Evolving WAAS to Serve L1/L5 Users

GPS has launched its first L5 capable satellites and plans to achieve L5 Full Operational Capability (FOC) in the 2019 time frame. L5 is of great interest to the Wide Area Augmentation System (WAAS) and the aviation community, as it will allow aircraft to measure and remove the ionospheric delay affecting each ranging observation. Currently, this error source is the most significant cause of unavailability for WAAS users. Its elimination will result in greater performance and a larger service area under WAAS. However, in order to take advantage of L5, both the aircraft and WAAS will need to be updated. We have previously recommended changes to the airborne protection level calculations to exploit these new signals. In this paper we describe changes that must be made to WAAS to support the new protection level equations and provide dual-frequency service.