A differential GPS or GLONASS system (collectively referred to herein as a GPS
system) is implemented for use by a base station of a wireless telephone
system (e.g., by a cellular telephone base station). Using the differential GPS
system, a differential location correction factor is determined
based on a difference between a received GPS location signal and a known fixed
location of a GPS system receiver for the base station. A differential GPS correction
signal containing the correction factor is transmitted to any or all cellular telephone
users of that base station to allow the cellular telephones to improve the accuracy
of location information independently measured by GPS receivers located in each
of the cellular telephones. The differential GPS signal may be used to increase
the accuracy of the GPS system, whatever the current accuracy of the GPS system,
allowing practical implementation of an emergency telephone system such as a 911
system using a wireless system such as a cellular telephone system.
