Research focusing on:

Outdoor optical wireless (OW) systems have recently gained attention as a broadband alternative in niche applications including semi-permanent office interconnections and MAN implementations. Despite the inherent advantages of outdoor OW systems, the transmission of light through the atmosphere can be challenging. Apart from weather-dependent static transmission losses that may limit the system availability, atmospheric turbulence induces time-varying changes in the refractive index, which in turn affect the amplitude, phase and propagation direction of the optical signal. These changes result in time-varying power fluctuations of the received signal and when the turbulence is intense enough, the received signal decreases below the receiver sensitivity and the link is lost. This corresponds to a fade event, which affects the OW system both in terms of capacity, as well as latency. Several million bits may be lost during a msec-long fade at 10 Gb/s, while the link will be in outage for an amount of time approximately equal to the fade duration. In this area, our research includes:

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The proposed optical wireless fade mitigation setup and principle of operation.

Fade probability at the output of a semiconductor optical amplifier versus the normalized threshold with small signal gain 20 dB.

Key Publications:

• K. Yiannopoulos, N. C. Sagias, A. C. Boucouvalas, M. Uysal and Z. Ghassemlooy, “Optimal combiners in optical wireless systems with spatial diversity and pre-amplification,” 2016 IEEE International Conference on Communications Workshops (ICC), Kuala Lumpur, 2016, pp. 399-404.
• K. Yiannopoulos, N. C. Sagias and A. C. Boucouvalas, “Semiconductor optical amplifier-assisted optical wireless links: The effect of noise and turbulence,” 2015 IEEE International Conference on Communications (ICC), London, 2015, pp. 4297-4302.
• N. C. Sagias, K. Yiannopoulos and A. C. Boucouvalas, “Semiconductor optical amplifiers in negative-exponential fading: regenerators and pre-amplifiers,” in IET Optoelectronics, vol. 9, no. 5, pp. 249-256, 10 2015.
• K. Yiannopoulos, N. C. Sagias and A. C. Boucouvalas, “On the Performance of Semiconductor Optical Amplifier-Assisted Outdoor Optical Wireless Links,” in IEEE Journal on Selected Areas in Communications, vol. 33, no. 9, pp. 1869-1876, Sept. 2015.
• K. Yiannopoulos, N. C. Sagias and A. C. Boucouvalas, “SOA nonlinear amplification: A promising fade mitigation technique for optical wireless systems,” 2014 IEEE Wireless Communications and Networking Conference (WCNC), Istanbul, 2014, pp. 287-292. (Best Paper Award)