Time varying ARMA processing on low cost GPS receiver data to improve the position accuracy
Data Collection
To study the function of receiver, the GPS receiver was installed and set up in a fixed position. There are several binary messages provided by MLP. One famous and general purpose of these messages is message No.103, which is available on the first receiver output port as default, when we configure the receiver in binary mode. The message 103 is contain of very useful detail information of position and time [5,6].
In order to setup the receiver, connecting to PC and data collection, a hardware designed and implemented. Fig.1 shows the hardware structure. The output data was collected for a few months. A Pentium III computer with 450 MHZ clock speed saved it.
Fig.1. Hardware structure
Position Components Errors
Since MLP is a low cost nonmilitary receiver, its measurement errors are not neglected (188 meters RMS 3D, when S/A was on and 60 meters RMS 3D, when S/A is off) [5,6]. To study the receiver data and achieving of the errors, the data of position were studied in World Geodetic System-1984 (WGS-84). Therefore the x,y and z magnitude in the No.103 Binary message were collected and saved in separate files every 1 second period.
We focus on variation of x,y and z components in studying ARMA model [7].A software was developed for this purpose. By calculating the average of each quantity in file length, the software provides difference of the instantaneous magnitude of each point with its corresponding quantity average according to equation (1) to (6) and saves them in other files [7].
Where x i,y i,z i are instantaneous magnitude of x,y,z and Ax, Ay, Az are the average magnitude of x,y,z and x i,y i,z i are instantaneous error magnitude of x,y,z respectively. n is number of samples.
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