Improving Pseudorange Estimation in GNSS Receivers with a Recursive Bayesian Approach

A Global Navigation Satellite System (GNSS) receiver provides essentially two independent measurements of pseudorange through the estimation of code delay and carrier phase. Although the code delay estimate is an absolute (unambiguous) measurement its accuracy is hindered by noise; on the contrary, the phase estimate has, in general, better accuracy but is ambiguous. The Hatch filter has been used as the conventional solution to merge the two kinds of measurements. Herein, we propose an alternative solution based on the joint code delay/phase estimation using a bank of stochastic nonlinear filters. The phase ambiguity is progressively reduced by merging the code delay estimates with the phase estimates provided by the selected nonlinear filter.