System employing dissipative pseudorandom dynamics and selective

Abstract

A communication and/or measurement system includes a transmitter that modulates a pseudo-random noise signal with a message signal to produce a wideband signal for transmission. A receiver, which demodulates the wideband signal to recover the message signal, includes an 'analog' feedback shift register that reproduces the noise signal based on samples of the received signal. The AFSR is characterized by a function that agrees with the function that characterizes the LFSR, at the points at which that function is defined. Further, the AFSR characterizing function has stable fixed points at these values, i.e., it has a slope of less than one in these regions. Specifically, the AFSR's function has stable fixed points at integer values and unstable fixed points at half-integer values and, the stable fixed points act as attractors. The AFSR thus produces a sequence that relaxes to the nearest integer-valued sequence. In one embodiment in which signal values that represent binary values are -1 and +1, the coupling circuitry compares the quantity .vertline.(.vertline.S.sub.n .vertline.-1).vertline. with a predetermined maximum value. If the quantity exceeds the maximum value, which indicates that the received signal sample provides a poor estimate of the transmitter LFSR state, the coupling circuitry uses the feedback signal y.sub.n to update the register. Otherwise, the coupling circuitry uses as an update signal y'.sub.n =(1-.epsilon.)y.sub.n +.epsilon.sgnS.sub.n, where sgnS.sub.n represents the sign of the received signal sample.