Voice-band data communication modems - A historical review: 1919-1988

The history of voice-band data modems is divided into four periods, and the activities in each of these eras is discussed. Before the early 1950s, work was done on quantitatively measuring phase distortion and equalizing lines with such distortion. The advent of the digital computer in the early 1950s and the resulting military and commercial interest in large-scale data processing systems led to interest in using telephone lines for transmitting digital information. The research efforts during this period and the resulting commercial products are described. The third era, during the 1970s was characterized by extensive research and technology advances. The discussion focuses on advances in timing recovery, adaptive filtering, semiconductor technology and modem design, and pulse-shaping filters. The late 1970s and early 1980s have seen the development of ultrahigh-speed modems. Coding for performance improvement and the development of 19.2 kb/s modems in this period are discussed.>