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Alun Lewis looks into the widening range of position-finding technologies which will soon be supplementing conventional GPS in mission-critical radio applications When it comes to finding out where people and assets are, the average man in the street could be forgiven for thinking that we already have all the answers. Global Navigation Satellite Systems (GNSS) technologies – specifically, so far, the US’s Global Positioning System (GPS) – have plummeted in price over the past ten years and have become incorporated into cellular phones, cars and cameras. Further advances in location-based services and applications such as Google Earth and Google Street View continue to shrink the planet even further. While GPS-based location services have grown into a multi-billion dollar industry for the cellular sector in just a few years – and continue to grow at around 50 per cent each year - the mission-critical nature of the environments where most TETRA systems operate mean that things are nowhere near as simple or straightforward. A wide – and growing – range of factors mean that there’s no ‘one-size-fits-all’ location solution for TETRA, especially where actual positioning technologies to find and track resources are involved. Fortunately, an increasing number of other technologies – RFID, Bluetooth, eLORAN, Wi-Fi and UltraWideband (UWB) radio can be brought into play to either enhance GPS or replace it entirely in some situations. More satellites In terms of generic GPS activity, things are going to be getting increasingly crowded in space over the next few years with a number of new satellite systems going up or expanding their areas of coverage. After numerous delays, budget problems and the inevitable politicking, Europe’s own Galileo project is hoped to go live around 2015 – though there still may be some coverage problems, given the small number of satellites initially. Both free and commercial positioning services will be available with reported accuracies ranging from one metre down to centimetres, while a short messaging function will allow limited communication functions with some terminals to confirm that help is on its way. Meanwhile, the Russians have been busy expanding GLONASS, their own system, which is expected to reach out beyond their borders in the next year or two as more satellites are launched. Commercialization of the services is lagging far behind the US’s GPS, but the compatibility between the two technologies means that dual-purpose chipsets are now available and the two systems are expected to work together to provide increased accuracy – especially in the far northern hemisphere and in the inevitable ‘urban canyons’ in downtown cities. ...and more GNSS Meanwhile, other GNSSs – both global and regional – are also in development by a range of countries, including India (IRNSS), China (BeiDou) and Japan (QZSS). For Chris Muir, director of sales at the GPS antenna design specialists Sarantel, there are a number of caveats to add about the current performance of GPSs – especially in TETRA systems. “While GPS has been a huge consumer success story, many of these implementations have failed to really exploit the real power and accuracy out there and lowered the market’s expectations”, he says. “There are a whole range of technical and design issues – like the proximity of the radiowave-absorbing human body – that must be taken into account if interference is to be eliminated, accuracy improved and the urban canyon issue resolved. In reality, there are currently only a handful of TETRA devices out there that are using GPS technology to full advantage.” Awareness of other vulnerabilities within GNSSs is leading, however, to some interesting innovation. For a start, attention has turned once again to the potential of LORAN – a low-frequency terrestrial beacon system whose history stretches right back to the early days of World War II. Though the US switched off its LORAN system last year as a budget-saving measure, an increased focus on public safety in that country and an awareness of the vulnerabilities of GPS – as well as further innovation in other parts of the world such as the UK – may bring Enhanced LORAN (eLORAN) increasingly into focus as a practical and complementary technology to GPS. Modernizing LORAN Roke Manor Research in the UK, for example, has developed a miniature integrated eLORAN module called MILOR. It also includes GPS and GSM functionalities as well as MEMS-based sensors that provide inertial navigation backup. |