System design considerations for the development of Iridium World Air Services

Iridium, Motorola, and AlliedSignal are implementing Iridium World Air Service (IWAS) to provide a seamless, common global telecommunications infrastructure to aeronautical users for both safety and non-safety uses. To achieve this lofty goal, a significant systems engineering effort looked at multiple aspects of the end-to-end service. An obvious design constraint in this process was the prior existence of key elements upon which IWAS is built. With this design constraint as the foundation, specific aeronautical requirements were added. These requirements included distinctions between safety and non-safety communications, implementation of priority, precedence and preemption for safety services, spectrum control to assure adequate protection of nearby communications, navigation, surveillance and radio astronomy services, overall system availability considerations, and error rate/throughput issues. This paper describes these key considerations and summarizes the approach taken to ensure that IWAS meets the expectations of both users and regulators to take its place providing aircraft the desired and required communications performance.