Incremental benefits of dual frequency signals for the Wide Area Augmentation System

Satellite Based Augmentation Systems (SBAS) have been implemented in the United States, Europe, and Japan and one is soon to be deployed in India as well. Today, SBAS systems utilize dual frequency L1-CA/L2 semi-codeless measurements to provide precise corrections and integrity bounds to aircraft for use in both enroute and precision approach operations. In contrast to the ground system, the aircraft are limited to the sole use of L1-CA measurements since the L2 frequency does not lie in a protected Aeronautical Radio Navigation Service (ARNS) frequency band. The single biggest source of error in an SBAS position solution and the limiting factor in system performance is the ionospheric corrections. Using two frequencies, the ground system is capable of creating corrections for ionospheric delays although the uncertainty bounds associated with these corrections must be inflated to account for the unpredictable effects of ionospheric storms. With the addition of the L5 signal in block IIF and block III GPS satellites, aviation receivers will be able to correct for ionospheric delay without SBAS corrections drastically improving availability of precision approach operations. Although clear benefits have been shown in the end state, a full constellation of L5 capable GPS satellites will not be available until 2018. This paper quantifies the availability and continuity benefits of utilizing the L5 signal from a partial constellation of GPS IIF and GPS III satellites.