Research On Data Processing Technology Of Global Navigation Satellite Systems In The Challenging Environment

Generally, satellite navigation and positioning system depends on the line of sight signal, in the challenging environment such as urban canyon, foliage-covered area, the tunnels and indoor environment, GNSS has difficulty in providing a continuous and precise positioning service due to signal regression, multipath signal and blockage. In particular, in the extreme challenging environment such as Navwar, the satellite signal might be jammed or be turned off. Towards the imperious requires of application techniques of data processing in the challenging environment, the primary researches and contributions in this dissertation are summarized as follows:(1) Considering that the positioning accuracy will be deteriorated in the blockage situation which causes the degression of carrier-to-noise density ratio, and the measurements error will be very large when the strong and weak signals exist at the same time. This dissertation presents a new algorithm of iterated Reduced Sigma Point Kalman Filter(IRSPKF) based on the Gauss-Newton method. Futhermore, the sequential processing for the satellite observations at each epoch is involved on this basis, which is represented as the Sequential Iterated Reduced Sigma Point Kalman Filter(SIRSPKF), and the computational complexity can be reduced effectively. The results of simulation and field experiments implied that, the positioning accuracy could be improved about 20% when compared with non-iterated algorithms, and it decreased more than 50% of the computational complexity when garanteed the positioning accuracy. In the urban environment with foliage cover, the positioning availability could be improved efficiently from less than 75% to more than 98%. Morover, the estimation performance of proposed algorithm is as same as the NovAtel commercial receiver to the whole.(2) Considering the requirement of multipath mitigation for monitoring stations, a novel SIRSPKF dual filter is proposed in this dissertation, and the improved algorithm which is represented as variable length SIRSPKF dual filter has been applied for the combined constellation by aiming at the characteristic of different types of satellites. The field experimental results showed that, more than 60% of psedurange-code multipath error could be eliminated by the proposed algorithm, and the standard deviations of filtering residuals for all the frequencies of BDS combined constellation were reduced more than 14% when compared with the fixed length SIRSPKF dual filter algorithm.(3) To solve the problem of measurement precision difference and heavy computational complexity caused by the high-dimension matrix operation in the GNSS/RFID integration system, this dissertation proposed an optimal selection method of RFID observations with the minimum positioning error under the weighted observation condition, which considers the precision of RFID measurement and geometric distribution at the same time. The filed experiments results indicated that, in the challenging environment of no signal or weak signal caused by the urban canyon or foliage canyon, when the RFID tags were distributed symmetrically on both sides of the road, the geometric distribution of precision in the above environments can be improved by using the proposed method, and the positioning accuracy was improved more than 50%. Moreover, the computational load was decreased about 38% in this proposed method when compared with the algorithm of all-in-view RFID observations selection. It also showed the positioning availability could be improved dramatically by involving the proposed method.(4) In the navigation war, the aim of preventing the adversaries to make use of friendly civilian positioning and timing service in local area can be achieved by turning off the civil signals partially, and the global positioning and timing service will be effected unavoidablely by this approach. Taking the turnoff of partial civil signals of GPS system as an example, this dissertation analyzes the performance of global positioning and service affected by partially turning off navigation signals for preventing positioning and timing service in local area, the strategy of turning off civil signals is presented as well, which leads the smallest area of unavailable positioning in global area. The evaluation method of positioning and timing performance is defined consequently in this dissertation. The results of simulation showed that, turning off the civil signals partially would make the civilian positioning service unavailable in more than 67% area of global scope. Besides, turing off civil signals would decrease the availability of positioning service to 90% in 17% area of global scope. Moreover, turning off the civil signals partially to prevent the timing service would make the civilian positioning service unavailable in half area of global scope, and the accuracy of positioning would deteriorate in the global area. Meanwhile, the availabilities of positioning and timing would be decreased.The contirbutions presented in this dissertation can be applied in the fields of monitoring receivers, the compatible receivers and high precision surveying receivers for multiple GNSS systems, the design of signal system for ground operation and control system, the management and control strategy of civil navigation signals.