An Automatic Equalizer for General-Purpose Communication Channels

Recent years have witnessed an increasingly intensive investigation of automatic equalization techniques. 1 Equalization, itself, is necessary because of the increased demand for efficient use of communication channels. Fixed compromise equalizers have been used in terminal equipment but they cannot remove all of the distortion because of variation between connections in a switched service. Two factors contribute to the distribution of distortion on different connections-- differences in the characteristics of the individual links that may be switched together and differences in the number of links in a connection. Better equalization and, therefore, greater transmission efficiency can be achieved by individually equalizing each connection after it has been established. Automatic equalization provides a practical means for rapidly and efficiently equalizing each connection. Several automatic equalization schemes have been published which provide equalization for specific, usually synchronous, communication systems. Some of the techniques for synchronous data transmission systems are those of Coll and George, 2 - 3 DiToro, 4 Funk et al,5 and Lucky and Becker et al. 6 - 7 - 8 These techniques are very powerful for the synchronous data transmission systems for which they are intended. Furthermore, the implementations of these equalization strategies possess considerable economy of design because they rely upon the peculiarities of the particular synchronous transmission systems for which they are intended.