Transmitter and Receiver Architectures for Molecular Communications: A Survey on Physical Design with Modulation, Coding and Detection Techniques <s> A. Design Requirements for MC-Rx <s> Molecular communications, where molecules are used to encode, transmit, and receive information, are 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 the nanoscale field effect transistor-based electrical biosensor technology (bioFET) is particularly a 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 FET-based molecular receiver. Finally, we discuss the practical challenges of implementing the receiver and present the future research avenues from a communication theoretical perspective. <s> BIB001 </s> Transmitter and Receiver Architectures for Molecular Communications: A Survey on Physical Design with Modulation, Coding and Detection Techniques <s> A. Design Requirements for MC-Rx <s> 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 intrabody 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 intrabody nanonetworks. <s> BIB002
While designing the MC-Rx, its integrability to a mobile nanomachine with limited computational, memory and energy resources, that requires to operate independently in an MC setup, must be taken into consideration. This dictates the following requirements for the functionality and physical design of the receiver BIB001 . • In situ operation: In-device processing of the molecular message must be one of the specifications of the receiver since it cannot rely on any post-processing of the transduced signals by an external macroscale device or a human controller. • Label-free detection: Detection of information carrying molecules, i.e., IMs, must be done based on their intrinsic characteristics, i.e., no additional molecular labeling procedure or preparation stage must be required. • Continuous operation: MC-Rx requires to observe the molecular channel continuously to detect the signal encoded into concentration, type/ratio/order or release time of molecules. Thus, the functionality of molecular antenna and the processing unit should not be interrupted. Since receptors are needed in the biorecognition unit for sensing target molecules, it is important to have re-usable receptors, i.e., they must return to their initial state after signal detection to be ready for the next channel use. • Energy efficiency: Due to limitations of nanomachines, the energy usage of the MC-Rx must be optimized. Additionally, as discussed in Section II-A, batteries may not be feasible solutions for long term activity of nanomachines, e.g., as an implanted device. Thus, the receiver may need to be designed with EH units to be energy self-reliance. • Biocompatibility and biodurability: One of the most important MC application areas is the life science, e.g., it promises diagnosis and treatment techniques for diseases caused by dysfunction of intrabody nanonetworks such as neurodegenerative diseases BIB002 . These in vivo applications dictate further requirements for the device. Firstly, it must not have any toxic effects on the living system. Moreover, the device needs to be flexible not to cause any injury to the living cells due to mechanical mismatches. Furthermore, there must not be any physiological reactions between device and environment and it must not cause immunological rejection. On the other hand, the physiological environment should not degrade the performance of the device with time. • Miniaturization: Lastly, to be integrated into a nanomachine, the MC-Rx must be built on micro/nanoscale components.