FFT-based approach for fast acquisition in spread spectrum communication systems

This paper describes a non-coherent technique for fast acquisition of direct sequence spread spectrum (DS/SS) signals in low earth orbit (LEO) satellite communication scenarios. Large Doppler offsets are inherent to such environments and are likely to cause major problems during the code acquisition phase due to the introduced frequency ambiguity. In the present paper we discuss the use of a set of partial correlators for code phase acquisition, combined with a fast Fourier transform (FFT) for the purpose of simultaneous Doppler estimation. We will show that the use of this architecture largely accelerates the synchronisation process compared to conventional techniques over a wide range of Doppler offsets. Furthermore we discuss the implementation of a zero-padded FFT that increases the frequency resolution to such an extent, that acquisition times identical to scenarios without existing Doppler offset can be achieved.