Technology Breakthrough Boosts Performance Of UK System

A recent breakthrough in ADS-B technology by Raytheon Systems Limited (RSL) is now being run through its paces by various air traffic authorities around the world. ADS-B (Automatic Dependent Surveillance - Broadcast) is the next generation of secondary surveillance techniques and complements Secondary Surveillance Radar (SSR).

RSL's solution for ADS-B uses 1090 MHz Mode S Extended Squitter (ES)for its data link and since carriage of TCAS, which also uses Mode S, is already mandated in Europe, all new and many existing commercial aircraft already have ADS-B capability.

This 1090 MHz frequency band is already extensively used and to overcome congestion, (also known as 'FRUIT' - False Replies Unsynchronized In Time) and RSL has conducted extensive development work to improve decoding capability. Trials have shown the system works very effectively in congested air traffic environments extracting and successfully decoding ADS-B messages even when overlapped or garbled by other signals.

Mike Speed, RSL's director of Air Traffic Management Systems, said: "RSL has established an enviable reputation for secondary surveillance radar and now we have invested in taking the next step in this area of technology. Following our visits to various air traffic authorities, demonstrating the considerable advantages of our ADS-B solution, we will then be concentrating on providing an ADS-B ATMS solution for our customers.

"Initial feedback is very positive," he added.

Demonstrator systems have been shipped from the UK to locations as diverse as Singapore, Mongolia, Canada, the USA, Ireland and Germany. These trials have been of varying duration and dependent on the requirements of the individual authority.

Raytheon says the introduction of ADS-B would enable the safe reduction in aircraft separation where there is currently no radar coverage. ADS-B also offers considerable cost and space benefits over existing SSR system. Unlike SSR, ADS-B does not use a rotating antenna and the system itself is highly compact compared with SSR electronics cabinets. Cost benefits could be substantial compared to those of a Secondary Radar in a 'green field' situation.

ADS-B is likely to enter operational service in the near future, initially to supplement and, potentially in the longer term, to replace SSR.

It is generally accepted that the 1090 MHz frequency band, already congested with SSR/IFF replies, TCAS communications and out of band interference from PSR, DME etc, will become even more congested with the future addition of ADS Extended Squitter (ES) messages. Hence to perform effectively in such a demanding RF environment, a high performance decoder will be a critical enabler for ADS-B on 1090 MHz ES. Hitherto no decoder has demonstrated the level of the performance required to support ADS-B in the highest traffic densities predicted for 2015 and beyond. RSL effort has been to develop a decoder that can meet the projected high FRUIT environment of the future.

The trials have been conducted in a very varied environment with contrasting operational needs with great success and support the extensive modelling results conducted during the development phase. The trials have been conducted under varying conditions:

The trial in Canada, which was set up at the new Nav Canada radar site at Almonte, near Ottawa, recorded data over a four week period. This enabled Nav Canada to evaluate the system's performance and, in particular, given Canada's unique geographical situation, the range over which the system is capable of accurately monitoring air traffic.

Frankfurt is recognized as one of Europe's most dense traffic environments. The emphasis of the trial here was the performance of the system in a high FRUIT environment. The system performed excellently providing high probability of detection, accuracy, as well as coverage out to 250 nm. In addition additional FRUIT was injected into the system to simulate future predictions.

The Irish trials focused on long range oceanic coverage. The Irish Aviation Authority has responsibility for oceanic traffic entering into U.K. airspace. Their interest was extending the surveillance range of the existing radar. The ADS-B ground station range was only limited by the earth's curvature with range in excess of 250 nm achieved.

The FAA are conducting extensive laboratory testing against the Minimum Operations Standards (MOPS) and previous system results. Whilst in the early stages results are very promising with the RSL solution outperforming previous systems in all aspects. The system will continue laboratory evaluation prior to being deployed for field trials including multi-sector antenna evaluation.

FMI: www.raytheon.co.uk