A Continuous Positioning Algorithm Based on Differential GNSS Techniques, MARG Sensors, and Barometers with Smartphones

Real-Time Kinematic positioning technique (RTK) is a differential positioning technology that can utilize pseudo-range measurements and carrier phase measurements to provide positioning results with centimeter-level accuracy in real time. However, RTK degenerates in urban areas where Global Navigation Satellite System (GNSS) signals are reflected and blocked. Positioning results can fluctuate immensely in a GNSS-hostile area. Besides, the carrier phase tracking loop is the weakest link of the GNSS receiver, and the carrier tracking loop is easier to lose lock than the code tracking loop. RTK cannot provide positioning results when satellites with valid carrier phases are less than four. The introduction of supplementary techniques and sensors can cover the shortage of RTK. Differential GNSS (DGNSS) is another differential technique that only utilizes pseudo-range measurements. DGNSS can bridge the RTK outage caused by the absence of carrier phase measurements. A Magnetic, Angular Rate, and Gravity (MARG) sensor and a barometer can help mitigate fluctuations of positioning results. Over past years, smartphones equipped with GNSS chipsets, MARG sensors, and barometers have become commodities and possess the capacity to combine these sensors to provide continuous positioning results in urban areas. This paper designs a continuous positioning algorithm based on differential GNSS techniques, MARG sensors, and barometers with a Xiaomi Mi 8. We carry out several walking tests in urban areas to evaluate the feasibility and accuracy of our algorithm. We also develop an Android application called CIGRLogger to collect sensor measurements. Researchers have access to the source code of this application and a version of RTK in C++ at https://github.com/Nronaldo.