  In this paper, we investigate the achievable rate of a diffusive Molecular
Communication (MC) channel with fully absorbing receiver, which counts
particles absorbed along each symbol interval and resets the counter at every
interval (reset-counting). The MC channel is affected by a memory effect and
thus inter-symbol interference (ISI), due to the delayed arrival of molecules.
To reduce complexity, our analysis is based on measuring the channel memory as
an integer number of symbol intervals and on a single-sample memoryless
detector. Thus, in our model the effect of released particles remains effective
for a limited number of symbol intervals. We optimize the detector threshold
for maximizing capacity, approximate as Gaussian the received signal
distribution, and calculate the channel mutual information affected by ISI, in
the case of binary concentration shift keying modulation. To the best of our
knowledge, in literature there are no previous investigations on the achievable
rate in this type of system. Our results demonstrate that, in general, the
optimal input probability distribution achieving the maximum achievable rate
may be not uniform. In particular, when the symbol interval is small (strong
ISI), the maximum achievable rate does not occur with equiprobable transmission
of bits.
