Trellis-coded modulation, or TCM, is a technique used in fax standards to improve transmission over noisy lines. It is specifically used for Group 3 in ITU fax standards from 1991 and can operate at speeds of 12,000 and 14,400 bps. TCM is also added to the V.29 standard at 7,200 and 9,600 bps to further improve transmission quality. For half-duplex operation, the V.17 standard includes special functions like echo protection and turn-off sequences.
What is Trellis-Coded Modulation (TCM)?
Trellis-coded modulation (TCM) is a data modulation technique used in digital communications. It is used for improving the data transmission rate and reliability over a noisy channel. TCM is an efficient technique that combines error-correcting codes and modulation schemes to enhance the quality of communication signals by improving their signal-to-noise ratio.
How is TCM used in ITU Fax Standards?
TCM is used for Group 3 in an ITU fax standard from 1991 that operates at 12,000 and 14,400 bps. ITU (International Telecommunication Union) is a specialized agency of the United Nations responsible for facilitating international communication standards.
For transmission over noisy lines, TCM additionally adds to the V.29 standard at 7,200 and 9,600 bps. The V.29 standard describes the characteristics of a modem to be used in Group 3 facsimile terminals operating in the public switched telephone network.
What is the Function of V.17 for Half-Duplex Operation?
V.17 defines special functions for half-duplex operation, which allows two devices to communicate with each other in both directions, but not at the same time. Such special functions include echo protection and turn-off sequences. Echo protection is an essential feature that ensures that the echo of transmitted signals does not interfere with the receiver’s ability to receive the data. Turn-off sequences, on the other hand, help in reducing the intersymbol interference by providing the necessary synchronization.
In The opinion, TCM is a powerful technique for improving the data transmission rate and reliability over a noisy channel. It is used in ITU fax standards and other digital communication systems to enhance the quality of communication signals. V.17 defines essential functions required for half-duplex operation to ensure smooth and effective communication between two devices.