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Pairwise optimization of modulation constellations for non-uniform sources

Summary: 167
Pairwise optimization of modulation
constellations for non-uniform sources
Modulation par optimisation de constellations
par paires pour sources non uniformes
The design of two-dimensional signal constellations for the transmission of binary non-uniform memoryless sources over additive white Gaussian noise chan-
nels is investigated. The main application of this problem is the implementation of improved constellations where transmitted data is highly non-uniform. A
simple algorithm, which optimizes a constellation by re-arranging its points in a pairwise fashion (i.e., two points are modified at a time, with all other points
remaining fixed), is presented. In general, the optimized constellations depend on both the source statistics and the signal-to-noise ratio (SNR) in the channel.
We show that constellations designed with source statistics considered can yield symbol error rate (SER) performance that is substantially better than rectangu-
lar quadrature amplitude modulation signal sets used with either Gray mapping or more recently developed maps. SER gains as high as 5 dB in Eb /No SNR
are obtained for highly non-uniform sources. Symbol mappings are also developed for the new constellations using a similar pairwise optimization method
whereby we assign and compare a weighted score for each pair. These maps, when compared to the mappings used in conjunction with the standard rectangu-
lar QAM constellation, again achieve considerable performance gains in terms of bit error rate (BER). Gains as high as 4 dB were achieved over rectangular
QAM with Gray mapping, or more than 1 dB better than previously improved mappings. Finally, the uncoded pairwise optimized system is compared to a
standard tandem (separate) source and channel coding system. Although neither system is universally better, the uncoded system with optimized constella-
tions outperforms the tandem coding system for low-to-mid SNRs. Performance/complexity trade-offs between the two systems are also discussed.
La conception de constellations d'un signal bidimensionnelles pour la transmission de sources binaires non uniformes sans mémoire avec addition de bruit
blanc Gaussien sur des canaux sonores est examinée en profondeur. La principale application de ce problème est la mise en oeuvre de constellations amé-
liorées où les données transmises sont fortement non uniformes. Un algorithme simple qui optimise une constellation en réarrangeant ses points dans un


Source: Alajaji, Fady - Department of Mathematics and Statistics, Queen's University (Kingston)
Linder, Tamás - Department of Mathematics and Statistics, Queen's University (Kingston)


Collections: Engineering