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I know devices that are jamming everyones Cellphones in a radius of X meters but this is only distracting the frequency cellphones work on. This is not very handy.

Is it be possible to jam just one persons chellphone on the protocol level by sending particular packets?

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I'm going to ignore the physical jamming possibilities and focus only jamming by "abusing" the protocol, thus by sending packets.

If you want to block the incoming SMS or call-setups then you are definitely out of luck. This kind of data is send over a channel that is used to send data to all cellphones in the coverage area. You could however interrupt an ongoing call as each call receives it's own channel (though they often swap from channel to channel over time but this can be accounted for) and as such sending data over this channel will create collisions and thus hinder the ongoing call.

To block a phone from sending SMS or making a call we need to interrupt the shared channel that all cellphones use to send data to the transmission tower. There are two common access protocols used for this, Time Division Multiple Access (TDMA, used in 2G for example) and Code Division Multiple Access (CDMA, used in 3G for example). Both obviously require a different approach, I won't go into details but will explain the general idea. These approaches can also be combined which would require for the methods below to be combined.

TDMA: This divides the channel into frames, these are just fixed length periods of time. These frames are then divided into time-slots. Each cellphone receives one time-slot per frame and can use that to send SMS or request a call setup. Abusing this system just requires you to send data during the correct time-slots. This will create collisions when this cellphone tries to send something.

CDMA: This one is a little more complex. Each user gets a seed to a pseudorandom number sequence, when the user sends data it XOR's its data with the pseudorandom number sequence. To jam the cellphone in this case requires you to determine the seed and then jam by sending data using the pseudorandom number sequence.

This should give a general idea of potential weaknesses that could be exploited, however to use these in a real world test one will have to check how different phones will react to these situations.

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  • I don't think jamming CDMA without affecting others is possible. Two devices sending using the same code would definitely exceed the power limit for that code and thus ruin the recovery of signals using other codes as well. – billc.cn Oct 1 '15 at 12:45
  • Well spotted, I hadn't fully considered that interaction, strictly speaking this is true though those occurrences should become more and more rare as the cellphone will start using exponential back-off. In the end I believe reducing the inconvenience to other cellphones to a minimum. – Selenog Oct 1 '15 at 13:04
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The police / military regularly set up fake towers, that you phone then associates with, and then transfers all data through to a legitimate tower - like an intelligent repeater with record, and DPI abilities. In theory, one could set up a fake transceiver, and then mess with communications to, and from the phone.

The handset should stick with the fake tower, because of the good signal strength. Its then just a matter of feeding garbage to phone.

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  • In 3G and 4G, device also authenticates Base Transceiver Station before connecting to it. IMSI catcher was a problem with 2G. You have to cause interference in 4G & 3G signal else the device will not connect to 2G. – defalt Aug 17 '19 at 11:57
  • en.wikipedia.org/wiki/… – Skye Bowen Aug 19 '19 at 15:27
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The simple answer would be yes, you could very easily just overflow a particular phone number with excessive calls, sms, or data (emails) effectively rendering your target 'jammed'. This is likely not the point of your question though.

More to your point, you could introduce static into a set frequency range and thus jam only a particular spectrum. Additionally, you could directionally jam to a degree by focusing your interference in a particular direction.

In my mind, these are the two ways to 'jam' an RF device unless you can attack the device itself -IE knowing the cell number and thus sending packets directly to it.

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  • The answer lacks specific details on TDMA/W-CDMA etc. jamming. – Deer Hunter Sep 30 '15 at 23:40
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    Jamming a particular spectrum is not quite the same thing as jamming a specific phone. Nor is jamming everyone in a particular area. – Neil Smithline Oct 1 '15 at 3:36
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The jammers I know of, which are intended to be used in jails, only activate when there is a signal in the air. So, an inmate, might dial a call, but it will not connect, since the jammer will start at any signal sent.

It would be possible to modify the trigger, but I am not sure whether commercial models would allow that easily.

Not sure about the reception of an SMS or whether the jammer will be fast enough to even block registration with the cell tower.

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