Performance comparison of Kalman filter and maximum likelihood carrier phase tracking for weak GNSS signals

GNSS carrier phase measurement capability is one of the most important features for high performance/accuracy receivers. However significant signal attenuation due to blockage and multipath as experienced indoors for example, degrades carrier phase quality in standard carrier phase tracking loops using PLL or KF-PLL. Under such conditions, the receiver may not be able to generate reliable carrier phase measurements either due to weak signal, fading or fragility of conventional tracking loops. One contribution of this paper is the proposed decoupled maximum likelihood carrier phase, Doppler and Doppler rate tracking architecture. This approach first independently estimates Doppler rate and Doppler based on power spectra and then estimates the carrier phase if possible. In order to assess the actual carrier phase measurement quality, controlled simulation is also conducted after analyzing the overall phase tracking performance. Double differenced carrier phase results as well as RTK solutions show that the proposed method works well and is able to generate reliable carrier phase measurement and centimeter level solution when the carrier-to-noise-density ratio (C/N0) is about 20 dB-Hz.