  In this paper, we consider the diffusive molecular communication channel
between a transmitter nano-machine and a receiver nano-machine in a fluid
environment. The information molecules released by the transmitter nano-machine
into the environment can degrade in the channel via a first-order degradation
reaction and those that reach the receiver nano-machine can participate in a
reversible bimolecular-reaction with receiver receptor proteins. We derive a
closed-form analytical expression for the expected received signal at the
receiver, i.e., the expected number of activated receptors on the surface of
the receiver. The accuracy of the derived analytical result is verified with a
Brownian motion particle-based simulation of the environment.
