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|YearOfPublication=2011
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The Wide Area Augmentation System ([[WAAS General Introduction|WAAS]]) is the United States [[SBAS General Introduction|Satellite Based Augmentation System]]. The programme, started in 1992, is being carried out by the [http://www.faa.gov/ Federal Aviation Agency (FAA)]<ref name="FAA_NAV_HISTORY">[http://www.faa.gov Navigation Services - History - Satellite Navigation,] [http://www.faa.gov/ FAA.]</ref> and is specially developed for the civil aviation community.<ref name="FAA_WAAS">[http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/waas/ Navigation Services - Wide Area Augmentation System (WAAS)], [http://www.faa.gov/ FAA.]</ref> The system, which was declared operational in late 2003,<ref name="STANFORD_WAAS">[https://gps.stanford.edu/research/currentcontinuing-research/waas-sbas Wide Area Differential GPS (WADGPS), Stanford University]</ref> currently supports thousands of aircraft instrument approaches in more than one thousand airports in USA and Canada.<ref name="APPROACHES">[http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/approaches/index.cfm GNSS - GPS/WAAS Approaches,] [http://www.faa.gov/ Federal Aviation Agency (FAA).]</ref> WAAS service area includes CONUS, Alaska, Canada and Mexico.<ref name="WAASExpanded">[http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/waas/news/ WAAS Service Expanded into Canada and Mexico, September 28, 2007,] [http://www.faa.gov/ Federal Aviation Agency (FAA).]</ref>  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.<ref name="EXTENSION">[http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/library/satnav/media/SatNav_March08.pdf SatNav News, Vol. 33, March 2008,] [http://www.faa.gov/ Federal Aviation Agency (FAA).]</ref>
==WAAS Receivers==


The Wide Area Augmentation System (WAAS) is an GPS Augmentation system developed by the [http://www.faa.gov Federal Aviation Administration (FAA)], with the goal of improving its accuracy, integrity, and availability. Essentially, WAAS is intended to enable aircraft to rely on GPS for all phases of flight, including precision approaches to any airport within its coverage area.
The WAAS signal-in-space (SIS) has been designed to minimize standard GPS receiver hardware modifications. Therefore, a WAAS-GPS receiver is like a GPS receiver but with special software inside that allows the receiver to lock onto the code used by the WAAS GEOs satellites and compute the WAAS corrections to the GPS signals. Apart from this, the receiver is just like a GPS receiver. This means that it can pick up GPS signals as well. It is also of the same size as a GPS receiver and uses the same type of antenna. Although the prime target of WAAS is the civil aviation user community, most of GPS receivers nowadays can be configured to receive and process WAAS signal-in-space (SIS), so they can benefit from the enhanced accuracy and/or integrity offered by WAAS.<ref name="SBAS RECEIVERS">[http://www.egnos-pro.esa.int/SBAS_receivers.pdf List of available SBAS receivers, ESA, March 2006.]</ref>


WAAS uses a network of ground-based reference stations, in North America and Hawaii, to measure small variations in the GPS satellites' signals in the western hemisphere. Measurements from the reference stations are routed to master stations, which queue the received Deviation Correction (DC) and send the correction messages to geostationary WAAS satellites in a timely manner (every 5 seconds or better). Those satellites broadcast the correction messages back to Earth, where WAAS-enabled GPS receivers use the corrections while computing their positions to improve accuracy.<ref>[http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System WAAS in Wikipedia]</ref>
* '''Receiver types''' <br> WAAS-GPS receivers can be designed using a chipset, hybrid component or an auxiliary card.<ref name=" EGNOS Portal-Receivers">[http://egnos-portal.gsa.europa.eu EGNOS Portal on EGNOS receivers ]</ref>
** Chipsets: the EGNOS solution is embedded in one or two components that are installed in a circuit board. Special care is to be put with the RF interface. This solution is the least expensive.
** Hybrid components: a single component includes RF functions and  data processing. With a cost higher than the chipset solution, the integration is simpler.
** Auxiliary cards (piggybacks): all the RF and processing functions are included in a single card designed to be attached to the main board. Although this is the highest cost solution, is also the best one for embedded applications.


==WAAS User Segment==


The WAAS User Segment is the GPS and [[Work in Progress:WAAS Receivers|WAAS receiver]], which uses the information broadcast from each GPS satellite to determine its location and the current time, and receives the WAAS corrections from the Space segment.
* '''Communication protocols and manufacturer’s specifications'''


The WAAS User segment is not under the control of the WAAS service provider, FAA, as it is driven by the WAAS application market. In general, the WAAS service operator provides different services aiming at different market sectors, namely an Open Service, a Safety of Life service (SoL) and even a Commercial Service.<ref>[[SBAS Fundamentals]]</ref>
Receiver manufacturers tend to provide output data in a combination of proprietary and standardized open formats, the most common of which include [http://www.nmea.org/ NMEA], [http://www.rtcm.org/ RTCM], NTRIP and RINEX (Receiver INdependent EXchange).
A GPS receiver with “WAAS Enabled” specification usually means that the receiver activates SBAS reception by default. It is important to have in mind that navigation services are developing swiftly, so keep in pace with [[SBAS Standards|international standards]] is mandatory.


For the Safety-of-Life (SoL) service, WAAS users include all aircraft with approved WAAS avionics using the WAAS for any approved phase of flight. The WAAS user equipment shall be compliant (certified) against several standards, i.e. RTCA MOPS DO 229  (see article [[SBAS Standards]]). The SoL civil aviation certified equipment is in the highest rank with respect its cost. There exist a large number of certified receivers manufacturers worldwide, in the US: GARMIN, Honeywell, Rockwell Collins, General Avionics, etc. The Open Service (OS) targets low cost, general purpose GPS equipment that uses the WAAS Signal-In-Space (SIS) to provide the user with an enhanced accuracy performance in comparison with the one provided by a standalone GPS device. In comparison with the certification requirements of the SoL user equipment, user equipment is not necessarily compliant with the RTCA MOPS DO 229 processing rules, but might only make use of the processing algorithms that render the accuracy corrections provided by the SBAS SIS.  
More information on communication protocols can be found [[Interfaces_and_Protocols| here]].


In the WAAS receiver, the two types of [[WAAS Messages|WAAS correction messages]] received (fast and slow) are used in different ways. The GPS receiver can immediately apply the fast type of correction data, which includes the corrected satellite position and clock data, and determines its current location using normal GPS calculations. Once an approximate position fix is obtained the receiver begins to use the slow corrections to improve its accuracy. Among the slow correction data is the ionospheric delay. As the GPS signal travels from the satellite to the receiver, it passes through the ionosphere. The receiver calculates the location where the signal pierced the ionosphere and, if it has received an ionospheric delay value for that location, corrects for the error the ionosphere created. While the slow data can be updated every minute if necessary, ephemeris errors and ionosphere errors do not change this frequently, so they are only updated every two minutes and are considered valid for up to six minutes.
* '''Certified receivers'''
The civil aviation certified equipment is in the highest rank with respect its cost. There exist a large number of certified receivers manufacturers worldwide, including:<ref name="WAAS STATUS">[http://www.afceaboston.com WAAS Program Update, 2011, FAA]</ref>
* [http://www.garmin.com/garmin/cms/site/us GARMIN]
* [http://honeywell.com/Pages/Home.aspx Honeywell]
* [http://www.rockwellcollins.com/ Rockwell Collins]
* [http://www.uasc.com Universal Avionics]
* [http://www.cmcelectronics.ca CMC Electronics]
* [http://www.avidyne.com/ Avidyne]


==Notes==
==Notes==

Latest revision as of 08:53, 16 February 2021


WAASWAAS
Title WAAS Receivers
Edited by GMV
Level Basic
Year of Publication 2011
Logo GMV.png

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 in late 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 Receivers

The WAAS signal-in-space (SIS) has been designed to minimize standard GPS receiver hardware modifications. Therefore, a WAAS-GPS receiver is like a GPS receiver but with special software inside that allows the receiver to lock onto the code used by the WAAS GEOs satellites and compute the WAAS corrections to the GPS signals. Apart from this, the receiver is just like a GPS receiver. This means that it can pick up GPS signals as well. It is also of the same size as a GPS receiver and uses the same type of antenna. Although the prime target of WAAS is the civil aviation user community, most of GPS receivers nowadays can be configured to receive and process WAAS signal-in-space (SIS), so they can benefit from the enhanced accuracy and/or integrity offered by WAAS.[7]

  • Receiver types
    WAAS-GPS receivers can be designed using a chipset, hybrid component or an auxiliary card.[8]
    • Chipsets: the EGNOS solution is embedded in one or two components that are installed in a circuit board. Special care is to be put with the RF interface. This solution is the least expensive.
    • Hybrid components: a single component includes RF functions and data processing. With a cost higher than the chipset solution, the integration is simpler.
    • Auxiliary cards (piggybacks): all the RF and processing functions are included in a single card designed to be attached to the main board. Although this is the highest cost solution, is also the best one for embedded applications.


  • Communication protocols and manufacturer’s specifications

Receiver manufacturers tend to provide output data in a combination of proprietary and standardized open formats, the most common of which include NMEA, RTCM, NTRIP and RINEX (Receiver INdependent EXchange). A GPS receiver with “WAAS Enabled” specification usually means that the receiver activates SBAS reception by default. It is important to have in mind that navigation services are developing swiftly, so keep in pace with international standards is mandatory.

More information on communication protocols can be found here.

  • Certified receivers

The civil aviation certified equipment is in the highest rank with respect its cost. There exist a large number of certified receivers manufacturers worldwide, including:[9]

Notes

References

  1. ^ Navigation Services - History - Satellite Navigation, FAA.
  2. ^ Navigation Services - Wide Area Augmentation System (WAAS), FAA.
  3. ^ Wide Area Differential GPS (WADGPS), Stanford University
  4. ^ GNSS - GPS/WAAS Approaches, Federal Aviation Agency (FAA).
  5. ^ WAAS Service Expanded into Canada and Mexico, September 28, 2007, Federal Aviation Agency (FAA).
  6. ^ SatNav News, Vol. 33, March 2008, Federal Aviation Agency (FAA).
  7. ^ List of available SBAS receivers, ESA, March 2006.
  8. ^ EGNOS Portal on EGNOS receivers
  9. ^ WAAS Program Update, 2011, FAA
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