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  • 1851.
    Weltz, Max
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Dial over Data solution2008Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The increased use of computer networks has lead to the adoption of Internet-based solutions for reducing telephony costs. This has proved to be a boon to callers who can reach the other party directly via the Internet. Unfortunately numerous business persons still need to call to and from mobile phones which are currently a domain where the customers are generally tightly bound to their operators.

    To provide a simple solution to this problem for companies, Opticall AB has designed an integrated system called the Dial over Data solution, coupling a mobile interface with a low-rate communication channel, which allows calls to be originated remotely at the best price, exploiting the customer company's existing network. This scheme allows the customer company to easily control telecommunications costs, to monitor their employees' efficiency, and more generally speaking to claim a central role in the communications of their employees. The proposed solution allows distant callers (usually employees of the customer company) to benefit from the company's internal network, which is usually more cost effective and offering connectivity to more networks than a cell phone. The Dial over Data solution enables communication between any phone accessible from the customer company's telephony network (such as SIP clients, landline phones, and mobile phones) at a lower cost.</p> This thesis project analyzes existing technologies and compares them to the pre-existing prototype to ascertain the validity of the method and of the components used. This project also explains the improvements brought to the features offered by the DoD solution: the initial prototype has been developed into a stable and functional product, and has been tested internally. Prompted by a need for scalability and additional features, the replacement of Asterisk for the handling of SIP calls by other SIP servers has also been considered and tested.

  • 1852.
    Wen, Daliang
    KTH, Superseded Departments, Teleinformatics.
    MPLS Label Distribution in an Edge Router1998Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The rapid growth of the Internet has increased the demand for higher bandwidth and better performance. One of the alternatives to satisfy such demands MPLS, (Multi-Protocol Label Switching). The key feature of MPLS is IP switching. It maps the destination address to a locally defined label. The packets can then be forwarded through the network by only examining the label value and no further routing table lookups are needed. One of the key components of MPLS’s is Label Distribution. The goal of Label Distribution is to negotiate labels with the neighbor MPLS nodes using a signaling protocol LDP (Label Distribution Protocol) and update the label information in a local database called LIB (Label Information Base).

    In this thesis, the author will present an overview of the MPLS network and the MPLS system components within an Label Edge Router (LER), which is a router located at the edge of an MPLS network. Furthermore, the implementation of the Label Distribution component in a Label Edge Router of an MPLS system is described and evaluated.

  • 1853.
    Wendelin, Kurt Kristoffer
    KTH, Superseded Departments, Teleinformatics.
    Platform Independent Software for Remote Control of a GPS Receiver1998Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With all of the excitement over the World Wide Web on the desktop, the benefits of applying the same technology to embedded devices were fully realized only recently. A device attached to the Internet with an HTTP server running on it can provide for remote access to documentation, monitoring, and configuration of the device from a Web browser on any platform.

    In this project, the Jupiter GPS receiver is used as a prototype device to explore this concept. A client-server system gives access to the full functionality of the GPS attached to a remote host. The client is written in Java and documented in HTML, and the GPS receiver is connected to a Motorola PowerPC board running the VxWorks real-time operating system. This integrates important Web technologies into an embedded environment.

  • 1854.
    Wennlund, Andreas
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Context-aware Wearable Device for Reconfigurable Application Networks2003Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Context information available in wearable devices is believed to be useful in many ways. It allows for hiding much of the complexity from the user, thus enabling simpler user interfaces and less user interaction when carrying out tasks on behalf of a user, as well as enabling network operators to provide a better interface to thirdparty service providers who will provide and deliver wireless services. Using the available context information from the wearable device, optimization of service delivery in wireless networks, such as setting up optimal delivery paths between two wearable devices, may be possible without using a third party to do negotiations. In order to fully enable context-awareness, a clear model for how to sense, manage, derive, store, and exchange context information must be defined. This will then provide the platform needed to enable development of context-aware applications that can exploit the possibilities of context-aware computing. The model must take into consideration parameters such as memory usage and power and bandwidth consumption, in order to be efficient on all types of platforms and in all types of networks. It must also be modular enough to survive replacing and upgrading of internal parts.

    Today little research is available about sensing context information, sensor management, APIs towards other applications, and how and how often to present context information to applications. Since context aware computing relies heavily on the ability to obtain and represent context information, sensing strategies greatly affect efficiency and performance. It is therefore of great interest to develop and evaluate models for carrying out these tasks in order to exploit the results of context awareness research. This thesis will identify and design several components of such a model, as well as test and evaluate the design, in order to be able to make conclusions to whether is lives up to the expectations stated.

    In order to make the proper design decisions, a full understanding of the context-awareness research area and the goals and purposes of context-aware computing are required. To understand the entire picture is crucial to find a suitable solution. Therefore, determining an efficient sensor input and management strategy, along with a powerful and flexible API for applications, which are the goals of this thesis, fully qualifies as a significant master thesis assignment.

  • 1855.
    Westergren, Urban
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics. KTH, School of Information and Communication Technology (ICT), Centres, Kista Photonics Research Center, KPRC.
    Yu, Yichuan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT. KTH, School of Information and Communication Technology (ICT), Centres, Kista Photonics Research Center, KPRC.
    Jänes, Peter
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Centres, Kista Photonics Research Center, KPRC.
    Holmström, Petter
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Centres, Kista Photonics Research Center, KPRC.
    Thylén, Lars
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT. KTH, School of Information and Communication Technology (ICT), Centres, Kista Photonics Research Center, KPRC.
    Efficient and compact light-intensity modulators for high frequencies and high bitrates2006In: ICTON 2006: 8th International Conference on Transparent Optical Networks, Vol 2, Proceedings: ESPC, NAON / [ed] Marciniak, M, 2006, p. 142-145Conference paper (Refereed)
    Abstract [en]

    Electroabsorption modulators (EAM) based on quantum-confined Stark effect (QCSE) in multiple-quantum wells (MQW) have been demonstrated to provide high-speed, low drive voltage, and high extinction ratio. They are compact in size and can be monolithically integrated with source lasers. In order to achieve both high speed and low drive-voltage operation, travelling-wave (TW) electrode structures can be used for EAMs. Modulation bandwidths of 100 GHz (-3 dBe) have been accomplished and transmission at 80 Gbit/s with non-return-to-zero (NRZ) code has been demonstrated for InP-based TWEAMs, indicating the possibility of reaching speeds of IOOGbit/s and beyond. In order to further increase the efficiency and reduce the drive voltage, MQW structures using intersubband (IS) instead of interband (QCSE) absorption are being investigated. Materials systems with large conduction band offset, such as GaN/Al(Ga)N or InGaAs/AlAsSb, are required for IS modulators. Critical for the performance of IS modulators is the linewidth of the absorption peak, hence IS modulators have the potential to outperform interband modulators given that a sufficiently high material quality can be achieved.

  • 1856.
    Westermark, Christian
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Mobile Multiplayer Gaming2007Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The last ten years, online multiplayer games have become very popular. During the same time period mobile terminals and cellular networks have undergone a tremendous technical evolution. Therefore it is natural to wonder why we have not seen an online mobile multiplayer gaming revolution yet. The answer to this question is of great value for companies selling mobile systems. This answer is important in order to understand how to fill up today’s empty networks with traffic and what kind of traffic these games will generate.

    This thesis is a continuation of Mattias Åkervik’s thesis. It gives the reader an understanding of what kind of wireless technologies are on the market today and how they perform. Given this performance background, some suitable games were chosen to examine how they perform over a particular cellular network and to determine the perceived gaming quality that a user experience. The thesis also examines the particular packet traffic characteristics generated by these games to gain a better understanding of how to better adapt cellular networks towards gaming.

    Finally the market will be analyzed. Not only how large this potential market is, but to examine if there are some market issues preventing the revolution in network cellular on-line multiplayer games.

  • 1857.
    Westin, Ola
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    TCP Performance in Wireless Mobile Multi-hop Ad Hoc Networks2003Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    There are many issues that limit the performance of wireless mobile multi-hop ad hoc networks (MANETs). One of them is that TCP is not well adapted to networks where routes can change or disappear often. In this paper the behaviour of a standard TCP implementation is studied in situations typical for MANETs and compared to the behaviour of a partial implementation of a ATCP, a TCP modification that is intended to increase performance in MANETs.

    Simulations with simple scenarios show that TCP easily creates a full network load which causes send failures and decreased throughput performance. In some cases the partial ATCP implementation increases throughput but more often it causes an increased amount of duplicate retransmissions. In these scenarios it is unlikely that even a complete ATCP implementation would increase throughput performance.

    A few modifications to ATCP and TCP are analysed. Especially a limit of the congestion window size shows a large throughput increase. The results are inconclusive, the simulations are too simple to show if the results are applicable in more complex scenarios. It is not clear if ATCP actually is useful in a MANET.

  • 1858. Weyres, Marco
    et al.
    Gross, James
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Effective Service Capacity Analysis of Interference-Limited Multi-Carrier Wireless Systems2013In: Proceedings of the 2013 19th European Wireless Conference (EW), VDE Verlag GmbH, 2013, p. 1-7Conference paper (Refereed)
    Abstract [en]

    A good utilization of a wireless network while still ensuring QoS-constraints for all users is a hard challenge for service providers. Especially for admission control or handover decisions it is important to have a good approximation of the possible rate a user can achieve with respect to QoS parameters like delay or outage probabilities. Since fourth generation cellular networks utilize a frequency reuse of one, especially terminals at the cell edge suffer from inter-cell interference. In order to provide them with rates that guarantee specific QoS parameters without reserving too much resources, a good prediction of their possible rates is needed. Unfortunately, the prediction of the rates in an interference-limited cell is a complex and hard problem. Hence, it is a common way to simplify calculations by treating interference as additional noise in the used system models. In this paper we derive closed-form solutions for the delay distribution of interference-limited cells with respect to an OFDMA and a round robin scheduling approach. These distributions can be used to predict the possible rates of users given their average received transmitter gains, interferer gains and their QoS-constraints in a very accurate way. We validate our derivations and show that a simplification by treating interference as noise leads to an underestimation of rates which lowers the cell throughput. Furthermore, we show that due to the resulting equations, there is no way to derive the rates for interference limited cells in a linear way from easier solutions given by noise-limited cells.

  • 1859. Wiatr, P
    et al.
    Chen, Jiajia
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Monti, Paolo
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Wosinska, Lena
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Yuan, D.
    Device reliability performance awareness: Impact of RWA on EDFA failure reparation cost in optical networks2017In: Proceedings of 2017 9th International Workshop on Resilient Networks Design and Modeling, RNDM 2017, Institute of Electrical and Electronics Engineers Inc. , 2017Conference paper (Refereed)
    Abstract [en]

    High reliability performance of network is essential to minimize the possible network service interruption time, particularly in optical backbone networks where a large amount of data can be affected by a single failure. The existing studies on improvement of network reliability performance assume that failures of network devices are not related to the traffic load, which on the other hand, is not always true. For example, the lifetime of erbium doped fiber amplifier (EDFA) depends on the number of amplified lightpaths passing through. Encouraged by this observation, in this paper, we investigate the impact of used routing and wavelength assignment (RWA) algorithm on the number of failures in the network, and as a consequence on the network operational cost related to the failure reparation. We propose and evaluate a novel RWA approach, referred to as reliability performance aware RWA (RA-RWA), taking into account particular EDFA reliability performance characteristics with the goal of reducing the number of EDFA failures. The assessment results show that the operational cost related to EDFA failure reparation is impacted by the chosen RWA. The proposed RA-RWA provides 6% reduction, while other analyzed RWA algorithm, i.e., least loaded path (LLP), causes significant rise (up to 27%) of EDFA related failure reparation cost compared to the classical shortest path (SP) approach. In addition, RA-RWA offers further benefits in terms of reduced blocking probability compared to the SP. Concluding, we show that considering device reliability performance characteristics in RWA is important for the optical network operators as it can impact the network operational cost related to EDFA failure reparation.

  • 1860. Wiatr, P.
    et al.
    Forchheimer, R.
    Furdek, Marija
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Chen, Jiajia
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Yuan, D.
    Hierarchical optical interconnects saving spectrum resources in data center networks2017In: Optics InfoBase Conference Papers, Optics Info Base, Optical Society of America, 2017, Vol. Part F53Conference paper (Refereed)
    Abstract [en]

    This paper presents a hierarchical interconnect architecture for optical data center networks composed of specially designed couplers allowing for significant reduction of required spectral resources.

  • 1861.
    Wiatr, Pawel
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Chen, Jiajia
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Monti, Paolo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Green WDM-PONs: Exploiting traffic diversity to guarantee packet delay limitation2013In: 2013 17th International Conference On Optical Networking Design And Modeling (ONDM), IEEE , 2013, p. 229-234Conference paper (Refereed)
    Abstract [en]

    In this paper we propose a scheme tailored for WDM-PONs, which employs dozing mode in transceivers not only at the user side but also at the central office. The objective is to reduce the energy consumption while minimizing the impact on the total packet delay. The proposed scheme is able to take into account the diverse delay requirement of multiple traffic classes by adapting the wakeup time of the transmitter. Simulation results confirm that the proposed scheme can significantly improve the power efficiency in WDM-PONs while maintaining the maximum packet delay at an acceptable level, in particular in cases where multiple traffic classes are considered.

  • 1862.
    Wiberg, Niklas
    KTH, Superseded Departments, Teleinformatics.
    Profile Handling Gateway/Proxy2000Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    When home users surf the Internet (i.e. use the World Wide Web) today, be it by dial-up or by other means, they are virtually anonymous to the sites they visit. Many sites would, according to Iquity Systems’ experience, like to know more about their visitors in order to target the advertisements (e.g. banners) displayed, services offered, etc. It is also likely that site owners are interested in the type of people that visit their site.

    Iquity Systems would like to provide a system that is capable of providing Internet site owners with profile data of the visitors, as well as sharing usage accounts with Iquity’s telephony products. The system should also be supportive of a rating model that lets an access provider running the system charge a user differently for the access, depending on whether the user is presented with targeted advertisements or not. This solution shall be able to be integrated with other parts of the company’s IQ platform. One of these parts is a system for accounting, while another is a user profile handling database.

    This paper discusses the design of such a system.

  • 1863.
    Wickbom, Carl
    KTH, Superseded Departments, Teleinformatics.
    SIP and payments: a way of controlling the price2000Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    IP-telephony is said to be the future of telephony, reducing infrastructure investments and enabling new services. IP-telephony solutions exist already in some business buildings as a replacement for PSTN or on the Internet as IP-to-IP telephony. However, before IP-telephony will be a realistic replacement for PSTN two major problems must be solved though; billing and guarantee of the expected QoS. Without the possibility of revenue no company would like to invest money and without QoS no customer will want to replace PSTN with IP-telephony. IP-to-IP telephony exists with best effort traffic for free today, and it will not be possible to charge for it in the future. By introducing value-added features such as PSTN gateway connection, bandwidth reservation and services such as call screening and redirecting, a way of charging the customer is presented in this report.

    The payment solution developed in this thesis is based on SIP and Jalda. The system is built in modules, all with a specific task, hence creating a distributed system, which does not depend on a central part, and following existing standards, avoiding a proprietary solution. It is also general enough to support other types of media than speech, enabling several business ideas including video on demand.

    Security has to be considered seriously when dealing with Internet payments. The solution presented contains both the advantages of SIP with authentication and message encryption, as well as authentication and accounting by Jalda. Authorization is not a problem, as no one will get access to the services without paying, and anyone willing to pay will be granted access. It ends up being a distributed payment solution.

    SIP has the necessary characteristics for constructing billing solutions. As payment seems to be a solvable problem there remains one major difficulty with IP-telephony. Until QoS can be guaranteed or the interference reduced to a minimum, it is not reasonable to imagine IP-telephony replacing PSTN except in well managed intranets where the network can be over dimensioned in such a way as to provide the necessary QoS.

  • 1864.
    Wickman, Tomas
    KTH, School of Information and Communication Technology (ICT).
    Evaluation of communication protocols between vehicle and server: Evaluation of data transmission overhead by communication protocols2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis project has studied a number of protocols that could be used to communicate between a vehicle and a remote server in the context of Scania’s connected services. While there are many factors that are of interest to Scania (such as response time, transmission speed, and amount of data overhead for each message), this thesis will evaluate each protocol in terms of how much data overhead is introduced and how packet loss affects this overhead. The thesis begins by giving an overview of how a number of alternative protocols work and what they offer with regards to Scania’s needs. Next these protocols are compared based on previous studies and each protocol’s specifications to determine which protocol would be the best choice for realizing Scania’s connected services. Finally, a test framework was set up using a virtual environment to simulate different networking conditions. Each of the candidate protocols were deployed in this environment and setup to send sample data. The behaviour of each protocol during these tests served as the basis for the analysis of all of these protocols. The thesis draws the conclusion that to reduce the data transmission overhead between vehicles and Scania’s servers the most suitable protocol is the UDP based MQTT SN.

  • 1865.
    Widfeldt, Fredrik
    KTH, Superseded Departments, Teleinformatics.
    sage of LDAP for managing users and resources in a computer network1997Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Today most organizations keep several separated information directories in which for example computer passwords, e-mail addresses, telephone numbers etc. are stored. A big problem is that much of the information is stored in more than one of the directories and thus it is easy for inconsistencies to develop between the directories. A solution to the problem is to store the information only once - in a central directory server where client applications could access it. LDAP is a protocol used by clients to retrieve information from a directory server.

    This report describes how an LDAP directory may be used to share user data in a computer network. First the concept of distributed directory information is presented. Then LDAP is carefully described and compared with X.500, a larger and more complex service. After that we look at the possibility to implement LDAP when developing own systems. Deployment issues and available LDAP products are discussed. A project demo system is presented and described. The demo system shows how different systems can share user information stored in an LDAP directory and how operating systems may be migrated with the directory. One of the more important parts of the system is a gateway server, forwarding NIS requests to the LDAP directory.

    The goal of the report is to make the reader aware of distributed directory services and what important role they probably will have in the near future.

  • 1866.
    Wiese, Moritz
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Oechtering, Tobias J.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Papadimitratos, Panos
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Uncertain wiretap channels and secure estimation2016In: 2016 IEEE International Symposium on Information Theory, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 2004-2008Conference paper (Refereed)
    Abstract [en]

    The zero-error secrecy capacity of uncertain wiretap channels is defined. If the sensor-estimator channel is perfect, it is also calculated. Further properties are discussed. The problem of estimating a dynamical system with nonstochastic disturbances is studied where the sensor is connected to the estimator and an eavesdropper via an uncertain wiretap channel. The estimator should obtain a uniformly bounded estimation error whereas the eavesdropper's error should tend to infinity. It is proved that the system can be estimated securely if the zero-error capacity of the sensor-estimator channel is strictly larger than the logarithm of the system's unstable pole and the zero-error secrecy capacity of the uncertain wiretap channel is positive.

  • 1867.
    Wiklander, Erik
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Mobile Resource Awareness2001Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    New types of cellular networks are appearing on the market, such as GPRS and UMTS. In addition to this, an increasing number of places are being equipped with wireless LAN extensions to the Internet. Simultaneously, new mobile devices are becoming available that can perform complex computations based on events from various input devices and/or information sources. The combination of extended network connectivity and new mobile devices creates new opportunities for network computing.

    This paper presents a scenario where network enabled applications can interact with mobile devices to create a smart space. The ambition is to create a system where mobile devices can be aware of what resources are present at a specific location. The prototype solution in this paper uses an XML-based protocol and a tuple space architecture as a message passing mechanism.

  • 1868. Willkomm, Daniel
    et al.
    Hollos, Daniel
    Bohge, Mathias
    Gross, James
    Wolisz, Adam
    Double Hopping: A new Approach for Dynamic Frequency Hopping in Cognitive Radio Networks2008In: IEEE 19th International Symposium on Personal, Indoor and Mobile Radio Communications, 2008. PIMRC 2008, IEEE conference proceedings, 2008, p. 1-6Conference paper (Refereed)
    Abstract [en]

    One of the major challenges in designing cellular cognitive radio (CR) networks is the avoidance of secondary user (SU) interference to so called primary users (PUs) operating in the licensed bands. Usually, SU operation has to be interrupted periodically in order to detect PU activity and avoid the respective frequencies. Recently, dynamic frequency hopping (DFH) mechanisms have been suggested to enable reliable PU detection and continuous SU operation at the same time. Applying DFH in a multi-cell environment adds the challenge of mitigating co-channel interference (CCI). In this paper, we introduce a new DFH approach for cellular CR networks to allow reliable PU detection and continuous SU operation while avoiding CCI: double hopping (DH). We present a distributed frequency assignment heuristic for DH and compare it to the optimal assignment. We show that the performance of the sub-optimal distributed assignment is only slightly worse than the optimal performance, and, thus, outperforms existing distributed approaches by far.

  • 1869.
    Wisell, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Gavle, Sweden.
    Isaksson, Magnus
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Gavle, Sweden.
    Keskitalo, N.
    A general evaluation criteria for behavioral power amplifier modeling2007In: 69th ARFTG Microwave Measurements Conference - Addressing Metrology Needs for Future High-Speed Information and Communications Systems, 2007, p. 5456311-Conference paper (Refereed)
    Abstract [en]

    In this paper a new goodness measure for behavioral complex envelope power amplifier models is defined in the frequency domain. The measure can be calculated for any input signal using the same formulas, which makes it general and easy to use. The results will however be dependent on the input signal. The total model error, or normalized mean-square error, for power amplifier models are normally dominated by the in-band error, often mainly caused by the linear distortion. The new measure is aimed at capturing the nonlinear modeling performance of the amplifier model. This is of interest since it is most often the nonlinear, rather than the linear, distortion that causes most harm in real-life power amplifier applications.

  • 1870. Wong, E.
    et al.
    Machuca, C. M.
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Survivable architectures for power-savings capable converged access networks2016In: 2016 IEEE International Conference on Communications, ICC 2016, IEEE conference proceedings, 2016, p. 365-371, article id 7510719Conference paper (Refereed)
    Abstract [en]

    The reliance on the loss-of-signal (LOS) of upstream transmissions to indicate fiber/component failure is potentially unsuitable in networks that implement sleep/doze mode operation. In such networks, the transition into sleep/doze mode would result in no signal transmission, and when used in conjunction with conventional LOS to indicate network failure, would result in erroneous triggering of false alarm and subsequently protection switching. Recently, converged access networks using a hybrid passive optical architecture, have been favored as a low-cost and high-bandwidth solution to deliver high-bandwidth applications to both fixed access and mobile users. These networks are referred to as Hybrid PON Converged Access Networks. Protection against fiber/equipment failures in these networks is critical considering the customer base, network span, and traffic supported. This paper proposes four survivable architectures for such converged access networks. These architectures combine rapid fault detection and protection switching against high impact failures but without the need to rely on upstream transmissions for LOS detection. A comparison of the four architectures across three different area densities under three deployment scenarios, is presented. Guidance for selecting the best protection architecture to be deployed, considering area densities and deployment scenarios, is provided.

  • 1871.
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Connection availability in WDM mesh networks with multiple failures2006In: ICTON 2006: 8th International Conference on Transparent Optical Networks, Vol 3, Proceedings / [ed] Marciniak, M, 2006, p. 126-129Conference paper (Refereed)
    Abstract [en]

    Wavelength Division Multiplexed (WDM) technology has revolutionized wide-area networks. As the amount of traffic carried is very large, any single failure can be catastrophic. Thus, survivability of a network that refers to a network's capability to provide continuous service in the presence of failures has become crucial in such networks. Communication networks are usually designed to survive single failure. However, in large networks the occurrence of multiple concurrent failures cannot be neglected. Therefore, in this paper we study connection availability in WDM networks assuming failures of any multiplicity. Shared Path Protection (SPP) scheme is an efficient network recovery mechanism in terms of network resource utilization and in many related works the SPP scheme has been studied to solve a single failure problem. We apply SPP scheme and propose an analytical model for calculation of connection unavailability in WDM mesh networks with multiple failure assumption. We have evaluated our model by simulations and show that the connection unavailability obtained by simulations is very close to the theoretical value obtained by our algorithm, which proves the accuracy of our model.

  • 1872.
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Optical network architectures for datacenters2017In: Optics InfoBase Conference Papers, Optics Info Base, Optical Society of America, 2017, Vol. Part F53Conference paper (Refereed)
    Abstract [en]

    The talk will highlight challenges related to dramatically growing datacenter traffic. The advantages of using photonic technology in intra-datacenter networks will be discussed and a crosslayer view of network architecture design will be presented.

  • 1873.
    Wosinska, Lena
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Chen, Jiajia
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Monti, Paolo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Next Generation Optical Access Network Architectures: What is the Best Option?2013Conference paper (Other academic)
  • 1874.
    Wosinska, Lena
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Haralson, Joanna
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Thylén, Lars
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Öberg, Johnny
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Hessmo, Björn
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Benefit of Implementing Novel Optical Buffers in an Asynchronous Photonic Packet Switch2004In: Proceedings of ECOC-04, 2004Conference paper (Refereed)
  • 1875.
    Wosinska, Lena
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Monti, Paolo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Fiorani, Matteo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Dreier, Dennis
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy and Climate Studies, ECS.
    Silveira, Semida
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy and Climate Studies, ECS.
    ICT Infrastructure for Smart Cities: Curitiba, Brazil2015Conference paper (Other academic)
  • 1876.
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Nanophotonic devices based on silicon-on-insulator nanowire waveguides2006In: ICTON 2006: 8th International Conference on Transparent Optical Networks, Vol 1, Proceedings: ICTON, MPM, INDUSTRIAL, PICAW, GOWN / [ed] Marciniak, M, 2006, p. 206-209Conference paper (Refereed)
    Abstract [en]

    While silica-on-silicon is recognized as one of the dominant platforms for microphotonics today, silicon-on-insulator nanowire waveguides appear to be the technology for next generation of super compact integrated devices. Due to very high refractive index contrast and strong light confinement in the core, the waveguide bend radius can be reduced to a few micrometers and the size reduction of the functional integrated circuits can reach several orders of magnitude. An array waveguide grating multi/demultiplexer that usually occupies several square centimetres in silica-on-silicon technology can be reduced to the size of 50 x 50 mu m(2). The performance of such miniaturized devices with submicrometer-size waveguides strongly depends on the fabrication accuracy: high resolution patterning and low roughness etching. High quality and high precision optimized processing is necessary to obtain satisfactory results. We discuss here the technology issues as well as present some fabricated devices based on silicon nanowire waveguides.

  • 1877.
    Wu, Chia-Lung
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Chen, P. -N
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Ming, Xiao
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Shin-Lin, S.
    A two-phase maximum-likelihood sequence estimation for receivers with partial CSI2013In: 9th International Conference on Information, Communications and Signal Processing, ICICS 2013, IEEE Computer Society, 2013, p. 6782818-Conference paper (Refereed)
    Abstract [en]

    The optimality of the conventional maximum-likelihood sequence estimation (MLSE), also known as the Viterbi Algorithm (VA), relies on the assumption that the receiver has perfect knowledge of the channel coefficients or channel state information (CSI). However, in practical situations that fail the assumption, the MLSE method becomes suboptimal and then exhaustive checking is the only way to obtain the ML sequence. At this background, considering directly the ML criterion for partial CSI, we propose a two-phase low-complexity MLSE algorithm, in which the first phase performs the conventional MLSE algorithm in order to retain necessary information for the backward VA performed in the second phase. Simulations show that when the training sequence is moderately long in comparison with the entire data block such as 1/3 of the block, the proposed two-phase MLSE can approach the performance of the optimal exhaustive checking. In a normal case, where the training sequence consumes only 0.14 of the bandwidth, our proposed method still outperforms evidently the conventional MLSE.

  • 1878. Wu, J.
    et al.
    Zhou, S.
    Niu, Z.
    Liu, C.
    Yang, P.
    Miao, Guowang
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Traffic-Aware Data and Signaling Resource Management for Green Cellular Networks2014Conference paper (Refereed)
    Abstract [en]

    The increasing traffic demands bring heavy load toboth the data and control planes of cellular networks, along withsubstantial energy consumption. To solve the issue, new networkarchitecture that separates signaling and data has been proposedin literature for future green cellular networks. In this paper, weanalyze the data and signaling resource configuration problemin this new network architecture. We find the optimal resourcepartitioning parameters to optimize the blocking performanceand to minimize the overall network power consumption witha blocking probability constraint. More specifically, we adopttraffic-aware resource allocation between the data and signalingbase stations (BSs) to improve network access capability whilereducing the overall network power consumption. Two typesof resource partitioning patterns, complete partitioning andpartial partitioning, are studied. Numerical results show thatgreat energy-saving gain can be achieved compared with thetraditional fixed and traffic-proportional resource partitioningpatterns. Moreover, power consumption and blocking performancetradeoffs are explored, based on which the appropriateresource partitioning pattern can be chosen according to differentquality of service (QoS) requirements.

  • 1879.
    Wu, Jiang
    et al.
    KTH, Superseded Departments, Teleinformatics.
    Maguire Jr., Gerald Q.
    KTH, Superseded Departments, Teleinformatics.
    Agent Based Seamless IP Multicast Receiver Handover2000In: Proceedings of the IFIP TC6/WG6.8 Working Conference on Personal Wireless Communications, Deventer, The Netherlands: Kluwer, B.V. , 2000, p. 213-226Conference paper (Refereed)
  • 1880. Wu, Jing
    et al.
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Jin, Yaohui
    Araki, Soichiro
    Special Issue on Optical Network Architectures and Management2011In: Optical Switching and Networkning Journal, ISSN 1573-4277, E-ISSN 1872-9770, Vol. 8, no 4, p. 225-225Article in journal (Other academic)
  • 1881. Wu, Jing
    et al.
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Shen, Gangxiang
    Spadaro, Salvatore
    Advances in optical networks control and management2013In: Optical Switching and Networkning Journal, ISSN 1573-4277, E-ISSN 1872-9770, Vol. 10, no 1, p. 1-2Article in journal (Other academic)
  • 1882. Wu, Jinsong
    et al.
    Bisio, Igor
    Gniady, Chris
    Hossain, Ekram
    Valla, Massimo
    Li, Haibo
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Context-aware networking and communications: Part 12014In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 52, no 6, p. 14-15Article in journal (Refereed)
  • 1883.
    Wu, Jun
    KTH, School of Information and Communication Technology (ICT).
    Signal Collecting Platform and "Handprint" Positioning System2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Mobile computing is an emerging research field in recent years. Although the computation capability of main stream smartphones are several orders of magnitude better than computers twenty years ago, the capacity of battery does not increase at same speed. To save energy, some recent work tries to schedule network traffic according to signal strength variations. To achieve this goal, a database that is used for storing signal strength distribution is essential.We first design and implement a platform to collect cellular network information, including Cell-ID and signal strength information. The platform is designed as a distributed system that supports collecting signal strength data by using crowdsourcing approach.We then deploy the platform and collect signal strength information in Otaniemi area (Finland). After analysing the collected data, we observe several interesting phenomenons. (1) the density of base stations is out of expectation; (2) cells is becoming smaller; (3) in most places a device may connect to different base stations. Based on these observations, we design a new energy-efficient positioning system called “handprint”, which utilises signal strength information from neighbouring smartphones to assist positioning. Compared with Google Geolocation API and other existing work, our “handprint” system can improve positioning accuracy by more than 20%.

  • 1884. Wu, L.
    et al.
    Sun, P.
    Xiao, Ming
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Hu, Y.
    Wang, Z.
    Sparse Signal Aloha: A Compressive Sensing-Based Method for Uncoordinated Multiple Access2017In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 21, no 6, p. 1301-1304, article id 7849200Article in journal (Refereed)
    Abstract [en]

    We investigate the problem of sparse signal medium access control in the wireless sensor networks. The proposed sparse signal Aloha (SSA) transmits sampled compressive data to the fusion center using Aloha random access protocol. In order to maximize the overall data transmission rate in the presence of packet collision, redundant data are randomly subsampled at individual sensor nodes according to an optimal subsampling rate before transmission. Data loss due to random subsampling and collision in the wireless channel are compensated using compressive sensing recovery method at the fusion center. Simulation results verify the theoretical analysis and show the significant improvement of SSA compared with existing CS-based random access method.

  • 1885.
    Wu, Xiao
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    SIP on an Overlay Network2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With the development of mobile (specifically: wide area cellular telephony) technology, users’ requirements have changed from the basic voice service based on circuit switch technology to a desire for high speed packet based data transmission services. Voice over IP (VoIP), a packet based service, is gaining increasing attention due to its high performance and low cost. However, VoIP does not work well in every situation. Today Network address translation (NAT) traversal has become the main obstruction for future VoIP deployment.

    In this thesis we analyze and compare the existing NAT traversal solutions. Following this, we introduce a VoIP over IPSec (VOIPSec) solution (i.e., a VoIP over IPSec virtual private network (VPN) scheme) and an extended VOIPSec solution mechanism. These two solutions were tested and compared to measure their performance in comparison to a version of the same Session Initiation Protocol (SIP) user agent running without IPSec.

    In the proposed VOIPSec solution, the IPSec VPN tunnel connects each of the SIP clients to a SIP server, thus making all of the potential SIP participants reachable, i.e., solving the NAT traversal problem. All SIP signaling and media traffic for VoIP calls are transmitted through this prior established tunnel. This VPN tunnel provides the desired universal means for VoIP traffic to traverse NAT equipment. Additionally, the IPSec VPN also guarantees the security of VoIP calls at the IP level.

    In order to improve the security level of media streams for the VOIPSec solution, we deployed and evaluated an extended VOIPSec solution which provides end-to-end protection of the real time media traffic. In this extended VOIPSec solution, we used SRTP instead of RTP to carry the media content. This extended method was shown to provide all of the advantages of VOIPSec and SRTP without any additional delay for the media traffic (as compared to the VoIPSec solution).

    Note that the solution proposed in this thesis may be of limited practical importance in the future as more NATs become VoIP capable; but the solution is currently essential for facilitating the increasing deployment of VoIP systems in practice. For VoIP calls that do not need end-to-end security, we recommend the use of the VOIPSec solution as a means to solve the NAT traversal problem and to protect traffic at the IP level. When application to application security is not needed we prefer the VOIPSec solution to the extended VOIPSec solution for the following reasons: (1) our test results show that the time for call setup for the extended VOIPSec solution is twice time the time needed for the VOIPSec solution and the extended VOIPSec solution requires the use of user agents that support SRTP. While, the VOIPSec solution does not require a special user agent and all VoIP clients in the market are compatible with this solution. However, when more SIP user agents add support for SRTP, the extended VOIPSec solution will be applicable for users of these SIP user agents.

  • 1886.
    Wu, Yiming
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Honeth, Nicholas
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Shi, Zhanpeng
    ABB AB, Substn Automat Prod, Vasteras, Sweden.
    Software Merging Unit based IED Functional Test Platform2015Conference paper (Refereed)
    Abstract [en]

    In Substation Automation Systems, application functions such as monitoring, control, and protection are deployed in intelligent electronic devices (IEDs). Before the IEDs are installed in the substation, functions are tested by the manufactures to ensure that the functions operate properly as designed. A conventional function test platform is made of amplifiers with copper wire connection to the IEDs. It has drawbacks such as high cost, limited flexibility, and limited number of signal channels. With the introduction of the IEC61850 standard, IEDs are able to obtain measurement from merging units (MU) via the process bus. Consequently, using MUs to replace the amplifier for IED function testing has been studied by several research groups. All of them use hardware MUs or power system simulator embedded MUs. These MUs based test platforms have weakness such as limitation of the number of MUs and lower flexibility in MU performance modification, This paper proposes a novel IED functional test platform using software MU (sMU), which mitigates the above limitations. Thanks to the software approach, different MU performance scenarios can be easily configured instead of using a complicated communications simulator. The sMU based test platform concept has been proved by performing accuracy and operate-time tests with transformer differential protection. Comparing with conventional test platform, sMU based test platform has better results in the accuracy tests and similar performance in the operate-time tests. Therefore, it is feasible to use sMU based platform for IED functional tests.

  • 1887.
    Wu, Yiming
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Saleem, Arshad
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    IEC61850 Logical Node Lookup Service Using Distributed Hash Tables2014In: 2014 IEEE PES Innovative Smart Grid Technologies Conference, ISGT 2014, IEEE Computer Society, 2014, p. 6816443-Conference paper (Refereed)
    Abstract [en]

    Development of Information and Communication Technology (ICT) increases the communication capability of equipment in power system and also creates large number of data sources. In order to reliably share these data sources with applications is a new challenge for power system. This paper presents an alternate data delivery system solution using IEC61850 standard Manufactory Messaging Specification (MMS) across wide area networks, utilizing Distributed Hash Table (DHT) for look-up of Logical Nodes addresses.  Result of the proposed scheme is a flexible, autonomous, scalable, and robust method to address Logical Nodes across a Wide Area Network. In comparison with IEC61850-90-2 solution, this solution can help reduce the manual work in configuration of each link, and enables greater flexibility for adding new data points. The presented platform also opens door of providing adaptive data acquisition for power system applications by implementing a filtering function in the ISG.

  • 1888.
    Wu, Yongliang
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Aggregating product reviews for the Chinese market2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As of December 2007, the number of Internet users in China had increased to 210 million people. The annual growth rate reached 53.3 percent in 2008, with the average number of Internet users increasing every day by 200,000 people. Currently, China's Internet population is slightly lower than the 215 million internet users in the United States. [1]

    Despite the rapid growth of the Chinese economy in the global Internet market, China’s e-commerce is not following the traditional pattern of commerce, but instead has developed based on user demand. This growth has extended into every area of the Internet.

    In the west, expert product reviews have been shown to be an important element in a user’s purchase decision. The higher the quality of product reviews that customers received, the more products they buy from on-line shops. As the number of products and options increase, Chinese customers need impersonal, impartial, and detailed products reviews. This thesis focuses on on-line product reviews and how they affect Chinese customer’s purchase decisions.

    E-commerce is a complex system. As a typical model of e-commerce, we examine a Business to Consumer (B2C) on-line retail site and consider a number of factors; including some seemingly subtitle factors that may influence a customer’s eventually decision to shop on website. Specifically this thesis project will examine aggregated product reviews from different on-line sources by analyzing some existing western companies. Following this the thesis demonstrates how to aggregate product reviews for an e-business website.

    During this thesis project we found that existing data mining techniques made it straight forward to collect reviews. These reviews were stored in a database and web applications can query this database to provide a user with a set of relevant product reviews. One of the important issues, just as with search engines is providing the relevant product reviews and determining what order they should be presented in. In our work we selected the reviews based upon matching the product (although in some cases there are ambiguities concerning if two products are actually identical or not) and ordering the matching reviews by date - with the most recent reviews present first.

    Some of the open questions that remain for the future are: (1) improving the matching - to avoid the ambiguity concerning if the reviews are about the same product or not and (2) determining if the availability of product reviews actually affect a Chinese user's decision to purchase a product.

  • 1889.
    Wuhib, Fetahi
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dam, Mads
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Stadler, Rolf
    KTH, School of Electrical Engineering (EES), Communication Networks.
    A Gossiping Protocol for Detecting Global Threshold Crossings2010In: IEEE Transactions on Network and Service Management, ISSN 1932-4537, E-ISSN 1932-4537, Vol. 7, no 1, p. 42-57Article in journal (Refereed)
    Abstract [en]

    We investigate the use of gossip protocols for the detection of network-wide threshold crossings. Our design goals are low protocol overhead, small detection delay, low probability of false positives and negatives, scalability, robustness to node failures and controllability of the trade-off between overhead and detection delay. Based on push-synopses, a gossip protocol introduced by Kempe et al., we present a protocol that indicates whether a global aggregate of static local values is above or below a given threshold. For this protocol, we prove correctness and show that it converges to a state with no overhead when the aggregate is sufficiently far from the threshold. Then, we introduce an extension we call TG-GAP, a protocol that (1) executes in a dynamic network environment where local values change and (2) implements hysteresis behavior with upper and lower thresholds. Key elements of its design are the construction of snapshots of the global aggregate for threshold detection and a mechanism for synchronizing local states, both of which are realized through the underlying gossip protocol. Simulation studies suggest that TG-GAP is efficient in that the protocol overhead is minimal when the aggregate is sufficiently far from the threshold, that its overhead and the detection delay are largely independent on the system size, and that the tradeoff between overhead and detection quality can be effectively controlled. Lastly, we perform a comparative evaluation of TG-GAP against a tree-based protocol. We conclude that, for detecting global threshold crossings in the type of scenarios investigated, the tree-based protocol incurs a significantly lower overhead and a smaller detection delay than a gossip protocol such as TG-GAP.

  • 1890.
    Wuhib, Fetahi
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Stadler, Rolf
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed monitoring and resource management for large cloud environments2011In: International Symposium on Integrated Network Management (IM), 2011 IFIP/IEEE, IEEE Communications Society, 2011, p. 970-975Conference paper (Refereed)
    Abstract [en]

    Over the last decade, the number, size and complexityof large-scale networked systems has been growing fast, andthis trend is expected to accelerate. The best known example of alarge-scale networked system is probably the Internet, while largedatacenters for cloud services are the most recent ones. In suchenvironments, a key challenge is to develop scalable and adaptivetechnologies for management functions. This thesis addressesthe challenge by engineering several protocols for distributedmonitoring and resource management that are suitable for largescalenetworked systems. The protocols are evaluated throughtheoretical analysis, simulation studies and testbed experimentation.The evaluation results show that the protocols achieve theirrespective design objectives with respect to quality, efficiency,scalability, controllability and adaptability.

  • 1891.
    Wuhib, Fetahi
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Stadler, Rolf
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dam, Mads
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Gossiping for Threshold Detection2009In: 2009 IFIP/IEEE INTERNATIONAL SYMPOSIUM ON INTEGRATED NETWORK MANAGEMENT (IM 2009) VOLS 1 AND 2, NEW YORK: IEEE , 2009, p. 259-266Conference paper (Refereed)
    Abstract [en]

    We investigate the use of gossip protocols to detect threshold crossings of network-wide aggregates. Aggregates are computed from local device variables using functions such as SUM, AVERAGE, COUNT, MAX and MIN. The process of aggregation and detection is performed using a standard gossiping scheme. A key design element is to let nodes dynamically adjust their neighbor interaction rates according to the distance between the nodes' local estimate of the global aggregate and the threshold itself. We show that this allows considerable savings in communication overhead. In particular, the overhead becomes negligible when the aggregate is sufficiently far above or far below the threshold. We present evaluation results from simulation studies regarding protocol efficiency, quality of threshold detection, scalability, and controllability.

  • 1892.
    Wuhib, Fetahi
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Stadler, Rolf
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Spreitzer, Mike
    Gossip-based Resource Management for Cloud Environments2010In: International Conference on Network and Service Management, 2010, p. 1-8Conference paper (Refereed)
    Abstract [en]

    We address the problem of resource management for a large-scale cloud environment that hosts sites. Our contribution centers around outlining a distributed middleware architecture and presenting one of its key elements, a gossip protocol that meets our design goals: fairness of resource allocation with respect to hosted sites, efficient adaptation to load changes and scalability in terms of both the number of machines and sites. We formalize the resource allocation problem as that of dynamically maximizing the cloud utility under CPU and memory constraints. While we can show that an optimal solution without considering memory constraints is straightforward (but not useful), we provide an efficient heuristic solution for the complete problem instead. We evaluate the protocol through simulation and find its performance to be well-aligned with our design goals.

  • 1893. Wuhib, Fetahi
    et al.
    Yanggratoke, Rerngvit
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Stadler, Rolf
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Allocating Compute and Network Resources under Management Objectives in Large-Scale Clouds2013In: Journal of Network and Systems Management, ISSN 1064-7570, E-ISSN 1573-7705Article in journal (Refereed)
    Abstract [en]

    We consider the problem of jointly allocating compute and network resources in a large Infrastructure-as-a-Service (IaaS) cloud. We formulate the problem of optimally allocating resources to virtual data centers (VDCs) for four well-known management objectives: balanced load, energy efficiency, fair allocation, and service differentiation.  Then, we outline an architecture for resource allocation, which centers around a set of cooperating controllers, each solving a problem related to the chosen management objective. We illustrate how a global management objective is mapped onto objectives that govern the execution of these controllers. For a key controller, the Dynamic Placement Controller, we give a detailed distributed design, which is based on a gossip protocol that can switch between management objectives. The design is applicable to a broad class of management objectives, which we characterize through a property of the objective function.  The property ensures the applicability of an iterative descent method that the gossip protocol implements.  We evaluate, through simulation, the dynamic placement of VDCs for a large cloud under changing load and VDC churn. Simulation results show that this controller is effective and highly scalable, up to 100'000 nodes, for the management objectives considered.

  • 1894.
    Wåhslén, Jonas
    KTH, School of Technology and Health (STH), Data- och elektroteknik.
    Multi-Sensor Data Synchronization using Mobile Phones2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Body sensor networking is a rapidly growing technology. Today wearable sensors are used to measure and monitor e.g. pulse, temperature, skin conductance, heart activity, and movement (through GPS or inertial measurement units). Mobile phones can act as coordinating nodes in wireless personal area networks used in home automation, healthcare, sport and wellness e.g. to measure pulse and distance. Integration of data from multiple sources sensors (data fusion) means that data from each sensor node needs to be associated with data from other sensor nodes sampled at approximately the same time. Accurate methods for time synchronization are therefore a necessary prerequisite for reliable data fusion.

    This thesis studies time synchronization problems in Bluetooth piconets between multiple wireless sensor nodes connected to a mobile phone that acts as coordinating node. Three different algorithms to enable correct data fusion have been developed, implemented and evaluated. The first is a single clock solution that synchronizes multiple wireless sensor nodes based solely on the mobile phone’s clock. The other two algorithms synchronize the clocks in sensor nodes to the clock in the coordinating node. 

  • 1895.
    Wåhslén, Jonas
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Computer and Electronic Engineering.
    Lindh, Thomas
    KTH, School of Technology and Health (STH), Medical Engineering, Computer and Electronic Engineering.
    Real-time Performance Management of Assisted Living Services for Bluetooth Low Energy Sensor Communication2017In: Integrated Network and Service Management (IM), 2017 IFIP/IEEE Symposium on, IEEE conference proceedings, 2017Conference paper (Refereed)
    Abstract [en]

    PerfMon is a prototype implementation of a realtime performance management method for sensor data communication in assisted living applications. It is implemented in accordance with the specification for GATT services in Bluetooth low energy (BLE). PerfMon provides a tool for real-time performance monitoring and control for caregivers and service providers. Test results from monitoring and control of packet loss ratio related to alarm thresholds are presented. PerfMon is adapted to cloud-based web services using RESTful APIs and established object models. Performance management is a necessary component in an overall management system of IoT devices for healthcare and assisted living applications.

  • 1896.
    Wåhslén, Jonas
    et al.
    KTH, School of Technology and Health (STH), Data- och elektroteknik (Closed 20130701).
    Orhan, Ibrahim
    KTH, School of Technology and Health (STH), Data- och elektroteknik (Closed 20130701).
    Lindh, Thomas
    KTH, School of Technology and Health (STH), Data- och elektroteknik (Closed 20130701).
    Eriksson, Martin
    KTH, School of Technology and Health (STH), Medical sensors, signals and systems (MSSS) (Closed 20130701).
    A novel approch to multi-sensor data synchronisation using mobile phones2013In: International Journal of Autonomous and Adaptive Communications Systems, ISSN 1754-8632, E-ISSN 1754-8640, Vol. 6, no 3, p. 289-303Article in journal (Refereed)
    Abstract [en]

    This paper presents a new algorithm for application layer synchronisation of data from multiple sensors arriving to a mobile phone's Bluetooth interface. A system that provides feedback signals to an athlete is one example where it is crucial to synchronise data from several wireless sensors. This paper also discusses synchronisation problems caused by unpredictable Bluetooth transmission performance. 

  • 1897.
    Wåhslén, Jonas
    et al.
    KTH, School of Technology and Health (STH), Data- och elektroteknik (Closed 20130701).
    Orhan, Ibrahim
    KTH, School of Technology and Health (STH), Data- och elektroteknik (Closed 20130701).
    Sturm, Dennis
    KTH, School of Technology and Health (STH), Centres, Centre for Technology in Medicine and Health, CTMH.
    Lindh, Thomas
    KTH, School of Technology and Health (STH), Data- och elektroteknik (Closed 20130701).
    Performance evaluation of time synchronization and clock drift compensation in wireless personal area networks2012In: BodyNets '12 Proceedings of the 7th International Conference on Body Area Networks, ICST , 2012, p. 153-158Conference paper (Refereed)
    Abstract [en]

    Efficient algorithms for time synchronization, including compensation for clock drift, are essential in order to obtain reliable fusion of data samples from multiple wireless sensor nodes. This paper evaluates the performance of algorithms based on three different approaches; one that synchronizes the local clocks on the sensor nodes, and a second that uses a single clock on the receiving node (e.g. a mobile phone), and a third that uses broadcast messages. The performances of the synchronization algorithms are evaluated in wireless personal area networks, especially Bluetooth piconets and ZigBee/IEEE 802.15.4 networks. A new approach for compensation of clock drift and a realtime implementation of single node synchronization from the mobile phone are presented and tested. Finally, applications of data fusion and time synchronization are shown in two different use cases; a kayaking sports case, and monitoring of heart and respiration of prematurely born infants. 

  • 1898.
    Xiang, Deliang
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics. National University of Defense Technology, China.
    Tang, Tao
    National University of Defense Technology, China.
    Ban, Yifang
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics.
    Su, Yi
    Kuang, Gangyao
    Unsupervised polarimetric SAR urban area classification based on model-based decomposition with cross scattering2016In: ISPRS journal of photogrammetry and remote sensing (Print), ISSN 0924-2716, E-ISSN 1872-8235, Vol. 116, p. 86-100Article in journal (Refereed)
    Abstract [en]

    Since it has been validated that cross-polarized scattering (HV) is caused not only by vegetation but also by rotated dihedrals, in this study, we use rotated dihedral corner reflectors to form a cross scattering matrix and propose an extended four-component model-based decomposition method for PolSAR data over urban areas. Unlike other urban area decomposition techniques which need to discriminate the urban and natural areas before decomposition, this proposed method is applied on PolSAR image directly. The building orientation angle is considered in this scattering matrix, making it flexible and adaptive in the decomposition. Therefore, we can separate cross scattering of urban areas from the overall HV component. Further, the cross and helix scattering components are also compared. Then, using these decomposed scattering powers, the buildings and natural areas can be easily discriminated from each other using a simple unsupervised K-means classifier. Moreover, buildings aligned and not aligned along the radar flight direction can be also distinguished clearly. Spaceborne RADARSAT-2 and airborne AIRSAR full polarimetric SAR data are used to validate the performance of our proposed method. The cross scattering power of oriented buildings is generated, leading to a better decomposition result for urban areas with respect to other state-of-the-art urban decomposition techniques. The decomposed scattering powers significantly improve the classification accuracy for urban areas.

  • 1899. Xiao, Lin
    et al.
    Johansson, Mikael
    Boyd, Stephen
    Simultaneous routing and resource allocation in wireless networks2001In: Proceedings of the Annual Allerton Conference on Communication, Control and Computing, 2001Conference paper (Refereed)
  • 1900. Xiao, Lin
    et al.
    Johansson, Mikael
    Boyd, Stephen
    Simultaneous routing and resource allocation via dual decomposition2002In: Asian Control Conference, 2002Conference paper (Refereed)
35363738394041 1851 - 1900 of 2063
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