Vol.:(0123456789) Optical and Quantum Electronics ( 2019) 51:244 https://doi.org/10.1007/s11082-019-1962-1 1 3 Compensating rain induced impairments in terrestrial FSO links using aperture averaging and receiver diversity Gireesh G. Soni 1,2  · Abhishek Tripathi 2  · Abhilash Mandloi 2  · Shilpi Gupta 2 Received: 25 March 2019 / Accepted: 3 July 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract In this paper, we investigate the performance of a free space optical link considering the deteriorations caused by heavy rain. The applicability of receiver diversity and aperture averaging techniques to compensate the rain-induced impairments is analyzed on the basis of outage probability and signal to noise ratio at varying rain intensities. A 10-Mbps on-of keying modulated optical signal is taken as the test signal for which rain specifc attenua- tion is calculated using a laboratory testbed having controlled rainfall conditions up to 250 mm/h. A 15-m single input multi output) optical link with selection combining technique at the receiver is used to observe diversity gain. Signifcant diversity improvement by a fac- tor of 1.35 is observed by comparing the results with the conventional single input single output link. Experimental observations with and without aperture averaging shows average SNR gain of 1.58 and outage probability reduction of 12.3%. Keywords Free space optics · Rainfall rate · Rain specifc attenuation · Aperture averaging · Receiver diversity 1 Introduction Free space optics (FSO) can be an attractive solution for high bandwidth radio frequency (RF) systems, particularly for last mile access by bridging the bandwidth gap between the end user and the backbone networks. This line of sight technology can be used in appli- cations where high data rate links are required like university campuses, hospitals, urban area etc. It ofers many advantages like license free spectrum, immunity to electromagnetic interference (EMI), no jamming, low power consumption etc. (Ghassemlooy et al. 2012; Yang et al. 2017). For deployment of such Terrestrial FSO links in tropical regions, rain becomes a limiting factor as it causes distortion of optical signals and attenuation up to tens of dB per kilometer (Al-Gailani et al. 2014). Proper characterization of rain attenu- ated channel can provide reliable information needed for the parameter design of the new FSO link (Basahel et al. 2017; Das and Maitra 2015). The attenuation caused by prevailing * Gireesh G. Soni gireeshsoni@gmail.com 1 Department of Applied Physics and Optoelectronics, S.G.S.I.T.S., Indore, India 2 Department of Electronics Engineering, S.V.N.I.T., Surat, India