In Situ GNSS Receiver Bias Calibrations using Picosecond Pulses

摘要

Direct-sampling Global Navigation Satellite System (GNSS) receivers present the possibility of traceable calibration of GNSS receiver biases at the picosecond level. This paper presents a technique using picosecond-duration pulses applied through the signal path of the receiver in parallel with the GNSS signals from an antenna. The signals are processed by a 2 gigasample/s, 8-bit, direct-sampling receiver containing broadband (low-Q) amplifiers and filters. From this single digital sample stream, the receiver extracts both the calibration pulses and the GNSS signal bands using bias-free digital downconversion techniques. The pulses, shaped by the aggregate impulse response of the receive chain, are post-processed to reveal the in situ amplitude and phase response of the system as a function of both frequency and time. This paper documents the calibration technique theory, techniques for processing the observed phase and group delay response into appropriate GNSS observation biases for given correlator designs, and bias observations over varying time and temperature. The work has direct applications to absolute ionospheric TEC observations, precise time-transfer, rapid convergence of precise point positioning, and GNSS system bias determination.