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Selective availability anti-spoofing module

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An SAASM, Selective Availability / Anti-Spoofing Module, is used by military Global Positioning System receivers to allow decryption of precision GPS coordinates, while the accuracy of civilian GPS receivers may be reduced by the US military through Selective Availability.

SAASM allows satellite authentication, over-the-air rekeying, and contingency recovery. Those features are not available with the similar, but older PPS-SM system. SAASM-enabled receivers also acquire the encrypted Y-code directly from satellite, without relying on local radio signals. This provides a substantialy increased resistance to GPS jamming, perhaps 10 to 20 db better than the PPS-SM system.

SAASM hardware modules are covered with a sophisticated anti-tampering coating, to deter analysis of their internal operation.

The next generation military signal for GPS, called M-code, will be implemented on satellites launched beginning in 2005. A complete constellation of 18 satellites with M-code capability is expected by 2016.


References

[[1]] - GPSworld.com article "Saving SAASM" by Robert Huffman (Webpage, January 2006)

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