Geo-stationary satellites broadcast error correction signals to improve GPS/GNSS accuracy and integrity.

GPS alone does not always provide adequate performance, particularly in demanding environments where a high level of integrity is required. The accuracy and integrity of GPS/GNSS can be greatly enhanced by the use of augmentation information derived from various sources (see below). The use of GPS/GNSS augmentation systems takes many forms but all share the same basic principle of providing supplementary information whose objective is improving GPS/GNSS performance and/or trustworthiness.

SPACE BASED AUGMENTATION SYSTEMS (SBAS)

Space Based Augmentation Systems (SBAS) are typically designed to improve GPS/GNSS system integrity and accuracy for aircraft navigation and particularly landing. SBAS satellites broadcast correction messages back to Earth, where suitably enabled receivers use the information to improve accuracy and integrity. The USA, Europe and Asia are developing their own SBAS systems. In Europe, the European Geostationary Navigation Overlay Service (EGNOS) system exists and is now operational. In the USA there is the Wide Area Augmentation System (WAAS), in Japan the Multi-functional Satellite Augmentation System (MSAS) and India is focusing on the GPS Aided Geo Augmented Navigation (GAGAN) system.

In Japan, in addition to MSAS, the Quasi-Zenith Satellite System (QZSS) is currently under development and scheduled for the first (of three) launches in 2010. QZSS will provide additional overhead ranging sources in the Japan area as an augmentation service to GPS. Highly elliptical orbits allow these satellites to dwell at high elevations in the sky allowing enhanced coverage in urban canyons. Spirent is the first simulator manufacturer to offer a QZSS simulation solution.

The accuracy and integrity of GNSS can be greatly enhanced by the use of information derived from observations on the ground in the area of interest to the GPS user. Spirent's GNSS simulators include the capability to place satellites at geostationary positions and to allocate channels to provide WAAS, EGNOS and MSAS signals to allow testing of these SBAS receiver functionality.

GROUND BASED AUGMENTATION SYSTEMS (GBAS)

An alternative approach to GPS augmentation is to transmit integrity and the correction messages from ground-based augmentation systems. An example is the Local Area Augmentation Systems (LAAS), which allows a suitably equipped receiver to derive enhanced accuracy and integrity information in a local area. LAAS can be tested using Spirent's unique LAAS VHF data broadcast signal simulator, the GSS4150.

ADVANTAGES OF SBAS AND GBAS SIMULATION

For both SBAS and GBAS, simulation lends itself ideally to certification and type approval applications. The availability of controlled, repeatable signals ensures that specific test conditions can be readily replicated for different units under test. In addition, simulation enables testing of safety cases that include errors or anomalies in the transmitted signals. Testing under these circumstances ensures that the way the system under test deals with these unusual conditions can be understood and verified.

Spirent’s GNSS and GPS augmentation simulation systems enable certification and type approval test applications.

GPS/GNSS Augmentation Products

• The GSS8000 Multi-GNSS Constellation Simulator provides GPS/SBAS, GLONASS and Galileo signals. GPS configurations can also support QZSS and SBAS. Classified signals and various options are also available.
• The GSS6700 Multi-GNSS Simulation System offers multiple channels of GPS/SBAS, GLONASS and/or Galileo L1 signals.
• The GSS6300 Multi-GNSS Signal Generator provides a single channel of GPS/SBAS, GLONASS and/or Galileo L1 signals for production testing of commercial GNSS receivers.
• GSS4150 Local Area Augmentation System Signal Simulator
  For more information on the GSS4150, please contact yourl local Spirent representative