Positioning Algorithm for Insufficient GPS Satellites
Date Issued
2005
Date
2005
Author(s)
Chen, Chih-Wei
DOI
zh-TW
Abstract
The minimum positioning requirement of the GPS is that the GPS receiver can observer at least four satellites. However, it is difficult to reach the minimum requirement in city environment. The theme of this text is how to utilize the insufficient satellites information and previous positioning result to position in such environment.
When the receiver observes three satellites, the altitude constraint method is used to positioning. Because driving on the road, the user’s altitude is usually changed slowly. Restricting the user's altitude to average height in recent ten seconds, the receiver can position in three satellites environment with the model that the earth is ellipsoid.
When the receiver observes two satellites, it can position by combining the altitude constraint method and the receiver clock bias estimation method. This approach is easy to produce positioning error but it can offer effective positioning result with the DOP check.
In addition, this article proposes a pseudorange predictor, which utilizes the current user and satellite’s positions and velocities to estimate the next time satellite’s pseudorange. When the satellite is blocked by with buildings or shelters, the GPS receiver can utilize the estimated pseudorange to position. While estimating the same satellites a few seconds, there is error accumulation phenomenon. It is unsuitable to utilize this predictor estimates the same satellites for a long time.
Utilizing the pseudorange predictor and the different satellites number positioning algorithm, it can release the restriction that the GPS receiver only works when at least four satellites are observable.
Subjects
衛星不足
鐘差
虛擬距離
預估
GPS
insufficient satellites
altitude constraint
receiver clock bias
pseudorange
predict
Type
thesis