  Molecular Communications (MC) is a bio-inspired communication technique that
uses molecules to transfer information among bio-nano devices. In this paper,
we focus on the detection problem for biological MC receivers employing ligand
receptors to infer the transmitted messages encoded into the concentration of
molecules, i.e., ligands. In practice, receptors are not ideally selective
against target ligands, and in physiological environments, they can interact
with multiple types of ligands at different reaction rates depending on their
binding affinity. This molecular cross-talk can cause a substantial
interference on MC. Here we consider a particular scenario, where there is
non-negligible concentration of interferer molecules in the channel, which have
similar receptor-binding characteristics with the information molecules, and
the receiver employs single type of receptors. We investigate the performance
of four different detection methods, which make use of different statistics of
the ligand-receptor binding reactions: instantaneous number of bound receptors,
unbound time durations of receptors, bound time durations of receptors, and
combination of unbound and bound time durations of receptors within a sampling
time interval. The performance of the introduced detection methods are
evaluated in terms of bit error probability for varying strength of molecular
interference, similarity between information and interferer molecules, number
of receptors, and received concentration difference between bit-0 and bit-1
transmissions. We propose synthetic receptor designs that can convert the
required receptor statistics to the concentration of intracellular molecules,
and chemical reaction networks that can chemically perform the computations
required for detection.
