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

SAIDJACK at aol.com SAIDJACK at aol.com
Thu May 15 22:39:55 UTC 2014

It would be good to understand which receivers are adversely  affected by 
this.. the USCG did not list affected vendors/devices..
In a message dated 5/15/2014 15:19:51 Pacific Daylight Time,  
magnus at rubidium.dyndns.org writes:

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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