Statistics of the sum of lognormal variables in wireless communications

Schwartz and Yeh´s method (1982) and Wilkinson´s method are widely used to compute the moments of the total co-channel interference in wireless communication, usually modeled as the sum of lognormal random variables. The accuracy of these methods has been studied in previous works, under the assumption of having all summands signals (individual interference signals) identically distributed. Such assumption rarely holds in practical cases of emerging wireless systems, where interference may stem from far-away macrocells and nearby transmitters, causing the interference signals to have different moments. In this paper we present an analysis of Wilkinson´s method and Schwartz and Yeh´s method, for the general case when the summands have different mean values and standard deviations in decibel units. We show that Schwartz and Yeh´s method provides better accuracy than Wilkinson´s method and is virtually invariant with the difference of the mean values and standard deviations of the summands, and the number of summands