Browse Prior Art Database

Trellis-Coded Modulation Coding Scheme for a 19.2 Kbps Modem

IP.com Disclosure Number: IPCOM000106436D
Original Publication Date: 1993-Nov-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 4 page(s) / 177K

Publishing Venue

IBM

Related People

Nobakht, RA: AUTHOR

Abstract

Described is a new TCM coding scheme for a 19.2 Kbps full duplex modem. This design is based on the CCITT's rate 2/3, 8 state trellis structure. This new rate will enable the modem to send more bits for the same bandwidth. This new rate with its QAM constellation scheme can be included as an addition to the V32bis protocols. Trellis-coded modulation (TCM) is used for data communication with the purpose of gaining noise immunity over uncoded transmission without altering the data rate. TCM is a combined coding and modulation scheme for improving reliability of a digital transmission system without increasing the transmitted power or the required bandwidth. In a power-limited environment, the desired system performance should be achieved with the smallest possible power.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 40% of the total text.

Trellis-Coded Modulation Coding Scheme for a 19.2 Kbps Modem

      Described is a new TCM coding scheme for a 19.2 Kbps full
duplex modem.  This design is based on the CCITT's rate 2/3, 8 state
trellis structure.  This new rate will enable the modem to send more
bits for the same bandwidth.  This new rate with its QAM
constellation scheme can be included as an addition to the V32bis
protocols.  Trellis-coded modulation (TCM) is used for data
communication with the purpose of gaining noise immunity over uncoded
transmission without altering the data rate.  TCM is a combined
coding and modulation scheme for improving reliability of a digital
transmission system without increasing the transmitted power or the
required bandwidth.  In a power-limited environment, the desired
system performance should be achieved with the smallest possible
power.  One solution is the use of error-correcting codes, which
increase the power efficiency by adding extra bits to the transmitted
symbol sequence.  This procedure requires the modulator to operate at
a higher data rate and, hence, requires a larger bandwidth.  In a
bandwidth-limited environment, increased efficiency in frequency
utilization can be obtained by choosing higher order modulation
schemes (e.g., 8-PSK instead of 4-PSK), but a larger signal power
would be needed to maintain the same signal separation and, hence,
the same error probability.  The trellis code solution combines the
choice of a higher-order modulation scheme with that of a
convolutional code, while the receiver, instead of performing
demodulation and decoding in two separate steps, combines the two
operations into one [1].  In this article, a 512 point constellation
scheme has been designed which is capable of transmitting 8 bits per
symbol duration (one bit is used for convolutional encoding).  With a
standard V32bis symbol rate of 2400 Hz [2], this yields an effective
bit rate of 19200 bits per second.  This design is based on the
CCITT's rate 2/3, 8 state trellis structure.  This new rate will
enable the modem to send more bits for the same bandwidth.  Also,
with its QAM constellation scheme, this new rate can be included as
an addition to the V32bis protocols.

      A discrete-time, continuous-amplitude model is assumed here for
the transmission of data on the additive white Gaussian noise
channel.  In this communication model, introduced independently and
at about the same time by the Russian scholar Kotel'nikov and by C.
E. Shannon, the messages to be delivered to the user are represented
by points, or vectors, in an N-dimensional Eculidean space R sup N,
called the signal space.  When the vector x is transmitted, the
received signal is represented by the vector

(1)                            z = x + v
where v is a noise vector whose components are independent Gaussian
random variables mean zero and the same variance Nu sub Omicron
divslash 2.  The vector x is chosen from a s...