An Evaluation of AM Data System Performance by Computer Simulation

The process of transmitting digital information and the problems relating to this type of communication have received much attention in recent years. Practical means of communication based on this type of information transmittal have been in use for a long time in the form of telegraph and teletype systems, but for both these systems the speed of operation is relatively slow, since the information is supplied either by a manual operator or by a mechanical device of some sort. Recently, however, many new sources of digital information have arisen for which the information rates may range from telegraph speed up to several orders of magnitude greater than that speed. This has created a need for new high-speed data transmission systems. To this need for higher speed has 675 67G THE BELL SYSTEM TECHNICAL JOURNAL, MAY 19G0 been added the requirement of greater accuracy -- amounting to, in some cases, essentially error-free transmission. For a given bandwidth both high speeds and accurate transmission are often difficult to realize. For this reason, a great deal of effort has been spent in devising means for utilizing a channel as effectively as possible in order that both speed and accuracy may be maximized. This effort may be divided into two areas. The first is concerned with what may be called the terminal problem, in which effort is directed toward developing data system terminal equipment that makes best use of the transmission channel. This has resulted in a number of competing schemes for data transmission based on different modulation methods, such as double and vestigial sideband amplitude modulation, frequency modulation and phase modulation.