An early, analog communications notion of mitigation bandwidth

In a conventional communication system in which analog information such as speech or video modulates a sinusoidal carrier, the presence of channel multipath causes frequency-selective distortion if its delay spread exceeds the reciprocal of the analog-signal bandwidth. By contrast, this paper considers the use of a pseudo-noise carrier, together with a receiver that has a multipath-matched RAKE filter in tandem with correlation against a replica of the pseudo-noise. It is shown that such a signal processing combination can convey an analog signal over non-time-varying multipath of practically arbitrary delay spread, without appreciable distortion. This is true only provided, that the multipath possesses a reasonably wide frequency-response support, even while it well may fade frequency-selectively. The suggested technique has existed in a largely theoretical form. Possible applications could be to signaling at high information rates over ionospheric channels (if frequency allocations become broader), or to cellular telephony when it is disturbed by reflections from buildings or terrain