This article focuses on the design of transmitters and receivers for molecular communication (MC). It also reviews existing literature on transmitter and receiver architectures for realizing MC, including both nanomaterial-based nanomachines and/or biological entities.

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Molecular communication (MC) is the most promising communication paradigm for nanonetwork realization since it is a natural phenomenon observed among living entities with nanoscale components. Since MC significantly differs from classical communication systems, it mandates reinvestigation of information and communication theoretical fundamentals.The closest examples of MC architectures are present inside our own body. Therefore, in this paper, we investigate the existing literature on intra-body nanonetworks and different MC paradigms to establish and introduce the fundamentals of molecular information and communication science. We highlight future research directions and open issues that need to be addressed for revealing the fundamental limits of this science. Although the scope of this development encompasses wide range of applications, we particularly emphasize its significance for life sciences by introducing potential diagnosis and treatment techniques for diseases caused by dysfunction of intra-body nanonetworks.

Molecular communications (MC), where molecules are used to encode, transmit, and receive information, is a promising means of enabling the coordination of nanoscale devices. The paradigm has been extensively studied from various aspects, including channel modeling and noise analysis. Comparatively little attention has been given to the physical design of molecular receiver and transmitter, envisioning biological synthetic cells with intrinsic molecular reception and transmission capabilities as the future nanomachines. However, this assumption leads to a discrepancy between the envisaged applications requiring complex communication interfaces and protocols, and the very limited computational capacities of the envisioned biological nanomachines. In this paper, we examine the feasibility of designing a molecular receiver, in a physical domain other than synthetic biology, meeting the basic requirements of nanonetwork applications. We first review the state-of-the-art biosensing approaches to determine whether they can inspire a receiver design. We reveal that nanoscale field effect transistor based electrical biosensor technology (bioFET) is a particularly useful starting point for designing a molecular receiver. Focusing on bioFET-based molecular receivers with a conceptual approach, we provide a guideline elaborating on their operation principles, performance metrics and design parameters. We then provide a simple model for signal flow in silicon nanowire (SiNW) FET-based molecular receiver. Lastly, we discuss the practical challenges of implementing the receiver and present the future research avenues from a communication theoretical perspective.

Nanonetworks refer to a group of nanosized machines with very basic operational capabilities communicating to each other in order to accomplish more complex tasks such as in-body drug delivery, or chemical defense. Realizing reliable and high-rate communication between these nanomachines is a fundamental problem for the practicality of these nanonetworks. Recently, we have proposed a molecular communication method based on Förster Resonance Energy Transfer (FRET) which is a nonradiative excited state energy transfer phenomenon observed among fluorescent molecules, i.e., fluorophores. We have modeled the FRET-based communication channel considering the fluorophores as single-molecular immobile nanomachines, and shown its reliability at high rates, and practicality at the current stage of nanotechnology. In this study, for the first time in the literature, we investigate the network of mobile nanomachines communicating through FRET. We introduce two novel mobile molecular nanonetworks: FRET-based mobile molecular sensor/actor nanonetwork (FRET-MSAN) which is a distributed system of mobile fluorophores acting as sensor or actor node; and FRET-based mobile ad hoc molecular nanonetwork (FRET-MAMNET) which consists of fluorophore-based nanotransmitter, nanoreceivers and nanorelays. We model the single message propagation based on birth-death processes with continuous time Markov chains. We evaluate the performance of FRET-MSAN and FRET-MAMNET in terms of successful transmission probability and mean extinction time of the messages, system throughput, channel capacity and achievable communication rates.

In this study, a novel and physically realizable nanoscale communication paradigm is introduced based on a well-known phenomenon, Förster Resonance Energy Transfer (FRET) for the first time in the literature. FRET is a nonradiative energy transfer process between fluorescent molecules based on the dipole-dipole interactions of molecules. Energy is transferred rapidly from a donor to an acceptor molecule in a close proximity such as 0 to 10 nm without radiation of a photon. Low dependency on the environmental factors, controllability of its parameters and relatively wide transfer range make FRET a promising candidate to be used for a high rate nanoscale communication channel. In this paper, the simplest form of the FRET-based molecular communication channel comprising a single transmitter-receiver nanomachine pair and an extended version of this channel with a relay nanomachine for long range applications are modeled considering nanomachines as nanoscale electromechanical devices with some sensing, computing and actuating capabilities. Furthermore, using the information theoretical approach, the capacities of these communication channels are investigated and the dependency of the capacity on some environmental and intrinsic parameters is analyzed. It is shown that the capacity can be increased by appropriately selecting the donor-acceptor pair, the medium, the intermolecular distance and the orientation of the molecules.

Molecular Communication (MC) is a bio-inspired communication technique that uses molecules as a method of information transfer among nanoscale devices. MC receiver is an essential component having profound impact on the communication system performance. However, the interaction of the receiver with information bearing molecules has been usually oversimplified in modeling the reception process and developing signal detection techniques. In this paper, we focus on the signal detection problem of MC receivers employing receptor molecules to infer the transmitted messages encoded into the concentration of molecules, i.e., ligands. Exploiting the observable characteristics of ligand-receptor binding reaction, we first introduce a Maximum Likelihood (ML) detection method based on instantaneous receptor occupation ratio, as aligned with the current MC literature. Then, we propose a novel ML detection technique, which exploits the amount of time the receptors stay unbound in an observation time window. A comprehensive analysis is carried out to compare the performance of the detectors in terms of bit error probability. In evaluating the detection performance, emphasis is given to the receptor saturation problem resulting from the accumulation of messenger molecules at the receiver as a consequence of intersymbol interference. The results reveal that detection based on receptor unbound time is quite reliable even in saturation, whereas the reliability of detection based on receptor occupation ratio substantially decreases as the receiver gets saturated. Finally, we also discuss the potential methods of implementing the detectors.

Nanoscale communication based on Förster Resonance Energy Transfer (FRET) is a promising paradigm that allows future molecular-size machines to communicate with each other over distances up to 10 nm using the excited state energies of fluorescent molecules. In this study, we propose a novel nanoscale communication method based on multi-step FRET using identical fluorophores as relay nodes between communicating nanomachines, and utilizing multi-exciton transmission scheme in order to improve the limited range of the communication and achievable transmission rate over the nanoscale channel. We investigate two communication scenarios: immobile nanomachines communicating through a channel in a host material with linearly located relay nodes, and mobile nanomachines communicating through a channel in a 3-dimensional aqueous environment with randomly deployed relay nodes. We simulate the communication over these channels with realistic algorithms considering the high degree of randomness intrinsic to FRET phenomenon. Using the simulation results and following a Monte Carlo approach, we evaluate the performance of the channels by means of information theoretical capacity and interference probability. We show that multi-step FRET-based communication significantly outperforms the other biologically inspired nanocommunication techniques proposed so far in terms of maximum achievable data transmission rates. The results underline the compatibility and practicality of the FRET-based communication for several applications ranging from molecular computers to nanosensor networks.