Archive for the 'RAIM' Category

ION GNSS – I’m hearing a lot about RAIM these days

September 19th, 2008 | Category: Dynamic Geometry Library,Navigation Accuracy Library,RAIM

I'm at the ION GNSS meeting here in balmy Savannah Georgia and I've now heard from several people regarding the RAIM issue.  Here's the issue.

Pilots flying with GPS as their main navigation system or as a secondary system on selected routes must submit a RAIM (Receiver Autonomous Integrity Monitoring) report for their destination before flying.  This report defines whether GPS will meet some fairly stringent requirements for satellite  and signal availability.  The Federal Aviation Administration (FAA) is mandating this requirement.  The pilots, concerned with how they will meet this requirement asked the FAA - "how do we meet this requirement?"  The FAA responded by tasking the VOLPE center to develop a RAIM assessment tool.  This tool technically calculates RAIM, but it turns out, is not very useful to any pilot.

One pilot I talked with at the ION GNSS show said that it was too difficult to plan a route with the VOLPE tool.  Look at the tool and you'll see why.  Well, it's a good thing he was talking to us!  AGI has long been in the business of calculating access and coverage along routes - for virtually any kind of metric you can think of (no jokes here Kevin).  Here's an example:  the blue line represents a route in a mountainous area (Breckenridge I think) where there's a threat (large colorful communications jammer).  The white potato chip shaped thing is the Azimuth-Elevation mask for the jammer.  Any place below the potato chip the jammer is unable to see - above the chip - watch out. 

Route1

This route can be edited in the 3-D window to reroute around threats (or, say RAIM outages?) and reports run easily to determine RAIM outage times, etc.

I bring this point up because AGI has the technology to solve this pilots problem today.  Using our STK Engine and our components, an application can be built to make the RAIM reporting requirement a breeze and we can add the benefit of being able to give the pilot some additional valuable information!  Here's how.

Our Navigation Accuracy Library calculates RAIM (Fault Detection) and can report three types of RAIM outages for any location and time.  (En Route, Terminal and Non-Precision Approach) Our Dynamic Geometry Library comes with a waypoint propagator, useful for propagating routes of aircraft, land vehicles, whatever.  Our STK Engine provides 3-D graphing capabilities that can display routes (colored if you like) as well as coverage (a RAIM outage contour map for example).  Put these together in a single application and add some features like the following:

  • Upload your own route file
  • Database of predefined routes the Airline flies
  • Recalculate the 'wheels up' time based on RAIM outages
  • Create a handheld mobile application the pilot can use to initially assess RAIM for standard flight routes - from anywhere prior to flight.

There are many different versions of this scheme that could be put together depending on how the particular pilot or airline wanted to use the system.

There's another stick in the mud I haven't touched on yet.  The VOLPE center calculates RAIM in a specific way, using predefined vertical and horizontal alert thresholds.  I say predefined, because there is nowhere on their tool to change these.  There is no standard RAIM algorithm to use when calculating RAIM outages.  There are accepted algorithms in the literature, but nothing mandated by and interface control document (ICD).  Each GPS receiver manufacturer is free to calculate RAIM any way they choose.  AGI uses the accepted algorithms in the literature, but we allow the user/developer to define any alert threshold they like.  This provides more flexibility in calculating different RAIM outage thresholds.  AGI components are also flexible enough to be able to incorporate receiver manufacturer algorithms - with our without source code.

So, there is a great opportunity here for pilots to have a better system and a way to grow when future GPS availability requirements are enacted.  For more information on our technologies in this area, please contact me.

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