Thus far, the G-III has met or exceeded the GII’s performance, with NovAtel’s latest version of the receiver certified to RTCA/DO-178B Software Considerations in Airborne Systems and Equipment Certification Level D. The increased level of rigor imposed by DO-178B, particularly in the requirements for development and testing phases, contributed to the improved end product.
The transition to the new receiver began last summer and has proven relatively seamless. As of June of this year, all 38 wide area reference stations have been converted. In that time, the FAA has experienced very few issues with the G-III, Thompson said, and when issues do arise, they work closely with NovAtel to make any necessary changes or adjustments.
“The FAA and NovAtel jointly work to correct any issues that might arise over time,” Thompson said. “Subsequent generations of the receiver have captured these improvements to increase reliability and performance.”
The Benefits of GNSS Modernization
GNSS modernization is important to WAAS for two primary reasons, Thompson said. First, the Department of Defense announced in a federal register notice that they would discontinue support for the GPS L2 P(Y) signal in the future. WAAS requires two frequencies (currently L1 and L2 P(Y)) to calculate signal delays caused by the ionosphere.
“The G-III incorporates the new GPS L5 signal into WAAS, allowing for the replacement of the L2 P(Y) signal,” Thompson said. “Quite simply, if FAA did not replace the L2 P(Y) signal, the existing single frequency service provided by WAAS would cease.”
Not only that, adding L5 to WAAS also provides more precise correction for ionospheric delay, Thompson added, which is currently the largest source of error within a GPS signal. WAAS uses models to calculate the estimated error at any given location within the WAAS service area. Because both L1 and L5 are within the protected spectrum allocated for aeronautical radionavigation service, future-dual frequency users will be able to use the L1 and L5 GPS signals to calculate ionospheric delay for their exact location, in real time, within the WAAS avionics.
“In addition, this will enable use outside of the existing service area,” Thompson explained. “For example, users in Hawaii do not currently have LPV service. Dual-frequency avionics will enable this.”