Acquisition of satellite navigation signals using dynamically chosen measurements

Abstract

A new approach to sequential acquisition of satellite navigation signals is presented where the collection of measurement statistics is steered dynamically during the acquisition process. The process consists of a fixed number of operation cycles during which the state of the receiver is maintained as a vector of conditional probabilities of acquisition hypotheses, each hypothesis being associated with a code delay and a Doppler frequency. During each operation cycle, one hypothesis is singled out by applying a suitable policy on the state vector. The down-converted satellite signal is then despread and frequency shifted according to the hypothesis. The resulting signal is integrated and squared to form a statistic that is used to update the state vector according to Bayes' theorem. After completing the cycles, a decision is made in favour of the hypothesis corresponding to the highest posterior probability. Two policies are investigated, one based on the maximisation of one-step posterior probability and the other based on the maximisation of information gain. Simulation results are presented indicating that the proposed approach provides a significant performance advantage over standard techniques for a wide range of signal-to-noise ratios.