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16 March 2015 Power-spectrum requirements in ultraviolet optical wireless networks
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Short range communications using an optical wireless channel in a non-line-of-sight regime can be attained by exploiting the solar-blind UVC band. Firstly, the power loss and the bandwidth of the diffused wireless channel are examined for several particle and molecular densities of the medium when a receiver with a wide Field-Of-View is considered. Proper transmissions were simulated for two channel cases in order to investigate how the channel affects the signals. The investigated modulation schemes were On-Off-Keying (OOK) and 4-Pulse-Position-Modulation (4-PPM). At the receiving side, estimations with photoelectrons were considered. Compared to OOK, 4-PPM is favored by the detection without threshold and the higher peak optical power. Concerning the influence of the transmission medium, it appears that a sparse medium may limit the performance of both PPM and OOK due to the increased losses and the slight Inter- Symbol-Interference that appears. On the contrary, the estimated channel with broader bandwidth and lower losses for a thicker atmosphere ameliorated the performance of both schemes. Using the previous indication, Code Division Multiple Access (CDMA) transmissions were investigated utilizing the already defined receiver configuration. In CDMA, if the coded signals are transmitted with the same mean and peak power, 4-PPM seems to need more power in order to achieve similar performance to OOK. This confinement of 4-PPM is mitigated in a dense channel. Finally, the linearity of the Power-Current curve of the LEDs at the transmitting side was also taken into account as a factor that may increase the consumption of the sources.
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Nikos Raptis, Eugenia Roditi, and Dimitris Syvridis "Power-spectrum requirements in ultraviolet optical wireless networks", Proc. SPIE 9354, Free-Space Laser Communication and Atmospheric Propagation XXVII, 935403 (16 March 2015);

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