In-Flight Performance Assessment of the Single-Frequency GPS/BDS Receiver for Yaogan-30 Series Satellites Real-Time Navigation

Within the Yaogan-30 series satellites, the low-cost single-frequency Global Positioning System/BeiDou Navigation Satellite System (GPS/BDS) receiver was employed for onboard real-time navigation. This article presents the in-flight performance of the single-frequency GPS/BDS receiver, including the tracking of GPS/BDS satellites, the noise of measurements, and the orbit accuracy of onboard real-time navigation results. First, in terms of satellites tracking, no BDS-2 satellites are tracked in 30–40% of all the time, four to seven BDS-2 satellites can be observed for less than 15% of the time, and only one to three BDS-2 satellites are available for the rest time, whereas 7–12 GPS satellites are tracked for the vast majority of the time. Obviously, the GPS observations play a more important role than BDS-2 data in real-time navigation and precise orbit determination (POD). Although the receivers only provide the single-frequency C/A-code pseudorange measurements without carrier-phases output, the accuracies of postprocessed POD could arrive at the level of 10–25 cm in terms of 3-D position. Hence, the post precise orbits are used as the reference for the assessment of real-time navigation accuracy. The assessment results demonstrate that the onboard real-time navigation accuracies of 2.0–3.5 m for 3-D position and 10.0–13.0 mm/s for 3-D velocity are achievable. At the same time, the statistics on the C/A-code pseudorange residuals after POD processing reflects that the noises of measurements from GPS and BDS-2 satellites are at the same level of 0.5–1.6 m. It should be noted that there is a notable velocity deviation of up to about 7.6 mm/s. Nevertheless, even with this obvious systematic error, the current velocity accuracy could still meet the real-time requirements of the small Yaogan-30 series satellites. In addition, some offline simulative solutions with tuned strategy settings are tested to validate the potential real-time navigation accuracy improvement. The simulation experiment tests results illustrate that a higher real-time orbit accuracy of roughly 1.0 m for 3-D position and 1.0 mm/s for 3-D velocity could be obtainable, if an optimized power spectral density of estimated empirical accelerations and a slightly higher order and degree of gravity model (50×50) are adopted. All the above analyses show that the single-frequency pseudorange Global Navigation Satellite System receiver is a high cost-effective sensor and has a wide horizon of application in the aerospace market.