High Precision Modeling And Receiving Techniques For Modern GNSS Signals

The need of the spectral separation of military and civil signals and the performance improvement of the system service promote the development of modernized satellite navigation signal. Several new techniques are adopted in next generation global navigation satellite system(GNSS), include the binary offset carrier(BOC) modulation, the pilot channel and so on. The high precision signal model and receiving technique is an important factor in determining the performance of next generation GNSS. So the research in the following areas is carried out in the paper:Multiple signal components are broadcast through a single carrier in GNSS. The correlation peak is influenced by the auto-correlation of useful signal and the cross-correlation of multiple signals. The symmetry of the correlation peak is the precondition of accurate pseudo-range measuring. Traditional GPS L1 signal uses quadrature phase shift keying(QPSK) modulation, and the impact of cross-correlation on correlation peak could be neglected due to the quadrature phase between the two components. However, the components of modernized signals may have identical carrier phase, and it is indicated that the cross-correlation between components in phase could have severe impact on the correlation peak symmetry and may cause tracking bias of meters for signal with low code rate. It is proved according to the theoretical expression of the tracking bias that it is related with partial cross-correlation, but only the cross-correlation within ±1 chip has effect; besides, it is also related with the relative sign of modulated symbols. In order to reduce the tracking bias caused by cross-correlation, the method by optimizing the partial cross-correlation and adding secondary code modulation simultaneously are proposed. The analysis on the signal structure of Beidou global system shows that there is still have space for improvement, and the tracking bias could be reduced to millimeters after optimization.The signal spectrum is shift to the dual sideband by square sub-carrier modulation. The upper and lower sideband is often considered as ideal binary phase shift keying(BPSK) modulated signal in dual sideband receiving techniques, and the effect of high order harmonic component is seldom considered. To solve this problem, it is strictly proved that the presence or not of the high order harmonic component have no effect on the symmetry of the correlation peak and also the accuracy of pseudo-range measuring, and only have impact on the signal to noise ratio(SNR). According to the SNR loss obtained from numerical computation, the simple model for the receiving performance of precise estimation is proposed through SNR modification. In the analysis of the ionosphere effect, the signal is approximated as a narrow band signal with identical code phase delay. However, the approximation would cause error of meters in the dual sideband receiving for BOC signals. The paper derives the theoretical expression of the ionosphere delay of upper and lower sideband by considering the dual sideband is considered as narrow band respectively. And the dual sideband model with the ionosphere effect is proposed, and the modeling error is less than 1 millimeter.Signal acquisition consists of three associated part including correlation, search and decision. In order to optimize the acquisition performance, the joint optimization is proposed. The goal of higher detection performance and less search time is to approach in signal acquisition. Current researches on correlation and search often focus on a single goal and neglect the restriction that the two goals are not independent. The criterion of best detection performance under identical computation complexity is proposed for the optimization of multiple goals and the optimum correlation algorithm and optimum search interval is given. In decision part, The optimum linear combinational detector is derived according to the great likelihood ratio testing rule. The simulation result shows that the performance of the optimum detector is improved by 1.0d B than that of traditional detector without increasing the computation complexity.It is well known that the multiple correlation peak of BOC modulation could cause false tracking for tracking with matched filtering. In order to remove the tracking ambiguity, the tracking algorithms are mainly focused on BOC(1,1) tracking algorithm with unmatched filtering, but they have disadvantage in implementation and tracking performance. Because of the low rate of code and sub-carrier, the feasibility of matched tracking is proved by approximate analysis, numerical simulation and experimental verification, and the performance approach the theoretical bound. The symmetry of correlation peak of BOC(14,2) is sensitive to the non-ideal channel because of its wider signal band; however, current research have not considered the tracking stability under non-ideal channel. To solve this problem, the dual sideband non-coherent combination tracking algorithm is proposed. The algorithm can track steadily and has similar performance of BPSK signals with the same code rate, and the performance loss is about 0.9d B.Current signal acquisition algorithm for pilot channel is the simple expansion of traditional method for single BPSK modulated signals, and has little focus on the optimum implementation and detector. For the acquisition of time division data multiplexing(TDDM) signals, traditional matched filter is difficult to achieve high efficiency of correlation, and the matched filter with two adder trees is proposed. The needed correlator is only half that of traditional scheme and extra performance loss is less than 1.0d B. The proposed pilot acquisition algorithm is the extension of traditional algorithm, not based on the optimal detection theory. So the optimum detector for data/pilot joint acquisition and pilot independent acquisition strategies is derived. The results show that the performance of optimal detector can be improved 3.0d B and 5.0d B than traditional non-coherent detector, respectively.Finally, this paper summarizes the achievement, and the future work is prospected. The main results of this paper have been applied in multi-system monitor receiver of Compass operation segment.