WAAS GPS

GPS Navigation Systems SandersGarmin Jeff www. GpsFrontier. com 04/05/2009

WAAS (Wide Area Augmentation System) was developed by the Federal Aviation Administration to extend the global positioning system to ensure the accuracy to improve the integrity and availability. WAAS was originally designed to allow aircraft is the use of GPS for all phases of flight, including precision approach to the airport to leave within its coverage area. The WAAS system provides generally better than 1 0 m 1 5 meters laterally and vertically in most areas of neighbors and the United States much of Canada and Alaska. This precision is provideing approaches with aircraft capable of precision flight safety and navigation for all weather conditions. WAAS integrity of information is not more than three seconds of bad data, by year, the system allows safe by the FAA for instrument flight rules.

Although originally developed for aviation can WAAS is limited not only received for the aviation industry in the GPS receiver, the WAAS signal is able to receive data, so the more accurate GPS positioning . In fact, a WAAS GPS receiver and you can open the way towards your car on the road (assuming the program is supported Maping “Lane Assist”, steering). Because the Wide Area Augmentation System is quickly becoming the standard in the GPS industry, most new GPS receiver today, WAAS. As with the standard GPS, WAAS does not come with additional costs or fees. All that is required is that GPS receivers are WAAS-enabled, so it can receive and decode data in a position corrections to the position it is. Currently, WAAS service is only for USA, Canada, Alaska and Hawaii. Although independent of WAAS, Europe and Asia are working on their own GPS systems further correction. Europe has the Euro Geostationary Navigation Overlay Service (EGNOS) and Japan working on its “Multi-Functional Satellite Augmentation System (MSAS).

WAAS uses a network of 25 ground stations for wide area reference (WRS) in North America and Hawaii, to measure small variations in GPS satellite signals in the Western Hemisphere. These ground stations monitor closely examined and gather information on the GPS signals and send their data to the three main stations extended (WMS). The WMS is to create two types of corrections: fast and slow. The quick fix for bugs that are rapidly changing and a priority for the current positions of GPS satellites and clock errors. These corrections are independent position of the user, where they can be used immediately by a receiver in WAAS zone. The fixes are slow for the error estimates of long-term clock ephemeric and information ionospheric delay.

After these corrections are generated, the master station sends two pairs of ground broadcasting stations (GUS) for Member States that the correction messages from a number of geostationary satellites, which broadcasts data correction Earth. Then, WAAS-enabled GPS receivers use this information to the GPS corrections signial home, what is WAAS GPS position more accurately. GPS receivers use the information broadcast by GPS satellites to determine their location and time. According to the GPS device, a GPS receiver needs only a signal of 3-4 satellites (the 31 satellites currently transmiting a signal to users receive civilan) to calculate its position. In addition to the GPS signal, a receiver WAAS GPS, WAAS geostationary satellite signal.

The two different types of messages from the WAAS correction system (fast and slow) are used by the GPS receiver in different ways. The rapid nature of the correction, the corrected data include the satellite position and clock data to determine its current location, using GPS calculations usual. Once an approximate location fix is obtained, the GPS receiver starts slow corrections used to improve their accuracy. Slow-Contains the data for the ionosphere delay. If the GPS signal from the satellite receiver moves, it passes through the ionosphere. The receiver calculates the position where the signal is broken and the ionosphere, where he received a value of the ionospheric delay for this, it corrects the error that has created the ionosphere. In contrast, the rapid transfer of data, the data is slow should not be updated frequently, because the ionospheric conditions do not change quickly. While the data may slow to be updated every minute, they are only updated every two minutes and are valid for a maximum of six minutes.

(1) WAAS is currently only for U.S. and many parts of Canada and Alaska, but it plans to extend the scheme to other countries and continents. (2) Since the WAAS satellites are geostationary broadcasting that will bring them less than 10 degrees above the horizon for the sites north of the 71st 4 ° latitude. This means that the aircraft in the territories of Alaska and northern Canada may have trouble maintaining a lock on the WAAS signal. (3) To calculate an ionospheric delay grid point, this point should be between a satellite and a reference station. The small number of satellites and ground stations, the number of points that can be calculated. (4) conducting WAAS approaches must have the aircraft certified GPS receiver.

GPS Navigation Systems SandersGarmin Jeff www. GpsFrontier. com 04/05/2009