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Distance Division (de)Multiplexing example

The following animated GIF illustrates DDM for separating sources emitting frequency modulated (FM) signals. In this simulation, three sources, at 0, 550 m and 1210 m, respectively, are each assumed to emit an FM signal comprising a carrier of frequency 1000 Hz modulated by a square-wave signal of 10 Hz, that is, frequency shift keying or FSK. These signals ordinarily produce identical, overlapping spectra at the receiver, as shown by the first three screen shots. Note: Low frequencies, and a low wave speed of 330 m/s corresponding to sound in air, are chosen for the simulation merely to avoid very large exponents in the computation. While the simulated data would be applicable as is to acoustic signals, designing with low frequencies is routine in the signal processing world and the scaling to practical radio or optical frequencies would be straightforward.

Temporal parallax is then applied in the form of the H operator, the "parallax angle" being the alpha value (lower right panel). The spectra then spreads out so that the contributions of the three sources are at different frequency bands (this can be verified on the actual simulator by unchecking the signal summation in the lower left panel, and selecting successive sources using the F selector.)

A band pass filter G is then configured around the shifted spectrum of the desired source, the one at 550 m in the example shown. When this filter is applied (controls for both H and G are in the lower middle panel), the shifted spectrum of the desired source remains and the contributions of the other sources are eliminated (to 80 dB or better in the example). This selected spectrum can be shifted back by applying the reverse H operator -- this part is still to be implemented. For now, the last screen shot shows, for comparison, the result of the H operator applied to the selected source alone i.e. without including the contributions of the other two by unchecking the source summation (see the sigma button, lower left).

DDM example - animated gif



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Last change: 2006.04.22 21:53:05. papers  licensing  news  contact  Please revisit - this site & i continue to evolve.