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  • 151. Beckman, Claes
    et al.
    Martin, Nilsson
    Jesper, Slettenmark
    Radio Propagation in Curved Road Tunnels1998In: Nordic Radio Symposium on Broadband Radio Access, NRS98 (Saltsjöbaden), 1998., 1998, p. 41-46Conference paper (Other academic)
    Abstract [en]

    This report investigates radio propagation in curved road tunnels at a mobile communications frequency of 925 MHz. This is done by comparing simulations with measurements taken in Norwegian road tunnels. The simulations are based on a simple model derived from geometrical optics and hybrid waveguide modes. The simulations agree well with measurements, indicating that the proposed model is reasonably good.

  • 152.
    Beermann, Mikael
    KTH, Superseded Departments, Teleinformatics.
    Implementation of the Mobile Floating Agent Technique1996Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The computer has undergone an explosive development since they first arrived. Today nearly everybody uses computers more or less frequently. The trend is now that everyone has a little computer connected to others in a network. The computing power has become more decentralized, and therefore the need for communication has increased. Another thing that has changed the pattern is that the computers has become so small that it is no longer any problem to move them as long as one does not care about the network support, but of course one would like to have both the mobility and the network support.

    In my master thesis project I have implemented and evaluated parts of a new approach for dealing with the problems with mobility. This approach is called the mobile floating agent technique, and was developed by George Y. Liu at Ericsson Radio Systems AB, Kista. The main idea behind this is to have floating agents in the network, i.e. software entities that are virtually floating around in the network, arranging files and resources for the mobile user so that he can connect to a server in his neighbourhood, instead of connecting to his own server far away.

    I have implemented a simple file system testbed that uses the floating agent technique for caching purposes. There are two reasons for doing this implementation. The reason is for evaluation of the caching features, and the second reason is to have a platform to implement more advanced agent functions on.

    The design of the system has been done in an object oriented style, and the implementation has been done in C++.The system consists of two parts. One part is the client software, which has been implemented in another project, but modified by me, and runs on aPC with the Windows95 OS. The other part is the network part of the system, i.e. the part of the system that is not running in the client, is made for running on an UNIX station. The network part of the system consists of two parts itself. There are mobile floating agent managers, that manages the whole system, and agents, that serves the mobile clients, and communicates with both the client software and the mobile floating agent managers.

    In the evaluation part of the project I have compared the delay acquired when accessing a file in a remote network with and without an agent. I finally came to the conclusion that the gain won with the use of caches in the agents is maybe not as large that one should use caching as the primary object of the agents.

  • 153.
    Beermann, Mikael
    KTH, Superseded Departments, Teleinformatics.
    Implementation of the Mobile Floating Agent Technique1996Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The computer has undergone an explosive development since they first arrived. Today nearly everybody uses computers more or less frequently. The trend is now that everyone has a little computer connected to others in a network. The computing power has become more decentralized, and therefore the need for communication has increased. Another thing that has changed the pattern is that the computers has become so small that it is no longer any problem to move them as long as one does not care about the network support, but of course one would like to have both the mobility and the network support.

    In my master thesis project I have implemented and evaluated parts of a new approach for dealing with the problems with mobility. This approach is called the mobile floating agent technique, and was developed by George Y. Liu at Ericsson Radio Systems AB, Kista. The main idea behind this is to have floating agents in the network, i.e. software entities that are virtually floating around in the network, arranging files and resources for the mobile user so that he can connect to a server in his neighbourhood, instead of connecting to his own server far away.  I have implemented a simple file system testbed that uses the floating agent technique for caching purposes. There are two reasons for doing this implementation. The reason is for evaluation of the caching features, and the second reason is to have a platform to implement more advanced agent functions on.

    The design of the system has been done in an object oriented style, and the implementation has been done in C++.The system consists of two parts. One part is the client software, which has been implemented in another project, but modified by me, and runs on aPC with the Windows95 OS. The other part is the network part of the system, i.e. the part of the system that is not running in the client, is made for running on an UNIX station. The network part of the system consists of two parts itself. There are mobile floating agent managers, that manages the whole system, and agents, that serves the mobile clients, and communicates with both the client software and the mobile floating agent managers.

    In the evaluation part of the project I have compared the delay acquired when accessing a file in a remote network with and without an agent. I finally came to the conclusion that the gain won with the use of caches in the agents is maybe not as large that one should use caching as the primary object of the agents.

  • 154. Behrooz, Alireza
    et al.
    Devlic, Alisa
    A Context-Aware Privacy Policy Language for Controlling Access to Context Information of Mobile Users2012In: Security and Privacy in Mobile Information and Communication Systems: Third International ICST Conference, MobiSec 2011, Aalborg, Denmark, May 17-19, 2011, Revised Selected Papers, Springer Berlin Heidelberg, 2012, p. 25-39Conference paper (Refereed)
    Abstract [en]

    This paper introduces a Context-aware Privacy Policy Language (CPPL) that enables mobile users to control who can access their context information, at what detail, and in which situation by specifying their context-aware privacy rules. Context-aware privacy rules map a set of privacy rules to one or more user's situations, in which these rules are valid. Each time a user's situation changes, a list of valid rules is updated, leaving only a subset of the specified rules to be evaluated by a privacy framework upon arrival of a context query. In the existing context-dependent privacy policy languages a user's context is used as an additional condition parameter in a privacy rule, thus all the specified privacy rules have to be evaluated when a request to access a user's context arrives. Keeping the number of rules that need to be evaluated small is important because evaluation of a large number of privacy rules can potentially increase the response time to a context query. CPPL also enables rules to be defined based on a user's social relationship with a context requestor, which reduces the number of rules that need to be defined by a user and that consequently need to be evaluated by a privacy mechanism. This paper shows that when compared to the existing context-dependent privacy policy languages, this number of rules (that are encoded using CPPL) decreases with an increasing number of user-defined situations and requestors that are represented by a small number of social relationship groups.

  • 155.
    Bektesevic, Edin
    KTH, Superseded Departments, Teleinformatics.
    Embedded Linux for Purposes of Internet Appliances: (a.k.a. ‘The Wanderer Project’)1999Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As the Internet continues to grow, now new Internet appliances are being marketed. At the same time, Linux is gradually becoming a competitive choice for desktop, server and embedded applications. How do these two facts relate to each other? What should be the position of Linux in Internet appliances, and how interesting is Linux? Where are the Internet appliances really positioned in terms of their needs for an operating system? How is Linux implemented in embedded applications?

    These are just some of the questions posed during this MSc. Project that this report aims to answer. In addition, we will examine how Linux is used in embedded applications and what it provides in terms of achieving their goals. Also, we will take a look at the compression methods that can be used for system size reduction and analyze their costs.

    The report will show that Linux is a competitive alternative for devices like WebPAD, that it leaves space for further time and cost efficient improvements, and that Internet appliances can get most of the benefits of Linux during its further evolution relatively cheaply.

  • 156.
    Bellagamba, Elisa
    et al.
    Ericsson Research.
    Andersson, Loa
    Ericsson AB.
    Sköldström, Pontus
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Ward, Dave
    Drake, John
    Configuration of Pro-Active Operations, Administration, and Maintenance (OAM) Functions for MPLS-based Transport Networks using LSP Ping2013Other (Other (popular science, discussion, etc.))
  • 157. Bellagamba, Elisa
    et al.
    Kempf, James
    Sköldström, Pontus
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Telecommunication Systems Laboratory, TSLab (closed 2012-01-01).
    Link Failure Detection and Traffic Redirection in an Openflow Network2010Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    Failure detection and traffic redirection are implemented in an OpenFlow switch. Link failure detection packets, such as Bidirectional Forwarding Detection (BFD) packets, are periodically sent out on links to peer OpenFlow switches, such as via the Multi-protocol Label Switching (MPLS) Transport Profile (MPLS-TP). Link failure detection packets are received from the peer OpenFlow switches on the links, and monitored. A link failure is detected if no incoming link failure detection packets are received on a link for a predetermined interval. In the event of a link failure, traffic is redirected from the failed link to a backup link by altering entries on a flow table of the OpenFlow switch.

  • 158. Beltran, M
    et al.
    Deng, L
    Pang, Xiaodan
    RISE ACREO AB.
    Zhang, X
    Arlunno, V
    Zhao, Y
    Yu, X
    Llorente, R
    Liu, D
    Tafur Monroy, I
    Single- and Multiband OFDM Photonic Wireless Links in the 75-110 GHz Band EmployingOptical Combs2012In: IEEE Photonics Journal, Vol. 4, no 5, p. 2027-2036Article in journal (Refereed)
  • 159. Beltrán, Marta
    et al.
    Deng, Lei
    Pang, Xiaodan
    RISE ACREO AB.
    Zhang, Xu
    Arlunno, Valeria
    Zhao, Ying
    Yu, Xianbin
    Llorente, Roberto
    Liu, Deming
    Tafur Monroy, Idelfonso
    38.2-Gb/s Optical-Wireless Transmission in 75-110 GHz Based on Electrical OFDM with Optical Comb Expansion2012In: Optical Fiber Communication Conference, 2012Conference paper (Refereed)
  • 160.
    Ben Slimane, Slimane
    KTH, Superseded Departments, Signals, Sensors and Systems.
    A low complexity antenna diversity receiver for OFDM based systems2001In: IEEE International Conference on Communications, 2001, p. 1147-1151Conference paper (Refereed)
    Abstract [en]

    A low complexity antenna diversity architecture with a new combining technique suitable for orthogonal frequency division (OFDM) based systems is introduced in this paper. For a two branch antenna diversity, this structure requires only one FFT at the receiver and allows optimum maximum ratio combining. For systems with a higher number of antennas, the number of required FFTs when using such technique is reduced by half as compared to the conventional case where a different FFT is used for each receive antenna. As a result a considerable reduction in processing complexity is obtained especially for systems with high number of subcarriers. This method can also be seen as a way of increasing the number of antennas in OFDM transceivers without any major complexity increase. Thus, a considerable increase in diversity gain can be achieved

  • 161.
    Ben Slimane, Slimane
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Bounds on the Distribution of a Sum of Independent Lognormal Random Variables2001In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 49, no 6, p. 975-978Article in journal (Refereed)
    Abstract [en]

    The distribution function of a sum of lognormal random variables (RVs) appears in several communication problems. Approximations are usually used for such distribution as no closed form nor bounds exist. Bounds can be very useful in assessing the performance of any given system. In this letter, we derive upper and lower bounds on the distribution function of a sum of independent lognormal RVs. These bounds are given in a closed form and can be used in studying the performance of cellular radio and broadcasting systems.

  • 162.
    Ben Slimane, Slimane
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Channel estimation for HIPERLAN/2 with transmitter diversity2002Conference paper (Refereed)
  • 163.
    Ben Slimane, Slimane
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Channel estimation for HIPERLAN/2 with transmitter diversity2002In: 2002 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-5, CONFERENCE PROCEEDINGS, 2002, p. 26-30Conference paper (Refereed)
    Abstract [en]

    In this paper we propose a channel estimation technique for OFDM based systems, such as HIPERLAN/2 and IEEE 802.11a, with transmitter diversity. The proposed technique estimates all channel frequency responses, corresponding to each transmitter and receiver antenna pair, required for space-time processing In this OFDM based system. This technique is able to extract the channel state Information for two transmitter antennas using the same preamble as defined in the standard of HIPERLAN/2. The feasibility of this channel estimation method Is made possible by exploiting the structure of the OFDM modulation scheme. The results showed that the accuracy provided by this proposed method is comparable to that obtained when a single transmitter antenna is used.

  • 164.
    Ben Slimane, Slimane
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Channel estimation for OFDM based systems with transmitter diversity2002In: 2002 IEEE International Conference on Systems, Man and Cybernetics,, 2002, p. 397-402Conference paper (Refereed)
  • 165.
    Ben Slimane, Slimane
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Peak-to-average power ratio reduction of OFDM signals using broadband pulse shaping2002In: IEEE 56TH VEHICULAR TECHNOLOGY CONFERENCE, VTC FALL 2002, VOLS 1-4, PROCEEDINGS, 2002, p. 889-893Conference paper (Refereed)
    Abstract [en]

    Orthogonal Frequency Division Multiplexing (OFDM) techniques allow the transmission of high data rates over broadband radio channels subject to multipath fading without the need for powerful channel equalization. However, they are very sensitive to nonlinear effects due to the high Peak-to-Average Power Ratio (PAPR) owned by the transmitted signal. This paper proposes an efficient technique for reducing the PAPR of OFDM signals. The proposed technique is very effective and flexible. The method avoids the use of extra Inverse Fast Fourier Transformations (IFFTs) as was done in some previously published techniques but instead is based on a proper selection of the time waveforms of the different sub-carriers of the OFDM modulation scheme. Thus, its implementation complexity is much low in comparison to the previous published methods. A closed form relation between the maximum PAPR and the used pulse shaping waveform is derived. The obtained results show that with broadband pulse shaping, the PAPR of OFDM modulated signals can be made very close to that of single carrier signals. The improved statistics of the PAPR in the transmitted signal is demonstrated through numerical results for some sets of time waveforms. The significant improvement in PAPR given by the present technique permits to reduce the complexity and cost of the transmitter significantly. In that, pulse shaping can be used not only to shape the spectrum of the transmitted signal but also to reduce its PAPR.

  • 166.
    Ben Slimane, Slimane
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Janssen, G.J.M.
    Delft University.
    Power optimization of M-PSK cochannel signals for a narrowband multiuser detector2001In: IEEE Pacific RIM Conference on Communications, Computers, and Signal Processing - Proceedings, 2001, p. 247-250Conference paper (Refereed)
    Abstract [en]

    An analytical method is presented to determine the optimum received power values for multiple cochannel multilevel phase-shift-keying (M-PSK) modulated signals. The aim is to achieve equal symbol error probability (SEP) for each of the signals when applying a narrowband multiuser detector based on successive cancellations. Power relations based on two approximations are derived and used to compute the average SEP for the different cochannel signals. The derived power relations are also compared against optimum power relations obtained through computer simulations

  • 167.
    Ben Slimane, Slimane
    et al.
    Concordia University.
    Le-Ngoc, Tho
    Concordia University.
    A doubly stochastic Poisson model for self-similar traffic1995In: IEEE International Conference on Communications, 1995, p. 456-460Conference paper (Refereed)
    Abstract [en]

    This paper presents a data traffic model capable of describing the long-range dependence and self-similar burstiness structure found in measurement studies of packet data traffic. The model introduced is based on doubly stochastic Poisson processes. The intensity of arrivals is modeled as a continuous stochastic process. This process satisfies most of the properties found in the measurement studies, namely long-range dependence and self-similarity. The generality and simplicity of this model makes it attractive in data traffic modeling

  • 168.
    Ben Slimane, Slimane
    et al.
    Concordia University.
    Le-Ngoc, Tho
    Concordia University.
    Coded quadrature pulse-overlapping modulation techniques for personal communications1992In: 1st International Conference on Universal Personal Communications, 1992. ICUPC '92 Proceedings, 1992, p. 11-03/1-11-03/5Conference paper (Refereed)
    Abstract [en]

    Hard-limited quadrature pulse-overlapping modulation (QPOM) techniques have a constant envelope, good spectral properties and good performance especially in fading channels. These modulation techniques are suitable to applications using nonlinear or saturated power amplifiers to obtain high power and bandwidth efficiencies. A technique to combine convolutional codes and QPOM schemes to further improve its performance in fading channels is introduced and evaluated. At first, the QPOM scheme is decomposed into an encoder followed by a memoryless modulator. Then, the binary convolutional encoder is concatenated to the QPOM encoder and considered as one entity to be optimized. Performance of the coded QPOM scheme is analyzed and compared to uncoded QPOM and coded QPSK schemes

  • 169.
    Ben Slimane, Slimane
    et al.
    Concordia University.
    Le-Ngoc, Tho
    Concordia University.
    IJF-OQPSK modulation schemes with MLSE receivers for portable/mobile communications1992Conference paper (Refereed)
    Abstract [en]

    A receiver structure for constant enveloped IJF-OQPSK modulation under fading channel conditions is introduced. Its performance in AWGN and Rayleigh fading channels was analyzed and verified by computer simulations. Results show the relation between the performance of the system and the memory introduced by the double-interval overlapping pulse shape. By properly using this memory, it is possible to achieve superior performance compared to conventional schemes. Even though no coding has been used, comparable results to coded schemes was obtained with no extra redundancy. Therefore, the complexity caused by multilevel modulation can be avoided, and transmission of signals with compact spectrum and good performance is possible. The constant envelope, compact spectrum, superior performance in fading channels and low complexity make the hardlimited IJF-OQPSK scheme a good choice for portable/mobile communications, to achieve low cost, small size, and high power and bandwidth efficiencies

  • 170.
    Ben Slimane, Slimane
    et al.
    Concordia University.
    Le-Ngoc, Tho
    Maximum likelihood sequence estimation of quadrature pulse-overlapping modulated signals for portable/mobile satellite1992In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 10, no 8Article in journal (Refereed)
  • 171.
    Ben Slimane, Slimane
    et al.
    Concordia University.
    Le-Ngoc, Tho
    Concordia University.
    Performance of 16-QAM signals on a fading mobile satellite channel1994In: AEU - International Journal of Electronics and Communications, ISSN 1434-8411, E-ISSN 1618-0399, Vol. 48, no 2, p. 68-75Article in journal (Refereed)
  • 172.
    Ben Slimane, Slimane
    et al.
    Concordia University.
    Le-Ngoc, Tho
    Concordia University.
    Performance of 16-QPOM signals on a fading mobile satellite channel1993In: Proceedings of the IEEE 1993 Pacific Rim Conference on Communications, Computers and Signal Processing, 1993, p. 674-677Conference paper (Refereed)
    Abstract [en]

    The authors present a maximum likelihood sequence estimation (MLSE) receiver structure for both linear and hard-limited 16-quadrature pulse overlapping modulation (QPOM) schemes. Using this structure, the performance of these schemes over shadowed Rician fading channels is studied. The structure of linear 16-QPOM schemes allowed the use of independent decoding for in-phase and quadrature components of the transmitted signal, thus reducing considerably the complexity of the MLSE receiver. The hard-limited 16-QPOM scheme used two hard-limited QPOM schemes in parallel. It is shown that an optimum MLSE receiver for this type of signal needs to consider both in-phase and quadrature components at the same time. Using the MLSE receiver, both schemes outperform conventional coherent 16-quadrature amplitude modulation (QAM)

  • 173.
    Ben Slimane, Slimane
    et al.
    Concordia University.
    Le-Ngoc, Tho
    Concordia University.
    Performance of 16-QPOM signals on a fading mobile satellite channel1993In: Proceedings of the IEEE Global Telecommunications Conference, IEEE , 1993, p. 1787-1791Conference paper (Refereed)
    Abstract [en]

    Presents the bit error probability of 16-QPOM schemes over mobile satellite shadowed Rician fading channels. An upper bound on the pairwise error probability is derived, and then combined with the transfer function bounding technique. The derived upper bound is given in a closed form without the need of any numerical integration. This upper bound is then used to evaluate the performance of both linear and hard-limited 16-QPOM signals. Simulation results are also performed to verify the analytical results

  • 174.
    Ben Slimane, Slimane
    et al.
    Concordia University.
    Le-Ngoc, Tho
    Concordia University.
    Performance of quadrature pulse-overlapping modulated signals in Rayleigh fading channels1991In: IEEE Global Telecommunications Conference and Exhibition, 1991, p. 1802-1806Conference paper (Refereed)
    Abstract [en]

    The authors discuss the average bit error probability of constant envelope quadrature pulse-overlapping modulation and maximum likelihood Viterbi decoding in a Rayleigh fading channel. The quadrature pulse-overlapping modulation is first decomposed into a linear encoder followed by a memoryless modulator. An upper bound on the average bit error probability as a function of the transfer function of the linear encoder is then developed under the assumption of using the Viterbi decoder with perfect fading amplitude measurement. Tightness of the bound was examined by means of computer simulation. A performance comparison with conventional quadrature phase shift keying is also provided

  • 175.
    Ben Slimane, Slimane
    et al.
    Concordia University.
    Le-Ngoc, Tho
    Concordia University.
    Quadrature Pulse-Overlapping Modulation Techniques1994In: Coded-Modulation Techniques for Fading Channels / [ed] S. Hamidreza Jamali, Tho Le-Ngoc, Kluwer Academic Publishers , 1994Chapter in book (Refereed)
  • 176.
    Ben Slimane, Slimane
    et al.
    Concordia University.
    Le-Ngoc, Tho
    Concordia University.
    Tight bounds on the error probability of coded modulation schemes in Rayleigh fading channels1994Conference paper (Refereed)
    Abstract [en]

    This paper presents a tight upper bound on the bit error performance of coded modulation schemes in Rayleigh fading channels. Upper and lower bounds on the pairwise error probability are first derived. The upper bound is then expressed in a product form to be used with the transfer function bounding technique. This upper bound has the same simplicity as the union-Chernoff bound while providing closer results to the exact expression. Examples for 4-state and 8-state TCM 8PSK schemes are also given to illustrate the tightness and the application of this upper bound

  • 177.
    Ben Slimane, Slimane
    et al.
    Concordia University.
    Le-Ngoc, Tho
    Concordia University.
    Tight Bounds on the Error Probability of Coded Modulation Schemes in Rayleigh Fading Channels1995In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 44, no 1, p. 121-130Article in journal (Refereed)
  • 178.
    Bennani, Zakaria
    KTH, Superseded Departments, Teleinformatics.
    Quality of Service Support for Wireless LANs2000Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As the research and development of mobile computing is becoming increasingly interesting and important to corporations and private users, great efforts are being made to ensure that the wireless network technology is being developed to match the performance level showed by wired network technologies. Introducing wireless mobile computing into already existing and operational situations, that have up to date been taken care of with wired technology, should not mean a degradation of the existing performance level. In other words, there should not be any decrease in the quality of service experienced by the end users due to the mobility or wireless factor.

    When developing quality of service support mechanisms that use characteristics specific to the Internet Protocol, considerations have to be made to make certain that the solutions and implementations developed will be deployable with the next generation Internet Protocol, IPv6. Since the ever decreasing address space in IPv4 is becoming more and more of a problem, at some point migration to IPv6 has to be made. Therefore, this thesis will base its developments on the use of IPv6.

    The thesis concerns the problem of providing statistical QoS guarantees for multimedia applications running over a wireless LAN such as WaveLAN. Using the DiffServ model and support of IPv6, we develop mechanisms for managing QoS and mobility. With the use of pre-connection schemes and a domain routing approach, Mobile Node mobility and Handoffs are handled in such a way to diminish latencies that occur when in-LAN and cross-LAN handoffs are made. To handle QoS guarantees, a bandwidth broker placed in the Access Points manages bandwidth allocations for different cells and configures the traffic parameters of each mobile so that the usage of the wireless MAC layer is controlled. The border router is connected via ATM to core routers in several places in France. Experimentation on the platform involves a DIS application (Distributed Interactive Simulation) running at different sites.

    The development work is done on FreeBSD systems in C.

  • 179.
    Bentahar, Younes
    KTH, School of Information and Communication Technology (ICT).
    DNS prestanda2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Use of computers and computer networks is nowadays a part of everyday life. You do not use them only at home when you sit at you computer, but you can use them all the time everywhere. This can involve everything from surf to any website when you are at home, to checking your email on your mobile when you are on your way to work. Most people do not think about how it really works when they try to access a web page by typing the address into their browser, but something that most people probably notice is how long it can sometimes take to access a web page.

    All items which are directly connected to the IP network have a unique IP address that is used to make it possible to communicate. The IP address is either a period separated sequence of digits representing 32 bits or a colon separated sequence of digits representing 128 bits, depending on whether the address is an IPv4 or IPv6 address. Such numeric sequences are often difficult for us humans to remember therefore, the domain name system (DNS) was constructed. DNS makes it possible for us to write addresses in a textual format to access an item stored in a device connected to the network. DNS can be seen as a directory for the network and can be compared to a telephone directory, where if you know the name of a person can find his or her phone number.

    This thesis will describe how the various address translations are done by using DNS. It will also examine how much impact DNS has on the experienced delay from the time you type a web page address in the address bar of your browser to the actual time you reach the website. A survey of DNS performance will be presented to investigate how much delay can be reduced by using one of Sweden's two most well-known public DNS servers (Google Public DNS and OpenDNS) instead of the normal default DNS server provided by one's Internet service provider (ISP).

    The survey will also show how the DNS lookup waiting time changes at different times of day and different days of the week. The purpose of this work is to provide a basic explanation of what DNS is and increase the understanding of how an everyday user in a simple way can make their network usage more effective by getting their DNS lookups to occur faster.

    The conclusion from this thesis is that the alternative DNS server, Google Public DNS has the fastest DNS lookup time for this particular computer which the measurement was carried on. But this tells us nothing about whether the case for any other network users because the observed DNS performance has a large extent dependent on the ISP you are connected to, and what place you are at.

  • 180. Bentley, Frank
    et al.
    Tollmar, Konrad
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Designing From Data: A Case Study From the Health Mashups Service2013In: Workshop on Informing Future Design via Large-Scale Research Methods and Big Data, 2013Conference paper (Refereed)
    Abstract [en]

    Instrumentation of mobile service interactions now allows for the ability to understand use in new ways and to base the design of system iterations as well as future services on data obtained from use “in the wild”over extended periods of time. This position paper will detail a few specific instances in the Health Mashupsproject where we were able to use usage data to improve the design and to create design implications to increase engagement in new services.

  • 181. Bentley, Frank
    et al.
    Tollmar, Konrad
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Mobile Service Laboratory (MS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Stephenson, Peter
    Levy, Laura
    Jones, Brian
    Robertson, Scott
    Price, Ed
    Catrambone, Richard
    Wilson, Jeff
    Health Mashups: Presenting Statistical Patterns between Wellbeing Data and Context in Natural Language to Promote Behavior Change2013In: ACM Transactions on Computer-Human Interaction, ISSN 1073-0516, E-ISSN 1557-7325, Vol. 20, no 5, p. 30-Article in journal (Refereed)
    Abstract [en]

    People now have access to many sources of data about their health and wellbeing. Yet, most people cannot wade through all of this data to answer basic questions about their long-term wellbeing: Do I gain weight when I have busy days? Do I walk more when I work in the city? Do I sleep better on nights after I work out? We built the Health Mashups system to identify connections that are significant over time between weight, sleep, step count, calendar data, location, weather, pain, food intake, and mood. These significant observations are displayed in a mobile application using natural language, for example, "You are happier on days when you sleep more." We performed a pilot study, made improvements to the system, and then conducted a 90-day trial with 60 diverse participants, learning that interactions between wellbeing and context are highly individual and that our system supported an increased self-understanding that lead to focused behavior changes.

  • 182. Berger, Andre
    et al.
    Gross, James
    RWTH Aachen University, Germany.
    Harks, Tobias
    The k–Constrained Bipartite Matching Problem: Approximation Algorithms and Applications to Wireless Networks2010In: Proceedings IEEE INFOCOM, 2010, IEEE conference proceedings, 2010, p. 1-9Conference paper (Refereed)
    Abstract [en]

    In communication networks, resource assignment problems appear in several different settings. These problems are often modeled by a maximum weight matching problem in bipartite graphs and efficient matching algorithms are well known. In several applications, the corresponding matching problem has to be solved many times in a row as the underlying system operates in a time-slotted fashion and the edge weights change over time. However, changing the assignments can come with a certain cost for reconfiguration that depends on the number of changed edges between subsequent assignments. In order to control the cost of reconfiguration, we propose the k-constrained bipartite matching problem for bipartite graphs, which seeks an optimal matching that realizes at most k changes from a previous matching. We provide fast approximation algorithms with provable guarantees for this problem. Furthermore, to cope with the sequential nature of assignment problems, we introduce an online variant of the k-constrained matching problem and derive online algorithms that are based on our approximation algorithms for the k-constrained bipartite matching problem. Finally, we establish the applicability of our model and our algorithms in the context of OFDMA wireless networks finding a significant performance improvement for the proposed algorithms.

  • 183.
    Berggren, Anders
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Borg, Martin
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    A Comparative Study ofTwo Multicast Routing Algorithms2002Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This Master Thesis examines several aspects of two different multicast forwarding algorithms. The scaling properties of the currently used algorithms were examined under different criteria, such as delay, traffic concentration, and size of the routing tables.

    Many new Internet applications, such as videoconferencing, resource discovery, Internet radio and online games, depend on a network support for efficient point-to-multipoint communication. Sending identical data to a group of receivers using a series of unicast transmissions obviously has massive scaling problems. Multicasting provides an efficient and elegant solution that significantly reduces the total bandwidth demand as well as the load on both senders and intermediate routers.

    In this report we study two multicast routing algorithms, source based trees (SBT) and core based trees (CBT). SBT builds one delivery tree per source and group by flooding the initial packet through the entire network, and then removing the links that do not lead to group members (“pruning”). To be able to discover new members, flooding must occur periodically. CBT on the other hand, builds one delivery tree per group, shared by all sources. There is one core router per group and members must explicitly join the delivery tree by notifying the core. Off-tree sources must tunnel their traffic to the core for distribution along the tree.

    SBT has two main drawbacks. Firstly, the maintenance of the delivery tree requires periodic flooding of the network. Furthermore, SBT routers must keep state that grows as the product of the number of sources and the number of groups. CBT solves both of these scaling problems, but the shared tree will often lead to sub-optimal paths and increased delay. The traffic may also be concentrated on fewer links than in SBT.

    We compared the characteristics of the SBT and CBT algorithms in different network topologies using a simulation program. Since existing network simulation tools were found to be poor when it came to multicasting, we decided to develop a new network generator and simulator tool with multicasting aspects in focus. We also developed a tool to visualize the networks generated by the simulator and monitor the traffic. The report presents many simulation results that illustrate the significance of different trade-offs between SBT and CBT. Performance characteristics such as delay, join latency, tree size, total traffic and traffic concentration are analysed and examined.

    The conclusion is that each protocol can be preferable in certain scenarios, depending on how important the different parameters are. CBT always performs better than SBT for single source applications if the core can be placed at the sender’s local router. However, this core placement is not necessarily optimal for CBT. The situation is more complex in groups with several sources. There is a trade-off between the scaling problems of SBT and the increased delay and traffic concentration of CBT.

  • 184.
    Berggren, Fredrik
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01).
    Capacity analysis for noncooperative interference environments2005In: VTC 2005-Spring: 2005 IEEE 61st Vehicular Technology Conference, Proceedings, IEEE , 2005, no 3, p. 1479-1483Conference paper (Refereed)
    Abstract [en]

    To enhance the wireless bandwidth utilization, new forms of innovative spectrum policies, dynamically sharing channels over time and space, have been discussed. Dynamic spectrum access lets systems share the spectrum, to achieve better band-width utilization and trunking gains. In this work, we consider a case where such access is performed in an uncoordinated fashion. The paradigm shift to open frequency bands implies a need to investigate and verify resulting capacity gains. Herein, we give a general method for evaluating system capacity subject to outage probability constraints over fading channels, in an unlicensed band environment with uncoordinated systems. The channel fading effects include both attenuation, shadowing and multipath propagation and we end up with expressions, which are solved by numerical integration. The spectrum sharing is here performed by means of autonomous dynamic channel allocation (DCA), and we compare two DCA methods, maximum SIR DCA and random DCA.

  • 185.
    Bergman, Svante
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Lattice based linear precoding for MIMO block codes2007In: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE , 2007, p. 329-332Conference paper (Refereed)
    Abstract [en]

    Herein, the design of linear dispersion codes for block based multiple-input multiple-output communication systems is investigated. The receiver as well as the transmitter are assumed to have perfect knowledge of the channel, and the receiver is assumed to employ maximum likelihood detection. We propose to use linear precoding and lattice invariant operations to transform the channel matrix into a lattice with large coding gain. With appropriate approximations, it is shown that this corresponds to selecting lattices with good sphere packing properties. Lattice invariant transformations are then used to minimize the power consumption. An algorithm for this power minimization is presented along with a lower bound on the optimization. Numerical results indicate that there is a potential gain of several dB by using the method compared to channel inversion with adaptive bit loading.

  • 186.
    Bergman, Svante
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Lattice-based linear precoding for MIMO channels with transmitter CSI2008In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 56, no 7, p. 2902-2914Article in journal (Refereed)
    Abstract [en]

    Herein, the design of linear dispersion codes for multiple-input multiple-output communication systems is investigated. The receiver as well as the transmitter are assumed to have perfect knowledge of the channel, and the receiver is assumed to employ maximum likelihood detection. We propose to use linear precoding and lattice invariant operations to transform the channel matrix into a lattice generator matrix with large minimum distance separation. With appropriate approximations, it is shown that this corresponds to selecting lattices with good sphere-packing properties. Lattice invariant transformations are then used to minimize the power consumption. An algorithm for this power minimization is presented along with a lower bound on the optimization. Numerical results indicate significant gains by using the proposed method compared to channel diagonalization with adaptive bit loading.

  • 187.
    Bergman, Svante
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Palomar, Daniel P.
    Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Joint Bit Allocation and Precoding for MIMO Systems With Decision Feedback Detection2009In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 57, no 11, p. 4509-4521Article in journal (Refereed)
    Abstract [en]

    This paper considers the joint design of bit loading, precoding and receive filters for a multiple-input multiple-output (MIMO) digital communication system employing decision feedback (DF) detection at the receiver. Both the transmitter as well as the receiver are assumed to know the channel matrix perfectly. It is well known that, for linear MIMO transceivers, a diagonal transmission (i.e., orthogonalization of the channel matrix) is optimal for some criteria. Surprisingly, it was shown five years ago that for the family of Schur-convex functions an additional rotation of the symbols is necessary. However, if the bit loading is optimized jointly with the linear transceiver, then this rotation is unnecessary. Similarly, for DF MIMO optimized transceivers a rotation of the symbols is sometimes needed. The main result of this paper shows that for a DF MIMO transceiver where the bit loading is jointly optimized with the transceiver filters, the rotation of the symbols becomes unnecessary, and because of this, also the DF part of the receiver is not required. The proof is based on a relaxation of the available bit rates on the individual substreams to the set of positive real numbers. In practice, the signal constellations are discrete and the optimal relaxed bit loading has to be rounded. It is shown that the loss due to rounding is small, and an upper bound on the maximum loss is derived. Numerical results are presented that confirm the theoretical results and demonstrate that orthogonal transmission and the truly optimal DF design perform almost equally well.

  • 188.
    Bergqvist, Joakim
    KTH, Superseded Departments, Teleinformatics.
    Dynamic modeling of real-time data sources1996Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis reports on the development and implementation of a method for dynamically generating a state model from the prerecorded trace of a cell-arrival process and the user of this state machine to drive a simulator to evaluate the effects of multiplexing multiple copies of traffic similar to the original trace.

  • 189.
    Besharat Pour, Shiva
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Li, Qi
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Connecting Silos: Automation system for thesis processing in Canvas and DiVA2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    As the era of digitalization dawns, the need to integrate separate silos into a synchronized connected system is becoming of ever greater significance. This thesis focuses on the Canvas Learning Management System (LMS) and the Digitala vetenskapliga arkive (DiVA) as examples of separate silos.

    The thesis presents several methods of automating document handling associated with a degree project. It exploits the fact that students will submit their thesis to their examiner via Canvas. Canvas is the LMS platform used by students to submit all their coursework. When the examiner approves the thesis, it will be archived in DiVA and optionally published on DiVA. DiVA is an institutional repository used for research publications and student theses.

    When manually archiving and publishing student theses on DiVA several fields need to be filled in. These fields provide meta data for the thesis itself. The content of these fields (author, title, keywords, abstract, …) can be used when searching via the DiVA portal. It might not seem like a massive task to enter this meta data for an individual thesis; however, given the number of theses that are submitted every year, this process takes a large amount of time and effort. Moreover, it is important to enter this data correctly, which is difficult when manually doing this task. Therefore, this thesis project seeks to automate this process for future theses.

    The proposed solution parses PDF documents and uses information from the LMS in order to automatically generate a cover for the thesis and fill in the required DiVA meta data. Additionally, information for inserting an announcement of the student's oral thesis presentation into a calendar system will be provided. Moreover, the data in each case will be checked for correctness and consistency.

    Manually filling in DiVA fields in order to publish theses has been a quite demanding and time-consuming process. Thus, there is often a delay before a thesis is published on DiVA. Therefore, this thesis project’s goal is to provide KTH with an automated means to handle thesis archiving and publication on DiVA, while doing so more efficiently, and with fewer errors. The correctness of the extracted meta data will be evaluated by comparing the results to the previously entered meta data for theses that have previously been achieved in DiVA. The automated process has been calculated to take roughly 50 seconds to prepare the information needed to publish a thesis to DiVA with ~71% accuracy, compared with 1 hour and 34% accuracy in the previous manual method.

  • 190.
    Bhatia, Nupur
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Policy Management in Context-Aware Networks2007Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Ambient Network (AN) Project is part of the European Commission’s 6th Framework Programme and aims to enable cooperation between heterogeneous networks, using current and future wireless technologies, minimising the effort of mobile users to gain access to the services that they are interested in - irrespective of their location or the network they are currently using. Because of the highly mobile nature of users and a demand for instant and dynamic access to services, these networks have to be composed ‘on the fly’ without any pre-configurations.

    The use of context information in AN can remove the need for pre-configuration of networks, hence making them autonomic. However, a concern exists that the free and uncontrolled dissemination of context information could breech the privacy of the participants. It is extremely important to address these privacy issues in order to control who has access to what context information. This control can be achieved through the use of well defined policies. This creates a requirement for a framework in the ContextWare architecture for protecting context information.

    This masters thesis project is part of an effort to create a policy based infrastructure for authorisation of access to network context information within the AN. The thesis investigates, models, and designs an architecture for a policy management system based on OASIS XACML, that creates an extension to the architecture for management of context information in the AN. In addition to a policy management architecture within an AN, a policy management architecture for composing ANs is also created. To facilitate the transfer of requests and policies, the thesis creates a Policy Management Protocol. The designed architecture was then implemented to create a proof of concept.

    The designed architecture and protocol were evaluated by running tests on the prototype. The measurements from the tests are analysed and presented in this thesis. The analysis of the experimental data indicates that a policy management system is both feasible and practical. The results show that the delay overhead caused by introducing policy management in a distributed context provisioning system, ranges from 1.7% in a system without load to 6% in a worst case scenario. The throughput of the policy management system is 15 requests per second under load.

  • 191.
    Bilien, Johan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Key Agreement for Secure Voice over IP2003Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis reviews the usual properties and requirements for key agreement protocols. It then focuses on MIKEY, a work-in-progress protocol designed to conduct key agreements for secure multimedia exchanges. The protocol was implemented and incorporated in a SIP user agent - minisip. This implementation was used to measure the additional delay required for key exchange during call establishment. Finally, some schemes are proposed regarding the use of MIKEY in advanced VoIP scenarios, such as conferences and terminal mobility.

  • 192.
    Bin, Yang
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Using Six Sigma Methodology to improve the performance of the Shipment Test2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Competition and lead-time pressure motivates us to find new and better ways of continuously improving the output of our work. The emphasis on improvement in both efficiency and quality has become more and more significant in daily activities. The performance of Ericsson’s AXE/APZ products during shipment test phase is one such activity and is the focus of this thesis project. One of the essential principles of shipment testing is to ensure that the test campaigns finish on time. Over the last several decades companies have spent large amounts of time and money on improving test quality and efficiency. Unfortunately, the results have not always been as good as expected. It seems that it is very difficult to improve shipment testing performance using traditional test management methods.

    Motorola introduced Six Sigma in 1986 and achieved 5.4 Sigma level which help them saved 2.2 Billion dollars during the first six years. From Statistic aspect, it means only 3.4 defects per million opportunities. The Six Sigma methodology has been applied as a management philosophy focused on improving efficiency and performance during the shipment test period.

    This thesis gives an introduction to the Six Sigma approach, including the concepts of Six Sigma, its history, development, and methodology. More specifically the author uses the Define, Measure, Analyze, Improve, and Control (DMAIC) approach to evaluate the performance of Ericsson’s AXE/APZ Shipment Testing. This project goal was defined: Compare with the performance of 08AXE shipment test which 87% of test campaigns (2.68 sigma level) were finished on time, 3 sigma level in 09AXE shipment test which means 93%of the test campaigns will be finished on time has to be achieved.  The thesis measured the 08AXE shipment test performance and analyzed the lead time of test campaigns, found the root causes such as poor documents quality from the legacy project, lack of test resources, no system impact analysis. The thesis also provided a set of proposals for improvements and control of the improved process in order to ensure sustainable improved performance results. Finally 93% test campaigns were finished on time in 09AXE and project goal was fulfilled.

  • 193.
    Björklund, Ulf
    KTH, Superseded Departments, Teleinformatics.
    Understanding the Performance of the Linux IPv6 Implementation1998Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The new version of the Internet protocol, IP version 6, will eventually replace the current version IP version 4. Before that change can take place the different implementations of IPv6 must be able to perform at least as well as their predecessors, The implementation that is considered here is that of the Linux operating system. All measurements considers native IPv6, e.g. no tunneling in IPv4 packets.

    A small network of two computers was set up on which the performance tests were performed. Throughput and response times were measured on both Ethernet and Fast Ethernet. The conclusions are that IPv6 performs almost as well as IPv4 in both cases. IPv4's slight advantage is due to the fact that it has less overhead on the network since the header is smaller.

    Later a connection to the 6bone is setup. It is run on an ATM network. The performance across that network is also tested.

  • 194.
    Björkman, Anders
    KTH, Superseded Departments, Teleinformatics.
    Configuration of IPv4 Hosts in Zero-Configuration Networks2000Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Zero-configuration networks are networks that require no/zero manual configuration or administration to operate. The essence of a zero-configuration network is that it can be used without having to think about the network at all. The most basic zero-configuration network just provides network communication but more advanced services can be provided as long as no configuration is needed. An important area of use is networks for homes and small businesses. Many of the devices that we have in our homes are or will in a near future be ‘networked’ i.e. capable of network communication. Examples are computers and computer equipment such as printers and scanners, the next generation home-appliances such as the refrigerator and the washing machine, the TV, the stereo, climate sensors etc. etc. The main driving forces for this development are the need for resource sharing e.g. of printers or Internet access, home automation and devices, applications or services that use network communication. Networks for the home must be ‘automatic’ because the average person today has problems programming his VCR and cannot be expected to configure or administrate his/her home-network. Today’s solutions are insufficient because they require manual configuration and some technical knowledge. The market potential is enormous. Almost all homes and most small businesses lack a network infrastructure and many will in a near future acquire it.

    In this thesis I discuss the need and areas of use for zero-configuration networks and I look at how to configure IP hosts in general. Solutions on configuration of hosts in zero-configuration networks are discussed and I propose a solution for IPv4 hosts that enables link-local communication, the most basic type of network communication using IP.

    This master’s thesis was carried out at Ericsson Research in Kista during the fall of 1999 and spring of 2000.

  • 195.
    Björnson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. Dept. of Electrical Engineering, Linkoping University, Sweden.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Optimal Multiuser Transmit Beamforming: A Difficult Problem with a Simple Solution Structure2014In: IEEE signal processing magazine (Print), ISSN 1053-5888, E-ISSN 1558-0792, Vol. 31, no 4, p. 142-148Article in journal (Refereed)
    Abstract [en]

    Transmit beamforming is a versatile technique for signal transmission from an array of antennas to one or multiple users [1]. In wireless communications, the goal is to increase the signal power at the intended user and reduce interference to nonintended users. A high signal power is achieved by transmitting the same data signal from all antennas but with different amplitudes and phases, such that the signal components add coherently at the user. Low interference is accomplished by making the signal components add destructively at nonintended users. This corresponds mathematically to designing beamforming vectors (that describe the amplitudes and phases) to have large inner products with the vectors describing the intended channels and small inner products with nonintended user channels.

  • 196.
    Björnson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jorswieck, Eduard
    Dresden University of Technology, Communications Theory, Communications Laboratory, Dresden, Germany.
    Optimal Resource Allocation in Coordinated Multi-Cell Systems2013Book (Refereed)
    Abstract [en]

    The use of multiple antennas at base stations is a key component in the design of cellular communication systems that can meet high-capacity demands in the downlink. Under ideal conditions, the gain of employing multiple antennas is well-recognized: the data throughput increases linearly with the number of transmit antennas if the spatial dimension is utilized to serve many users in parallel. The practical performance of multi-cell systems is, however, limited by a variety of nonidealities, such as insufficient channel knowledge, high computational complexity, heterogeneous user conditions, limited backhaul capacity, transceiver impairments, and the constrained level of coordination between base stations.

    This tutorial presents a general framework for modeling different multi-cell scenarios, including clustered joint transmission, coordinated beamforming, interference channels, cognitive radio, and spectrum sharing between operators. The framework enables joint analysis and insights that are both scenario independent and dependent.

    The performance of multi-cell systems depends on the resource allocation; that is, how the time, power, frequency, and spatial resources are divided among users. A comprehensive characterization of resource allocation problem categories is provided, along with the signal processing algorithms that solve them. The inherent difficulties are revealed: (a) the overwhelming spatial degrees-of-freedom created by the multitude of transmit antennas; and (b) the fundamental tradeoff between maximizing aggregate system throughput and maintaining user fairness. The tutorial provides a pragmatic foundation for resource allocation where the system utility metric can be selected to achieve practical feasibility. The structure of optimal resource allocation is also derived, in terms of beamforming parameterizations and optimal operating points.

    This tutorial provides a solid ground and understanding for optimization of practical multi-cell systems, including the impact of the nonidealities mentioned above. The Matlab code is available online for some of the examples and algorithms in this tutorial.

    Note: The supplementary Matlab Code is available at http://dx.doi.org/10.1561/0100000069_supp

  • 197.
    Björnson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. Alcatel-Lucent Chair on Flexible Radio, Supélec, France.
    Jorswieck, Eduard
    Dresden University of Technology, Communications Theory, Communications Laboratory, Dresden, Germany.
    Optimal Resource Allocation in Coordinated Multi-Cell Systems: Matlab Code2013Report (Other academic)
    Abstract [en]

    This is the documentation of the Matlab code supplement to the monograph "Optimal Resource Allocation in Coordinated Multi-Cell Systems" by Emil Björnson and Eduard Jorswieck; see [1] for the full publication details.

    This documentation is distributed along with the code package mentioned above. The package contains Matlab implementations of many of the algorithms described in [1]. The use of these algorithms is exemplified by Matlab scripts (m-files) that generate some of the figures shown in the monograph. The algorithms are briefly described in Section 5 and the selected example figures are described and shown in Section 6. Please note that the all channel vectors are generated randomly as Rayleigh fading in these examples, thus this code package is not able to reproduce exactly the same curves as was shown in the monograph.

  • 198.
    Björnson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sanguinetti, Luca
    SUPELEC, Alcatel Lucent Chair Flexible Radio, Gif Sur Yvette, France.;Univ Pisa, Dip Ingn Informaz, Pisa, Italy..
    Hoydis, Jakob
    Bell Labs, Alcatel Lucent, Stuttgart, Germany..
    Debbah, Merouane
    SUPELEC, Alcatel Lucent Chair Flexible Radio, Gif Sur Yvette, France..
    Designing Multi-User MIMO for Energy Efficiency: When is Massive MIMO the Answer?2014In: 2014 IEEE WIRELESS COMMUNICATIONS AND NETWORKING CONFERENCE (WCNC), IEEE , 2014, p. 242-247Conference paper (Refereed)
    Abstract [en]

    Assume that a multi-user multiple-input multiple output (MIMO) communication system must be designed to cover a given area with maximal energy efficiency (bits/Joule). What are the optimal values for the number of antennas, active users, and transmit power? By using a new model that describes how these three parameters affect the total energy efficiency of the system, this work provides closed-form expressions for their optimal values and interactions. In sharp contrast to common belief, the transmit power is found to increase (not decrease) with the number of antennas. This implies that energy efficient systems can operate at high signal-to-noise ratio (SNR) regimes in which the use of interference-suppressing precoding schemes is essential. Numerical results show that the maximal energy efficiency is achieved by a massive MIMO setup wherein hundreds of antennas are deployed to serve relatively many users using interference-suppressing regularized zero-forcing precoding.

  • 199.
    Blank, Bruno
    et al.
    KTH, Superseded Departments, Teleinformatics.
    Häggström, Mattias
    KTH, Superseded Departments, Teleinformatics.
    Mobile Communication In a Multiple Device Environment1998Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    It is nowadays common that users have more than one computer. At the office, a stationary computer or possibly a laptop is used. When travelling, a Personal Digital Assistant is better suited for e-mail, address book, and scheduling. Probably the user also has an advanced mobile phone. A problem for many users is it has traditionally been quite complex to handle having multiple computers, since the support for mobile use has been insufficient.

    We have looked into common scenarios for mobile users and given and overview of related products and technologies. Some of the traditional protocols for e-mail have been reviewed. We have listed problems with those and suggested improvements. Sendit has a proprietary protocol, which we have compared to traditional protocols.

    This report gives an overview from the user’s point of view. From what we have seen, there are lots of upcoming technologies and solutions to assist mobile users. However, many problems still remain and need to be solved to facilitate the mobile user’s situation.

  • 200.
    Blomberg, Patrik
    KTH, Superseded Departments, Teleinformatics.
    Construction and Implementation of a Walkstation Mobile-distributed File System Testbed1995Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this Master's Thesis an investigation, design and implementation of an object-oriented prototype of a new kind of client-agent-server based distributed file system, suited for wireless mobile computing, are presented. An overview is given of the characteristics and the inherent problems of mobile-wireless computing. Some solutions and techniques to reduce the effects of these problems are described. A presentation of a project (the Walkstation project) that tries to solve these problems is also given. Software to support a mobile-distributed file system is designed and implemented. Various software development techniques and mobile file system design solutions are proposed, and used in the implementation. An integrated caching and prefetching scheme with dynamically loadable cache and prefetch manager objects is designed and implemented. It is proposed that different cache and prefetch algorithms should be used for different kinds of network links. A cache/prefetch-manager object architecture with automatically location-dependant dynamical swapping of network specific manager objects at run-time is therefore proposed and implemented. A mechanism is designed with which an application optionally can be mobility-aware by subscribing for network-change events. Finally, an expedient example of a methodology to achieve easy-understandable and well-designed code, and good extensibility possibilities is explained and used in the development. This is done by utilizing an object-oriented software development methodology in the entire software development cycle.

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