On the right track

The UK government is about to trial electronic tagging devices that keep tabs on offenders via satellite. Oliver Leisten reports.

The idea of using celestial bodies to pinpoint location is not new. It has been around since Columbus used the stars to plot his course to the New World.

However, though the use of artificial satellites to track position first became available via the Global Positioning System (GPS) in the mid-1980s, it is only recently that we have seen a sharp rise in its adoption through a broad range of applications.

E-911 legislation in the US is driving its adoption in mobile phones and it is likely that all mobiles in the future will feature it.

Businesses are increasingly using GPS to improve asset management and drive down operational expenditure. Most recently the UK government, following the lead of the US, has outlined its vision for tagging offenders – ‘prison without bars’.

However, GPS is a highly complex technology in terms of space communications infrastructure and its robustness for mass-market applications.

The key issues concern cost, size and reliability. Obviously reliability becomes of crucial importance when you are talking about tagging offenders and managing them in the community. Commercial organisations in the mobile and wireless industry have driven forward significant advances in this area as they seek to integrate GPS into mobile phones and PDAs.

It is now possible for the UK and US governments to take advantage of these improvements to make electronic tagging and satellite tracking as reliable and secure as it can possibly be.

The current UK government trial involves fitting each offender with a tracking device about the size of a video-cassette on a belt around the waist, and a second bracelet on the ankle. The video-sized box transmits co-ordinates to the tracking system, which then informs police of the wearer’s location; the ankle bracelet monitors the transmitter to make sure that it is not tampered with.

However, there are issues with reliable GPS performance when receivers are in such close proximity to the human body. This is because human tissue has a high dielectric constant, which can influence the antenna, spoiling its tuning and efficiency and affecting reception and battery life. Ensuring the best-possible performance is crucial given the weak nature of satellite signals that have travelled approximately 11,000 miles back to Earth.

One approach to improving the current satellite tracking solutions might be to make the tagging device more manageable by getting rid of the waist device and incorporating powerful GPS antennas that use a high-dielectric core into an ankle or wrist strap. Such antennas are able to work in close proximity to the human body and bolster signal reception.

The UK government will start to roll out ‘prison without bars’ over the next four years and we can expect other countries to follow the lead of both the US and UK. It will be necessary for governments to take advantage of advances in GPS antenna technology driven via the commercial sector to ensure that communities get the best-possible solution available for the electronic tagging and satellite tracking of offenders.

Dr. Oliver Leisten is chief technology officer of Sarantel.