23-01-2013, 04:54 PM
REAL TIME TRACKING IN WIRELESS NETWORK USING GPS/AVL
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ABSTRACT
The Paper entitled as “Real Time Tracking in Wireless Network Using GPS/AVL”. The main Objective of this Paper is to tracking the vehicle using Wireless Network. Tracking and Positioning system helps the server to locate the position by sending an SMS to the receiver which in turn sends back a SMS informing its current Global Position.
As companies wanting to tracking their vehicles/employees begin their search for information about GPS tracking devices, many come upon what appears to be an easy, affordable solution. To the buyer who in not familiar with how GPS systems work, GPS enabled phones appear to offer the cheapest way to start tracking your employees and your fleet. To the buyer who is uneducated with GPS equipment, GPS phones seem to be an easy way to begin reaping the benefits of GPS tracking.
Vehicle tracking is a way of monitoring the location, movements, status and behavior of a vehicle or fleet of vehicles. This is achieved through a combination of an electronic vehicle location unit (VLU) fitted in the vehicle, a method of returning the data to the user and PC or web based software. The data is turned into information by management reporting tools in conjunction with a visual display on computerized mapping software.
INTRODUCTION
GPS-The Global Positioning System (GPS) is a group of 27 Earth-orbiting satellites (24 in operation and three extras in case one fails). When people talk about a "GPS," they usually mean a GPS receiver. The U.S. military developed and implemented this satellite network as a military navigation system, but now lets everyone use the signals. A typical GPS receiver calculates its position using the signals from four or more GPS satellites. Four Satellites are needed since the process needs a very accurate local time, more accurate than any normal clock can provide, so the receiver internally solves for time as well as position. In other words ,the receiver uses four measurements to solve for 4 variables –x,y,z and t. These values are then turned into more user friendly forms, such as latitude/ longitude or location on a map,then displayed to the user.Each GPS satellite has an atomic clock, and continually transmits messages containing the current time at the start of the message, parameters to calculate the location of the satellite and the general system health . The signals travel at a known speed - the speed of light through outer space, and slightly slower through the atmosphere.
System segmentation of GPS
The current GPS consists of three major segments. These are the space segment (SS), a control segment (CS), and a user segment (US).
Space segment
Orbiting at an altitude of approximately 20,200 kilometers (12,600 miles or 10,900 nautical miles; orbital radius of 26,600 km (16,500 mi or 14,400 NM)), each SV makes two complete orbits each sidereal day. The ground track of each satellite therefore repeats each (sidereal) day. This was very helpful during development, since even with just 4 satellites, correct alignment means all 4 are visible from one spot for a few hours each day. For military operations, the ground track repeat can be used to ensure good coverage in combat zones.The additional satellites improve the precision of GPS receiver calculations by providing redundant measurements. With the increased number of satellites, the constellation was changed to a no uniform arrangement. Such an arrangement was shown to improve reliability and availability of the system, relative to a uniform system, when multiple satellites fail.
Control Segment
GPS standards. So to change the orbit of a satellite, the satellite must be marked 'unhealthy', so receivers will not use it in their calculation. Then the maneuver can be carried out, and the resulting orbit tracked from the ground. Then the new ephemeris is uploaded and the satellite marked healthy again. Even if just one satellite is maneuvered at a time, this implies at least five satellites must be visible to be sure of getting data from four.
User Segment
The user's GPS receiver is the user segment (US) of the GPS system. In general, GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly-stable clock (often a crystal oscillator). They may also include a display for providing location and speed information to the user. A receiver is often described by its number of channels: this signifies how many satellites it can monitor simultaneously. Originally limited to four or five, this has progressively increased over the years so that, receivers typically have between twelve and twenty channels
How does GPS work?
Calculating a Position
A GPS receiver calculates its position by a technique called satellite ranging, which involves measuring the distance between the GPS receiver and the GPS satellites it is tracking. The range (the range a receiver calculates is actually a pseudo-range, or an estimate of range rather than a true range) or distance, is measured as elapsed transit time. The position of each satellite is known, and the satellites transmit their positions as part of the "messages" they send via radio waves. The GPS receiver on the ground is the unknown point, and must compute its position based on the information it receives from the satellites.
Measuring Distance to Satellites
The first step in measuring the distance between the GPS receiver and a satellite requires measuring the time it takes for the signal to travel from the satellite to the receiver. Once the receiver knows how much time has elapsed, it multiplies the travel time of the signal times the speed of light (because the satellite signals travel at the speed of light, approximately 186,000 miles per second) to compute the distance. Distance measurements to four satellites are required to compute a 3-dimensional (latitude, longitude and altitude) position.In order to measure the travel time of the satellite signal, the receiver has to know when the signal left the satellite and when the signal reached the receiver. Knowing when the signal reaches the receiver is easy, the GPS receiver just "checks" its internal clock when the signal arrives to see what time it is. But how does it "know" when the signal left the satellite? All GPS receivers are synchronized with the satellites so they generate the same digital code at the same time. When the GPS receiver receives a code from a satellite, it can look back in its memory bank and "remember" when it emitted the same code. This little "trick" allows the GPS receiver to determine when the signal left the satellite.
Conclusion:
GPS/AVL allows fleet managers to improve their businesses with returns on investment with the efficiency gained from the technology. Quicker dispatch times for public safety agencies can save lives. Drivers and passengers are safer, and customer service is improved.In this paper, we had proposed a GPS based AVL system to identify the location of the vehicle. The monitoring of events at a central control center can allow the user to dynamically monitor the state of the vehicle.