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# Two-State Rate-One 4-PSK Trellis-Coded Modulation Achieving 3 DB Gain Over Uncoded Signaling

IP.com Disclosure Number: IPCOM000100267D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 1 page(s) / 32K

IBM

Feig, E: AUTHOR

## Abstract

Conventional trellis-coded modulation schemes are expensive to implement because they typically require many states for Viterbi decoding. This article discloses phase-shift keying (PSK) scheme of a 4-PSK type which uses only two states, has a very simple implementation, and achieves a 3 dB gain over uncoded binary signaling.

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Two-State Rate-One 4-PSK Trellis-Coded Modulation Achieving 3 DB Gain Over Uncoded Signaling

Conventional trellis-coded modulation schemes are expen-
sive to implement because they typically require many states for
scheme of a 4-PSK type which uses only two states, has a very simple
implementation, and achieves a 3 dB gain over uncoded binary
signaling.

The scheme uses a 4-PSK constellation.  Pairs of complex points
are transmitted every two time intervals. Allowable pairs are
A0 = (1,1)                      A4 = (i,i)
A1 = (1,-1)                     A5 = (i,-i)
A2 = (-1,1)                     A6 = (-i,i)
A3 = (-1,-1)                    A7 = (-i,-i)
where i=!-1.  The coded modulation follows the trellis depicted in
the figure.  It can be seen that one of four possible paths can be
chosen from one state to the next. Thus, the transmission rate is two
bits of information per two sample points.  This scheme has a minimum
free distance d2free = 8, and hence it achieves a 3 dB gain over
uncoded 2-PSK signaling with the same rate.  Each path of length two
has seven nearest neighbors.

Decoding is particularly simple because the real and imaginary
parts of the constellation members are all Å1. It can be seen
theref...