On the feasibility of cm-accurate positioning via a smartphone's antenna and GNSS chip

The feasibility of centimeter-accurate carrier-phase differential GNSS (CDGNSS) positioning using a smartphone's internal GNSS antenna and GNSS chip is investigated. Precise positioning on a mass-market platform would significantly influence the world economy, ushering in a host of consumer-focused applications that have so far been hampered by the several-meter-level errors in traditional GNSS positioning. Previous work has shown that GNSS signals received through a mass-market smartphone's GNSS antenna can be processed to yield a centimeter-accurate CDGNSS position solution, but this earlier work processed all GNSS signals externally to the smartphone. The question remains whether a smartphone's internal oscillator and GNSS chip can produce observables of sufficient quality to support centimeter-accurate carrier-phase-based positioning. This paper answers the question by accessing and processing the raw code- and carrier-phase observables produced by a mass-market smartphone GNSS chip — observables that have heretofore been unavailable to the research community. The phone's carrier phase measurements are shown to suffer from five anomalies compared to those from a survey-grade GNSS receiver, four of which are readily fixed in post-processing. The remaining anomaly, an error in the phase measurement that grows approximately linearly with time, currently prevents the phone's phase measurements from satisfying the conditions for CDGNSS positioning. But the phone's measurements seem otherwise fully capable of supporting cm-accurate carrier-phase differential GNSS positioning. A separate analysis of a smartphone's GNSS signal strength dependency on azimuth and elevation reveals that multipath-induced deep fading and large phase errors remain a significant challenge for centimeter-accurate smartphone positioning.