GPS moving performance on open sky and forested paths

In this paper we present a systematic study of the performance of seven different configurations of GPS on a moving vehicle using three different GPS receivers. The seven different configurations are 1) single frequency code differential DGPS, 2) double frequency code differential DGPS, 3) RTK-GPS receiving RTCM correction from a mobile phone, 4) RTK-GPS receiving RTCM correction information via wireless module from base antenna, 5) StarFire WADGPS, 6) StarFire-DGPS dual mode and 7) StarFire-RTK GPS dual mode. As GPS is mostly used in loosely coupled configurations where receiver output is fused with other sensors, the contribution of this paper is the statistical comparison in two dimensions of different GPS configurations using as performance index availability, precision (using standard deviation parameters of each measurement) and reliability. Two types of study environments were tested, open sky and under tree shading. Time for re-acquiring fix solution for RTK-GPS configurations and re-acquiring dual frequency solution by dual frequency configurations are discussed as well. Finally, experimental measurement results show how under tree shading, biased position data with small covariance can be rejected thresholding measurements with small HDOP values and large number of satellites used for solution.