  In diffusion based molecular communication, the intersymbol interference
(ISI) is an important reason for system performance degradation, which is
caused by the random movement, out-of-order arrival and indistinguishability of
the moleclues. In this paper, a new metric called crossover distance is
introduced to measure the distance between the received bit sequence and the
probably tranmitted bit sequences. A new decoding scheme of conventional codes
is proposed based on crossover distance, which can enhance the communication
reliability significantly. The theoretic analysis indicates that the proposed
decoding algorithm provides an approximately maximal likelihood estimation of
the information bits. The numerical results show that compared with uncoded
systems and some existing channel codes, the proposed convolutional codes offer
good performance with same throughputs.
