Multipath Mitigation Techniques for Satellite-Based Positioning Applications

The ever-growing public interest on location and positioning services has originated a demand for a high performance Global Navigation Satellite System (GNSS), such as the Global Positioning System (GPS) or the future European satellite navigation system, Galileo. The performance of GNSS is subject to several errors, such as ionosphere delay, troposphere delay, receiver noise and multipath. Among all these errors, multipath is the main limiting factor in precision-oriented GNSS applications. The reception of multipath creates a bias into the time delay estimate of the Delay Lock Loop (DLL) of a conventional navigation receiver, which eventually leads to an error in the receiver’s position estimate. In order to mitigate the multipath influence on navigation receivers, the multipath problem has been approached from several directions. Among them, the use of special multipath limiting antennas (i.e., choke ring or multi-beam antennas), the post-processing techniques to reduce carrier multipath, the carrier smoothing to reduce code multipath, and the code tracking techniques based on receiver internal correlation function are the most prominent approaches.