Correlative coding: A bandwidth-efficient signaling scheme

In most transmission channels, bandwidth is at a premium and an important attribute of any good digital signaling scheme is its ability to make efficient use of the bandwidth. Conventional Nyquist-type pulse amplitude modulation signaling schemes, which are designed to eliminate intersymbol interference, achieve high data rates only at the expense of a large number of signal levels. In many applications, correlative coding or partial response signaling, which introduces intersymbol interference in a controlled way, is able to achieve high data rates with fewer levels and hence with better error rate performance. In addition to higher data rates, correlative schemes achieve convenient spectral shapes and have error-detecting capabilities without introducing redundancy into the data stream. This paper explains how correlative schemes work and why they are advantageous.