Wavelet transform application to C/A code multipath mitigation at GPS reference stations for accuracy improved differential GPS corrections | |
| Author | Dammalage, Thilantha Lakmal |
| Call Number | AIT Diss. no.RS-09-02 |
| Subject(s) | Wavelets (Mathematics) Global Positioning System |
| Note | A disseriation submitted in pa1iial fulfillment of the requirements for the Degree of Doctor of Engineering in Remote Sensing and Geographic Information Systems |
| Publisher | Asian Institute of Technology |
| Abstract | Global Positioning System (GPS) enables instantaneous positioning and navigation in three dimensional spaces. Most of the presently available GPS receivers are utilizing highly improved hardware and processing algorithms. However, still these GPS receivers are suffering comparatively large positioning errors due to several limitations caused by receiver itself, medium of signal travel, satellite parameters, etc. The said error sources are grouped into common and non-common mode errors, considering its nature on instantaneous observations. However, there are many different augmentation techniques to enhance the accuracy of GPS observations. Among those, Differential GPS (DGPS) technique is one of the most popular and accurate techniques to enhance GPS positioning accuracies by minimizing most of the common mode errors (e.g. ionospheric, tropospheric and satellite clock errors) as a collective process. In this regard, several DGPS processing algorithms can also be used, for instance, single differencing and double differencing which are very common in practice. Irrespective of the DGPS processing algorithms used, the ultimate accuracy of the user location depends on the existence of non-common mode (site-dependent) errors, which occur at both sites; the points of observation and at the reference. Of these, 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 dissertation evaluates the potential of applying wavelets transform to Cl A code multipath mitigation at GPS reference stations, for improved differential GPS corrections. Experiments were conducted making Cl 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 hours 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 using 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. Comparing the calculated and extracted multipath, the best wavelet and level of decomposition were identified. Also, the Cl A code DGPS positioning accuracies prior to and after multipath correction are analyzed. Based on the results of this research, where it is concluded that about 50% of accuracy improvement is made possible by multipath mitigation of Cl A code DGPS corrections. Further, careful investigations of resulted accuracies after multipath mitigation indicate that three factors; cycle slip, remaining un-modeled linear error terms, and observation length contribute as accuracy diminishing sources of pseudo-range multipath residuals calculated based on carrier and code combination. Therefore, the research study was further extended to accomplish improved accuracies by minimizing the identified factors. Further, it was found that, biorthogonal wavelet family (bior3.5) and 8 levels of decomposition as the best filter bank for the de-noising of noisier pseudo-range multipath residuals. The improved Cl A code DGPS positioning accuracies prior to and after multipath correction are also presented. |
| Year | 2009 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Remote Sensing (RS) |
| Chairperson(s) | Kibe, Seishiro; |
| Examination Committee(s) | Samarakoon, Lal;Shrestha, Rajendra Prasad;Chalermchon Satirapod;Yasuda, Akio; |
| Scholarship Donor(s) | Japan; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2009 |