Efficient signal acquisition and tracking for a real time GPS/Galileo software receiver

In a global navigation satellite system (GGNS) receiver the acquisition algorithms as well as the signal tracking play an important role in the receiver functioning. When the receiver is implemented in software radio technology the demanding computational complexity becomes a critical issue as much as the algorithms performance and stability. This paper presents the solutions adopted for the signal acquisition and tracking for the N-Gene fully software receiver. The acquisition algorithm is a variant of the classical "fast acquisition algorithm" where the signal correlation is obtained in time domain by means of two Fast Fourier Transforms (FFTs) and a single inverse fast Fourier transform (IFFT). A solution for improving the tracking performance in case of low C/N0, is also proposed. The work on the signal tracking focuses on a robust normalization of the discrimination functions within the tracking loops. The algorithms are presented highlighting case by case the advantages both in terms of computational complexity, robustness and performance.