Space and Frequency Diversity Characterization of Mobile GNSS Receivers in Multipath Fading Channels

Diversity reception of multipath Global Navigation Satellte System (GNSS) signals offers a new insight into carrier phase-based high-precision positioning. The focus of this paper is to demonstrate the fading independence between space and frequency diversity GNSS signals. In harsh urban environments, multipath components arrive to the mobile receiver antenna with different phases and Doppler shifts, therefore giving rise to the discontinuity of code and Doppler observations and large tracking errors. In this paper, an empirical model of fading GNSS signals is constructed, including power fluctuations and spread metrics. Based on this model, real BeiDou Navigation Satellite System (BDS) signals from two GNSS dual-frequency antennas are characterized, at both information and signal level. The block processing algorithm is utilized for signal investigation. Results show that: (1) a high proportion of asynchronous loss-of-lock (around 16%) is experienced by observations of diversity signals; and (2) power fluctuations of fading signals are uncorrelated in frequency separated branches unconditionally, yet for space diversity signals the independency exists in dynamic fading channels only. The results above corroborate the significant potential gain of diversity reception, and could be further implemented in researches of diversity combined GNSS parameter estimation in dense fading conditions.