Multipath and Attitude Estimation Phase Lock Loop for Antenna Array Signal Processing

Abstract

This work presents a new GNSS array processing algorithm to estimate simultaneously the antenna array attitude and the direction of incoming multipath wave fronts. The multipath and attitude estimating phase lock loop (MAEPLL) is a post-correlation technique based on the parallel processing of the prompt correlator values from the antenna elements, forming double-differenced prompt correlator (DDPC) values between antenna elements and satellites. With a geometrical based model of the derived DDPC values the attitude and the multipath direction of arrival (DOA) can be estimated. Non-adaptive beamforming techniques can use the estimated platform attitude and multipath DOA to obtain conventional (not differenced) correlation values. With classical DLL/FLL/PLL filters the position, velocity and timing (PVT) solution is derived after the beamforming process. On the basis of a self developed wideband multipath channel simulation framework we present our first results for the attitude and multipath DOA estimation accuracy. The results show, that the attitude accuracy is quite independent of the environmental conditions due to the double-differencing. It is also shown, that it is possible to jointly estimate antenna array attitude and multipath direction of arrival. This work outlines the mathematical foundations of a combined multipath and attitude estimation based on DDPC values. The simulation results show attitude accuracies below one degree in all three spatial directions, as well as high robustness in terms of initially assumed attitudes, multipath environments and signal strengths. The MAEPLL technique has the potential to extend the DDPC model to include an estimation of the antenna element phase center corrections (PCCs), enabling the use of cheap, supoptimal, uncalibrated and integrated antenna arrays in mass-market applications with on-the-fly antenna phase center variation calibration.