A Novel Inter-Symbol Interference Model and Weighted Sum Detection for Diffusion-Based Molecular Communication Systems

Inter-symbol interference (ISI) may result in substantial performance degradation in molecular communication systems. In this paper, we propose a more accurate and realistic ISI model compared to the literature, by quantifying the ISI in a three-dimensional fluid environment with a spherical receiver. Moreover, due to the propagation delay in a fluid environment, a large number of the molecules absorbed earlier in a transmission interval are due to the previous transmissions. Therefore, we find the optimal delay time, that the receiver should wait at the beginning of each time interval before counting the absorbed molecules, to reduce the effect of the ISI. Further, and to enhance the performance of the system, we adopt a detection approach based on multiple molecular observations at the receiver, and introduce a weighted sum detector, in which the transmission interval is divided into a number of sub-intervals. We analytically derive the weights, assigned to different sub-intervals, that minimize the bit error rate (BER). Simulations, based on the presented approaches, show the impact of the transmitter-receiver distance, the reaction rate, and the diffusion constant of the environment on the BER performance. We also show that using a weighted sum detector significantly improves the BER performance.