Enhanced GPS receiver utilizing wireless infrastructure
A locator using Navstar constellation signals for determining geographical location of a mobile receiver. The locator is integrated with a mobile unit of a cellular network, which derives its reference frequency from a local oscillator ( 26 ). A frequency measuring module ( 28 ) counts the number of digital numbers derived from the local oscillator passing between two consecutive time-tagged indicators of the cellular network. The estimated frequency is calculated by dividing the number of digital numbers by the nominal time interval (T 0 ) between the indicators.
1. A locator integrated with a mobile receiver unit of a cellular network for determining pseudoranges to Navstar satellites, wherein a local oscillator of said locator receives synchronization data from said cellular network for correcting a frequency shift of said local oscillator relative to time-tagged indications of said cellular network, comprising:
a frequency measuring module for determining a number of digital numbers produced by said local oscillator per nominal interval between time-tagged indications transmitted by said cellular network, and
a GPS processor for Navstar signals and for receiving said local oscillator frequency, and for receiving an output of said frequency measuring module.
2. A method for correcting oscillator frequency of a locator integrated with a mobile unit, wherein said locator calculates pseudoranges to Navstar satellites based on timing of said satellite code arrivals, and wherein cellular network data is used for calibrating said oscillator of said locator, said method comprising:
receiving time-tagged indications transmitted by said cellular network,
digitizing said time-tagged indications with reference to said oscillator of said locator,
determining a fractional number of digital numbers of said oscillator in a time interval between two time-tagged indications transmitted by said wireless network,
estimating a frequency for said oscillator by dividing said number of digital numbers by said time interval, and
sending said estimated frequency for use by a GPS processor.
3. A method for correcting a local oscillator frequency of a locator integrated with a mobile unit as in claim 2 , and wherein said time-tagged signals are synchronization frames of said cellular network.