Keeping track of offenders

The effectiveness of satellite navigation systems will be improved by up to 1,000 times, allowing signals to be picked up inside buildings, in a system that could soon be used by the government to track offenders.

The new tagging technology would be used to relieve pressure on the UK’s prisons, which were reported this week to be in imminent danger of being declared full. The government has approved a multi-million pound package to build two new jails, but other methods are now being sought to allow offenders back into thecommunity under the watchful eye of a satellite.

The Home Office has revealed it is looking into the use of satellite tracking for offender monitoring, and discussing with suppliers the various technologies available.

But existing GPS systems are affected by disruption to the signal from the satellite to the receiver caused by buildings, foliage from trees and the high water content of human bodies.

Technology specialist Qinetiq is developing an enhanced GPS system that can operate in extreme environments, including inside buildings. The company is working with Leicester-based Guidance Control Systems, which supplies radio frequency tagging equipment to the Home Office through its home curfew programme, to use this tracking technology in its next generation of offender monitoring equipment.

The Home Office has already made it clear it wants tracking technology to be introduced, said Keith Phillips, business development manager at GCS. ‘The Home Office has said it wants those companies providing services into the next offender monitoring programme to include tracking technology. The government is not being specific about how offenders should be tracked, but GPS is obviously one possibility,’ he said.

The prison population has expanded dramatically in recent years, and has reached almost 72,000. Reducing this number would allow more dangerous criminals to be locked up more quickly, such as sex offenders considered a significant danger to the public, said Phillips. There is also a considerable economic benefit – it costs around £27,000 a year to keep an offender in prison, while tagging is 40 per cent cheaper (around £16,000), he said.

The new technology is far more robust than existing GPS systems, said Chris Langrish of Qinetiq’s GPS-enabled telematics team (see panel). This makes it more suitable for use in offender tracking, where criminals would need to be constantly monitored for the programme to be effective and acceptable to the public. ‘With existing GPS systems, the second you go into the shade of a building, your signal would be chopped off, and it is the same with foliage – the moment you step into somewhere like the New Forest you are no longer tracked. So this [new system] really does bring you benefits in terms of tracking where you were not able to do so before.’

The technology could be used to create geofenced environments, such as areas around schools, into which the offender cannot enter. For a low-risk offender a passive system could be used to record any attempt to enter a forbidden area, and the information downloaded later. An active system, which could potentially be used on more dangerous criminals such as paedophiles or violent offenders, could be programmed to send a message every 30 seconds detailing their movements and immediately sending an alert to the relevant authorities if they step inside the area, said Langrish.

‘The unit itself could have pre-programmed exclusion areas, to ensure fast response times. So rather than sending a signal back to the base station and alerting the system, the device could flag up an emergency when it enters an area it shouldn’t be going into.’

A message could also be displayed to the offender, warning them if they are getting close to a forbidden area, said Richard Noel, another member of Qinetiq’s GPS-enabled telematics team.

The technology could also help the police to eliminate people from their inquiries, which is particularly important in child abduction cases where the first few hours can be crucial. ‘If you have a number of suspects in the area, you could speed up the number of people who need to be eliminated from your inquiries because they still have their bracelet on, and you know the data is correct. This means you can focus attention where it is required, rather than unnecessarily crossing off a huge list,’ said Noel.

Ensuring the police have confidence in the technology means encryption must be used to prevent tampering. while any attempt by the offender to remove the device and dump it, or leave it with someone else while they commit a crime, would be automatically detected, and without a suitable explanation they would be sent back to prison.

A Home Office spokesman said the government is still gathering information about what satellite tracking technologies may be applicable to the criminal justice system. ‘We are still in discussion with a number of manufacturers of GPS devices and are analysing what they could do for us.

‘An area of particular interest is the idea of setting up an exclusion zone to ensure offenders are keeping to their licence conditions. But despite a lot of speculation that sex offenders will be placed under the system we have not made any decision about which type of offenders would be tagged.’

Tracking technology is already used in Florida, where 800 offenders are currently being tagged by police, 543 of which are using GPS-enabled devices. Just under half are sex offenders.

The system can be offered as an alternative to prison for those on probation, allowing them to take part in community service while ensuring that conditions such as avoiding contact with their victim are observed.

Offenders wear a pager-sized unit strapped to the ankle. Those likely to be ordered to wear a GPS-enabled tracking device include sex attackers, robbers and murderers. Those convicted of theft or drugs offences are more likely to be issued with an RF tag.

Sidebar: Signalling a change

The Qinetiq system is based on enhanced low-signal strength GPS technology, allowing receivers to pick up transmissions far quicker than existing systems, or to detect much weaker codes.

Each GPS satellite transmits a 1023-bit Course Acquisition code at a rate of 1.023 MHz. GPS receivers detect these signals by effectively running a copy of that signal on the ground, and then trying to correlate the two.

The more satellite transmissions picked up by the device, the better the signal and greater the accuracy, so the Qinetiq system works on 12 channels.

But the signals acquired can be of such a low level within the GPS bandwidth that they are below random noise. To strengthen them, the system continues to sample more and more signals and integrates them with each other, until they accumulate to a detectable level.

Rather than using a single correlator to detect signals, the system uses massive parallel correlation. The technology has 1,023 correlators, to look at each of the individual cells within the code simultaneously, allowing it to immediately find a match.

But navigation satellites constantly move in their orbit, causing a shift in transmission frequency, while a smaller adjustment is also created by the movement of the receiver.

So time and satellite-position aiding data is also provided, via a wireless link, or is collected by the GPS receiver during normal signal strength operation, said Langrish. ‘With an aided receiver, where we have given it some prior information, we still have to search at individual points within the code space, but we have tied down the amount of frequency we need to look at, so we can perform that search much more quickly.’

Combining massive parallel correlation and satellite-position aiding allows the system to search 1,000 times faster, or to dwell 1,000 times longer at each point, building up the signal and tracking down to much lower signal strengths.

Increasing the speed of acquisition will also reduce the amount of battery power needed by GPS receivers, as they can detect signals in around two-tenths of a second, so do not need to be left on continuously.

The technology can also be used for tracking animals and would be useful to the military, where hiding troops to prevent them being seen by the enemy also makes it impossible for them to be tracked by the army command’s own satellite systems.

The technology could allow GPS tracking to make congestion charging fairer, by using geofencing to charge people for the time they are within the area, and at different rates for different times of the day.

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