Capacity of optical wireless communication system over correlated log-normal channels

The performance of an optical wireless communication (OWC) system subjected to atmospheric turbulence induced fading can be significantly improved by using spatial diversity reception. Diversity reception also suffers from correlation among diversity branches due to insufficient spacing between multiple photodetectors at the receiver. In this paper, average channel capacity of OWC system employing maximal ratio combing (MRC) and equal gain combining (EGC) diversity reception with correlated diversity branches is evaluated using a simple expression based on point estimate. A weak atmospheric turbulence condition known to be modeled by log-normal distribution is considered. In addition, the impact of correlation is also investigated considering identical as well as non-identical turbulence induced fading among diversity branches. This analysis reveals that the channel capacity decreases with the increase in correlation coefficient and impact of fading correlation is higher in case of identically distributed diversity branches as compared to non-identically distributed branches. Validity of the analysis is demonstrated with the results obtained using Monte-carlo simulation.