How to Survive a Total Constellation Outage

April 3, 2014  - By 0 Comments

Yesterday we posted news of an 11-hour downtime for the full GLONASS constellation, due to an upload of bad ephemerides. Coincidentally, during that 11-hour period, the mass-market chip company Broadcom was conducting multi-constellation receiver tests in Asia. Frank van Diggelen, Broadcom’s chief GNSS scientist and vice president says, “We have definitive data to show how a multi-constellation receiver survives such an outage.”

Here are the pictures, and the story they tell.

Test data coincident with the GLONASS ephemeris disruption of April 1 and 2 showing conclusively how a GPS/GLONASS/QZSS/BEIDOU receiver survives the complete disruption of one of the constellations.

On April 2 at 1:00 a.m. Moscow time, bad ephemeris was uploaded to all satellites (see chart at the bottom of this story).

There are two receivers shown here, from two different manufacturers, both in smartphones. The yellow dots are for a GPS/GLONASS receiver; the blue dots are from the Broadcom 47531 receiver which tracks GPS/GLONASS/QZSS/BeiDou signals simultaneously. The 47531 receiver includes logic to use redundant measurements to check the validity of all measurements. It successfully identified and removed the bad GLONASS ephemeris 100 percent of the time, as can be seen by the continuity and accuracy of the positions.

Broadcom2

Here is the satellite outage chart from yesterday’s story.  All GLONASS satellites were restored to healthy state after the 11-hour interruption.

Current plot from the Roscosmos GLONASS Information-Analytical Centre. Things are almost back to normal this morning.

Current plot from the Roscosmos GLONASS Information-Analytical Centre. Things are almost back to normal this morning.

 

 

Alan Cameron

About the Author:

Alan Cameron is editor-in-chief and publisher of GPS World magazine, where he has worked since 2000. He also writes the monthly GNSS System Design e-mail newsletter and the Wide Awake blog.

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