A Survey on Modulation Techniques in Molecular Communication via Diffusion

This survey paper focuses on modulation aspects of molecular communication, an emerging field focused on building biologically-inspired systems that embed data within chemical signals. The primary challenges in designing these systems are how to encode and modulate information onto chemical signals, and how to design a receiver that can detect and decode the information from the corrupted chemical signal observed at the destination. In this paper, we focus on modulation design for molecular communication via diffusion systems. In these systems, chemical signals are transported using diffusion, possibly assisted by flow, from the transmitter to the receiver. This tutorial presents recent advancements in modulation and demodulation schemes for molecular communication via diffusion. We compare five different modulation types: concentration-based, type-based, timing-based, spatial, and higher-order modulation techniques. The end-to-end system designs for each modulation scheme are presented. In addition, the key metrics used in the literature to evaluate the performance of these techniques are also presented. Finally, we provide a numerical bit error rate comparison of prominent modulation techniques using analytical models. We close the tutorial with a discussion of key open issues and future research directions for design of molecular communication via diffusion systems.Comment: Preprint of the accepted manuscript for publication in IEEE Surveys and Tutorial

Normal Inverse Gaussian Approximation for Arrival Time Difference in Flow-Induced Molecular Communications

In this paper, we consider molecular communications in one-dimensional flow-induced diffusion channels with a perfectly absorbing receiver. In such channels, the random propagation delay until the molecules are absorbed follows an inverse Gaussian (IG) distribution and is referred to as first hitting time. Knowing the distribution for the difference of the first hitting times of two molecules is very important if the information is encoded by a limited set of molecules and the receiver exploits their arrival time and/or order. Hence, we propose a moment matching approximation by a normal inverse Gaussian (NIG) distribution and we derive an expression for the asymptotic tail probability. Numerical evaluations showed that the NIG approximation matches very well with the exact solution obtained by numerical convolution of the IG density functions. Moreover, the asymptotic tail probability outperforms state-of-the-art tail approximations.Comment: This paper has been submitted to IEEE Transactions on Molecular, Biological and Multi-Scale Communication

On the Impact of Transposition Errors in Diffusion-Based Channels

In this work, we consider diffusion-based molecular communication with and without drift between two static nano-machines. We employ type-based information encoding, releasing a single molecule per information bit. At the receiver, we consider an asynchronous detection algorithm which exploits the arrival order of the molecules. In such systems, transposition errors fundamentally undermine reliability and capacity. Thus, in this work we study the impact of transpositions on the system performance. Towards this, we present an analytical expression for the exact bit error probability (BEP) caused by transpositions and derive computationally tractable approximations of the BEP for diffusion-based channels with and without drift. Based on these results, we analyze the BEP when background is not negligible and derive the optimal bit interval that minimizes the BEP. Simulation results confirm the theoretical results and show the error and goodput performance for different parameters such as block size or noise generation rate.Comment: This paper has been submitted to IEEE Transactions on Communication

Adaptive detection and ISI mitigation for mobile molecular communication

Current studies on modulation and detection schemes in molecular communication mainly focus on the scenarios with static transmitters and receivers. However, mobile molecular communication is needed in many envisioned applications, such as target tracking and drug delivery. Until now, investigations about mobile molecular communication have been limited. In this paper, a static transmitter and a mobile bacterium-based receiver performing random walk are considered. In this mobile scenario, the channel impulse response changes due to the dynamic change of the distance between the transmitter and the receiver. Detection schemes based on fixed distance fail in signal detection in such a scenario. Furthermore, the intersymbol interference (ISI) effect becomes more complex due to the dynamic character of the signal which makes the estimation and mitigation of the ISI even more difficult. In this paper, an adaptive ISI mitigation method and two adaptive detection schemes are proposed for this mobile scenario. In the proposed scheme, adaptive ISI mitigation, estimation of dynamic distance and the corresponding impulse response reconstruction are performed in each symbol interval. Based on the dynamic channel impulse response in each interval, two adaptive detection schemes, concentration-based adaptive threshold detection (CATD) and peak-time-based adaptive detection (PAD), are proposed for signal detection. Simulations demonstrate that, the ISI effect is significantly reduced and the adaptive detection schemes are reliable and robust for mobile molecular communication

Diffusion Based Anti-Interference Joint Modulation in MIMO Molecular Communication

Molecular communication(MC) is a significant technology in the field of nano-biology, which uses molecules as message carriers to transmit information. Diffusion channel model is the most common channel model base on Brownian motion in molecular communication since molecules can diffuse to the destination without the need of extra energy supply. However, the random Brownian motion brings high delay and uncertainty to the communication process and thus modulation methods are required to improve the communication performance. The molecular communication system in the SISO (Single Input Single Output) scenario will be seriously affected by ISI (Inter Symbol Interference). In MIMO(Multi-Input Multi-Output) scenario, since there are multiple transmitters and receivers, in addition to ISI, there will be ILI (Inter Link Interference) as well. At present, most modulations are based on the concentration, type, time and space of molecules and only focus on SISO scenario. In this study, inspired by the MoSK(Molecule Shift Keying) modulation method, we proposed a new joint modulation method for MIMO communication in order to minimize the effect of ISI and ILI. Numerical results show that compared with the current modulation scheme, the proposed scheme allows the MIMO system achieve better BER(Bit error rate) performance and transmission rate

Dendritic neurotransmitter release and its modulation in accessory olfactory bulb circuits

Dendrites are classically regarded as the brain's "listeners," while neuronal output is thought to be the exclusive privilege of the axon. Although we now appreciate the complexity of dendritic integration, the role of dendrites as output structures has received less attention. This is becoming an increasingly important topic, as the list of cell types with release competent dendrites continues to grow. One boon of coupling dendritic activity to dendritic release is that outputs from a single neuron - typically thought to occur from fixed sites with stereotyped dynamics - may occur for signals of varying spatial extent, timecourse, and release efficacy. In essence, dendritic output may "inherit" the same diversity characteristic of events in excitable dendrites. Here I studied dendritic transmitter output and its modulation in cells of the accessory olfactory bulb - a CNS structure critical for processing species-specific chemical signals called pheromones. Because of the stereotypy of its inputs, the prevalence of dendritic transmitter release from its cells, and its well-defined outputs, the AOB offers a superb model system for studying the integrative and output properties of dendrites. I first characterized basic excitable properties of the apical dendrites of mitral cells (the principal AOB neurons), and observed that they conduct non-decremental action potentials (APs). In addition to APs, these dendrites were also found to support compartmentalized, synaptically-evoked calcium spikes. Both APs and local spikes were triggers of dendritic glutamate release and feedback inhibition, suggesting that neuronal output can be flexibly routed to particular populations of postysynaptic cells. I next asked whether the relative efficacy of particular dendritic events as triggers of transmitter release can be altered, as this could provide an additional level of control over single neuron output. I found that metabotropic glutamate receptors (mGluRs) play a key role in controlling dendritic output from AOB mitral cells and an obligatory role in concomitant feedback inhibition. This work culminates with the demonstration of a new principle of neuronal signaling: the ability of mGluRs to gate a transition between phasic and tonic dendritic transmitter release. Taken in total, these results extend our understanding of how the outputs from single neurons are controlled

INTEGRATED SINGLE-PHOTON SENSING AND PROCESSING PLATFORM IN STANDARD CMOS

Practical implementation of large SPAD-based sensor arrays in the standard CMOS process has been fraught with challenges due to the many performance trade-offs existing at both the device and the system level [1]. At the device level the performance challenge stems from the suboptimal optical characteristics associated with the standard CMOS fabrication process. The challenge at the system level is the development of monolithic readout architecture capable of supporting the large volume of dynamic traffic, associated with multiple single-photon pixels, without limiting the dynamic range and throughput of the sensor. Due to trade-offs in both functionality and performance, no general solution currently exists for an integrated single-photon sensor in standard CMOS single photon sensing and multi-photon resolution. The research described herein is directed towards the development of a versatile high performance integrated SPAD sensor in the standard CMOS process. Towards this purpose a SPAD device with elongated junction geometry and a perimeter field gate that features a large detection area and a highly reduced dark noise has been presented and characterized. Additionally, a novel front-end system for optimizing the dynamic range and after-pulsing noise of the pixel has been developed. The pixel is also equipped with an output interface with an adjustable pulse width response. In order to further enhance the effective dynamic range of the pixel a theoretical model for accurate dead time related loss compensation has been developed and verified. This thesis also introduces a new paradigm for electrical generation and encoding of the SPAD array response that supports fully digital operation at the pixel level while enabling dynamic discrete time amplitude encoding of the array response. Thus offering a first ever system solution to simultaneously exploit both the dynamic nature and the digital profile of the SPAD response. The array interface, comprising of multiple digital inputs capacitively coupled onto a shared quasi-floating sense node, in conjunction with the integrated digital decoding and readout electronics represents the first ever solid state single-photon sensor capable of both photon counting and photon number resolution. The viability of the readout architecture is demonstrated through simulations and preliminary proof of concept measurements