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Comparison of optical and electrical based amplify-and-forward relay-assisted FSO links over gamma-gamma channels

Relay-assisted or multi-hop free space optical communications is an efficient solution that offers diversity, which can significantly improve the link availability. Albeit this potential, the turbulence-induced fading can still impact the system performance. This paper investigates through numerical simulations the effect of turbulence by comparing the bit error rate (BER) performance for all-optical and conventional amplify-and-forward dual-hop relaying systems. For the latter case, two options of the erbium-doped fiber amplifier (EDFA) and the semiconductor optical amplifier (SOA) are studied, showing that the advantages of the EDFA solution where EDFA outperforms SOA by ~3 dB in term of signal to noise ratio (SNR) for Rytov variance σ2R = 1.6 at a target BER of 10-5. Under the same turbulence regime, we further investigate the effect of aperture averaging in relay-assisted links and show that a significant BER improvement can be achieved. The results show that SNR gain of ~5.5 dB is achieved when the receiver aperture size increases from 100 mm to 300 mm at a target BER of 10-5.