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Multipath is the most critical source of error for GNSS measurements, in urban environments. Besides the introduction of a bias in the raw measurements, the building occlusion of the signals leads also to the intermittent reception of satellite signals which causes a loss of signal tracking lock. The well-known Code-Minus-Carrier (CMC) approach isolates multipath and thermal noise by taking the difference between the code and the carrier phase measurements. This methodology is widely applied in precise positioning techniques, such as Real Time Kinematics (RTK) and Precise Point Positioning (PPP), as well as in the aviation domain. However, the use of CMC for multipath characterization in urban environments is challenging because cycle slips induce continuous loss-of-Iock. This article analyzes and compares two alternatives to CMC, that are unaffected by cycle slips: a Double Difference method (DD) between target measurements and reference station measurements, and a Differential method obtained by leveraging Satellite Based Augmentation System (SBAS) correction technique, used in aviation applications. A comparative analysis between the reference methodology (CMC) and the proposed methodologies (DD and SBAS-corrected) has been performed. The comparative results are based on temporal and statistical analysis of the estimated multipath error based on a static data campaign.
Matera et al. (Tue,) studied this question.