Molecular Communications (MC) uses molecules as information carriers between
nanomachines. MC channel in practice can be crowded with different types of
molecules, i.e., ligands, which can have similar binding properties causing
severe cross-talk on ligand receptors. Simultaneous sensing of multiple ligand
types provides opportunities for eliminating interference of external molecular
sources and multi-user interference (MUI), and developing new multiple access
techniques for MC nanonetworks. In this paper, we investigate channel sensing
methods that use only a single type of receptors and exploit the amount of time
receptors stay bound and unbound during ligand-receptor binding reaction to
concurrently estimate the concentration of multiple types of ligands. We derive
the Cram\'er-Rao Lower Bound (CRLB) for multi-ligand estimation, and propose
practical and low-complexity suboptimal estimators for channel sensing. We
analyze the performance of the proposed methods in terms of normalized mean
squared error (NMSE), and show that they can efficiently estimate the
concentration of ligands up to 10 different types with an average NMSE far
below 10−2. Lastly, we propose a synthetic receptor design based on
modified kinetic proofreading (KPR) scheme to sample the unbound and bound time
durations, and a Chemical Reaction Network (CRN) to perform the required
computations in synthetic cells.This work was supported in part by the ERC projects
MINERVA (ERC-2013-CoG #616922), and MINERGRACE (ERC-2017-
PoC #780645)
