Whether it’s radio communications, SONAR or radar, how effectively can jamming be defeated?
How effectively can frequency hopping be predicted? Does the use of frequency hopping pretty much force the jammer to use barrage jamming?
How about spread-spectrum like active electronically scanned arrays? If 10% of the frequencies used by an AESA radar get jammed, how much will that impede its effectiveness? Does AESA require more power than non-spread spectrum
How good is signal processing hardware and software at filtering out jamming? Jamming must have a particular profile and look rather different than most electromagnetic receptions.
I’m not sure I get pulse compression (chirping) as an anti-jamming technique.
I think, ultimately, the anti-jammers beat the jammers. This is because one method you haven’t mentioned is selecting signals based upon their position in space.
Suppose you have a marauding drone, traveling enemy territory gunning down enemy soldiers. The enemy has state of the art equipment that emits some powerful signal meant to jam your communications with the drone.
Except, you know the position of the drone - it has onboard GPS, dead reckoning, and terrain feature matching sensors, and has been giving you that data in a telemetry stream. You also know when any communication packets that do get through are valid, as each one is cryptographically signed with a OTP, so there is no way for the enemy to give you false information.
So you aim your antenna - mechanically or digitally - to basically ignore all signals not coming from the rough position of the drone.
Not sure how the jammers can beat that, given that no matter how advanced a technique they may be using, the signals they send are being filtered out.
It depends. How good are the good guys and how good are the bad guys. etc.
It’s driven by crypto and essentially totally unpredictable. However, the total bandwidth of a given comm channel is known, so you don’t need to barrage jam from DC to gamma rays, just the freq band of interest. e.g. US military aircraft voice radios’ range is roughly 225 to 350 Mhz. That’s still a huge space to jam effectively though.
That’s bleeding edge stuff. Anyone who knows isn’t talking.
That was seriously secret stuff when I knew about the then-current state of the art 25 years ago. Again anyone who knows won’t be posting. And anybody who posts won’t be knowing.
If you can finish your transmission faster than they can detect it and fire off counter-noise, you defeat anything smarter / more power efficient than continuous barrage.
That is a type of signal processing I hadn’t thought of, thanks. I suppose you’d need three receivers to triangulate the location. A radar might also combine and vary its pulses and frequencies as a sort of self-encryption.
Right, I’m thinking of enemies which are in the same broad weight category. Russia/China/UK/US, for example. It’s pretty likely that the US was able to jam everything in Panama and Grenada.
What happens if I’m transmitting at 230Mhz and you jam at 231Mhz? Or 235Mhz? Is there spillover or do you need to jam the exact frequency?
If my frequency range is from 100 to 200Mhz and you want to barrage jam me, by what factor will you have to divide your jamming power?
Thanks.
Spot jamming is largely defeated by hopping. Sweep jamming is largely defeated by signal processing. So what does that leave in terms of smarter/power efficient jamming?
Having looked into it a bit, can someone explain how direct sequence spread spectrum and the active part of active electronically scanned arrays differ much in terms of how they resist jamming and lower their probability of interception? It seems that they use much the same technique to defeat detection and jamming. Yet DSSS has been used for a long time in telecommunications whereas AESA is recent stuff in radars. Surely, as soon as someone saw the utility of DSSS in telecommunications, someone else quickly saw its potential in radars.
I don’t think they are related at all.
DSSS spreads the information over a large number of frequencies, while active scanning radars use a large number of antennas to simulate the single rotating antenna of conventional radar. The antenna array is sent a time-correlated signal so that the resulting wavefront sweeps across the desired area.
Just talking dumb voice comm AM radios here, not fancy digital stuff. …
Channel spacing varies. US mil-standard aircraft comm radios had 25 KHz = 0.025 MHz spacing. So the normal function of the radio was to reject 100% of the energy from frequencies just 25 KHz away from the tuned channel.
So for your example of a 100-200 MHz range you’d be looking at jamming (200-100) * 40 distinct channels or 4000. So if you barrage jammed across the entire spectrum only 1 / 4000th of the power would be seen in any single channel. It’s actually about twice that bad (i.e. 1 / 8000) because each channel actually consists of a live band and a dead band between it and the adjacent channels. The transmitters try to focus all the energy in the live band and the receivers try to pay attention to only the live band, with strong roll-off attenuation into the dead band.
So any barrage noise transmitted into the dead band will be mostly ignored.