Multirate RZ communications for dispersive wireless optical channels

Free Space Optical Communications through cloud-obscured channels suffer from severe degradations due to multiscattering, which induces delay spread in the received signal. The delay spread of FSO channel can vary considerably according to channel conditions, varying from nanoseconds to microseconds for clear and cloudy channel, respectively. In this paper, we present the use of return-to-zero (RZ) modulation in conjunction with multirate modulation schemes as viable means for minimizing the dispersive effects of the channels. We show that multirate communications provide diversity against channel degradation and fluctuation, while RZ modulation is more robust to dispersive channels than non return-to-zero (NRZ) modulation, thus providing an overall improvement in system performance, reliability and availability.