Joint Processing For Satellite Navigation Signals

GPS chips are widely applied in the consumer electronics and multiple Global Satellite Navigation Systems(GNSS) develop, so the GNSS signals are expected to provide better positioning service in the fading environments(e.g., urban canyon and indoors).The research and development of the high sensitivity GNSS receivers are urgent. Based on performance improvement brought by the assisted information and redundancy satellites, the thesis focuses on the joint acquisition, vector tracking and integrity monitoring.(1) Two-dimensional search is performed in the Doppler frequency and code phase.Differently, The joint acquisition performs search in the position, velocity and clock error, which project to the signal synchronization parameters to estimate the code phase and doppler frequency. The joint acquisition exploits the correlation among the available satellites to improve the sensitivity. In view of the lack of theoretical analysis on the joint acquisition, the detector is derived in principle of the generalized likelihood ratio test(GLRT). The analytical expressions of the false alarm probability and the detection probability are also derived. The detection losses caused by the errors of the estimated code phase and Doppler frequency are analyzed quantitively. The theoretical results form the basis of the threshold determination and the performance evaluation. The simplified implementation architecture with satellites selection is proposed to reduce the computation load. The simulated results show that the acquisition sensitivity is improved along with the increasing number of the available satellites, and the sensitivity is increased by almost7.5 d B with 1 ms coherent integration time and 12 available satellites.(2) Considering the condition of the navigation message modulation, a modified joint acquisition based on the differential coherent integration is proposed to restrain the effect of the bit transition. The analytical expressions of the probability density function under two different assumption are derived. The Monte Carlo simulation is performed to verify the theoretical results. Within the specified delay and doppler error conditions, the optimal coherent integration time and differential coherent integration time is presented, which avoid the balance problem between the precision and computation load in the optimization based on the numerical simulation. Besides, the experiments for collecting and processing GPS simulated signal are performed to verify the modified joint acquisition.(3) The problems on the accuracy and convergence of the vector delay lock loop(VDLL) are investigated and solved. Firstly, the improved problem VDLL with the adaptive bandwidth is proposed to solve the difficult balance between the convergence speed and tracking accuracy. Secondly, aiming at the phenomenon of the tracking bias with more than 4 satellites available, two modified algorithms based on parity space projection are proposed. One algorithm adds the the variables projected by the residual errors to realize monitoring in the traditional VDLL architecture. The other algorithm works in the low-dimension state under normal condition and works in the high-dimension state under the biased tracking condition. Simulated results with the same signals show that the maximum code phase error is 1m for the the modified VDLLs, while the maximum bias is 16.706 m for traditional VDLL. because the modified VDLL based on variable dimensions uses the adaptive bandwidth and complex architecture, so it performs better in convergence and accuracy than those based on residual error projection.(4) Aiming at the multiple outliers difficult to handle for the conventional receiver autonomous integrity monitoring(RAIM), the robust positioning algorithm based on the M-estimation is presented. The actual GPS observation data and simulated outliers are used to verify the robust positioning algorithm. To meet the integrity monitoring demand in the robust positioning, the robust RAIM based on the robust positioning results is proposed, which provides the protection levels to evaluate the position error at the worst case.The experimental results of the actual GPS data show that the robust positioning algorithm is able to restrain 3 outliers with 12 satellites available. The experimental results also show that the robust RAIM is able to provide more stringent protection levels than those of the conventional RAIM, actually the horizontal protection level is reduced to 50% and the vertical is almost reduced to 33%.Finally, The thesis research results and engineering application are summarized,while the future work are discussed. Some parts of the research results have been applied to the design and demonstration in the development of the high performance receiver and simulator.