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WAAS Receivers
| WAAS | |
|---|---|
| Title | WAAS Receivers |
| Author(s) | GMV. |
| Level | Basic |
| Year of Publication | 2011 |
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; two development phases have been already covered, a third is in progress, and there are 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
WASS-GPS receivers can be designed using a chipset, hybrid component or an auxiliary card.- Chipset: consists of one or two components that must be installed on a circuit board. The routing of the RF part is sensitive. This compact solution is also the least expensive.
- Hybrid component: consists of a single component integrating the RF and signal processing parts to be installed on a circuit board. Routing is easier compared to chipsets. The price is higher than for the chipset solution.
- Auxiliary card (piggyback): all the receiver and peripheral components are integrated on a ready-to-use card connected to the final product’s main circuit board. It is an ideal solution for prototyping embedded applications. This is the most expensive solution.
- Communication protocols and manufacturer’s specifications
Manufacturers generally use proprietary protocols which give access to almost all the data (pseudoranges, satellite navigation messages, SBAS messages, etc.) associated with a standardised protocol, NMEA 0183. Some receivers also generate data in RINEX (Receiver INdependent EXchange) format. 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.
- 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:[8]
Notes
References
- ^ Navigation Services - History - Satellite Navigation, FAA.
- ^ Navigation Services - Wide Area Augmentation System (WAAS), FAA.
- ^ Wide Area Differential GPS (WADGPS), Stanford University
- ^ GNSS - GPS/WAAS Approaches, Federal Aviation Agency (FAA).
- ^ WAAS Service Expanded into Canada and Mexico, September 28, 2007, Federal Aviation Agency (FAA).
- ^ SatNav News, Vol. 33, March 2008, Federal Aviation Agency (FAA).
- ^ List of available SBAS receivers, ESA, March 2006.
- ^ WAAS Program Update, 2011, FAA