Global Positioning System, usually called GPS, is the only fully-functional satellite navigation system. A constellation of more than two dozen GPS satellites broadcasts precise timing signals by radio, allowing any GPS receiver (abbreviated to GPSr) to accurately determine its location (longitude, latitude, and altitude) in any weather, day or night, anywhere on Earth.
GPS has become a vital global utility, indispensable for modern navigation on land, sea, and air around the world, as well as an important tool for map-making and land surveying. GPS also provides an extremely precise time reference, required for telecommunications and some scientific research, including the study of earthquakes. GPS receivers can also gauge altitude and speed with a very high degree of accuracy.
The United States Department of Defense developed the system, officially named NAVSTAR GPS (Navigation Signal Timing and Ranging Global Positioning System), and launched the first experimental satellite in 1978. The satellite constellation is managed by the 50th Space Wing. Although the cost of maintaining the system is approximately US$400 million per year, including the replacement of aging satellites, GPS is available for free use in civilian applications as a public good.
A GPS reciever placed in a car can recieve signals from these satellites and will calculate the exact location of the car in terms of latitude and longitude. This data can be sent to a owner?s computer that can monitor the location. A GSM modem can be integrated into this project for providing security and remote control. The current location of the car can be found out by sending an SMS. The car can also be disabled by sending an SMS.
GSM/GPRS, Embedded Systems and Computer Programming
AUTOMATIC VEHICLE LOCATOR
Is your car or a vehicle stolen or is it not visible in the thickest snow or is one among the several cars present? Do you wa nt to know the arrival of the bus for which you are waiting? Are your children going alone in a vehicle and you want to track their moments? Does your cargo consists of costly load and want to protect them? Do you want to keep track of your little playing kids about where they are? ANS: Automatic Vehicle Locator. This Paper gives us a novel approach of using certain GPS technology in tracking not only vehicles, but even children and to protect precious goods. So this technology has gained a lot of importance in the recent years. This paper tells us how this technology works, its applications. It is still under research and development stage.
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1. AUTOMATIC VEHICLE LOCATOR Automatic vehicle location (AVL) is a
computer -based vehicle tracking system. For transit, the actual real -time position of each vehicle is determined and relayed to a control center. Actual position determination and relay techniques vary, depending on the needs of the transit system and the technologies employed. Transit agencies often incorporate other advanced system features in conjunction with AVL system implementation. Simple AVL systems include: computer -aided dispatch software, mobile data terminals, emergency alarms, and digital communications. More sophist icated AVL Systems may integrate: real-time passenger information, automatic passenger counters, and automated fare payment systems. Other components that may be integrated with AVL systems include automatic stop annunciation, automated destination signs, Vehicle component monitoring, and Traffic signal priority. AVL technology allows improved schedule adherence and timed transfers, more accessible passenger information, increased availability of data for transit management and planning, efficiency/productivity improvements in transit services .
2. What is AVL technology? Automated Vehicle Locator (AVL) systems use satellite and land communications to display each vehicle's location, status, heading, and speed on the computer's screen. AVL systems use one of four types of navigation technology, or may combine two of these technologies to compensate for inevitable shortcomings of any one technology. The four principal technologies employed for AVL systems are:
1. Global Positioning System
2. Dead-Reckoning System
3. Signpost/Odometer Systems 4. Radio Navigation/Location
3. TRACKING SYSTEMS There are two types of tracking systems. 3.1.
PASSIVE TRACKING: The Passive Tracking System modality refers to standalone GPS Receivers, which store data for further process. Passive systems are typically limited to vehicle tracking only. When a Passive ?Tracking Device is installed in a vehicle, the location, time, velocity and heading data is usually stored in the unit or transferred to a handheld device and downloaded from the vehicle when the vehicle returns to their base station.
3.2. REAL TIME TRACKING Real Time
Tracking Systems are based on mobile stand-alone terminals which combine GPS and GSM technology to determinate and transmit their position. A two-way wireless communication link connects the unit with the control center at all times. A portable GPS tracking device can be used as an emergency cellular phone with speed dialing for two -way voice communication. It can silently call any emergency number in the world for immediate assistance. The emergency silent call feature also provides a digitized voice message which can report the time, date, speed, heading, and location of a person in distress. Figure1. GPS
Receiver The AVL tracking system consists of a GPS receiver inside the vehicle and a communications link betwee n the vehicle and the control Center as well as pc -based tracking software for dispatch. The communication system is usually a cellular network similar to the one used by cellular phone. Currently all kind of communications networks permit Real-Time Tracking for mobile assets.
4. WORKING OF A GPS BASED AUTOMATIC VEHICLE LOCATOR 4.1. GPS SATELLITES
The GPS satellites locate the transit vehicles by sending out GPS signals to be picked up by vehicles GPS UNITS. The GPS unit in the vehicle absorbs the signals and gives radio signals to the RADIO system. Figure2. A GPS Based AVL System 4.2. RADIO SYSTEM The RADIO
systems receive the vehicle GEO - LOCATION coordinates and transmits th
is radio signals to communication center.
4.3. COMMUNICATION CENTER The communication center receives this information and uses it to determine the location of transit vehicle and sends this to dispatch stations and other stations for further analysis of the information either through wire line or wireless networks.
4.4. DISPATCH SECTION The dispatch section uses the vehicle information to help maintain transit schedules and provide operational support to the drivers.
4.5. CUSTOMER ASSISTANCE UNIT The customer assistance planning/scheduling operations analysis unit also receives the vehicle location information through wire line or wireless network. This section use vehicle location map to help maintain transit schedules to analyze and provide traffic information for other road way driver.
Figure3. Working of a GPS based AVL
5. INTEGRATING AVL WITH OTHER SYSTEMS Buses equipped with AVL offer many possibilities for transit interface with highway and traffic organizations or transportation management centers. Opportunities include: providing transit buses with traffic signal priority; obtaining traffic congestion data at the dispatch center to allow rerouting of buses or informing customers of delay; incorporating transit information in traveler information systems; developing multi -application electronic payment systems; using buses to automatically communicat e traffic speed; and reporting of roadway incidents by transit vehicle operators. 6. MORE ABOUT GPS
6.1. Use of Differential GPS For AVL systems which do require more accurate positions, differential GPS can be employed. These systems normally employ the transmission of correction information to the GPS receiver; this correction information has corrections for each satellite in view. This is done because each satellite has its own error; the error in GPS is not simply an X-Y error which will be the same for all receivers. The error on any two given receivers will only be the same if those receivers are using the SAME satellites.
This can?t normally be guaranteed as satellites may be obscured at one location, making the error slightly different for two receivers.
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