Spread spectrum enables low power

A radio control system is reliable and low enough powered to allow its use in aircraft safety systems. Tom Shelley reports Spread spectrum allows in-cabin aircraft safety systems to be run using low power radio, potentially saving two passenger weights of wiring and a considerable amount of installation time and cost. Modules hand on messages and instructions from one to another by the most convenient path found at the time, further reducing required power levels and ensuring redundancy. Interest is already being expressed by designers of systems to be used on the ground. STG Aerospace, based in Norfolk, is best known for its photoluminescent 'SafTGlo' floor path lighting systems which show passengers the way out in the event of an emergency evacuation in darkness or smoke. Doing away with the need for wiring, bulbs and consequent maintenance, they never fail, and save airlines a pile of money. Following the same philosophy, the company has now developed 'Secure Control', primarily to activate emergency lights, but also for other safety related systems. Regulations require that radio signal emissions be below 44dBµV/m, which requires the use of spread spectrum techniques, originally developed for military communications but now declassified. Each unit is a transceiver, and transmits to every other unit within its range. In a large airliner cabin, messages are thus passed from unit to unit. So low powered is the system, that when fitted to a Boeing 747-400, Boeing engineers using field strength sensors outside the aircraft at window height were unable to detect the signals at all The first application is in activating battery powered emergency lights, which can either be switched on by the pilot or automatically in response to loss of power. Master control units can periodically ask every lighting unit whether it is working, indicating green for all OK, amber for a problem but not such that the aircraft should not be allowed to fly, or red for a problem requiring attention. A cabin alert monitoring system could include key fob buttons for stewardesses and a vibration alarm for the sky marshall. Other self powered applications include oxygen deployment systems, and fire and smoke detection and monitoring. Applied to aircraft powered applications, the system could be applied to interior lights, lavatory door monitoring and power supply units. In addition, there are said to be some 1500 sensor applications in a modern airliner, and the system could be used to eliminate wiring in many of these, air quality sensors for example. For the moment, the company intends to market its products only to designers and owners of aircraft, but it is also prepared to consider licensing the technology to other areas, such as architects and owners of major office buildings and builders of automation systems. The system is the culmination of three years development work, assisted by a SMART Award in 2002. STG Aerospace Pointers * System uses very low power radio, so low powered that it cannot be detected outside the aircraft, to operate emergency systems * Operating technology is spread spectrum, and each unit is a transceiver, communicating with every other unit within range * The company is presently only targeting aerospace customers, but it prepared to consider licensing to other industries