  Scaling up the number of base stations per unit area is one of the major
trends in mobile cellular systems of the fourth (4G)- and fifth generation
(5G), making it increasingly difficult to characterize aggregate interference
statistics with system models of low complexity. This paper proposes a new
circular interference model that aggregates given interferer deployments to
power profiles along circles. The model accurately preserves the original
interference statistics while considerably reducing the amount of relevant
interferers. In comparison to common approaches from stochastic geometry, it
enables to characterize cell-center- and cell-edge users, and preserves effects
that are otherwise concealed by spatial averaging. To enhance the analysis of
given power profiles and to validate the accuracy of the circular model, a new
finite sum representation for the sum of Gamma random variables with
integer-valued shape parameter is introduced. The approach allows to decompose
the distribution of the aggregate interference into the contributions of the
individual interferers. Such knowledge is particularly expedient for the
application of base station coordination- and cooperation schemes. Moreover,
the proposed approach enables to accurately predict the corresponding
signal-to-interference-ratio- and rate statistics.
