Study On Techniques Of Accuracy Augmenting And Integrity Monitoring For Satellite Based Navigation System

Accuracy and integrity are both the key performance of the satellite navigation system, the technology of augmenting accuracy and monitoring integrity should be researched from the system designing and the user preocessing. In the system designing, the inter-satellite link (ISL), multi-frequency signal and Binary Offset Carrier (BOC) modulation are introduced in the inevitable trend. In the user processing, many problems such as ionospheric delay high-precision correction, signal distortion influence analysis, receiver autonomous integrity monitoring (RAIM) and so on are focused on. Herein, five aspects are studied in this thesis .(1) Conventional triple-frequency ionospheric delay correction algorithm assumes that the variances of three frequency pseudoranges are equal. However, the variances are unequal since the signal bandwidth and carrier noise ratio of each frequency are different in fact. With this consideration, a new triple-frequency first order ionosphere correction algorithm, which minimizes the variance of the pesuod-range ionosphere-free combination on the assumation that pesudorange noise variances are unequal, was presented. Two experiments were carried out using triple-frequency data of the narrow correlator pseudoranges of Compass and the wide correlator pseudoranges of GPS. In the two experiments'results, the noise deviation of the new algorithm was reduced to 12cm and to to 61cm respectively, while the noise deviation of the best traditional algorithm was 26cm and 64cm respectively. Considering that the 2nd-order item of ionospheric delay can not be neglected in high-precision carrier-based application, a multi-frequncy ionosphere correction algorithm, which is based on optimizing the weighted combination of noise error and high-order residual error, was firstly developed. It can reduce the combined error by changing the weight coefficient.(2)The differential coherent detection method can be used in the inter-satellite link signal acquisition. Since the conventional approximating formula of its detection probability is not accurate, it cannot be used to optimize the parameters. The coherent integration time is also fixed in former researches. For the two points, a combined analysing method of simulating the detecton probability and calculating the false alarm probability theoretically was proposed. Based on the method, the coherent integration time is optimized. After optimization, the detection loss was reduced by up to 2dB. Under the situation that false alarm probability is 10^-6, the data of detection loss vs signal noise ratio is fitted by the curve, which can be used for establishing the mathematical model of the detection performance.(3) In the traditional error analysis of space-ground-based combined orbit determination, the random error is only considered. In the thesis a error analysis model and simulation method considering the random error and the systemic error were proposed. The error of space-ground-based orbit determination caused by many factors, such as measuring time's uncertainty, the measuring interval, the I systemic residual error and the antenna beam selection of ISL, was alos researched to guide the design and selection of different inter-satellite link parameters. Besides, under two scenarios that interference comes from fixed ground area and some satellites are interfered in the whole time span, the performance of orbit determination was evaluated.(4) In former researches of BOC signal distortion, there was no analytical method to describe the ICAO digitial distortion of BOC signal, and the non-ideal channel characteric was not considered when analyzing the BOC signal distortion effect. For the points, the analytical fomula of power spectrum of BOC digital distortion was first developed and the model of analyzing the ranging bias of BOC distortion was built. The relationship between ranging bias and receiver design parameters for BOC(14,2) and BOC(1,1) was analyzed, under the assumptions of ideal receiver low-pass filter and non-ideal channel respectively. The conclusions were as followed: the channel's group delay non-ideal characteric would degrade the ranging bias in BOC(14,2) ; The interval of early code and late code for non-coherent processing should be selected in the range of 0.3chip⁰.35chip in BOC(1,1) to weaken the distortion effect.(5) Since the traditional RAIM algorithms cannot detect weak pseudorange bias, a new RAIM algorithm based on the time-accumulated parity vector (TPV-RAIM) was presented to detect weak bias effectively. By the accumulation of several epochs, the ratio of equivalent pseudo-range bias to noise error can be enlarged and the detection performance of weak pseudorange bias can be enhanced. In the simulation, the minimum detectable bias of TPV-RAIM based on 10 epochs was reduced to 0.75m, while that of traditional RAIM was 2.3m.Finally, the research work of this thesis and its engineering application are summarized and reviewed, the future work is also presented. The research results have been used in many projects of Chinese satellite navigation system.