Differential GPS supported navigation for a mobile robot

The objective of this work is the development of a low cost differential GPS system suited for mobile robotics applications which enhances positioning accuracy compared to a single receiver system. In order to keep costs minimal we used single frequency (L1) receivers, namely U-Blox AEK-4T. We adapted the GPS Toolkit (GPSTk) to work with single frequency (L1) observations in real-time. This allowed us to apply an already existing algorithm, originally intended for Precise Point Positioning (PPP) applications using a double frequency receiver. The core of this algorithm is a Kalman filter that processes code and carrier phase single differences. Carrier phase ambiguities are treated as real (float) values, we do not try to fix them to their correct integer values. In a static test with a baseline length of 11m, observations were collected for five minutes. The developed system achieved a horizontal RMS of 6.9cm. Furthermore we carried out a dynamic test where the rover drove around in a circle. Seven circles were driven in about five minutes. The system determined the circle's radius with an RMS error of 13.2cm.