Transmitter and Receiver Architectures for Molecular Communications: A Survey on Physical Design with Modulation, Coding and Detection Techniques <s> B. Communication Theoretical Performance Metrics <s> Biosensors based on silicon nanowires (Si-NWs) promise highly sensitive dynamic label-free electrical detection of biomolecules. Despite the tremendous potential and promising experimental results, the fundamental mechanism of electrical sensing of biomolecules and the design considerations of NW sensors remain poorly understood. In this paper, we discuss the prospects and challenges of biomolecule detection using Si-NW biosensors as a function of device parameters, fluidic environment, charge polarity of biomolecules, etc., and refer to experimental results in literature to support the nonintuitive predictions wherever possible. Our results indicate that the design of Si nanobiosensor is nontrivial and as such, only careful optimization supported by numerical simulation would ensure optimal sensor performance. <s> BIB001 </s> Transmitter and Receiver Architectures for Molecular Communications: A Survey on Physical Design with Modulation, Coding and Detection Techniques <s> B. Communication Theoretical Performance Metrics <s> * Limit of Blank (LoB), Limit of Detection (LoD), and Limit of Quantitation (LoQ) are terms used to describe the smallest concentration of a measurand that can be reliably measured by an analytical procedure. * LoB is the highest apparent analyte concentration expected to be found when replicates of a blank sample containing no analyte are tested. LoB = mean(blank) + 1.645(SD(blank)). * LoD is the lowest analyte concentration likely to be reliably distinguished from the LoB and at which detection is feasible. LoD is determined by utilising both the measured LoB and test replicates of a sample known to contain a low concentration of analyte. * LoD = LoB + 1.645(SD (low concentration sample)). * LoQ is the lowest concentration at which the analyte can not only be reliably detected but at which some predefined goals for bias and imprecision are met. The LoQ may be equivalent to the LoD or it could be at a much higher concentration. <s> BIB002 </s> Transmitter and Receiver Architectures for Molecular Communications: A Survey on Physical Design with Modulation, Coding and Detection Techniques <s> B. Communication Theoretical Performance Metrics <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> BIB003
In addition to the general performance metrics defined for EM communications, e.g., Signal-to-noise ratio (SNR), Bit error rate (BER), and mutual information, new performance metrics are needed to fully evaluate the functionality of an MC-Rx since molecules are used as IMs in MC. The most important performance metrics are summarized as follows. • Limit of detection (LoD): LoD is a well-known performance metric in biosensing literature, which shows the minimum molecular concentration in the vicinity of the biosensor needed for distinguishing between the existence and the absence of target molecules BIB002 . Since the input signal in MC-Rxs is a physical probability of information carriers, LoD corresponds to the sensitivity metric used for evaluating the performance of EM communication receivers, which indicates the minimum input signal power needed to generate a specified SNR at the output of the device. • Selectivity: This metric is defined based on the relative affinity of the biorecognition unit to the information molecules and interferer molecules BIB001 , which can be non-IMs in the medium or other type of IMs in case of MC system with multiple IMs such as MoSK. High selectivity, i.e., very lower probability of interfererreceptor binding compared to target molecule-receptor binding, is needed to uniquely detect the information molecules in the vicinity of the MC-Rx. • Operation range: The biorecognition unit does not provide infinite range of molecular concentration detection as it has finite receptor density. The response of the device can be divided into two regions, (i) the linear operation, which is the range of molecular concentration in the vicinity of the MC-Rx that does not lead to saturation of receptors, and (ii) the saturation region  . When the information is encoded into the concentration of molecules, the receiver must work in the linear operation region as the output of molecular antenna provides better information about changes in the molecular concentration. However, for other encoding mechanisms, e.g., MoSK, the receiver can work in both regions. • Molecular sensitivity: In addition to the aforementioned sensitivity metric that is mapped to LoD for MC-Rxs, a molecular sensitivity can also be defined for an MCRx. This metric indicates the smallest difference in the concentration of molecules that can be detected by an MC-Rx BIB001 . It is of utmost importance when the information is encoded in molecular concentration. The metric can be defined as the ratio of changes in the output of the molecular receiver antenna to changes in the molecular concentration in the vicinity of the MC-Rx when the device performs in the linear operation region. • Temporal resolution: This metric is defined to evaluate the speed of sampling the molecular concentration by the receiver. Since the electrical processes are much faster than molecular processes, it is expected that the diffusion and binding kinetics limit the temporal resolution. Thus, biorecognition unit should be realized in transport-limited manner to detect all the messages carried by molecules into the vicinity of the MC-Rx, i.e., the binding kinetics should not be a limiting factor on the sampling rate BIB003 .