Cooperative diversity is an important method that has been widely studied in the recent years. In this scheme, a source node wishing to transmit data to a destination node can benefit from other nodes in its neighborhood (relay nodes) to forward copies of the original signal to the destination. However, the performance of cooperative systems can be significantly improved by using the constellation rearrangement technique (CoRe), in which different signal constellations are used in different retransmissions. In this context, this paper proposes the use of a hybrid search algorithm, which uses genetic mutation and clonal selection, to perform the optimization of the constellation mapping. The performance evaluation of the algorithm shows that a good performance is achieved when compared to other approaches outlined in the literature.

Resumo-A adoção do esquema de modulação adaptativa torna possível a realização de transmissões robustas e espectralmente eficientes. No entanto, o desempenho dos sistemas de modulação adaptativaé afetado pela precisão das informações do estado de canal, o que pode resultar em decisões incorretas do modulador, causando uma degradação da taxa de erro de bit. Neste trabalho, os autores avaliam o efeito dos erros de estimação em sistemas de modulação adaptativa. Um novo arcabouço analíticoé proposto para modelar a relação sinal-ruído estimada instantânea. Diferentemente das abordagens anteriores, este modelo não está relacionado a uma técnica de estimativa específica e pode ser usado para comparar estratégias de estimação de canal com diferentes níveis de precisão. Palavras-Chave-Modulação adaptativa, Erro de estimação do canal, Desvanecimento Rayleigh.Abstract-The adoption of the adaptive modulation scheme leads to robust and spectrally efficient transmissions. However, the performance of the adaptive modulation systems is affected by the accuracy of the channel state information, which can result in incorrect modulator decisions, causing a bit error rate degradation. In this paper, the authors evaluate the effect of channel estimation errors in adaptive modulation systems. A novel analytical framework is proposed to model the instantaneous estimated signal-to-noise ratio. Different from previous approaches, this model is not related to a specific estimation technique and can be used to compare channel estimation strategies with different accuracy levels.