RTK and PPP-RTK Using Smartphones: From Short-Baseline to Long-Baseline Applications

Low cost receivers providing GNSS code and phase raw measurements for multiple frequencies and multiple GNSS constellations have recently become available on the market. This significantly increases the number of devices equipped with the necessary sensors to perform precise GNSS positioning like Network-RTK or PPP. The smartphone GNSS measurements often suffer from low signal-to-noise, inhomogeneous antenna gain and high levels of multipath. Here, we show how to tackle several of currently present obstacles and demonstrate centimeter-level kinematic positioning with a low-cost GNSS antenna and a low-cost GNSS receiver built into an off-the-shelf smartphone. For some devices we found that the phase observations do not have integer characteristic but appear to have random biases. To some extend these observations can still be used in a “float”- type precise algorithm. Low cost GNSS sensors like the ones built into smartphones are generally used with antennas that have a uniform gain pattern and do not reject LHCP signals. Accordingly, strong multipath influence is observed in many applications. Experiments both in a zero-baseline and a short-baseline configuration have been performed, to evaluate the aforementioned biases and discontinuities. We demonstrate instantaneous ambiguity resolution in the zero-baseline setup, showing the potential for RTK-positioning with low-cost sensors available inside smartphones. Positioning with PPP-RTK or Network-RTK is more challenging because additional residual atmospheric noise is present. Experiments with different baseline lengths have been performed in different ionospheric conditions and the achieved accuracies are reported.