A Fast Satellite Acquisition Method

Abstract

The fast acquisition techniques are suggested to acquire the code phase and the residual frequency modulation after carrier wipe-off in a GPS receiver. The methods are intended for acquiring signals also indoors where the satellite signals are weak and the detection requires the noise bandwidth of few Hz. In this case the two-dimensional search in (code phase/frequency) domain requires significant amount of computations and the paper suggests fast algorithms where many operations are shared when performing search for different options by using Fast Fourier Transform and DFT domain replica shifting approach. The search space is divided in a way to apply the FFT for the search in frequency domain. At the same time FFT could be applied for the search also in code phase dimension. Thus the acceleration property of FFT is utilized in both directions. With slight degradation in performance the algorithm has a modified version which implements the technique using 2-dimensional FFT. Numerous efficient 2D FFT algorithms are known and could be utilized. A single FFT based approach for performing DFT decomposition in both directions is also derived. The techniques are then extended to reduce significantly the computational complexity by shifting replica approach in frequency domain.