Optimal Doppler-aided smoothing strategy for GNSS navigation

Carrier-phase-smoothed code (CPSC), i.e., smoothing of the code using carrier phases, has widely been used to reduce the code noise in GNSS applications. However, the efficiency of CPSC suffers significantly from cycle slips, interruptions and jitters. The GNSS Doppler, as an instantaneous measurement, is robust and immune to cycle slips and proven useful in GNSS-challenged environments. We develop optimal Doppler-smoothed code based on the principle of minimum variance using the Hatch filter for two typical applications, which are called pure Doppler-smoothed code (PDSC) and continued Doppler-smoothed code. PDSC results from smoothing the code using only Doppler, whereas in case of continued Doppler-smoothed code, the smoothing continues using Doppler once the carrier phase becomes unavailable. Furthermore, in order to refine the Doppler-smoothed code model, a balance factor is introduced for adjusting the contributions of raw code and Doppler measurements to the smoothed code in case the Doppler noise is relatively large. Finally, experiments are carried out to demonstrate the performance of the theory, which verifies its validity and efficiency.