GNSS Precise Point Positioning Using Low-Cost GNSS Receivers
Gill, Maninder Singh
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There are positioning techniques available such as Real-Time Kinematic (RTK) which allow user to obtain few cm-level positioning, but require infrastructure cost, i.e., setting up local or regional networks of base stations to provide corrections. Precise Point Positioning (PPP) using dual-frequency receivers is a popular standalone technique to process GNSS data by applying precise satellite orbit and clock correction along with other corrections to produce cm to dm-level positioning. At the time of writing, almost all low-cost and ultra-low-cost (few $10s) GNSS units are single-frequency chips. Single-frequency PPP poses challenges in terms of effectively mitigating ionospheric delay and the multipath, as there is no second frequency to remove the ionospheric delay. The quality of measurements also deteriorates drastically from geodetic-grade to ultra-low-cost hardware. Given these challenges, this study attempts to improve the performance of single-frequency PPP using geodetic-grade hardware, and to capture the potential positioning performance of this new generation of low-cost and ultra-low-cost GNSS chips. Raw measurement analysis and post-fit residuals show that measurements from cellphones are more prone to multipath compared to signals from geodetic-grade and low-cost receivers. Horizontal accuracy of a few-centimetres is demonstrated with geodetic-grade hardware. Whereas accuracy of few-decimetres is observed from low-cost and ultra-low-cost GNSS hardware. With multi-constellation processing, improvements in accuracy and reductions in convergence time over initial 60 minutes period, are also demonstrated with three different set of GNSS hardware. Horizontal and vertical rms of 37 cm and 51 cm, respectively, is achieved using a cellphone.