On the ergodic capacity of optical space shift keying based FSO-MIMO system under atmospheric turbulence

Abstract

In this paper, the ergodic capacity of optical space shift keying (OSSK) based multiple-input multiple-output (MIMO) system under atmospheric turbulence (AT) is investigated. Negative exponential (NE) and Gamma-Gamma (G-G) channel models are used to characterize the AT. At first, a novel expression of the distribution of a sum of square of the difference between two NE/G-G random variables is evaluated. Later, a closed-form expression of the ergodic capacity for OSSK-MIMO system under different AT conditions is obtained with the help of derived distributions. It is shown by the analysis that the value of signal-to-noise ratio (γth) to reach 90% of the maximum achievable capacity (Cmax) is same under moderate, strong, and saturation AT regimes for a particular OSSK-MIMO system. The required value of γth remains constant irrespective of number of transmitter (Txs); however, C max is enhanced with increasing number of Txs. On the other hand, a reduction in requirement of 7th is observed when the number of receivers (Rxs) is increased, while C max remains constant irrespective of number of Rxs. Additionally, a new series based average bit error rate (ABER) expression, which has better accuracy and less mathematical complexity than a previously known ABER expression for OSSK-MIMO system, is obtained using the proposed distributions.