Free-space optical communication using on-off keying (OOK) and source information transformation is proposed. It is shown that source information transformation allows the proposed system to detect the OOK signal without requiring the knowledge of instantaneous channel state information and the probability density function (pdf) of the turbulence model. Analytical expressions are derived for the pdf of the detection threshold, and an upper bound is obtained on the average bit error rate (BER). Numerical studies show that the proposed system can achieve comparable performance to the idealized adaptive detection system, with a greatly reduced level of implementation complexity and a signal-to-noise ratio performance loss of only 1.8 dB at a BER of 1 × 10 −9 for a lognormal turbulence channel with σ = 0.25.
In this work, the on-going challenges are addressed for the application of the lognormal-Rician turbulence model to free-space optical communication systems. Maximum likelihood estimation is applied to characterize the lognormal-Rician turbulence model parameters, and the expectation-maximization algorithm is used to compute maximum likelihood estimates of the unknown parameters. The performance is investigated, by way of the mean square error, and it is found that the proposed technique can accurately characterize free-space optical communication channels over a wide range of turbulence conditions, with reduced demand on the quantity of data samples.Index Terms-Free-space optical communications, lognormal-Rician turbulence model, maximum likelihood estimation.
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