A new fast code/frequency acquisition algorithm for GPS C/A signals

We propose a new algorithm for code and frequency acquisition of GPS C/A signals based on the stochastic nonlinear filtering framework. First, the delay and multiply method is used for code acquisition in the presence of Doppler frequency shift (DFS). Then, we resort to a bank of stochastic nonlinear filters (NLFs) to estimate the phase associated with the DFS using the despread signals. A criterion based on the NLFs innovations processes selects the phase estimates which feed a (modified) Kay algorithm that produces the DFS estimates. The same basic structure is also utilized in tracking mode by simply increasing the number of samples per phase estimate, thus allowing the tracking errors to be minimized (this comes at the cost of diminishing the tracking bandwidth). The proposed architecture yields small code/frequency acquisition intervals and reduced tracking errors; it is an alternative to conventional phase-lock loop circuits and has great potentialities for software radio implementation.