77 research outputs found
Reliable Cognitive Ultra Wideband Communication Systems Under Coexistence Constraints
RÉSUMÉ La croissance rapide des systèmes de communication sans fil et la rareté du spectre ont motivé les industries et les fournisseurs ouvrant dans le domaine de communication sans fil de développer des stratégies et des technologies de communication qui peuvent utiliser efficacement les ressources spectrales. La réutilisation pacifique du spectre sous-licence et sous-utilisé peut être une solution prometteuse pour certaines initiatives en cours telles que la communication mobile à haut débit, la communication machine-à -machine, et la connectivité WiFi. Un des plus gros facteurs qui empêche l'approche de cette réutilisation de fréquences est l'effet d'environnements bruyants sur les dispositifs coexistent dans la même bande de fréquence. Par conséquent, la demande pour une stratégie de coexistence pacifique entre les utilisateurs du spectre, des défis et des questions techniques qu'elle engêndre, motive notre recherche. Il est à noter que dans cette thèse, nous considérons un système pratique appelé MB-OFDM UWB (en anglais multiband orthogonal frequency division multiplexing ultra wideband) pour donner un aperçu pratique de ce concept. Pour atteindre cet objectif, d'abord nous examinons le problème d'interférence des utilisateurs secondaires sur les utilisateurs principaux. A cet effet, tenant compte d'un système secondaire OFDM, nous proposons des méthodes de mise en forme du spectre pour les applications de transmission à antennes simples et multiples. Nous présentons une technique débit-efficace nommée “Enhanced active interference cancellation (E - AIC)qui est en effet capable de créer des encoches ayant des caractéristiques flexibles. Afin de résoudre le problème de dépassement du spectre causé pas la technique classique-AIC, nous utilisons une approche multi-contraintes qui à son tour cause un problème multi-contrainte de minimisation (en anglais multi-constraint minimization problem, MCMP). Cependant, un nouvel algorithme itératif basé sur la technique SVD (en anglais singular value decomposition) est proposé, permettant ainsi de réduire la complexité de la solution de MCMP. Les résultats de simulation obtenus montrent que la technique E-AIC proposée fournit de meilleures performances en termes de suppression des lobes latéraux avec 0 dB de dépassement, moins de complexité de calcul et moins de perte de débit par rapport aux méthodes AIC précédentes. Quant aux antennes multiples, nous proposons deux nouvelles techniques AIC, qui utilisent l'idée principale des approches de sélection d'antennes d'émission (en anglais transmit antenna selection, TAS). Bien que les résultats montrent que les deux techniques permettent la création d'encoche identique, la technique per-tone TAS-AIC a la plus grande efficacité spectrale.
Après avoir obtenu une emission sans interférence pour le système MB-OFDM UWB, nous analysons, modélisons et atténuons le bruit impulsif au récepteur MB-OFDM UWB. Pour ce faire, d'abord, nous proposons un cadre analytique qui décrit les principales caractéristiques d'interférence d'un système à ultra large bande et saut temporel (en anglais time-hopping UWB, TH-UWB) niveau de ces paramètres de signalisation. Les résultats montrent que la distribution d'interférence dépend fortement aux paramètres de saut temporel du système TH-UWB.----------ABSTRACT The rapid growth of wireless communication systems along with the radio spectrum's scarcity and regulatory considerations have put the onus on the wireless industries and service providers to develop wireless communication strategies and technologies that can efficiently utilize the spectral resources. Hence, peaceful reuse of underutilized licensed radio frequencies (by secondary users) can be a promising solution for some ongoing initiatives such as mobile broadband, machine-to-machine applications and WiFi connectivity. One of the biggest factors that prevents the spectrum reusing approach to effectively address the spectrum scarcity, is noisy environments result from coexistence of different devices in the same frequency band. Therefore, the request for a peaceful coexistence strategy between spectrum users, which leads to various challenges, and technical issues, motivates our research. It is worth noting that, in this thesis, we consider a practical system called multiband orthogonal frequency division multiplexing ultra wideband (MB-OFDM UWB) as an underlay system to provide a practical insight into this concept. However, all the obtained results and contributions are applicable to other OFDM-based communication systems. Towards this goal, we first investigate the problem of the interference from secondary users to the primary users. For this purpose, considering an OFDM-based secondary communication system, we propose spectrum-shaping methods for single and multiple transmit antennas applications. For single antenna scenario, we present a throughput-efficient enhanced active interference cancellation (E-AIC) technique, which is indeed capable of creating notches with flexible characteristics. In order to address the spectrum overshoot problem of conventional-AIC techniques, we employed a multi-constraint approach, which leads to a multi-constraint minimization problem (MCMP). Hence, a novel iterative singular value decomposition (SVD) based algorithm is proposed to reduce the complexity of the MCMP's solution. The obtained simulation results show that the proposed enhanced-AIC technique provides higher performance in terms of sidelobes suppression with 0 dB overshoot, less computational complexity and less throughput-loss compared to previous constrained-AIC methods. For multiple transmit antennas, we propose two novel AIC techniques employing main ideas behind bulk and per-tone transmit antenna selection (TAS) approaches. Simulation results show that although both techniques provide identical notch creation, the per-tone TAS-AIC technique has higher spectral efficiency
Review on Radio Resource Allocation Optimization in LTE/LTE-Advanced using Game Theory
Recently, there has been a growing trend toward ap-plying game theory (GT) to various engineering fields in order to solve optimization problems with different competing entities/con-tributors/players. Researches in the fourth generation (4G) wireless network field also exploited this advanced theory to overcome long term evolution (LTE) challenges such as resource allocation, which is one of the most important research topics. In fact, an efficient de-sign of resource allocation schemes is the key to higher performance. However, the standard does not specify the optimization approach to execute the radio resource management and therefore it was left open for studies. This paper presents a survey of the existing game theory based solution for 4G-LTE radio resource allocation problem and its optimization
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Scheduling heuristic for reduced complexity of coordinated beamforming in large multi-carrier heterogeneous wireless networks
The research and development of wireless communication systems is often based on relatively simple models of the network topology, the radio channel and the radio propagation. This is considered to be mostly appropriate, as only under these conditions the complex technical problems in this field can be fully solved to their theoretical boundaries. However, it can also be the case that algorithms or concepts created under simplified assumptions perform in a significantly different way, when they are applied in more realistic scenarios.
This Thesis presents research work which can be seen as a step towards extending the existing research on Coordinated Beamforming to a complex network scenario, i.e. to a large-scale heterogeneous multi-carrier network. For this purpose, a complex simulation framework has been developed. This is used to analyse the significant implications the conditions in a complex network can have on the achievable performance gains. In more detail, the out of cluster interference and the number of mobile stations are identified as factors which heavily influence the performance. This knowledge is then used to design a novel scheduling heuristic, designed to be able to adapt to the particular network scenarios and to estimate the extent of the achievable performance gains. Our simulation results show that the new heuristic achieves significant performance gains for a low number of mobile stations (by applying zero forcing precoding) as well as for a high number of mobile stations (by a coordinated resource assignment that intelligently pairs mobile stations when applying maximum ratio transmission). The Thesis also demonstrates that the effect of the out of cluster interference can cause the reduction of the achievable gains. Due to the knowledge of performance limiting factors, the scheduling heuristic is in addition able to realize a trade-off between complexity and performance by excluding transmission parameters from the scheduling process which are not expected to be beneficial
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