Integrity Monitoring and Augmentation
An integrity monitoring solution uses GNSS signals to detect changes or anomalies in satellite signal characteristics that could affect the accuracy of the position calculated by the user equipment. Integrity monitoring is essential to any application that relies on GNSS measurements, particularly for those for which misleading, undetected errors could affect safety of life. A pplications include:
Civil Aircraft Landing Systems
The use of GNSS technology in civil aircraft landing systems presents an excellent example. Integrity monitoring networks consisting of fixed ground reference stations are frequently set up to continuously measure GNSS signal characteristics.
Slight changes in the signals can be tolerated by sending correction information to the receiver on board an aircraft. If certain integrity limits are exceeded, the system will notify the user equipment within seconds so that the affected satellite is excluded from the user's position calculation.
Satellite-Based Augmentation Systems (SBAS)
Augmentation systems provide additional data to users of GNSS equipment to improve accuracy, reliability and availability. The United States' WAAS, the European EGNOS and the Japanese QZSS, are examples of SBAS.
Integrity and correction data is generated based on measurements from a ground network and transmitted to geostationary satellites (GEO's), which then relay the information to the GNSS users. By using the same frequencies, modulation and signal structure as the GNSS signals, the SBAS GEO is able to provide information to the user's receiver(s) via one of the GNSS receiver channels.
- Detects changes or anomalies in GNSS signals
- Enhances the accuracy of GNSS systems by providing integrity and correction data
- System integrity is increased by having ability to trust the system within certain accuracy limits
- Improves position accuracy with correction data transmitted from SBAS systems
- Enhances GNSS measurement availability and continuity of service by using the SBAS system signals themselves for additional GNSS range measurements
GNSS Reference Receivers:
- Used to create integrity monitoring and augmentation systems
- Designed to provide accurate reference measurements of pseudorange and carrier phase and other parameters used to assess signal quality and system integrity
- Provide an accurate, faithful and independent measurement of each GNSS signal tracked. They do not assess the system integrity or provide corrections or alarms
- Generally utilized in government operated SBAS networks and research laboratory applications
Ground Uplink Station Equipment:
NovAtel manufactures signal generator and reference receivers for use in the ground uplink stations of SBAS networks. This equipment generates, controls and adjusts the SBAS signals for broadcast by the GEO satellites.
Scintillation Monitoring Receivers:
Scintillation is a localized effect not included in the wide area augmentation system measurements. Scintillation is the result of disturbances in the ionosphere caused by solar flares and is becoming more pronounced as we approach the 2013 peak in solar activity. These receivers:
- Measure ionospheric scintillation and Total Electron Count (TEC)
- Are commonly referred to as GPS/GNSS Ionospheric Scintillation and TEC Monitors (GISTM)
Receiver Autonomous Integrity Monitoring (RAIM) Receivers:
Our RAIM technology, based on RTCA DO-229D (2006), provides receiver autonomous integrity monitoring for broadcast GNSS signals. RAIM supported receivers:
- Are primarily utilized in aviation navigation systems requiring signal and position integrity during various stages of flight
- Employ Fault Detection and Exclusion (FDE) which uses redundant pseudorange measurements to detect and exclude faulty signals that may cause positioning instability
- Recompute the position solution to ensure continuous operation in the presence of a GNSS failure
- Can be used in non-aviation applications that require continuous operation confirmation by customizing parameters to meet unique application needs
Fixed Reference GNSS Antennas:
Fixed reference antennas are GNSS antennas optimized for reference station applications. Each antenna contains a choke ring to reduce the strength of undesired reflected signals (multipath) that degrade positioning accuracy.