Exact Evaluation of Outage Probability in Correlated Lognormal Shadowing Environment

Outage probability computation has been extensively studied in cellular radio systems where the interference is modeled by a sum of lognormal random variables. Since the sum of correlated lognormal random variables distribution does not have a closed-form expression, many approximation methods and bounds were proposed in the literature. However the accuracy of each method relies highly on the region of the resulting distribution being examined and the individual lognormal parameters, i.e., mean and variance. There is no such method which can provide the needed accuracy for all cases. This paper proposes a universal yet very simple approximation method for the sum of correlated lognormal random variables based on log skew normal approximation. Hence, the outage probability is accurately computed over the whole range of dB spreads for any correlation coefficient. We show that our method provides same results as Monte Carlo simulation for all cases.