Hal Murray wrote:
[email protected] said:
What makes you think it needs to be CW, and cannot be pulsed and
chirped?
All it has to do is confuse the receiver enough so that you can't
trust its readings.
Why is pulse or chirp likely to be more confusing per W of jamming power?
I thought the GPS signal was spread spectrum so I wouldn't expect any simple
pulse or chirp to be better at jamming than noise over the appropriate
bandwidth.
If you know the spread spectrum details (which must be public or the receiver
can't listen to the signal), then you might be able to mimic a satellite
signal. I think that needs the time, so you probably need to listen to the
signal you are jamming.
Am I on the right track? Is there a trick I'm missing? (If so, how
complicated is it?)
I think you are running into the jamming/spoofing definition of the
problem. When you are jamming, you are transmitting a signal which just
overshadows the propper signal but when you are spoofing you try to send
a signal which looks like the propper signal.
A spoofing attack is a different story altogether. For a spoofer to
confuse a receiver, it either needs to be there when the receiver turns
on or the spoofer needs to transmitt signals having a position so near
the receivers current signals that it can't discriminate them and then
track onto the wrong signals.
The counter-measure towards spoofers is to used a keyed signal, in which
case only delayed signal is available to the attacker, but for most
cases the receiver should be able to handle that.
For jamming I think chirps or phase-noise transmitters is effective
since they select no particular feature of the spreading code, but
induces error into both the weak and strong features, which is then
shifted by the expected doppler frequency. The sensitivity of jamming
energy for various offsets from the carrier for a pseudo-random sequence
can be retrieved by Fourier-transform (DFT).
Cheers,
Magnus
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