Integrated navigation and communication satellite system

Abstract

A system and method for improving the accuracy of pseudorange error measurements at a receiving or user station by utilizing a communications satellite as an additional ranging source for providing navigational signal information, wherein the user station, in fixing its position on the Earth, receives a pseudorange signal directly from a GPS satellite and also a pseudorange indicative or pseudorange-error indicative signal from a communications satellite which re-broadcasts, a time tagged, indicative signal to serve as another observable in pseudorange equations computed in the user station. The communications satellite may receive a pseudorange signal directly, or an error indicative signal from an Earth-based station, for conversion into the pseudorange indicative or error indicative signal it transmits. A particular embodiment for incorporation in a communications satellite constellation, such as Globalstar.TM., involves a reference station, or network of reference stations disposed at appropriate Earth locations, for providing pseudorange error signals from their locations that are collected at a masterstation in a satellite gateway for processing and then transmitting by the gateway to a communications satellite. The satellite converts and re-transmits the processed information to a user station at another Earth location where the received information is used, along with directly received GPS information signals, to enhance the navigational position accuracy of the user station. Thus, an additional ranging source is provided that improves the accuracy, availability, and integrity of the pseudorange measurements.