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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

New Method for Directional Modulation Using Beamforming: Applications to Simultaneous Wireless Information and Power Transfer and Increased Secrecy Capacity

Yamada, Randy Matthew 20 October 2017 (has links)
The proliferation of connected embedded devices has driven wireless communications into commercial, military, industrial, and personal systems. It is unreasonable to expect privacy and security to be inherent in these networks given the spatial density of these devices, limited spectral resources, and the broadcast nature of wireless communications systems. Communications for these systems must have sufficient information capacity and secrecy capacity while typically maintaining small size, light weight, and minimized power consumption. With increasing crowding of the electromagnetic spectrum, interference must be leveraged as an available resource. This work develops a new beamforming method for direction-dependent modulation that provides wireless communications devices with enhanced physical layer security and the ability to simultaneously communicate and harvest energy by exploiting co-channel interference. We propose a method that optimizes a set of time-varying array steering vectors to enable direction-dependent modulation, thus exploiting a new degree of freedom in the space-time-frequency paradigm. We formulate steering vector selection as a convex optimization problem for rapid computation given arbitrarily positioned array antenna elements. We show that this method allows us to spectrally separate co-channel interference from an information-bearing signal in the analog domain, enabling the energy from the interference to be diverted for harvesting during the digitization and decoding of the information-bearing signal. We also show that this method provides wireless communications devices with not only enhanced information capacity, but also enhanced secrecy capacity in a broadcast channel. By using the proposed method, we can increase the overall channel capacity in a broadcast system beyond the current state-of-the-art for wireless broadcast channels, which is based on static coding techniques. Further, we also increase the overall secrecy capacity of the system by enabling secrecy for each user in the system. In practical terms, this results in higher-rate, confidential messages delivered to multiple devices in a broadcast channel for a given power constraint. Finally, we corroborate these claims with simulation and experimental results for the proposed method. / PHD / The proliferation of connected devices has driven wireless communications into commercial, military, industrial, and personal systems. It is unreasonable to expect privacy and security to be inherent in these networks given the spatial density of these devices, limited available resources, and the broadcast nature of wireless communications systems. Communications for these systems need not only sufficient information capacity, but also the assurance that the available information capacity remains confidential while typically maintaining small size, light weight, and minimized power consumption. With increasing crowding of the electromagnetic spectrum due to the numerous connected devices, interference between them must be leveraged as an available resource. This work develops a new method for electrically steering an array of antennas to overlay or encode information onto a signal in a way that is direction-dependent and provides wireless communications devices with enhanced security and the ability to simultaneously communicate and harvest energy from interfering devices. We propose a method that optimizes a set of time-varying array steering vectors to enable direction-dependent modulation, thus exploiting a new degree of freedom in the traditional space-time-frequency paradigm. We formulate the selection of steering vectors as a convex optimization problem for rapid computation given arbitrarily positioned array antenna elements in three dimensions. We show that this method allows us to separate interference from an information-bearing signal in the analog domain, enabling the energy from the interference to be diverted for harvesting during the digitization and decoding of the information-bearing signal. We also show that this method provides broadcast wireless communications devices with not only increased information capacity, but also assured secrecy. By using the proposed time-varying method, we can increase the overall channel capacity in a broadcast system beyond the current state-of-the-art, which is based on static encoding techniques. Further, we also increase the overall secrecy capacity of the system by ensuring that each user in the system receives separate and confidential signals. In practical terms, this results in higher-rate, confidential messages delivered to multiple devices in a broadcast channel for a given power constraint. Finally, we corroborate these claims with simulation and experimental results for the proposed method.
12

Shuffled Faster Than Nyquist Signaling For Spectrally Efficient And Secure Wireless Communication

Gharib, John 01 June 2024 (has links) (PDF)
This thesis investigates the implementation and performance of Shuffled Faster than Nyquist (SFTN) signaling, a communication method that enhances spectral efficiency and provides physical layer security (PLS) in wireless communications. In Faster than Nyquist signaling, the Nyquist inter-symbol interference (ISI) criterion is exceeded, thereby increasing spectral efficiency. By varying the transmission rate of symbols above the Nyquist rate, SFTN signaling is able to obfuscate the timing of transmitted symbols with ISI. The work in this thesis evaluates the performance of SFTN in Additive White Gaussian Noise (AWGN) channels and the MATLAB 802.11ax fading channels. Results show that while SFTN signaling offers the ability to introduce PLS, the sensitivity of the waveform is significantly influenced by the choice of symbol transmission rates and channel conditions.
13

Physical Layer Data Integrity Attacks and Defenses in Cyber-Physical Systems

Mohammed, Abdullah Zubair 24 January 2025 (has links)
Loss of data integrity in a safety-critical cyber-physical system (CPS), such as healthcare or intelligent transport, has a severe impact on its operation that can potentially lead to life-threatening consequences. This work investigates the vulnerability of CPS to physical-layer data integrity attacks and proposes countermeasures to enhance system resilience. Software-based cybersecurity approaches may not be efficient in mitigating threats aimed at the physical layer, leaving CPS particularly susceptible to manipulation through methods that exploit hardware vectors such as electromagnetic interference and data transmission medium. This work begins with a focus on using intentional electromagnetic interference (IEMI) to manipulate data and further explores other physical layer characteristics that can be exploited to conduct physical-layer attacks across various CPS environments. In the first phase of the research, the use of IEMI to induce controlled bit flips in widely used serial digital communication protocols is examined. In contrast to state-of-the-art IEMI attacks that use a narrow-band sinusoid as an attack signal, a complex, wideband, rectangular waveform is designed to improve the attack success rate from less than 50% to 75%. Further, the vulnerabilities of printed circuit board (PCB) traces to IEMI in highly safety-critical applications, such as electric vehicle (EV) charging, is addressed. On PCBs, IEMI attacks exploit the signal-carrying traces, that act as unintentional antennas under an adversarial electromagnetic field. Experiments demonstrated that such attacks are more challenging due to the PCB's structure but are still feasible with sufficient attacker power. A suite of passive countermeasures is evaluated, including differential signaling, via-fencing, and optical fiber interconnects, along with a novel multiplexer-based defense that dynamically modifies signal paths to evade detection. Each countermeasure is extensively evaluated and ranked based on its effectiveness, and adaptive attack strategies are analyzed to address potential future threats. In the IoT domain, this work presented a preliminary investigation on a novel "wireless spiking" technique on smart locks, that enables attackers to bypass standard security measures and unlock/lock with no physical contact. Using IEMI, the control circuitry is manipulated to unlock devices remotely. The methodology, involving hardware reverse engineering and attack point identification, is presented, which applies to other IoT devices in smart home environments. In the field of automotive cybersecurity, bit manipulation attacks targeting the Controller Area Network (CAN) bus are investigated. By exploiting its transmission line nature, these attacks challenge the fundamental assumptions of the CAN's physical layer and are capable of inducing bidirectional bit flips, from recessive to dominant (R→D) and significantly difficult dominant to recessive (D→R). The flips are further made undetectable to CAN's standard error-checking mechanisms. These attacks are simulated and validated in both lab and real-world vehicle environments. Finally, a defense mechanism for vehicle identification security in intelligent transportation systems using device fingerprinting is proposed. This approach utilizes inductive loop detectors (ILD) to capture unique electromagnetic signatures of vehicles, achieving up to 93% accuracy in identifying their make, model, and year. The ILD-based technique secures access control in automated systems and provides a cost-effective, drop-in solution for existing infrastructure, mitigating risks such as unauthorized vehicle impersonation and charging station exploitation. This work establishes a systematic framework for understanding, detecting, and defending against physical-layer data integrity attacks in CPS. Through the development of novel attack vectors and robust countermeasures, this research enhances the field of CPS security, emphasizing the need for comprehensive defenses that extend beyond conventional software-based approaches. / Doctor of Philosophy / In our increasingly connected world, cyber-physical systems (CPS)—technologies that combine digital and physical processes—are essential to modern life. These systems, from smart homes to intelligent vehicles, integrate sensors, actuators, and controllers to manage everything from personal security to automated transportation. While they bring convenience and efficiency, these systems are also vulnerable to attacks that can alter their data and disrupt operations, specifically at the hardware level, posing serious risks to safety and security. The adversary can attack the communication channels between sensors/actuators and the controller seeking to manipulate the signals and falsify data. Incorrect decision-making based on manipulated data leads to safety risks or system failure. Unlike typical cyberattacks, which often exploit software vulnerabilities, these threats target the hardware layer directly, bypassing conventional cybersecurity defenses designed only to protect software. This work investigates attacks against data integrity, where attackers use intentional electromagnetic interference (IEMI) to corrupt data exchanged between CPS components. For instance, it is demonstrated that attackers can, without physical access, interfere with communication channels in industrial and automotive systems, altering data exchanged between sensors and controllers. By sending precisely crafted electromagnetic signals, an attacker can inject or modify data in real-time, allowing them to influence system behavior wirelessly. In addition to IEMI, this work also highlights how vulnerabilities in hardware could compromise critical systems in modern automobiles. For example, we demonstrate how attackers could subtly alter messages on a vehicle's communication network (the controller area network), interfering with safety-critical functions. These attacks evade standard error-checking systems, further underscoring the need for hardware-level defenses that software cannot address. Additionally, we tackle the growing challenge of vehicle identification security in intelligent transportation systems. Unauthorized access to restricted areas or privileges, such as electric vehicle (EV) charging stations, could be exploited if attackers impersonate legitimate vehicles. To counter this, we propose a new method that "fingerprints" each vehicle based on its unique physical characteristics, helping ensure only authorized vehicles gain access. Through extensive testing, we validate our proposed countermeasures across different CPS environments, offering practical defenses against these physical-layer attacks. By providing solutions that secure both communication and identification in CPS, this work lays the groundwork for a safer and more resilient future where these critical systems are better protected from physical-layer attacks.
14

Physical layer security in co-operative MIMO networks - key generation and reliability evaluation

Chen, Kan January 1900 (has links)
Doctor of Philosophy / Department of Electrical and Computer Engineering / Balasubramaniam Natarajan / Widely recognized security vulnerabilities in current wireless radio access technologies undermine the benefits of ubiquitous mobile connectivity. Security strategies typically rely on bit-level cryptographic techniques and associated protocols at various levels of the data processing stack. These solutions have drawbacks that have slowed down the progress of new wireless services. Physical layer security approaches derived from an information theoretic framework have been recently proposed with secret key generation being the primary focus of this dissertation. Previous studies of physical layer secret key generation (PHY-SKG) indicate that a low secret key generation rate (SKGR) is the primary limitation of this approach. To overcome this drawback, we propose novel SKG schemes to increase the SKGR as well as improve the security strength of generated secret keys by exploiting multiple input and multiple output (MIMO), cooperative MIMO (co-op MIMO) networks. Both theoretical and numerical results indicate that relay-based co-op MIMO schemes, traditionally used to enhance LTE-A network throughput and coverage, can also increase SKGR. Based on the proposed SKG schemes, we introduce innovative power allocation strategies to further enhance SKGR. Results indicate that the proposed power allocation scheme can offer 15% to 30% increase in SKGR relative to MIMO/co-op MIMO networks with equal power allocation at low-power region, thereby improving network security. Although co-op MIMO architecture can offer significant improvements in both performance and security, the concept of joint transmission and reception with relay nodes introduce new vulnerabilities. For example, even if the transmitted information is secured, it is difficult but essential to monitor the behavior of relay nodes. Selfish or malicious intentions of relay nodes may manifest as non-cooperation. Therefore, we propose relay node reliability evaluation schemes to measure and monitor the misbehavior of relay nodes. Using a power-sensing based reliability evaluation scheme, we attempt to detect selfish nodes thereby measuring the level of non-cooperation. An overall node reliability evaluation, which can be used as a guide for mobile users interested in collaboration with relay nodes, is performed at the basestation. For malicious behavior, we propose a network tomography technique to arrive at node reliability metrics. We estimate the delay distribution of each internal link within a co-op MIMO framework and use this estimate as an indicator of reliability. The effectiveness of the proposed node reliability evaluations are demonstrated via both theoretical analysis and simulations results. The proposed PHY-SKG strategies used in conjunction with node reliability evaluation schemes represent a novel cross-layer approach to enhance security of cooperative networks.
15

Non-Gaussian Interference in High Frequency, Underwater Acoustic, and Molecular Communication

Hung-Yi Lo (6417014) 10 June 2019 (has links)
The implications of non-Gaussian interference for various communication systemsare explored. The focus is on the Kappa distribution, Generalized Gaussian distribu-tions, and the distribution of the interference in molecular communication systems.A review of how dynamic systems that are not in equilibrium are modeled by theKappa distribution and how this distribution models interference in HF communica-tions systems at sunrise is provided. The channel model, bit error rate for single andmultiple antennas, channel capacity, and polar code performance are shown.<div><br><div>Next, a review of the Generalized Gaussian distribution that has been found tomodel the interference resulting from surface activities is provided. This modeling isextended to find the secrecy capacity so that information cannot be obtained by theeavesdropper.</div><div><br></div><div>Finally, future nanomachnines are examined. The vulnerability to a receptorantagonist of a ligand-based molecule receiver is explored. These effects are consideredto be interference as in other wireless systems and the damage to signal reception isquantified.</div></div>
16

Impact of Antenna Mutual Coupling, Propagation, and Nonreciprocity on Propagation-Based Key Establishment

Mahmood, Attiya 01 May 2018 (has links)
Propagation-based key establishment is a physical layer method for generating encryption keys based on two radios observing a reciprocal propagation channel. This work explores the impact of mutual coupling when communicating nodes are equipped with multiple antennas, multipath richness in the propagation environment, and practical limitations caused by the nonreciprocal nature of RF circuits on key establishment. First, network theory is used to formulate a model of a realistic communication system which incorporates transmit sources and receive loads, impedance matching networks, low-noise amplifiers (LNAs), mutually coupled antenna arrays, and a passive eavesdropper. Afterwards, a detailed analysis is performed to quantify the impact of coupling, type of impedance matching network, and proximity of a multi-antenna eavesdropper on key rate metrics. Next, the degradation on key establishment caused by the radiocircuitry non-reciprocal contributions to the propagation channel is analyzed. A calibration technique based on total least square algorithm is used to overcome the non-reciprocity. Results demonstrate that the method is highly effective in removing the impact of non-reciprocal circuit contributions over a range of operational parameters. Lastly, for key establishment, the propagation conditions can cause the available key rate to be significantly different from the secure key rate which takes into account the presence of a passive eavesdropper. To study this in detail, a realistic multiple-input multiple-output (MIMO) propagation environment is modeled for two communicating radios and an eavesdropper. Afterwards different propagation conditions are assumed and results demonstrate that secure key rate converges to available key rate when K-factor is small and the eavesdropper is not located very close (< 2.5 wavelength) to one of the nodes.
17

Communication With Reconstruction and Privacy Constraints

Kittichokechai, Kittipong January 2014 (has links)
Communication networks are an integral part of the Internet of Things (IoT) era. They enable endless opportunities for connectivity in a wide range of applications, leading to advances in efficiency of day-to-day life. While creating opportunities, they also incur several new challenges. In general, we wish to design a system that performs optimally well in all aspects. However, there usually exist competing objectives which lead to tradeoffs. In this thesis, driven by several applications, new features and objectives are included into the system model, making it closer to reality and needs. The results presented in this thesis aim at providing insight into the fundamental tradeoff of the system performance which can serve as a guideline for the optimal design of real-world communication systems. The thesis is divided into two parts. The first part considers the aspect of signal reconstruction requirement as a new objective in the source and channel coding problems. In this part, we consider the framework where the quality and/or availability of the side information can be influenced by a cost-constrained action sequence. In the source coding problem, we impose a constraint on the reconstruction sequence at the receiver that it should be reproduced at the sender, and characterize the fundamental tradeoff in the form of the rate-distortion-cost region, revealing the optimal relation between compression rate, distortion, and action cost. The channel coding counterpart is then studied where a reconstruction constraint is imposed on the channel input sequence such that it should be reconstructed at the receiver. An extension to the multi-stage channel coding problem is also considered where inner and outer bounds to the capacity region are given. The result on the channel capacity reveals interesting consequence of imposing an additional reconstruction requirement on the system model which has a causal processing structure. In the second part, we consider the aspect of information security and privacy in lossy source coding problems. The sender wishes to compress the source sequence in order to satisfy a distortion criterion at the receiver, while revealing only limited knowledge about the source to an unintended user. We consider three different aspects of information privacy. First, we consider privacy of the source sequence against the eavesdropper in the problem of source coding with action-dependent side information. Next, we study privacy of the source sequence due to the presence of a public helper in distributed lossy source coding problems. The public helper is assumed to be either a user who provides side information over a public link which can be eavesdropped, or a legitimate user in the network who helps to relay information to the receiver, but may not ignore the information that is not intended for it. Lastly, we take on a new perspective of information privacy in the source coding problem. That is, instead of protecting the source sequence, we are interested in the privacy of the reconstruction sequence with respect to a user in the system. For above settings, we provide the complete characterization of the rate-distortion(-cost)-leakage/equivocation region or corresponding inner and outer bounds for discrete memoryless systems. / <p>QC 20140514</p>
18

DESIGN AND ANALYSIS OF COGNITIVE MASSIVE MIMO NETWORKS WITH UNDERLAY SPECTRUM SHARING

Al-Hraishawi, Hayder Abed Hussein 01 August 2017 (has links)
Recently, massive multiple-input multiple-output (MIMO) systems have gained significant attention as a new network architecture to not only achieving unprecedented spectral and energy efficiencies, but also to alleviating propagation losses and inter-user/inter-cell interference. Therefore, massive MIMO has been identified as one of the key candidate technologies for the 5th generation wireless standard. This dissertation thus focuses on (1) developing a performance analysis framework for cognitive massive MIMO systems by investigating the uplink transmissions of multi-cell multi-user massive MIMO secondary systems, which are underlaid in multi-cell multi-user primary massive MIMO systems, with taking into consideration the detrimental effects of practical transmission impairments, (2) proposing a new wireless-powered underlay cognitive massive MIMO system model, as the secondary user nodes is empowered by the ability to efficiently harvest energy from the primary user transmissions, and then access and utilize the primary network spectrum for information transmission, and (3) developing a secure communication strategy for cognitive multi-user massive MIMO systems, where physical layer secure transmissions are provisioned for both primary and secondary systems by exploiting linear precoders and artificial noise (AN) generation in order to degrade the signal decodability at eavesdropper. The key design feature of the proposed cognitive systems is to leverage the spatial multiplexing strategies to serve a large number of spatially distributed user nodes by using very large numbers of antennas at the base-stations. Moreover, the fundamental performance metrics, the secondary transmit power constraints, which constitute the underlay secondary transmissions subject to a predefined primary interference temperature, and the achievable sum rates of the primary and secondary systems, are characterized under different antenna array configurations. Additionally, the detrimental impact of practical wireless transmission impairments on the performance of the aforementioned systems are quantified. The important insights obtained throughout these analyses can be used as benchmarks for designing practical cognitive spectrum sharing networks.
19

Physical Layer Security in Training-Based Single-Hop/Dual-Hop Massive MIMO Systems

Timilsina, Santosh 01 August 2018 (has links)
The broadcast nature of wireless medium has made information security as one of the most important and critical issues in wireless systems. Physical layer security, which is based on information-theoretic secrecy concepts, can be used to secure the wireless channels by exploiting the noisiness and imperfections of the channels. Massive multiple-input multiple-output (MIMO) systems, which are equipped with very large antenna arrays at the base stations, have a great potential to boost the physical layer security by generating the artificial noise (AN) with the exploitation of excess degrees-of-freedom available at the base stations. In this thesis, we investigate physical layer security provisions in the presence of passive/active eavesdroppers for single-hop massive MIMO, dual-hop relay-assisted massive MIMO and underlay spectrum-sharing massive MIMO systems. The performance of the proposed security provisions is investigated by deriving the achievable rates at the user nodes, the information rate leaked into the eavesdroppers, and the achievable secrecy rates. Moreover, the effects of active pilot contamination attacks, imperfect channel state information (CSI) acquisition at the base-stations, and the availability of statistical CSI at the user nodes are quantified. The secrecy rate/performance gap between two AN precoders, namely the random AN precoder and the null-space based AN precoder, is investigated. The performance of hybrid analog/digital precoding is compared with the full-dimensional digital precoding. Furthermore, the physical layer security breaches in underlay spectrum-sharing massive MIMO systems are investigated, and thereby, security provisions are designed/analyzed against active pilot contamination attacks during the channel estimation phase. A power-ratio based active pilot attack detection scheme is investigated, and thereby, the probability of detection is derived. Thereby, the vulnerability of uplink channel estimation based on the pilots transmitted by the user nodes in time division duplexing based massive MIMO systems is revealed, and the fundamental trade-offs among physical layer security provisions, implementation complexity and performance gains are discussed.
20

Performance of physical layer security with different service integrity parameters

Padala, Akhila Naga Sree Ravali, Kommana, Kavya January 2018 (has links)
Information security has been a very important issue in wireless networks. With the ever-increasing amount of data being exchanged over wireless networks, the confidentiality of information needs to be protected from unauthorized users called eavesdropper. Due to the broadcast nature of the wireless medium, the transmissions between legitimate users maybe overheard and intercepted by the unauthorized parties, which makes wireless transmission vulnerable to potential eavesdropping attacks. The security of wireless communications plays an increasingly important role in the cybercrime defense against unauthorized activities.     We consider the wireless physical layer security which has been explored for the sake of enhancing the protection of wireless communications against eavesdroppers. We consider the problem of secret communication through Rayleigh fading channel in the presence of an eavesdropper in which the transmitter knows the channel state information of both the main and eavesdropper channel. Then, we analyze the average capacity of the main channel and eavesdropper channel from which an expression of secrecy capacity is derived based on the cumulative distribution function and probability density function of the signal to noise ratio. We also analyze an expression for the symbol error rate of the main channel, and the outage probability is obtained for the main transmission. Finally, we perform the numerical results in MATLAB.

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