronization Technology

As one important part of IF signal processing in GPS receivers, the acquisition of satellite signals is the precondition and foundation to extract navigation information, which will directly affect the hardware scale and system performance. In high speed environments, the Doppler effect will be apparent for GPS signals, and the acquisition of GPS C/A code becomes a big challenge without the help of ephemeris and velocity information. Classical sliding correlation approach cannot meet the requirements, so it is necessary to explore the fast acquisition technology for GPS signals.By way of theory study, computer simulation and software & hardware implementation, deep research is taken on different fast acquisition algorithms and key issues in the process of acquisition. The innovative work and the main results will be stated next.(1) After describing the acquisition principle for GPS signals, the joint effects of code delay, carrier Doppler frequency shift and code velocity Doppler on the signal correlation output are analyzed to provide important references for the selection of the 2D search strategies and step interval.(2) Although to implement circular correlation in the frequency domain using FFT is a fast acquisition approach for GPS C/A code, its FPGA implementation takes a large amount of resources, and the number of FFT operation needs to be 2 to the power of an integer. Based on this fact, the thesis proposes an approach called Averaging Correlation to fulfill circular correlation using smaller FFT blocks by averaging the input and local C/A code, solving the problem of FPGA resources and the number of computation points.(3) Research is taken on three parallel acquisition approaches which are matched filter, circular correlation and PMF-FFT. Comparison of these methods is presented about acquisition time and hardware resources utilization with different structures and different parameters.(4) The use of frequency-domain Doppler search, based on FFT acquisition of GPS C/A code, speeds up the acquisition process by one time, or even more, by comparison with the conventional FFT acquisition approach performing Doppler search in the time domain. When the input Doppler frequency falls exactly between two successive frequency components of the FFT of the input digital IF signals, there is a loss in the amplitude of pre-detection integration. Two approaches, generating a new frequency component using the two successive frequency components and downconverting the input signal by different local carriers, are proposed to solve the above-mentioned problem. These make the approach a fast and practical acquisition scheme. The new algorithm is the innovative part of the thesis.(5) FPGA implementation of Averaging Correlation is achieved by the use of Hardware Description Language. Comparison of the results of ModelSim functional simulation, MATLAB simulation and GPS hardware receiver verifies the validity of Averaging Correlation approach.