Cyclic Spectral Analysis of GPS signal

The aim of this thesis is to propose cyclostationary–based techniques in order to improve GPS system performance with respect to synchronization and parameter estimation problems, in severe noise and interference environments. A detailed analytical model is derived for the GPS-L1 signal which is shown to be second-order cyclostationary. Closed forms for the the cyclic autocorrelation functions and cyclic spectra are derived for the complex envelope of this signal. It is shown that different signal models must be considered for different data-record lengths of interest in the applications. Effect of the satellite motion on the received GPS signal is investigated in order to correctly model the propagation channel between a GPS satellite and a stationary receiver on the Earth surface. A general Doppler model is assumed, where the so–called narrow band condition is not satisfied. Thus, the Doppler effect is modeled not only as a frequency shift on the carrier but also as a stretching of the complex envelope. A new cyclostationary–based synchronization technique for the coarse acquisition code is proposed, which assumes this general model for the GPS received signal. As a consequence, observation intervals significantly longer than those adopted in conventional techniques can be adopted, leading to a higher immunity against disturbance signals. Numerical results are presented to corroborate the analytic results. Simulation results show that the proposed method significantly enhance the performance with respect to the conventional GPS synchronization techniques.