Real time fast acquisition based on hardware FFT for a GPS/EGNOS receiver

GPS receivers spend a large time performing the acquisition. This is due to the great amount of required operations in order to fulfil a satellite search by using the traditional searching methods. The convolution function is necessary to acquire the signal. It can be substituted by a Discrete Fourier Transform operation using the application of the domain transform. In this paper, we describe a new method for a real time acquisition based on the frequency domain transformation. The frequency domain has gained some popularity in the field of software receivers, because of the fast to acquisition of satellites. The software implementation of the acquisition carry out all operations "off-line" by using a powerful microprocessor or a PC. Some "hard" receivers employ a hardware DFT with a small number of resolution points, which perform a low-accuracy acquisition and increase both the operational complexity and the duration of the tracking loops. Regarding the frequency tra nsformation, the acquisition requires at least one pair of FFT/IFFT provided that the replica FFT can be pre-calculated and stored within the memory. This paper presents a hardware multistandard GPS/EGNOS receiver. The prototype receiver implements a RF sampling down-conversion architecture that converts directly RF signals to digital. The RF sampling hardware architecture permits to down-convert signals up to 2 GHz at a high sampling rate (172.5 MHz) with a hardware high precision. A hardware FFT is also presented for the fast acquisition algorithm.