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WAAS Future and Evolutions

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Title WAAS Future and Evolutions
Edited by GMV
Level Basic
Year of Publication 2011
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The Wide Area Augmentation System (WAAS) is the United States Satellite Based Augmentation System. The programme, started in 1992, is being carried out by the Federal Aviation Agency (FAA)[1] and is specially developed for the civil aviation community.[2] The system, which was declared operational on July 10, 2003,[3] currently supports thousands of aircraft instrument approaches in more than one thousand airports in USA and Canada.[4] WAAS service area includes CONUS, Alaska, Canada and Mexico.[5] The WAAS programme is continuously in evolution; three development phases have been already covered, and there are on-going plans to improve the capability of the system in parallel with the evolution of the SBAS standards towards a dual-frequency augmentation service.[6]

WAAS Future and Evolutions

The WAAS Development Phases are:[7][8][9][10]

  1. Phase I –Initial Operating Capability (IOC). Completed in 2003.
  2. Phase II -Full LPV Performance. Completed in 2008.
  3. Phase III -Full LPV-200 Performance. Completed in 2013.
  4. Phase IV -Dual Frequency Operations. Planned for 2014-2028.

In Phase I, WAAS

  • Achieved Initial Operating Capability (IOC)
  • Provided LNAV/ VNAV/ Limited LPV Capability

In Phase II, WAAS provided:

  • Improved LPV availability in CONUS and Alaska
  • Expanded coverage to Mexico and Canada

Phase III, implied the following changes:[7][10]

  • Technology refresh covering development, modifications, and enhancements in the system.
  • Steady state operations and maintenance, such as replacement of legacy WRSs, router upgrades,...
  • Space segment upgrades, with the broadcast of WAAS signal-in-space form a a third GEO satellite, Inmarsat AMR (PRN #133), since November 2010, complementing Galaxy 15 (PRN #135) and Anik F1R (PRN #138).
  • Begin GPS L5 activities: specifications, planning, definition of interfaces and standards, receiver development, etc.

For Phase IV, WAAS shall begin to operate with Dual Frequency (L1-L5). This would imply:[7][10]

  • Complete the transition to SBAS L1/L5 dual frequency service.
  • Provision of the SBAS-L1 single-frequency legacy service until 2028.
  • Maintain a robust, reliable, and sustainable LPV-200 capability.
  • Maintenance of the LPV-200 capability, paying special attention to its robustness and reliability.
  • High availability performance, with steady operations and smooth maintenance.
  • Improve service during severe solar activity.

In addition, space segment updates are foreseen in this timeframe. In April 2015, the Federal Aviation Administration (FAA) awarded a $103-million contract to the Raytheon Company to maintain the GPS Wide Area Augmentation System (WAAS). The company would develop a payload to be incorporated into a new geostationary satellite and two associated ground uplink stations to support the WAAS system within U.S. airspace. The WAAS GEO 6 payload is hosted aboard a commercial host satellite in a geostationary earth orbit (GEO). The GEO 6 system, along with GEO 5 (under a contract awarded to Raytheon in 2012), will replace two WAAS GEO payloads that are approaching the end of their service leases. Projected launch of the WAAS GEO 6 payload occurred in the second quarter of 2019. Three more GEO satellites (GEO 7/8/9) are going to be developped to replace legacy GEO's upon lease expiration. The first of them, GEO 7, is expected to be operational in 2022.[11] The agency is in the process of converting WAAS from a single-frequency (L1) system to dual-frequency (L1/L5) operation. The FAA plans to sustain dual-frequency WAAS GEOs until at least 2044.[12]

Dual frequency WAAS offers great potential to eliminate the current system’s vulnerability to ionospheric storms. The removal of ionospheric uncertainty, coupled with other improvements to integrity monitoring, may allow guidance under even more demanding environments than currently allowed. Further, elimination of dependency on ionospheric corrections allows for better coverage at the edges of the current system. However, the change to ionospheric-free combination in the aircraft introduces some changes that must be overcome. Accuracy will be degraded, but still within specifications for all known operations. However, certain threats, most notably code-carrier divergence and signal deformations, runs the risk of now dominating and determining availability.[13]

WAAS Schedule

In the following figure is shown a time diagram with the FAA plans for WAAS GEOs and the Dual frequency operations for the period 2015-2022.

WAAS Schedule[14]

In addition, the transition between phase A and B of the Phase IV takes place during 2020 and 2021. This transition entails the following points:

  • Two year continuation of the WAAS program prior to Phase 4B FID
  • Two releases to focused on continued sustainment of the operational WAAS (Releases 6 and 7)
    • Release 6 will improve WAAS performance enhancements by correcting anomalies to the O&M, Test Support Software (TSS) and network critical message logging capabilities
    • Release 7 will integrate GEO 7 into WAAS and upgrade with new Signal Generator including the retrofitting of new
    • SIGGENs at the GEO 5 and GEO 6 legacy GUS sites. GEO 7 projected to be operational by September 2021
  • Continued definition of DFO Phase 4B requirements and alignment with GPS modernization schedule
  • Demonstration of alternatives to transition the communications network from Time Division Multiplexing (TDM) to Internet Protocol (IP)
  • Additional work will include:
    • Completion of L5 Dual Frequency (DF) signal analysis and support Minimal Operational Performance Standards (MOPS) development to facilitate requirements definition
    • Resolution of WAAS Operations & Maintenance software reliability and maintainability issues
    • Integration of GEO 7
    • Replacement of obsolete Signal Generator (SIGGEN)
    • Generation of WAAS Phase 4B FID Artifacts