Introduction to Global Navigation Satellite Systems
Introduction to Global Navigation Satellite Systems
Prof. Letizia Lo Presti
Politecnico di Torino
A Global Navigation Satellite System (GNSS) consists of a constellation of satellites, whose payloads are especially designed to provide positioning of objects with global coverage. It implements the trilateration method, which uses the geometry of triangles to determine the relative positions of objects with respect to some reference points, located at known positions. In GNSSs the reference points are the satellites, and the objects are located at the Earth surface or fly around the globe.
Each satellite broadcasts a signal that contains the position of the satellite and the precise time the signal was transmitted. The position of the satellite and the timing information is transmitted in a data message by adopting the CDMA (Code Division Multiple Access) technique. The receiver implements the trilateration method by measuring the time-of-flight from the satellites. Several such measurements can be made at the same time from different satellites, allowing a continual fix to be generated in real time.
The United States' Global Positioning System (GPS) is the only fully functional GNSS system, operational since 1978 and globally available since 1994. The Russian system GLONASS was fully functional in the past, and now is only partially available. It is expected to return to full global availability by 2010. Galileo is the European contribution to GNSS. Agreed on March 2002 between the European Union and the European Space Agency, it will be operational by after 2012. The first experimental satellite was launched on 28 December2005. China is implementing its GNSS system called COMPASS.
In this lecture some selected topics from the GNSS field will be presented with the aim of giving the basic principles to understand how a receiver (possibly a very simple handset) can implement the trilateration methodto fix its position. In particular the following subjects will be covered:
- First lesson: the trilateration method, thee structure of the transmitted signal,
- Second lesson: the scheme of the receiver,an introductory outline of the acquisition and tracking algorithms.
Letizia Lo Presti () is full professor at the Department of Electronics of Politecnico di Torino. She is the head of the NavSAS research group. Her research activities cover the field of digital signal processing, simulation of telecommunication systems, array processing for adaptive antennas, and the technology of navigation and positioning systems. Currently she is involved in several international research projects and is WP leader in several projects funded by the GJU (Galileo Joint Undertaking), and by the European Framework programs. She is author of several papers in the research areas of signal processing, and satellite navigation. She is associated editor of the Indawi International Journal of Navigation and Observation.
Her teaching activity is mainly focused on signal processing (from the fundamentals to advanced concepts, such as array processing, statistical signal analysis, time-frequency distribution, and estimation theory), digital communications, and architectures and algorithms for GPS and Galileo receivers. She is author of three books. Her book on ”Signal Analysis” (in Italian) is widely adopted in all thecourses of Signal Theory held in Politecnico. She is the scientific coordinator of the Master on Navigation and Related Applications held by Politecnico di Torino. She actively cooperates with the officers of the UN-OOSA (United Nations - Office for Outer Space Affair) in Vienna (Austria) in the framework of the UN/Italy fellowship program, with the aim of keeping the Master program permanently aligned with the UN needs and suggestions. She was the moderator of the Forum ”Means and Infrastructures for Education” in the framework of the ESA/GJU workshop ”Promoting tools and facilities for satellite navigation applications” held in April 2005.
She is a member of the Working Group of ICG (International Committee of Global Navigation Satellite Systems) leaded by UN-OOSA (United Nations – Office for Outer Space Affair). She is the coordinator of the working group on Navigation and Telecommunication of ASI.