Navigation system and method

US4445118A · kind A · utility

Assignee

• The United States of America as represented by the Administrator of the National Aeronautics and Space Administration · US

Inventors

• Ralph Taylor · Lake Zurich, US
• James W. Sennott · Bloomington, US

Key dates

• Filing date: May 22, 1981
• Grant date: Apr 24, 1984
• Expiry date: May 22, 2001

Classification

• Technology area (CPC G): Physics
• CPC primary: G01S5/0036
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

In a global positioning system (GPS), such as the NAVSTAR/GPS system, wherein the position coordinates of user terminals (14) are obtained by processing multiple signals transmitted by a constellation of orbiting satellites (16), an acquisition-aiding signal generated by an earth-based control station (12) is relayed to user terminals via a geostationary satellite (10) to simplify user equipment. The aiding signal is FSK modulated on a reference channel slightly offset from the standard GPS channel. The aiding signal identifies satellites in view having best geometry and includes Doppler prediction data as well as GPS satellite coordinates and identification data associated with user terminals within an area being served by the control station (12) and relay satellite (10). The aiding signal significantly reduces user equipment by simplifying spread spectrum signal demodulation and reducing data processing functions previously carried out at the user terminals (14).