Pseudometric difference is one of the most widely used techniques. Almost all commercial differential GPS receivers use this technique. The RTCM SC-104, recommended by the International Maritime Radio Commission, also uses this technology.

　　The receiver on the reference station asks for its distance to the visible satellite and compares this calculated distance with a measurement containing errors. An α-β filter is used to filter the difference and find the deviation. Then the ranging errors of all the satellites are transmitted to the user, and the user uses the ranging errors to correct the pseudo-range. Finally, the user uses the corrected pseuddistance to solve its own position, so that the common error can be eliminated and the positioning accuracy can be improved.

　　Similar to position difference, pseudo-range difference can cancel the common error of the two stations, but with the increase of the distance between the user and the reference station, there will be systematic error, which can not be eliminated by any difference method. The distance between the user and the reference station has a decisive effect on the accuracy.

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