Change search
Refine search result
78910111213 451 - 500 of 3285
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the 'Create feeds' function.
  • 451.
    Casselgren, Johan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Bodin, Ulf
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Reusable road condition information system for traffic safety and targeted maintenance2017In: IET Intelligent Transport Systems, ISSN 1751-956X, E-ISSN 1751-9578, Vol. 11, no 4, p. 230-238Article in journal (Refereed)
    Abstract [en]

    Driver awareness of current winter road conditions (RCs) is known to affect the frequency of accidents due to sudden changes in these conditions. For example, partially icy roads that appear during autumn in northern areas typically result in collisions and ditch runs unless the drivers are generally aware of the situation. Availing motorists who drive under winter RCs of enhanced information is therefore highly desirable to increase their awareness of hazardous driving conditions. Such conditions need to be predicted ahead of time and presented to drivers before they attempt slippery road sections. Moreover, the identification of slippery RCs should quickly trigger targeted road maintenance to reduce the risk of accidents. This study presents a scalable and reusable collaborative intelligent transport system, herein referred to as an RC information system (RCIS). RCIS provides accurate RC predictions and forecasts based on RC measurements, road weather observations, and short-term weather forecasts. The prediction methods in the context of the distributed RCIS have been tested using a prototype implementation. These tests confirmed that these inputs could be combined into useful and accurate information about winter RCs that can be adapted for different types of users.

  • 452.
    Castellanos Ardila, Julieth Patricia
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Gallina, Barbara
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Towards Efficiently Checking Compliance Against Automotive Security and Safety Standards2017In: The 7th IEEE International Workshop on Software Certification WoSoCer 2017, 2017, p. 317-324Conference paper (Refereed)
    Abstract [en]

    The growing connectivity of the systems that we rely on e.g. transportation vehicles is pushing towards the introduction of new standards aimed at providing a baseline to address cybersecurity besides safety. If the interplay of the two normative spaces is not mastered, compliance management might become more time consuming and costly, preventing engineers from dedicating their energies to system engineering. In this paper, we build on top of previous work aimed at increasing efficiency and confidence in compliance management. More specifically, we contribute to building a terminological framework needed to enable the systematization of commonalities and variabilities within ISO 26262 and SAE J3061. Then, we focus our attention on the requirements for software design and implementation and we use defeasible logic to prove compliance. Based on the compliance checking results, we reveal reuse opportunities. Finally, we draw our conclusions and sketch future research directions.

  • 453.
    Cavdar, Cicek
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Ruiz, M.
    Monti, Paolo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Velasco, L.
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Design of green optical networks with signal quality guarantee2012In: IEEE International Conference on Communications, IEEE , 2012, p. 3025-3030Conference paper (Refereed)
    Abstract [en]

    Energy consumption of communication networks is growing very fast due to the rapidly increasing traffic demand. Consequently, design of green communication networks gained a lot of attention. In this paper we focus on optical Wavelength Division Multiplexing (WDM) networks, able to support this growing traffic demand. Several energy-aware routing and wavelength assignment (EA-RWA) techniques have been proposed for WDM networks in order to minimize their operational cost. These techniques aim at minimizing the number of active links by packing the traffic as much as possible, thus avoiding the use of lightly loaded links. As a result, EA-RWA techniques may lead to longer routes and to a high utilization on some specific links. This has a detrimental effect on the signal quality of the optical connections, i.e., lightpaths. In this study we quantify the impact of power consumption minimization on the optical signal quality. and address this problem by proposing a combined impairment and energy-aware RWA (IEA-RWA) approach. Towards this goal we developed a complete mathematical model that incorporates both linear and non-linear physical impairments together with an energy efficiency objective. The IEA-RWA problem is formulized as a Mixed Integer Linear Programming (MILP) model where both energy efficiency and signal quality considerations are jointly optimized. By comparing the proposed IEA-RWA approach with existing RWA (IA-RWA and EA-RWA) schemes, we demonstrate that our solution allows for a reduction of energy consumption close to the one obtained by EA-RWA approaches, while still guaranteeing a sufficient level of the optical signal quality.

  • 454. Cea, Mauricio G.
    et al.
    Goodwin, Graham C.
    Wigren, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Model predictive zooming power control in future cellular systems under coarse quantization2012In: Proc. 76th Vehicular Technology Conference, Piscataway, NJ: IEEE, 2012Conference paper (Refereed)
  • 455. Cen, M.
    et al.
    Chen, Jiajia
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Mégret, P.
    Moeyaert, V.
    Wuilpart, M.
    Fast and simple fault monitoring for long-reach passive optical networks2014In: 2014 European Conference on Optical Communication, (ECOC), IEEE , 2014, p. 6964070-Conference paper (Refereed)
    Abstract [en]

    We propose a fast and simple monitoring system based on multi-wavelength bi-directional transmission reflection analysis approach for long-reach passive optical networks. Both experimental and simulation results have demonstrated the proposed system can reach high accuracy for fault localization.

  • 456.
    Chabouni (nee Talbi), Sami
    KTH, Superseded Departments, Teleinformatics. KTH, School of Information and Communication Technology (ICT).
    Investigation and Prototyping of a web based manager in a GSM SIM Application Platform1998Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The growing need for communication in the world has increased the use of telephony and has therefore led to several technical innovations and improvements in the field of telecommunications. As countries develop their infrastructure new ways of communicating arise. But the technical innovations do not completely guide the evolution of the infrastructure. Many times, the way people act, i.e., their mentality and traditions, decides how to invest in the infrastructure. As basic infrastructure is being built in some developing countries, others come up with new revolutionary solutions to replace old infrastructure and, for some developing countries the question arises whether to continue to invest several hundreds of millions of dollars in traditional telephony wiring. The cellular technique is revolutionary enough to be applied in countries that haven’t yet built a telephony network covering an adequate area of the country. In these countries, investments might therefore be focused on the cellular technique, rather than continuing to invest in cable networking. Thus adapting cellular technology to a worldwide distribution is necessary when it comes to administration and subscriber payment. The communication providers meet administrative obstacles when it comes to telephony services for a large-scale distribution. Will the subscribers pay for the services we offer them?

    Using Subscriber Identity Modules (SIM) one way to solve this problem is to define a prepaid scheme. It is based on the fact that the subscriber uses a unique identifier to make a connection and is billed using this identifier. The service provider is free to choose if the subscriber is thrustworthy or not and thus must pay in advance for the services or billed retroactively. This general way of solving administration problems does not apply only to developing countries where retroactive billing isn’t a common tradition. It is equally applicable to industrial countries where some people are banned from credibility for a couple of years because they haven’t paid their bills in time, or just because they don’t have employment at the time of their subscription application.

    To be in possession of a telephone is everyone’s right in most of the industrialized countries.

  • 457.
    Chairetakis, Eleftherios
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
    Alkudhir, Bassam
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
    Mystridis, Panagiotis
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
    Deployment of Low Interaction Honeypots in University Campus Network2013Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Large scale networks face daily thousands of network attacks. No matter the strength of the existing security defending mechanisms, these networks remain vulnerable, as new tools and techniques are being constantly developed by hackers. A new promising technology that lures the attackers in order to monitor their malicious activities and divulge their intentions is emerging with Virtual Honeypots. In the present thesis, we examine an extensive security mechanism based on three different open source low interaction honeypots. We implement this mechanism at our university campus network in an attempt to identify the potential threats and methods used against our network. The data gathered by our honeypots reveal valuable information regarding the types of attacks, the vulnerable network services within the network and the malicious activities launched by attackers.

  • 458.
    Chamoun, Michel
    et al.
    Linnaeus University, Faculty of Technology, Department of Computer Science.
    Alizadeh, Maryam
    Linnaeus University, Faculty of Technology, Department of Computer Science.
    Enhancing Integrated Systems Through Automation2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In general, when working with the robot industry, there are many factors to consider. Therefore, the process from a non-existing product to an existing product involves many steps that can be time-to consume and error-prone. This thesis will examine the opportunities for automation in the industrial system and the problems that could occur. A little bit of the focus will also be put on Domain Specific Language (DSL) and the exchange of data between two DSLs.The automation of the industry is getting a big thing and there exist ways to integrate software automation within the industry. The research has been done by literature studies and experimenting with a software to exchange information between two DSL-applications. The result shows that there are some standard technologies that could be used in the integration of automation software, but also why automatization could create other problems. The result also shows that it’s possible to exchange information between two DSLs but it can be a little bit complicated.

  • 459.
    Chandhar, Prabhu
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Danev, Danyo
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Massive MIMO as Enabler for Communications with Drone Swarms2016In: 2016 INTERNATIONAL CONFERENCE ON UNMANNED AIRCRAFT SYSTEMS (ICUAS), IEEE , 2016, p. 347-354Conference paper (Refereed)
    Abstract [en]

    Massive multiple-input multiple-output (MIMO) is an emerging technology for mobile communications, where a large number of antennas are employed at the base station to simultaneously serve multiple single-antenna terminals with very high capacity. In this paper, we study the potentials and challenges of utilizing massive MIMO for unmanned aerial vehicles (UAVs) communication. We consider a scenario where multiple single-antenna UAVs simultaneously communicate with a ground station (GS) equipped with a large number of antennas. Speci[1]cally, we discuss the achievable uplink (UAV to GS) capacity performance in the case of line-of-sight (LoS) conditions. We also study the type of antenna polarization that should be used in order to maintain a reliable communication link between the GS and the UAVs. The results obtained using a realistic geometric model show that massive MIMO is a potential enabler for high-capacity UAV network

  • 460.
    Chandhar, Prabhu
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Danev, Danyo
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    On Ergodic Rates and Optimal Array Geometry in Line-of-Sight Massive MIMO2016Conference paper (Refereed)
    Abstract [en]

    We investigate the achievable ergodic rate of Massive multi-input-multi-output (MIMO) system in environments with high mobility and line-of-sight (LoS). A 3-dimensional geometric model with uniform rectangular array at the basestation (BS) is used for the investigation. We derive a closed formexpression for a lower bound on the uplink ergodic rate takinginto account imperfections of the channel state information,number of BS antennas, antenna spacing, and spatial distributionof user terminals. The results show that, in LoS Massive MIMO, when the terminals are spherically uniformly distributed around the BS, the ergodic rate is maximized for antenna spacing equal to integer multiples of one-half wavelength.

  • 461. Chandu, Chiranjeevi
    Region of Interest Aware and Impairment Based Image Quality Assessment2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 462.
    Chang, Peiliang
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Miao, Guowang
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Area Spectral and Energy Efficiency Analysis of Cellular Networks with Cell DTX2015In: IEEE Globecom 2015 , San Diego, December 6th-10th, 2015, IEEE conference proceedings, 2015, p. 1-6Conference paper (Refereed)
    Abstract [en]

    Cell discontinuous transmission (DTX) has been proposed as an effective solution to reduce energy consumption of cellular networks. In this paper, we investigate the impact of network traffic load on area spectral efficiency (ASE) and energy efficiency (EE) of cellular networks with cell DTX. Closedform expressions of ASE and EE as functions of traffic load for cellular networks with cell DTX are derived. It is shown that ASE increases monotonically in traffic load, while EE depends on the power consumption of base stations in sleep mode. If this power consumption is larger than a percentage of the active-mode power consumption, EE increases monotonically with traffic load and is maximized when the network is fully loaded. Otherwise, EE first increases and then decreases in traffic load. In this case, ASE and EE are maximized with different loads. The percentage threshold only depends on the path loss exponent of radio propagation environment and is calculated to be 56.2% when the path loss exponent is 4.

  • 463.
    Chang, Peiliang
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Miao, Guowang
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Energy and Spectral Efficiency of Cellular Networks with Discontinuous Transmission2017In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, no 5, p. 2991-3002Article in journal (Refereed)
    Abstract [en]

    Cell discontinuous transmission (DTX) has been proposed as a solution to reduce energy consumption of cellular networks. This paper investigates the impact of network traffic load on spectral and energy efficiency of cellular networks with DTX. The SINR distribution as a function of traffic load is derived firstly. Then sufficient condition for ignoring thermal noise and simplifying the SINR distribution is investigated. Based on the simplified SINR distribution, the network spectral and energy efficiency as functions of network traffic load are derived. It is shown that the network spectral efficiency increases monotonically in traffic load, while the optimal network energy efficiency depends on the ratio of the sleep-mode power consumption to the active-mode power consumption of base stations. If the ratio is larger than a certain threshold, the network energy efficiency increases monotonically with network traffic load and is maximized when the network is fully loaded. Otherwise, the network energy efficiency firstly increases and then decreases in network traffic load. The optimal load can be identified with a binary search algorithm. The power ratio threshold depends solely on the path loss exponent α, e.g. 56% for α = 4. All these analytic results are further validated by the numerical simulations.

  • 464. Chaporkar, P.
    et al.
    Proutière, Alexandre
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Optimal distributed scheduling in wireless networks under SINR interference model2013In: 2013 51st Annual Allerton Conference on Communication, Control, and Computing, Allerton 2013, IEEE conference proceedings, 2013, p. 1372-1379Conference paper (Refereed)
    Abstract [en]

    Radio resource sharing mechanisms are key to ensuring good performance in wireless networks. In their seminal paper [1], Tassiulas and Ephremides introduced the Maximum Weighted Scheduling algorithm, and proved its throughput-optimality. Since then, there have been extensive research efforts to devise distributed implementations of this algorithm. Recently, distributed adaptive CSMA scheduling schemes [2] have been proposed and shown to be optimal, without the need of message passing among transmitters. However their analysis relies on the assumption that interference can be accurately modelled by a simple interference graph. In this paper, we consider the more realistic and challenging SINR interference model. We present the first distributed scheduling algorithms that (i) are optimal under the SINR interference model, and (ii) that do not require any message passing. They are based on a combination of a simple and efficient power allocation strategy referred to as Power Packing and randomization techniques. These algorithms are rate-optimal in the sense that they perform as well as the best centralized scheduling schemes in scenarios where each transmitter is aware of the rate at which it should send packets to the corresponding receiver. As shown in [3], rate-optimal algorithms can be extended easily so that they reach throughput-optimality.

  • 465.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Kalyviannaki, Evangelia
    City University London.
    Hadjicostis, Christoforos N.
    Electrical and Computer Engineering Department, University of Cyprus.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Distributed Offline Load Balancing in MapReduce Networks2013In: 2013 IEEE 52ND ANNUAL CONFERENCE ON DECISION AND CONTROL (CDC), IEEE conference proceedings, 2013, p. 835-840Conference paper (Refereed)
    Abstract [en]

    In this paper we address the problem of balancing the processing load of MapReduce tasks running on heterogeneous clusters, i.e., clusters with different capacities and update cycles. We present a fully decentralized algorithm, based on ratio consensus, where each mapper decides the amount of workload data to handle for a single user job using only job specific local information, i.e., information that can be collected from directly connected neighboring mappers, regarding their current workload and capacity. In contrast to other algorithms in the literature, the proposed algorithm can be deployed in heterogeneous networks and can operate asynchronously in both directed and undirected communication topologies. The performance of the proposed algorithm is demonstrated via simulation experiments on large-scale strongly connected topologies. 

  • 466.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Krikidis, I.
    Medium access control via contention-based distributed power control2012In: 2012 8th International Wireless Communications And Mobile Computing Conference (IWCMC), IEEE , 2012, p. 555-560Conference paper (Refereed)
    Abstract [en]

    A successful distributed power control algorithm requires only local measurements for updating the power level of a transmitting node, so that eventually all transmitters meet their QoS requirements. Nevertheless, the problem arises when the QoS requirements cannot be achieved for all the users in the network. In this paper, a distributed algorithm for wireless ad hoc networks which is contention-based and makes use of a back off mechanism is proposed. This algorithm aims to eliminate overhead communication, improve fairness, allow nodes to operate asynchronously while establishing some performance level. The performance of the algorithm is evaluated via simulations.

  • 467.
    Chareonvisal, Tanakorn
    KTH, School of Electrical Engineering (EES), Communication Theory.
    ImplementingDistributed Storage System by Network Coding in Presence of Link Failure2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Nowadays increasing multimedia applications e.g., video and voice over IP, social networks and emails poses higher demands for sever storages and bandwidth in the networks. There is a concern that existing resource may not able to support higher demands and reliability. Network coding was introduced to improve distributed storage system. This thesis proposes the way to improve distributed storage system such as increase a chance to recover data in case there is a fail storage node or link fail in a network.

    In this thesis, we study the concept of network coding in distributed storage systems. We start our description from easy code which is replication coding then follow with higher complex code such as erasure coding. After that we implement these concepts in our test bed and measure performance by the probability of success in download and repair criteria. Moreover we compare success probability for reconstruction of original data between minimum storage regenerating (MSR) and minimum bandwidth regenerating (MBR) method. We also increase field size to increase probability of success. Finally, link failure was added in the test bed for measure reliability in a network. The results are analyzed and it shows that using maximum distance separable and increasing field size can improve the performance of a network. Moreover it also improves reliability of network in case there is a link failure in the repair process.

  • 468.
    Charvandeh, Jenny
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Location aware web access2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The user's mobile communication device has an increasing sense of where the user is. This location information may be very fine grained or very coarse. Given some amount of location information it is possible to create location aware services.

    This thesis presents and evaluates a system for location aware web browsing. Indoors the user can click on a point on a map (to establish a virtual location using a previously installed user application), outdoors the location can be provided by GPS, or the location might be provided by some other location system (indoors or outdoors), then each HTTP GET request for a URL will be augmented with information about the user's location or their virtual location. Subsequently a web query is created. Then the location information encoded as longitude and latitude is appended to this web query. The web server uses this location information to generate dynamically location aware web pages. Finally a web browser shows the web pages.

  • 469.
    Chatterjee, Saikat
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Hari, K. V. S.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Projection-based atom selection in orthogonal matching pursuit for compressive sensing2012In: 2012 National Conference on Communications, NCC 2012, IEEE , 2012, p. 6176797-Conference paper (Refereed)
    Abstract [en]

    For compressive sensing, we endeavor to improve the atom selection strategy of the existing orthogonal matching pursuit (OMP) algorithm. To achieve a better estimate of the underlying support set progressively through iterations, we use a least squares solution based atom selection method. From a set of promising atoms, the choice of an atom is performed through a new method that uses orthogonal projection along-with a standard matched filter. Through experimental evaluations, the effect of projection based atom selection strategy is shown to provide a significant improvement for the support set recovery performance, in turn, the compressive sensing recovery.

  • 470.
    Chatzaras, Anargyros
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Savvidis, Georgios
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Seamless speaker recognition2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In a technologically advanced society, the average person manages dozens of accounts for e-mail, social networks, e-banking, and other electronic services. As the number of these accounts increases, the need for automatic user identification becomes more essential. Biometrics have long been used to identify people and are the most common (if not the only) method to achieve this task.

    Over the past few years, smartphones have become frequently used gadgets.  These devices have built-in microphones and are commonly used by a single user or a small set of users, such as a couple or a family. This thesis uses a smartphone’s microphone to capture user’s speech and identify him/her. Existing speaker recognition systems typically prompt the user to provide long voice samples in order to provide accurate results. This results in a poor user experience and discourages users who do not have the patience to go through such a process.  The main idea behind the speaker recognition approach presented in this thesis is to provide a seamless user experience where the recording of the user’s voice takes place in the background.

    An Android application is developed which silently collects voices samples and performs speaker recognition without requiring extensive user interaction.  Two variants of the proposed tool have been developed and are described in depth in this thesis. The open source framework Recognito is used to perform the speaker recognition task. The analysis of Recognito showed that it is not capable of achieving high accuracy especially when the voice samples contain background noise. Finally, the comparison between the two architectures showed that they do not differ significantly in terms of performance.

  • 471.
    Chatzidrossos, Ilias
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Maximizing streaming quality in heterogeneous overlays through incentives2009In: Proceedings of the 2009 ACM Conference on Emerging Networking Experiments and Technologies, CoNEXT'09 - Co-located Student Workshop, CoNext Student Workshop '09, 2009, p. 35-36Conference paper (Refereed)
    Abstract [en]

    The upload contribution of peers in a peer-to-peer streaming system depends on their willingness to contribute as well as their physical limitation. Several incentive schemes have been proposed to enforce non-willing peers to cooperate. But we find it of great interest to see how physically constrained, with respect to resources, peers can be supported by a streaming application. In this paper we investigate how free-riders, namely non-contributing peers, can be served in a peer-to-peer streaming system. We examine different prioritization schemes that are used by high contributing peers to prioritize other contributing peers over free-riders and show that as the level of prioritization increases, contributing peers receive higher quality but the average quality drops. To avoid this, we propose an incentive mechanism that encourages contributing peers to upload to free-riders so that the average quality experienced by the peers in the overlay is maximized.

  • 472. Chatzigiannakis, I.
    et al.
    Strikos, Andreas
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01).
    A decentralized intrusion detection system for increasing security of wireless sensor networks2007In: ETFA 2007: 12th IEEE International Conference on Emerging Technologies and Factory Automation, IEEE , 2007, p. 1408-1411Conference paper (Refereed)
    Abstract [en]

    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.

  • 473.
    Chatzimisios, Periklis
    et al.
    Alexander Technological Educational Institute of Thessaloniki.
    Habib, Ibrahim
    University of New York.
    Bellavista, Paolo
    University of Bologna.
    Vinel, Alexey
    Saint-Petersburg Institute for Informatics and Automation, Russian Academy of Sciences.
    Guest editorial for the special issue on "Next generation networks service management"2011In: Computer Communications, ISSN 0140-3664, E-ISSN 1873-703X, Vol. 34, no 9, p. 1043-1044Article in journal (Refereed)
  • 474.
    Chazalet, Boris
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Opportunistic Content Delivery utilizing Optimized Context Dissemination via the Service Interface in Ambient Networks2007Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    One of the novel and important features of Ambient Networks is the use of context information. Context in Ambient Networks concerns any information that describes the current situation of entities connected to the network (e.g. location, available connectivity and devices, etc.). Such context information can be used by applications, services, or network resources enabling them to automatically adapt their behavior without requiring user intervention. Thus, context in Ambient Networks provides a better user experience due to the auto-configuration, as well as auto-arrangement of service delivery and transport.

    This thesis presents an optimized version and implementation of the Distributed Context eXchange Protocol. This protocol is part of the context-aware architecture for Ambient Networks. The design and architecture of the Distributed Context eXchange Protocol (DCXP), utilizes a P2P overlay on top of UDP. This design and architecture have been revised to enable real-time context dissemination, while simultaneously removing bottlenecks. An analysis of this revised design including measurements in real-world scenarios, shows that DXCP offers a practical approach to context-sensing and dissemination, allowing rapid context changes and spontaneous use of new context sources as these become (un)available in dynamic rearrangements of network connectivity, facilitating the use of Ambient Network technologies. Finally, the thesis presents and demonstrates a novel use and the advantages of Optimized Context Dissemination as the Ambient Networks Service Interface (ASI) for Opportunistic Content Delivery. This is achieved by adding an (subset) API to the ASI which enables a Content Delivery Proxy to interface with DCXP and leverage context information to enable opportunistic content delivery across Ambient Networks.

  • 475.
    Chen, Bolin
    et al.
    Department of Electronic and Electrical Engineering, The University of Sheffield, Sheffield, UK.
    Chen, Zheng
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Zhang, Jie
    Department of Electronic and Electrical Engineering, The University of Sheffield, Sheffield, UK.
    Modeling and Analysis of MPTCP Proxy-based LTE-WLAN Path Aggregation2017In: IEEE Global Communications Conference (GLOBECOM) 2017, IEEE Communications Society, 2017Conference paper (Refereed)
    Abstract [en]

    Long Term Evolution (LTE)-Wireless Local Area Network (WLAN) Path Aggregation (LWPA) based on Multi- path Transmission Control Protocol (MPTCP) has been under standardization procedure as a promising and cost-efficient solution to boost Downlink (DL) data rate and handle the rapidly increasing data traffic. This paper aims at providing tractable analysis for the DL performance evaluation of large-scale LWPA networks with the help of tools from stochastic geometry. We consider a simple yet practical model to determine under which conditions a native WLAN Access Point (AP) will work under LWPA mode to help increasing the received data rate. Using stochastic spatial models for the distribution of WLAN APs and LTE Base Stations (BSs), we analyze the density of active LWPA- mode WiFi APs in the considered network model, which further leads to closed-form expressions on the DL data rate and area spectral efficiency (ASE) improvement. Our numerical results illustrate the impact of different network parameters on the performance of LWPA networks, which can be useful for further performance optimization. 

  • 476.
    Chen, Chengshang
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
    Rear Approaching Vehicle Detection with Microphone2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    When a cyclist is cycling on a suburban road, it’s a problem to notice fast rear approaching vehicles in some cases. Looking back frequently is not a good idea. Finding some technical way to help cyclist perceiving rear approaching vehicles is quite necessary.

    This project aims to find some proper sensor to detect rear approaching vehicles. It’s separated into three steps. First, choose the suitable sensor and capture data. Then, find proper analyzing tool to analyze the capture data. Last but not least, draw a conclusion after analyzing contrast.

    Microphone is chosen as the sensor to recording the sounds form rear approaching vehicles. ”iRig Recorder FREE” is the program to transfer audio format. And the analyzing tool is to be Matlab. Matlab audio analysis makes good frequency spectrum for each piece of audio data. According to the frequency spectrum, the unique amplitude change around 1000 Hz is found when there is a rear approaching vehicle. This change is always distinct with or without noise.

    After getting the spectrum of different audio sources, the cross-correlation coefficient between 800 Hz and 1200 Hz is computed to see the correlation level. Then according to cross-correlation coefficient between new captured data and knowledge data, we can determine if there is a rear approaching vehicle in the new data or not.

    So, this project proves that the cross-correlation coefficient of frequency spectrum can determine if there is rear approaching vehicles or not. The future work would be automatic computer detect depending on this method.

  • 477.
    Chen, Jiajia
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Efficient resiliency mechanisms for next generation passive optical networks2013In: ICICS 2013 - Conference Guide of the 9th International Conference on Information, Communications and Signal Processing, IEEE Computer Society, 2013, p. 6782903-Conference paper (Refereed)
    Abstract [en]

    Future broadband access networks are expected to cover large service areas while fulfilling high bandwidth request on a per-user basis. The rapidly increasing traffic demand is also driven by the growing popularity of mobile data services, which is placing high-capacity requirement on the backhaul. Due to advances in wavelength division multiplexing (WDM) technology, WDM based architectures have been considered as promising candidates for next generation optical access, such as WDM passive optical network (PON), and hybrid WDM/time division multiplexing (TDM) PON. Meanwhile, resilience technique will play a more prominent role in emerging access networks due to their significantly increased capacity and coverage compared to the current deployments. Therefore, efficient resiliency mechanisms are highly required to enable uninterrupted network operation where a certain level of reliability performance can be guaranteed. In this work, we first evaluate reliability performance of each segment of next generation optical access networks and then identify the most important part for protection. A particular attention is paid to the reduction of failure impact.

  • 478.
    Chen, Jiajia
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Mahloo, Mozhgan
    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).
    Reducing the Impact of Failures in Next Generation Optical Access Networks2012In: 2012 Asia Communications And Photonics Conference (ACP), 2012, p. AS1D.2-Conference paper (Refereed)
    Abstract [en]

    Reliability performance of next generation optical access (NGOA) networks offering high bandwidth and large service coverage is evaluated. A particular attention is paid to the reduction of the impact of failures in NGOA.

  • 479.
    Chen, Jiajia
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Urban, Patryk J.
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Fast fault monitoring technique for reliable WDM PON: Achieving significant operational saving2013In: 2013 Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference, OFC/NFOEC 2013, IEEE , 2013, p. 6532499-Conference paper (Refereed)
    Abstract [en]

    We propose a fast fault supervision technique compatible with an efficient resilience scheme for WDM PON. Several drop fibres can be monitored simultaneously so that a significant reduction of operational cost can be achieved.

  • 480.
    Chen, Kairang
    Linköping University, Department of Electrical Engineering, Integrated Circuits and Systems. Linköping University, Faculty of Science & Engineering.
    Energy-Efficient Data Converters for Low-Power Sensors2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wireless sensor networks (WSNs) are employed in many applications, such as for monitoring bio-potential signals and environmental information. These applications require high-resolution (> 12-bit) analog-to-digital converters (ADCs) at low-sampling rates (several kS/s). Such sensor nodes are usually powered by batteries or energy-harvesting sources hence low power consumption is primary for such ADCs. Normally, tens or hundreds of autonomously powered sensor nodes are utilized to capture and transmit data to the central processor. Hence it is profitable to fabricate the relevant electronics, such as the ADCs, in a low-cost standard complementary metal-oxide-semiconductor (CMOS) process. The two-stage pipelined successive approximation register (SAR) ADC has shown to be an energy-efficient architecture for high resolution. This thesis further studies and explores the design limitations of the pipelined SAR ADC for high-resolution and low-speed applications.

    The first work is a 15-bit, 1 kS/s two-stage pipelined SAR ADC that has been implemented in 0.35-μm CMOS process. The use of aggressive gain reduction in the residue amplifier combined with a suitable capacitive array digital-to-analog converter (DAC) topology in the second-stage simplifies the design of the operational transconductance amplifier (OTA) while eliminating excessive capacitive load and consequent power consumption. A comprehensive power consumption analysis of the entire ADC is performed to determine the number of bits in each stage of the pipeline. Choice of a segmented capacitive array DAC and attenuation capacitorbased DAC for the first and second stages respectively enable significant reduction in power consumption and area. Fabricated in a low-cost 0.35-μm CMOS process, the prototype ADC achieves a peak signal-to-noise-and-distortion ratio (SNDR) of 78.9 dB corresponding to an effective number of bits (ENOB) of 12.8-bit at a sampling frequency of 1 kS/s and provides a Schreier figure-of-merit (FoM) of 157.6 dB. Without any form of calibration, the ADC maintains an ENOB > 12.1-bit up to the Nyquist bandwidth of 500 Hz while consuming 6.7 μW. Core area of the ADC is 0.679 mm2.

    The second work is a 14-bit, tunable bandwidth two-stage pipelined SAR ADC which is suitable for low-power, cost-effective sensor readout circuits. To overcome the high open-loop DC gain requirement of the OTA in the gain-stage, a 3-stage capacitive charge pump (CCP) is utilized to achieve the gain-stage instead of using the switch capacitor (SC) amplifier. Unity-gain OTAs have been used as the analog buffers to prevent the charge sharing between the CCP stages. The detailed design considerations are given in this work. The prototype ADC, designed and fabricated in a low-cost 0.35-μm CMOS process, achieves a peak SNDR of 75.6 dB at a sampling rate of 20 kS/s and 76.1 dB at 200 kS/s while consuming 7.68 μW and 96 μW, respectively. The corresponding Schreier FoM are 166.7 dB and 166.3 dB. Since the bandwidth of CCP is tunable, the ADC maintains a SNDR > 75 dB up

    to 260 kHz. The core area occupied by the ADC is 0.589 mm2.

    As the low-power sensors might be active only for very short time triggered by an external pulse to acquire the data, the third work is a 14-bit asynchronous two-stage pipelined SAR ADC which has been designed and simulated in 0.18-μm CMOS process. A self-synchronous loop based on an edge detector is utilized to generate an internal clock with variable phase. A tunable delay element enables to allocate the available time for the switch capacitor DACs and the gain-stage. Three separate asynchronous clock generators are implemented to create the control signals for two sub-ADCs and the gain-stage between. Aiming to reduce the power consumption of the gain-stage, simple source followers as the analog buffers are implemented in the 3-stage CCP gain-stage. Post-layout simulation results show that the ADC achieves a SNDR of 83.5 dB while consuming 2.39 μW with a sampling rate of 10 kS/s. The corresponding Schreier FoM is 176.7 dB.

  • 481.
    Chen, Lei
    et al.
    Research Institutes of Sweden, RISE Viktoria, Gothenburg, Sweden.
    Englund, Cristofer
    Research Institutes of Sweden, RISE Viktoria, Gothenburg, Sweden.
    Choreographing services for smart cities: smart traffic demonstration2017In: Vehicular Technology Conference (VTC Spring), 2017 IEEE 85th, Sydney, Australia: IEEE, 2017Conference paper (Refereed)
    Abstract [en]

    With the fifth generation (5G) communication technologies on the horizon, the society is rapidly transformed into a fully connected world. The Future Internet (FI) is foreseeable to consist of an infinite number of software components and things that coordinate with each other to enable different applications. Transport systems, as one of the most important systems in future smart cities, will embrace the connectivity, together with the fast development of cooperative and automated vehicles to enable smart traffic. To facilitate this transformation, a service choreography composition platform is under development to enable fast innovation and prototyping of choreography-based Internet of Things (IoT) applications by automatically synthesizing choreographies. Based on the method, a smart traffic application is developed and demonstrated.

  • 482.
    Chen, Lei
    et al.
    Viktoria Swedish ICT, Gothenburg, Sweden.
    Englund, Cristofer
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), CAISR - Center for Applied Intelligent Systems Research. Viktoria Swedish ICT, Gothenburg, Sweden & SAFER Vehicle and Traffic Safety Centre, Chalmers University of Technology, Gothenburg.
    Cooperative Intersection Management: A Survey2016In: IEEE transactions on intelligent transportation systems (Print), ISSN 1524-9050, E-ISSN 1558-0016, Vol. 17, no 2, p. 570-586Article, review/survey (Refereed)
    Abstract [en]

    Intersection management is one of the most challenging problems within the transport system. Traffic light-based methods have been efficient but are not able to deal with the growing mobility and social challenges. On the other hand, the advancements of automation and communications have enabled cooperative intersection management, where road users, infrastructure, and traffic control centers are able to communicate and coordinate the traffic safely and efficiently. Major techniques and solutions for cooperative intersections are surveyed in this paper for both signalized and nonsignalized intersections, whereas focuses are put on the latter. Cooperative methods, including time slots and space reservation, trajectory planning, and virtual traffic lights, are discussed in detail. Vehicle collision warning and avoidance methods are discussed to deal with uncertainties. Concerning vulnerable road users, pedestrian collision avoidance methods are discussed. In addition, an introduction to major projects related to cooperative intersection management is presented. A further discussion of the presented works is given with highlights of future research topics. This paper serves as a comprehensive survey of the field, aiming at stimulating new methods and accelerating the advancement of automated and cooperative intersections. © 2015 IEEE.

  • 483. Chen, Lei
    et al.
    Englund, Cristofer
    RISE, Swedish ICT, Viktoria.
    Cooperative Intersection Management: A Survey2016In: IEEE transactions on intelligent transportation systems (Print), ISSN 1524-9050, E-ISSN 1558-0016, Vol. 17, no 2, p. 570-586Article in journal (Refereed)
    Abstract [en]

    Intersection management is one of the most challenging problems within the transport system. Traffic light-based methods have been efficient but are not able to deal with the growing mobility and social challenges. On the other hand, the advancements of automation and communications have enabled cooperative intersection management, where road users, infrastructure, and traffic control centers are able to communicate and coordinate the traffic safely and efficiently. Major techniques and solutions for cooperative intersections are surveyed in this paper for both signalized and nonsignalized intersections, whereas focuses are put on the latter. Cooperative methods, including time slots and space reservation, trajectory planning, and virtual traffic lights, are discussed in detail. Vehicle collision warning and avoidance methods are discussed to deal with uncertainties. Concerning vulnerable road users, pedestrian collision avoidance methods are discussed. In addition, an introduction to major projects related to cooperative intersection management is presented. A further discussion of the presented works is given with highlights of future research topics. This paper serves as a comprehensive survey of the field, aiming at stimulating new methods and accelerating the advancement of automated and cooperative intersections.

  • 484. Chen, Lei
    et al.
    Englund, Cristofer
    RISE, Swedish ICT, Viktoria.
    Cooperative ITS - EU standards to accelerate cooperative mobility2014In: The 3rd International Conference on Connected Vehicles & Expo (ICCVE 2014), 2014, p. 681-686Conference paper (Refereed)
  • 485. Chen, Lei
    et al.
    Habibovic, Azra
    Englund, Cristofer
    RISE, Swedish ICT, Viktoria.
    Voronov, Alexey
    Walter, Anders
    Coordinating Dangerous Goods Vehicles: C-ITS Applications for Safe Road Tunnels2015In: Intelligent Vehicles Symposium (IV), 2015Conference paper (Refereed)
  • 486.
    Chen, Lei
    et al.
    Viktoria Swedish ICT, Sweden.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Design of in-building distributed antenna systems: mathematical models and efficient algorithms2015In: 2015 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATION WORKSHOP, IEEE , 2015, p. 1497-1502Conference paper (Refereed)
    Abstract [en]

    In order to provide sufficient coverage and capacity for indoor users, in-building distributed antenna system (IB-DAS) has been considered. A passive IB-DAS deploys distributed antennas inside the building and connects the antennas to a base station (BS) through coaxial cables and power equipment. Power is distributed from the BS to each of the antennas. We consider an optimal design of passive IB-DAS with the target to minimize the cable usage, together with the consideration of power distribution. We decompose the problem into two sub-problems, namely the topological design and the equipment selection. Mixed integer linear models are developed for solving the sub-problems. Local search is designed to combine the sub-problems and balance their objectives. Application over realistic IB-DAS deployment and comparison with previous studies demonstrate the effectiveness of the algorithm.

  • 487.
    Chen, Lisan
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Schiller Shi, Tingting
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Targeted News in an Intranet2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In SharePoint 2013, Microsoft added a social networking function in the personal sites (My Site) of a user. In this version, a personal news feed has been added which shows events regarding subjects the user follows, such as document changes, user updates, tagged posts, and site activities. The purpose of the thesis is to investigate whether or not it is possible to extend the news feed function by adding an independent component as part of My Site, to allow users to follow corporate news by choosing their categories of interests.

    A prototype of the component was implemented and it met most of the objectives stated in the thesis. It is added to the default page of the user’s My Site as a web part and it is able to retrieve and display news that matches the user’s subscription. Although the web part still needs improvements in both functionality and design, it still confirms that it is possible to extend the current My Site news feed with such a component.

    Since the students working on this thesis had no prior knowledge of SharePoint or .NET development, the project brought new challenges, as the students needed to learn how to work in a SharePoint environment and to learn to use Microsoft Visual Studio for .NET development.

  • 488.
    Chen, Ta-wei
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Optimization of Transport Security for Securing Peer-to-Peer Communication in Heterogeneous Networks2005Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis concerns the security of tomorrow’s peer-to-peer real-time communication in heterogeneous networks. Because of the additional delay caused by inband handshake and the poor compatibilities of some transport protocols, it was determined that existing security protocols such as transport layer security (TLS) and datagram transport layer security (DTLS) are not suitable in such a user scenario and a new security protocol should be designed. This new security protocol is called transport encapsulation security payload (TESP). TESP not only has the advantage of low initialization delay, but also fully supports transport protocols including TCP, UDP, stream control transmission protocol (SCTP), and datagram congestion control protocol (DCCP). Also a security analysis of TESP was carried out and no security flaws were found.

  • 489.
    Chen, Xu
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Performance Analysis of Wireless Multiplayer Games on Terraplay Systems2005Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis project was sponsored by Terraplay System AB. Terraplay System is a wireless online multiplayer game service provider in Europe. The purpose of this project was to provide a convenient and free latency test tool named Terraplay Test Toolkit (TTK) for game developers who utilize the Terraplay platform. Since wireless multiplayer games are latency sensitive, it’s necessary for game developers to estimate the real-time game latency before their development. TTK is based on Java Mobile Edition (J2me) technology, it can performs a real-time Round Trip Time (RTT) latency test. This project explored the application of the mobile development. Mobile development is a brand new field and becoming more and more popular. The design process and source code can be used as reference for mobile developers. Based on the Terraplay Test Toolkit, a series of experiments were conducted to test the ability of TTK. These experiments focused on end-to-end latency effects of wireless multiplayer games under different situations such as different packet size, different sending rates, high speed movement, and so on. Although TTK is not a professional test tool, it still reflects the latency variance under different conditions correctly. From these experiments, it was found that for the Terraplay enabled wireless multiplayer games, large average packet size (300 bytes) is NOT a factor with regard to the latency on the Terraplay System; the packet rate can affect the game latency. In a high speed-moving environment, game latency doesn’t obvious increase. Using HTTP can cause three times higher latency than simply using TCP. These conclusions are based on experimental results. These conclusions should guide wireless multiplayer game developers and game players.

  • 490.
    Chen, Zhaofei
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Demo of a collaborative music sharing system2012In: MobiOpp'12 - Proceedings of the 3rd ACM International Workshop on Mobile Opportunistic Networks, New york: ACM , 2012, p. 77-78Conference paper (Refereed)
    Abstract [en]

    We demonstrate a wireless real-time music-sharing application that lets users play music directly from their mobiles through a jukebox. We have designed and implemented the application by using a previously developed content-centric opportunistic networking middleware. The jukebox plays the music file that is first in its playlist by streaming it in real-time from the publishing user device. All users can observe the collaboratively formed playlist on their mobiles in real-time. The application shows the usefulness of our middleware and demonstrates a new form of situated applications. The application handles churn and garbage collection after departed users.

  • 491.
    Chen, Zhaofei
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre Altug
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    What a juke! A collaborative music sharing system2012In: 2012 IEEE International Symposium on a World of Wireless, Mobile and Multimedia Networks, WoWMoM 2012 - Digital Proceedings, IEEE , 2012, p. 6263751-Conference paper (Refereed)
    Abstract [en]

    The fast spreading of smart mobile devices has changed the way people create and share multimedia contents. A recently proposed idea is to distribute contents opportunistically when devices are within each other's communication range. In this work we have seized this idea and designed and implemented a real-time music-sharing application that allows people to share a sound system for collective listening. The system utilizes a content-centric opportunistic networking middleware. The application provides an interface for users to play audio files stored in their own mobile devices through a shared jukebox that is within direct communication range. The jukebox plays the audio file that is first in queue in its playlist by streaming it from the publishing user device. All devices synchronize with the jukebox so that the users can observe the contents of the playlist on their displays in real-time. This paper presents the idea and motivation for such a system as well as its design and evaluation.

  • 492.
    Chen, Zheng
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. University of Paris Sud, France.
    Lee, Jemin
    Daegu Gyeongbuk Institute Science and Technology, South Korea.
    Quek, Tony Q. S.
    Singapore University of Technology and Design, Singapore.
    Kountouris, Marios
    Huawei Technology France SASU, France.
    Cooperative Caching and Transmission Design in Cluster-Centric Small Cell Networks2017In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, no 5, p. 3401-3415Article in journal (Refereed)
    Abstract [en]

    Wireless content caching in small cell networks (SCNs) has recently been considered as an efficient way to reduce the data traffic and the energy consumption of the backhaul in emerging heterogeneous cellular networks. In this paper, we consider a cluster-centric SCN with combined design of cooperative caching and transmission policy. Small base stations (SBSs) are grouped into disjoint clusters, in which in-cluster cache space is utilized as an entity. We propose a combined caching scheme, where part of the cache space in each cluster is reserved for caching the most popular content in every SBS, while the remaining is used for cooperatively caching different partitions of the less popular content in different SBSs, as a means to increase local content diversity. Depending on the availability and placement of the requested content, coordinated multi-point technique with either joint transmission or parallel transmission is used to deliver content to the served user. Using Poisson point process for the SBS location distribution and a hexagonal grid model for the clusters, we provide analytical results on the successful content delivery probability of both transmission schemes for a user located at the cluster center. Our analysis shows an inherent tradeoff between transmission diversity and content diversity in our cooperation design. We also study the optimal cache space assignment for two objective functions: maximization of the cache service performance and the energy efficiency. Simulation results show that the proposed scheme achieves performance gain by leveraging cache-level and signal-level cooperation and adapting to the network environment and user quality-of-service requirements.

  • 493.
    Chen, Zheng
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Huawei Technologies, France.
    Energy Harvesting in Delay-Aware Cognitive Shared Access Networks2017In: IEEE Workshop on Emerging Energy Harvesting Solutions for 5G Networks (5G-NRG), IEEE, 2017Conference paper (Refereed)
    Abstract [en]

    In this work, we study the effect of energy harvesting in a cognitive shared access network with delay constraints on the primary user. We model the distribution of secondary nodes by a homogeneous Poisson point process (PPP), while the primary user is located at fixed location. The secondary users are assumed to have always packets to transmit whilst the primary transmitter has bursty traffic. We assume an energy harvesting zone around the primary transmitter and a guard zone around the primary receiver. The secondary users are transmitting in a random access manner, however, transmissions of secondary nodes are restricted by their battery status and location. Targeting at achieving the maximum secondary throughput under primary delay constraints, we analyze the impact of various parameters on the performance of the considered network. Our results provide insights into the optimization of access protocol parameters for the energy harvesting-based cognitive shared access network with delay constraints. 

  • 494.
    Chen, Zheng
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Mathematical and Algorithmic Sciences Lab, France Research Center, Huawei Technologies France SASU, Boulogne-Billancourt, France.
    Energy Harvesting in Delay-Aware Cognitive Shared Access Networks2017In: IEEE Workshop on Emerging Energy Harvesting Solutions for 5G Networks (5G-NRG): May 2017, Paris, France., 2017Conference paper (Refereed)
    Abstract [en]

    In this work, we study the effect of energy harvesting in a cognitive shared access network with delay constraints on the primary user. We model the distribution of secondary nodes by a homogeneous Poisson point process (PPP), while the primary user is located at fixed location. The secondary users are assumed to have always packets to transmit whilst the primary transmitter has bursty traffic. We assume an energy harvesting zone around the primary transmitter and a guard zone around the primary receiver. The secondary users are transmitting in a random access manner, however, transmissions of secondary nodes are restricted by their battery status and location. Targeting at achieving the maximum secondary throughput under primary delay constraints, we analyze the impact of various parameters on the performance of the considered network. Our results provide insights into the optimization of access protocol parameters for the energy harvesting-based cognitive shared access network with delay constraints.

  • 495.
    Chen, Zheng
    et al.
    University of Paris Sud, France.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Huawei Technology Co Ltd, Peoples R China.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Throughput Analysis of Smart Objects with Delay Constraints2016In: 2016 IEEE 17TH INTERNATIONAL SYMPOSIUM ON A WORLD OF WIRELESS, MOBILE AND MULTIMEDIA NETWORKS (WOWMOM), IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    In this paper, we analyze a shared access network with one primary device and randomly distributed smart objects with secondary priority. Assuming random traffic at the primary device and saturated queues at the smart objects with secondary priority, an access protocol is employed to adjust the random access probabilities of the smart objects depending on the congestion level of the primary. We characterize the maximum throughput of the secondary network with respect to delay constraints on the primary. Our results highlight the impact of system design parameters on the delay and throughput behavior of the shared access network with massive number of connected objects.

  • 496.
    Cheng, Hei Victor
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Aspects of Power Allocation in Massive MIMO2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The past decades have seen a rapid growth of mobile data trac, both in terms of connected devices and data rate. To satisfy the ever growing data trac demand in wireless communication systems, the current cellular systems have to be redesigned to increase both spectral eciency and energy eciency. Massive MIMO (Multiple-Input-Multiple-Output) is one solution that satisfy both requirements. In massive MIMO systems, hundreds of antennas are employed at the base station to provide service to many users at the same time and frequency. This enables the system to serve the users with uniformly good quality of service simultaneously, with low-cost hardware and without using extra bandwidth and energy. To achieve this, proper resource allocation is needed. Among the available resources, transmit power is one of the most important degree of freedom to control the spectral eciency and energy eciency. Due to the use of excessive number of antennas and low-end hardware at the base station, new aspects of power allocation compared to current systems arises. In the rst part of the thesis, a new uplink power allocation schemes that based on long term channel statistics is proposed. Since quality of the channel estimates is crucial in massive MIMO, in addition to data power allocation, joint power allocation that includes the pilot power as additional variable should be considered. Therefore a new framework for power allocation that matches practical systems is developed, as the methods developed in the literature cannot be applied directly to massive MIMO systems. Simulation results conrm the advantages brought by the the proposed new framework. In the second part of the thesis, we investigate the eects of using low-end ampliers at the base stations. The non-linear behavior of power consumption in these ampliers changes the power consumption model at the base station, thereby changes the power allocation. Two dierent scenarios are investigated and both results show that a certain number of antennas can be turned o in low load scenarios.

  • 497.
    Cheng, Yuelong
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences.
    Ma, Xiaoying
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences.
    Cyclic Redundancy Check for Zigbee-Based Meeting Attendance Registration System2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The research accomplished in this dissertation is focused on the design of effective solutions to the problem that error codes occur in the ZigBee-based meeting attendance registration system. In this work, several different check algorithms are compared, and the powerful error-detecting Cyclic Redundancy Check (CRC) algorithm is studied. In view of the features of the meeting attendance registration system, we implement the check module of CRC-8. This work also considers the data reliability. We assume use retransmission mechanism to ensure the validity and completeness of transmission data. Finally, the potential technical improvement and future work are presented.

  • 498.
    Cheng, Yuxin
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Passive Optical Top-of-Rack Interconnect for Data Center Networks2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Optical networks offering ultra-high capacity and low energy consumption per bit are considered as a good option to handle the rapidly growing traffic volume inside data center (DCs). However, most of the optical interconnect architectures proposed for DCs so far are mainly focused on the aggregation/core tiers of the data center networks (DCNs), while relying on the conventional top-of-rack (ToR) electronic packet switches (EPS) in the access tier. A large number of ToR switches in the current DCNs brings serious scalability limitations due to high cost and power consumption. Thus, it is important to investigate and evaluate new optical interconnects tailored for the access tier of the DCNs.

    We propose and evaluate a passive optical ToR interconnect (POTORI) architecture for the access tier. The data plane of the POTORI consists mainly of passive components to interconnect the servers within the rack as well as the interfaces toward the aggregation/core tiers. Using the passive components makes it possible to significantly reduce power consumption while achieving high reliability in a cost-efficient way.

    Meanwhile, our proposed POTORI’s control plane is based on a centralized rack controller, which is responsible for coordinating the communications among the servers in the rack. It can be reconfigured by software-defined networking (SDN) operation. A cycle-based medium access control (MAC) protocol and a dynamic bandwidth allocation (DBA) algorithm are designed for the POTORI to efficiently manage the exchange of control messages and the data transmission inside the rack.

    Simulation results show that under realistic DC traffic scenarios, the POTORI with the proposed DBA algorithm is able to achieve an average packet delay below 10 μs with the use of fast tunable optical transceivers. Moreover, we further quantify the impact of different network configuration parameters on the average packet delay. 

  • 499.
    Cheng, Yuxin
    et al.
    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).
    Wosinska, Lena
    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).
    Reliable and Cost Efficient Passive Optical Interconnects for Data Centers2015In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 19, no 11, p. 1913-1916Article in journal (Refereed)
    Abstract [en]

    To address the sustainability, scalability, and reliability problems that data centers are currently facing, we propose three passive optical interconnect (POI) architectures on top of the rack. The evaluation results show that all three architectures offer high reliability performance (connection availability for intra-rack interconnections higher than 99.999%) in a cost-efficient way.

  • 500.
    Cheng, Zhuo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Hybrid Power Control in Time Division Scheduling Wideband Code Division Multiplex Access2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With high date rates using Enhanced Uplink (EUL), a conventional signal to interference ratio (SIR) based power control algorithm may lead to a power rush due to self interference or incompatible SIR target [2]. Time division (TD) scheduling in Wideband Code Division Multiplex Access (WCDMA) is considered to be a key feature in achieving high user data rates. Unfortunately, power oscillation/peak is observed in time division multiplexing (TDM) at the transition between active and inactive transmission time intervals [1]. Therefore there is a need to revisit power control algorithms for different time division scheduling scenarios.

    The objective of power control in the context of this study is to minimize the required rise over thermal noise (RoT) for a given data rate, subject to the constraint that the physical layer control channel quality is sufficient (assuming that the dedicated physical control channel (DPCCH) SIR should not go below 3dB with a probability of at most 5%). Another goal is to minimize the local oscillation in power (power peaks) that may occur, for example due to transitions between active and inactive transmission time intervals.

    The considered hybrid power control schemes are: (1) non-parametric Generalized rake receiver SIR (GSIR) Inner Loop Power Control (ILPC) during active transmission time intervals + Received Signal Code Power (RSCP) ILPC during inactive transmission time intervals and (2) RSCP ILPC during active transmission time intervals + GSIR ILPC during inactive transmission time intervals. Both schemes are compared with pure GSIR and pure RSCP ILPC.

    Link level simulations with multiple users connected to a single cell show that:

    • The power peak problem is obviously observed in GSIR + GSIR transmit power control (TPC), but in general it performs well in all time division scenarios studied. GSIR outperforms other TPC methods in terms of RoT, especially in the TU channel model. This is because it is good in combating instantaneously changed fading and accurately estimates SIR. Among all TPC methods presented, GSIR + GSIR TPC is best in maintaining the quality of the DPCCH channel. No power rush is observed when using GSIR + GSIR TPC.
    • RSCP + RSCP eliminates the power peak problem and outperforms other TPC methods presented under the 3GPP Pedestrial A (pedA) 3km/h channel in terms of RoT. However, in general it is worse in maintaining the control channel’s quality than GSIR + GSIR TPC.
    • GSIR + RSCP ILPC eliminates the power peak problem and out-performs GSIR power control in the scenario of 2 and 4 TDM high data rate (HDR) UE and 2 TDM HDR UE coexistence with 4 Code DivisionMultiplex (CDM) LDR UE, in the pedA 3km/h channel, in terms of RoT. However, the control channel quality is not maintained as well during inactive transmission time intervals.
    • It is not recommended to use RSCP + GSIR TPC since it performs worst among these TPC methods for most of the cases in terms of RoT, even though it is the second best in maintaining the control channel quality. The power peak is visible when using RSCP + GSIR TPC.

    To maintain the control channel’s quality, a minimum SIR condition is always used on top of all proposed TPC methods. However, when there are several connected TDM HDR UEs in the cell, results indicates that it is challenging to meet the quality requirement on the control channels. So it may become necessary to limit the number of connected terminals in a cell in a time division scenario.

78910111213 451 - 500 of 3285
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf