Receiver autonomous integrity monitoring

Receiver autonomous integrity monitoring (RAIM) is a technology developed to assess the integrity of individual signals collected and integrated by the receiver units employed in a Global Navigation Satellite System (GNSS). The integrity of received signals and resulting correctness and precision of derived receiver location are of special importance in safety-critical GNSS applications, such as in aviation or marine navigation.

The Global Positioning System (GPS) does not include any internal information about the integrity of its signals. It is possible for a GPS satellite to broadcast slightly incorrect information that will cause navigation information to be incorrect, but there is no way for the receiver to determine this using the standard techniques. RAIM uses redundant signals to produce several GPS position fixes and compare them, and a statistical function determines whether or not a fault can be associated with any of the signals. RAIM is considered available if 24 GPS satellites or more are operative. If the number of GPS satellites is 23 or fewer, RAIM availability must be checked using approved ground-based prediction software.

Several GPS-related systems also provide integrity signals separate from GPS. Among these is the WAAS system, which uses separate signals broadcast from different satellites to indicate these problems directly.

The FAA's RAIM prediction website "AC 90–100" covers US territories in graphical map format (showing green for RAIM available and red for RAIM not available)

USCG

Since 2006, the N-RAIM Prediction Service, hosted by NAVBLUE, offers worldwide coverage for all applications including RNP 10, RNAV 5, RNAV 2, RNAV 1, RNP 4, RNP 1, RNP Approach and RNP AR Approach down to 0.1NM. The online tool is an alternative to the automated service integrated directly into flight planning software. It is kept up-to-date in line with new editions of the ICAO PBN Manual and any worldwide specific regulation.

PBN

The SPACEKEYS RAIM prediction and avoidance system developed and hosted by FLIGHTKEYS offers worldwide coverage for any type of RAIM prediction and covers all integrity levels from RNP10 (Enroute) to RNP Approach and RNP AR Approach (down to 0.1NM). The online tool allows RAIM predictions for locations and full trajectories (routes) as well as area based RAIM predictions. and SOAP APIs are also available for 3rd party system integrations.

REST

To enable pilots to quickly determine whether en route or approach level RAIM will be available, the FAA and EUROCONTROL have created "dispatch level" websites that predict RAIM status to meet pre-flight check requirements.

: FAA ADS-B and AC90-100A GPS RAIM Service Availability Prediction Tool (SAPT).

ADS-B & RAIM PREDICTION

from the FAA.

Worldwide Coverage

: the Eurocontrol GPS RAIM prediction tool.

AUGUR

: the NAVBLUE prediction tool.

N-RAIM

paper.

GPSEasysuite II KaI Borre Aalborg University

: SPACEKEYS RAIM prediction and avoidance system (developed by FLIGHTKEYS).