Theses supervised by Prof. Dr. Özgür Barış Akan
26 theses · Koç University
N4Sim: The first nervous nanonetwork simulator with synaptic molecular communications
The unconventional nature of molecular communication necessitates contributions from a host of scientific fields making the simulator design for such systems to be quite challenging. The nervous system is one of the largest and most important nanonetworks of the body. Several molecular and nano communication simulators exist in literature along with a few neural network simulators, however, most exist- ing simulators are neither specific for the nervous system nor they ignore synaptic diffusion because of the computational complexity required to model it. Addition- ally, information and communication theoretical (ICT) analysis of the system is not directly supported by existing neural network simulators. In this work, we present and describe Neural NaNoNetwork Simulator, N4Sim, which can resolve the issues in existing simulators. We describe key components of the simulator and methods to solve the synaptic communication in a fast and efficient manner. Our results are comparable to those achieved by Monte Carlo simulations for the synapse while using a fraction of time and processing resources. The presented simulator opens a large set of design options for applications in nervous system.
Communication theoretical modeling and analysis of neuronal communication with synaptic plasticity
Emergence of nanoscale devices and their applications mandates the facilitation of communication between these devices, and hence, the development of nanonetworks, to overcome their computational and power limitations owing to their size. The nanonetworks need novel communication paradigms since they are fundamentally different from the traditional communication networks. The human body is a large-scale network of molecular nanonetworks composed of billions of nanomachines, i.e., cells, where molecules are used to encode, transmit and receive information. The largest and the most vital intra-body nanonetwork is the nervous nanonetwork. Thus, the aim of this thesis is to investigate the nervous nanonetwork from information and communication theoretical perspective, to lay down the foundations of a novel bio-inspired communication paradigm for nanonetworks. We focus on the communication theoretical analysis of single-input-single-output (SISO) as well as multiple-input-single-output (MISO) neuro-spike communication channels, considering memory and metabolic energy constraints. Synaptic plasticity is a ubiquitous phenomenon in central as well as peripheral nervous systems and is associated with memory and learning new behaviors and skills. Thus, we further aim to analyze the neuro-spike communication incorporating the plasticity. The results obtained from this study would allow us to select optimal parameters to realize effıcient bio-inspired nanonetworks. Moreover, since neurodegenerative diseases such as Alzheimer's Disease, Parkinson's Disease and Multiple Sclerosis are caused by the malfunction of the sub-processes of the neuro-spike communication, these results can be compared with the results obtained from diseased synapses to develop the future ICT-inspired diagnostic and treatment techniques for neural disorders.
Transceiver architectures and physical layer techniques for unconventional communications in the internet of everything
This thesis explores the emerging Internet of Everything (IoE) framework, a transformative paradigm in Information and Communication Technologies (ICT) that extends human connectivity beyond traditional boundaries. The IoE conceptualizes a comprehensive network architecture that mirrors the complexity of interconnected systems in nature, integrating a diverse array of ICT technologies across different scales and environments. This advancement presents numerous opportunities but also poses significant challenges, particularly in aligning communication technology with the IoE's complex and dynamic nature. The thesis considers the challenges and the solutions at the physical layer/device level linked to unconventional communications essential for realizing the IoE. It focuses on two emerging communication paradigms: Molecular communications (MC) and Terahertz (THz)-band communications. These paradigms are key to expanding beyond the limitations of existing networks and are instrumental in actualizing the IoE. A comprehensive exploration is conducted into the challenges and potential solutions associated with these unconventional communications. The thesis first introduces the universal IoE transceiver, a novel device concept for integrating heterogeneous networks within the IoE framework. It discusses transceiver architectures based on graphene and related materials, which are promising for unconventional communication modalities, especially in the context of the Internet of Bio-Nano Things (IoBNT), an emerging subset of the IoE. The thesis further investigates advanced physical layer techniques for practical MC systems and explores effective solutions for facilitating THz-band communication in space. These in-depth studies aim to enhance connectivity and communication on a universal scale, shaping the future landscape of the IoE. The work presented provides pathways toward mitigating the complexities inherent in unconventional communications, thereby contributing to the advancement of IoE technologies.
Perceptual Shift Keying: A Novel Modulation Technique for Odor-Based Molecular Communication
Odor-based molecular communication (OMC) has emerged as an innovative paradigm with substantial potential across diverse application domains. This thesis introduces Odor Perceptual Shift Keying (OPSK), a novel modulation technique that encodes information by strategically shifting perceptual dimensions of odor molecules, such as pleasantness, intensity, and edibility. OPSK's effectiveness is theoretically demonstrated through comprehensive analyses of system parameters, yielding promising results in terms of bit error rate and symbol rate across distances ranging from millimeters to kilometers. To bridge theoretical advancements with practical realization, the development of a macro-scale experimental OMC end-to-end testbed was contributed to, facilitating odor transmission using Arduino-controlled odor reservoirs, air compressors, and precise airflow management within plexiglass channels, along with sensor-based detection at the receiver using a Bosch BME688 Development Kit. Furthermore, to illustrate potential practical applications, interplant communication was explored, demonstrating how plants interact through molecular signals and symbiotic relationships with mycorrhizal fungi. A novel architecture leveraging these natural interactions for energy harvesting via glucose extraction was proposed and validated through comprehensive analyses. Collectively, these contributions establish OPSK as a viable and versatile molecular communication method, significantly expanding the applicability of OMC systems in both engineered and natural contexts.
Data compression and run-length-limited ISI-mitigation (RLIM) coding for molecular communication
Molecular Communication (MC) enables information transfer at the nanoscale by encoding messages into sequences of released molecules, but its practical deployment is hindered by two fundamental constraints: the high cost of molecule releases and severe inter-symbol interference (ISI) arising from residual molecules in the diffusion channel. This thesis develops coding techniques to tackle each challenge. We first introduce source‐coding schemes that reduce both average code length and molecule usage. Building on an MC-adapted Huffman baseline (MoHuffman), we propose Optimized Molecular Prefix Coding (MoPC) to select a prefix codebook with minimal expected length and fewest number of 1-symbols. To push compression further, we derive Molecular Arithmetic Coding (MoAC) using an existing constrained arithmetic coding construction scheme and show its superior efficiency over substitution arithmetic coding (SAC), our different adaptation of arithmetic source coding to MC. Finally, we design Molecular Arithmetic with Prefix Coding (MoAPC) to ensure unique decodability under finite-precision arithmetic. Using two nucleotide alphabets, we then demonstrate that MoAPC has a better compression ratio than MoPC. Through MC simulations, the effectiveness of the proposed methods is also shown. To mitigate ISI at the channel coding level, we develop an infinite family of Run-Length-Limited ISI-Mitigation (RLIM) codes with a corresponding built-in error correction algorithm. We then demonstrate, via binomial and diffusion channel simulations, that RLIM codes reduce bit-error rate compared to prominent coding schemes. Together, these contributions lay a comprehensive foundation for reliable and efficient diffusion-based Molecular Communication.
Information and communication theoretical modeling and analysis of the gut-brain axis
The gut-brain axis (GBA) represents one of the most sophisticated and crucial communication networks in the human body. However, a quantitative understanding of its signaling mechanisms has remained elusive, as conventional approaches fail to capture the inherently stochastic, nonlinear, and multi-scale nature of intra-body communication. The most promising paradigm to address these challenges is Molecular Communication (MC). Understanding biological signaling from an information and communication theoretical perspective provides insight into the fundamental dynamics of these systems. Therefore, this thesis applies MC principles to the GBA to establish a comprehensive and quantitative communication framework. Building on this objective, the thesis constructs a multi-scale understanding of the GBA through a deliberate progression from a foundational single channel to a complete, bidirectional communication network. The research first develops a channel model for the propagation of a single microbial metabolite (p-cresol), deriving its impulse response and linking gut dysbiosis to a neurological outcome. It then advances the analysis to a complete end-to-end model of molecular-to-neural communication, modeling the short-chain fatty acid (SCFA)-driven vagal nerve pathway and quantifying its information-theoretic performance. Finally, the work culminates in a novel system-level model of the bidirectional communication within GBA that incorporates closed-loop feedback between the hypothalamic-pituitary-adrenal (HPA) axis, immune system, and gut barrier. This framework is used to analyze the system's transition into a pathological state and quantify its corresponding loss of channel capacity. Collectively, the developed communication framework provides the tools to unravel the fundamental signaling mechanisms within the GBA, allowing for a detailed analysis of how signaling disruptions contribute to disease progression. This in-depth, quantitative understanding creates a foundation for a new generation of medical technologies, providing a roadmap for ICT-inspired diagnostic tools and therapeutic strategies to detect and repair communication failures. Furthermore, it lays the essential theoretical groundwork for future Internet of Bio-Nano Things (IoBNT) applications to restore healthy information flow within the body.
Molecular communication-inspired particle collector-transmitter (PaCoT) for heavy metal removal from human circulatory system
This study proposes a novel molecular communication (MC)-inspired nanomachine, the PArticle COllector-Transmitter (PaCoT), designed for intrabody detection and removal of toxic heavy metal particles. PaCoT detects, collects, and transports these particles from the bloodstream to release sites, such as lymphatic capillaries, before they reach vital organs. The system incorporates key physical parameters and operates through particle reception, storage, and release mechanisms. Reception is modeled via ligand–receptor binding reactions as a continuous-time Markov process (CTMP), where metallothionein proteins serve as receptors and heavy metals (e.g., Zn, Pb, Cd) act as ligands. Toxicity is detected by estimating heavy metal concentration ratios based on receptor binding durations in the presence of interferers and multiple heavy metal types. Captured particles are stored in a liquid-filled chamber within PaCoT and released using a single-disc viscous micropump for advection, combined with Brownian motion for diffusion. PaCoT's performance is evaluated through MATLAB simulations, focusing on toxicity detection error probability, particle release time, and energy consumption.
Nano-nesnelerin internetinde moleküler haberleşme için pratik alıcı mimarilerinin geliştirilmesi
This thesis aims to bridge the gap between theoretical approaches and practical receiver architectures in the field of Molecular Communication (MC). Within this framework, it focuses on the development of mechanical transduction–based and bio-inspired receiver architectures for the Internet of Nano Things (IoNT) and their integration within the vision of the Internet of Everything (IoE). To this end, an MC receiver based on a Flexure-FET (flexure-sensitive field-effect transistor) biosensor is proposed. By exploiting mechanical transduction, the receiver achieves high-sensitivity detection of both charged and neutral molecules. Building on this capability, the first practical implementation of Weight Shift Keying (WSK) modulation is introduced, in which information is encoded through variations in molecular weight. Analytical modeling and numerical analyses confirm its effectiveness under biologically relevant interference conditions, demonstrating the feasibility of mechanical transduction–based MC. A competitive binding framework is applied to model receptor–ligand interactions and molecular interference, improving both system reliability and molecular selectivity. This framework accounts for multi-ligand dynamics in complex biochemical communication channels. In addition, a cylindrical nanowire array receiver design is proposed, integrating distributed electromechanical coupling and geometrically tunable properties into the MC receiver for enhanced scalability and performance. In the final stage, the MC framework is revisited within an odor-based context. In this approach, odor molecules serve as information carriers, broadening the scope and applicability of MC to more tangible and perceptual domains. Guided by the vision of the Internet of Everything (IoE), this framework establishes a communication bridge that spans from molecular signal detection at the micro/nanoscale to higher-level sensory and cognitive processes, paving the way for the evolution of human-centered and intelligent communication networks. Throughout this thesis, the architectural developments extending from the mechanically transducing receiver to the competitive binding model and the nanowire array design progressively enhance detection sensitivity, reliability, and physical realizability. The integration of the competitive binding framework and the cylindrical nanowire array structure lays the groundwork for future functional receiver architectures in odor-based MC. Overall, the proposed models and architectures provide a foundation for practical, scalable, and biocompatible MC systems, contributing to the advancement of next-generation adaptive and interconnected networks envisioned under the IoE.
Bilişsel radyo ağlarında tayf-bilinçli ve güvenilir dağıtık algılama
The ever increasing demand for wireless communication technologies causes spectrum scarcity and inspires researchers to envision the dynamic spectrum access techniques, i.e., cognitive radio, for efficient utilization of spectrum. Wireless sensor networks (WSN) have been considered as operating at unlicensed bands, however, sensor nodes can access licensed spectrum opportunistically with incorporation of cognitive radio capability. Sensor nodes equipped with cognitive radio emerges a new distributed sensing paradigm, i.e., Cognitive Radio Sensor Networks (CRSN). CRSN alleviates spectrum scarcity via enabling access to and distributed sensing operation over licensed bands. The unique characteristics and research challenges posed by CRSN call for novel networking solutions tailored to realize reliable and energy-efficient distributed sensing.The objective of this research is to design, develop and analyze new advanced communication schemes for reliable and energy-efficient distributed sensing in CRSN.More specifically, a comprehensive performance evaluation of existing transport protocols is performed for reliability and congestion control in CRSN. Delay-sensitive and multimedia communication in CRSN is investigated for various smart grid environments. Furthermore, the spectrum-aware and energy-adaptive reliable transport (SERT) protocol for event delivery is first proposed for CRSN. Next, a new spectrum hole assignment for reliable estimation (SHARE) scheme is proposed to achieve reliable local estimation at actor and reach global consensus among actor nodes. The analysis of dedicated radio utilization for spectrum handoff and efficiency is presented for the cognitive radio networks. Moreover, spectrum-aware and cognitive sensor networks (SCSN) are introduced to address the unique challenges of the smart grid environments for distributed sensing. Finally, Spectrum-aware Underwater Networks are investigated to increase achievable capacity under the limited availability and harsh conditions of the underwater acoustic spectrum.
En az enerjili kanal ve ağ kodlaması ve nano boyutta haberleşme üzerine uygulamaları
Channel coding, as indicated by Claude E. Shannon, is mostly used to achieve the capacity, by means of introducing redundancy to combat the effects of noise. In this thesis, an energy minimizing novel channel code (MEC) with controllable reliability is proposed for the first time. The motivation stems from the severe energy constraints of nano communications. Due to their tiny size, nanodevices can only supply a limited amount of energy. The need to optimize communication techniques for minimum energy includes the development of a novel channel code that provides reliability, while keeping the transmitter energy at minimum. We develop minimum energy channel code (MEC), which uses the idea of increasing the frequency of the modulation state that requires less energy. On-off keying (OOK) modulation is the simplest of such techniques and assumed to be the underlying modulation throughout the thesis. MEC provides the desired reliability with varying delay, when source set cardinality is less than the inverse of symbol error probability. The proposed channel code is shown useful in nanosensor networks. The performance of MEC is also evaluated considering the random interference due to multiple uncoordinated users in the ad-hoc nanonetworks. The theoretical maximum node density limit in an ad-hoc nanonetwork with reliable communications between the nodes is derived. Investigating delay via varying codeword length, rate-delay-energy tradeoffs with MEC are analyzed. Lastly, for the first time in the literature, network codes that minimize energy is developed in network coding nodes with two incoming edges. To minimize the overall network energy in in-two networks, each node is assumed to employ MEC with OOK. Therefore, MENC provides the best mapping between input edges and output edge of the coding node, that minimizes the average energy at the output of the coding node, by minimizing the average weight.
Heterojen nano-ölçekli haberleşme kanallarının bilgi ve iletişim kuramsal modellemesi, tasarımı ve analizi
Nanoscale communication between nanodevices is a novel and interdisciplinary concept including nanotechnology, biotechnology and communication technology. The construction of nanonetworks by interconnecting nanodevices expands the capabilities of single nanodevices by means of cooperation between them. In this thesis, we first investigate the nanoscale molecular communication channel between cardiomyocytes, i.e., Gap Junction (GJ) communication channel, from an information theoretical perspective. In addition, we use the GJ communication model to establish relations between cardiac diseases and GJ communication parameters for diagnosis and treatment of cardiac diseases, which is promising for future nanomedicine and bio-inspired nanoscale communication applications. Next, we present several receiver designs for diffusion-based molecular communication which is very prone to intersymbol interference (ISI) due to residual molecules emitted previously. Furthermore, the stochastic nature of the molecule movements adds a signal dependent noise to the diffusion-based molecular communication. We introduce optimal sequence detection and channel equalization methods to mitigate ISI and signal dependent noise, which arise in the diffusion-based molecular communication. Afterwards, we introduce a novel nanoscale wireless communication technique: Wireless Nanoscale Magneto-Inductive (WNMI) communication in which the magnetic coupling between nanocoils is used to form a wireless communication channel. Then, we investigate the WNMI communication channel to reveal its communication capabilities using information theory. The numerical results reveal that the WNMI communication stands as a promising solution to nanoscale communication between nanodevices. Finally, we present another novel and radically different nanoscale communication method: Nanoscale Heat Communication (NHC) in which the heat transfer via diffusion of the thermal energy is used for communication at the nanoscale. In addition, we present an information theoretical analysis of the NHC channel to find its capacity.
Molekül çeşitliliğine dayalı nanoölçekli haberleşme kanalları üzerine bilgi kuramsal bir inceleme
Molecular communication is a promising technique to establish communication at nanoscale in which molecules are used to carry messages between nanomachines. It has many applications areas such as environmental applications, which include water and air pollution control, industrial applications, which include development of intelligent materials, nano-processors and nano-memory, and biomedical applications, which are drug delivery, disease diagnosis&treatment and health monitoring. In this thesis, we introduce a new model for molecular communication which exploits molecule diversity. An information theoretical analysis of this channel is conducted to investigate the rate-delay trade-o , the capacity and the bit error rate. Our aim in this thesis is to nd the feasible conditions and techniques to realize a molecular communication system. Furthermore, we derived analogies between the conventional electromagnetic communications and the emerging molecular communication elds to exploit the techniques used in conventional networks such as network coding and forward error correction for optimizing the performance of molecular networks.
Förster rezonans enerji transferi (FRET) tabanlı nano-haberleşme
Nanoscale communication is a novel and quite interdisciplinary research area which aims to design and develop communication networks among nano-size machines to extend their limited capabilities for groundbreaking biomedical, industrial and environmental applications. In this thesis, we propose and investigate a novel nanoscale wireless communication method based on a physically realizable phenomenon, F örster Resonance Energy Transfer (FRET) which is observed among fluorescent molecules such as semiconductor nanoparticles and organic dyes. Based on the well-established theory of FRET, we first information theoretically model FRET-based point-to-point communication channel between a single pair of fluorophore-based nanomachines with single-exciton transmission scheme. Furthermore, we analyze the performance of FRET-based point-to-point and broadcast nanoscale communications with multi-exciton transmission scheme performing realistic Monte Carlo simulations. We also propose a long range nanoscale communication channel based on multi-step FRET. We develop electrically and chemically controllable information routing techniques that are applicable to FRET-based nanonetworks. Moreover, we analyze FRETbased mobile molecular nanonetworks deriving analytical models for FRET-based mobile ad hoc molecular nanonetworks (FRET-MAMNET) and FRET-based mobile molecular sensor/actor nanonetworks (FRET-MSAN). Lastly, we perform an experiment in which we achieve to transfer data with the transmission rates of 50, 150 and 250 kbps through the mixture of Fluorescein and Rhodamine B as the donor/acceptor pair. This experiment is one of the rst physical realizations of communications at nanoscale.
Bilişsel radyo algılayıcı ağlarda kümeleme, ağ kodlaması ve kapsama alanı azamileştirilmesi
The spectrum scarcity challenge is a natural consequence of increasing demand for wireless communication. This situation has triggered the use of opportunistic spectrum access schemes in wireless communications. The key technology addressing this challenge and enabling opportunistic spectrum access is cognitive radio. Wireless sensor network (WSN) suffers from the spectrum scarcity problem due to the fixed frequency assignment policy. Cognitive radio stands as a promising solution to this problem in WSNs. Wireless sensor nodes with cognitive radio capability can access different spectrum bands dynamically. This defines a new sensor networking paradigm, i.e., Cognitive Radio Sensor Networks (CRSN). The unique characteristics of CRSN necessitates energy-efficient and spectrum-aware solutions. In this thesis, we first propose a spectrum-aware clustering protocol for CRSN. We form non-isolated clusters between event and sink in accordance with event-driven communication nature. Simulation results show that our protocol is more energy-efficient than other protocols in literature. Next, we investigate the effect of network coding in CRSN. Network Coding is a novel technique enabling encoding operation instead of store-and-forward approach. The advantages and disadvantages of using network coding are presented. Finally, we consider wireless networked control system consisting of separate cognitive radio sensor subnetworks. The system state is estimated using Kalman filter. We find critical packet arrival probability for bounded expected state estimation covariance and obtain the maximum total coverage area of CRSN with maximum cost-efficiency.
Kuantum haberleşmede öncelik ve depolama
Quantum Computation and Quantum Communication are emerging fi elds of science, in which principles of quantum mechanics are exploited to reach extraordinary results that may even seem counter-intuitive. However, the power of quantum computers are limited due to the fact that qubits cannot be stored or recalled as bits due to the no cloning theorem. In the rst part of this thesis we focus on the problem of qubit storage. First, we propose the essential requirements for a good qubit storage system, which are access delay complexity, circuit complexity, maximum connectivity and use of ancillary qubits. Later, we introduce diff erent possible qubit storage systems fi rst as building blocks and then for large systems and comment on the feasibility of constructing these systems. As another consequence of no cloning theorem, in quantum communications, a corrupt data cannot be retransmitted. Therefore, we may have to use corrupt data to its fullest. Moreover, since it is not yet possible to read and measure qubits as readily as bits, sometimes it may be necessary to evaluate which qubits should be handled first. In the second part of this thesis, in order to quantify the damage on a corrupt data and to prioritize our qubit reading, we propose a novel measure of bitwise information priority. We simulate our results in classical block codes in GF(2).
Rescue: Deprem kurtarma uygulaması için pasif kablosuz sensör ağ mimarisi
Deprem gibi bir afet zamanında, enkaz altında kalmış insan sayısını bilmek hayati onem taşır. Bu problemi ele almak için bu çalışmada RESCUE - Kablosuz Geri Saçılım Temelli Afet Yönetimi Sistemi önerilmektedir. Bilgimiz çercevesinde, bu sistem, çökmüş binaların altında kalmış insan sayısını belirlemek için afet yönetimi sürecine uygulanmış olan ilk çozümdür. RESCUE, yıkıntı altında kalmış toplam insan sayısını belirlemek için ozel tasarlanmış RFID okuyucu ve sensörlerden oluşmaktadır. Deprem anında bina içerisinin resmini çeken bir kameraya sahip olan pasif kablosuz sensör dügümleri bina yapım zamanı binanın içine kurulur . Deprem sonrasında, yıkıntının dışarısında bulunan okuyucu geri sacılımlı haberleşme aracılığı ile sensörlerin icindeki göruntü bilgisini okur. Bu resimler, depremin hemen oncesinde binanın içinde bulunan insan sayısını hesaplamak için kullanılır. Bu çalısmada RESCUE okuyucu ve sensörleri arasındaki pasif haberleşme kanalının analizi yapılmaktadır. Bunun icin pasif kablosuz haberleşme kanalı modellenmekte ve pasif RFID simülatörü kullanılarak simülasyonlar gerçekleştirilmektedir. Ayrıca, çıkarılmış kanal modelini doğrulamak için yapılan deneysel calışmanın sonucları sunulmaktadır. Deney sonuçları, RESCUE'nın nispeten kısa sürüde yüksek performansla veri toplanmasını sağladığını ve bu nedenle, umut vadeden bir afet yönetimi sistemi olduğunu göstermektedir.
Kablosuz Sosyal Sensör Ağlar
Online Social Networks (OSNs) have recently become the essential means of communication, networking and entertainment. One of the prominent applications of OSNs has originated from their frequent use during major events, known as social sensing, which is the utilization of the information shared in OSNs to estimate an observed yet unknown phenomenon. In this thesis, we analytically investigate social sensing capabilities of OSNs. To this end, we introduce Wireless Sensor Network (WSN) paradigm, Wireless Social Sensor Network (WSSN) and explore the WSSNs within the most widely used OSNs, i.e., Twitter and Facebook. First, we develop communication theoretical models for the mechanisms of information propagation in Twitter and then analytically model the social sensing with Twitter. The accuracy of the estimated signal is investigated with mean square error analysis. Later, using a simple observation model by considering the features of Twitter, i.e., tweet and retweet, we extend the performance analysis (in terms of mean square error) of social sensing by comparing with fundamental estimators in classical and Bayesian estimation theory for various factors such as user behavior, number of people participating to social sensing and geotag use percentage. Lastly, we model and investigate the main social sensing mechanism in Facebook, i.e., Facebook Comment Thread Network (FCTN). By developing an analytical model for user observations in CTN, we analyze the reliability of social sensing with Facebook CTN for varying user behaviors and relationships, event characteristics, Facebook features and network size. The results indicate that, in addition to network conditions, the reliability of social sensing, i.e., the accuracy of the estimated signal, is affected by the features of the OSN, user behavior patterns and source event characteristics.
Gelecek nesil heterojen ağlar için bilişsel iletişim teknikleri
Recently, cognitive radio emerged as a promising solution to spectrum scarcity problem. Cognitive radio introduces appealing features such as improved spectrum utilization and increased communication quality by making use of opportunistic and dynamic spectrum access. However, these capabilities impose additional tasks like spectrum sensing and spectrum management. In the following years, cognitive radio technology will inevitably be used in various network platforms, such as wireless sensor networks, smart grid, machine-to-machine communications, public protection and disaster relief networks, and vehicular networks. In each of the areas where cognitive radio is to be introduced, optimal techniques that address the trade-off between additional capabilities and requirements of cognitive radio must be developed. The aim of this thesis is to intelligently exploit the characteristic of various network platforms to develop cognitive communication solutions tailored specifically to each of them. For the areas mentioned earlier, we provide a comprehensive discussion of how cognitive radio technology may be applied to alleviate the problems, mainly related to spectrum scarcity. Then we present solutions related to spectrum sensing, throughput maximization and achievable reliability for cognitive radio sensor networks as applied to some of these communication systems. Specifically, we present our solutions for a two-stage spectrum sensing technique developed for resource constrained cognitive radio sensor networks. The first stage is to determine roughly a set of channels which are more likely to be available. In the second stage, a more accurate fine sensing scheme is used to locate vacant channels with higher precision. We also present our analysis on throughput maximization for electromagnetic energy harvesting cognitive radio networks, as well as an analysis of achievable reliability under opportunistic spectrum access for cognitive sensor-actor networks in smart grid. We target smart grid specifically for the later analysis, since reliability is a key requirement in both securing expansive backbone smart grid equipment and adaptive pricing using up-to-date demand response information. We discuss the viability of using cognitive radio technology in public protection and disaster relief networks, and propose a network architecture based on cognitive radio. We present comparisons of our architecture with the state-of-the-art and give simulation results to emphasize the importance of cognitive radio when used properly in such systems. Finally, we investigate the routing problem in cognitive vehicular networks. We list the challenges for routing in this network type, mainly due to its highly dynamic nature. We also lay out the advantages that are specific to vehicular networks. We present the state-of-the-art on both routing for vehicular and cognitive vehicular networks and discuss open research areas.
Atmosfer olukları ve troposferik saçılım ile ufuk ötesi haberleşme kanalları ve ağları
Network centric operations (NCO) aim to provide a competitive advantage through information superiority. Modern military communication systems require communication links having low transmission delays and high data rates in order to provide effective command and control in challenging warfare areas. Available wireless communication systems are inefficient at b-LoS ranges. For this reason, new b-LoS communication techniques are required to provide high data rates, reliability and security. The main motivation of the proposed thesis is to analyze b-LoS wireless communications and networks with troposcatter and atmospheric ducts in order to tackle these problems. Tropospheric scatter that is widely known as troposcatter, is the scattering of the propagating signals in all directions due to the irregularities in the troposphere. The scattered signals are directed especially in the forward direction, but some of the signal power is directed to the receiver. As a result, the effects of troposcatter can be utilized as a b-LoS communication medium. To this end, we investigate the viability of troposcatter channel as a b-LoS communication medium through physical layer channel modeling studies. In addition, we propose models for the fading correlation and rain attenuation in troposcatter links. At the end, our models show that troposcatter communication is especially promising for fixed links with low probability of detect/intercept, low transmission delays and high data rates. Near-surface wave propagation at microwave frequencies especially 2 GHz and above shows significant dependence on atmospheric ducts that are the layer in which rapid decrease in the refractive index occurs. The propagating signals in the atmospheric ducts are trapped between the ducting layer and the sea surface, so that the power of the propagating signals do not spread isotropically through the atmosphere. As a result, these signals have low path-loss and can travel over-the-horizon. Since atmospheric ducts are nearly permanent at maritime and coastal environments, ducting layer communication is a promising method for beyond-Line-of-Sight (b-LoS) communications especially in naval communications. Although the wave propagation in atmospheric ducts has been studied, there are only a few papers which consider the ducting channel as a high data rate communication medium. Therefore, the communication aspects of this channel is mostly missing. To this end, we assess the viability of ducting communications for modern naval communications. Our results show that ducting communication can be utilized in challenging naval warfare conditions with secure and high data rate communications. To this end, we develop a channel modeling approach based on parabolic equation and ray-tracing methods. We analyze the viability of diversity techniques and investigate physical layer parameters of the ducting channels. At the end, we introduced a beam-forming method for ducting channels and investigate the feasibility of ducting ad hoc networks.
Terahertz band 5G kablosuz iletişimin fiziksel katman tasarımı
The emerging technology Terahertz Band (0.3 - 10 THz) communication is envisioned to accommodate high speed wireless communication. Large bandwidth makes it a good candidate for 5G mobile networks as it can alleviate the problem for spectrum congestion. In this thesis, we propose the first ever physical layer design of communication in THz Band not only for single-input single-output (SISO) based networks but also multiple-input multiple-output (MIMO). We first introduce the testbed system and present its use for carrying fundamental experiments in THz Band. Path loss and phase delay measurements from 260 GHz to 400 GHz for different distances, angles of arrival and objects acting as reflectors are then discussed. We have shown links reaching speeds of terabits per second that confirms THz Band as an excellent candidate for 5G wireless networks. Furthermore, we statistically analyze the THz Band channel and determine the exponent of a path loss exponent model with log-normal shadowing. Channel coherence bandwidth is also determined using the power delay profile information. We also analyze different modulation schemes based on there energy consumption, data speed and bit-error rate. The analysis helps us determine the most energy-efficient modulation scheme for THz Band, which is very important as energy-consumption is a challenging problem for high speed wireless data transmission. Moreover, we propose a THz Band transceiver design that can be used for network demonstration and can be extended for protocol testing. Furthermore, we present the first ever experimental results of a THz Band line-of-sight (LOS) $ 2 \times 2 $ MIMO channel using the principles of diffraction limited optics. Finally, we look at a some networking scenarios in full-dimension multiple-input multiple-output (FD-MIMO) based THz Band indoor wireless networks to determine the number of nodes that can be connected to a base station as a function of the antenna characteristics.
Gelecek-nesil bilişsel kablosuz ağlar için gelişmiş haberleşme teknikleri
As wireless devices become ubiquitous, demand for the electromagnetic spectrum has increased to a level that leads to two problems in wireless communications. First problem is spectrum scarcity problem. Since most of the spectrum is allocated to licensed users, unlicensed users are facing with the problem of insufficient spectrum bands. Electromagnetic spectrum band is scarce, hence, it must be utilized efficiently. Although unlicensed spectrum bands are overcrowded, licensed ones are underutilized. Second problem is inefficient spectrum utilization. Cognitive radio technology stands as a promising approach to overcome these problems and to enable next-generation cognitive wireless networks, which are the wireless networks with spectrum-awareness. This technology enables using the licensed spectrum bands in an opportunistic manner with limited interference to the licensed users. In this thesis, cognitive radio is adopted in different types of wireless networks to realize next-generation cognitive wireless networks. Due to greatness of the domain of next-generation cognitive wireless networks, this thesis focuses on a subset of these networks. Hence, this thesis investigates four different wireless networks with cognitive radio capability for next-generation cognitive wireless networks. Advanced communication techniques are proposed and analyzed in these four main pillars of wireless networks. First pillar of next-generation cognitive wireless networks is cognitive radio ad hoc and sensor networks. Spectrum opportunity characterization is performed, mobility-aware clustering protocol is proposed, clustering in multi-channel spectrum-aware environment is investigated, energy optimal transmission range is found, network coding is studied for multicast communication in this type of networks. Second pillar of them is wireless networked control systems with cognitive radio capability. Maximum coverage area and maximum energy-efficiency under Kalman filter convergence with maximum cost-efficiency are studied. Third pillar is cognitive wireless multimedia networks. Challenges and requirements are analyzed to enable spectrum-aware communications in cognitive wireless multimedia networks. Existing solutions are investigated and open research issues are determined. Last pillar is Internet of Things. Spectrum scarcity problem is worsened by this paradigm, and nodes within Internet of Things are resource-constrianed. Hence, it benefits from cognitive radio technology to overcome these challenges. Hence, network coding application is utilized to decrease transmission efforts, and energy harvesting in the domain of smart grid and smart cities is investigated to overcome limited energy supply challenge. The analysis and studies in this thesis help realization of next-generation cognitive wireless networks. The thesis also points out open research issues and how cognitive radio can be applied in next-generation wireless networks.
Biyo-nano nesnelerin interneti için nano-ölçekli ve biyolojik-esinli haberleşme teknikleri
Internet of Bio-Nano Things (IoBNT) is a novel ICT framework, in which nanomachines and biological entities, such as nanobiosensors, living cells, engineered bacteria, are connected with each other and with conventional macroscale networks to cooperatively perform sensing, actuation and processing. The framework has an enormous potential to transform the way we connect with and understand the world "at the bottom" by enabling new methods of interfering with the processes inside living organisms at the single-molecular level, and extending the human consciousness and control with bio-nano things collaboratively sensing and acting upon the environments never explored by any other paradigm before. Realization of IoBNT, however, demands novel engineering solutions to overcome unique challenges regarding miniaturization and connectivity subject to peculiarities of nanoscale-physics and limited capabilities of bio-nano things. These challenges call for novel approaches to devise solutions for a set of modeling, analysis and implementation problems on a highly interdisciplinary domain covering engineering, nanotechnology and biophysics. This thesis is focused on the challenges regarding the physical layer of IoBNT. To this end, communication techniques that can enable high-speed and reliable wireless communication in nanonetworks and at the same time provide a seamless interface between the nanonetworks and the macroscale cyber networks are investigated. The first part of the thesis is concentrated on the use of fluorescent molecules, i.e., fluorophores, to enable wireless communication at nanoscale through a quantum mechanical phenomenon, which is F\"orster Resonance Energy Transfer (FRET). Communication and information theoretical models for FRET-based, graphene plasmon-assisted FRET-based and multi-step FRET-based propagation channels are developed. Accounting for the natural optical interface between the nanoscale and macroscale worlds provided by the intrinsic characteristics of fluorophores, the novel concept of Internet of Molecular Things is introduced to further extend the coverage of IoBNT with networks of sub-100nm primitive molecular devices, such as fluorophore-based molecular logic gates, sensors and actuators. Moreover, the first practical realization of a wireless nanoscale communication network is achieved with a network of single molecular fluorescent transceivers. The second part is focused on molecular communications, which has been extensively studied from various aspects including channel and noise models. Different from the existing literature, the feasibility of designing a molecular receiver, in a physical domain other than synthetic biology, meeting the basic requirements of nanonetwork applications and also serving the needs of an electromagnetic nano-macro interface between the chemical domain of nanonetworks and the electrical domain of the cyber networks is thoroughly examined. Based on the advancements in the biosensing literature, Field Effect Transistor-based Biosensors (BioFETs) is proposed as the most viable solution to design a molecular receiver, which can transduce molecular messages into electrical signals. A communication theoretical model for Silicon Nanowire (SiNW) bioFET-based MC receiver is developed and the noise statistics at the receiver output is derived. The performance of this receiver is evaluated with common ICT metrics such as Signal to Noise Ratio (SNR), Symbol Error Probability (SEP) and information theoretical capacity.
Gelecek-nesil nesnelerin interneti için enerji ve tayf-verimli haberleşme teknikleri
Internet of Things (IoT) is a recent paradigm, rapidly gaining traction across a variety of disciplines, including but not limited to communications, electronics, computer engineering and social sciences. In its fundamentals, IoT provides a link between cyber and physical world by connecting devices over the Internet. Recent advances in hardware systems, signal processing and wireless communications have made it possible to manufacture low cost, low complexity wireless communicating things; which are the key to full scale adoption of the IoT paradigm. On the other hand, with the recent progress in nanotechnology, things are also quickly moving into to microscales and nanoscales. As the offspring of nanotechnology, nanomachines are strong candidates for realization of Internet of Bio-Nano Things (IoBNT). Full realization of IoT and IoBNT, however, will require surmounting of additional challenges. One of the upcoming difficulties is spectrum scarcity, which is a result of the inefficiency of the fi xed spectrum assignment paradigm. Additionally, most of the communicating entities are traditionally batter-powered and run out of batteries at fairly random instants after their deployment, which makes battery replenishments an unfeasible operation. With the scale game, rising need for self-sustainability and coordination is a clear reality. Whilst IoBNT opens doors for advanced applications such as nanoscale sensing and intelligent drug delivery, they depend on nanomachines with scarce processing, memory, and networking capabilities. There is clearly a need for energy and medium-efficient nanonetworking techniques, that would help nanomachines carry out more complex tasks, towards the IoBNT vision. To that end, in this thesis, we focus on energy and spectrum-efficient communication techniques for next-generation networks that are likely to constitute the backbones of IoT and IoBNT. We address key challenges brought by IoT and IoBNT applications, and solutions provided by next-generation networks and techniques thereof in two main parts: In Part I, we consider next-generation ad hoc networks, which are enhanced with energy and spectrum-efficient communication techniques to satisfy demanding future IoT functions. More specifically, architectures and techniques in Cognitive Radio Ad Hoc Networks (CRAHN) and Cognitive Radio Sensor Networks (CRSN) are studied to optimize performance in critical metrics such as sensing coverage, connectivity, spectrum- and energy-efficient communication duration and goodput-meters-per-Joule toward the fusion center. For future IoT applications in which demanding data rates cannot be achieved with today's traditional spectrum, a self-organizing capacity optimization procedure for low THZ band is developed. Lastly, a novel electric- field base energy harvesting method is proposed, tested and studied in detail to enable self-sustaining networks for real-life IoT applications. In Part II, we consider architectures that will help realization of nanonetworks, composed of nanomachines. Different communication types, namely; acoustic, electromagnetic, nanomechanical and molecular communications could be viable alternatives nanonetworking. However, acoustic and electromagnetic communications require entities that can carry out acoustic or electromagnetic operations at nanoscale. On the other hand, nanomechanical communications require direct contact between communicating parties and is not suitable for distant applications. In this context, we focused on Molecular Communications (MC) in this thesis, as it is a viable method for nanonetworking, backed by the fact that similar mechanisms are already present in many living organisms and environments. We extensively review in detail the existing modulation schemes in MC, and propose a novel messenger-based modulation scheme to increase channel performance in terms of achievable channel capacity without the need for synchronization.
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