Multilateration – a technology whose time has come
Multilateration – a technology whose time has come
Keywords: Airports, Sensors, Radar, Aircraft
Traditionally, most civil aviation traffic surveillance has been carried out using primary and secondary radar techniques. However, over the last 15 years a competing technology, known as multilateration, has emerged. This involves the fixing of a position by reference to the time difference of arrival of a signal at a collection of sensors.
Today, major airports across the world use multilateration to pinpoint the position of an aircraft on the ground as part of an advanced surface movement guidance and control system. However, in recent years, many new applications for the technology have emerged.
A myriad benefits
Multilateration is now widely used for tracking aircraft in the air and has made a significant contribution to reducing delay and easing congestion in the skies. Originally employed for specialist applications like reduced vertical separation minima height monitoring, it has grown in comprehensive surveillance solution covering vast tranches of airspace and increasingly capable of competing strongly with secondary surveillance radar (SSR).
Multilateration has a number of key benefits. Key to its success is its scalability. The technology uses a distributed network of receiving sensors. As a result, it is easy for users to add in sensors to increase the overall coverage area, to improve accuracy or just to fill gaps in reception.
In contrast, within a single radar system, the quality of low altitude coverage diminishes with distance and extending coverage typically requires a new installation with associated cost and infrastructure implications.
Multilateration is also cost-effective. Each sensor has a simple design and uses a straightforward omni-directional antenna, whereas radar systems rely on complex, mechanical rotating antennae, which are more expensive to install and maintain. In fact, the through-life costs of a typical wide area multilateration(WAM) system using prepared sites are around 25 per cent of the cost of a comparable SSR system.
In addition, the use of an omni- directional antenna enables multilateration systems to receive aircraft signals from all directions simultaneously and therefore to achieve higher update rates than are possible with conventional radar.
Multilateration has also proven to be robust and reliable. The system uses several distributed receivers. This means it can confer a degree of redundancy whereby one receiver failure will not adversely affect either coverage or accuracy. This increases availability, as continuity of service can be maintained while repairs are carried out. Roke's in-depth experience of the marketplace, which stretches back to 1989, enables it to optimise the benefits of multilataration for its customers. It was the first company to deploy a WAM system in the field in 1993.
Its patented common view global navigation satellite system synchronisation technique provides end-users with the highest level of accuracy. And Poke's system makes the equipment siting process easier and mere cost-effective because it does not require line-of-sight to be in place between individual sensors.
Bright prospects
As, the multilateration industry looks to the future, WAM, in particular, is expected to see strong growth. Applications have been growing rapidly in recant years. As the technology is maturing and the price is coming down, it is becoming more affordable to many smaller airports.
Previously, he high cost of radar and consequent lack of available surveillance coverage prevented smaller airports from growing quickly. The emergence of multilateration is changing all this.
Crucially, multilateration precision tracking of aircraft enables them to increase capacity and manage traffic more efficiently, particularly in low visibility conditions. Moreover, it does this at an affordable price. For this reason, even airports with limited financial resources are able to take advantage of many of the additional benefits of the data that is collected from the multilateration process.
For example, using the technology enables airports to carry out environmental modelling, correlating noise measurements with aircraft positions to provide internet updates to nearby residents. Details of the aircraft involved and the reasons for the excessive noise can be published on the internet. In addition,the ability to monitor aircraft movements on the ground efficiently will streamline the management of arrival and departure time!
Multilateration can also add value to the business of airports by alerting car rental firms to the impending arrival of aircraft.
Making life easier
This paper has outlined many of the key benefits of multilateration. However,if airport authorities and traffic control organisations are to be tempted to turn away from their tried and tested radar implementations, they need to be persuaded that the new technology is easy to install, use and maintain.
These are the guiding principles behind Roke Manor Research's development of Vigilance, the latest generation of its mutlilateration technology.
Roke Manor Research demonstrated the capabilities of Vigilance, which is specifically aimed at the air traffic management (ATM) market at the recent ATC Maastricht show in The Netherlands.
In developing Vigilance, the company drew on the experience not only of its previous work for ATM applications but also of a recent cellular project carried out for parent company Siemens.
Roke has effectively brought together the best of both worlds. It has combined the skills and technique used to manufacture high volume products,taking advantage of commercial off- the-shelf technology where appropriate, with extensive knowledge of its legacy of tried end tested multilateration solutions for ATM, built up over the last seventeen years.
The result is a solution that is compact, cost-effective to manufacture and maintain and easily integrated as part of a larger solution. Roke is confident that its use will reduce the time and cost involved in commissioning systems,rolling them out across a wide area and keeping them fully optimised and maintained.
At the show, the display featured a sensor assembly from the new enhanced solution consisting of the new compact receiver box together with its associated antenna. In addition, Roke was also able to demonstrate to visitors to its stand recorded track data from one of its working systems.
Shaping the future
It is our belief at Roke Manor Research that systems like Vigilance represent the future for multilateration, WAM systems already offer significant technical advantages over SSR. However, if users are to commit to a change in technology,it is crucial that they are offered low cost receivers that are simple to deploy in a wide range of locations. This is where Roke is now concentrating its research and development efforts.
At Roke, we see great potential in drawing on the experience of the cellular industry in terms of system design and deployment, if the approach is right, we believe we can make a significant contribution to turning multilateration from a promising technology commercially into a genuine competitor to radar as the primary air traffic surveillance technique.
Details available from: Roke Manor Research Ltd. Tel: +44 1794 833000; Fax:+44 (0) 1794 833433; e-mail: info@roke.co.uk;web site: www.roke.co.uk
