>There is a CRC or something similar on the C/A code, and this is all
>publicly documented. I'm quite sure there is nothing that would
>qualify as 'authentication' in any strong sense. One of the
It's actually a Hamming code. But yes, it it used only for error detection, and
does not qualify as any kind of authentication.
>DOD certainly has the capability to jam, probably with incorrect
>signals in addition to just noise. There have been public notices for
>various areas over the last few years. (If they couldn't do this,
Here's a typical notice (NOTAM) for the White Sands area:
For the Aviation Community
GPS UNRELIABLE WITHIN A 390NM RADIUS OF TCS VORTAC AT FL400 AND ABOVE,
DECREASING IN AREA AS YOU DECREASE IN ALTITUDE TO 300 NMR AT FL250,
200 NMR AT 10,000 FT MSL, AND 125 NMR AT THE SURFACE. IFR OPERATIONS
BASED UPON GPS NAVIGATION SHOULD NOT BE PLANNED IN THE AFFECTED
AREA DURING THE PERIODS INDICATED (WHICH WILL BE PUBLISHED IN A GPS
NOTAM). THESE OPERATIONS INCLUDE DOMESTIC RNAV OR LONG-RANGE
NAVIGATION REQUIRING GPS. THESE OPERATIONS ALSO INCLUDE GPS
STANDALONE AND OVERLAY INSTRUMENT APPROACH OPERATIONS.
ON THE FOLLOWING DATES AND TIMES:
Between the hours of 0200-0800Z (2000-0200 MDT)
MAY - 7, 10, 12, 14, 17, 19, 21, 24, 26, 28, & 31.
JUN - 2, 4, 7, 9, 11, 14, 16, 18, 21, 23, 25, 28, & 30.
JUL - 2, 5, 9, 14, 16, 26, 28, & 30.
Between the hours of 0001-0600Z (1800-2400 MDT)
JUL - 7, 12, 19, 21, & 23.
Phil
