Wireless systems in which multiple users simultaneously access the propagation medium suffer from co-channel interference. Untreated interference limits the total amount of data that can be communicated reliably across the wireless links. If interfering users allocate a portion of the system's resources for information exchange and coordination, the effect of interference can be mitigated. Interference alignment (IA) is an example of a cooperative signaling strategy that alleviates the problem of co-channel interference and promises large gains in spectral efficiency. To enable alignment in practical wireless systems, channel state information (CSI) must be shared both efficiently and accurately. In this dissertation, I develop low-overhead CSI feedback strategies that help networks realize the information-theoretic performance of IA and facilitate its adoption in practical systems. The developed strategies leverage the concepts of analog, digital, and differential feedback to provide IA networks with significantly more accurate and affordable CSI when compared to existing solutions. In my first contribution, I develop an analog feedback strategy to enable IA in multiple antenna systems; multiple antennas are one of IA's key enabling technologies and perhaps the most promising IA use case. In my second contribution, I leverage temporal correlation to improve CSI quantization in limited feedback single-antenna systems. The Grassmannian differential strategy developed provides several orders of magnitude in CSI compression and ensures almost-perfect IA performance in various fading scenarios. In my final contribution, I complete my practical treatment of IA by revisiting its performance when CSI acquisition overhead is explicitly accounted for. This last contribution settles the viability of IA, from a CSI acquisition perspective, and demonstrates the utility of the proposed feedback strategies in transitioning interference alignment from theory to practice. / text

Wireless interference networks refer to communication systems in which multiple source–destination pairs share the same transmission medium, and each source’s transmission interferes with the reception at non-intended destinations. Optimizing the transmission of each source–destination pair is interrelated with that of the other pairs, and characterizing the performance limits of these networks is a challenging task. Solving the problem of managing the interference and data communications for these networks would potentially make it possible to apply solutions to several existing and emerging communication systems. Wireless devices can carefully coordinate the use of scarce radio resources in order to deal effectively with interference and establish successful communications. In order to enable coordinated transmission, terminals must usually have a certain level of knowledge about the propagation environment; that is, channel state information (CSI). In practice, however, no CSI is a priori available at terminals (transmitters and receivers), and proper channel training mechanisms (such as pilot-based channel training and channel state feedback) should be employed to acquire CSI. This requires each terminal to share available radio resources between channel training and data transmissions. Allocating more resources for channel training leads to an accurate CSI estimation, and consequently, a precise coordination. However, it leaves fewer resources for data transmissions. This creates the need to investigate optimum resource allocation. This thesis investigates an information-theoretic approach towards the performance analysis of interference networks, and employs signal processing techniques to design transmission schemes for achieving these limits in the following scenarios. First, the smallest interference network with two single-input single-output (SISO) source–destination pairs is considered. A fixed-rate transmission is desired between each source–destination pair. Transmission schemes based on point-to-point codes are developed. The transmissions may not always attain successful communication, which means that outage events may be declared. The outage probability is quantified and the ε-outage achievable rate region is characterized. Next, a multi-user SISO interference network is studied. A pilot-assisted ergodic interference alignment (PAEIA) scheme is proposed to conduct channel training, channel state feedback, and data communications. The performance limits are evaluated, and optimum radio resource allocation problems are investigated. The analysis is extended to multi-cell wireless interference networks. A low-complexity pilot-assisted opportunistic user scheduling (PAOUS) scheme is proposed. The proposed scheme includes channel training, one-bit feedback transmission, user scheduling and data transmissions. The achievable rate region is computed, and the optimum number of cells that should be active simultaneously is determined. A multi-user MIMO interference network is also studied. Here, each source sends multiple data streams; specifically, the same number as the degrees of freedom of the network. Distributed transceiver design and power control algorithms are proposed that only require local CSI at terminals. / <p>QC 20141201</p>

The scarce and overpopulated radio spectrum is going to present a major barrier to the growth and development of future wireless networks. As such, spectrum sharing seems to be inevitable to accommodate the exploding demand for high data rate applications. A major challenge to realizing the potential advantages of spectrum sharing is interference management. This thesis deals with interference management techniques in noncooperative networks. In specific, interference alignment is used as a powerful technique for interference management. We use the degrees of freedom (DoF) as the figure of merit to evaluate the performance improvement due to the interference management schemes. This dissertation is organized in two parts. In the first part, we consider the K-user multiple input multiple output (MIMO) Gaussian interference channel (IC) with M antennas at each transmitter and N antennas at each receiver. This channel models the interaction between K transmitter-receiver pairs sharing the same spectrum for data communication. It is assumed that the channel coefficients are constant and are available at all nodes prior to data transmission. A new cooperative upper-bound on the DoF of this channel is developed which outperforms the known bounds. Also, a new achievable transmission scheme is provided based on the idea of interference alignment. It is shown that the achievable DoF meets the upper-bound when the number of users is greater than a certain threshold, and thus it reveals the channel DoF. In the second part, we consider communication over MIMO interference and X channels in a fast fading environment. It is assumed that the transmitters obtain the channel state information (CSI) after a finite delay which is greater than the coherence time of the channel. In other words, the CSI at the transmitters becomes outdated prior to being exploited for the current transmission. New transmission schemes are proposed which exploit the knowledge of the past CSI at the transmitters to retrospectively align interference in the subsequent channel uses. The proposed transmission schemes offer DoF gain compared to having no CSI at transmitters. The achievable DoF results are the best known results for these channels. Simple cooperative upper-bounds are developed to prove the tightness of our achievable results for some network configurations.

Several efficient low complexity interference management techniques were developed for improving the performance of multiple-input multiple-output (MIMO) networks. Sub-optimal techniques involving optimal antenna selection-aided stream control were proposed for joint optimization of co-channel MIMO links in a space division multiple access (SDMA) network. Results indicated that the use of the SDMA scheme along with partial channel state information at the transmitters significantly reduces the signaling overhead with minimal loss in throughput performance. Next, a mean squared error (MSE) based antenna selection framework was presented for developing low complexity algorithms for finite complexity receivers. These selection algorithms were shown to provide reasonable bit-error rate performance while keeping the overall system complexity low. Furthermore, some new algebraic properties of linear orthogonal space-time block codes (OSTBCs) were utilized to develop a single-stage and minimum MSE optimal detector for two co-channel users employing unity rate real and derived rate-1/2 complex OSTBCs. A sub-optimal space-time interference cancellation (IC) technique was also developed for a spatial-multiplexing link subjected to Alamouti interference. The performance of proposed interference management techniques and their implications for future research are discussed.

We study the two-user multiple-input single-output (MISO) Gaussian interference channel where the transmitters have perfect channel state information and employ single-stream beamforming. The receivers are capable of performing successive interference cancellation, so when the interfering signal is strong enough, it can be decoded, treating the desired signal as noise, and subtracted from the received signal, before the desired signal is decoded. We propose efficient methods to compute the Pareto-optimal rate points and corresponding beamforming vector pairs, by maximizing the rate of one link given the rate of the other link. We do so by splitting the original problem into four subproblems corresponding to the combinations of the receivers' decoding strategies - either decode the interference or treat it as additive noise. We utilize recently proposed parameterizations of the optimal beamforming vectors to equivalently reformulate each subproblem as a quasi-concave problem, which we solve very efficiently either analytically or via scalar numerical optimization. The computational complexity of the proposed methods is several orders-of-magnitude less than the complexity of the state-of-the-art methods. We use the proposed methods to illustrate the effect of the strength and spatial correlation of the channels on the shape of the rate region.

La sécurité des systèmes d'information sont primordiales dans la vie d'aujourd'hui, en particulier avec la croissance des systèmes informatiques complexes et fortement interconnectés. Par exemple, les systèmes bancaires ont l'obligation de garantir l'intégrité et la confidentialité de leurs comptes clients. Le vote électronique, des ventes aux enchères et le commerce doit aussi assurer leurs la confidentialité et l'intégrité.Cependant, la vérification de la sécurité et sa mise en œuvre en distribuée sont des processus lourds en général, les compétences de sécurité avancées sont nécessaires puisque les deux configuration de sécurité et l'implementation de systèmes distribué sont complexes et sujette d'erreurs. Avec les attaques de sécurité divers menés par l'environnement Internet, comment pouvons-nous être sûrs que les systèmes informatiques que nous construisons ne satisfont la propriété de sécurité prévu?La propriété de la sécurité que nous étudions dans cette thèse est la non-ingérence, qui est une propriété globale qui permet de suivre les informations sensibles dans l'ensemble du système et de garantir la confidentialité et l'intégrité. La non-ingérence est exprimée par l'exigence selon laquelle aucune information sur des données secrètes est une fuite à travers l'observation de la variation des données publiques. Cette définition est plus subtile qu'une spécification de base de l'accès légitime pour les informations sensibles, ce qui permet d'exploiter et de détecter les dysfonctionnements et malveillants programmes intrusions pour les données sensibles (par exemple, un cheval de Troie qui envoie des données confidentielles aux utilisateurs non fiables). Cependant, comme une propriété globale, la non-interférence est difficile à vérifier et à mettre en œuvre.À cette fin, nous proposons un flux de conception basée sur un modèle qui assure la propriété non-interference dans un logiciel d'application de son modèle de haut niveau conduisant à la mise en œuvre sécurisée décentralisée. Nous présentons la plateforme secureBIP, qui est une extension pour le modèle à base de composants avec des interactions multi-partie pour la sécurité. La non-interference est garantie à l'aide de deux manières pratiques: (1) nous annotons les variables et les ports du modèle, puis selon un ensemble défini de contraintes syntaxiques suffisantes, nous vérifions la satisfaction de la propriété, (2), nous annotons partiellement le modèle, puis en extrayant ses graphes de dépendances de composition nous appliquons un algorithme de synthèse qui calcule la configuration sécurisée moins restrictive du modèle si elle existe.Une fois que la sécurité des flux d'information est établie et la non-interference est établie sur un modèle de haut niveau du système, nous suivons une méthode automatisée pratique pour construire une application distribuée sécurisée. Un ensemble de transformations sont appliquées sur le modèle abstrait de transformer progressivement en bas niveau des modèles distribués et enfin à la mise en œuvre distribuée, tout en préservant la sécurité des flux d'information. La transformations du modèles remplacent coordination de haut niveau en utilisant des interactions multi-partites par des protocoles en utilisant des envoies et reception de messages asynchrone. La distribution est donc prouvé "sécuriser par construction" qui est, le code final est conforme à la politique de sécurité souhaitée. Pour montrer la facilité d'utilisation de notre méthode, nous appliquons et d'expérimenter sur des études et des exemples de cas réels de domaines d'application distincts. / The security of information systems are paramount in today’s life, especially with the growth of complex and highly interconnected computer systems. For instance, bank systems have the obligation to guarantee the integrity and confidentiality of their costumers accounts. The electronic voting, auctions and commerce also needs confidentiality and integrity preservation.However, security verification and its distributed implementation are heavy processes in general, advanced security skills are required since both security configuration and coding distributed systems are complex and error-prone. With the diverse security attacks leaded by the Internet advent, how can we be sure that computer systems that we are building do satisfy the intended security property?The security property that we investigate in this thesis is the noninterference, which is a global property that tracks sensitive information in the entire system and ensures confidentiality and integrity. Non-interference is expressed by the requirement that no information about secret data is leaked through the observation of public data variation. Such definition is more subtle than a basic specification of legitimate access for sensitive information, allowing to exploit and detect malfunctioning and malicious programs intrusions for sensitive data (e.g, Trojan horse that sends confidential data to untrusted users). However as a global property, the noninterference is hard to verify and implement.To this end, we propose a model-based design flow that ensures the noninterference property in an application software from its high-level model leading to decentralized secure implementation. We present the secureBIP framework that is an extension for the component-based model with multyparty interactions for security. Non-interference is guaranteed using two practical manners: (1) we annotate the entire variables and ports of the model and then according to a defined set of sufficient syntactic constraints we check the satisfaction of the property, (2) we partially annotate the model way and then by extracting its compositional dependency graphswe apply a synthesis algorithm that computes the less restrictive secure configuration of the model if it exists.Once the information flow security is established and non-interference is established on an high-level model of the system, we follow a practical automated method to build a secure distributed implementation. A set of transformations are applied on the abstract model to progressively transform it into low-level distributed models and finally to distributed implementation, while preserving information flow security. Model transformations replace high-level coordination using multiparty interactions by protocols using asynchronous Send/Receive message-passing. The distributedimplementation is therefore proven ”secure-by-construction” that is, the final code conforms to the desired security policy. To show the usability of our method, we apply and experiment it on real case studies and examples from distinct application domains.

In order to support the new paradigm shift in fifth generation (5G) mobile communication, radically different network architectures, associated technologies and network operation algorithms, need to be developed compared to existing fourth generation (4G) cellular solutions. The evolution toward 5G mobile networks will be characterized by an increasing number of wireless devices, increasing device and service complexity, and the requirement to access mobile services ubiquitously. To realise the dramatic increase in data rates in particular, research is focused on improving the capacity of current, Long Term Evolution (LTE)-based, 4G network standards, before radical changes are exploited which could include acquiring additional spectrum. The LTE network has a reuse factor of one; hence neighbouring cells/sectors use the same spectrum, therefore making the cell-edge users vulnerable to heavy inter cell interference in addition to the other factors such as fading and path-loss. In this direction, this thesis focuses on improving the performance of cell-edge users in LTE and LTE-Advanced networks by initially implementing a new Coordinated Multi-Point (CoMP) technique to support future 5G networks using smart antennas to mitigate cell-edge user interference in uplink. Successively a novel cooperative uplink inter-cell interference mitigation algorithm based on joint reception at the base station using receiver adaptive beamforming is investigated. Subsequently interference mitigation in a heterogeneous environment for inter Device-to-Device (D2D) communication underlaying cellular network is investigated as the enabling technology for maximising resource block (RB) utilisation in emerging 5G networks. The proximity of users in a network, achieving higher data rates with maximum RB utilisation (as the technology reuses the cellular RB simultaneously), while taking some load off the evolved Node B (eNodeB) i.e. by direct communication between User Equipment (UE), has been explored. Simulation results show that the proximity and transmission power of D2D transmission yields high performance gains for D2D receivers, which was demonstrated to be better than that of cellular UEs with better channel conditions or in close proximity to the eNodeB in the network. It is finally demonstrated that the application, as an extension to the above, of a novel receiver beamforming technique to reduce interference from D2D users, can further enhance network performance. To be able to develop the aforementioned technologies and evaluate the performance of new algorithms in emerging network scenarios, a beyond the-state-of-the-art LTE system-level-simulator (SLS) was implemented. The new simulator includes Multiple-Input Multiple-Output (MIMO) antenna functionalities, comprehensive channel models (such as Wireless World initiative New Radio II i.e. WINNER II) and adaptive modulation and coding schemes to accurately emulate the LTE and LTE-A network standards.

One hypothesis regarding the etiology of Attention-Deficit/Hyperactivity Disorder (ADHD), is to conceptualize the disorder as an "inhibition" disorder. Furthermore, it has been suggested that inhibition is not a single all-encompassing construct, but rather a series of closely related processes. There has been limited examination as to whether children with ADHD are impaired on measures of cognitive inhibition (also known as proactive and retroactive interference). This project examined children with ADHD's susceptibility to proactive and retroactive interference in both verbal and visual-spatial modalities in comparison to typically developing children utilizing a novel coding system of the Children's Memory Scale (CMS). It was found that children with ADHD exhibited greater levels of visual-spatial retroactive interference than their typically developing peers. Additionally, children with ADHD did not differ from controls on any measure of verbal interference. Implications for clinical practice and future directions for research are discussed.

Abstract Conventional versions of linear multiuser detectors (MUD) are not feasible in the wideband code division multiple access (WCDMA) downlink due to the use of long scrambling sequences. As an alternative, linear channel equalizers restore the orthogonality of the spreading sequences lost in frequency-selective channels, thus, suppressing multiple access interference (MAI) in the WCDMA downlink. In this thesis, linear channel equalizers in WCDMA terminals are studied. The purpose of the thesis is to develop novel receivers that provide performance enhancement over conventional rake receivers with an acceptable increase in complexity, and to validate their performance under WCDMA downlink conditions. Although the WCDMA standard is emphasized as the candidate system, the receivers presented are suitable for any synchronous direct sequence code division multiple access downlink employing coherent data detection and orthogonal user or channel separation. Two adaptive channel equalizers are developed based on the constrained minimum output energy (MOE) criterion and sample matrix inversion method. An existing equalizer based on the matrix inversion lemma is also developed further to become a prefilter-rake equalizer. Performance analysis is carried out for equalizers trained using a common pilot channel and for the channel response constrained MOE (CR-MOE) and sample matrix inversion (SMI) based equalizers developed in the thesis. The linear minimum mean square error (LMMSE) channel equalizer, which assumes a random scrambling sequence, is shown to approximate the performance of the LMMSE MUD. The adaptive CR-MOE, SMI-based, and prefilter-rake equalizers are observed to attain performance close to that of an approximate LMMSE channel equalizer. The equalizers considered are also shown to be suitable for implementation with fixed-point arithmetic. The SMI-based equalizer is shown to provide good performance and to require an acceptable increase in complexity. It is also well suited for symbol rate equalization after despreading, which allows for computationally efficient receiver designs for low data rate terminals. Hence, the SMI-based equalizer is a suitable receiver candidate for both high and low data rate terminals. Adaptive equalizers are considered in conjunction with forward error correction (FEC) coding, soft handover, transmit diversity and high speed downlink packet access (HSDPA). The adaptive equalizers are shown to provide significant performance gains over the rake receiver in frequency selective channels. The performance gains provided by one antenna equalizers are noted to decrease near the edges of a cell, whereas the equalizers with two receive antennas achieve significant performance improvements also with soft handover. The performance gains of one or two antenna equalizers are shown to be marginal in conjunction with transmit antenna diversity. Otherwise the equalizers are observed to attain good signal-to-noise-plus-interference ratio performance. Therefore, they are also suitable receiver candidates for HSDPA.

Les monocytes inflammatoires Ly-6Chigh murins, et leurs homologues humains CD14+CD16-, jouent un rôle important dans l'initiation et la persistance des maladies inflammatoires chroniques. Leur action délétère dans ces pathologies a mené au développement de stratégies thérapeutiques visant à les éliminer ou empêcher leur recrutement aux sites inflammatoires. Toutefois, ces méthodes se sont avérées peu spécifiques des monocytes et surtout d'une faible efficacité compte tenu de l'aspect hautement inflammatoire des monocytes. Le besoin de développer de nouvelles stratégies est donc nécessaire. Les objectifs de ma thèse ont donc été dans un premier temps de caractériser in vivo le ciblage spécifique des monocytes inflammatoires par la formulation liposomale DMAPAP. Dans un second temps, l'utilisation de DMAPAP pour formuler des siRNA a permis d'évaluer l'efficacité thérapeutique d'une stratégie basée sur l'inhibition spécifique de gènes jouant un rôle clef dans l'inflammation dans les monocytes inflammatoires. Mon travail a permis de montrer dans un modèle préclinique d'arthrite que l'inhibition de gènes régulateurs de l'inflammation dans les monocytes Ly-6Chigh est une approche thérapeutique efficace permettant d'induire une immunomodulation des réponses pathogéniques des lymphocytes T effecteurs, aboutissant au défaut de recrutement des cellules immunitaires dans les articulations et à une amélioration des signes cliniques. J'ai également validé le transfert de cette technologie ex vivo sur cellules humaines primaires. L'inhibition de gènes clefs dans les monocytes inflammatoires représente donc une stratégie prometteuse pour le développement de futures thérapies dans la polyarthrite rhumatoïde. Par ailleurs, mes résultats confirment le rôle central des monocytes inflammatoires dans les pathologies inflammatoires chroniques. / Inflammatory mouse Ly6Chigh monocyte subset and its human counterpart, defined as CD14+ CD16-, play key roles in the initiation and chronicization of immune-mediated inflammatory disorders (IMID). Deleterious effects of monocytes led to the development of therapeutic strategies aiming at depleting them or preventing their recruitment to inflamed tissues. However, these methods are poorly specific with weak efficacy considering the high number of inflammatory monocytes and their marked level of activation. The need for developing new therapeutic approaches is obvious. The aim of my thesis was to characterize selective delivery of a siRNA-containing lipid formulation to the Ly-6Chigh monocyte population and at evaluating the therapeutic potential of this targeted strategy. Using the cationic lipid-based DMAPAP vehicle for in vivo RNAi-mediated gene silencing, my work allowed demonstrating, in a preclinical mouse model of arthritis, the efficacy to inhibit master genes of inflammation specifically within Ly-6Chigh monocytes upon systemic injection. Reduced disease severity in mice was associated with an overall systemic immunomodulation of the pathogenic T cell populations and led to defective mobilization of immune cells to arthritic joints. Importantly, the formulation was successfully optimized in a perspective of clinical application and the targeting of human CD14+CD16- inflammatory monocytes was validated ex vivo. Overall, my findings demonstrate that the silencing of a key gene within Ly-6Chigh monocytes is a promising strategy for future therapeutic intervention in the context of IMID and reinforces the pivotal role of Ly-6Chigh monocytes in inflammatory processes.