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

GT2006-90011 Comparative Investigation of Advanced Combined Cycles

ABSTRACT Combined cycles, at present, have a prominent role in the power generation and advanced combined cycles efficiencies have now reached to 60 percent. Examination of thermodynamic behavior of these cycles is still carried out to determine optimum configuration and optimum design conditions for any cycle arrangement. Actually the performance parameters of these cycles are under the influence of various parameters and therefore the recognition of the optimum conditions is quiet complicated. In this research an extensive thermodynamic model was developed for analyzing major parameters variations on gas turbine performance and different configurations of advanced steam cycles: dual and triple pressure cycles with and without reheating in steam turbine sections. In this model it is attempted to consider all factors that affect on actual behavior of these cycles such as blade cooling (air cooling) in gas turbine and different formulations for Heat Recovery Steam Generator (HRSG) performance calculation. Results show good agreement with manufactures data. In the case of gas turbine cycle, location of coolant extraction has large influence on cycle performance. For extraction from compressor end, improving blade cooling technology is suitable than increasing TIT. For mid stage extraction, improving blade cooling technology and TIT has similar effects on efficiency, while power is more sensitive to TIT. Coolant air precooling has large positive effect in high TIT and medium blade cooling technology, but always it increases power. Turbine exhaust temperature has large influence on optimum layout and configuration of HRSG, while for low exhaust temperatures increasing number of pressure levels increase power and heat recovery greatly, for high exhaust temperatures this leads lower enhancement in power and recovery. Second law efficiency of HRSG is proportional to power production in steam cycle. It decreases with increasing gas turbine exhaust temperature. NOMENCLATUR

Assessing the capability of satellite data for soil mapping

The purpose of this research is to evaluate the potential of using landsat ETM+ data for soil mapping. The study area is located in center of Iran and covers about 1300 ha. The database of studied area was created by introducing topographic map (1:25,000), soil map (1:20,000) and reports and satellite data. After pre-possessing stage, selection of the best informative bands was carried out using optimum index factor (OIF) calculation and principle component analysis (PCA). Results showed that bands TM1, TM4 and TM6-2 contain the highest information and the lowest redundancy. Besides the mentioned bands, TM5 and TM7 were considered for digital image classification. The images were classified using maximum likelihood classifier into seven mapping units. Separability of mapping units examined at 95% confidence level. Comparison of the prepared soil map from satellite data and ground truth showed a relatively high accuracy of 80%. Also, comparison of prepared soil map from satellite data and detailed soil maps prepared using conventional methods showed imagery data could increase the classification and interpretative purity percentage up to 50% and 85%, respectively. The results indicated high potential of imagery data for inventory and increasing the precision of existing soil maps. Therefore, incorporation of high-resolution satellite data for soil survey especially in arid and semi-arid regions is highly recommended

On the Use of Adaptive Loading algorithms in MIMO-OFDM Systems

Abstract- In this paper, Optimum adaptive loading algorithms are applied to Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system. Chaw’s and Compello’s algorithms have been implemented to obtain a bit and power allocation for each subcarrier assuming instantaneous channel knowledge. Channel matrix singular value decomposition (SVD) method has been employed in MIMO-OFDM system in order to overcome subchannel interference. The effectiveness of these techniques has demonstrated through the simulation of an Adaptive MIMO-OFDM system, and the comparison shown that the proposed algorithms ensure better performance in the case of MIMO vs. SISO

Quantitative Prediction of Twitter Message Dissemination: A Machine Learning Approach

Predicting the popularity of contents in social networks is quite important for several applications such as viral marketing, news propagation and personalization. In this work, we developed an statistical learning approach to predict the popularity of tweets in the twitter social network. We extracted several user-based, tweet-based and network-based features from each tweet and adopted several classifiers to predict the popularity of tweets. We model this problem with a binary classification problem where popular tweets are considered as the positive and non-popular tweets are considered as the negative class. Popularity is defined by a threshold which indicates how many time a tweet is retweeted. We defined several popularity thresholds and examined the performance of different classifiers based on different threshold values. Our experimental results show that there is no global best classifier for the problem of popularity prediction in twitter but depending on the dataset, popularity threshold and our interest, we can adopt an optimal classifier with a proper set of features for this task.Information ArchitectureMedia and Knowledge EngineeringElectrical Engineering, Mathematics and Computer Scienc