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.

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>

"In this thesis, a transmission frequency rendezvous approach for secondary users deployed in decentralized dynamic spectrum access networks is proposed. Frequency rendezvous is a critical step in bootstrapping a wireless network that does not possess centralized control. Current techniques for enabling frequency rendezvous in decentralized dynamic spectrum access networks either require pre-existing infrastructure or use one of several simplifying assumptions regarding the architecture, such as the use of regularly spaced frequency channels for communications. Our proposed approach is designed to be operated in a strictly decentralized wireless networking environment, where no centralized control is present and the spectrum does not possess pre-defined channels. In our proposed rendezvous algorithm, the most important step is pilot tone detection and receiver query. In order to realize a shortest search time for the target receiver, an efficient scanning rule should be employed. In this thesis, three scanning rules are proposed and evaluated, namely: frequency sequence scanning, pilot tone strength scanning, and cluster scanning. To validate our result, we test our scanning rules with actual paging band spectrum measurements. Previous research on security of network coding focuses on the protection of data dissemination procedures and the detection of malicious activities such as pollusion attacks. The capabilities of network coding to detect other attacks has not been fully explored. In this thesis, a new mechanism based on physical layer network coding to detect wormhole attacks is proposed. When two signal sequences collide at the receiver, the difference between the two received sequences is determined by its distances to the senders. Therefore, by comparing the differences between the received sequences at two nodes, we can estimate the distance between them and detect those fake neighbor connections through wormholes. While the basic idea is clear, we design many schemes at both physical and network layers to turn the idea into a practical approach. Simulations using BPSK modulation at the physical layer show that the wireless nodes can effectively detect fake neighbor connections without the adoption of any special hardware on them."

Este trabalho apresenta uma visão geral do modo de transmissão OFDM do padrão IEEE 802.16. O controle de acesso ao meio (MAC) e da camada física (PHY) são descritos em detalhes. Especialmente a estrutura do frame na camada (PHY). Além disso, as diferentes configurações da camada PHY com diferentes níveis de robustez são analisadas. Em seguida a simulação de um frame de dados com ADS (Advanced Design System) com todas as especificações da camada PHY são incluídas: Randomização, FEC, modulação adaptativa e IFFT/FFT. Um canal com multipercursos Rayleigh fading é implementada também. Finalmente são analisadas as curvas de espectro em freqüência e tempo, e a constelação no transmissor e receptor Downlink e Uplink, respectivamente. / This works presents a general overview of the mode of transmission OFDM standard IEEE 802.16. The medium access control (MAC) and physical layer (PHY) are described in detail, especially the structure of frame layer (PHY). Moreover, the different configurations PHY layers with different level strengths are analyzed. Then the simulation of a frame data with ADS (Advanced Design System) with all the specifications of PHY layer are included: Randomização, FEC, adaptive modulation and IFFT / FFT. A breaking multipath Rayleigh fading is implemented as well. In analyzes the curves of spectrum in frequency and time, and constellation in the transmitter and receiver Uplink and Downlink, respectively.

Este trabalho apresenta uma visão geral do modo de transmissão OFDM do padrão IEEE 802.16. O controle de acesso ao meio (MAC) e da camada física (PHY) são descritos em detalhes. Especialmente a estrutura do frame na camada (PHY). Além disso, as diferentes configurações da camada PHY com diferentes níveis de robustez são analisadas. Em seguida a simulação de um frame de dados com ADS (Advanced Design System) com todas as especificações da camada PHY são incluídas: Randomização, FEC, modulação adaptativa e IFFT/FFT. Um canal com multipercursos Rayleigh fading é implementada também. Finalmente são analisadas as curvas de espectro em freqüência e tempo, e a constelação no transmissor e receptor Downlink e Uplink, respectivamente. / This works presents a general overview of the mode of transmission OFDM standard IEEE 802.16. The medium access control (MAC) and physical layer (PHY) are described in detail, especially the structure of frame layer (PHY). Moreover, the different configurations PHY layers with different level strengths are analyzed. Then the simulation of a frame data with ADS (Advanced Design System) with all the specifications of PHY layer are included: Randomização, FEC, adaptive modulation and IFFT / FFT. A breaking multipath Rayleigh fading is implemented as well. In analyzes the curves of spectrum in frequency and time, and constellation in the transmitter and receiver Uplink and Downlink, respectively.

Fréquemment exploités pour venir en complément aux réseaux mobiles traditionnels, les réseaux sans-fil multi-sauts, aussi appelés réseaux ad-hoc, sont particulièrement mis à profit dans le domaine des communications d'urgence du fait de leur capacité à s'affranchir de toute infrastructure. Néanmoins, la capacité de ces réseaux étant limitée dès lors que le nombre d'utilisateurs augmente, la communauté scientifique s'efforce à en redéfinir les contours afin d'étendre leur utilisation aux communications civiles. La gestion des interférences, considérée comme l'un des principaux défis à relever pour augmenter les débits atteignables dans les réseaux sans-fil multi-sauts, a notamment connu un changement de paradigme au cours des dernières années. Alors qu'historiquement cette gestion est régie par les protocoles de la couche d'accès dont l'objectif consiste à éviter les interférences entre utilisateurs, il est désormais possible, grâce à différentes techniques avancées de communication numérique, de traiter ces interférences, et même de les exploiter. Ces techniques de transmission, dites techniques de gestion des interférences, viennent alors concurrencer les mécanismes d'ordonnancement traditionnels en autorisant plusieurs transmissions simultanées et dans la même bande de fréquence vers un même récepteur. Dans cette thèse, nous nous intéressons à l'une de ces techniques, le Physical-Layer Network Coding (PLNC), en vue de son intégration dans des réseaux ad-hoc composés de plusieurs dizaines de nœuds. Les premiers travaux se concentrant principalement sur des petites topologies, nous avons tout d'abord développé un framework permettant d'évaluer les gains en débit à large échelle du PLNC par rapport à des transmissions traditionnelles sans interférence. Motivés par les résultats obtenus, nous avons ensuite défini un nouveau cadre d'utilisation à cette technique visant à élargir sa sphère d'application. Le schéma de PLNC proposé, testé à la fois sur de vrais équipements radio et par simulation, s'est alors révélé offrir des gains significatifs en débit et en fiabilité en comparaison aux solutions existantes.

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.

<p>Wireless communication is facing one of the fastest developments of the last years in the fields of technology and computer science in the world. There are several standards that deal with it. In this work, the IEEE standard 802.11a, which deals with wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, is going to be discussed in detail. </p><p>Taking this into consideration, PHY specifications and its environment are going to be studied. </p><p>The work that the ISY department at the Institute of Technology of the Linköping University has proposed is to design a PHY layer implementation for WLANs, in a CPU, using MATLAB/Simulink and in a DSP processor, using Embedded Target for C6000 DSP and Code Composer Studio and, once implemented both, to perform and analyse the performance of the system under those implementations.</p>

<p>This master thesis is as a final project in the Division of Computer Engineering at the Department of Electrical of Engineering, Linköping University, Sweden. The purpose of the project is to set up a baseband behavioral model for a Bluetooth system based on standards. In the model, synchronization in demodulation part has been focused on. Simulation results are analyzed later in the report to see how the method in demodulation works. Some suggestions and future works for receiver are provided to improve the performances of the model.</p>

Physical-Layer Network Coding (PNC) is a promising technique that has great potentials for improving the achievable data rates of end-to-end flows through higher packet transmission rates, thereby increasing the overall network throughput. In this thesis, we study the performance of the PNC transmission techniques for unidirectional end-to-end flows in multi-hop wireless networks, and compare it with that of the traditional transmission techniques. We first derive the bit-error rate (BER) that the PNC transmission technique achieves. Then, using the derived BER, we evaluate and quantify the achievable network throughput under both the PNC transmission technique and the traditional technique, where the network throughput is measured as the aggregate/sum of all end-to-end flows' achievable data rates in the wireless network. Using extensive simulations, we show that PNC increases the overall achievable end-to-end flow throughput in multi-hop wireless networks, especially under medium to high signal-to-noise ratios. / Graduation date: 2012