Summary: 1130 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 48, NO. 4, JULY 1999
Sequence MAP Decoding of Trellis Codes for
Gaussian and Rayleigh Channels
Saud A. Al-Semari, Fady Alajaji, Member, IEEE, and Tom Fuja, Senior Member, IEEE
Abstract--This paper considers the use of sequence maximum
a posterioria posterioria posteriori (MAP) decoding of trellis codes. A MAP receiver can
exploit any "residual redundancy" that may exist in the channel-
encoded signal in the form of memory and/or a nonuniform
distribution, thereby providing enhanced performance over very
noisy channels, relative to maximum likelihood (ML) decoding.
The paper begins with a first-order two-state Markov model
for the channel encoder input. A variety of different systems
with different source parameters, different modulation schemes,
and different encoder complexities are simulated. Sequence MAP
decoding is shown to substantially improve performance under
very noisy channel conditions for systems with low-to-moderate
redundancy, with relative gain increasing as the rate increases.
As a result, coding schemes with multidimensional constellations
are shown to have higher MAP gains than comparable schemes
with two-dimensional (2-D) constellations.