Improving GNSS carrier phase tracking using a long coherent integration architecture

High-sensitivity carrier phase tracking is essential for new GNSS high-precision applications such as unmanned vehicles and smartphones. Increasing coherent integration time is the primary way to improve the sensitivity of carrier phase tracking, which is, however, significantly restricted by the receiver local oscillator instability. We propose a long coherent integration (LCI) architecture to improve carrier phase tracking. The architecture is equipped with a multichannel cooperative loop to track receiver oscillator errors and local loops to perform super-long coherent integration periods. The transfer function of LCI tracking loops is established in s-domain, and the tracking error models induced by thermal noise and Allan deviation oscillator phase noise are derived in z-domain. The performance of the LCI tracking architecture is tested through both simulation and actual GNSS signals. The proposed error models of LCI are validated through the semi-analytic simulation. Both simulation and real signal testing results indicate that LCI tracking loops can perform coherent integration up to 3 s and track extremely weak signals of 6 dB-Hz with carrier phase accuracy of around 4 degrees.