On the scalability limits of communication networks to the nanoscale

Nanosystems, integrated systems with a total size of a few micrometers, are capable of interacting at the nanoscale, but their short operating range limits their usefulness in practical macro-scale scenarios. Nanonetworks, the interconnection of nanosystems, will extend their range of operation by allowing communication among nanosystems, thereby greatly enhancing their potential applications. In order to integrate communication capabilities into nanosystems, their communication subsystem needs to shrink to a size of a few micrometers. There are doubts about the feasibility of scaling down current metallic antennas to such a small size, mainly because their resonant frequency would be extremely high (in the optical domain) leading to a large free-space attenuation of the radiated EM waves. In consequence, as an alternative to implement wireless communications among nanosystems, two novel paradigms have emerged: molecular communication and graphene-enabled wireless communications. On the one hand, molecular communication is based on the exchange of molecules among nanosystems, inspired by communication among living cells. In Diffusion-based Molecular Communication (DMC), the emitted molecules propagate throughout the environment following a diffusion process until they reach the receiver. On the other hand, graphene, a one-atom-thick sheet of carbon atoms, has been proposed to implement graphene plasmonic RF antennas, or graphennas. Graphennas with a size in the order of a few micrometers show plasmonic effects which allow them to radiate EM waves in the terahertz band. Graphennas are the enabling technology of Graphene-enabled Wireless Communications (GWC). In order to answer the question of how communication networks will scale when their size shrinks, this thesis presents a scalability analysis of the performance metrics of communication networks to the nanoscale, following a general model with as few assumptions as possible. In the case of DMC, two detection schemes are proposed: amplitude detection and energy detection. Key performance metrics are identified and their scalability with respect to the transmission distance is found to differ significantly from the case of traditional wireless communications. These unique scaling trends present novel challenges which require the design of novel networking protocols specially adapted to DMC networks. The analysis of the propagation of plasmonic waves in graphennas allows determining their radiation performance. In particular, the resonant frequency of graphennas is not only lower than in metallic antennas, but it also increases more slowly as their length is reduced to the nanoscale. Moreover, the study of parameters such as the graphenna dimensions, the relaxation time of graphene and the applied chemical potential shows the tunability of graphennas in a wide frequency range. Furthermore, an experimental setup to measure graphennas based on feeding them by means of a photoconductive source is described. The effects of molecular absorption in the short-range terahertz channel, which corresponds to the expected operating scenario of graphennas, are analyzed. Molecular absorption is a process in which molecules present in the atmosphere absorb part of the energy of the terahertz EM waves radiated by graphennas, causing impairments in the performance of GWC. The study of molecular absorption allows quantifying this loss by deriving relevant performance metrics in this scenario, which show novel scalability trends as a function of the transmission distance with respect to the case of free-space propagation. Finally, the channel capacity of GWC is found to scale better as the antenna size is reduced than in traditional wireless communications. In consequence, GWC will require lower transmission power to achieve a given performance target. These results establish a general framework which may serve designers as a guide to implement wireless communication networks among nanosystems

Pulse interspersing in static multipath chip environments for Impulse Radio communications

Communications are becoming the bottleneck in the performance of Chip Multiprocessor (CMP). To address this issue, the use of wireless communications within a chip has been proposed, since they offer a low latency among nodes and high reconfigurability. The chip scenario has the particularity that is static, and the multipath can be known a priori. Within this context, we propose in this paper a simple yet very efficient modulation technique, based on Impulse Radio-On–Off-Keying (IR-OOK), which significantly optimizes the performance in Wireless Network-on-Chip (WNoC) as well as off-chip scenarios. This technique is based on interspersing information pulses among the reflected pulses in order to reduce the time between pulses, thus increasing the data rate. We prove that the final data rate can be considerably increased without increasing the hardware complexity of the transceiver.Peer ReviewedPostprint (published version

Scalability of the channel capacity in graphene-enabled wireless communications to the nanoscale

Graphene is a promising material which has been proposed to build graphene plasmonic miniaturized antennas, or graphennas, which show excellent conditions for the propagation of Surface Plasmon Polariton (SPP) waves in the terahertz band. Due to their small size of just a few micrometers, graphennas allow the implementation of wireless communications among nanosystems, leading to a novel paradigm known as Graphene-enabled Wireless Communications (GWC). In this paper, an analytical framework is developed to evaluate how the channel capacity of a GWC system scales as its dimensions shrink. In particular, we study how the unique propagation of SPP waves in graphennas will impact the channel capacity. Next, we further compare these results with respect to the case when metallic antennas are used, in which these plasmonic effects do not appear. In addition, asymptotic expressions for the channel capacity are derived in the limit when the system dimensions tend to zero. In this scenario, necessary conditions to ensure the feasibility of GWC networks are found. Finally, using these conditions, new guidelines are derived to explore the scalability of various parameters, such as transmission range and transmitted power. These results may be helpful for designers of future GWC systems and networks.Peer ReviewedPostprint (author’s final draft

Exploring the physical channel of diffusion-based molecular communication by simulation

Diffusion-based molecular communication is a promising bio-inspired paradigm to implement nanonetworks, i.e., the interconnection of nanomachines. The peculiarities of the physical channel in diffusion-based molecular communication require the development of novel models, architectures and protocols for this new scenario, which need to be validated by simulation. With this purpose, we present N3Sim, a simulation framework for diffusion-based molecular communication. N3Sim allows to simulate scenarios where transmitters encode the information by releasing molecules into the medium, thus varying their local concentration. N3Sim models the movement of these molecules according to Brownian dynamics, and it also takes into account their inertia and the interactions among them. Receivers decode the information by sensing the particle concentration in their neighborhood. The benefits of N3Sim are multiple: the validation of channel models for molecular communication and the evaluation of novel modulation schemes are just a few examples.Peer ReviewedPostprint (author’s final draft

Wireless nanosensor networks using graphene-based nano-antennas

Postprint (published version

Diffusion-based channel characterization in molecular nanonetworks

Nanotechnology is enabling the development of devices in a scale ranging from one to a few hundred nanometers, known as nanomachines. How these nanomachines will communicate is still an open debate. Molecular communication is a promising paradigm that has been proposed to implement nanonetworks, i.e., the interconnection of nanomachines. Recent studies have attempted to model the physical channel of molecular communication, mainly from a communication or information-theoretical point of view. In this work, we focus on the diffusion-based molecular communication, whose physical channel is governed by Fick's laws of diffusion. We characterize the molecular channel following two complementary approaches: first, we obtain the channel impulse response, transfer function and group delay; second, we propose a pulse-based modulation scheme and we obtain analytical expressions for the most relevant performance evaluation metrics, which we also validate by simulation. Finally, we compare the scalability of these metrics with their equivalents in a wireless electromagnetic channel. We consider that these results provide interesting insights which may serve designers as a guide to implement future molecular nanonetworks.Peer ReviewedPostprint (published version

Diffusion-based channel characterization in molecular nanonetworks

Nanotechnology is enabling the development of devices in a scale ranging from one to a few hundred nanometers, known as nanomachines. How these nanomachines will communicate is still an open debate. Molecular communication is a promising paradigm that has been proposed to implement nanonetworks, i.e., the interconnection of nanomachines. Recent studies have attempted to model the physical channel of molecular communication, mainly from a communication or information-theoretical point of view. In this work, we focus on the diffusion-based molecular communication, whose physical channel is governed by Fick's laws of diffusion. We characterize the molecular channel following two complementary approaches: first, we obtain the channel impulse response, transfer function and group delay; second, we propose a pulse-based modulation scheme and we obtain analytical expressions for the most relevant performance evaluation metrics, which we also validate by simulation. Finally, we compare the scalability of these metrics with their equivalents in a wireless electromagnetic channel. We consider that these results provide interesting insights which may serve designers as a guide to implement future molecular nanonetworks.Peer Reviewe

Networking challenges and principles in diffusion-based molecular communication

Nanotechnology has allowed building nanomachines capable of performing simple tasks, such as sensing, data storage, and actuation. Nanonetworks, networks of nanomachines, will allow cooperation and information sharing among them, thereby greatly expanding the applications of nanotechnology in the biomedical, environmental,and industrial fields. One of the most promising paradigms to implement nanonetworks is diffusion-based molecular communication (DMC). In DMC, nanomachines transmit information by the emission of molecules that diffuse throughout the medium until they reach their destination. Most of the existing literature in DMC has focused on the analysis of its physical channel. In this work, the key differences of the physical channel of DMC with respect to the wireless electromagnetic channel are reviewed with the purpose of learning how they impact the design of networks using DMC. In particular, we find that the uniqueness of the physical channel of DMC will require revisiting most of the protocols and techniques developed for traditional wireless networks in order to adapt them to DMC networks. Furthermore, guidelines for the design of a novel network architecture for DMC networks, including fundamental aspects such as coding, medium access control, addressing, routing and synchronization, are provided

Positive pillar corrosion in the lead acid battery

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Physical channel characterization for medium-range nanonetworks using flagellated bacteria

Nano-networks are the interconnection of nano-machines and as such expand the limited capabilities of a single nano-machine. Several techniques have been proposed so far to interconnect nano-machines. For short dis- tances (nm-mm ranges), researchers are proposing to use molecular motors and calcium signaling. For long distances (mm-m), pheromones are envisioned to transport information. In this work we propose a new mechanism for medium-range communications (nm- m): agellated bacteria. This technique is based on the transport of DNA-encoded information between emitters and receivers by means of a bacterium. We present a physical channel characterization and a simulator that, based on the previous characterization, simulates the transmission of a DNA-packet between two nano-machines