[time-nuts] Fwd: CGSIC: Known Problem With Certain GPS Devices

Magnus Danielson magnus at rubidium.dyndns.org
Thu May 15 22:18:59 UTC 2014

Hi fellow time-nuts,

I think this message is interesting. It shows that some receiver vendors 
have been cheating on an important detail, ignoring the health status 
and being confused as a result.


-------- Original Message --------
Subject: CGSIC: Known Problem With Certain GPS Devices
Date: Thu, 15 May 2014 21:20:23 +0000
From: Civil Global Positioning System Service Interface Committee 
(CGSIC) <cgsic at cgls.uscg.mil>
Reply-To: cgsic at cgls.uscg.mil
To: cgsic at cgls.uscg.mil <cgsic at cgls.uscg.mil>


May 15, 2014

Recently, many GPS users have reported intermittent GPS outages in their 
devices.  After investigating, the U.S. government has linked the 
problem to flawed processing of GPS satellite data within certain GPS 
receiver chipsets.  The GPS satellite service continues to function as 
designed and is fully operational and available worldwide.

The problem affects only user equipment that erroneously ignores the 
satellite health status information broadcast from every GPS satellite. 
  The problem is not related to the April 28, 2014, activation of civil 
navigation messages on the GPS L2C and L5 signals.

Since March 15, 2014, the Air Force has been conducting functional 
checkout on a GPS satellite, designated Space Vehicle Number (SVN) 64. 
SVN 64 broadcasts a data message that clearly indicates SVN 64 is 
unusable for navigation.  Nevertheless, the U.S. government has 
confirmed that certain GPS receivers are using data from SVN 64, in 
violation of GPS interface specifications, resulting in outages or 
corrupted, inaccurate position calculations.

The Air Force testing is scheduled to end in mid-May 2014 at which time 
SVN 64 will begin normal operation.  At that point, these problems may 
stop occurring.   Meanwhile, the U.S. government urges all GPS device 
makers to review their products for compliance with the GPS interface 
specifications, and if necessary, to issue software/firmware updates to 
users as soon as possible. View specifications 

Users experiencing GPS outages should check with their device 
manufacturers for available software/firmware updates.  In addition, any 
civil user seeing unusual behavior in GPS user equipment should report 
it to the U.S. Coast Guard Navigation Center (NAVCEN).  Aviation users 
should file reports consistent with FAA-approved procedures.  Military 
users seeing unusual behavior should report it the GPS Operations Center 

Please direct any civil user questions to NAVCEN at (703) 313-5900, 
Please direct any military user questions to the GPSOC at (719) 
567-2541, DSN: 560-2541, gpsoperationscenter at us.af.mil 
Military alternate: Joint Space Operations Center, (805) 606-3514, DSN: 
276-3514, jspoccombatops at vandenberg.af.mil
See also:
Technical explanation for device makers (PDF) 
http://www.navcen.uscg.gov/pdf/gps/GPSOC_PRN 30_Notice.pdf

Rick Hamilton
CGSIC Executive Secretariat
GPS Information Analysis Team Lead
USCG Navigation Center

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