Wide Area Augmentation System

Wide Area Augmentation System (WAAS ) is a part of the extension system (Satellite Based Augmentation System SBAS ) to improve the existing U.S. GPS. WAAS signals are sent through separate additional satellites on the same frequencies as GPS and intended for the distribution of correction data for the distorted by the signal propagation in the ionosphere GPS signals.

WAAS is being emitted from two to four geostationary satellites over the territory of the United States and is not available for all other regions of the earth. In Europe and Japan EGNOS and MSAS compatible contact systems to the point of WAAS. Some systems are currently under construction.

Since the navigation using civilian GPS usually only at a transmission frequency based (C / A code on the so-called L1 frequency ), so that can not be corrected sufficiently accurate atmospheric effects. Many inexpensive GPS receivers have only one receiver for only one frequency.

After the artificial defect in the civil usable C / A code of GPS on 1 May 2000 were shut down, are the largest remaining error term of atmospheric effects. This means that the radio signal is not always exactly the same time it takes to pass through the atmosphere, and therefore the key for determining the position does not match the exact time of measurement.

With systems such as WAAS and EGNOS compatible fully to the additional correction signals are transmitted on the L1 frequency transmission from geostationary satellites such as Inmarsat. Thus, even simple single-channel receiver will enjoy this correction signal, the correction data is transmitted on the same frequency as the GPS data - but with other GPS identifiers ( satellite number 33 upwards).

Are obtained, the correction data from a variety of fixed ground stations that detect lying in their reception area atmospherically induced errors and then calculate correction factors for different geographic regions. This WAAS / EGNOS -enabled GPS receiver can determine the additional run-time effects of the signals in the atmosphere more accurately, leading accuracies of 0.3 to 1 m can be achieved. In comparison, only maximum spatial resolution with civil GPS 5-15 meters are possible without this correction data.

The use of signal enhancement techniques often has a higher energy needs of the beneficiary result. However, users of mobile receiver on the ground often have the problem of not having enough free sight to the geostationary satellite orbits. The reception of WAAS-/EGNOS-Signalen is usually only possible on high ground or the open sea.

Global Systems Historically: United States Transit · Soviet Union Parus / Zikada Operating: United States Russia GLONASS GPS · In construction: People's Republic of China Beidou · Galileo Europaische Union

Regional systems or regional augmentation systems Operating: People's Republic of China Beidou · In construction: Japan QZSS · India IRNSS

Supporting satellite-based systems ( SBAS ) Operating: United States WAAS · Japan · MSAS Europaische Union EGNOS in Development: India GAGAN · Japan · Russia SAIF QZSS SDKM