square of the grid represents a single code out of 16 possible to encode information (thus a nibble – two nibbles makes a byte). You now see the basis of how data is encoded with modern modems.
Last night I started coming down with something – scratchy throat, body aches, tired. My sleep was fitful – and broken with dreams about radio signals, mixing and more.
A radio signal can be represented by two quantities – I and Q – I is the In-phase amplitude and Q is the Quadrature-amplitude ( the quadrature is just a sample 90 deg from I ). The values of I and Q can be represented on a graph (Use x and Y instead of I and Q).
The amplitude and sign of I and Q end up providing a unique point on the plane at any given instance in time.
I and Q were used in color TV signals with the phase and amplitude of the color sub carrier representing a point on a color plane.
NTSC (Never Twice The Same Color) is now becoming part of history, but you can see how
well they packed the data into what was available.
(The axis are tilted, but our friends I and Q are still here).
Now imagine we go place a 4 x 4 grid on this plane and each
square of the grid represents a single code out of 16 possible to
encode information (thus a nibble – two nibbles makes a byte). You
now see the basis of how data is encoded with modern modems.
Some time in the early ’80s I met a young man from Russia at a new-years eve party. Turns out he was quite involved in electronics and instead of getting drunk like the rest of the people, we talked for some hours. He was telling me about frequency hopping radio – spread spectrum – where instead of broadcasting on one frequency the transmitter and radio kept shifting which frequency they used based on a pseudo-random number generator. He was telling me how this system was defeated using correlation that would eventually crack the pseudo-random number. Frequency hopping was first alluded to by Nikola Tesla in a couple of patents issued in 1903 according to wikipedia http://en.wikipedia.org/wiki/Spread_spectrum
I was beginning to realize this guy was not your typical college student – he obviously was telling me about classified technology (I think he must have defected – but why was he at KU?). He mentioned that they were moving to a system that changed frequencies so fast, that only a single wavelet of RF is used at a time. This system is now in common knowledge, but our government refuses to let us use it. Of course the ban only hurts honest people – “When a radio technology is outlawed, only outlaws will use that radio technology”kps.
So with that bit of background, I get back to what I was dreaming about. In my dream, I invented a system that used two(or more) transmitters – and two receivers – which would add the I and Q of both channels to get the real I and Q. This seemed like a good idea, but in my dream I criticized it as not being any better than a one-time-key, then I thought further – what if the transmitter and receiver, besides hopping in frequency used gated transmission – only outputting a wavelet at random times? And the signal strength is suppressed so that the receiving radio sees a signal that is below the noise floor? The signal can now be scrambled in time and only recovered by repeated adding, again the samples to be combined are pseudo-randomized in time and order so that to reconstruct the signal becomes highly computationally intensive. A 1 second message could be spread out over the course of 24 hours. Direction finding would first require cracking the algorithms. I think such a system would be very hard to even detect and crack. The biggest problem is multi-path interference which can change the amount of signal delay – It still can be worked around.
If a drop-out like me can think of this, I’m sure other countries all around the world have as well – I was tempted to say bad people in the world – but I’m not sure who is bad anymore, after all the US seems quite willing to support dictators even if it supports immoral pragmatic goals.
That we, as common people, are prevented from having a technology that provides private means of communication, and makes efficient use of the spectrum is quite sad.