Contribution to the Worldwide multimodal SBAS standard

Several studies have been done or have been started in order to extend the current aeronautical Space Based Augmentation System (SBAS) DO-229D Minimum Operational Performance Specification (MOPS) SBAS standard mainly defined by the Radio Technical ComiteeCommittee for Aeronautical applications (RTCA), Sub-Committee 159, Working Group 2 (RTCA SC-159 WG-2). The SBAS message is transmitted by geostationary satellites using a modulation scheme similar to GPS wherein the same Gold code family, chipping rate, BPSK modulation of the same GPS carrier frequency of 1575.42 MHz with the difference being that the a 500 bps bit stream is also modulated instead of the 50 bps data stream as in GPS. The 500 bps data stream are symbol bits which encode the actual and already standardized through GPS-like C/A codes carrying navigation and integrity 250 bps SBAS message stream at 1575,42 MHz. The aeronautical SBAS is an ICAO standard and can be adopted by any state. The intent is to have aeronautical SBAS establish itself as a world-wide standard and service. Aeronautical SBAS main purpose was to provide near real-time GNSS integrity world-wide. That concept evolved to also providing differential corrections and optionally a ranging signal. In addition, every aeronautical SBAS service provider has the ability to certify and then designate his service for Safety-of-Life (SoL) service. Once certified as a SoL service, the respective aeronautical SBAS service provider would also transmit the appropriate messages and data indicating that the particular transmission (and data) can be used for SoL applications. Data within the aeronautical SBAS message stream indicates over which regions the differential messages can used. Today, aeronautical SBAS is capable of supporting LPV (Localaizer with Precision Vertical) approaches to 200 foot (about 66 meters) minimums. These are CAT-I ILS (Category 1 International Landing System) equivalent approaches. For further technical details, the reader is referred to the RTCA/DO-229D MOPS.