Open main menu
Home
Random
Recent changes
Special pages
Community portal
Preferences
About Wikipedia
Disclaimers
Incubator escapee wiki
Search
User menu
Talk
Dark mode
Contributions
Create account
Log in
Editing
Trellis coded modulation
(section)
Warning:
You are not logged in. Your IP address will be publicly visible if you make any edits. If you
log in
or
create an account
, your edits will be attributed to your username, along with other benefits.
Anti-spam check. Do
not
fill this in!
{{Short description|Modulation scheme in telecommunication}} {{Modulation techniques}} '''Trellis coded modulation''' ('''TCM''') is a [[modulation]] scheme that transmits information with high efficiency over band-limited channels such as [[telephone line]]s. [[Gottfried Ungerboeck]] invented trellis modulation while working for IBM in the 1970s, and first described it in a conference paper in 1976. It went largely unnoticed, however, until he published a new, detailed exposition in 1982 that achieved sudden and widespread recognition. In the late 1980s, [[modem]]s operating over [[plain old telephone service]] (''POTS'') typically achieved 9.6 [[kbit/s]] by employing four bits per symbol [[quadrature amplitude modulation|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 Γ 4 bits/symbol, using QAM).{{Citation needed|date=December 2008}} 14 kbit/s is only 40% of the theoretical maximum bit rate predicted by [[Shannon's theorem]] for POTS lines (approximately 35 kbit/s).<ref>{{cite journal|last1=Forney|first1=G. David|title=Efficient modulation for band-limited channels|journal=IEEE Journal on Selected Areas in Communications|date=September 1984|volume=2|issue=5|pages=632β647|display-authors=etal|doi=10.1109/jsac.1984.1146101|s2cid=13818684}}</ref> Ungerboeck's theories demonstrated that there was considerable untapped potential in the system, and by applying the concept to new modem standards, speed rapidly increased to 14.4, 28.8 and ultimately 33.6 kbit/s.
Edit summary
(Briefly describe your changes)
By publishing changes, you agree to the
Terms of Use
, and you irrevocably agree to release your contribution under the
CC BY-SA 4.0 License
and the
GFDL
. You agree that a hyperlink or URL is sufficient attribution under the Creative Commons license.
Cancel
Editing help
(opens in new window)