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GPS – A Vital Component in a Fleet Management System
What is GPS?
GPS is a location-based technology relying on a network of 24 active satellites orbiting the earth at an altitude of 20,000 km. These satellites constantly transmit radio signals to earth stations and GPS receivers. At any instant of time there will be at-least three satellites available anywhere under the sky. A configured GPS receiver can receive the signals from all available satellites in sky and can decide the position of itself in the form of latitude and longitude values.
To calculate a positional value, a receiver needs to acquire information from at least three satellites. The position is calculated based on triangulation method. The greater the number of satellites within line of sight ranges of the receiver, the greater the accuracy of the location data. Using the permutations of the same data, GPS can also calculate the vehicles speed and direction.
Why GPS?
The core functionality in any Fleet Management system is calculation of the positional value of the vehicle. Single positional value or a set of positional values can be analyzed for various fleet management related tasks. Technology used for obtaining the calculated value and the accuracy of the calculated value is of prime importance. Most of the position calculation technologies use the method of triangulation for calculation.
Position calculation technologies mostly use an existing network for the method of triangulation. Triangulation requires the measurement of distance from a minimum of three pre-defined points to calculate the fourth distance and its location. Depending upon the method of calculating the distances from the pre-defined points, the position calculation can be of different types as described below
- Ground based network technology, using the earth based ground towers from cell sites serving the mobile phones. In order to calculate the positional value it can use any of the following techniques:
- Cell-id: This technology employs a cellular network's inherent capability to recognize which sector of a cell site a phone is communicating with. It then enhances the data to determine which area of the cell sector the caller is in.
- TDOA: Time Difference of Arrival (TDOA), the mobile device is the source of the signal. Equipment at the wireless operator's base stations then detects the signal and calculates the location. Since mobile devices do not need to be modified to work, this technology can operate with all existing handsets and devices.
- AOA: In Angle of arrival (AOA) method, the angle of arrival of a signal between the mobile phone and the cellular antenna is analysed. AOA in conjunction with network-based position determination equipment is used to position the mobile device.
- E-OTD: Enhanced- observed Time Difference (E-OTD) operates on the same principle as GPS except that, instead of originating from satellites, signals are sent from cellular base stations and then picked up by special handsets. In E-OTD, the location is calculated in the phone.
- Use of smart devices is another technique that can be used for position calculation. Smart devices are located at fixed places and once the vehicle comes with its range required parameters are recorded which either get stored for later retrieval or get transmitted to base station in real time.
- Based on the satellite technology like GPS. By itself, GPS can be the most accurate (when satellites are acquired/available). GPS technology calculates the positional values depending on the distance calculations from the available constellation of 24 satellites.
The ground-based network for faster and accurate calculation of the positional value often enhances this technology. This method of calculation is referred to as Assisted GPS (A-GPS). This refers to a system that makes use of additional network equipment that is deployed to help acquire the mobile device (much faster than non-assisted GPS) and provide positioning when the A-GPS system is unsuccessful in acquiring any/enough satellites.
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