Importance

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Abstract

The methods and apparatus of the present invention provides for determining accurate positions using a global positioning satellite system (GPS), either the United States Navstar or Russian Glonass, without the use of radio broadcast differential corrections. The method contemplates that selective availability (S/A) is either disabled or satellites with S/A active can be identified and not used. In one method, a GPS receiver is positioned at a reference location with a known position. The apparent position determined by the GPS receiver is then compared to the known position to determine an error correction. Preferably, the error correction is made to each satellite's pseudorange as a timing or range correction. When the GPS receiver moves, the error correction is applied to each satellite's pseudorange. The satellites used for position determination are chosen based on the 'quality' of the satellite. Here, 'quality' can mean the geometry of the satellite relative to the earth and the absence of SIA. With the combination of GPS and Glonass satellites to choose from, the four or five highest quality satellites are used for the position calculation. The method contemplates the addition of a new satellite to the current 'quality' set of satellites being used for position determination. Range from the new satellite is compared to the range of the GPS receiver using the position based on the current 'quality' set of satellites. Thus, a range correction for the new satellite is continuously computed. Once the new satellite is added to the 'quality' set of satellites being used for position determination, the range correction is continuously applied to the new satellite to enhance accuracy.

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First Claim