Simple estimate of signal to interference ratio with randomly located antennas

We consider a propagation model under path loss, shadowing and multipath effects, where each cell are a Voronoi tessellation and the generating points of this cells are a uniform Poisson point process in R². In addition, the antennas are located in each point generated by the Poisson process. With this model, we calculate the mean interference to signal ratio ISR, which actually gives us a physical information, but once we are interest in apply this mean in the Shannon´s formula, we simulated the real mean value of signal to interference ratio SIR and compared the result with the calculated ISR^-1.