  In measurements of in-room radio channel responses an avalanche effect can be
observed: earliest signal components, which appear well separated in delay, are
followed by an avalanche of components arriving with increasing rate of
occurrence, gradually merging into a diffuse tail with exponentially decaying
power. We model the channel as a propagation graph in which vertices represent
transmitters, receivers, and scatterers, while edges represent propagation
conditions between vertices. The recursive structure of the graph accounts for
the exponential power decay and the avalanche effect. We derive a closed form
expression for the graph's transfer matrix. This expression is valid for any
number of interactions and is straightforward to use in numerical simulations.
We discuss an example where time dispersion occurs only due to propagation in
between vertices. Numerical experiments reveal that the graph's recursive
structure yields both an exponential power decay and an avalanche effect.
