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Sociedade Brasileira de Telecomunicações

Improving the Performance of Adaptive Modulation Systems by the Modulation Diversity Technique

This paper proposes a combination of the adap- tive modulation with the modulation diversity technique, which associates a suitable constellation rotation angle θ with the independent interleaving of the symbol components. Since the optimal rotation angle depends on the chosen modulation order and fading severity degree, the constellation rotation angle is dynamically changed according to the channel parameters. A new approximate expression for the pairwise error probability (PEP) is derived to allow the dynamic evaluation of the optimal value of θ. A performance analysis considering a system with parameters similar to the UMTS/HSDPA protocol is performed. The evaluation of the proposed system has shown that significant gains, in terms of the average system bit error rate, are achieved for high signal-to-noise ratio values.

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