Construction Progress and Aviation Flight Test of BDSBAS

As an important part of the BeiDou global navigation satellite system (BDS-3), the BeiDou satellite-based augmentation system (BDSBAS) aims to provide a high-integrity navigation service for users in China and its surrounding areas. At present, BDSBAS has completed the preliminary construction of the system and formed the single frequency (SF) augmentation service. The paper introduces the composition and working process of BDSBAS, and expounds the solution and performance evaluation methods of the BDSBAS SF service. Tests based on a general aviation aircraft were carried out at Caihu Airport in Shenyang, China, which simulated the aircraft’s take-off and landing operation during the approach phase and the transition flight operation during the en-route phase. On this basis, the BDSBAS SF service performance was analyzed and evaluated. The horizontal positioning errors of the three flight tests are 1.62, 1.27, and 1.49 m, respectively, and the vertical positioning errors are 4.38, 4.30, and 4.04 m, respectively. In the first two tests, the APV-I availability and continuity of the service reach 100%. In the last test, a receiver false alarm event occurred, resulting in an APV-I availability and continuity of 99.993% and 99.989%, respectively. The event was confirmed to be caused by some aviation environmental factors and was not related to the system service. No integrity events occurred during the tests. The test results show that the positioning accuracy, availability, and integrity of the BDSBAS SF service meet the APV-I level requirements of the ICAO standards, which preliminarily illustrates the ability of BDSBAS to be used in the field of civil aviation

Inter-satellite clock offsets adjustment based on closed-loop residual detection of BDS inter-satellite link

It is a common and effective method in engineering science to use the "closed-loop detection" idea to detect and correct the cumulative error of system measurement. This paper indicates the favorable closed-loop conditions in the global inter-satellite link (ISL) of BeiDou-3 navigation satellite system (BDS-3), and proposes to detect and analyze the closed residuals. On this basis, a network adjustment model of the closed residuals is constructed by which the correction of inter-satellite clock offsets is realized. Calculations based on the on-orbit measured data indicate that the obvious constant or periodic non-zero closed residuals really exist in the global ISL of BDS-3. Attributed to the correction of the closed-loop residuals of the ISL, the non-closed inter-satellite clock corrections are basically eliminated, the random noise of the inter-satellite clock corrections is reduced by 30% to 50% and the accuracy of the inter-satellite clock corrections are effectively improved. It is helpful forthe service capability of BeiDou

Characterization of pesudorange bias and its effect on positioning for BDS satellites

Distortions of GNSS signals result in pesudorange biases. The biases are different for different receivers depending on frontend bandwidth and employed filters of receivers. Pesudorange biases are treated as a new error sources in this paper. Firstly, two pesudorange bias calibration calculation methods namely collocated receivers-based method and differential code bias (DCB) based method are proposed to separate pesudorange biases and other error sources. Then pesudorange biases are calculated, estimated and separated from other error sources using collocated receivers-based method. The STD of BDS estimated pesudorange biases series is approximately 0.1 m. The BDS estimated pesudorange biases keep constant with time. Pesudorange biases are also irrelevant with geographical locations of receivers. At 1.5 G band, B1I pesudorange bias is the largest. The pesudorange biases of BDS new signal B1C improve a lot compared with pesudorange biases of BDS B1I and are also much better than the GPS L1C/A. At other bands, pesudorange biases of GPS L2C are slightly larger than BDS B3I, followed by GPS L5C, pesudorange biases of BDS B2a are the smallest. The influence of pesudorange biases is also analyzed with measurements. Pesudorange biases are highly-correlated with total group delay (TGD). If the user receivers are quite different with those used for TGD calculation, the positioning accuracy will get worse