European Space Agency, ESA-Estec

Theoretical analyses supported by simulation and test results indicate that GPS-based attitude determination can yield accuracy of 0.5 to 1 deg. The limiting factor in the achievable accuracy is the multipath error, which arises when the GPS signal is reflected or diffracted by surfaces around the antenna. This paper considers three multipath compensation techniques. All three techniques can be implemented in the GPS receiver software. Their effectiveness was verified on a GPS test facility consisting of a tilt table with two degrees of freedom supporting a baseline of 1 m in length with two antennas connected to a commercial GPS receiver modified to process differential phase measurements. The first technique compensates multipath using a look-up table that stores the expected multipath error as a function of the azimuth and elevation angles of the incoming GPS signal. The second technique treats the multipath component of the attitude estimation error as a stationary correlated (colored) noise and uses a Kalman Filter to remove it. The third technique relies on signal-to-noise measurements to compensate multipath effects