Method and apparatus for weak data frame sync in a positioning system

摘要

The present invention is related to location positioning systems, and more particularly, to a method and apparatus of synchronizing to data frames in a positioning system signal. According to one aspect, the invention speeds up the frame synchronization process by computing a frame synchronization metric for each satellite and then combining together the metrics for all tracked satellites together, after compensating for respective signal transit times. Then the invention makes a frame sync decision on the combined satellite metric. In embodiments, an optimal combining algorithm is used based on CNO of each satellite. According to further aspects, the invention further speeds up the frame synchronization process by predicting many bits in the subframe so that more bits are known in addition to the 8-bit preamble. For example, the invention recognizes that many bits in a subframe rarely change or don't change very often. Moreover, the invention uses old ephemeris used to predict new ephemeris parameters. These parameters are translated into predicted bits in the signal. Still further, old ephemeris can be used to predict almanac parameters, and the almanac can be used to predict ephemeris parameters.