|Algorithmic improvements will increase service availability with improved modeling of ionospheric signal distortion. Because of the availability impacts due to ionospheric storms, SBAS providers are making plans to implement dual-frequency in order to increase SBAS availability and performance by direct mitigation of ionospheric signal delay using two civil frequencies.
Dual frequency extends coverage outside reference networks & allows LPV operation in equatorial areas because of its superior properties to mitigate ionospheric interference. Expanding SBAS networks into Southern Hemisphere would allow global coverage of land masses. A further benefit is improved robustness against unintentional interference.
Phase IV of WAAS will introduce Dual Frequency operation by 2018, taking advantage of new GPS satellites broadcasting the current L1 signal (1575.42 MHz) along with the new, civilian, L5 Safety of Life signal (1176.45 MHz). EGNOS version 3 will introduce Dual Frequency operation by 2020 and other SBAS systems are also planning its implementation.
With the use of L5, a dual-frequency SBAS avionics receiver could use the SBAS corrections message or generate its own ionospheric delay corrections by comparing the L1 and L5signals. Dual-frequency SBAS avionics receivers promise to provide greater accuracy and increased service availability.
Under the concept of Interoperability, methods for seamless transitions between SBAS service regions are being developed. This includes analysis for transitions between SBAS and RAIM, two SBAS regions and between SBAS and GBAS service areas.
There are also options being considered regarding inclusion of additional GNSS constellations in SBAS such as GLONASS, Galileo and BeiDou (COMPASS). Multiple constellations will allow SBAS avionics receiver manufacturers to develop Interchangeability. With interchangeability a given SBAS avionics receiver can select all satellites in view from any constellation and use the four best suited for an optimal navigational solution. Additional constellations allow even greater coverage with fewer stations.
SBAS operators are committed to deploy and maintain a sufficient number of GEO satellites to ensure availability requirements are met across each SBAS service volume.
SBAS deployments will continue to support legacy single frequency users by ensuring backward compatibility.
LPV-200 service is expected to be available world-wide with the development of dual frequency operation, extended network service areas and additional GNSS constellations.