  A molecule traveling in a realistic propagation environment can experience
stochastic interactions with other molecules and the environment boundary. The
statistical behavior of some isolated phenomena, such as dilute unbounded
molecular diffusion, are well understood. However, the coupling of multiple
interactions can impede closed-form analysis, such that simulations are
required to determine the statistics. This paper compares the statistics of
molecular reaction-diffusion simulation models from the perspective of
molecular communication systems. Microscopic methods track the location and
state of every molecule, whereas mesoscopic methods partition the environment
into virtual containers that hold molecules. The properties of each model are
described and compared with a hybrid of both models. Simulation results also
assess the accuracy of Poisson and Gaussian approximations of the underlying
Binomial statistics.
