Frédéric Chastellain
The Global Positioning System (GPS) is a trilateration system which allows to compute the position of a receiver from the time the signals need to propagate from the satellites down to the receiver. Since the Selective Availability (SA) was turned off in 2000, the most important source of error is due to the variable delay experienced by the signals when traveling through the ionosphere. Today, the majority of GPS receivers use the L1C/A signal, the only civil signal currently transmitted by a full constellation of satellites, to compute their positions. The United States' GPS is actually only one of several Global Navigation Satellite Systems (GNSS) under development, such as the european Galileo or the Japanese Quasi-Zenith Satellite System (QZSS). In the years to come, the constellations of these new GNSS will be fully deployed, providing new modernized signals. The GPS is actually also being modernized and will provide two new civil signals, the first in the L2 band (1227.6 MHz) and the second in the L5 band (1176.45 MHz), as well as an improved version of the L1C/A signal in the L1 band (1575.42 MHz). The first fully available new civil signal will certainly be the GPS civil signal in the L2 band called the L2C signal. The availability of two civil signals in two different bands will give the opportunity to correct the ionospheric error to a great extent! However, receiving two signals located in different bands will add complexity in the receiver, particularly in the radio-frequency (RF) front-end. This is a major issue since, for the mass market, improved performances do usually not justify a higher power consumption and cost. As a consequence, the first objective of this thesis was to design a low-power dual-frequency RF front-end architecture for the L1C/A and L2C signals that could be integrated using standard CMOS technology and which would have a power consumption and performances comparable with that of state-of-the-art single-frequency GPS RF front-ends. Dual-frequency correction of the ionospheric error will also allow to improve the performances of another application of GPS called GPS timing. Indeed, the GPS provides the most precise time reference globally available anywhere on earth! As a consequence, an attractive solution to synchronize telecommunication networks consists to use the time reference provided by the GPS. However, the accuracy provided by single-frequency GPS receiver will soon not be sufficient anymore to be compliant with upcoming telecommunication standards. For this reason, the second objective of this thesis was the development of a dual-frequency RF front-end for an L1C/A + L2C GPS receiver for timing applications.
EPFL2010
