In telecommunication, trellis modulation (also known as trellis coded modulation, or simply TCM) is a modulation scheme which allows highly efficient transmission of information over band-limited channels such as telephone lines. Trellis modulation was invented by Gottfried Ungerboeck working for IBM in the 1970s, and first described in a conference paper in 1976; but it went largely unnoticed until he published a new detailed exposition in 1982 which achieved sudden widespread recognition.
In the late 1980s, modems operating over plain old telephone service (POTS) typically achieved 9.6 kbit/s by employing 4 bits per symbol QAM modulation at 2,400 baud (symbols/second). This bit rate ceiling existed despite the best efforts of many researchers, and some engineers predicted that without a major upgrade of the public phone infrastructure, the maximum achievable rate for a POTS modem might be 14 kbit/s for two-way communication (3,429 baud × 4 bits/symbol, using QAM). However, 14 kbit/s is only 40% of the theoretical maximum bit rate predicted by Shannon's Theorem for POTS lines (approximately 35 kbit/s).
Read more about Trellis Modulation: A New Modulation Method
Famous quotes containing the words trellis and/or modulation:
“Then a small rainbow like a trellis gate,
A very small moon-made prismatic bow,
Stood closely over us through which to go.”
—Robert Frost (1874–1963)
“Every accent, every emphasis, every modulation of voice, was so perfectly well turned and well placed, that, without being interested in the subject, one could not help being pleased with the discourse; a pleasure of much the same kind with that received from an excellent piece of music. This is an advantage itinerant preachers have over those who are stationary, as the latter can not well improve their delivery of a sermon by so many rehearsals.”
—Benjamin Franklin (1706–1790)