Webinar Brief – A Closer Look at L5: The Future of High-Precision GNSS

March 18, 2011  - By

Yesterday I conducted a webinar titled “A Closer Look at L5: The Future of High-Precision GNSS.” Preparing for it was quite interesting, so I thought I’d share some of the slides I produced (and had produced) for the webinar. I think you’ll find them interesting.

The webinar was focused on discussing the value of the new L5 civilan frequency for GPS/GNSS receivers. An interesting challenge in preparing for the webinar was my attempt at estimating what a satellite constellation of satellites (GPS and others) broadcasting at least L1 and L5 would look like four or five years from now. The point of it was to illustrate that a useful constellation of satellites broadcasting L1 and L5 (as well as L2C) is potentially only four to five years away.

In that timeframe, there are potentially 30 satellites that would be healthy and broadcasting navigation signals on the L1 and L5 frequencies that we can use. How is that possible?

Both GPS and Europe’s Galileo support the new L5 civil frequency (as well as L1). The U.S. has already launched one of the new GPS model IIF satellites. The IIF is currently healthy and broadcasting three civil frequencies; L1 C/A, L2C and L5. There are 11 more of the IIF satellites being built. It’s estimated that all 11 will have been launched into their orbits by ~2015. On the other hand, the first 18 Galileo satellites have been contracted to be built, and it’s estimated that the 18 will be launched into their orbits by ~2015. The Galileo satellites are designed to support L1 and L5 (as well as others). That’s a total of 30 satellites broadcasting L1 and L5.

In an ideal world and in the best interest of the civilian user community, the Americans and Europeans would coordinate orbits planes/slots of the 30 satellites so they would be in an optimal configuration (steady # of visible satellites, reasonable PDOP) for the user community. But, I seriously doubt that’s going to happen.

So, the next best thing is to attempt to estimate what an “uncoordinated” constellation of 30 GPS/Galileo satellites would look like in 2015 (assuming the launch schedules hold). Fortunately, our friends at the Galileo Supervisory Authority (GSA) have already mapped out the orbit plane/slot data for the 18 satellites. Without that data, none of these projections would have been possible.

GPS was a little tougher to estimate. The U.S. Air Force doesn’t have (or at least they don’t share) a long-range plan for where the next 11 IIF satellites are going to be inserted in the GPS constellation. They look out one satellite at a time. That’s understandable because the health of the GPS constellation changes over time. However, the U.S. Air Force does present a “watch list” of the weaker satellites in the constellation so we have some idea of where the new ones are going to be placed.

Once we compiled the information from the Galileo folks and our projections on where the next 11 IIF GPS satellites will be inserted, we were able to come up with some interesting plots I’d like to share with you.

All of the following satellite visibility plots are based on my location in Portland, Oregon, USA, and with a 15º elevation mask. Using a 15º elevation mask is pretty conservative so the plots are pretty conservative if you’re working in an open-sky environment like in agriculture.

The first plot is of the 12 GPS IIF satellites only. You can see there’s an average of about three IIF satellites in view between 6 a.m. and 8 p.m. Thanks to Analytical Graphics, Inc. for help generate the following plots.



The next plot is of the 18 Galileo satellites. You can see there’s an average of 4-5 Galileo satellites in view between 6 a.m. and 8 p.m.



The next plot is of both the 12 GPS IIF satellites and the 18 Galileo satellites. You can see there’s an average of 8 GPS IIF and Galileo satellites in view between 6 a.m. and 8 p.m.



Finally, the last plot is of the 12 GPS IIF satellites, 18 Galileo satellites, and the 19 remaining legacy GPS satellites (broadcasting L1 and L2). You can see there’s an average of 12 GPS IIF, Galileo, and legacy GPS satellites in view between 6 a.m. and 8 p.m.


For a different perspective, here are 3D orbit plots of the 18 Galileo satellites and the 12 GPS IIF satellites.

3D orbit plot of 18 Galileo satellites


3D orbit plot of 12 GPS IIF satellites

There are several more plots similar to these in my webinar for different locations around the world including London, Rio de Janeiro, New Dehli, Perth, and Bangkok. In the webinar presentation, I also provide more details about the benefits of L5. You can view a recording of the webinar by registering here. After registering, you’ll receive an e-mail with instructions on how to view the webinar.

Thanks, and see you next time.

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