The model and design of a generic security provider provides a comprehensive set of security services, mechanisms, encapsulation methods, and security protocols for Java applications. The model is structured in four layers; each layer provides services to the upper layer and the top layer provide services to applications. The services reflect security requirements derived from a wide range of applications; from small desktop applications to large distributed enterprise environments. Based on the abstract model, this paper describes design and implementation of an instance of the provider comprising various generic security modules: symmetric key cryptography, asymmetric key cryptography, hashing, encapsulation, certificates management, creation and verification of signatures, and various network security protocols. This paper also describes the properties extensibility, flexibility, abstraction, and compatibility of the Java Security Provider.
The model and design of a generic security provider provides a comprehensive set of security services, mechanisms, encapsulation methods, and security protocols for Java applications. The model is structured in four layers; each layer provides services to the upper layer and the top layer provide services to applications. The services reflect security requirements derived from a wide range of applications; from small desktop applications to large distributed enterprise environments. Based on the abstract model, this paper describes design and implementation of an instance of the provider comprising various generic security modules: symmetric key cryptography, asymmetric key cryptography, hashing, encapsulation, certificates management, creation and verification of signatures, and various network security protocols. This paper also describes the properties for extensibility, flexibility, abstraction, and compatibility of the Java security provider.
This paper describes the design and implementation of a comprehensive system for protection of Web contents. In this design, new security components and extended security features are introduced in order to protect Web contents ageist various Web attacks. Components and extended security features are: protection of Web pages using strong encryption techniques, encapsulation of Web contents and resources in PKCS#7, extended secure execution environment for Java Web Server, eXtensible Access Control Markup Language (XACML) based authorization policies, and secure Web proxy. Design and implementation of our system is based on the concepts of generic security objects and component-based architecture that makes it compatible with exiting Web infrastructures without any modification.
This paper describes security extensions of various Windows components based on usage of FIPS 201 (PIV) smart cards. Compared to some other similar solutions, this system has two significant advantages: first, smart cards are based on FIPS 201 standard and not on some proprietary technology; second, smart card security extensions represent an integrated solution, so the same card is used for security of several Microsoft products. Furthermore, our smart card system uses FIPS 201 applet and middleware with smart card APIs, so it can also be used by other developers to extend their own applications with smart card functions in a Windows environment. We support the following security features with smart cards: start-up authentication (based on PIN and/or fingerprint), certificate-based domain authentication, strong authentication, and protection of local resources. We also integrated our middleware and smart cards with MS Outlook and MS Internet Explorer.
KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Communication Systems, CoS.
Multiple constellations has been proposed recently as a way of improving the system performance when used in conjunction with Orthogonal Transmit Diversity (OTD) for high level linear modulation schemes. This paper considers the use of multiple constellations in Multiple Input Multiple Output (MIMO) antenna systems. The premise is that the same modulation scheme is used with different bits to symbols mapping for each branch. This improved beamforming results in better performance as compared to MIMO-MRC where the same bits to symbols mapping is used on all branches. Analytical expression for Symbol Error Probability (SEP) is derived. The results obtained show that the new proposed improved beamforming scheme outperforms conventional MIMO-MRC with a performance dividend that increases with the linear modulation level.
To enhance the wireless bandwidth utilization, new forms of innovative spectrum policies, dynamically sharing channels over time and space, have been discussed. Dynamic spectrum access lets systems share the spectrum, to achieve better band-width utilization and trunking gains. In this work, we consider a case where such access is performed in an uncoordinated fashion. The paradigm shift to open frequency bands implies a need to investigate and verify resulting capacity gains. Herein, we give a general method for evaluating system capacity subject to outage probability constraints over fading channels, in an unlicensed band environment with uncoordinated systems. The channel fading effects include both attenuation, shadowing and multipath propagation and we end up with expressions, which are solved by numerical integration. The spectrum sharing is here performed by means of autonomous dynamic channel allocation (DCA), and we compare two DCA methods, maximum SIR DCA and random DCA.
Lane detection is an important element of most driver assistance applications. A new lane detection technique that is able to withstand some of the common issues like illumination changes, surface irregularities, scattered shadows, and presence of neighboring vehicles is presented in this paper. At first, inverse perspective mapping and color space conversion is performed on the input image. Then, the images are cross-correlated with a collection of predefined templates to find candidate lane regions. These regions then undergo connected components analysis, morphological operations, and elliptical projections to approximate positions of the lane markers. The implementation of the Kalman filter enables tracking lane markers on curved roads while RANSAC helps improve estimates by eliminating outliers. Finally, a new method for calculating errors between the detected lane markers and ground truth is presented. The developed system showed good performance when tested with real-world driving videos containing variations in illumination, road surface, and traffic conditions.
This thesis addresses the problem of low-cost multicast delivery of multimedia content in future mobile networks. The trend towards reuse of existing infrastructure for cellular and broadcasting for building new systems is challenged, with respect to the opportunities for low cost service provision and scalable deployment of networks.
The studies outline significant potential of hybrid cellular-broadcasting infrastructure to deliver lower-cost mobile multimedia, compared to conventional telecom or broadcasting systems. Even with simple interworking techniques the achievable cost savings can be significant, at least under some specific settings.
The work starts with a foresight study shaped around four scenarios of the future, and continues with the introduction of a high-level framework for radio resource management in Ambient Networks. Two approaches on the hybrid system architecture are considered. The first one assumes different degrees of interworking between conventional cellular and broadcasting systems, in single and multi-operator environments. Second, is a broadcast only system where cellular sites are used for synchronized, complementary transmitters for the broadcasting site. In the first approach, the key issue is the multi-radio resource management, which is strongly affected by the degree of integration between the two networks. Two case studies deal with the problem of delivering, for lowest cost, a data item to a certain number of recipient users. A flexible broadcasting air interface, which offers several transmission data rates that can be dynamically changed, is demonstrated to significantly increase cost efficiency under certain conditions. An interesting result is that real-time monitoring of the user reception conditions is not needed, at least when multicast group is large. This indicates a high degree of integration between cellular and broadcasting networks may not by generally justified by visible cost savings.
Scalability of the hybrid infrastructure deployment is the main topic in the second approach. For a DVB-H type of network, the numerical evaluations show that achievement of economies of scale while increasing network capacity and coverage, by employing higher modulation and coding rate or installing new transmission sites, is difficult. Therefore, a technique based on application-layer forward error correction with Raptor codingA is suggested for enabling a flexible trading between system capacity, perceived coverage and delay, in the case of mobile users.
Contemporary trusted execution environments provide a good foundation for implementing secure user credentials, but these are not properly bound to the application instances that implement their use. This paper introduces a framework for application-specific credentials and provides a prototype implementation using TCG MTM and DRTM technologies. Measurements and a security analysis is presented for the realised architecture.
Large-scale sensor networks, monitoring an environment at close range with high spatial and temporal resolutions are expected to play an important role in various applications, e.g., assessing the "health" of machines; environmental, medical, food-safety, and habitat monitoring; inventory control, building automation, etc. Ensuring the security of these complex and yet resource-constrained systems has emerged as one of the most pressing challenges for researchers. In this paper (i) we present the major threats, and (ii) we present a new approach for decentralized energy efficient intrusion detection that can be used to improve security from both external and internal adversaries.
An optical communications network ( 10) comprising an optical line termination ( 12), and a first optical multiplexer/demultiplexer (MUX/DEMUX) ( 14), comprising N input ports and N output ports. The network (10) further comprises a plurality of wavelength division multiplexed passive optical network (WDM PON) distribution networks (22) coupled to a respective one of the MUX/DEMUX output ports and comprising optical network units (20). Feeder fibres ( 16) are coupled between the optical line termination and a respective one of the MUX/DEMUX input ports. Interconnection fibres ( 18) are coupled between respective pairs of the optical network units.
This research concerns exploiting knowledge of the user's environment (i.e., context information) to enrich a user's communication making it more personal, by ensuring that the user receives only relevant messages and calls in his/her current context, and to facilitate more opportunities for communication interactions with people that are in the same context and that share the same interests as this user. We describe in this licentiate thesis the concepts of context-addressed messaging and context-aware session control that enable users to: (1) send messages to others based on their context, rather than their network address and (2) to initiate, adapt, and terminate user's communication sessions based on this user's current context, respectively. These concepts address questions such as: how to discover, select, and switch to an optimal communication means to meet varying user, contextual, communication, and device resource requirements and preferences. A key to solving these problems is to create a representation of the user's context-dependent preferences and to process the user's context-dependent preferences which are part of context triggers. These context triggers can initiate a communication event upon a particular context update. Additionally, in order to provide the described context-aware communication functions, these mechanisms need timely access to the acquired (desired) context information. This in turn raises a plethora of other questions, such as how to discover sensors that provide the desired context information; how to acquire raw context data from these sensors; how to abstract, process, and model this data to become "understandable" to applications and system components; and how to distribute this context to applications that are running on different nodes.
This research is split into three different parts. The first part concerns investigating and implementing context management functions. As part of this research we propose a novel approach for context synthesis using context operators. We also propose a design architecture for context-aware middleware that mediates between the sensors and applications, and that is able to share and retrieve context from other nodes in the network. The second part of our research concerns our proposed mechanism for context-addressed messaging. To implement this mechanism we designed our own message format, called the Common Profile for Context-Addressed Messaging (CPCAM) that is able to use any high level context to compose a context-based address. Additionally, we proposed to use context-based filtering to find the correct message recipients and determine if this message is relevant to these potential message recipients in their current context, as well as to deliver this message to the recipients' preferred device that is adapted using their preferred communication means. At the end of this second part we design context-addressed messaging system operations on top of a SIP and SIMPLE-based network infrastructure. The third part of our research describes context-aware session control mechanisms using context switch and context trigger constructs. A context-switch selects an action from a set of context-dependent actions upon an incoming communication event based on the receiver's current context. In contrast, a context trigger initiates an action based on a context update and the user's preferences that are specified in this updated context. This part illustrates in several examples the context-aware session control mechanisms, i.e. the initiation of a communication session based on the match of a user's preferences and current context, as well as adaptation and (if necessary) termination of an ongoing communication session based upon the user's context-dependent preferences.
The research leading to this licentiate has created network and system level models necessary for implementation of a context-addressed communication system that would enable users to easily design their own personalized, context-aware communication services. The necessary constructs and properties of these models are designed and analyzed in the thesis, as well as in conference papers and other documents published in the process of doing the research for this thesis. A number of remaining open issues and challenges have been outlined as part of the future work.
Context-aware applications need quickly access to current context information, in order to adapt their behavior before this context changes. To achieve this, the context distribution mechanism has to timely discover context sources that can provide a particular context type, then acquire and distribute context information from these sources to the applications that requested this type of information. This paper reviews the state-of-the-art context distribution mechanisms according to identified requirements, then introduces a resource list-based subscription/notification mechanism for context sharing. This SIP-based mechanism enables subscriptions to a resource list containing URIs of multiple context sources that can provide the same context type and delivery of aggregated notifications containing context updates from each of these sources. Aggregation of context is thought to be important as it reduces the network traffic between entities involved in context distribution. However, it introduces an additional delay due to waiting for context updates and their aggregation. To investigate if this aggregation actually pays off, we measured and compared the time needed by an application to receive context updates after subscribing to a particular resource list (using RLS) versus after subscribing to each of the individual context sources (using SIMPLE) for different numbers of context sources. Our results show that RLS aggregation outperforms the SIMPLE presence mechanism with 3 or more context sources, regardless of their context updates size. Database performance was identified as a major bottleneck during aggregation, hence we used in-memory tables & prepared statements, leading to up to 57% database time improvement, resulting in a reduction of the aggregation time by up to 34%. With this reduction and an increase in context size, we pushed the aggregation payoff threshold closer to 2 context sources.
KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01). Appear Networks, Sweden.
In ubiquitous computing environments there are an increasing number and variety of devices that can generate context data. The challenge is to timely acquire, process, and deliver these data to context-aware applications. The role of context synthesis is to generate new knowledge, as a result of a reasoning process applied to context information that is already present in the system. The success of this mechanism mainly depends on the response time that the end-user or an application must wait for the response to a context query. This paper describes and evaluates an approach to context synthesis on a mobile device to be used by a set of applications in a sports domain. A scenario based on a live race at the Super Prestige Cyclocross in Gieten, Netherlands demonstrates the use of context synthesis to dynamically compose gaps and groups of cyclists in order to provide a nearly real-time virtual ranking service.
KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01). Appear Networks, Sweden .
Inference of high-level context is becoming crucial in development of context-aware applications. An example is social context inference i.e., deriving social relations based upon the user's daily communication with other people. The efficiency of this mechanism mnaimily depends on the method(s) used to draw inferences based on existing evidence and sample information, such as a training data. Our approach uses rule-based data mining. Bayesian network inference, and user feedback to compute the probabilities of another user being in the specific social relationship with a user whose daily communication is logged by a mobile phone. In addition, a privacy mechanism is required to ensure the user's personal integrity and privacy when sharing this user's sensitive context data. Therefore, the derived social relations are used to define a user's policies for context access control, which grant the restricted context information scope depending on the user's current context. Finally, we propose a distributed architecture capable of managing this context information based upon these context access policies.
Markendahl, JanKTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
Network advance reservation is an area of growing interest and focus today. However most proposed solutions in this field have only focused on the scheduling of point-to-point client connections. Now as applications and user communities continue to expand, there is a growing need to extend advance reservation support for multipoint services. To address this concern, a heuristic solution is presented for virtual overlay network scheduling. The scheme uses graph-theoretic schemes and is analyzed in detail using network simulation.
Wireless communications are experiencing a great increasing demand, both user and bandwidth capacity. The efficiency in the resource management and usage will be a dramatically important issue since spectrum and power is a scarce resource, even more in the wireless environment. Under these circumstances, adaptive resource management will lead to high spectral efficiency rates and power saving algorithms. Previous works have focused on increasing the system capacity by means of complex power and rate adaptation techniques at the expense of unfair systems. The present proposal proposes a low complexity algorithm for adaptive resource allocation considering different quality of service classes in a Multicarrier-Code Division Multiple Access (MC-CDMA) system, which is considered according to several researches, as a promising air interface scheme for the Beyond 3G systems.
This article investigates efficient broadcast delivery of file download (filecasting) services in hybrid broadcast and cellular systems formed by a DVB-H network and an evolved 3G+ cellular network with HSDPA and MBMS capabilities. In particular, we investigate the delivery cost savings that can be achieved using HSDPA and MBMS to repair errors of the initial DVB-H broadcast transmission. In a realistic scenario, there may be users that experience significantly worse DVB-H reception conditions than the majority, such that it may be more efficient to serve them through the cellular network. To enable an easy and efficient implementation of the repair mechanisms in the hybrid DVB-H/3G+ system, we adopt application layer forward error correction (AL-FEC) with Raptor coding. With AL-FEC specific packets are not required to be retransmitted, and repair transmissions consist of additional repair packets that can be used for all users. Hence, repair data can be seamlessly delivered with unicast HSDPA, multicast MBMS, and broadcast DVB-H transmissions. Furthermore, AL-FEC provides a multiburst protection of the DVB-H transmission to exploit the time diversity of the mobile broadcast channel.
This paper presents several smart card security extensions to the FIPS 201 PIV standard of security and authentication of mobile health. Our contributions are designed to better protect the patient's data and to increase the functionality and interoperability of smart cards in health care. Our solution, called SAMSON, consists of two types of smart cards. The first, a security card, is issued to all personnel within any medical organization, while the second, the medical card, is issued to patients and used to securely store and retrieve health care information. These smart cards are being tested within a 14 hospital federated consortium in Michigan's Upper Peninsula.
This dissertation presents adaptation techniques that can achieve high spectral efficiency for single user multiple-input multiple-output (MIMO) systems. Two types of adaptation techniques, adaptive modulation and adaptive powe allocation, are employed to adapt the rate and the transmit power to fading channels. We start by investigating the adaptive modulation subject to a certain bit-error-ratio (BER) constraint, either instantaneous BER constraint or average BER constraint. The resulting average spectral efficiencies are obtained in closed-form expressions. It turns out that, by employing the average BER constraint, we can achieve the optimal average spectra efficiency at the cost of prohibitive computational complexity. On the other hand, instantaneous BER constraint leads to inferior performance with little computational complexity. In order to achieve comparable performance to the average BER constraint with limited complexity, a non-linear optimization method is proposed. To further enhance the average spectra efficiency, adaptive power allocation schemes are considered to adjust the transmit power across the temporal domain or the spatial domain, depending on the specific situation. Provided the closed-form expressions of the average spectral efficiency, the optimal MIMO coding scheme that offers the highest average spectral efficiency under the same circumstances can be identified. As we take into account the effect of imperfect channel estimation, the adaptation techniques are revised to tolerate interference introduced by the channel estimation errors. As a result, the degradation with respect to the average spectral efficiency is in proportion to signal-to-noise ratio (SNR). In order to facilitate fast development and verification of the adaptation schemes proposed for various MIMO systems, a reconfigurable Link Layer Simulator (LiLaS) which accommodates a variety of wireless/wireline applications is designed in the environment of MATLAB/OCTAVE. The idea of the simulator is originated from Software Defined Radio (SDR) and evolved to suit Cognitive Radio (CR) applications. For the convenience of modification and reconfiguration, LiLaS is functionally divided into generic blocks and all blocks are parameterized.
Adaptive modulation and power allocation schemes have been widely used in multiple-input multiple-output(MIMO) systems to enhance spectral efficiency while maintaining bit error ratio (BER) to a target level. We derivethe spectral efficiency of orthogonal space-time block codes (OSTBC) that can be achieved by applying adaptivemodulation and power allocation. Compared to non-adaptive power scheme, the adaptive power allocation canachieve substantial gain in the spectral efficiency. Moreover, channel estimation errors are taken into account andthe impact on the spectral efficiency is investigated.
This letter investigates the asymptotic performance of minimum-mean-square error (MMSE) in MIMO systemsusing adaptive modulation. The asymptotic average spectral efficiency and bit-error rate (BER) are derived basedon three approximations of the probability density function (p.d.f.) of effective SNR. Simulations suggest that themost accurate estimation of average spectral efficiency is obtained by using Gamma distribution.
Adaptive modulation scheme has been widely used in multiple-input multiple-output (MIMO) systems to enhance spectral efficiency while maintaining the bit error rate (BER) under a target level. We consider two MIMO schemes, orthogonal space-time block codes (OSTBC) and spatial multiplexing with zero-forcing receiver (SM-ZF), that apply adaptive modulation scheme and derive closed-form expressions of the average spectral efficiency and BER. Based on the closed-form expression of spectral efficiency, a low complexity switching method is utilized to obtain high spectral efficiency gain over an adaptive system using a single scheme.
Adaptive modulation scheme has been widely used in multiple-input multiple-output (MIMO) systems to enhance the spectral efficiency while maintaining the bit-error-rate (BER) under a target level. In this work, we investigate the performance of adaptive modulation in the presence of imperfect channel estimation and the impact of estimation noise on the spectral efficiency. The closed-form expressions for the average spectral efficiency are derived. Two MIMO schemes are considered, i.e., orthogonal space-time block codes (OSTBC) and spatial multiplexing with zero-forcing receiver (SM-ZF), and a low complexity method to enable the transmitter to switch between OSTBC and SM-ZF is utilized to achieve higher spectral efficiency than adaptive OSTBC and adaptive SM-ZF.
We provide a systematic study of adaptive modulation schemes in multiple-input multiple-output (MIMO)orthogonal space-time block codes (OSTBC) systems. Closed-form expressions are obtained to evaluate systemperformance, e.g., average spectral efficiency, bit-error-ratio (BER), and outage probability. Provided the closedformexpressions, the optimal SNR thresholds that yield the maximal average spectral efficiency can be solved. Inorder to reduce complexity of the optimal algorithm, an original method which can achieve approximately the sameperformance as the optimal one is proposed. Furthermore, we apply these methods in a more practical situation,where channel estimation is imperfect, and examine how the performance is affected due to channel estimationerrors.
Future wireless networks will be composed of multiple radio access technologies (RATs). To benefit from these, users must utilize the appropriate RAT, and access points (APs). In this thesis we evaluate the efficiency of selection criteria that, in addition to path-loss and system bandwidth, also consider load. The problem is studied for closed as well as open systems. In the former both terminals and infrastructure are controlled by a single actor (e.g., mobile operator), while the latter refers to situations where terminals, selfishly, decide which AP it wants to use (as in a common market-place). We divide the overall problem into the prioritization between available RATs and, within a RAT, between the APs. The results from our studies suggest that data users, in general, should be served by the RAT offering highest peak data rate.
As this can be estimated by terminals, the benefits from centralized RAT selection is limited. Within a subsystem, however, load-sensitive AP selection criteria can increase data-rates. Highest gains are obtained when the subsystem is noise-limited, deployment unplanned, and the relative difference in number of users per AP significant. Under these circumstances the maximum supported load can be increased by an order of magnitude. However, also decentralized AP selection, where greedy autonomous terminal-based agents are in charge of the selection, were shown to give these gains as long they accounted for load. We also developed a game-theoretic framework, where users competed for wireless resources by bidding in a proportionally fair divisible auction. The framework was applied to a scenario where revenue-seeking APs competed for traffic by selecting an appropriate price. Compared to when APs cooperated, modelled by the Nash bargaining solution, our results suggest that a competitive access market, where infrastructure is shared implicitly, generally, offers users better service at a lower cost. Although AP revenues reduce, this reduction is, relatively, small and were shown to decrease with the concavity of demand. Lastly we studied whether data services could be offered in a discontinuous high-capacity network by letting a terminal-based agent pre-fetch information that its user potentially may request at some future time-instant. This decouples the period where the information is transferred, from the time-instant when it is consumed. Our results show that above some critical AP density, considerably lower than that required for continuous coverage, services start to perform well.
Future wireless networks will combine multiple radio technologies and subsystems, possibly managed by competing network providers. For such systems it may be advantageous to let the end nodes (terminals) make some or all of the resource management decisions. In addition to reducing complexity and costs, increasing redundancy, and facilitating more timely decisions; distributed resource sharing regimes can decouple the individual subsystems. Decoupled subsystems could be desirable both because competing operators can be business-wise separated and because it allows new technologies to be added (removed) in a modular fashion. However, distributed regimes can also lead to "selfish" wireless nodes who only try to maximize their own performance. The first part of this dissertation studies if selfish nodes can make efficient use of wireless resources, using multiaccess and network layers as examples. The related problems are formulated as noncooperative games between nodes. To maintain tractability nodes are confined to simple strategies that neither account for future payoffs nor allow for coordination. Yet, it is demonstrated that selfish nodes can achieve comparable performance to traditional protocols. These results should be interpreted as an argument in favor of distributed regimes.
The second part of this dissertation evaluates the effects of multi-provider network architectures where users can roam freely across all networks. From a supply side perspective the benefits are improved path gain statistics and the fact that different networks may have non-overlapping busy hours. Several network configurations are analyzed and it is shown that cooperation between symmetric providers can yield significant capacity gains for both downlink and uplink; even if the providers have nearly collocated sites. When the providers have different site densities the gains from cooperation are reduced and the provider with a sparse network always gains more from cooperating. This suggests that initially, voluntary cooperation may be limited to some special cases. Lastly, the architecture is analyzed in a context where the providers compete for users on a per session basis by offering access at different prices. Although such architectures currently only exist in a few special cases, they could emerge in domestic markets where the costs to switch and search for new networks are low. Based on a game theoretic formulation it is shown that a competitive market for wireless access can be advantageous for both users and providers. The results presented suggest that the advantages of cooperation of competing providers occur in more than just a few cases.
KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Communication Systems, CoS.
We consider a slotted ALOHA setting where backlogged, energy-constrained users selfishly select the probability with which they transmit packets. Packets are successfully received, even in case of collision, if the signal to interference plus noise ratio at the access point exceeds some threshold (power capture). The user problem of finding appropriate transmission probabilities is formulated as a static non-cooperative game and the performance limits for stationary and mobile scenarios are determined. The equilibrium analyses show that for stationary scenarios, users with high pathgains share the channel fairly while others never transmit. In the mobile case users utilize a binary strategy where they try to monopolize the channel when their pathgain exceeds some threshold that depends on system parameters (number of users, transmission costs, etc.). Otherwise they shut their transmitters off. Compared to traditional nondiscriminatory distributed multiaccess protocols the operating points achieved by selfish users generally increase sum-utility although this comes at the expense of larger user performance variations.
In this paper we propose cooperative/noncooperative operation models for revenue seeking spectrum brokers who coordinate to manage access to the same spectrum bands in adjacent areas. We consider a setting where users of spectrum are involved in peer-to-peer links with QoS requirements. Each wireless transmission (link) is priced collectively by all revenue seeking brokers whose responsibility areas are affected by the transmission (via interference). We propose a two-level coordination mechanism. At the pricing-level, the brokers affected by a given link collectively determine prices. At the admission level, all brokers potentially affected by all transmissions collectively determine the set of link requests that are to be permitted. The links are modeled as price sensitive users who may or may not form connections, based on the total price asked. Experimental results show that cooperation significantly increases both the number of active links and broker revenues. Relative gains achieved by pricing level cooperation alone or admission level cooperation alone depend on price sensitivity parameters for the links as well as the total number of link formation requests.
KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
Multi-access networks and hierarchical cell structures are two common capacity expansion strategies for mobilenetwork operators. In both cases costs can be minimized fora set of available radio access technologies, given heterogeneous requirements on area coverage, capacity and quality of service. In this paper we quantify the infrastructure cost for a multi-accessnetwork composed of macro cellular HSDPA base stations and IEEE 802.11g WLAN access points. The network is dimensioned for an urban environment using a stochastic model for heterogeneous traffic density.With the used assumptions and modelling it is shown that a combination of HSDPA base stations deployed with 400mcell radius together with WLAN in hot spots are suffcient foraver age traffic densities up to around 50Mbps/km2 (50 timesthe traffic of typical private voice users today). In order to evaluate the sensitivity to different design features, we introducethe elasticity of infrastructure cost and can thereby show that it is more important to improve capacity in HSDPA than coverageper 802.11g access point. However, with a sparse deployment of HSDPA macro cells (800m radius) infrastructure cost ismore elastic to 802.11g coverage. The paper also indicatessome possibilities to differentiate future radio access technologies towards current systems.
Document printing has long been considered an indispensable part of the workspace. While this process is considered trivial and simple for environments where resources are ample (e.g. desktop computers connected to printers within a corporate network), it becomes complicated when applied in a mobile context. Contemporary mobile devices have the computational resources required for document processing and are affordable enough for an increasingly large number of users. Therefore, document printing using mobile devices is now both technically feasible and relevant to users' needs. In this study, we present an infrastructure for document printing using mobile devices. In order to realize the vision, we utilize an existing set of network protocols, a set of common programming languages, standard concepts of ubiquitous computing, and machine learning, in order to automate the printing process.
Context distribution is a key aspect for successful applications within mobile and ubiquitous computing environments. In such environments, context information is acquired by several and multiple context sensors distributed over the environment. Applications collect and react to these data, according to predefined adaptation mechanisms. The success of these mechanisms depends on the availability of context information, which is disseminated over the network. However, in practice, only a fraction of the observable context information is required by the adaptation mechanisms. Moreover, for privacy reasons, it is important to delimitate a scope for context dissemination. In this work we address these issues by proposing a context grouping mechanism which allows the definition of groups based on the context characteristics. Each group is defined by these characteristics and delimitate a given context information set that can be distributed among group members. This approach of context grouping acts as a two-fold mechanism. On the one hand, it controls and organizes context distribution over a peer-to-peer network. On the other hand, it proposes a primary and low-level privacy mechanism for context distribution, which is an important aspect influencing context distribution.
The effect of the TCP congestion control mechanism over rapidly fluctuating wireless links is a deterioration of the TCP performance. The utilization of multi-radio accesses in future networks by means of packet scheduling and dynamic access selection enriches the arsenal of solutions that mitigate radio channel variations. Packet scheduling over multiple radio accesses at link level provides a novel diversity scheme referred to as Multi-Radio Transmission Diversity (MRTD). This work evaluates, through simulations, the effects of different MRTD schemes for TCP flows over heterogeneous radio links. Results indicate that MRTD schemes provide substantial gains in terms of goodput and show a significant reduction in file download times. These gains are due to the diversity obtained and the suppression of the unwanted duplicate acknowledgements that frequently cause degradation in TCP performance over a radio channel.
Multihop cellular networks that base the forwarding process on user terminals are challenged by a lack of forwarding incentive. In this paper 1, we present the novel concept of Resource Delegation which, applied in combination with pricing based rewards, guarantees both the separation of resources between originating transmitters and relays and the economic compensation of the energy investments of the relays. The results show that this strategy leads to the definition of a broad region of prices in which multihopping solutions can achieve the following advantages over classical single-hop architectures: operator's revenues and provided datarates increase significantly, the users' appreciation of the service is enhanced, and the average interference level of the network is lowered.
In the last few years we have been witnessing the beginning of a revolution in the world of wireless communication. The recent launch of advanced smartphones in the mobile market has been welcomed by mobile operators as an opportunity to finally fulfill the promises of 3G and increase the uptake of mobile services. Driven by unprecedented user experience and flat rate pricing, the success of novel mobile platforms for accessing multimedia content and applications has gone far beyond the most optimistic of expectations. Data-hungry services are currently creating significant capacity limitations in many networks, and projections on future content consumption anticipate that with the next generation of mobile devices the stress on cellular infrastructures will increase. Rolling-out additional capacity is not the most profitable of solutions given the current cost structure of mobile infrastructures. Instead, a significant cost reduction can be achieved by revolutionizing the current content provision paradigm. Accordingly, this thesis proposes solutions for making future services and infrastructures more affordable. From an operator perspective, terminal-to-terminal information forwarding has the potential to increase both coverage and capacity, however it introduces opportunity costs and energy losses at the user side. Resource delegation, together with an energy reimbursement scheme, is presented in this thesis to induce user cooperation. The results show that this approach is successful in fostering significant cooperation among users and can create a simultaneous improvement in user utility, data rates and operator revenues. Opening up for public access privately deployed WLANs might radically lower the cost of wireless services. However, since these networks are deployed in an uncoordinated manner, only discontinuous coverage can be provided. To hide the sparsity of the infrastructure to the end-user perception we propose the adoption of opportunistic schemes for content pre-fetching. Results show that already with moderate AP densities a set of archetypical services, including web-browsing, can be provided with sufficient user perceived quality. Epidemic exchange of popular content, and inter-AP cooperation are also shown to further decrease the required AP density. Moreover, to support informed access selection decisions when performing vertical handovers to WLANs, we propose "Word-of-Mouth", a reputation-based scheme for revealing the QoS of different networks. By epidemically exchanging grades on their experienced service quality, we show that terminal agents can collectively improve their decision making, avoiding selecting networks not meeting the required QoS. Context-based content delivery is presented in this thesis as means to improve the utilization of wireless resources in cellular systems. Since networks are typically dimensioned for peak hour traffic, the BSs are underutilized for significant portions of the day. By adopting context-based architectures, capable of opportunistically utilizing the instantaneous excess of resources for content pre-fetching, we show that a significant amount of additional traffic can be served in already existing networks. The gains introduced by this content provision paradigm over the current "on-demand" solutions are further expressed in terms of lower requirements on BS density, more users in the system and larger files served while reaching the same level of user experience.
To support the future requirements on wireless systems in an affordable manner it is commonly believed that multiple radio access technologies have to be combined. These technologies can be deployed by a single operator or, even, be managed by different competing operators. In order to cope with the increased complexity of such a multifaced wireless environment it has been argued that a transfer of Radio Resource Management (RRM) functionalities towards the network edges (access ports and, ultimately, user terminals) may be beneficial. In addition to detecting varying system conditions in a faster manner this would also allow a more responsive service adaptation. In this thesis we evaluate a set of self-organizing regimes, all with the purpose of supporting the distribution of control at the edge node.
Particular emphasis is put on the design of a mechanism for dynamically establishing cooperation between different network entities whether these are access ports or user terminals.
Terminal cooperation by means of multihopping is considered in the context of service provision in cellular access systems. Previously the opportunity cost associated with sharing own bandwidth, and energy loss have been seen as a major obstacle for relaying other users' traffic. To mitigate the effects of this selfish behavior the concept of resource delegation is introduced and evaluated in combination with a rewarding scheme designed for compensating the energy losses induced by forwarding. The results show that our proposed schemes not only are capable of fostering significant cooperation among users, but also to create a simultaneous improvement in user utility, data rates as well as in operator revenues.
Opening up networks of user-deployed Access Points (APs) for service provision is considered a means to radically lower the cost of future wireless services. However, since these networks are deployed in an uncoordinated manner, only discontinuous coverage will be provided. The question of how dense these networks need to be, to deliver acceptable user perception, is investigated in this thesis for a set of archetypical services. The results show that already at moderate AP densities the investigated services can be provided with sufficient quality. Epidemic exchange of popular content and inter-AP cooperation are also shown to further decrease the required infrastructure density and improve the APs' utilization respectively.
As last contribution, "Word-of-Mouth", a distributed reputation-based scheme, is investigated in the context of access selection in multi-operator environments. By exchanging information concerning the Quality of Service (QoS) associated with the different networks, terminal agents can collectively reveal the capabilities of individual networks. For a vertical handover scenario we show that our proposed scheme can reward access providers capable of ensuring some degrees of QoS. By introducing a model for collusion, between low performing APs and terminal agents, we show that our proposed scheme is also robust to the dissemination of false information.
The purpose of this study is to report further about the statistically significant results from a prospective study, which suggests that fusion of prone F-18 Fluoro-deoxy-glucose (FDG) positron emission tomography (PET) and magnetic resonance (MR) breast scans increases the positive predictive value (PPV) and specificity for patients in whom the MR outcome alone would be nonspecific. Thirty-six women (mean age, 43 years; range, 24-65 years) with 90 lesions detected on MR consented to undergo a FDG-PET scan. Two blinded readers evaluated the MR and the computer tomography (CT) attenuation-corrected prone FDG-PET scans side-by-side, then after the volumes were superimposed (fused). A semiautomatic, landmark-based program was used to perform nonrigid fusion. Pathology and radiologic follow-up were used as the reference standard. The sensitivity, specificity, PPV, negative predictive value (NPV), and accuracy (with 95% confidence intervals) for MR alone, FDG-PET alone, and fused MR and FDG-PET were calculated. The median lesion size measured from the MR was 2.5 cm (range, 0.5-10 cm). Histologically, 56 lesions were malignant, and 15 were benign. Nineteen lesions were benign after 20-47 months of clinical and radiologic surveillance. The sensitivity of MR alone was 95%, FDG-PET alone was 57%, and fusion was 83%. The increase in PPV from 77% in MR alone to 98% when fused and the increase in specificity from 53% to 97% were statistically significant (p < 0.05). The false-negative rate on FDG-PET alone was 26.7%, and after fusion this number was reduced to 9%. FDG-PET and MR fusions were helpful in selecting which lesion to biopsy, especially in women with multiple suspicious MR breast lesions.
This paper presents a novel network context monitoring system, known as the Context Monitoring System (CMS), that is designed to accommodate the rapidly changing network context requirements and network context availability in dynamically (de)composing Ambient Networks (ANs). CMS is designed to support dynamic deployment, activation, and (re)configuration of Context Sensors in ANs in an efficient and scalable way, and to locate available distributed network context in a scalable and distributed manner once Context Sensors are deployed, in order to support subsequent efficient and scalable network context retrieval.
In a wireless radio network system, with an evolving standard, there is a need to increase system capacity due to the increase in the traffic demands, the higher data rate usage, and the need to further extend the coverage of the system. One possible solution is to use multiple antennas (co-located or distributed) for the radio links. The aim of this thesis is to estimate the capacity gain for these advanced antenna scenarios in comparison to the ones in current use (e.g. single antenna in a 3-sector site) with special emphasis on transmit diversity and beamforming techniques. The quantification of such gain is mainly performed, evaluated and analyzed in dynamic system simulators with an accurate interference modeling. A generalized Signal to Interference Noise Ratio (SINR) estimation for a MIMO DS-CDMA system is derived, and as a by-product a closed-form solution of the orthogonality factor is obtained. Moreover the effectiveness of an antenna system is evaluated in a MIMO-test bed.
Transmit diversity (TXDiv) is evaluated in WCDMA systems for flat fading (i.e. Pedestrian A (PedA)) and frequency selective channels (i.e. Typical Urban (TU)). While in flat fading channels, TXDiv schemes such as Space Time Transmit Diversity (STTD) and Closed Loop Mode 1 (CL1) offer a substantial system capacity gain, the gain is negligible in frequency selective channels. In HSDPA systems, TXDiv offers negligible gain in flat fading channels and causes a significant loss in frequency selective channels. The loss is mainly due to random spatial interference patterns (the so called Flashlight Effect), that are present in the HSDPA system. A simple scheme that mitigates this phenomena is presented. The scheme yields a 70% gain for CL1 in a PedA channel, while 10% gain is observed in the TU channel.
The introduction of beamforming in WCDMA systems leads to a substantial system capacity and coverage gain. Three different implementations are evaluated and analyzed: Higher Order Sectorization (HOS), Fixed Beams (FB) with S-CPICH as a phase reference and finally FB as P-CPICH as a phase reference. Further, the impact of angular spread, the interaction and impact of radio resource management as power tuning of the common channel, scrambling code allocation technique, admission control, handovers and various antenna configurations are analyzed. The 12-sector sites yield the best system capacity gain in comparison to 3-sector sites equipped with a single antenna, slightly more than a 3-sector sites equipped with 4 FB each. In HSDPA systems, FB offers an impressive capacity gain, up to 200% for a 4 FB system.
Capacity estimations with a dynamic system simulator give a clear indication about the gain of the simulated system, but the robustness of any method have to be verified through test-beds. STTD with receive diversity is implemented and tested in a real-time DSP MIMO test-bed for a single carrier frequency domain equalization system. A new pilot structure for joint Carrier Frequency Offset (CFO) and channel estimation is proposed and evaluated to address the inter-symbol interference and the severe CFO due to hardware impairments. The new pilot scheme results in significant reduction of the required overhead signalling compared to previous schemes.
Instead of having antennas co-located and connected to the same radio unit (i.e. BS or UE), antennas can be distributed but having the potential to cooperate together. Furthermore, the system provides a macro-diversity gain and also relaxes the hardware complexity at the BS and/or UE. Two novel methods that provide frequency and spatial diversity are proposed. The first one called Relay Cyclic Delay Diversity (RCDD), provides frequency and spatial diversity for a multihop system while requiring a lower overhead than the methods proposed in the literature. RCDD yields a high SINR gain which translates into a substantial cell throughput gain in comparison to a single hop system. The second method called two dimensional cyclic prefix (2D-CP), introduces artificial time diversity and requires only a single transmission phase for each direction in a cooperative relaying wireless communication system. Besides not requiring an antenna specific pilots, the 2D-CP provides a substantial data rate increase.
A dynamic range boosting (DRB) technique is proposed in this paper. By applying this technique, the designed pipelined analog-to-digital converter could sample a wide dynamic range analog input, which is even larger than the output swing of the opamp used in SHA and MDAC. A 13b 5MS/s pipelined A/D converter based on single stage telescopic opamps is implemented and achieves a dynamic range up to 2.4VPP, while its supply voltage is 1.8V.
KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01). Fudan University, China .
A workload-balanced multiplying digital-to-analog converter (WB-MDAC) is proposed to improve the settling efficiency of multi-bit pipeline stages, and demonstrated in a 14-bit 50-MS/s digital calibrated pipelined ADC. The presented ADC occupies an active area of 1.3 mm 2 in 0.13-μm 1P8M CMOS technology, including internal reference buffers. It dissipates 76mW from a 1.2-V supply, and achieves 64.4 dB SNDR and over 80 dB SFDR.
KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01). Fudan University, China.
This paper describes a robust and effective calibration algorithm for pipelined analog-to-digital converters, which compensates for large gain errors, without the requirement for a long startup time as required by the other dither-based algorithms presented in literature. The proposed technique, time-spreading self-calibration, operates the front-end sample-and-hold stage in half rate at startup and cancels out the strong input-interference by using subtractive correlation, achieves a quick convergence. When the sample-and-hold stage operates in full rate as normal, the algorithm works as a background dither-based scheme and enables to calibrate time-variant gain errors. Simulation results show that it only needs wake-up time of 3 × 10 5·T s to correct a 15-bit pipelined ADC in the presence of realistic capacitor mismatch and finite op-amp gain, where T s is the sampling period.
In a very simple form a Mobile Agent is an independent piece of code that has mobility and autonomy behavior. One of the main advantages of using Mobile Agent in a network is - it reduces network traffic load. In an, ad hoc network Mobile Agent can be used to protect the network by using agent based IDS or IPS. Besides, to deploy dynamic software in the network or to retrieve information from network nodes Mobile Agent can be useful. But in an ad hoc network the Mobile Agent itself needs some security. Security services should be guaranteed both for Mobile Agent and for Agent Server. In this paper to protect the Mobile Agent and Agent Server in an ad hoc network we have proposed a solution which is based on Threshold Cryptography, a new vibe in the cryptographic world where trust is distributed among multiple nodes in the network.
This paper presents SYNAPSE++, a system for over the air reprogramming of wireless sensor networks (WSNs). In contrast to previous solutions, which implement plain negative acknowledgment-based ARQ strategies, SYNAPSE++ adopts a more sophisticated error recovery approach exploiting rateless fountain codes (FCs). This allows it to scale considerably better in dense networks and to better cope with noisy environments. In order to speed up the decoding process and decrease its computational complexity, we engineered the FC encoding distribution through an original genetic optimization approach. Furthermore, novel channel access and pipelining techniques have been jointly designed so as to fully exploit the benefits of fountain codes, mitigate the hidden terminal problem and reduce the number of collisions. All of this makes it possible for SYNAPSE++ to recover data over multiple hops through overhearing by limiting, as much as possible, the number of explicit retransmissions. We finally created new bootloader and memory management modules so that SYNAPSE++ could disseminate and load program images written using any language. At the end of this paper, the effectiveness of SYNAPSE++ is demonstrated through experimental results over actual multihop deployments, and its performance is compared with that of Deluge, the de facto standard protocol for code dissemination in WSNs. The TinyOS 2 code of SYNAPSE++ is available at http://dgt.dei.unipd.it/download.
KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. CSEE, University of Maryland, Baltimore County, United States.
This paper presents the Mobile Services Living Laboratory - a practical approach for evaluating service provision in cellular networks. Our approach promotes an end-to-end view of the system by providing an effective means to store information from both terminal and network sides, together with integrated mechanisms for retrieving feedback on user-perceived service quality. The current implementation of the Living Laboratory is described and evaluated. Further, we show how the Living Laboratory is used to investigate both the effectiveness of context-aware opportunistic content delivery schemes in cellular networks, and the coexistence between M2M and user-generated traffic.
One approach to authorisation of mobile agents is to use extensible access control mark-up language (XACML) policies by assigning roles to agents and then enforcing role-based authorisation. In this paper we show how traditional XACML polices, used for user access control in distributed environments, can be used for mobile agents' access control. We use such polices to manage delegation of access rights from users to agents, while at the same time following the core principles of the XACML standard. We also propose a combination of policies that map users to their mobile agents and make access control decisions for mobile agents by evaluating complex policy sets. We have identified all architectural components along with the operations required for enforcement of authorisations of mobile agents during execution.
Current research in the area of mobile agents' security mainly deals with protection and security for agents and agents' runtime platforms. Mobile agent systems usually do not provide an extensive security methodology for the entire agent's life cycle, from agent's creation to its deployment and execution. In this paper we propose a comprehensive secure system for deployment of mobile agents. The system provides methodology that spans a number of phases in agent's lifetime: it starts from agent creation and ends with agent's execution. It addresses classification, validation, publishing, discovery, adoption, authentication and authorization of agents. Our system is based on secure web services and uses RBAC XACML policies and SAML protocol.