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Tracking by mobile phone – a serious alternative?

Until lately, satellites (usually GPS) and dedicated data networks were the main technologies behind tracking systems, but now you can do it just using the Internet and a mobile phone. How does this approach compare?

Until a couple of years ago, the most popular way to track vehicles and assets was to use navigation satellites (usually GPS) to pinpoint their location, and some kind of wireless data link (possibly GSM/GPRS mobile phone networks) to relay the information back to base.

The main alternative was to use the Eutelsat or Inmarsat satellites to fix the location and also do the tracking (useful if you’re tracking across borders). In the UK there are also a few dedicated tracking networks, of which the best known is the Datatrak system, now owned by Siemens. Newcomer QuikTrak started to develop a rival system, but has now retrenched in the UK.

However, in a short space of time an entirely new option has emerged – tracking people or things purely by mobile phone. This technology, sometimes called cell (or cell-site) location, relies on the fact that the mobile phone network operators automatically track all active units on their systems all the time. It’s not as accurate as GPS tracking, but it’s probably good enough for many business uses.

Initially there were doubts about how the network operators could to make this information available to the world without compromising the confidentiality of the information, but these have now been resolved. If you want to track someone’s mobile phone, you have to subscribe to one of the tracking services, which are run by independent third parties, and you have to have the individual’s permission. You can’t just track anyone’s mobile.

During the past eighteen months numerous firms have sprung into existence to offer mobile phone-based tracking on these lines. Two of the best-established are FleetOnline and Verilocation, but there are many others such as Trackaphone.

So are GPS and GSM tracking interchangeable? Well, GPS system retains an advantage in that it is reliable and accurate regardless of where the vehicle is in UK (or, for that matter, anywhere on the globe). The orbiting GPS satellites continually transmit time and position data. This is picked by the GPS receiver on the vehicle, which then calculates its exact latitude and longitude. In theory this will be accurate to 100 metres at worst, and in most cases it will be much better than this.

The GSM modem used to transmit the GPS-derived data back to base has the added benefit of allowing SMS or other forms of data message to be passed between the driver and transport office via a suitable in-cab interface.

That’s not the whole picture however. In urban areas, the GPS signal can be blocked by tall buildings in a phenomenon known as the “urban canyon syndrome”. To get a position fix requires a line of sight to at least three satellites, and the signals can bounce off buildings, reducing accuracy.

GSM tracking relies on Cell Identification, or Cell-ID – the means by which the phone networks track individual phones form cell to cell. Positional accuracy relies on the number of mobile masts in the area, so it can be accurate to 100 metres or as imprecise as within 10km or more.

When it comes to cost, there are pros and cons to both technologies. GSM tracking offers low set-up costs and fast roll-out. It works with any current mobile phone via its GSM SIM card. So long as the user gives you permission, you can track existing mobile phones simply by registering them with your chosen LBS provider.

GPS can be more expensive to install, and systems are often hard-wired into the vehicle, so drivers cannot be tracked away from the vehicle. In the UK at least, most rely on GSM anyway to transmit the data between vehicles and base.

On the plus side, though, GPS is passive; the receiver continually updates it position relative to the satellites, so it always knows where it is. By contrast, if a mobile phone or GSM modem is turned off, you will not be able to locate it.

It’s also worth pointing out that GPS has a distinct advantage if you don’t actually want to download your positioning fixes in real time at all, and are content instead to capture them on the vehicle-mounted equipment and analyse them when the vehicle gets back to base. Using GSM mobile tracking, you have to pay for every position fix, even if you don’t want it until later.

While initially the mobile phone-based tracking systems were marketed as a quick-start, low-cost alternative to GPS-based tracking, a more pragmatic spirit is evident in the market now. Some of the GSM tracking suppliers also offer GPS-style tracking, and allow greater integration with other on-board or in-field systems. In other words, GSM tracking is turning into just one of various technologies available in the telematics repertoire. And perhaps that’s as it should be.

Making it more accurate

Both GPS and GSM tracking technologies are being enhanced to give better accuracy. “Assisted GPS”, or A-GPS, is already available in some countries, and speeds up the time it takes to get a position fix. GPS satellites broadcast data at a comparatively slow rate of 50 bits per second; by contrast, with A-GPS the terminals are able to search more efficiently, because some of the data that GPS receivers usually download from the satellite is held on a GSM server, speeding up the computation.

Position fixes are also quicker; they take less than five seconds, compared with at least 15 seconds for a standard GPS fix. A-GPS can be network-based or handset-based. It is currently trialling in Japan and Korea where accuracy is up to 60 metres.

For really accurate positioning there is already a system called differential GPS or D-GPS, which in effect corrects the “fix” to a 1 metre accuracy by means of a terrestrial reference signal. This is available in various countries including the UK, but it’s aimed mainly at applications such as surveying that need a high level of accuracy. For routine applications the licence fee would probably be prohibitively expensive.

The main rival to A-GPS looks like being Enhanced Observed Time Difference (E-OTD) which will improve on GSM location accuracy. One reason positioning accuracy is relatively poor on both GSM and the emerging 3G networks is that neither uses synchronised timing signals. So although the phone will triangulate its position using three transmitters, the time signals from the transmitters may not synchronise with each other. E-OTD could solve this problem.

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