Determination and analysis of front-end and correlator-spacing-induced biases for code and carrier phase observations

Global navigation satellite system (GNSS) biases preclude integer ambiguity resolution and degrade positioning accuracy if they are not corrected in GNSS precise applications. Biases in GNSS positioning applications occur because of imperfections and physical limitations in satellite and receiver hardware. Consequently, these biases will affect the accuracy of positioning solutions, particularly for precise applications due to the existence of biases in the code and carrier phase observations. Various types of biases between systems, frequencies, and satellites have been defined and analyzed. In addition, receiver biases are often assumed to be eliminated by differencing observations between satellites, although this is not always true. This paper investigates the determination of the receiver front-end and correlator-spacing-induced biases in code and carrier phase observations with a focus on how receiver front-end and correlator spacing affect the code and carrier phase measurements, and how such biases vary with respect to the use of different correlator spacings and frontends. Firstly, oscillator, front-end chip, and ADC-induced biases, as well as their observability, will be discussed. Several groups of datasets with different frontends have been collected and used to determine the inter-front-end (including oscillator, chip, and ADC) pseudorange and carrier phase biases. Then, a software receiver that allows the tracking of a satellite with a series of different correlator spacings has been developed to assess measurement biases with different datasets. The results show that the inter-front-end biases and correlator-spacing-induced biases are significantly different among satellites, which can not be ignored during the GNSS positioning. This is because the single-difference of measurements between satellites can not eliminate all these biases. The results with the software receiver connected to different frontends and different correlator spacings indicate that the satellite-dependent biases depend on the configuration of the in-receiver hardware and software.