Many large-scale distributed Multi-Agent Systems (MAS) exchange information over low- power communication networks. In such scenarios, agents communicate intermittently with each other, often with limited power and over unlicensed spectrum bands that are susceptible to interference, eavesdropping, and Denial-of-Service (DoS) attacks. In this work, we consider a popular low-power, long-range communication protocol known as LoRa. Despite LoRa's high tolerance for noise and interference, it was found vulnerable to interference from particular chirp-type signals. State-of-the-art signal jamming techniques that exploit this property require the knowledge of two sensitive parameters - Bandwidth (BW) and Spreading Factor (SF). However, such information is available only to authenticated parties on the network and not to an eavesdropping adversary. We expose LoRa's vulnerability to DoS attacks by designing an intelligent jammer that surpasses the need for prior knowledge of these parameters. Exploiting a structural pattern in LoRa signals, we propose a Neural Network (NN) implementation for jointly inferring the two parameters by eavesdropping. Through simulation and experimentation, we analyze the detection vulnerability of LoRa for each combination of these parameters at various Signal to Noise Ratio (SNR) values. This work also presents a Radio Frequency (RF) dataset of LoRa signals, which is used to validate our inference model through experimentation. / Master of Science / When many independent devices (or agents) work together in a large system, they often need to communicate with each other. They do so using low-powered networks and often in an intermittent manner. These networks operate on unlicensed radio frequencies, which are open to interference, unwanted snooping, and 'denial-of-service' attacks that could shut down communication. In our study, we focus on a popular low-power, long-distance communication protocol called LoRa. Despite being designed to handle interference and noise well, related literature revealed that LoRa is vulnerable to a specific type of interference caused by 'chirp' signals. Current techniques to jam these signals and disrupt communication require the knowledge of two important factors - bandwidth and spreading factor. Normally, only authorized parties in the network would know these details, not any outsiders looking to interfere. However, we exploit LoRa's vulnerability without knowing these two parameters. By identifying a pattern in LoRa signals, we designed an artificial intelligence model that can determine these two parameters just by listening in. We then ran simulations and conducted experiments to understand how susceptible LoRa is to being detected under various levels of signal strength and noise. We also prepared a dataset of LoRa signals and used this data to confirm the effectiveness of our model.

No description available.

We implement reinforcement learning in the context of wireless communications in two very different settings. In the first setting, we study the use of reinforcement learning in an underwater acoustic communications network to adapt its transmission frequencies to avoid interference and potential malicious jammers. To that effect, we implement a reinforcement learning algorithm called contextual bandits. The harsh environment of an underwater channel provides a challenging problem. The channel may induce multipath and time delays which lead to time-varying, frequency-selective attenuation. These factors are also influenced by the distance between the transmitter and receiver, the subbands the interference is located within, and the power of the transmitter. We show that the agent is effectively able to avoid frequency bands that have degraded channel quality or that contain interference, both of which are dynamic or time-varying . In the second setting, we study the use of reinforcement learning to adapt the modulation and power scheme of a jammer seeking to disrupt a wireless communications system. To achieve this, we make use of a linear contextual bandit to learn to jam the victim system. Prior work has shown that with the use of linear bandits, improved convergence is achieved to jam a single-carrier system using time-domain jamming schemes. However, communications systems today typically employ orthogonal frequency division multiplexing (OFDM) to transmit data, particularly in 4G/5G networks. This work explores the use of linear Thompson Sampling (TS) to jam OFDM-modulated signals. The jammer may select from both time-domain and frequency-domain jamming schemes. We demonstrate that the linear TS algorithm is able to perform better than a traditional reinforcement learning algorithm, upper confidence bound-1 (UCB-1), in terms of maximizing the victim's symbol error rate. We also draw novel insights by observing the action states, to which the reinforcement learning algorithm converges. We then investigate the design and modification of the context vector in the hope of in- creasing overall performance of the bandit, such as decreased learning period and increased symbol error rate caused to the victim. This includes running experiments on particular features and examining how the bandit weights the importance of the features in the context vector. Lastly, we study how to jam an OFDM-modulated signal which employs forward error correction coding. We extend this to leverage reinforcement learning to jam a 5G-based system implementing some aspects of the 5G protocol. This model is then modified to introduce unreliable reward feedback in the form of ACK/NACK observations to the jammer to understand the effect of how imperfect observations of errors can affect the jammer's ability to learn. We gain insights into the convergence time of the jammer and its ability to jam the victim, as well as improvements to the algorithm, and insights into the vulnerabilities of wireless communications for reinforcement learning based jamming. / Master of Science / In this thesis we implement a class of reinforcement learning known as contextual bandits in two different applications of communications systems and jamming. In the first setting, we study the use of reinforcement learning in an underwater acoustic communications network to adapt its transmission frequencies to avoid interference and potential malicious jammers. We show that the agent is effectively able to avoid frequency bands that have degraded channel quality or that contain interference, both of which are dynamic or time-varying. In the second setting, we study the use of reinforcement learning to adapt the jamming type, such as using additive white Gaussian noise, and power scheme of a jammer seeking to disrupt a wireless communications system. To achieve this, we make use of a linear contextual bandit which implies that the contexts that the jammer is able to observe and the sampled probability of each arm has a linear relationship with the reward function. We demonstrate that the linear algorithm is able to outperform a traditional reinforcement learning algorithm in terms of maximizing the victim's symbol error rate. We extend this work by examining the impact of the context feature vector design, LTE/5G-based protocol specifics (such as error correction coding), and imperfect reward feedback information. We gain insights into the convergence time of the jammer and its ability to jam the victim, as well as improvements to the algorithm, and insights into the vulnerabilities of wireless communications for reinforcement learning based jamming.

Many species of bats primarily use echolocation, a type of active sensing wherein bats emit ultrasonic pulses and listen to echoes, for guidance and navigation. Swarms of such bats are a unique type of multi-agent systems that feature bats's echolocation and flight behaviors. In the work of this dissertation, we used bat swarming as an inspiration for multi-agent systems to study various topics which include predation success, active sensing, and collision avoidance. To investigate the predation success, we modeled a group of bats hunting a number of collectively behaving prey. The modeling results demonstrated the benefit of localized grouping of prey in avoiding predation by bats. In the topics regarding active sensing and collision avoidance, we studied individual behavior in swarms as bats could potentially benefit from information sharing while suffering from frequency jamming, i.e., bats having difficulty in distinguishing between self and peers's information. We conducted field experiments in a cave and found that individual bat increased biosonar output as swarm size increased. The experimental finding indicated that individual bat acquired more sensory information in larger swarms even though there could be frequency jamming risk. In a simulation wherein we modeled bats flying through a tunnel, we showed the increasing collision risk in larger swarms for bats either sharing information or flying independently. Thus, we hypothesized that individual bat increased pulse emissions for more sensory information for collision avoidance while possibly taking advantage of information sharing and coping with frequency jamming during swarming. / Ph. D.

Esta dissertação apresenta uma reflexão sobre as interseções entre práticas artísticas e ativismo contemporâneo, especialmente nas décadas de 1990 e 2000. A partir de diferentes contextos, o estudo investiga os conceitos e objetivos de uma arte coletiva e engajada socialmente, considerando seus modos de experimentação estética e expressão política. Utilizando-se de entrevistas, manifestos, textos críticos, reportagens e documentos como fotografias, vídeos e filmes, a dissertação apresenta no primeiro capítulo um histórico detalhado sobre as diversas concatenações entre arte, ativismo político e produção coletiva no século XX. No segundo capítulo, este trabalho analisa a formulação de uma \"estética anti-corporativa\", baseada em táticas intervencionistas criadas por artistas e coletivos radicados nos EEUU, Espanha, França, Canadá, Austrália e Brasil. Seus projetos envolvem instalações artísticas com experimentos biológicos, mídia tática, cartografias, protestos contra a globalização capitalista, performances e Culture Jamming. O terceiro capítulo apresenta um estudo sobre o coletivismo artístico no Brasil e algumas de suas estratégias de ação, como intervenções urbanas, circuitos alternativos de produção e de distribuição, projetos com comunidades específicas e colaborações com movimentos sociais. Além disso, o texto faz uma breve reflexão sobre a atitude e o impacto destes grupos sobre o sistema de arte, caracterizado pelo apoio institucional de museus, galerias, mostras internacionais, críticos, curadores e patrocínio corporativo / This dissertation presents a reflection about the intersections between artistic practices and contemporary activism, especially in the decades of 1990 and 2000. From different contexts, teh study investigates the concepts and objectives of a collective art, socially engaged, considering their modes of aesthetic experimentation and political expression. Utilizing interviews, manifests, critical texts, newsprints and documents as photographies, videos and movies, the dissertation presnts in the first chapter a historical account about the concatenations between art, political activism and collective production in the twentieth century. In the second chapter, this work analyses a formulation of an \"anti-corporate aesthetics\", based in interventionist tactics created by artists and collectives in USA, Spain, France, Canada, Australia and Brazil. Their projects involve artistic installations with biological experiments, tactical media cartographies, protests against capitalist globalization, performances and culture jamming. The third chapter presents a study about the artistic collectivism in Brazil and some of their strategies of action, as urban interventions, alternative circuits of production and distribution, projects with specific communities and collaborations with social movements. Besides, the next makes a brief reflection about the attitude and impact of these groups in the art system, characterized by institutional support of museums, galleries, international exhibitions, art critics, curators and corporate sponsorship

Esta dissertação apresenta uma reflexão sobre as interseções entre práticas artísticas e ativismo contemporâneo, especialmente nas décadas de 1990 e 2000. A partir de diferentes contextos, o estudo investiga os conceitos e objetivos de uma arte coletiva e engajada socialmente, considerando seus modos de experimentação estética e expressão política. Utilizando-se de entrevistas, manifestos, textos críticos, reportagens e documentos como fotografias, vídeos e filmes, a dissertação apresenta no primeiro capítulo um histórico detalhado sobre as diversas concatenações entre arte, ativismo político e produção coletiva no século XX. No segundo capítulo, este trabalho analisa a formulação de uma \"estética anti-corporativa\", baseada em táticas intervencionistas criadas por artistas e coletivos radicados nos EEUU, Espanha, França, Canadá, Austrália e Brasil. Seus projetos envolvem instalações artísticas com experimentos biológicos, mídia tática, cartografias, protestos contra a globalização capitalista, performances e Culture Jamming. O terceiro capítulo apresenta um estudo sobre o coletivismo artístico no Brasil e algumas de suas estratégias de ação, como intervenções urbanas, circuitos alternativos de produção e de distribuição, projetos com comunidades específicas e colaborações com movimentos sociais. Além disso, o texto faz uma breve reflexão sobre a atitude e o impacto destes grupos sobre o sistema de arte, caracterizado pelo apoio institucional de museus, galerias, mostras internacionais, críticos, curadores e patrocínio corporativo / This dissertation presents a reflection about the intersections between artistic practices and contemporary activism, especially in the decades of 1990 and 2000. From different contexts, teh study investigates the concepts and objectives of a collective art, socially engaged, considering their modes of aesthetic experimentation and political expression. Utilizing interviews, manifests, critical texts, newsprints and documents as photographies, videos and movies, the dissertation presnts in the first chapter a historical account about the concatenations between art, political activism and collective production in the twentieth century. In the second chapter, this work analyses a formulation of an \"anti-corporate aesthetics\", based in interventionist tactics created by artists and collectives in USA, Spain, France, Canada, Australia and Brazil. Their projects involve artistic installations with biological experiments, tactical media cartographies, protests against capitalist globalization, performances and culture jamming. The third chapter presents a study about the artistic collectivism in Brazil and some of their strategies of action, as urban interventions, alternative circuits of production and distribution, projects with specific communities and collaborations with social movements. Besides, the next makes a brief reflection about the attitude and impact of these groups in the art system, characterized by institutional support of museums, galleries, international exhibitions, art critics, curators and corporate sponsorship

In this report metrics for jamming resistance and radar performance of waveform sets are described and developed, and different sets of waveforms are optimized, evaluated and compared. It is shown that without additional processing or PRI jitter, waveform sets can reach jamming resistance a few dB worse than what is provided by PRI jitter alone, and together with PRI jitter a few dB better. Waveforms with better jamming resistance tend to have worse range sidelobes and Doppler tolerance, but show less structure in their spectrograms, suggesting better LPI properties. The Doppler tolerance metric is new, as well as the comparative analysis of waveform sets on multiple metrics including jamming resistance. / Radar är fundamentalt i modern krigsföring. Med en radar kan man avfyra vapen från säkra avstånd och med precision mäta in mål. En radarstörare har som mål att förhindra en radar från att mäta in sitt mål. Då radarn fungerar genom att sända ut specifikt modulerade radiovågspulser och lyssna efter ekot från omgivningen kan störaren förhindra detta genom att antingen sända mycket starkt brus, eller genom att sända radiovågspulser med samma specifika modulation. Den senare metoden kallas för DRFM-störning, där förkortningen står för Digitalt RadioFrekvens-Minne, vilket antyder att störaren kan minnas radarns modulation och själv använda den. Om radarn använder en ny modulation (eng: waveform) för varje puls kan störaren inte använda modulationen den minns från förra pulsen utan måste vänta på att nästa puls träffar den innan den kan repetera pulsen, vilket begränsar dess störförmåga. Denna rapport tänker sig att radarn har en begränsad uppsättning av modulationer att byta mellan, och undersöker olika sådana uppsättningar och bedömer och jämför dem på olika mått av radarprestanda och störtålighet. Radioprestandamåtten inkluderar hur mycket förstärkning och hur fin upplösning man får av modulationen, hur väl modulationen kan hantera mycket snabba mål, och hur stora "sidolober" som uppstår runt starka mål. Sidolobsfenomenet är jämförbart med det optiska fenomenet där små men ljusstarka saker på natten kan se ut att ha en ljus halo eller ljusa utstrålningar runt sig. Störtålighetsmåtten kvantifierar hur distinkta de olika modulationerna i radarns uppsättning är, och på så vis hur väl radarn kan urskilja en modulation från de andra, tillsammans med hur liten sannolikheten är att störaren lyckas välja just den modulation vi kommer använda till nästa puls. Resultaten visar att metoden av modulationsbyten kan ge nästan lika stor störtålighet som en välkänd metod, PRI-jitter, ger själv och något högre i kombination med den metoden. Bättre störtålighet visas gå hand i hand med sämre mått på radarprestanda, men mindre strukturerade spektrogram vilket antyder att de kan vara svårare att upptäckas av radarspanare. Försämringen i måtten på radarprestanda innebär inte nödvändigtvis en lika stor försämring i faktisk radarprestanda, då sidoloberna tar an en brusartad karaktär vilket leder till praktiska fördelar gentemot de vanliga fixa sidoloberna.

The ability of tissues and cells to move and rearrange is central to a broad range of diverse biological processes such as tissue remodeling and rearrangement in embryogenesis, cell migration in wound healing, or cancer progression. These processes are linked to a solidlike to fluid-like transition, also known as unjamming transition, a not rigorously defined framework that describes switching between a stable, resting state and an active, moving state. Various mechanisms, that is, proliferation and motility, are critical drivers for the (un) jamming transition on the cellular scale. However, beyond the scope of these fundamental mechanisms of cells, a unifying understanding remains to be established. During embryogenesis, the proliferation rate of cells is high, and the number density is continuously increasing, which indicates number-density-driven jamming. In contrast, cells have to unjam in tissues that are already densely packed during tumor progression, pointing toward a shape-driven unjamming transition. Here, we review recent investigations of jamming transitions during embryogenesis and cancer progression and pursue the question of how they might be interlinked. We discuss the role of density and shape during the jamming transition and the different biological factors driving it.

No description available.

The ever-increasing demand for private and sensitive data transmission over wireless networks has made security a crucial concern in the current and future large-scale, dynamic, and heterogeneous wireless communication systems. To address this challenge, wireless researchers have tried hard to continuously analyze the jamming threats and come up with improved countermeausres. In this research, we have analyzed the jamming-vulnerabilities of the leading multi-carrier communication systems, Orthogonal Frequency Division Multiplexing (OFDM) and Single-Carrier Frequency Division Multiple Access (SC-FDMA). In order to lay the necessary theoretical groundwork, first we derived the analytical BER expressions for BPSK/QPSK and analytical upper and lower bounds for 16-QAM for OFDMA and SC-FDMA using Pilot Symbol Assisted Channel Estimation (PSACE) techniques in Rayleigh slow-fading channel that takes into account channel estimation error as well as pilot-jamming effect. From there we advanced to propose more novel attacks on the Cyclic Prefix (CP) of SC-FDMA. The associated countermeasures developed prove to be very effective to restore the system. We are first to consider the effect of frequency-selectivity and fading correlation of channel on the achievable rates of the legitimate system under pilot-spoofing attack. With respect to jamming mitigation techniques, our approaches are more focused on Anti-Jamming (AJ) techniques rather than Low Probability of Intercept (LPI) methods. The Channel State Information (CSI) of the two transceivers and the CSI between the jammer and the target play critical roles in ensuring the effectiveness of jamming and nulling attacks. Although current literature is rich with different channel estimation techniques between two legitimate transceivers, it does not have much to offer in the area of channel estimation from jammer's perspective. In this dissertation, we have proposed novel, computationally simple, deterministic, and optimal blind channel estimation techniques for PSK-OFDM as well as QAM-OFDM that estimate the jammer channel to the target precisely in high Signal-to-Noise (SNR) environment from a single OFDM symbol and thus perform well in mobile radio channel. We have also presented the feasibility analysis of estimating transceiver channel from jammer's perspective at the transmitter as well as receiver side of the underlying OFDM system. / Ph. D.