2009 Volume 2 Issue 4 Pages 206-212
To measure a position by GPS (Global Positioning System), observing more than three satellites is usually needed. If there are not obstacles near a receiver, more than three satellites are generally observed and the position is located. However, in an urban area or a forest, more than three satellites can not be frequently acquired because of buildings and trees. Then we suggest a new algorithm for positioning using only three satellites. When only three satellites are observed, the data for positioning is not enough. To solve the problem, we use consecutive data and measure the position. Other methods using only three satellites usually need past data of the receiver such as the position or external data by the reference station or devices other than the receiver. However our method does not need other data and has only to fix a receiver for a few seconds. Therefore our method is useful for pedestrians. When consecutive data is used, noise of pseudo range influences the positioning accuracy. Then we use carrier phase in the L2 signal and make the noise less. In this paper, we show the effectiveness of our method using a dual frequency receiver and received data from three satellites whose elevation angles are high.