WAAS

WAAS/EGNOS (GPS)

What is it and how does it work?
Many GPS receivers are now labelled as being 'WAAS enabled'. WAAS is the acronym for the Wide Area Augmentation System, a system designed to increase the accuracy of civilian GPS position information in North American. Europe has it's own system known as EGNOS (European Geostationary Navigation Overlay Service). Both systems work by using a network of base stations which continuously monitor their GPS position using the currently available GPS satellite signals. Knowing their own position very precisely, the base stations can compare their actual and GPS position, and therefore calculate the current error in the GPS signal, which they then transmit to compatible GPS receivers via a secondary system of geostationary satellites (WAAS - 2 over North America, EGNOS - 3 over Europe).

What are it’s benefits?

This 'error' information allows an approximate 5x increase in the accuracy of GPS position calculation. This means that 95% of the time, a WAAS/EGNOS enabled GPS receiver can calculate it's position to within 1-3m (as opposed to the normal 10-15m).
It's free.

What are it’s drawbacks?

Due to the relatively few satellites used to transmit the WAAS/EGNOS information, the signals are very easily subject to interference or complete blockage by surrounding terrain when used on land. The system was primarily designed for automatic navigation of aircraft and shipping - uses where signal blockage by mountains or buildings are not a problem.
Searching for WAAS/EGNOS signals requires increased time and power consumption from a GPS receiver - battery life is reduced and initial satellite acquisition time is increased.
Although the North American WAAS has been operational for some time, EGNOS is still currently in it's testing stages - it is not clear when it will be fully operational.
Due to the reduced chance of getting a WAAS/EGNOS signal on land (as opposed to air or sea use), the increased power consumption and slower satellite acquisition, many GPS receivers have their WAAS/EGNOS capability turned off by default. You need to remember to activate it if you think you will benefit from it.

What does it cost?
Like the GPS system, WAAS and EGNOS have been paid for with taxpayer's money, so they are free to use (no licence, contract, etc. is required). All you need is a WAAS/EGNOS enabled GPS receiver.

How do I find out more?

[ www.garmin.com ] [ www.magellangps.com ] [ European Space Agency ] [ WAAS ]

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