Generation of Digital Signaling Waveforms

Data transmission (digital signaling) systems generally transmit continuous, essentially bandlimited signals that represent alphanumeric sequences. The transmitting apparatus in such systems must therefore convert discrete symbols-often binary pulses-into prescribed analog waveforms. Current commercial systems do this via simple filtering, gating, and conventional modulation. These practices limit the types of waveforms that can be used and they are not always amenable to variable rate signaling. This paper describes a hybrid digital-analog method for approximating closely almost any reasonable digital signaling waveform. The basic idea is very simple: a "staircase" approximation of the desired signal can be generated via a shift-register version of a transversal filter. Variations on this idea, such as derivative approximation and multirate shifting, enhance its accuracy without destroying its simplicity and time-frequency scalability.