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Time varying ARMA processing on low cost GPS receiver data to improve the position accuracy
M. H. Refan
Department of Computer Engineering
Shahid Rajaee Teachers Training University
Lavizan, Tehran, Iran
M.Mosavi@srttu.edu
K. Mohammadi
Department of Electrical Engineering
Iran University of Science and Technology
Narmak, Tehran, Iran
Mohammadi@iust.ac.ir
M. R. Mosavi
Department of Computer Engineering
Shahid Rajaee Teachers Training University
Lavizan, Tehran, Iran
mailto:M.Mosavi@srttu.edu
Abstract
This paper presents a method to determine an accurate position by using a low cost GPS receiver and proposes a new time varying ARMA model for better accuracy in GPS positioning. At first the GPS systems errors are defined. Then calculating the position component errors, real and dynamic patterns of the errors will be created and applied in to time varying ARMA model. The parameter matrix is obtained with such real data to predict the later seconds errors. The steps of design and implementation of the time varying ARMA model are presented and the experimental results of the tests are stated with real data. They show the position components errors decrease by using of time varying ARMA processing.
Introduction
Global Positioning System (GPS) has replaced prior positioning systems. It can cover all the earth by satellites to measure accurate time, altitude, longitude and latitude in every desirable point [1,2]. Positioning began from 1950s and improved in 1970s. In 1980s, GPS became an operational positioning system. At first it was designed and used for military purposes. But later its commercial applications have been increased. Nowadays commercial receivers take a great part in its market [1,2].
There is some error sources that cause the position and time measuring from GPS receivers to be inaccurate. Significant error sources are signal delays from ionospheric and tropospheric effects, satellite clock drift, satellite orbital position errors, signal multi path and noise generated within the receiver itself. Table1 shows the common errors of GPS system in meter and nanoseconds.
Table1. The common errors of GPS system in meter and nanoseconds [3,4]
Error
Component |
Standard
Deviation
(m) |
Standard
Deviation
(ns) |
Time
Constant |
| Satellite Parameters of Broadcast |
30 |
100 |
More than 1
Hour |
| S/A |
30 |
100 |
2 Minute |
| Ionosphere |
5 |
17 |
More than 1
Hour |
| Multi path |
5 |
17 |
0.5 to 10
Minute |
| Troposphere |
2 |
7 |
More than 1
Hour |
Because of above mentioned error sources, all GPS receivers have a certain number of errors. This means that received data from GPS receiver will not reflect the real location. Therefore, users who wish to increase the accuracy of their GPS receiver must take steps to minimize the errors.
In this paper, a new modeling to decrease the positioning measurement errors in low cost GPS receiver is described. The theoretical background for better accuracy is based on time varying ARMA model.
GPS Receiver
To achieve information of position and implementing an operational system, MicroTracker Low Power (MLP) as a low cost GPS engine manufactured by Rockwell Company was used. This miniature receiver with a small volume is appropriate for a vast range of Original Equipment Manufacturer (OEM) products. OEM receiver provides the possibility of improving software by presenting raw data [5,6].
This receiver has 5 parallel channels. It can track up to 9 satellites simultaneously. This receiver supports approved and improved NMEA-0183 protocol. It can receive differential RTCM messages to improve the accuracy of positioning in differential mode. Its serial port can receive and transmit NMEA or Binary data with the rate of 4800 or 9600 bit per second. The Binary protocol provides more detailed information compare with NMEA protocol [5,6].
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