The focus of this thesis is on cooperative spectrum sensing and related security issues in multi-channel cognitive radio networks (MCCRNs). We first study the channel assignment for cooperative spectrum sensing in MCCRNs to maximize the number of available channels. In centralized implementation, a heuristic scheme is proposed along with a greedy scheme to reduce the reported information from the cognitive radios (CRs). In distributed scenario, a novel scheme with multi-round operation is designed following the coalitional game theory. Next, we focus on the physical layer security issues for cooperative spectrum sensing in MCCRNs, caused by Byzantine attacks. New counterattacks are proposed to combat attacks comprising coalition head and CRs as Byzantine attackers, which target to reduce the number of available channels for sensing in distributed MCCRNs. First, a new secure coalition head selection is proposed, by using statistical properties of the exchanged SNRs in the coalitions. Then, an iterative algorithm is proposed to block out attackers, if they continue attacking the system. The important problem of key management is considered next, and an energy-efficient identity-based and a certificate-based distributed key management schemes are proposed. First, a new elliptic curve cryptography (ECC)-based distributed private key generation scheme is proposed to combat the single point of failure problem along with novel distributed private key generator (DPKG) selection schemes to preserve security and energy-efficiency. Because of its importance in the proposed identity-based key management scheme, we further propose a low-complexity DPKG assignment, based on multi-objective programming, which can capture DPKG fairness in addition to energy-efficiency. Finally, a more powerful and intelligent distributed cooperative Byzantine attack on the proposed multi-channel cooperative spectrum sensing is proposed, where attackers collude by applying coalitional game theory to maximize the number of invaded channels in a distributed manner. As a remedy, a hierarchical identity-based key management scheme is proposed, in which CRs can only play on a certain number of requested channels and channel access for sensing is limited to the honest CRs selected in the coalitional game. Simulation results show that the proposed schemes can significantly improve cooperative spectrum sensing and secure the system against Byzantine attacks.

This thesis presents a framework for automatic recognition of human actions in uncontrolled, realistic video data such as movies, internet and surveillance videos. In this thesis, the human action recognition problem is solved from the perspective of local spatio-temporal feature and bag-of-features representation. The bag-of-features model only contains statistics of unordered low-level primitives, and any information concerning temporal ordering and spatial structure is lost. To address this issue, we proposed a novel multiscale local part model on the purpose of maintaining both structure information and ordering of local events for action recognition. The method includes both a coarse primitive level root feature covering event-content statistics and higher resolution overlapping part features incorporating local structure and temporal relationships. To extract the local spatio-temporal features, we investigated a random sampling strategy for efficient action recognition. We also introduced the idea of using very high sampling density for efficient and accurate classification. We further explored the potential of the method with the joint optimization of two constraints: the classification accuracy and its efficiency. On the performance side, we proposed a new local descriptor, called GBH, based on spatial and temporal gradients. It significantly improved the performance of the pure spatial gradient-based HOG descriptor on action recognition while preserving high computational efficiency. We have also shown that the performance of the state-of-the-art MBH descriptor can be improved with a discontinuity-preserving optical flow algorithm. In addition, a new method based on histogram intersection kernel was introduced to combine multiple channels of different descriptors. This method has the advantages of improving recognition accuracy with multiple descriptors and speeding up the classification process. On the efficiency side, we applied PCA to reduce the feature dimension which resulted in fast bag-of-features matching. We also evaluated the FLANN method on real-time action recognition. We conducted extensive experiments on real-world videos from challenging public action datasets. We showed that our methods achieved the state-of-the-art with real-time computational potential, thus highlighting the effectiveness and efficiency of the proposed methods.

Background – Previous research has evaluated different distribution systems and chan-nels that companies operate through. However, research primarily has focused on the richness of online channels rather than the value of physical stores. The following report will examine the reasons and implications underlying the choice of channel strategy. Purpose – The purpose of this thesis is to examine the reason why companies within the fashion and apparel industry, operating in Sweden, choose to operate through a certain market channel strategy. The thesis aims to evaluate four types of market channel strat-egies with the help of case companies. Method – A qualitative approach to the research has been chosen which consists of a case study including four companies representing different channel strategies. Data col-lection for the analysis where conducted through interviews with persons having vital positions within one of the four companies. Results and Discussion – The case companies ASOS, Bubbleroom, Cubus and Dressmann each represent one of the chosen market channels. The interviews presented in the results section implied that the companies chosen channel was more appropriate for the market they operated in as well as the target group they were aiming to reach. Conclusion – Even though research states that today’s society is moving away from the physical store market channel, this study proved that one single strategy is not appropri-ate for all businesses. A company will have to research their target market before ap-propriately selecting a channel strategy.

This thesis addresses the problem of `efficient' broadcast in a multi-radio multi-channel multi-rate wireless mesh network (MR$^2$-MC WMN). In such a MR$^2$-MC WMN, nodes are equipped with multiple radio network interface cards, each tuned to an orthogonal channel, that can dynamically adjust transmission rate by choosing a modulation scheme appropriate for the channel conditions. We choose `broadcast latency', defined as the maximum delay between a packet's network-wide broadcast at the source and its eventual reception at all network nodes, as the `efficiency' metric of broadcast performance. The problem of constructing a broadcast forwarding structure having minimal broadcast latency is referred to as the `minimum-latency-broadcasting' (MLB) problem. While previous research for broadcast in single-radio single-rate wireless networks has highlighted the wireless medium's `\emph{wireless broadcast advantage}' (WBA); little is known regarding how the new features of MR$^2$-MC WMN may be exploited. We study in this thesis how the availability of multiple radio interfaces (tuned to orthogonal channels) at WMN nodes, and WMN's multi-rate transmission capability and WBA, might be exploited to improve the `broadcast latency' performance. We show the MLB problem for MR$^2$-MC WMN to be NP-hard, and resort to heuristics for its solution. We divide the overall problem into two sub-problems, which we address in two separate parts of this thesis. \emph{In the first part of this thesis}, the MLB problem is defined for the case of single-radio single-channel multi-rate WMNs where WMN nodes are equipped with a single radio tuned to a common channel. \emph{In the second part of this thesis}, the MLB problem is defined for MR$^2$-MC WMNs where WMN nodes are equipped with multiple radios tuned to multiple orthogonal channels. We demonstrate that broadcasting in multi-rate WMNs is significantly different to broadcasting in single-rate WMNs, and that broadcast performance in multi-rate WMNs can be significantly improved by exploiting the availability of multi-rate feature and multiple interfaces. We also present two alternative MLB broadcast frameworks and specific algorithms, centralized and distributed, for each framework that can exploit multiple interfaces at a WMN node, and the multi-rate feature and WBA of MR$^2$-MC WMN to return improved `broadcast latency' performance.

One of the most important steps in the search for life on Mars is to determine if a specific sub-surface location it is "habitable", or that it provides the conditions and requirements to support life as we know it. In this thesis, I present a miniature, thermal-IR radiometer and reflectometer designed to determine temperature, the presence of water ice, and the discrimination of minerals, all necessary for a habitable environment. A dual use detector was selected for the thermal and five reflectance channels. The IR source is provided by five LEDs. These components were embedded in a thermally controlled aluminium block. Integrated electronics provided signal amplification and demodulation. This device will be suitable for drilling applications with less than 25 mm diameter boreholes and with limited available power (<5watts). Thermal testing was within a simulated borehole mounted in a thermal vacuum chamber. The results were compared to a theoretical model of the expected temperature. The maximum temperature error between predicted and measured was 0.21 K (∼0.08%). The total RMS error of all sources were calculated to be <3%. Reflectance testing in all five channels included a variety of minerals and a two point calibration method. The results were compared to the predicted reflectance values for the samples. The results of the reflectance channel testing demonstrated that the measured values matched the predicted values with a 2.5% measured error. The total RMS error was 6.1%. Detection and discrimination of water ice and hydrated minerals included a non-linear mixing model and/or testing. The model predicted that water ice mixed in a pyroxene mineral matrix can be detected and discriminated from 5% to 60% concentration by weight. Testing with a hydrated mineral mixed within a non-hydrated mineral matrix demonstrated that the measured result matched the predicted result from 5-45% concentration by weight.

abstract: Today, many wireless networks are single-channel systems. However, as the interest in wireless services increases, the contention by nodes to occupy the medium is more intense and interference worsens. One direction with the potential to increase system throughput is multi-channel systems. Multi-channel systems have been shown to reduce collisions and increase concurrency thus producing better bandwidth usage. However, the well-known hidden- and exposed-terminal problems inherited from single-channel systems remain, and a new channel selection problem is introduced. In this dissertation, Multi-channel medium access control (MAC) protocols are proposed for mobile ad hoc networks (MANETs) for nodes equipped with a single half-duplex transceiver, using more sophisticated physical layer technologies. These include code division multiple access (CDMA), orthogonal frequency division multiple access (OFDMA), and diversity. CDMA increases channel reuse, while OFDMA enables communication by multiple users in parallel. There is a challenge to using each technology in MANETs, where there is no fixed infrastructure or centralized control. CDMA suffers from the near-far problem, while OFDMA requires channel synchronization to decode the signal. As a result CDMA and OFDMA are not yet widely used. Cooperative (diversity) mechanisms provide vital information to facilitate communication set-up between source-destination node pairs and help overcome limitations of physical layer technologies in MANETs. In this dissertation, the Cooperative CDMA-based Multi-channel MAC (CCM-MAC) protocol uses CDMA to enable concurrent transmissions on each channel. The Power-controlled CDMA-based Multi-channel MAC (PCC-MAC) protocol uses transmission power control at each node and mitigates collisions of control packets on the control channel by using different sizes of the spreading factor to have different processing gains for the control signals. The Cooperative Dual-access Multi-channel MAC (CDM-MAC) protocol combines the use of OFDMA and CDMA and minimizes channel interference by a resolvable balanced incomplete block design (BIBD). In each protocol, cooperating nodes help reduce the incidence of the multi-channel hidden- and exposed-terminal and help address the near-far problem of CDMA by supplying information. Simulation results show that each of the proposed protocols achieve significantly better system performance when compared to IEEE 802.11, other multi-channel protocols, and another protocol CDMA-based. / Dissertation/Thesis / Ph.D. Computer Science 2010

Previous studies have revealed that the creation of synergy among retailers’ channels can enhance customers’ satisfaction and loyalty. Nevertheless, little is known about utilising such synergy in inducing customers’ purchasing behaviour in electronic commerce. In an attempt to address this issue, few empirical studies have been conducted into the role of trust transference from brick to click channels in order to understand customers’ purchasing intentions. These empirical studies have mainly focused on interpersonal trust as a proxy of the transference process. Therefore, the present study seeks to articulate the importance of impersonal trust, and shed light on its expected role in the transference process during the introductory stage of customers’ interaction. Impersonal trust, or perceived structural assurance as labelled in this study, refers to customers’ beliefs in the legal and technological structures of retailers’ websites. However, the introductory stage describes the state of customers when they have not yet been exposed to a retailer’s website. These notions are thoroughly reviewed and synthesised to achieve a proper conceptualisation and operationalisation for the perceived structural assurance. Then, on the basis of previous theories and studies, a conceptual model is constructed to determine several drivers of the perceived structural assurance, as well as its consequences. With regard to the research methodology, a quantitative triangulation choice is adopted in the present study. This choice involves the design of a survey questionnaire, which is employed after relying on several explorative instruments. However, upon the insights of a pilot study, a total of 304 responses are used to analyse the overall research data. Then, the results are generated through an advanced stage of statistical analysis which is performed by Structural Equation Modelling (SEM). The results indicate that the validated model is robust and can be used in generalising the findings of the current research. The novelty of this study involves several contributions to the body of knowledge and practice. This study develops a model that theoretically extends the existing knowledge on the trust transference phenomenon and posits an effective approach of triangulating methods in quantitative research. Lastly, this study contributes to the practice by presenting evidence to support the synergy among retailers’ brick and click channels.

Dans cette thèse, nous nous concentrons sur la conception et l’optimisation de performances inter-couches dans les réseaux maillés radio multi-canal multi-interface. Afin de profiter de l'augmentation de la capacité de ces réseaux, un certain nombre de problèmes doit être résolu. La première contribution de cette thèse est une nouvelle classification et une évaluation formelle des différentes stratégies d’assignation de canaux et d’interfaces. Nous adressons en particulier la connectivité en termes de formation de topologie, densité de connexions et découverte de voisinage. La deuxième contribution présente des algorithmes de broadcast fonctionnant pour n’importe quelle stratégie d’assignation multi-canal multi-interface. Ces algorithmes garantissent qu’un paquet de broadcast est délivré avec une probabilité minimale à tous les voisins. La troisième contribution de cette thèse propose d’évaluer la capacité (débit) obtenue à travers les différentes solutions d’assignation de canaux et d’interfaces. Plus précisément, nous proposons trois formulations de programmation linéaire mixte pour modéliser le routage et les contraintes de partage de bande passante en présence d'interférences. Nous dérivons ensuite des bornes supérieures et inférieures pour deux stratégies MAC différentes. Notre dernière contribution propose de développer une solution de routage inter-couches pour les réseaux maillés multi-canal multi-interface. En particulier, nous proposons une métrique de qualité de lien estimant la bande passante résiduelle d'un lien. Un protocole de routage adapté permet ensuite de trouver les routes offrant le meilleur débit. Toutes nos contributions sont validées par des nombreuses simulations qui démontrent l'efficacité de nos solutions. En résumé, cette thèse fournit une analyse en profondeur des réseaux maillés radio multi-canal multi-interface, ainsi que des lignes directrices pour les concepteurs de réseaux afin de déployer des réseaux performants. / In this PhD thesis, we focus on the design and performance optimization of multi-channel multi-interface wireless mesh networks. To take advantage of the increased capacity in such networks, a number of issues has to be handled properly. The first contribution of this thesis is a novel classification and formal evaluation of different channel and interface assignment strategies. In particular, we focus on connectivity in terms of topology formation, density of connections, and neighbor discovery. Our second contribution presents broadcast algorithms able to handle any of the multi-channel multi-interface assignment strategies. These algorithms guarantee a broadcast packet to be delivered with a minimum probability to all neighbors. The third contribution of this thesis consists in evaluating the network capacity (i.e., throughput) obtained through the different channel and interface assignments schemes. More specifically, we propose three mixed integer linear programming formulations to model the routing and bandwidth sharing constraints in presence of interference. We derive then upper and lower bounds for different MAC strategies. The fourth and last contribution of this thesis is the development of a novel cross-layer routing solution for multi-channel multi-interface mesh networks. In particular, we propose a link-quality aware metric to estimate the residual bandwidth of a link. An on-demand routing protocol selects the routes offering the best throughput. All our contributions are validated through extensive simulations that demonstrate the efficiency of our solutions. In summary, this thesis provide insight into the improvement of multi-channel multi-interface wireless mesh networks, as well as guidelines for network designers in planning efficient deployments.

Med hjälp av digitalisering och IT-utvecklingen har både marknadsförare och svenska konsumenter större valfrihet och möjligheter gällande försäljningskanaler och konsumtion. Med denna utveckling har det även skapats utmaningar för såväl marknadsförare som konsumenter. Å ena sidan behöver marknadsförare kunna erbjuda konsumenter försäljning via olika kanaler såsom fysiska butiker och nätbutiker, å andra sidan behöver konsumenter vara aktiva informationssökare och fatta många beslut som exempelvis pålitlighet gällande val av nätaktörer och deras erbjudanden. Enligt en undersökning, som genomförts av Kreditor, vill konsumenter överlag ha säkerhet och trygghet gällande konsumtion via internet (Dagens Handel 2007). Man kan tyda att näthandel kan innebära risker. Trots detta verkar näthandel fått fotfäste på den svenska marknaden och denna typ av konsumtion verkar bli allt vanligare bland svenska konsumenter (PostNord 2017 & Statistiska Centralbyrån 2017). Vår studie baseras bland annat på teorier inom konsumentbeteendevetenskap och olika marknadsföringsstrategier. För att få djupare kunskap om vad som gör att svenska konsumenter handlar i allt större utsträckning via nätet har vi genomfört en enkätundersökning gällande svenska konsumenternas åsikter kring näthandel, hur ofta de handlar och vilka faktorer som ligger bakom deras val av okända nätaktörer. Enkäten redovisar bland annat att positiva erfarenheter och att imitation driver svenska konsumenter till att vilja handla via internet. Faktorer som skapar förtroende och viljan att handla hos okända nätaktörer är olika betalningsalternativ, konsumentskydd, omdömen och rekommendationer från andra konsumenter och att företag använder sig av multikanalförsäljning såsom fysisk- och nätbutik. I vår undersökning fann vi att förtroende bland svenska konsumenter uppstår av konsumenterna själva och detta grundas på marknadsföringsstrategier såsom mun till mun metoden och principen om sociala bevis. Vi fann även att konsumenter verkar vara aktiva informationssökare gällande handel hos okända nätaktörer. / Based on digitalization and IT development marketers and Swedish consumers have increased the number of choices and opportunities regarding sales channels and consumption and through this development new challenges have been introduced to the actors on the market. On the one hand, marketers need to be able to offer consumers sales through various channels such as physical stores and online stores, on the other hand, consumers need to be active information seekers and make many decisions such as judging reliability in selecting online actors and their offers. According to a survey conducted by Kreditor, consumers in general are conscious when it comes to reliability and security regarding consumption via the Internet (Dagens Handel 2007). It can be argued that online shopping can pose risks. Nevertheless, online shopping seems to have been a foothold in the Swedish market and this type of consumption seems to be becoming more common among Swedish consumers (PostNord 2017 & Statistiska Centralbyrån 2017). Our study is based, among other things, on theories in consumer behavioral science and different marketing strategies. In order to get a deeper knowledge of factors behind Swedish consumers increasing online shopping we have conducted a survey of the Swedish consumers' opinions about online trading, how often they are trading together with which underlying factors that are important when buying from unknown online players. The survey states, among other things, that positive experiences and imitation drive Swedish consumers to want to shop online. Factors that create trust and willingness to trade with unknown online actors are for example different payment options, consumer privacy-policy, ratings and recommendations from other consumers but also if the companies use multi-channel sales such as both physical and online stores. In our survey we found that trustfulness for online shopping among Swedish consumers arises from marketing strategies such as word of mouth-method and the principle of social evidence. We also found that consumers seem to be active information seekers regarding trade with unknown online operators.

This thesis aims to answer the research question of how an industrial retailer’s level of channel integration can be evaluated and improved. A conceptual model is developed and applied in a case study context of the shop channel of a large international industrial distributor of maintenance, repair and operations goods. Marketing channel integration is proven to improve customer satisfaction, customer loyalty and customer expenditure - despite these benefits, there does not exist any evaluation method that helps researchers or practitioners determine the level of channel integration of an industrial retail channel. The case study follows a mixed method approach and uses qualitative data from in-depth interviews with 11 managers and 24 employees, as well as quantitative data from a management survey with 26 respondents. Using the conceptual model the shop channel of the German parent company was rated at a multi-channel level of integration and the Dutch shop channel at a multiple channel level of integration. Any improvement to the level of channel integration of an industrial retail channel depends on the understanding of and commitment to the integrated channel strategy by the shop management.