  We propose and prove a theorem that allows the calculation of a class of
functionals on Poisson point processes that have the form of expected values of
sum-products of functions. In proving the theorem, we present a variant of the
Campbell-Mecke theorem from stochastic geometry. We proceed to apply our result
in the calculation of expected values involving interference in wireless
Poisson networks. Based on this, we derive outage probabilities for
transmissions in a Poisson network with Nakagami fading. Our results extend the
stochastic geometry toolbox used for the mathematical analysis of
interference-limited wireless networks.
