OVERVIEW

It is a pleasure to have Dr. Adam Lender as the author of this important chapter. He discovered the concept of correlative transmission techniques and developed many operational duobinary and other partial response systems. Dr. Lender is recognized as an authority in the digital communications field.

Dr. K.Feher

Duobinary, modified duobinary, and correlative techniques were originated in 1962 and 1963 [7.1, 7.2]. Duo-means doubling the speed of binary. Correlative implies correlation or finite-memory systems rather than zero-memory. Subsequently [7.3], in 1965 the term partial response was introduced. Correlative and partial response are synonymous; both terms are used in the literature.

This chapter is an in-depth treatment of many aspects of the correlative techniques, as applicable to digital microwave systems. However, the same techniques are used widely in data transmission and cable PCM and may find applications in fiber optics, satellite and tropo-scatter systems.

The Nyquist criteria for binary and multi-level signaling, postulated in 1924 [7.4], are based on the premise that each digit must be confined to its own time slot to as great an extent as possible. This implies that the intersymbol interference (ISI) in a particular time interval, due to the tails of preceding and succeeding pulses, should be eliminated or, at least, minimized. The Nyquist rate cannot be achieved in practice, even if the ideal rectangular filter were synthesized, because it is not possible to have a precise relationship between the...