C/A CODE MULTIPATH MITIGATION AT GPS BASE STATIONS FOR IMPROVED DGPS CORRECTIONS USING WAVELETS

Differential GPS (DGPS) correction technique is one of the most popular and accurate techniques to enhance GPS positioning accuracies by minimizing most of the common mode errors as a collective process. Several DGPS processing techniques can he used, for instance, single differencing and double differencing which are very common in practice. Irrespective of the DGPS processing techniques used, the ultimate accuracy of the user location depends on the existence of non-common mode (site-dependent) errors, which occur at the points of observation and the reference. Of these errors, the most common site-dependent error is the multipath. Several researchers have proposed different strategies and approaches to minimize the multipath effect on the final GPS position estimates. This manauscript evaluates the potential of applying wavelets transform to C/A code multipath mitigation at GPS reference stations, for improved differential GPS corrections. An experiment was conducted making C/A code DGPS observations at three precisely known ground control stations assuming that two of them were permanent reference stations and the third as a user station. Four segments of about 24-hour continuous static observations were made by introducing four different multipath environments at one of the reference stations, each segment using a different type of artificial signal reflector. By making use of the known GPS receiver-reflector configuration, pseudo-range multipath was precisely calculated for each observation segment In a subsequent analysis, different wavelet families and decomposition levels were applied to extract multipath from the pseudo-range residuals. By comparison, the best wavelet and level of decomposition were identified. The accuracy of this process is highly dependent on selecting the best suiting wavelet family and level of decomposition. The C/A code DGPS positioning accuracies prior to and after multipath correction are also presented.