Abstract
GPS/GNSS (Global Positioning System/Global Navigation Satellite System) is a 3D positioning system using space satellites for measuring a receiver's current position. Recently, many people use GPS as the navigation system in car and cellular phone, so the positioning accuracy of several meters is required to satisfy the user's need. However the measurement error reaches hundreds of meters in urban areas. One of the reasons is that the receiver fails to measure pseudo range accurately due to multipath from the buildings and so on. The other reason is that the satellite constellation is biased because of the decreasing number of observable satellites. Therefore, we proposed methods for reducing the multipath error and the lack of visible satellites. At the present day, although multipath error is reduced by the choke ring antenna and the correlators, this method has a problem that the antenna is expensive, big or complex. We devise methods to reduce the multipath error by only using measurement data. By these methods, we can reduce the size of the receiver and to use the satellite that contains the multipath error for the measurement. We achieved the improvement from 35.3m to 30.5m in 2drms by this method. We achieved about 69% improvement in 2drms and about 5% increase in measurement rate. We can describe that we succeeded not only in improving the measurement accuracy but also in increasing the measurement rate in urban area. The results show that our proposed method is effective in urban areas measurement.
