Method and apparatus for detecting and processing GPS signals

摘要

A method acquires a location system signal where the location system signal includes a first data signal and a second data signal superimposed on the first data signal. The method includes generating an initial Doppler frequency offset value, the initial Doppler frequency offset representing a variance from a nominal frequency for the location system signal and a frequency of a received location system signal. The method also includes using the initial Doppler frequency offset value to generate a plurality of error signals, each error signal representing a difference between a sum of consecutive correlation values and a corresponding estimated ideal value. Each error signal corresponds to a different time offset and an associated time period in which the consecutive correlation values pertain. The second data signal has a bit edge that occurs during the time period of each of at least some of the sums of consecutive correlation values. A bit transition at the bit edge causes an increase in the error signal if the bit edge occurs during a time period associated with the error signal. The method also includes using a Kalman filter to generate a new initial Doppler frequency offset value, and generating new error signals.