Line-Of-Sight Based Multipath Avoidance for GNSS Signals: Data Structures and Algorithms
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This paper presents a computational geometric approach that utilizes the digital elevation model (DEM), shapefiles, and GNSS satellite flight schedules to identify satellites that are (not) susceptible to multipath transmission interference. Using DEM maps and shapefiles as input, we use Line of Sight (LOS) analysis to create the viewshed skyplot (VSP), which presents the lowest elevation angle that is free of obstruction for each azimuth. By projecting the satellite flight trajectory on the VSP, one can identify which of the satellites are free from multipath interference. The compiled result can be represented in a compact LOS table, which can then be disseminated via the Internet to consumer grade receivers around the affected region. We tested the proposed scheme on selected areas of the Texas A&M University campus using a GPS software defined radio (SDR) based on the USRP N200 and open source GNSS software. The empirical results confirm validity of the computational model. It also suggests the significance of the tree canopy in the local region, as well as the twilight zone effect in terms of the carrier to noise ratio (CNR) when satellites phase in and phase out the open vs. blocked areas of the VSP.
