A subspace-based code tracking loop design for GPS multi-antenna receiver in multipath environment

Global Navigation Satellites Systems have been greatly developed in recent years, but receivers usually suffer the undesired measurement bias errors caused by multipath incidence in an urban area. We propose an effective subspace-based estimator cooperating with the conventional delay-locked loop (DLL) for Global Positioning System L1 C/A Signal. With the help of the multi-antenna, the incident rays could be distinguished in space. A forward and backward space spatial smooth technique is then taken to solve the coherent problem in signal subspace estimation. By using the structure of the receiving array, a subspace rotation invariance can be built, and the angles of arrival and relative delays of incident rays could be estimated jointly. After combining the estimates from DLL and subspace-based estimators, we can enhance the strength of the line-of-sight ray and achieve a modified delay tracking output without multipath bias effectively. Simulation results prove that compared with the existing methods, such as the narrow early-minus-late and the multipath estimating delay lock loop, the proposed method has the best multipath mitigation in the delay estimation.