Research On Key Technologies Of BDS/GPS Receiver For Weak Signal

With the construction and operation of increasing global satellite navigation system,GNSS has been widely used in many aspects of life and has achieved great success.However,GNSS is designed for navigation and positioning in open space,rather than for inner space,jungle,urban canyon,deep space and other weak signal environment.The current weak signal receiver technology is mostly for the GPS civilian signal,while this paper focus on the weak signal reception technology of BDS IGSO/MEO civilian frequency.The main contents of this paper are as follows.(1)Half-bit zero-padding algorithm and full-bit zero-padding algorithm with no auxiliary information are proposed for the BDS signal modulated with the NH code.Both methods can effectively avoid the data bit jump and strip NH code;and the full-bit zero-padding algorithm is also available to GNSS signals without NH code.Then,the application of A-GNSS technology to reduce the huge amount of computation and shorten the acquision time is analyzed.In terms of code phase acquisition,assisted part-bit zero-padding algorithm and the assisted full-bit zero-padding algorithm are put forward;As for the frequency acquisition,the application of auxiliary information to reduce the search space is analyzed.Experiments show that the acquisition sensitivity of full-bit zero-padding algorithm and half-bit zero-padding algorithm is better than-160 dBm and-155 dBm respectively.(2)In order to solve the problem of data bit jump limiting the coherent integration time,the tracking loop based on non-coherent structure is designed,which uses the non-coherent phase detector to avoid the effect of data bits.The two-quadrant arctangent phase detector is often used to track signal modulated with navigation message,but its phase range is very limited.So tracking loop based on A-GNSS that can strip the navigation data is designed to achieve coherent integrationa of longer time and to use four-quadrant arctangent phase detector which has a wider phase range.Experiments show that the tracking loop with non-coherent structure can track no less than-155 dBm signal and that the tracking loop based on A-GNSS can track no less than-160 dBm signal.(3)Van Diggelen‘s technology and five-state coarse time navigation are studied to solve the problem that the signal transmit time cannot be assembled under weak signal condition.And pseudorange-assisted and A-GNSS-based unbiased recovery method of signal transmit time is proposed.The method of BDS/GPS coarse time navigation is put forward to solve the problem that the number of visible satellite is small and that the satellite geometry is poor under weak signal condition.Positioning experiment is carried out under the weak signal condition in underground garage with precision around 50 m where assisted height is used to lower the PDOP.