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Automatic Vehicle Location and fleet management

By Edited Nov 13, 2013 0 0

Automatic Vehicle Location (AVL) devices are used to monitor asset location, speed, heading, altitude and other GPS (Global Positioning System) related variables. Some of these devices are also capable of reporting data from attached sensors or RFID readers.

Data reported by AVL devices can serve different purposes for different industries:

  1. monitor of real-time position and status of public safety vehicles

  2. schedule adherence of public transportation vehicles

  3. delivery confirmation of refrigerated goods to clients

  4. mileage estimates to determine when to service vehicles

  5. real-time detection of misuse of companies vehicles

  6. asset recovery after a burglary or carjacking 

 

Besides reporting location data some devices can have additional capabilities as add-ons:

  1. integrated RFID reader

  2. panic button

  3. temperature sensors

  4. ignition control

  5. opening or locking doors

  6. Wi-Fi communication

 

Devices with Wi-Fi capabilities can be meshed to effectively create a data network between assets such as public transportation vehicles.

There are a few formats for AVL devices to compose GPS data based on the National Marine Electronics Association (NMEA) standards (http://www.nmea.org):

  1. GPRMC - minimum recommended GPS data

  2. GPGSV - satellites in view

  3. GPGGA - essential fix data which provide 3D location and accuracy data

  4. GPGLL - geographic coordinates, latitude and longitude

Not all protocols are implemented by all vendors, although the GPRMC format or sentence seems to be the least common denominator. These are examples of messages generated by an NMEA compatible GPS device:

$GPGGA,171537,3350.975,N,11823.991,W,2,07,1.1,-25.8,M,,M,1.8,,D*17
$GPGLL,3350.975,N,11823.991,W,171537,A,D*50
$GPRMC,171537,A,3350.975,N,11823.991,W,0.0,096.5,060401,013.0,E,D*07
$GPVTG,096.5,T,083.5,M,0.0,N,0.0,K,D*22
$GPGSA,A,2,04,09,07,24,02,05,26,,,,,,,1.1,*3C
$GPGSV,2,1,07,04,62,120,47,09,52,292,53,07,42,044,41,24,38,179,45*7B

Some common challenges that influence the performance of AVL devices are:

  1. cellular network coverage - since modern AVL equipment relies in the cellular network as their main mean of communication, areas of poor coverage will cause the devices to appear "frozen" to the user. However during the “frozen” state data is stored in an internal buffer and as soon as the device connects again to the network the stored data is sent.

  2. GPS satellites availability and location - at least three GPS satellites are required by a receiver to accurately compute location and four satellites to have a good altitude estimate. If the minimum number of satellites is not available, the GPS data from the receiver cannot be trusted.

  3. GPS receiver power - a weak GPS receiver will not be able to contact satellites reliably causing loss of precision in the readings

Vehicle tracking and fleet management is a fascinating industry that adds a lot of value to companies and public agencies by helping them manage their fleets effectively.


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