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Rate Three-Halves Trellis-Coded 8-PSK for Transmission in Very Low SNR Environments

IP.com Disclosure Number: IPCOM000100296D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 75K

Publishing Venue

IBM

Related People

Feig, E: AUTHOR

Abstract

A state-varying trellis-coded modulation scheme using phase-shift keying ("PSK") is disclosed which is particularly suitable for transmitting information in environments of low signal-to-noise ratio (SNR). It uses signaling at a rate of three information bits per two samples and has a minimum free distance considerably greater than a comparable uncoded 2-PSK scheme with rate one bit per sample.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Rate Three-Halves Trellis-Coded 8-PSK for Transmission in Very Low SNR Environments

       A state-varying trellis-coded modulation scheme using
phase-shift keying ("PSK") is disclosed which is particularly
suitable for transmitting information in environments of low
signal-to-noise ratio (SNR).  It uses signaling at a rate of three
information bits per two samples and has a minimum free distance
considerably greater than a comparable uncoded 2-PSK scheme with rate
one bit per sample.

      The proposed coded modulation scheme is based on the trellis
depicted in the figure.  The trellis is built as an alternating
sequence of two four-state trellises.  One is Ungerboeck's 8-PSK
trellis [*], transmitting 2 bits per sample.  The other is a 4-PSK
trellis, transmitting one bit per sample.  The first is well known.
The second is designed so that any pair of paths either leaving a
state or merging into a state correspond to antipodal signals.  The
key idea disclosed herein is to blow up the 8-PSK constellation so
that all its points lie on a circle with radius

                            (Image Omitted)

                              a = 2
                                  !3-a2  ,
where a = sin(f/8), and to shrink the 4-PSK constellation so that all
its points lie on a circle with radius b = !2-a2 . These
modifications were made so that the average transmitted energy is
precisely 1 and that the minimum square distance between any two
competing paths will be d2free,c = (2a)2 = (2b)2 + (2aa)2 + (2b)2
By direct calculation, the coded minimum free distance is seen to be
d2free,c = 4a2 = 5...