2012 International Conference on Future Communication Networks
Performance of Differential GPS Based on a Real-Time Algorithm Using SMS Services of GSM Network Dr. Asaad Al-Hindawi
Majeed Nader Sulaymaniyah International Airport
Communication Eng. Department Sulaimani Technical College Sulaymaniyah, Iraq
[email protected]
Sulaymaniyah, Iraq
[email protected]
Abstract— A real-time simple algorithm of differential GPS is adopted tested experimentally using an existing GSM network utilizing SMS service that takes short time with low cost. A system of DGPS is designed and implemented. The implemented system includes basically reference station (RS) and mobile station (MS). The RS consists of a personal computer (PC_A) with a GPS receiver and a modem of GSM. The differential data (DD) between the GPS reading and the original position of RS is determined and sent to MS via GSM modem. The mobile station consists also of a GPS receiver and a GSM modem connected with a personal computer (PC_B). The DD is received by GSM modem and compared with the GPS readings at MS to determine the exact position of the mobile station. The system is tested experimentally and a horizontal accuracy of 0.44m and a vertical accuracy of 0.55m are obtained.
Ground speed Doppler radar and one MEMS gyroscope has been used to augment differential GPS and provide accurate navigation during DGPS outages [3]. A method of IGS ultra rapid product calculating vector differential GPS correction has been proposed [4] and this method may be considered toward real time measurements but it needs complex algorithm. The DGPS can transmit the correction data to the user receiver reception area via a suitable broadcaster (VHF, MF and LF radio system, GSM-GPRS, Internet and satellite communication, etc) [5]. However; the Global System for Mobile Communication (GSM) is one of the most important communication systems nowadays since it has given people the ability to communicate with each other anywhere and at anytime. The world has witnessed a tremendous growth in people’s use of cellular technology. It has many services: voice communication, MMS, EMS, SMS and GPRS, and one of the most popular GSM services is the Short Message Service (SMS). This service allows SMS subscribers to exchange short text messages [6]. This paper presents a performance of DGPS based on a real-time algorithm using a SMS services instead of GPRS due to simplicity and ease to use.
Keywords-differential GPS, GSM, GPRS
I.
INTRODUCTION
The Global Positioning System (GPS) allows properly equipped users to determine their position based on the measured pseudo-ranges to at least four satellites, GPS positioning accuracy is limited by measurement errors. The GPS greatly increases the accuracy and reduces the cost and complexity of navigation for land, marine, and air and space users. Under normal operating conditions, it is able to provide positioning accuracies in the range of 15-25m [1]. But the accuracy of positioning can be increased using Differential Global Positioning System (DGPS) technique. The Differential GPS (DGPS) is a potential means for improving navigation accuracy in a local area. A single DGPS monitor station at a known location can compute range error corrections for all GPS satellites in view. These error corrections are then broadcast to users in the vicinity. By applying the corrections to the signals received, a user within a 100km range can typically improve the accuracy [1]. The ability of DGPS to provide real-time sub meter or even decimeter level accuracy has revolutionized the agricultural industry. GPS application in precision farming includes soil sample collection, chemical application control, and harvest yield monitors [2].
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II.
SYSTEM DESCRIPTION
The studied DGPS in this paper is designed from two parts: the Reference Station (RS) and Mobile Station (MS), therefore they are implemented. Each part has several components and devices as shown in figure (1). The proposed system (DGPS based on GSM-SMS) is composed of Part A and Part B as follows: A. Part A (The Reference Station (RS) As shown in figure 1, it contains a GPS receiver and a computer system with a software program to perform the calculations, and then transmits the differences data to the Mobile Station (MS) via GSM telecommunication service. It includes:
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consideration the received Differential data (DD) from the Reference Station (RS) via GSM telecommunication network. 3. GSM Modem-B: It also contains SIM Card; it is used for receiving the Differential data (DD) from the Reference Station (RS). 4. Interface cable: It is used for connecting and interfacing between the GSM modem and computer through the USB port. III.
The original data and GPS receiver data of the reference station is known, also the GPS receiver data of the mobile station is known, but the original data of the mobile station is unknown. The received signal of GPS Sm at mobile station can be expressed as: Sm = (Sm)error + (Sm)original (1)
Figure 1: Reference Station Block Diagram
1.
GPS receiver: it receives the signal from the GPS satellite and provides the Reference Station (RS) with instantaneous position coordinates of the (RS). There are two different types of GPS receivers which are used in this paper; they are manufactured by GARMIN Corporation. Computer system-A: it is a personal computer (Laptop PC) for calculating the differential data (DD) in Reference Station (RS). The Differential data (DD) represents the difference in position coordinate of the RS. (This difference is between the readings of GPS receiver and the RS original coordinates that are kept in the PC previously). GSM Modem-A: it is a GSM modem that is connected with a computer system A and works as a cellular phone, it contains the SIM card and serves as GSM transmitter to send the Differential data (DD) to the Mobile Station (MS) by using the short message services SMS protocol. Interface cable: It is used to connect and interface between the GSM the computer system A with GSM modem through the USB port.
2.
3.
4.
SYSTEM ALGORITHM
(Sm)original = Sm - (Sm)error
Where (Sm)original represents the original position of mobile station, (Sm)error represents the error signal occurring in GPS reading at mobile station. The received signal of GPS Sr at reference station can be expressed as: Sr = (Sr) error + (Sr)original (3) Where (Sr)original represents the reference station original position, (Sr)error represents error signal occurring in GPS reading at reference station. Since the two readings of GPS at both mobile and reference stations are achieved at the same time therefore; the error signal occurring in both GPS readings at mobile and reference stations are the same or: (Sr) error = (Sm) error = Serror .The error signal Serror in this paper is represented as the differential data (DD); and can be represented as:
B. Part B (The Mobile Station (RS) As shown in figure 2, this part could be anywhere within a circle of radius about 50km around the Reference Station (RS) or could be anywhere that have coverage of the utilized GSM network. It receives two signals: the first one is recorded by GPS receiver and represents the position coordinate of the MS, while the second signal is received by the GSM modem as SMS text protocol and it represents the differential data (DD). The Mobile Station includes: 1.
2.
(2)
GPS receiver: it receives the signal data from the GPS satellite and provides the Mobile Station (MS) with the current position coordinates. Computer system-B: it is a personal computer (Laptop PC) which contains the dedicated program for processing and calculating the position coordinate of Mobile Station (MS) accurately taking into
Figure 2: Mobile Station Block Diagram
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Yo: represents the orignal Y component of RS ,in meter (m). Zo: represents the orignal Z component of RS ,in meter (m).
(4)
DD = (Sr) - (Sr)original
The original position of mobile station can be calculated as bellow: (Sm)original = Sm – DD
Now, the Differential data (DD) can be found as the position difference between the orignal coordinates of the Reference Station and the coordinates that are recorded by GPS receiver. This data could be expressed as:
(5)
The GPS receiver recordes normally the position coordinates in the form of Longitude, Latitude and Altitude (LLA) and for the reference station (RS) these parameters are assumed as follows: Lonr: represents the longitude in Degree Minute Second (DMS) at RS. Latr: represents the latitude in Digree Minute Second (DMS) at RS. Altr: represents the altitude in Meter (m) at RS.
(6)
Y = (N+h) cosφ sinλ
(7)
Z = ((1-f)2. N + H) sinφ
(8)
Where: φ is the Longitude in decimal degree, λ is the Latitude in decimal degree, h is the Altitude, N radius of curvature in the prime vertical and is defined by the equation:
ܰ=
ඥ(ଵି మ ௦మ
φ)
(10)
Yd = Yr – Yo
(11)
Zd = Zr – Zo
(12)
Where Xd is X component differential data, Yd is Y component differential data and Zd is Z component differential data, or DD = { Xd , Yd , Zd }. The differential data (DD) is sent as SMS text message via GSM network, from the RS to the MS. At the mobile station, the computer receives two signals: the first one is received by GPS receiver from the GPS satellites, to record position coordinate of the Mobile Station and the second one is received from the GSM network in the form of SMS text message which contains the differential data (DD) and the time of GPS receiver readings at RS. The readings of GPS receiver at mobile station (MS) are represented by the followings: Lonm: represents the longitude in Degree Minute Second (DMS) at MS. Latm: represents the latitude in Digree Minute Second (DMS) at MS. Altm: represents the altitude in Meter (m) at MS.
The above data are transformed to XYZ coordinate system as [7][8]: X = (N+h) cosφ cosλ
Xd = Xr – Xo
(9)
Those data are also transformed to XYZ coordinate system using equations (10), (11), and (12) as follows: Xm: represents X component of the GPS reading at MS ,in meter (m). Ym: represents Y component of the GPS reading at MS ,in meter (m). Zm: represents Z component of the GPS reading at MS ,in meter (m). Based on the received differential data (DD), the GPS readings at mobile station (MS) in the form of Xm, Ym and Zm can be corrected accuratly as follows:
Where a is the semi-major axis of the earth = 6378137.0 m and the X Y Z coordinate system are denoted in reference station as follows: Xr: represents X comonent of the GPS reading at RS ,in meter (m). Yr: represents Y comonent of the GPS reading at RS ,in Meter (m). Zr: represents Z comonent of the GPS reading at RS ,in Meter (m). Also the orignal position coordinate of the reference station (RS) is kept in the PC of the RS, it is expressed in the form of LLA as follows: Lono: represents the original longitude of RS in digree Minute Second (DMS). Lato: represents the original latitude of RS in digree Minute Second (DMS). Alto: represents the original altitude of RS in meter (m).
Xmc = Xm – Xd
(13)
Ymc = Ym – Yd
(14)
Zmc = Zm – Zd
(15)
Where Xmc: is the X component of the corrected position coordinate of the mobile Station. Ymc: is the Y component of the corrected position cooridnate of the mobile Station. Zmc: is the Z component of the corrected position coordinate of the mobile Station.
The orignal Longitude and Latitude are converted to Decimal Degree, and then position coordinates are transformed to the XYZ coordinate system, as follows: Xo: represents the orignal X component of RS ,in meter (m).
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Now, the corrected data is again transformed to LLA coordinate system as [7][8]:
ି݊ܽݐ = )ߣ( ݁݀ݑݐ݅ݐܽܮଵ ି݊ܽݐ = )߮( ݁݀ݑݐ݅݃݊ܮଵ
(17)
( ݁݀ݑݐ݅ݐ݈ܣℎ) =
ඥ( మ ା మ )
(18)
௦(ఝ)ି ே
RESULTS OF TESTED SYSTEM
The testing procedure for the designed DGPS system has been executed at both reference and mobile stations. The testing procedure of DGPS based on GSM-SMS proposed model were executed at (Sulaimani City -IRAQ), it involves the execution of both parts of the system: the Reference Station and the Mobile Station. There are seven known locations (P): some of them have been selected as the reference stations and the others as the mobile stations. The original position data of the seven locations are shown in Table 1. Seven experiments of different positions for reference and mobile stations have been performed as they are described in Table 2.
(16)
ට( మ ା మ )൫ଵି(ଶି)൯( )
V.
Where: Lonmc: represents the corrected longitude in Degree Minute Second (DMS) at MS. Latmc: represents the corrected latitude in Degree Minute Second (DMS) at MS. Altmc: represents the corrected altitude in Meter (m) at MS. f is the flatening which is adopted value is: 1/f = 298.257223563 according to WGS84 paramiters[6].
Table 3 shows the summarized the average of horizontal errors before and after correction for all experiments. On the other hand Table 4 shows the summarized average of vertical errors before and after correction for each experiment.
TABLE 1: The original coordinates of seven positions selected for RS and MS
IV.
SOFTWARE PROGRAMS
The DGPS based on GSM-SMS proposed model is developed and designed by the software to provide the communication and control of the hardware practical model. There are two software programs and are used to achieve the needed procedure for implementing the DGPS based on GSM-SMS system. They are MATLAB program and Microsoft Visual Basic program. Both programs are linked together with special link commands by the Microsoft Visual Basic program, to get the MATLAB cooperation. However the software was written by Microsoft Visual Basic Programming languages (Version 6), but for the main calculation and GPS data processing as well as GPS data transformation from Longitude/Latitude/Altitude (LLA) form to X/Y/Z form and vice versa, it depends upon the MATLAB Programming (version R2008a). TABLE 2: The positions of RS and MS for seven experiments
The software part which is written by MTLAB programming is depending on some professional Matlab toolboxes and m.files. Also there is incorporate dedicated software which used for controlling and monitoring the GSM modem which is Light Wave GPRS Wireless Modem\DataCard (LW-UGPRS Software). The Microsoft Visual Basic program will achieve the connection link with the LW-UGPRS software for reading the received SMS in Mobile Station. Also the extracted differential data (DD) in the Reference Station will be sent by using the LW-UGPRS software. The software programs are consisting of two main parts: The Reference Station (RS) Software and The Mobile Station (MS) software programs.
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TABLE 3: The average of horizontal error for executed experiments
vertical accuracy of 0.55m are obtained. The designed system can operate with many mobile stations. Each mobile station can request the differential data from the reference station at any time through SIM of the mobile station. Integrating the whole software implementation on a single smart-phone instead of using PCs might be a good step forward.
REFERENCES [1] M. R. Mosavi, “An Adaptive Correction Technique for DGPS using Recurrent Wavelet Neural Network”, IEEE Spectrum, PP: 3029-3033, 2007. [2] Ahmed El-Rabbany, “Introduction to GPS, the Global Positioning System”, Artech House Inc., Boston.London, 2002. [3] J. Parviainen, Manuel A. V. L´opez, O. Pekkalin, J. Hautam¨aki, J. Collin and P. Davidson, “Using Doppler Radar and MEMS Gyro to Augment DGPS for Land Vehicle Navigation”, 18th IEEE International Conference on Control Applications Part of 2009 IEEE Multi-conference on Systems and Control Saint Petersburg, Russia, July 8-10, 2009. [4] H. Chen , Y. Chiang, F. Chang and H. Wang, “Toward Real-Time Precise Point Positioning: Differential GPS Based on IGS Ultra Rapid Product”, SICE Annual Conference 2010, The Grand Hotel, Taipei, Taiwan August 18-21, 2010. [5] Jean Marie Zogg, “Essentials of Satellite Navigation”, U-Blox AG, Switzerland, www.u-blox.com, 2007. [6] Gwenael Le Bodic, “MOBILE MESSAGING, Technologies and Services SMS, EMS and MMS”, Second Edition, John Wiley & Sons Ltd, England, 2005. [7] Per K. Enge, Rudolph M Kalafus and Michael F. Ruane, “Differential Operation of the Global Positioning System”, IEEE Communications Magazine, Vol. 26, No. 7, PP: 48-60, July 1988. [8] Department of Defense, “World Geodetic System 1984”, NIMA Technical Report, Third Edition, July 1997.
TABLE 4: The average of vertical error for executed experiments
BIOGRAPHY It can be noticed that the average horizontal error of the average mobile station positions of all experiments is about 2.5 meters before correction, but after achieving DGPS technique the average horizontal error is reduced to 0.44 meter, it means that the correction percentage of 81% is obtained for horizontal error. Also the average vertical error of the average mobile station positions of all experiments is about 7.3 meters before correction, but after the correction, the average vertical error is reduced to 0.55 meter, it means that the correction percentage of 91% is obtained for vertical error.
VI.
Dr. Asaad Al-Hindawi has earned his B.Sc. in electrical engineering from the University of Baghdad, Baghdad, Iraq. In addition, he has received M.Sc. in communication engineering from the University of Technology, Baghdad, Iraq and a Ph.D. in Radio and communication engineering, from Varna Technical University, Varna, Bulgaria. Currently he is an Assistant Professor of communication Engineering and Laboratories Advisor in Communication Engineering Department, Sulaimani Technical College, Sulaymaniyah, Iraq.
Majeed M. Nader has received his B.Sc. in Electrical Engineering from Salahaddin University, Electrical Engineering College in Erbil, Iraq and he has received his M.Sc. in Electronics and Communications from Slulaimani University, Electrical Engineering College in Sulaymaniyah, Iraq. Presently he is a Ph. D. student at Wayne State University, Detroit, Michigan, USA.
CONCLUSIONS
The SMS service in GSM Telecommunication system can be used as terrestrial link for DGPS technique in order to transmit the differential data (DD) from reference station (RS) to mobile station (MS), the differential data (DD) which has been processed and calculated by the reference station (RS) has been sent to the mobile station (MS). The system is tested experimentally and a horizontal accuracy of 0.44m and a
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