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.

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