In a diffusion-based molecular communication network, transmitters and receivers communicate by using signalling molecules (or ligands) in a fluid medium. This paper assumes that the transmitter uses different chemical reactions to generate different emission patterns of signalling molecules to represent different transmission symbols, and the receiver consists of receptors. When the signalling molecules arrive at the receiver, they may react with the receptors to form ligand-receptor complexes. Our goal is to study the demodulation in this setup assuming that the transmitter and receiver are synchronised. We derive an optimal demodulator using the continuous history of the number of complexes at the receiver as the input to the demodulator. We do that by first deriving a communication model which includes the chemical reactions in the transmitter, diffusion in the transmission medium and the ligand-receptor process in the receiver. This model, which takes the form of a continuous-time Markov process, captures the noise in the receiver signal due to the stochastic nature of chemical reactions and diffusion. We then adopt a maximum a posteriori framework and use Bayesian filtering to derive the optimal demodulator. We use numerical examples to illustrate the properties of this optimal demodulator.
We consider diffusion-based molecular communication networks where the receivers consist of a set of chemical reactions or a molecular circuit. At the receivers of these networks, the signalling molecules react with the molecular circuit to produce output molecules. The counts of output molecules over time is the output signal of the receiver. The aim of this paper is to investigate the impact of different molecular circuits on the noise properties and information transmission capacity of molecular communication networks. In particular, we show that some molecular circuits have lower noise and higher information transmission capacity. Abstract A key research question in the design of molecular nano-communication networks is how the information is to be encoded and decoded. One particular encoding method is to use different frequencies to represent different symbols. This paper will investigate the decoding of such frequency coded signals. To the best of our knowledge, the current literature on molecular communication has only used simple ligand–receptor models as decoders and the decoding of frequency coded signals has not been studied. There are two key issues in the design of such decoders. First, the decoder must exhibit frequency selective behaviour which means that encoder symbol of a specific frequency causes a bigger response at the decoder than symbols of other frequencies. Second, the decoder must take into account inter-symbol interference which earlier studies on concentration coding have pointed out to be a major performance issue. In order to study the design of decoder, we propose a system of reaction–diffusion and reaction kinetic equations to model the system of encoder, channel and decoder. We use this model to show that enzymatic circuit of a particular inter-connection has frequency selective properties. We also explore how decoder can be designed to avoid inter-symbol interference. Molecular Communication (MC), i.e., the exchange of information through the emission, propagation, and reception of molecules, is a promising paradigm for the interconnection of autonomous nanoscale devices, known as nanomachines. Synthetic biology techniques, and in particular the engineering of biological circuits, are enabling research towards the programming of functions within biological cells, thus paving the way for the realization of biological nanomachines. The design of MC systems built upon biological circuits is particularly interesting since cells naturally employ the MC paradigm in their interactions, and possess many of the elements required to realize this type of communication. This paper focuses on the identification and systems-theoretic modeling of a minimal subset of biological circuit elements necessary to be included in an MC system design where the message-bearing molecules are propagated via free diffusion between two cells. The system-theoretic models are here detailed in terms of transfer functions, from which analytical expressions are derived for the attenuation and the delay experienced by an information signal through the MC system. Numerical results are presented to evaluate the attenuation and delay expressions as functions of realistic biological parameters.