Vehicle Recovery-The Electronic Way
Tyler, Geoff, Management Services
Vehicle tracking systems have appeared only in the last couple of years or so in any commercial way.
Geoff Tyler asks if they are worth fitting to company cars and lorries.
Satellite based tracking of vehicles has been around as a practical possibility ever since navigation satellites first appeared in the sky. The satellite which can give a ship's captain his location can, in reverse, tell ground stations' operators where that vessel is. It is, of course, a common civil as well as military satellite application.
Extending the service to the land based sector was originally looked upon as a fleet management control - knowing, without the driver having to call in, where one's vehicles were located in order to vary in an instant their sequence of deliveries and collections, perhaps to add new stops, to cover for a breakdown or simply to tell a customer what time the delivery will be.
Then the matter of security came up.
Fitting a vehicle fleet with a location system would allow one to track vehicles reported stolen and guide police to the thieves - in principle. In practice it was not that easy for reasons I shall detail in a moment. It was not until the two major vehicle tracking services we now have in the UK - Tracker and TrakBak - entered the world market that vehicle tracking primarily for security reasons was seriously marketed.
TrakBak and Tracker do not use satellites. Theirs is a terrestrial based network constructed specially for their vehicle tracking operations. TrakBak evolved from the successful Securicor system used on its cash-in-transit vehicles and Tracker is the UK child of America's Lowjack service.
Satellite based services do exist though they are not so famous. Most were started as vehicle locating services for fleet management purposes and, as such, needed to deliver only an approximation of the vehicle's position. Something as close as the particular block of roads or section of highway the vehicle is in - or in which it was last reported in a regular polling operation - would suffice for routine management purposes. The satellite based services have improved on that in their new security applications but it seems they still do not have the accuracy of terrestrial based services. (A proposed service, Skynet, may address these matters but no information is available about it as yet.)
Let's look into the reasons for the comparative inaccuracy before proceeding to ask if any of the tracking services is worthwhile. It is all to do with the conflict between USA and former USSR satellites. Intriguing stuff.
The Global Positioning System, GPS, satellites are owned by the USA Department of Defense and have a builtin inaccuracy to prevent usage by enemy forces. The corresponding Russian GLONASS satellites can also be used, either on their own or in conjunction with GPS to combat the inaccuracy with confirmation signals. To use both, however, would mean having in the vehicle a receiver capable of using both satellite systems together and that would be expensive. One reason is that the receiver would need the ability to track up to 10 satellites at once. Another reason is that the GLONASS system uses frequency division multiple access to differentiate between the different satellites' signals and this can introduce delays into the receiver which have to be calculated and allowed for. In GPS the satellites all emit at the same frequency so the delays are identical.
Three experts in this field, Drs Walsh and Riley and Prof Daly, all of Leeds University, conducted a study of this problem using a vehicle in urban and semi-urban areas. The vehicle was fitted with their own design of receiver and they measured accuracies with GPS and GLONASS together and separately.
They found that achievable accuracies with GLONASS, once its complications are mastered, can be within 20 metres but with GPS, only within 100 metres. That is due to the built-in inaccuracy called Selective Availability. …