LOPES, R. F.; http://lattes.cnpq.br/1972734433460838; LOPES, Rafael Fernandes.
Abstract:
Diversity techniques have been proposed in order to improve the performance of communication
systems, with different characteristics in terms of complexity and performance. This
thesis presents the use of diversity techniques combined with the adoption of the θ-QAM
(Theta Quadrature Amplitude Modulation) scheme.
The θ-QAM constellations represent a family of parametric quadrature modulation schemes,
in which the adjacent symbols are vertices of isosceles triangles with the angle parameter
θ. The change of the angle θ produces different signal constellations, a feature that can be
exploited to improve the performance of different diversity techniques. In addition, θ-QAM
constellations are used to increase the performance gain of the adaptive modulation schemes
by the dynamic change of the constellation density and of its internal structure
In this thesis, the modulation and the cooperative diversity techniques are analyzed and
their performance is evaluated considering the use of the θ-QAM schemes. Additionally, the
optimization of the internal constellation structure (angle θ) and the operating parameters of
each technique is performed. Suitable approximations for the symbol and bit error rates of
the proposed schemes are derived. Evaluations are conducted considering the Nakagami-m
and κ-μ fading models for the communication channel.
Among the main contributions obtained, the following are noteworthy: development of
an expression to evaluate the optimal value of the angle θ as a function of SNR; development
and evaluation of an adaptive modulation system based on the use of the θ-QAM schemes in
different fading conditions, using the κ-μ fading model; performance evaluation of the modulation
diversity technique and its operating parameters in Nakagami-m e κ-μ fading channels
using different analytical expressions proposed in this thesis; combination of the adaptive
modulation and modulation diversity schemes in order to improve system performance; performance
evaluation of the modulation diversity technique in channels subject to temporal
correlation and estimation errors; evaluation of the modulation diversity technique in κ-μ
channels combined with a spatial diversity scheme based on a Maximum-Ratio Combining
(MRC) receiver; development of an expression to evaluate the symbol error probability of
θ-QAM systems with cooperative diversity subject to κ-μ fading channels; and optimization
of cooperative diversity systems using the constellation rearrangement technique.
