In-Band Generation of Synchronous Linear Data Signals

In-band generation of synchronous linear data signals eliminates the need for preliminary generation of a baseband signal and sharp cutoff filtering. However, the ratio of carrier frequency to pulsing rate must, in general, be an integer if the signal is to be produced by successive pulsing of a single fixed filter. As a consequence, a single-sideband signal of bandwidth W and transmission rate 2W must occupy the frequency band [2NW, (2N + 1)W], N an integer, when it is generated from a single fixed filter. A partial-response signal satisfying this condition is described in this paper. A further analysis demonstrates that a finite number of fixed filters can be used to produce a pulse train in any band where the ratio of carrier frequency to pulsing rate is a rational number. Since this relaxed condition allows any transmission band to be approximated to an arbitrary degree of accuracy, frequency translation can be avoided. A single transversal filter with periodically variedtap weights is shown to be a practical realization.