05422813 is referenced by 253 patents and cites 56 patents.

The present invention relates to a no outage GPS/AM position finding system wherein a GPS system having a plurality of satellites transmits time and location data over radio frequency signals to enable a mobile GPS receiver station on the ground to determine its position, and a cellular telephone is carried with the mobile GPS receiver, traveling in range of a plurality of conventional ground based amplitude modulated (AM) transmitters for transmitting AM signals. Each mobile GPS receiver station includes phase detection means for simultaneously receiving a predetermined number of the AM signals, and measuring the changes in phase of each of the AM signals as the mobile GPS receiver travels, and deriving therefrom an AM position signal. A reference station for receiving the GPS and AM signals provides correction signals via a cellular telephone network which receives and transmits the correction signals to the mobile GPS receiver station. The last accurate GPS position signal is used for resolving any ambiguities in the AM radio position signal and to accommodate the lack of synchronization in the AM transmitters. The reference station measures the frequency and wavelength variations in the AM signals and conveys same to the mobile GPS receiver station by the cellular telephone. The AM position signal is activated upon detecting outages or blockages in the GPS signals.

Title
No-outage GPS/commercial RF positioning system
Application Number
79810
Publication Number
5422813
Application Date
September 2, 1993
Publication Date
June 6, 1995
Inventor
Lloyd Engelbrecht
Reston
VA, US
Aaron Weinberg
Potomac
MD, US
Leonard Schuchman
Potomac
MD, US
Agent
Jim Zegeer
Assignee
Stanford Telecommunications
VA, US
IPC
H04B 7/185
G01S 5/02
G06G 7/78
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