Pseudorange-bias characteristics and the weakening method of BDS satellites

Abstract

The nonideal characteristics of a navigation satellite signal will cause a pseudorange bias, which is manifested by the same type of receiver with the same pseudorange biases and different types of receivers with different pseudorange biases. When the technical state of receivers providing the navigation product is inconsistent with that of the users, the pseudorange bias will cause degradation of navigation and positioning service performance. In this paper, the pseudorange bias of BDS (Beidou Satellite Navigation System) is calculated using the ultrashort baseline pseudorange double-difference O−C (Observation Minus Computation) method. A large bias of B1I is obtained between two different juxtapositional receivers in the early stage of the experimental satellites. Thereafter, three methods, including the adjustment of the parameters of the loop of the receiver, a change in the multipath reduction algorithm, and an adjustment of the filter parameter of the predistortion of the satellite, are designed to reduce the bias. Experimental results indicate that the adjustment of parameters of the loop of the receiver can significantly reduce the pseudorange bias between the satellites, and the standard deviation of the pseudorange bias of B1I can be reduced from 0.63 to 0.36 m. Compared with the antimultipath observation, the observation of a narrow correlation can significantly reduce the pseudorange bias, and the standard deviation of the pseudorange bias of BII can be reduced from 0.36 to 0.18 m. Further, an adjustment of the filter parameters of the predistortion of the satellite can reduce the pseudorange bias of a single satellite by 0.3–0.4 m. There is no fixed reference satellite to evaluate the pseudorange biases of BDS satellites. A non-real-time double-difference O−C method that is based on the same external time and frequency controls of different receivers is designed to calculate the pseudorange bias. Employing this method, the characteristics of the pseudorange biases of BDS and GPS (Global Positioning System) satellites are compared. It is confirmed that (1) pseudorange biases exist in both BDS and GPS satellites, (2) the pseudorange bias of the L2C signal of GPS satellites is equivalent to that of the B1C data branch of BDS satellites, (3) the pseudorange bias of L1CA of GPS satellites is equivalent to the interoperable B1C pilot branch of BDS satellites, and (4) the pseudorange bias of L5C of GPS satellites is larger than that of the interoperable B2a signal of BDS satellites.