  We introduce a simple yet powerful and versatile analytical framework to
approximate the SIR distribution in the downlink of cellular systems. It is
based on the mean interference-to-signal ratio and yields the horizontal gap
(SIR gain) between the SIR distribution in question and a reference SIR
distribution. As applications, we determine the SIR gain for base station
silencing, cooperation, and lattice deployment over a baseline architecture
that is based on a Poisson deployment of base stations and strongest-base
station association. The applications demonstrate that the proposed approach
unifies several recent results and provides a convenient framework for the
analysis and comparison of future network architectures and transmission
schemes, including amorphous networks where a user is served by multiple base
stations and, consequently, (hard) cell association becomes obsolete.
