Experimental and Analytical Investigations of an Optically Pre-Amplified FSO-MIMO System With Repetition Coding Over Non-Identically Distributed Correlated Channels

Priyadarshani, Richa, Bhatnagar, Manav R., Bohata, Jan, Zvanovec, Stanislav and Ghassemlooy, Zabih (2020) Experimental and Analytical Investigations of an Optically Pre-Amplified FSO-MIMO System With Repetition Coding Over Non-Identically Distributed Correlated Channels. IEEE Access, 8. pp. 12188-12203. ISSN 2169-3536

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Abstract

This paper presents theoretical and experimental bit error rate (BER) results for a freespace optical (FSO) multiple-input-multiple-output system over an arbitrarily correlated turbulence channel.
We employ an erbium-doped fiber amplifier at the receiver (Rx), which results in an improved Rx’s sensitivity
at the cost of an additional non-Gaussian amplified spontaneous emission noise. Repetition coding is used
to combat turbulence and to improve the BER performance of the FSO links. A mathematical framework
is provided for the considered FSO system over a correlated non-identically distributed Gamma-Gamma
channel; and analytical BER results are derived with and without the pre-amplifier for a comparative study.
Moreover, novel closed-form expressions for the asymptotic BER are derived; a comprehensive discussion
about the diversity order and coding gain is presented by performing asymptotic analysis at high signal-tonoise ratio (SNR). To verify the analytical results, an experimental set-up of a 2 × 1 FSO-multiple-inputsingle-output (MISO) system with pre-amplifier at the Rx is developed. It is shown analytically that, both
correlation and pre-amplification do not affect the diversity order of the system, however, both factors have
contrasting behaviour with respect to coding gain. Further, to achieve the target forward error correction
BER limit of 3.8 × 10−3
, a 2 × 1 FSO-MISO system with a pre-amplifier requires 6.5 dB lower SNR
compared with the system with no pre-amplifier. Moreover, an SNR penalty of 2.5 dB is incurred at a higher
correlation level for the developed 2×1 experimental FSO set-up, which is in agreement with the analytical
findings.

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