What is it about?
Free-space optical communication uses laser beams to transmit information through the atmosphere, but atmospheric turbulence causes the received signal to fluctuate. Diversity techniques using multiple lasers and photodetectors can improve reliability. However, the conventional diversity-order measure becomes infinite for lognormal turbulence channels and therefore provides little useful information about how performance actually improves. We introduce a new measure called incremental diversity order, which describes how the rate of improvement in bit error probability changes as signal-to-noise ratio increases.
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Why is it important?
The key contribution is a new performance measure for a situation where the conventional diversity definition becomes uninformative. Unlike an earlier alternative measure, incremental diversity order does not require a separate benchmark system and directly reflects important physical parameters such as the number of transmit lasers, number of photodetectors and turbulence strength. This gives researchers a more meaningful way to compare free-space optical systems operating over lognormal turbulence channels and to understand how much diversity gain can actually be extracted.
Perspectives
The analysis also highlights an important distinction between theoretical diversity and practically achievable diversity. Full spatial diversity may only emerge when the fading variance is sufficiently small, and convergence can require extremely large signal-to-noise ratios. Incremental diversity order therefore provides a useful basis for evaluating optical systems at realistic operating conditions instead of relying only on an asymptotic result that may never be reached in practice.
Assist. Prof. Mohammed Elamassie
Ozyegin Universitesi
Read the Original
This page is a summary of: Incremental Diversity Order for Characterization of FSO Communication Systems Over Lognormal Fading Channels, IEEE Communications Letters, April 2020, Institute of Electrical & Electronics Engineers (IEEE),
DOI: 10.1109/lcomm.2020.2966479.
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