Time Reversal (TR) is often used in RF communication as it enables space time focusing of EM waves. Time focusing is an interesting property because it reduces intersymbol interference. Spatial focusing on the intended receiver is also interesting because it implies that the communication has a low probability of intercept (LPI) by another receiver located nearby.
My question is: is it nevertheless possible to intercept and decode a TR communication?
In TR communication, the emittors encode their signals using the complex conjugate of the time reversed impulse response of the communication channel between them and the receiver. Interception means that a spy may catch these signals at a different space-time place than the receiver. The code will then not be suited for this spying receiver and the arrival times of all the signals from all the emittors will be altered, implying additional distorsion.
If the spy is close to the receiver, then the spy's channel is not so different from the normal channel, and its impulse response may be a simple small variation from it.
But what if the distance is larger? Is it possible, knowing the relative positions of the emittor, the receiver and the spy, for the spy to reconstruct the signal?
Amrit says: "Time is not reversal........time does not run at all. Changes run and time is their numerical order."
Finally, I heard somebody saying that which I have been shouting for three hundred years!
More about my view of time can be found in my paper "On the Nature of Time" (on RG). Needless to say, my paper was rejected (in a hostile way) by several journals to which I submitted it.
Somebody recently wrote (somewhere on web) the following statement: "The best treatment of time I have seen is by Mario Radovan of the University of Rijeka, Croatia. I suggest you read him. Do a google search for his essay "On the Nature of Time".
However, a huge majority of "experts" refuse to think in the way Amrit suggests, and which I advocate in my paper
Anyway, I rounded up my story about time; I now write about communication, which is part of my professional activities. Time was a matter of passion & curiosity.
Do you mean intercepting wireless comm where the signal was focused by RT ? If yes, it depends of the wavelength and the structure of the focusing mechanism used. It has been shown at 2.4GHz by some guys that the signal was successfully hidden around the Rx with a 20 dB reduction of the power at 0.5 m. I may have some papers dealing with if you want. There is also a research group which was working at the University in Maryland on RT for ComSec. For further discussions on this topic, private messages would be better.
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