Cognitive radio network has emerged as a prevailing technique and an exciting and promising technology which has the potential of dealing with the inflexible prerequisites and the inadequacy of the radio spectrum usage. In cognitive radios, in-band sensing is fundamental for the protection of the licensed spectrum users, enabling secondary users to vacate channels immediately upon detection of primary users. This channel sensing scheme directly affects the quality-of-service of cognitive radio user and licensed user especially with the undesirable delay induced into the system. In this thesis, a combination of different delay reduction schemes from different papers has been introduced, the first paper [47] argues about performing fine sensing for non-real time traffic, while real time traffic continues transmission in the channel. The second paper [46] argues about performing fine sensing after multiple alarms that have been triggered. Both schemes have combined with applying data rate reservation as well in order to reduce as much as possible this crucial factor of delay for IEEE 802.22 wireless regional area network and to improve the channel utilization. Data rate reservation for real time users has been applied in order to reduce the queuing delay for real time services [47]. The average packet delay for the proposed scheme combination has been analyzed, with both numerical and simulation results. The results show that the scheme combination considerably reduces the average packet delay for both real time and non-real time services and hence satisfies the performance of IEEE 802.22 wireless regional networks. Index terms–Channel sensing, Cognitive radio, energy and feature detection, IEEE 802.22, quiet period. / Kognitiv radio nätverk har vuxit fram som en rådande teknik och en spännande och lovande teknik som har potential att hantera de oflexibla förutsättningar och den bristfälliga Radiospektrumanvändningens. I kognitiv radio, är i-band Sensing grundläggande för skyddet av de licensierade spektrumanvändare, möjliggör sekundära användare att utrymma kanaler omedelbart vid detektering av primära användare. Denna kanal sensing system påverkar direkt kvaliteten på tjänsterna för kognitiv radio användare och licensierade användaren särskilt med oönskad fördröjning induceras i systemet.   I denna avhandling har en kombination av olika system delay minskning från olika tidningar införts, den första papper [47] argumenterar om att utföra fina avkänning för icke-realtid trafik, medan realtid trafiken fortsätter sändningen i kanalen. Den andra artikeln [46] argumenterar om att utföra fina avkänning efter flera larm som har utlösts. Båda systemen har i kombination med tillämpning datahastighet bokning samt för att minska så mycket som möjligt denna avgörande faktor för försening för IEEE 802,22 trådlös regionala nätverk och förbättra kanalutnyttjandet. Datahastighet reservation för realtidanvändare har tillämpats för att minska den queuing fördröjningen för realtidstjänster [47]. Den genomsnittliga paket fördröjning för det föreslagna systemet kombinationen har analyserats, med både numeriska och simulering resultat. Resultaten visar att systemet kombinationen avsevärt minskar den genomsnittliga paket fördröjning för både realtid och icke-verkliga tjänster tiden och därmed uppfyller prestanda IEEE 802,22 trådlösa regionala nätverk. / Kungsmarksvagen 71, karlskrona +4520939959

This study examines the long-run accuracy of analyst recommendations issued at the expiration of the initial public offering (IPO) quiet period and examines the relation between the Global Settlement, NYSE Rule 472, NASD Rule 2711, and analyst recommendations. It is expected that firms which receive positive recommendations will outperform the market and firms with neutral recommendations. In addition, it is expected that banks named in the Global Settlement will become more selective when issuing recommendations. This study examines firms engaging in IPOs from July 9, 2002 through December 31, 2005 and finds that analyst ratings have become more balanced following the Global Settlement, NYSE Rule 472, and NASD Rule 2711. When controlling for firm size, underpricing, rating heterogeneity, and analyst affiliation, firms which receive positive analyst ratings experience greater buy-and-hold abnormal returns than firms which do not. Furthermore, firms which receive multiple “buy” ratings outperform firms which receive only one “buy” rating when controlling for underpricing firm size, and the number of neutral ratings. Banks named in the Global Settlement appear to be more selective when issuing positive recommendations. Firms which receive a positive rating from a bank named in the Global Settlement outperform firms which receive a positive rating from a bank not named in the Global Settlement. Lastly, prior to the Global Settlement, it appears that sanctioned banks issued ratings one level higher than they should have. Firms which received positive ratings experienced neutral performance and firms which received natural ratings experienced negative performance. Since the Global Settlement, sanctioned banks appear to issue accurate ratings since positive ratings are associated with increased buy-and-hold abnormal returns and neutral ratings do not significantly impact firm performance.

Le bruit de la circulation routière, et en particulier le bruit des deux-roues motorisés, constituent une importante source de gêne sonore. Afin d’estimer l’exposition sonore dans les villes de plus 100 000 habitants, la directive européenne 2002/49/CE impose la réalisation de cartes de bruit stratégiques, basées sur l’indice Lden. Cet indice est également utilisé dans des relations exposition-réponse, afin de prédire les pourcentages de personnes gênées, notamment par le bruit du trafic routier. En couplant les cartes de bruit stratégiques et ces relations exposition-réponse, des cartes de gêne pourraient être établies. Toutefois, la pertinence de cet indice pour prédire la gêne due au bruit en milieu urbain est souvent remise en cause, car de nombreux facteurs acoustiques influents (e.g. les caractéristiques spectrales et temporelles) ne sont pas pris en compte par cet indice. Cette thèse vise à améliorer la caractérisation de la gêne due au bruit de trafic routier urbain en considérant différentes compositions de trafic et la présence des deux-roues motorisés. Dans ce but, des expériences sont menées en conditions contrôlées. Une première étude a porté sur l’influence de plusieurs facteurs acoustiques relatifs aux périodes de calme et aux bruits de passage de véhicules sur la gêne due au bruit de trafic routier urbain. Cette étude a conclu à l’influence de la présence de périodes de calme et du nombre de véhicules au sein du trafic routier urbain et à l’absence d’influence de l’ordre des véhicules routiers, de la position et de la durée des périodes de calme. Ces résultats ont été utilisés afin de mener la caractérisation physique et perceptive de différentes compositions de trafic routier urbain. La régression multi-niveau a été utilisée pour calculer la gêne, en considérant 1) des facteurs acoustiques influents à l’aide de combinaisons pertinentes d’indices et 2) un facteur non acoustique : la sensibilité au bruit. Dans les villes, le bruit routier est souvent entendu en situation de multi-exposition avec d’autres bruits. Dans le cadre de ces travaux de thèse, les situations de multi-exposition aux bruits routier et d’avion ont été étudiées. Pour cela, un travail semblable à celui mené pour le bruit de trafic routier urbain a été mené pour le bruit d’avion conduisant également à des combinaisons pertinentes d’indices. En vue de caractériser les gênes dues aux bruits de trafic routier et d’avion pour des situations de multi-exposition sonore, les données des précédentes expériences ainsi que celles d’une expérience conduite en situation de multi-exposition à ces bruits combinés ont été utilisées au travers d’une régression multi-niveau adaptée, comme cela a pu être mené dans la littérature. La régression multi-niveau a ainsi permis la proposition de modèles de gêne pour chaque source de bruit. Puis, la gêne totale due à des situations de multi-exposition à ces bruits a été étudiée, afin de mettre en évidence les phénomènes perceptifs mis en jeu. Des modèles de gêne totale ont été proposés, en utilisant les modèles de gêne due à chaque source. Enfin, les modèles de gêne obtenus pour chaque source et les modèles de gêne totale ont été confrontés aux données d’une enquête socio-acoustique. A cet effet, une méthodologie a été proposée afin d’estimer les différents indices des modèles à partir des valeurs du Lden, issues de cartes de bruit et utilisées pour définir l’exposition au bruit des personnes enquêtées. Cette confrontation a montré que les modèles proposés à partir d’expériences menées en laboratoire et couplés à la méthodologie d’estimation des indices à partir des valeurs du Lden permettent une bonne prédiction de la gêne in situ. / Road traffic noise, and in particular powered two-wheeler noise, constitute an important source of noise annoyance. In order to estimate the noise exposure in cities of more than 100 000 inhabitants, the European directive 2002/49/EC requires the elaboration of strategic noise maps, based on the Lden index. This index is also used in exposureresponse relationships, to predict the percentages of annoyed people, by road traffic noise for example. By coupling strategic noise maps and these exposure-response relationships, noise annoyance maps could be established. The relevance of this index to predict noise annoyance in cities is however often questioned, since many influential acoustical factors (e.g. spectral and temporal features) are not considered by this index. The aim of this thesis is to enhance the characterization of noise annoyance due to different compositions of urban road traffic including powered two-wheelers. To achieve this goal, experiments were carried out under controlled conditions. A first study concerned the influence of several acoustical features related to quiet periods and vehicle pass-by noises on the annoyance due to urban road traffic noise. This study demonstrated the influence of the presence of quiet periods and of the number of vehicles within the urban road traffic and to the absence of the influence of the order of the vehicle pass-by noises, the position and duration of quiet periods. These results were used to carry out the physical and perceptual characterization of different compositions of urban road traffic noise. Multilevel regression was used to calculate noise annoyance, by coupling combinations of indices relating to influential acoustical features and an individual factor: noise sensitivity. In cities, road traffic noise is often combined with other noises. In the framework of this thesis, noise exposure to road traffic noise combined with aircraft noise was studied. Therefore, the same work as the one performed for urban road traffic noise was carried out for aircraft noise, leading also to relevant combinations of noise indices. In order to characterize annoyances due to road traffic noise and to aircraft noise in a combined exposure situation, data from the previous experiments and from an experiment dealing with these combined noises were used through an appropriate multilevel regression, as done in literature. The regression allows annoyance models for each noise source to be proposed. Then, total annoyance due to combined noises was studied, in order to highlight the perceptual phenomena related to the combined exposure. Total noise annoyance models were proposed, using proposed annoyance model of each noise source. Finally, these single source annoyance models and total annoyance models were tested using data of a socio-acoustic survey. To do this, a methodology has been proposed to estimate the different indices involved in the annoyance models, from the Lden values obtained from the strategic noise maps and used to define the noise exposure of the respondents. This confrontation showed that the models proposed on the basis of experiments carried out under laboratory conditions and coupled with a methodology of estimation of the noise indices from Lden values, enabled a good prediction of in situ annoyance.