NAVSTAR Global Positioning System (GPS)


Twenty four plus satellites (21 navigation, 3 spares) in four orbital planes at 11,000 mile orbits. Run by US Air Force, Falcon Air Force Base, Colorado, with 1 master and 4 monitor stations.


DEFINED SERVICES


SATELLITE VEHICLE TYPES

Block IIR:

Block IIF:

Commercial sales estimated at more than $40 billion by 2004.


DIFFERENTIAL GPS

Correction data broadcast by fixed stations.


SELECTIVE AVAILABILITY

Your government is lying to you (and everyone else).

Affects the code and carrier phase measurements on L1 and L2.


ANTI-SPOOF

Anti-Spoof (A-S)


ANTI-JAM

Anti-Jam (A-J)


DEFINED FREQUENCIES

Defined frequencies for GPS:


ACCURACY

Mode Circular Error
Probable (50%)
2 distance root
mean square (95%)
Time
PPS 8m 21m 100 nanosecond
SA = 0 (off) 13m 30m
Current SA 42m 100m 167 nanosecond


NAVIGATION MESSAGE

A GPS navigation message is transmitted on L1 at 50 bits per second. It contains:


HYPOTHETICAL ATTACKS

Here are a few hypothetical attacks on the GPS service.

GPS spoof
Pseudolite. Overcome Receiver Autonomous Integrity Monitor (RAIM), which needs signals from at least six satellites.

GPS jamming
L band is spread spectrum at 1575 MHz with known PN codes.

DGPS spoof
Incorrect "corrections".

DGPS jamming
Block VHF updates at opportune moments.


FUTURE GPS ENHANCEMENTS

Some future GPS Enhancements:


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