WAAS (Wide Area Augmentation System) was developed by the Federal Aviation Administration to improve the global positioning system to complement the accuracy, integrity and availability. WAAS was originally to allow the plane to the airport, rely on GPS for all phases of flight, including precision approach in its coverage area. WAAS is usually greater than 1.0 meters laterally and 1.5 m vertically over much of the contiguous UnitedStates and in most of Canada and Alaska. This accuracy is provideing approaches with aircraft capable of precision flight safety and navigation for all conditions. WAAS integrity of the information no more than 3 seconds of invalid data by year allows the system to be considered safe by the FAA for instrument flight rules.
Although originally developed for aviation, not only from WAAS limited to aviation, all GPS receiver is able toThe WAAS signal reception in a position to benefit from the reduced data so that the accuracy of GPS position. In fact, a WAAS-enabled GPS receiver can also point the way into the lane the car is traveling through (provided that the program supports Maping directions, "Lane Assist"). Since the Wide Area Augmentation System quickly today is standard in the field of GPS, most new GPS receivers are WAAS capable. Only with suchConventinal GPS, WAAS makes the application will not be any additional costs or taxes. All you need is that the corrections WAAS-enabled GPS receiver will then be able to decrypt the data and can then apply. Currently, the service is limited WAAS in the United States, Canada, Alaska and Hawaii. Although independent of WAAS, Europe and Asia are working on their systems, some GPS fix. Europe has the Euro Geostationary NavigationOverlay Service Multi-Satellite Augmentation System (MSAS) (EGNOS) and Japan on their working conditions. "
How does the WAAS
WAAS uses a network of 25 land-based wide-area reference stations (WRS) in North America and Hawaii measure, to small variations in the Western Hemisphere GPS satellite signals. These precisely surveyed ground stations monitor and collect information on GPS signals and transmit their data tothree wide-area master stations (WMS). The WMS to create two different types of fixes: fast and slow. Fixes for bugs that change rapidly and are a major concern of the current positions of GPS satellites and clock errors. These corrections are independent of the user's location, which can immediately of any receiver in the WAAS coverage area may be applied. Corrections slow long-term estimates of the errors and ephemeric clock and ionosphereDelay of information.
Once these corrections are generated, the master sends Ground stations have two pairs of uplink stations (GUS), the transfer of messages of correction of a number of geostationary satellites to broadcast its correction data on the Earth. WAAS-enabled GPS receiver, then use this information to signial corrections to the original GPS, WAAS-enabled GPS receiver to give a more precise location. GPS receiver uses the informationeach GPS satellite to determine the transmission of their position and the current time. According to the GPS device, a GPS receiver needs only) of the signal received from 3 to 4 satellites (the 31 satellites currently transmiting a signal to the user civilan be able to calculate its position. In addition to GPS, WAAS - enabled GPS receiver can also download the geostationary WAAS satellite signal.
The two different types of correctionNews from the WAAS (fast and slow) are the type used by the GPS receiver. The rapid nature of the correction data includes the correct satellite position and clock data, calculations can his current position with GPS. The more time a approximate location of the fixed GPS receiver begins to use the corrections for the slow improvement of its accuracy. Contains data for Slow-to delay the ionosphere. If the GPS signal moves fromreach the satellite to the receiver through the ionosphere. The receiver calculates the position in which the signal penetrates the ionosphere and, if given a value of ionospheric delay for this place, it corrects the error that created the ionosphere. In contrast to the fast data transfer, the data are slow can not be updated regularly, because the ionospheric conditions do not change quickly. During the slow data can be updated every minute, as required, are only updated every twoMinutes and to be valid for a maximum of six minutes.
Limitations of the WAAS
(1) WAAS is currently only the U.S. and in most of Canada and Alaska, but will expand the system in other continents and countries.
(2) Since the WAAS geostationary satellite transmission means that travel less than 10 degrees above the horizon for positions in the north to 71.4.This means that aircraft can be used in areas of Alaska and northern Canada have difficulty maintaining a lock on the WAAS signal.
(3) For the calculation of a grid station ionospheric delay that a reference point and must choose between a satellite. The small number of satellites and ground stations, the number of points that can be calculated.
(4) Aircraft conducting WAAS approaches must be certified GPS receiver.
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