An investigation into timing extraction in digital transmission

Digital techniques now dominate the communications field. A main reason for this is the ability to achieve almost perfect transmission over long distances by digital methods, which in turn depends on the use of digital regenerators. The configuration of a typical regenerator is shown. It performs three main operations. It amplifies and recovers the incoming signals, it reshapes them and it retimes them. Retiming is usually accomplished through the extraction of a timing reference from the incoming signal. This process of extraction of timing information is probably the least well understood aspect of digital transmission. Mathematical accounts of the process are available but these fail to yield any insight into its nature. The purpose of the paper is to re-examine timing extraction from a `physical´ viewpoint with the object of obtaining a better understanding of the process