Error analysis for the Global Positioning System: Difference between revisions

Revision as of 05:31, 8 August 2023

Revision as of 07:51, 2 September 2023

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{{anchor|GPS_SA}}

== Selective availabilityAvailability ==

GPS formerly included a (currently disabled) feature called ''Selective Availability'' (''SA'') that addsadded intentional, time varying errors of up to 100 meters (328 ft) to the publicly available navigation signals. This was intended to deny an enemy the use of civilian GPS receivers for precision weapon guidance.

SA errors are actually pseudorandom, generated by a cryptographic algorithm from a classified ''seed'' [[key (cryptography)|key]] available only to authorized users (the U.S. military, its allies and a few other users, mostly government) with a special military GPS receiver. Mere possession of the receiver is insufficient; it still needs the tightly controlled daily key.