Abstract

A method for fast acquisition of Satellite Positioning System (SATPS) signals from a satellite-based positioning system, such as GPS or GLONASS, that does not require permanent storage of satellite almanac information at an SATPS ground station. This SATPS signal acquisition method can be used whenever the "new" station initially powers up or has lost lock on one or more SATPS signals that must be reacquired. A nearby reference SATPS station, whose location coordinates are known with high accuracy, provides the new SATPS station with differential positioning SATPS information, and, optionally, with SATPS satellite ephemeride information on each SATPS satellite visible from the reference station. The new station then uses this differential SATPS information to establish channels to search for (only) the SATPS satellites that are visible from the reference station. By limiting the search to the frequency range and code-phase attributes, such as the distinctive pseudo-random noise code used by each SATPS satellite, corresponding to these visible SATPS satellites, the ranges to be searched are decreased. When a first SATPS satellite signal is acquired and locked onto by the new station, the frequency range for searching is narrowed to a range corresponding to the Doppler shift frequency range for the visible satellites, and acquisition of additional SATPS satellite signals proceeds quickly. This system also allows the use of less accurate timing sources for the new stations. A new station need not store the ephemeride information for the SATPS satellites but may call upon and use the ephemeride information stored at the reference station.