  In this paper, we consider non-coherent detection for molecular communication
systems in the presence of inter-symbol-interference. In particular, we study
non-coherent detectors based on memory-bits-based thresholds in order to
achieve low bit-error-ratio (BER) transmission. The main challenge of realizing
detectors based on memory-bits-based thresholds is to obtain the channel state
information based only on the received signals. We tackle this issue by
reformulating the thresholds through intermediate variables, which can be
obtained by clustering multi-dimensional data from the received signals, and by
using the K-means clustering algorithm. In addition to estimating the
thresholds, we show that the transmitted bits can be retrieved from the
clustered data. To reduce clustering errors, we propose iterative clustering
methods from one-dimensional to multi-dimensional data, which are shown to
reduce the BER. Simulation results are presented to verify the effectiveness of
the proposed methods.
