Recent results on correlated lognormal atmospheric turbulence channels

Abstract

The performance of free-space optical (FSO) communication systems is often compromised by atmospheric attenuation and fading effects. One effective counter fading technique is the spatial diversity. In this paper, an FSO system with spatial diversity is analyzed over correlated lognormal fading channels that may have nonidentical variance. We use a novel lognormal-Nakagami composite channel model to reveal the asymptotic behaviors of the correlated lognormal fading channels. We discover that the correlation among the lognormal channels can impose large signal-to-noise ratio (SNR) penalty when compared to the same system with independent lognormal channels. This property is not shared with the other commonly used fading channels. In addition, we also derive a compact expression for the asymptotic relative diversity order (ARDO) between an L branch maximal ratio combing system over correlated lognormal channels and a single branch system. It is found that the ARDO is related to the number of diversity branches as well as entry-wise norm of the covariance matrix of the logarithm of the lognormal channel states.