Esquemas de Quantização para Sistemas OOK FSO

This paper considers Free Space Optic (FSO)) communication systems using On-Off Keying modulation and channel coding. The focus of the article is a practical aspect of the implementation of these systems: the choice of quantization thresholds at the output of the demodulator. It is assumed that the receiver has the knowledge of the Channel State Information. Quantization schemes for FSO systems have been proposed previously in the literature. The cut-off rate of the discrete channel created by the quantization was used as a performance comparison criterion. The cutoff rate increases with increasing number of quantization levels used. However, even a high number of levels is not enough to achieve performance close to that of an ideal non-quantized scheme. This paper uses the Generalized Cutoff Rate concept to choose the appropriate quantization thresholds. The results now show that a relatively small number of levels leads to performance close to that of an ideal non- quantized scheme. Therefore, the schemes proposed in this paper present considerable performance gains when compared to those previously proposed in the literature.