WAAS Receivers

WAAS
Title	WAAS Receivers
Edited by	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) and is specially developed for the civil aviation community. The system, which was declared operational in late 2003, currently supports thousands of aircraft instrument approaches in more than one thousand airports in USA and Canada. WAAS service area includes CONUS, Alaska, Canada and Mexico. 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.

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.

• Receiver types
  WASS-GPS receivers can be designed using a chipset, hybrid component or an auxiliary card.
  • 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.

• 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:

• GARMIN
• Honeywell
• Rockwell Collins
• Universal Avionics
• CMC Electronics
• Avidyne