A New FFT-Based Algorithm for Secondary Code Acquisition for Galileo Signals

Abstract

The innovative spreading codes used to modulate the new Galileo signals creates new challenges for receiver designers. It is well known in GNSS systems that longer integration times are needed to obtain a better sensitivity. However, the existence of the new tiered code concept that consists of the presence of a secondary code on top of the primary code to modulate the RF signal puts a limitation on the coherent integration time for pilot channels similarly to the effect of data bit ambiguity in data channels. Within this context, this paper tackles this issue by introducing a new algorithm for wiping off the secondary code and increase the coherent integration time. The algorithm is based on the combination of serial and parallel searches. The search for the primary code phase is performed serially within one primary code length, and the secondary code phase is searched in parallel over the entire length of the secondary code. Furthermore, the proposed algorithm improves the Doppler offset estimation and reduces the overall acquisition time.