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  • 101. Ahlberg, M.
    et al.
    Lindmark, B.
    Simons, J.
    Beckman, Claes
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Downlink propagation measurements in the GSM 900 and 1800 MHz bands1999In: IEEE Antennas and Propagation Society International Symposium. 1999 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.99CH37010), 1999, Vol. 3, p. 1506-1509 vol.3Conference paper (Refereed)
    Abstract [en]

    The authors investigate radio propagation in the GSM 900 and 1800 MHz bands in a typical Swedish suburban environment to determine whether or not it is practically feasible to co-site GSM 900 with GSM 1800 systems. They show that propagation in the GSM 1800 band is considerable higher (about 12 dB) than in the old GSM 900. In many cases this difference can be reduced by using dual band sector antennas with 3 dB higher gain at 1800 MHz. However, they also show that in small cells (radius <1000 m) this difference is of little concern and therefore it is possible to co-locate GSM 1800 sites within existing 900 MHz sites as a cost-effective way to increase the system capacity.

  • 102.
    Ahlberg, Michael
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    Vlassov, Vladimir
    KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    Yasui, Terumasa
    Advanced Technology Research and Development Center, Mitsubishi Electric Corporation, Amagasaki, Japan.
    Router placement in wireless sensor networks2006In: 2006 IEEE International Conference on Mobile Adhoc and Sensor Systems, Vols 1 and 2, IEEE , 2006, p. 498-501Conference paper (Refereed)
    Abstract [en]

    In this paper we propose and evaluate algorithms for placement of routers in a wireless sensor network. There are two major requirements on router placement First, a placement must guarantee connectivity, i.e. every sensor must be able to communicate through routers with a predefined computer-connected gateway node. Second, a placement must provide robust communication in the case of router failures. This is achieved by placing redundant routers that increase the number of possible routes. Both requirements should be met by placing as few routers as possible. The proposed algorithms compute placement in an efficient and reasonably fast way.

  • 103.
    Ahlbom, Fredrik
    KTH, School of Information and Communication Technology (ICT).
    Analysis of the Performance of Different DWDM FilterTechnologies for Mobile Fronthaul Applications2016Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In recent years, several studies and simulations have been made on changing the current Radio Access Network (RAN) architecture into a more centralized access network where the base band processing is done in a central oce (CO) instead of out by the antenna site. This new architecture is denoted as the mobile fronthaul and is planned to be in use for the coming 5G network. The studies that have been made so far suggest that the new architecture can reduce cost, power usage and latency which are important factors regarding environmental, economical and data transmission issues. Furthermore, the new architecture allows a smarter distribution of data for each sector covered by the antennas, reducing redundant data transmission and thus increases the data eciency. The disadvantage or challenge however is that some of the optical components will be transferred from the currently controlled environment in the CO to an uncontrolled outdoor environment at the antenna site, which may generate risks as these components may be sensitive to especially changes in temperature.

    In this master thesis, the optical performance of four di erent passive lter setups, using a thin lm lter (TFF), an arrayed waveguide grating (AWG) and an interleaver, has been studied and compared in order to nd the most suitable lter setup for the mobile fronthaul. These optical parameters include insertion loss, isolation, crosstalk, 3 dB passband, center wavelength drift and also bit error-rate (BER) which have all been measured over a temperature interval of -40-85oC. Moreover, the measurement results have been compared with results from simulations done with VPItransmissionmaker.

    From the measurement results, the TFF had a better optical performance and reliability compared to the AWG mainly due to a higher isolation and a lower BER penalty of 0.2 dB compared to 0.5-1.5 dB for the AWG. Considering data capacity and economical aspects for a more realistic mobile fronthaul scenario with 80 channels using dense wavelength division multiplexing (DWDM) however, the AWG connected to the interleaver is more benecial without risking negative a ects on trac performance.

  • 104.
    Ahlbom, Gabriella
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Åman, Anna
    KTH, School of Information and Communication Technology (ICT).
    Defining the TECHNOLOGY TRANSFER ALLIANCE2011Independent thesis Advanced level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of this project was to define the Technology Transfer Alliance (TTA), a nonprofit organization for Higher Education Institutions supporting capacity building in ICT and renewable energy through a project-driven learning. TTA is today still only an idea, waiting to be launched, which is why the goals for this bachelor thesis are to establish partnerships with institutions that will support the reaching of the goals of TTA, as well as providing a more solid definition of the functions of TTA, as to make the alliance more attracting for future partners. Functions include for example the project-driven framework that will serve as template for the educational process within TTA.

    To reach the goals with this project, several interviews were conducted with potential partners of TTA in African countries and other individuals that hold an expertise within the scope of this project. The interviews were meant to establish the expectations of TTA in terms of what a partnership would entail as well as to prelude discussions for which the potential partner would ultimately agree to sign a formal partnership agreement. The interviews also served as research about the open source solutions, which originally were developed by Master students at the Royal Institute of Technology (KTH), and that will be focused on in futureTTA-projects.

    Ultimately were the goals of this project succeeded, in terms of defining the aim and functions of TTA. During the time frame of this project, vision and scope of TTA were set. This resulted in a restructuring of existing websites and in a production of an official partnership agreement, which entailsthe objectives of a partnership. The project resulted also resulted in that several African institutions expressed a great deal of interest of joining TTA as partners. Getting them to sign the partnership agreement will however be a task for future project teams to fulfill.

  • 105. Ahlfeldt, H.
    et al.
    Holm, J.
    Lindgren, S.
    Backlin, L.
    Vieider, C.
    Klinga, T.
    Kerzar, B.
    Nilsson, M.
    Svensson, M.
    Nilsson, S.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    20 GHz bandwidth of lasers flip-chip-mounted on microstructured carriers with integrated electrical waveguides1998In: Optical Communication, 1998. 24th European Conference on, 1998, Vol. 1, p. 205-206Conference paper (Refereed)
    Abstract [en]

    A flip-chip-mounting scheme for high-speed lasers has been realised. The mounting scheme involves a microstructured silicon carrier with integrated membrane transmission lines and self-aligning solder bumps

  • 106. Ahlgren, B.
    et al.
    Hidell, Markus
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Ngai, E. C. -H
    Internet of Things for Smart Cities: Interoperability and Open Data2016In: IEEE Internet Computing, ISSN 1089-7801, E-ISSN 1941-0131, Vol. 20, no 6, p. 52-56, article id 7781549Article in journal (Refereed)
    Abstract [en]

    The Internet of Things (IoT) has become a promising technology for addressing societal challenges by connecting smart devices and leveraging Big Data analytics to create smart cities worldwide. As the IoT scales up, it's important to provide interoperability among different devices. Yet current simple standard protocols lack sufficient openness and interoperability. IoT for smart cities needs to guarantee the accessibility of open data and cloud services to allow industries and citizens to develop new services and applications. Here, the authors provide a case study of the GreenIoT platform in Uppsala, Sweden, to demonstrate the idea of interoperability and open data for smart cities.

  • 107. Ahlgren, B.
    et al.
    Ohlman, B.
    Axelsson, Erik
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101).
    Brown, Lars
    KTH, School of Information and Communication Technology (ICT).
    Subversion over OpenNetInf and CCNx2011In: Proceedings - Conference on Local Computer Networks, LCN, 2011, p. 1056-1063Conference paper (Refereed)
    Abstract [en]

    We describe experiences and insights from adapting the Subversion version control system to use the network service of two information-centric networking (ICN) prototypes: OpenNetInf and CCNx. The evaluation is done using a local collaboration scenario, common in our own project work where a group of people meet and share documents through a Subversion repository. The measurements show a performance benefit already with two clients in some of the studied scenarios, despite being done on un-optimised research prototypes. The conclusion is that ICN clearly is beneficial also for non mass-distribution applications. It was straightforward to adapt Subversion to fetch updated files from the repository using the ICN network service. The adaptation however neglected access control which will need a different approach in ICN than an authenticated SSL tunnel. Another insight from the experiments is that care needs to be taken when implementing the heavy ICN hash and signature calculations. In the prototypes, these are done serially, but we see an opportunity for parallelisation, making use of current multi-core processors.

  • 108.
    Ahlin, Lars
    et al.
    FOI.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT).
    Ben Slimane, Slimane
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Principles of Wireless Communications2006Book (Refereed)
    Abstract [en]

    This textbook provides the reader with a basic understanding of the design and analysis of wireless and mobile communication systems. It deals with the most important techniques, models and tools used today in the design of mobile wireless links and gives an introduction to the design of wireless networks. Topics covered include: fundamentals of radio propagation and antennas; transmission schemes, including modulation, coding and equalising schemes for broadband wireless communications; diversity systems; wireless data transmission; introduction to Wireless Network design and resource management. The fundamentals are illustrated by examples from state-of-the-art technologies such as OFDM, WCDMA, WLANs and others. The book contains a significant number of worked examples and more than 160 problems with answers. It is intended for use in a first graduate course in wireless communications and the reader should be familiar with the fundamentals of probability and communication theory.

  • 109.
    Ahlinder, Ludvig
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Eriksson, Anders
    KTH, School of Information and Communication Technology (ICT).
    Accelerating Adoption of IPv62011Independent thesis Advanced level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    It has long been known that the number of unique IPv4-addresses would be exhausted because of the rapid expansion of the Internet and because countries such as China and India are becoming more and more connected to the rest of the world.

    IPv6 is a new version of the Internet Protocol which is supposed to succeed the old version, IPv4, in providing more addresses and new services. The biggest challenge of information and communication technology (ICT) today is to transition from IPv4 to IPv6. The purpose of this thesis is to accelerate the adoption of IPv6 by highlighting the benefits of it compared to IPv4.

    Although the need for more IP-addresses is the most urgent incentive for the transition to IPv6, other factors also exist. IPv6 offers many improvements to IPv4 which are necessary for the continued expansion of Internet-based applications and services.

    Some argue that we do not need to transition to IPv6 as the problems with IPv4, mainly the addressshortage, can be solved in other ways. One of the methods of doing this is by extending the use of Network Address Translators (NATs), but the majority of experts and specialists believe that NATs should not be seen as a long-term solution.

    Another difficulty with the new protocol is explaining its benefits and areas of use to both the business world and the public. Understanding these benefits are necessary in order create awareness of these benefits, thus to accelerating the adoption of IPv6. This thesis aims to explain the incentives for both businesses and the public to adopt IPv6.

  • 110.
    Ahlstrand, Rebecca
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Xu, Annie
    KTH, School of Information and Communication Technology (ICT).
    Guidelines to improve teamwork in software projects2015Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In consulting firms one of the goals is to have the consultants on an assignment with an external client to bring in capital. In some consulting firms, when the consultants are not on an assignment with a client, they work on internal projects until a new assignment arrives. Since most of the team members do not work for more than a few days or weeks on the projects, it leads to a high team member turnover. In projects with such a turnover, problems such as hasty handovers, unclear roles and responsibilities and low-quality documentation may occur.

    The purpose of this thesis was to create guidelines to improve teamwork in teams with a high team member turnover. This thesis was based on a case study of a company specializing in information technology and management consulting. To begin to tackle this problem, a literature review was conducted and the data was collected by conducting interviews. The interviews were performed with team members that had been on a project for the longest and shortest period of time in order to identify problems from different perspectives.

    Based on the interviews and the literature study, guidelines were created to counteract the problems experienced in this type of volatile teams. The guidelines are categorized in four areas: processes, resources, people and long-term perspective. The areas cover the problems experienced and can be ultimately implemented in all teams with high team member turnover to improve teamwork in software projects.

  • 111. Ahlund, John
    et al.
    Nilson, Katharina
    Palmgren, Pål
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Gothelid, Emmanuelle
    Schiessling, Joachim
    Göthelid, Mats
    Martensson, Nils
    Puglia, Carla
    Molecular growth determined by surface domain patterns2008In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 17, p. 6887-6890Article in journal (Refereed)
    Abstract [en]

    The growth of iron phthalocyanine (FePc) on InSb(001) c(8 x 2) at submonolayer coverage has been investigated with scanning tunneling microscopy (STM). FePc adsorbs flat centered on the In rows both at 70 K and at room temperature (RT). However, the shapes of the two-dimensional molecular islands are fundamentally different; while the RT growth results in chainlike structures along the [I 10] direction, as already observed for other Pc's adsorbed on the same surface, the islands are prolonged along [110], i.e., perpendicular to the substrate rows, at 70 K. These observations are explained on the basis of a recently observed new surface phase at low temperature, resulting in structural domains on the surface. The molecular growth front follows the propagating domain boundary that freezes at low temperature.

  • 112.
    Ahmad, Ashfaq
    et al.
    Univ Engn & Technol, ACTSENA Res Grp, Taxila 47050, Pakistan..
    Arshad, Farzana
    Univ Engn & Technol, ACTSENA Res Grp, Taxila 47050, Pakistan..
    Naqvi, Syeda I.
    Univ Engn & Technol, ACTSENA Res Grp, Taxila 47050, Pakistan..
    Amin, Yasar
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK. Univ Engn & Technol, ACTSENA Res Grp, Taxila 47050, Pakistan.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK. Univ Turku, Dept Informat Technol, TUCS, FIN-20520 Turku, Finland..
    Design, Fabrication, and Measurements of Extended L-Shaped Multiband Antenna for Wireless Applications2018In: Applied Computational Electromagnetics Society Journal, ISSN 1054-4887, Vol. 33, no 4, p. 388-393Article in journal (Refereed)
    Abstract [en]

    This article expounds a multi-band compact shaped antenna, which is based on CPW ground plane. FR-4 with a thickness of 1.6 mm is used as a substrate for the proposed antenna. The proposed antenna is capable of operating at 1.56 GHz for (Global Positioning System), 2.45 GHz (Wireless Local Area Network) and 4.49 GHz (Aeronautical Mobile Telemetry (AMT) fixed services). The efficiency at 1.56, 2.45, and 4.49 GHz is 79.7, 76.9 and 76.7%, respectively. The VSWR of the presented antenna is less than 1.5 at all the desired resonance modes, which confirms its good impedance matching. The performance of the proposed antenna is evaluated in terms of VSWR, return loss, radiation pattern and efficiency. CST (R) MWS (R) software is used for simulations. In order to validate the simulation results, a prototype of the designed antenna is fabricated and a good agreement is found between the simulated and measured results.

  • 113.
    Ahmad, Bilal
    KTH, School of Information and Communication Technology (ICT).
    ID-REPLICATION FOR PEER-TO-PEER SYSTEMS2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Replication provides fault-­tolerance in distributed systems. This thesis presents ID-­replication, which is a new replication scheme for structured overlays. We first discuss the shortcomings of existing replication schemes and show how ID-­replication does not suffer from many of these issues. We present a detailed design, algorithmic specification and evaluation of ID-­replication.

    ID-replication is less sensitive to churn which makes it better suited for building consistent services on top of it and for working in asynchronous networks where inaccurate failure detections are a norm. ID­‐replication does not require requests to go through a particular replica before forwarding them to another node for processing and thus does not suffer from the bottleneck. ID-­‐replication provides variable replication degree, which makes it suitable for systems which need to provide extra backup for more critical data. It also makes the system easily handle hotspots/popular and is easier to load balance.

    We evaluate ID­‐replication and provide a comprehensive comparison of ID-­replication with SL-­replication, which is among the most popular replication scheme in use today.

  • 114.
    Ahmad, Maqsood
    KTH, School of Information and Communication Technology (ICT).
    Anonymous Authentication Using Secure Multi-Party Computations2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Typical authentication systems provide a method to allow registered users access to protected resources after the user successfully authenticates. A user successfully authenticates by proving his or her valid identity if he or she is a registered user. During a typical authentication process, the authentication server can directly or indirectly learn the actual identity of the user who authenticates. However, the user might not want any one to know the actual identity of the user, while still able to authenticate. This problem of user’s anonymous authentication is the focus of this thesis project. This thesis project provides a solution for user’s anonymous authentication using Secure Multi-party Computation (SMPC). In SMPC, the user information is distributed among the authentication servers, using a secret sharing scheme, in such a way that none of the authentication servers individually possesses all the information of a user.

    However, these authentication servers can validate the user using some SMPC arithmetic operations. This thesis project provides a model for anonymous authentication and couples this anonymous authentication system with the Open Authentication Protocol (OAuth) to allow the user access to protected resources on the server. The model is explained using UML collaborations and SDL state transition diagrams. An analysis of the model is provided to ensure the security of the proposed system. A skeleton of the proposed model is provided which needs to be completed with appropriate code to realize the functionalities. This thesis project also provides an implementation of a simplified prototype which represents the core of the proposed model for anonymous authentication

  • 115.
    Ahmad, Mirwary
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Kaur, Birgeet
    KTH, School of Information and Communication Technology (ICT).
    Sustainability Aspects in ICT Engineering Thesis Works2016Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    An evaluation of thesis reports performed by students from the degree programme Computer Engineering, TIDAB, that was made by UKÄ, The Swedish Higher Education Authority, showed that there was a lack of consideration of environmental and sustainability aspects in the thesis reports, leading to many students not meeting the criteria in the degree objectives regarding this aspect. The purpose of this bachelor thesis is to improve students’ ability in considering the important aspects of sustainability in their thesis works, by providing them with guidelines which they can follow and implement during their thesis work that will enable them to reach the level ‘Very High Quality’.

    A literature study was performed thoroughly in conjunction with reviewing previous thesis reports and conducting expert interviews as an approach to find a solution to the problem.

    The outcome of the analysis was three methods that was developed, which the students can use as guidelines in their thesis work. A set of guidelines, a table with skill sets and the SEMAT Essence Kernel card for sustainable development was the resulting methods that will help the students to at minimum accomplish the criteria for ‘High Quality’ on the objective "Demonstrate an understanding of technology capabilities and limitations, its role in society and people’s responsibility for its use, including social and economic aspects, environmental and safety aspects" when the methods are followed.

  • 116.
    Ahmad, Waqar
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Core Switching Noise for On-Chip 3D Power Distribution Networks2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Reducing the interconnect size with each technology node and increasing speed with each generation increases IR-drop and Ldi/dt noise. In addition to this, the drive for more integration increases the average current requirement for modern ULSI design. Simultaneous switching of core logic blocks and I/O drivers produces large current transients due to power distribution network parasitics at high clock frequency. The current transients are injected into the power distribution planes thereby inducing noise in the supply voltage. The part of the noise that is caused by switching of the internal logic load is core switching noise. The core logic switches at much higher speed than driver speed whereas the package inductance is less than the on-chip inductance in modern BGA packages. The core switching noise is currently gaining more attention for three-dimensional integrated circuits where on-chip inductance is much higher than the board and package inductance due to smaller board, and package. The switching noise of the driver is smaller than the core switching noise due to small driver size and reduced capacitance associated with short on-board wires for three-dimensional integrated circuits. The load increases with the addition of each die. The power distribution TSV pairs to supply each extra die also introduce additional parasitic. The core switching noise may propagate through substrate and consequently through interconnecting TSVs to different dies in heterogeneous integrated system. Core switching noise may lead to decreased device drive capability, increased gate delays, logic errors, and reduced noise margins. The actual behavior of the on-chip load is not well known in the beginning of the design cycle whereas altering the design during later stages is not cost effective. The size of a three-dimensional power distribution network may reach billions of nodes with the addition of dies in a vertical stack. The traditional tools may run out of time and memory during simulation of a three-dimensional power distribution network whereas, the CAD tools for the analysis of 3D power distribution network are in the process of evolution. Compact mathematical models for the estimation of core switching noise are necessary in order to overcome the power integrity challenges associated with the 3D power distribution network design. This thesis presents three different mathematical models to estimate core switching noise for 3D stacked power distribution networks. A time-domain-based mathematical model for the estimation of design parameters of a power distribution TSV pair is also proposed. Design guidelines for the estimation of optimum decoupling capacitance based on flat output impedance are also proposed for each stage of the vertical chain of power distribution TSV pairs. A mathematical model for tradeoff between TSV resistance and amount of decoupling capacitance on each DRAM die is proposed for a 3D-DRAM-Over-Logic system. The models are developed by following a three step approach: 1) design physical model, 2) convert it to equivalent electrical model, and 3) formulate the mathematical model based on the electrical model. The accuracy, speed and memory requirement of the proposed mathematical model is compared with equivalent Ansoft Nexxim models.

  • 117.
    Ahmad, Waqar
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Chen, Qiang
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Zheng, Lirong
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Decoupling capacitance for the power integrity of 3D-DRAM-over-logic system2012In: IEEE 13th Electronics Packaging Technology Conference (EPTC), 2011, IEEE conference proceedings, 2012, p. 590-594Conference paper (Refereed)
    Abstract [en]

    The 3D-DRAM stacked over the processor is a vibrant technique in order to overcome the memory wall as well as the bandwidth wall problems. We considered a system with two DRAM dies over a single processor die. We assumed the decoupling capacitors to be placed on each DRAM die and connected to the power distribution TSV pairs, where the TSVs pass through the DRAM stack. In this paper we proposed a mathematical model for the optimum value of the decoupling capacitance on each DRAM die along with the optimum values of the effective resistance of the interconnecting power distribution TSV pairs in order to ensure the power integrity of the logic load during switching. The proposed model has a maximum of 1.1% error as compared to the Ansoft Nexxim4.1.

  • 118.
    Ahmad, Waqar
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Chen, Qiang
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Zheng, Li-Rong
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Modeling of peak-to-peak core switching noise, output impedance, and decoupling capacitance along a vertical chain of power distribution TSV pairs2012In: Analog Integrated Circuits and Signal Processing, ISSN 0925-1030, E-ISSN 1573-1979, Vol. 73, no 1, p. 311-328Article in journal (Refereed)
    Abstract [en]

    In this article we propose an efficient and accurate model to estimate peak-to-peak core switching noise, caused by simultaneous switching of logic loads along a vertical chain of power distribution TSV pairs in a 3D stack of dies interconnected through TSVs. The proposed model is accurate with only a 2–3% difference in peak-to-peak core switching noise as compared to the Ansoft Nexxim4.1 equivalent model. The proposed model is 3–4 times faster than Ansoft Nexxim4.1 and uses two times less memory as compared to the Ansoft Nexxim4.1 equivalent model. In this article we also thoroughly establish design guidelines for almost flat output impedance magnitude at each stage of a vertical chain of power distribution TSV pairs to realize a resonance free scenario over a wide operating frequency range. We also establish decoupling capacitance design guidelines based on the optimum output impedance and critically damped supply voltage for the core logic for each stage of a vertical chain of power distribution TSV pairs.

  • 119.
    Ahmad, Waqar
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Chen, Qiang
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Zheng, Li-Rong
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Modeling of peak-to-peak switching noise along a vertical chain of power distribution TSV pairs in a 3D stack of ICs interconnected through TSVs2010In: 28th Norchip Conference, NORCHIP 2010, 2010, article id 5669473Conference paper (Refereed)
    Abstract [en]

    On-chip power supply noise has become a bottleneck in 3D ICs as scaling of the supply network impedance has not been kept up with increasing device densities and operating currents with each technology node due to limited wire resources. In this paper we proposed an efficient and accurate model to estimate peak-to-peak switching noise, caused by simultaneous switching of logic loads along a vertical chain of power distribution TSV pairs in a 3D stack of ICs. The proposed model is quite accurate with only 2-3% difference from Ansoft Nexxim4.1 equivalent model. The proposed model is 3-4 times faster than Nexxim4.1 as well as consumes two times less memory as compared to Nexxim4.1equivalent model. We analyzed peak-to-peak switching noise along a vertical chain of power distribution TSV pairs by varying physical dimensions of TSVs and value of decoupling capacitance. We also thoroughly investigated the peak-to-peak noise sensitivity to TSV effective inductance and decoupling capacitance.

  • 120.
    Ahmad, Waqar
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Chen, Qiang
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Zheng, Lirong
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Peak-to-peak Switching Noise and LC Resonance on a Power Distribution TSV Pair2010In: 2010 IEEE 19th Conference on Electrical Performance of Electronic Packaging and Systems, EPEPS 2010, Institute of Electrical and Electronics Engineers (IEEE), 2010, p. 173-176, article id 5642574Conference paper (Refereed)
    Abstract [en]

    How peak-to-peak switching noise as well as the LC resonance term varies by varying different circuit parameters of a power distribution TSV pair (having decoupling capacitance and logic load), within a 3D stack of ICs interconnected through TSVs.

  • 121.
    Ahmad, Waqar
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Kanth, Rajeev Kumar
    Turku Centre for Computer Science .
    Chen, Qiang
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Zheng, Lirong
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Fast Transient Simulation Algorithm for a 3D Power distribution Bus2010In: Proceedings of IEEE Asia Symposium on Quality Electronic Design, 2010, p. 343-350Conference paper (Refereed)
    Abstract [en]

    Extensive transient simulations for on-chip power delivery networks are required to analyze power delivery fluctuations caused by dynamic IR and Ldi/dt drops. Speed and memory has become a bottleneck for simulation of power distribution networks in modern VLSI design where clock frequency is of the order of GHz. The traditional SPICE based tools are very slow and consume a lot of memory during simulation. The problem is further aggravated for huge networks like power distribution network within a stack of ICs inter-connected through TSVs. This type of 3D power distribution network may contain billions of nodes at a time. In this paper we proposed a faster transient simulation algorithm using visual C++. First we reduce 3D power distribution bus containing n nodes to a two terminal 7 network. Then we solve this two terminal reduced network for voltages and currents. After this, we apply back solving algorithm to the network to solve it for each of the intermediate nodes using visual C++. The proposed algorithm is quite accurate with 1-2% error when compared with Ansoft Nexxim4.1. The proposed algorithm is several times faster than Ansoft Nexxim as well as consumes significantly less memory as compared to Nexxim.

  • 122.
    Ahmad, Waqar
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Kanth, Rajeev Kumar
    Turku Centre for Computer Science .
    Chen, Qiang
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Zheng, Lirong
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Power distribution TSVs induced core switching noise2011In: Electrical Design of Advanced Packaging & Systems Symposium (EDAPS), 2010 IEEE, IEEE conference proceedings, 2011Conference paper (Refereed)
    Abstract [en]

    Size of on-chip interconnects as well as the supply voltage is reducing with each technology node whereas the operating speed is increasing in modern VLSI design. Today, the package inductance and resistance has been reduced to such an extent that core switching noise caused by on-chip inductance and on-chip resistance is gaining importance as compared to I/O drivers switching noise. Both on-chip inductance and skin effect are prime players at frequencies of the order of GHz. The problem is further aggravated when chips are interconnected through TSVs to form a 3D integrated stack in order to achieve low form factor and high integration density. In this paper we analysed peak core switching noise in a 3D stack of integrated chips interconnected through power distribution TSV pairs, through our comprehensive mathematical model which has been proved to be quite accurate as compared to SPICE. We analysed the effect of number of chips in a 3D stack, rise time, decoupling capacitance, and skin effect on power distribution TSVs induced core switching noise in this paper.

  • 123.
    Ahmad, Waqar
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Switching Noise in 3D Power Distribution Networks: an Overview2012In: VLSI  design / [ed] Esteban Tlelo-Cuautle, Sheldon Tan, Intech , 2012, p. 209-224Chapter in book (Refereed)
  • 124.
    Ahmad, Waqar
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Zheng, Li-Rong
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Chen, Qiang
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Peak-to-Peak Ground Noise on a Power Distribution TSV Pair as a Function of Rise Time in 3-D Stack of Dies Interconnected Through TSVs2011In: IEEE Transactions on Components Packaging and Manufacturing Technology, ISSN 2156-3950, Vol. 1, no 2, p. 196-207Article in journal (Refereed)
    Abstract [en]

    Supply grids of integrated chips are interconnected through through-silicon vias (TSVs) in modern design techniques to form a 3-D stack in vertical direction. The load on each chip is supplied through (power/ground) TSV pairs. Accurate estimation of power/ground noise on each TSV pair of a 3-D power distribution network is necessary for a robust power supply design. The worst case noise obtained with fast switching characteristics may not be significantly accurate. The behavior of power/ground noise as a function of rise time for an inductive power distribution TSV pair with decoupling capacitance, is investigated in this paper. An equivalent rise time corresponding to resonance is presented to accurately estimate the worst case power/ground noise in the time domain. In addition noise sensitivity to decoupling capacitance and TSV inductance is evaluated as a function of rise time. We also discuss noise accumulation as a result of worst case damping factor in this paper.

  • 125.
    Ahmad, Waqar
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    Zheng, Li-Rong
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK. KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    Weerasekera, Roshan
    KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    Chen, Qiang
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK. KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    Weldezion, Awet Yemane
    KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK. KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    Power Integrity Optimization of 3D Chips Stacked Through TSVs2009In: ELECTRICAL PERFORMANCE OF ELECTRONIC PACKAGING AND SYSTEMS, NEW YORK: IEEE , 2009, p. 105-108Conference paper (Refereed)
    Abstract [en]

    On-chip power distribution network model for simultaneous switching of 3D ICs stacked through TSVs to choose TSV pattern, maximum number of chips in a stack and location of the decoupling capacitor for early design trade-offs.

  • 126.
    Ahmadi, Sareh
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Structure-dependent charge transfer at the interafce between organic thin films, and metals and metal oxides2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The purpose of the research work, presented in this thesis is to offer a detailed atomic level study of interfaces created by adsorption of organic molecules on metals and metal oxides to point out significant impact of substrate, dye structure as well as different mediators on the charge transfer at these interfaces, which is proven to influence the device performance to a great extent.

    Adsorption of organic photosensitive molecules on metals and metal-oxides is the main focus of this thesis. Phthalocyanines which are organic semiconductors offer a broad range of properties, such as thermal and chemical stability, high charge mobility and strong absorption coefficient in the visible and near-IR regions, which make them very attractive to be applied in various systems and devices. Fuel cells, organic field-effect transistors (OFETs), organic light emitting diodes (OLEDs) and solar cells are examples of phthalocyanine’s applications. The main focus of this work is to characterize the interfaces of Dye Sensitized Solar Cells (DSSCs).

    DSSC was invented by Michael Grätzel and Brian O’Regan in 1988. At the heart of this cell there is an oxide which is coated by a photosensitive dye. Under illumination, an electron is excited from HOMO to LUMO of the molecule, which can be further transferred to the conduction band of the oxide by a proper energy level alignment. The original state of the dye is regenerated by electron donation via the electrolyte, which usually is an organic solvent containing a redox couple e.g., iodide/triiodide. The iodide is regenerated by reduction of triiodide at the counter electrode. To improve the functionality of the cell, different additives can be added to the electrolyte.

    To mimic the interfaces of this cell, molecular layers of MPc (M: Fe, Zn, Mg) are adsorbed on both metallic surfaces, Au(111) and Pt(111), and rutile TiO2(110). Layers of iodine were inserted between metallic substrates and dyes to investigate the electronic properties and charge transfer at these multi-interface systems. 4-tert-butyl pyridine is a significant additive to the electrolyte and has proven to enhance the cell’s performance. This molecule was also adsorbed on Pt(111) and TiO2(110). Phthalocyanines were deposited by organic molecular beam deposition and 4TBP was evaporated at room temperature. Surface structures and reconstructions were confirmed by LEED measurements. Surface sensitive synchrotron radiation based spectroscopy methods, XPS and NEXAFS were applied to characterize these surfaces and interfaces. STM images directly give a topographical and electronic map over the surface. All measurements were carried out in UHV condition.

    When MPc was adsorbed on Au(111) and TiO2(110), charge transfer from molecule to substrate is suggested, while the opposite holds for MPc adsorbed on Pt(111). Moreover, stronger interaction between MPc and Pt(111) and TiO2(110) compared to Au(111) also demonstrates the effect of substrate on the charge transfer at the interface. The stronger interaction observed for these two substrates disturbed the smooth growth of a monolayer; it also resulted in bending of the molecular plane. Interaction of MPc with metallic surfaces was modified by inserting iodine at the interface. Another substrate-related effect was observed when MgPc was adsorbed on TiO2(110);  and -cross linked surfaces, where the surface reconstruction directly affect the molecular configuration as well as electronic structure at the interface. Besides, it is shown that the d-orbital filling of the central metal atom in MPc plays an important role for the properties of the molecular layer as well as charge transfer at the interface.

    Upon adsorption of 4TBP on Pt(111), C-H bond is dissociatively broken and molecules is adsorbed with N atoms down. Modification of surface by iodine, prevent this dissociation. In the low coverage of iodine, there is a competition between 4TBP and iodine to directly bind to Pt(111). Investigation on the adsorption of 4TBP on TiO2(110) illustrated that these molecules in low coverage regime, prefer the oxygen vacancy sites and their adsorption on these sites, results in a downward band bending at the substrate’s surface. 

  • 127.
    Ahmadi, Sareh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Agnarsson, Björn
    Bidermane, Ieva
    Wojek, Bastian M.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Noël, Quentin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sun, Chenghua
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Site-dependent charge transfer at the Pt(111)-ZnPc interface and the effect of iodine2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 17, p. 174702-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of ZnPc, from sub-monolayers to thick films, on bare and iodated Pt(111) is studied by means of X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and scanning tunneling microscopy. Our results suggest that at low coverage ZnPc lies almost parallel to the Pt(111) substrate, in a non-planar configuration induced by Zn-Pt attraction, leading to an inhomogeneous charge distribution within the molecule and an inhomogeneous charge transfer to the molecule. ZnPc does not form a complete monolayer on the Pt surface, due to a surface-mediated intermolecular repulsion. At higher coverage ZnPc adopts a tilted geometry, due to a reduced molecule-substrate interaction. Our photoemission results illustrate that ZnPc is practically decoupled from Pt, already from the second layer. Pre-deposition of iodine on Pt hinders the Zn-Pt attraction, leading to a non-distorted first layer ZnPc in contact with Pt(111)-I(root 3x root 3) or Pt(111)-I(root 7x root 7), and a more homogeneous charge distribution and charge transfer at the interface. On increased ZnPc thickness iodine is dissolved in the organic film where it acts as an electron acceptor dopant.

  • 128.
    Ahmadi, Sareh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Agnarsson, Björn
    Bidermane, Leva
    Wojek, Bastian M.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Noël, Quentin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sun, Chenghua
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Effect of the iodineon the site-dependent charge transfer at the Pt(111)-ZnPc interfaceManuscript (preprint) (Other academic)
  • 129.
    Ahmadi, Sareh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Bidermane, Leva
    Noël, Quentin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sun, Chenghua
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Dissociative bonding of 4-tert-butyl pyridine to Pt(111) and surface passivation by iodineManuscript (preprint) (Other academic)
  • 130.
    Ahmadi, Sareh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Shariati, M. Nina
    Yu, Shun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Molecular layers of ZnPc and FePc on Au(111) surface: Charge transfer and chemical interaction2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 8, p. 084705-Article in journal (Refereed)
    Abstract [en]

    We have studied zinc phthalocyanine (ZnPc) and iron phthalocyanine (FePc) thick films and monolayers on Au(111) using photoelectron spectroscopy and x-ray absorption spectroscopy. Both molecules are adsorbed flat on the surface at monolayer. ZnPc keeps this orientation in all investigated coverages, whereas FePc molecules stand up in the thick film. The stronger inter-molecular interaction of FePc molecules leads to change of orientation, as well as higher conductivity in FePc layer in comparison with ZnPc, which is reflected in thickness-dependent differences in core-level shifts. Work function changes indicate that both molecules donate charge to Au; through the pi-system. However, the Fe3d derived lowest unoccupied molecular orbital receives charge from the substrate when forming an interface state at the Fermi level. Thus, the central atom plays an important role in mediating the charge, but the charge transfer as a whole is a balance between the two different charge transfer channels; pi-system and the central atom.

  • 131.
    Ahmadi, Sareh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Yu, Shun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sun, Chenghua
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Reduced Au-MPc hole injection barrier by an intermediate iodine layerManuscript (preprint) (Other academic)
  • 132.
    Ahmadi, Sareh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Yu, Shun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Zuleta, Marcelo
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Palmgren, Pål
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Charge transfer and band bending on TiO2(110)-MgPcManuscript (preprint) (Other academic)
  • 133.
    Ahmed, Ashraf Awadelkarim Widaa
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Towards Affordable Provisioning Strategies for Local Mobile Services in Dense Urban Areas: A Techno-economic Study2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The future mobile communication networks are expected to cope with growing local usage patterns especially in dense urban areas at more affordable deployment and operation expenses. Beyond leveraging small cell architectures and advanced radio access technologies; more radio spectrum are expected to be required to achieve the desired techno-economic targets. Therefore, the research activity has been directed towards discussing the benefits and needs for more flexible and local spectrum authorization schemes. This thesis work is meant to be a contribution to this ongoing discussion from a techno-economic perspective.

     

    In chapter three, the engineering value of the different flexible authorization options are evaluated from the perspective of established mobile network operators using the opportunity cost approach. The main results in chapter three indicate the economic incentives to deploy more small cells based on flexible spectrum authorization options are subject to the potential saving in the deployment and operation costs. Nonetheless; high engineering value can be anticipated when the density of small cells is equal or larger than the active mobile subscribers’ density.

     

    While in chapter four, the possible local business models around different flexible authorization options are investigated from the perspective of emerging actors with limited or ’no’ licensed spectrum resources. In this context, dependent or independent local business can be identified according to surrounding spectrum regulations. On possible independent local business models for those emerging actors is to exploit the different flexible spectrum authorization options to provision tailored local mobile services. Other viable dependent local business models rest with the possibility to enter into different cooperation agreements to deploy and operate dedicated local mobile infrastructure on behalf established mobile network operators.

  • 134.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Chatzimichail, Konstantinos
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Cavdar, Cicek
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Techno-economics of Green Mobile Networks Considering Backhauling2014In: European Wireless 2014; 20th European Wireless Conference; Proceedings of, Barcelona: VDE Verlag GmbH, 2014, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In this paper we consider a comparative analysis of different deployment solutions in terms of total cost of ownership (TCO) and impact of energy efficiency as a cost parameter, i.e. mobile operator's electric bill. Different deployment options for the wireless segment of the network are considered: macro only versus heterogeneous networks with femto cells to support indoor traffic demand. In addition to the wireless segment different technologies for the backhauling segment are also considered: microwave versus fiber (10G-PON). Considering different user traffic intensities in an urban area and different environments such as business and residential areas, the impact of energy consumption on the TCO has been analyzed. The scope of the paper is extended to compare different backhaul technologies considering the annual increase in the traffic demand up to year 2020. The obtained results indicate that the impact of electric bill becomes more significant over the TCO especially after year 2018. Moreover, the heterogeneous deployment strategy utilizing indoor femto-cells achieves significant savings in terms of electric bill and TCO compared to the macro only solution. However, the saving ratio varies according to the adopted backhauling technology.

  • 135.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Impact of the flexible spectrum aggregation schemes on the cost of future mobile network2015In: 2015 22nd International Conference on Telecommunications, ICT 2015, IEEE conference proceedings, 2015, p. 96-101Conference paper (Refereed)
    Abstract [en]

    Nowadays the spectrum regulations landscape is changing towards more flexible spectrum management schemes, such trends are expected to make additional spectrum resources available and lowers the spectrum access hurdles. In this paper, different spectrum aggregation scenarios have been compared focusing on the tradeoff between the total cost of ownership and the targeted QoS under different market conditions. The main finding in this study thereof indicates that the addition of more spectrum resources will lead to an overall reduction in the total cost of ownership (TCO) as long as the spectrum price remains small compared to the cost of the network infrastructure. Moreover, schemes such as LSA and secondary access will enable operators who have insufficient licensed spectrum resource to expand their mobile network infrastructure especially in hotspots with high subscribers demand in a cost-effective way. In this regard, the harmonization of spectrum use for LSA and TVWS across multiple countries stands as a key requirement for the reduction of the production cost of equipment and hence, the creation of an economy of scale considering both of the network equipment (i.e. radio base station) and end-subscriber devices. © 2015 IEEE.

  • 136.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Markendahl, Jan
    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.
    Cavdar, Cicek
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Interplay Between Cost,Capacity and Power Consumption in Heterogeneous Mobile Networks2014In: 2014 21st International Conference on Telecommunications, ICT 2014, Lisbon: IEEE Press, 2014, , p. 5p. 98-102Conference paper (Refereed)
    Abstract [en]

    Mobile operators nowadays tend to deploy dense heterogeneous layers of 3G and 4G networks in outdoor and indoor environments by adding more macrocells and small cells (e.g. microcells, picocells and femtocells) in response to the increasing demand for coverage and capacity. Another main driver and enabler behind this tendency is the phenomenon that around 80% of power consumption in mobile communication networks stems from the radio base stations. This situation makes mobile operators opt for the use of lowpower radio base stations to provide better coverage, capacity and an environmentally-friendly operation. In this paper the interplay between the deployment costs, targeted QoS and power consumptions have been studied considering two deployment options for the provisioning of the required mobile broadband coverage and capacity; namely the heterogeneous network (HetNet) option versus the homogenous macrocell deployment option. The main findings indicate that, the perceived saving in the total cost of ownership (TCO) resulting from offloading percentage of network traffic to indoor smallcell, in the case of HetNet, is bounded by the mobile subscriber density per area, their usage patterns, the adopted backhaul solution and the used spectrum resources. In general, a quite paying cost and power saving can be achieved by the heterogonous deployment solution for scenarios with high demand levels especially when there is a need to use the spectrum resources more efficiently.

  • 137.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Cavdar, Cicek
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Ghanbari, Amirhossein
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Study on the effects of backhual solutions on indoor mobile deployment "macrocell vs. femtocell"2013In: 2013 IEEE 24th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC), IEEE conference proceedings, 2013, p. 2444-2448Conference paper (Refereed)
    Abstract [en]

    The deployment of low cost and low power base stations has been recognized in recent years as a promising cost-efficient solution and energy-efficient strategy. In this paper the femtocell and macrocell deployment options have been compared in the context of indoor mobile broadband deployment, with focus on the effect of different backhauling solutions in power consumption and the total deployment cost. This study has been based on the deployment of mobile broadband services within an area of one square kilometers in a new densely populated business district where the different user demands, spectrum bandwidths, backhaul technologies and radio access technologies are taken into account. Moreover, various deployment scenarios reflecting the business perspectives of mobile operators have been looked into as well. The main findings reached indicate that backhaul solutions contribute differently to cost and power consumption depending on the employed deployment strategy. However, contributions to the total power consumption and to the CapEx and OpEx elements of the total deployment cost elements turned to be more significant in the case of femtocell deployment scenarios than in the case of macrocell ones. It is worthy of notice that the femtocell deployment is more cost-efficient, especially in high demand situation when new macro sites are needed to be deployed.

  • 138.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Ghanbari, Amirhossein
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Evaluation of Spectrum Access Options for Indoor Mobile Network Deployment2013In: 2013 IEEE 24th International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC Workshops), IEEE , 2013, p. 138-142Conference paper (Refereed)
    Abstract [en]

    The investments in indoor mobile networks are highly related to the spectrum availability and its associated authorization options. The aim of this paper is to discuss the differences in the spectrum demand taking into consideration both wide and local area network deployment requirements and the kind of actor that provides the indoor wireless access. The analysis covers different authorizations options namely licensed, unlicensed, licensed shared access (LSA) and secondary access. A quantitative approach is used to analyze the differences between macrocell and femtocell deployments focusing on deployment cost and spectrum demand. This is complemented by a qualitative study to explore and discuss the strategic business decisions of different actors in view of the available spectrum bands and spectrum authorization options. The main conclusions from this study are; spectrum has more value in macrocell deployment scenarios than in femtocell ones. More spectrum in macrocell deployment scenarios means that operators can deploy less number of new sites and exploit previous infrastructure investments. Femtocell networks are often coverage limited which allows for frequency re-use. As a consequence, the value of spectrum is not the same for mobile network operators (MNOs) and for local network operator (LNOs). MNOs are traditionally confined to macrocell deployment strategies which entail the exclusive usage of licensed bands. While, the use of licensed spectrum by LNOs may incur more cost than the cost of infrastructure deployment. This explains why the use of unlicensed bands is lucrative and viable for LNOs. Furthermore, the LSA scheme may or could soon become an enabler for LNO's business due to the prevailing technical, regulation and policies developments.

  • 139.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Ghanbari, Amirhossein
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Investment strategies for different actors in indoor mobile market: "in view of the emerging spectrum authorization schemes"2013In: 24th European Regional Conference of the International Telecommunication Society, Florence, Italy, 20-23 October 2013, 2013Conference paper (Refereed)
    Abstract [en]

    The regulatory landscape is changing towards more flexible spectrum management schemes. Such schemes are expected to make additional spectrum resources available and lower the spectrum access barriers. Emerging spectrum authorization schemes such as secondary access (TV White Space) and Licensed Shared Access (LSA) are expected to open doors for new actors rather than traditional MNOs to access licensed spectrum resources at reasonable costs. These schemes will allow actors such as Facility Owners (FO), Mobile Virtual Network Operators (MVNO) and Internet Service Providers (ISPs) to invest in indoor mobile network infrastructure. These actors can act as Local Network Operators (LNO) and build their business models around provisioning of mobile services in locations where there seems to be a hole or lack of service coverage in a particular area within the mobile network operators (MNOs) service footprint. This paper highlights the differences between indoor deployment and outdoor deployment in the light of the available spectrum bands to be used and the possible business models for MNOs and LNOs. In short, the possible investment strategies for provisioning indoor mobile services vary between MNOs and LNOs cases due to economic and regulatory aspects surrounding them. The main finding in this study indicates that the willingness of MNOs to invest in dedicated indoor solutions is driven by the balance between the potential revenues and the deployment cost. Moreover MNOs have more spectrum and investment options compared to LNOs who must bond their investment strategies to the available spectrum resources (i.e. the regulations of spectrum access).

  • 140.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Ghanbari, Amirhossein
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    The Incentives and Challenges of Delivering Linear Broadcasting Services over Cellular Network in Developing Countries: Sudan as Case study2014In: The 25th European Regional Conference of the International Telecommunications Society,Brussels, Belgium, 22nd - 25th June 2014, Brussels: nternational Telecommunications Society , 2014Conference paper (Other academic)
    Abstract [en]

    The Broadcasting sector has been evolved in terms of service production, transmission platform and reception devices in the last few decades. In contrast to cable and satellite platform, which are suitable for fixed reception only, the terrestrial digital platform can support portable, mobile and fixed reception scenarios. In general, there are two options of mobile multimedia service; one is based on a mobile communication network with IP cast known as MBMS (Multimedia Broadcast Multicast Services), while the other is based on broadcast technology. In the context of convergence, the players in the mobile sector argues that unlike traditional mobile  network systems, where the use was restricted to a given application, emerging  mobile networks will be able to carry a variety of services and accordingly separate broadcasting networks will no longer be required. In line with argument, it is not economically viable to roll out dedicated wireless broadband networks by the broadcasters to meet the increasing demand for interactive broadcasting services. That is why the broadcasters may look for innovative mechanism to deliver the broadcast services over mobile broadband network owned by the telecommunication operators.

    The focus on this paper is to investigate the incentives and challenges for such trend in developing countries; taking Sudan as case study. The main conclusion in this paper indicate that a potential economic incentive for delivering the broadcasting service over cellular network in Sudan subject to the deployment of high efficient mobile network. Moreover, the mobile operators may consider support such approach considering the increase demand for additional frequency resource.  However, the key challenges remain in how to develop a suitable regulations landscape to assure fair and competitive business practices on hand while guaranteeing the continuation of the public broadcasting service. In this regard, a new regulation framework needs to be developed to separate the three key functions in digital terrestrial broadcasting value chain (namely the content production and distribution). Further on, the necessary interconnection regulations need to put on place in order to pave the way for rollout of common platform that are necessary for interactive and nonlinear services. 

  • 141.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Ghanbari, Amirhossein
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Toward capacity-efficient, cost-efficient and power-efficient deployment strategy for indoor mobile broadband2013In: 24th European Regional ITS Conference, Florence 2013, 2013Conference paper (Refereed)
    Abstract [en]

    Mobile operators nowadays tend to deploy dense heterogeneous layers of 3G and 4G networks in outdoor and indoor environments by adding more macrocells and smallcells (e.g. microcells, picocells and femtocells) in response to the increasing subscriber demand for coverage and capacity. The main driver and enabler behind this tendency is the phenomenon that around 80% of power consumption in mobile communication networks stems from the radio base stations. This situation makes mobile operators opt for the use low-power radio base stations to provide better coverage, capacity and a more environment-friendly operation. The use of low-power radio base stations leads to reduction of energy consumption in mobile communication networks power. The aim of this study is to conduct a comparative study between homogenous macrocell deployment and indoor smallcell deployments as alternative solutions for provision of the required indoor coverage and capacity. Moreover, the study highlights the importance of backhaul solutions being critical components in the smallcell network deployment. Furthermore, the scope of the study is extended to cover the investigation of the value of the heterogeneous (i.e. hybrid marcocell-femtocell) deployment scenario as a cost and power-efficient solution versus the homogenous marcocell deployment scenario in view of the variations in the mobile network traffic during the day. The main findings indicate that the CapEx and OpEx of the backhaul solution represent the major part of the total deployment cost in the indoor smallcell deployment scenario (i.e. femtocell case) compared to those of the macrocell deployment scenario. Nonetheless, the perceived saving in the total cost of ownership (TCO) resulting from the use of indoor smallcell (i.e. femtocell) remains a satisfactory and convenient motivation considering the traffic variation across the day, traffic distribution between indoor and outdoor locations and the keenness to use the spectrum resources more efficiently.

  • 142.
    Ahmed, Ashraf
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Yang, Yanpeng
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Won Sung, Ki
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    On the Engineering Value of Spectrum in Dense Mobile Network Deployment Scenarios2015Conference paper (Refereed)
    Abstract [en]

    the continuing growth in the mobile data traffic magnifies the challenges for the design and deployment of scalable high-capacity mobile networks that can meet the future demand at reasonable cost levels. In order to meet the future traffic demand, an operator should invest on both infrastructure, i.e. densification of base stations, and more radio spectrum. Knowing the effectiveness of each element is thus of utmost importance for minimizing the investment cost. In this paper, we study the economic substitutability between spectrum and densification. For this, we measure the engineering value of spectrum, which refers to the potential saving in the total cost of ownership (TCO) as result of acquiring additional spectrum resources. Two countries are considered to represent different market situations: India with dense population and high spectrum price and Sweden with moderate population density and low spectrum fee. Numerical results indicate that additional amount of spectrum substantially relieves the need for densifying radio base stations, particularly for providing high user data rate in dense India. Nonetheless, the engineering value of spectrum is low in India (i.e. spectrum acquisition has less cost benefit) under the high spectrum price of today, whereas spectrum is instrumental in lowering the total cost of ownership in Sweden. Our finding highlights the importance of affordable and sufficient spectrum resources for future mobile broadband provisioning.

  • 143.
    Ahmed, Furqan
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Alfredo Dowhuszko, Alexis
    Tirkkonen, Olav
    Self-Organizing Algorithms for Interference Coordination in Small Cell Networks2017In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 66, no 9, p. 8333-8346Article in journal (Refereed)
    Abstract [en]

    This paper discusses novel joint (intracell and intercell) resource allocation algorithms for self-organized interference coordination in multicarrier multiple-input multiple-output (MIMO) small cell networks. The proposed algorithms enable interference coordination autonomously, over multiple degrees of freedom, such as base station transmit powers, transmit precoders, and user scheduling weights. A generic a-fair utility maximization framework is considered to analyze performance-fairness tradeoff and to quantify the gains achievable in interference-limited networks. The proposed scheme involves limited inter-base station signaling in the form of two step (power and precoder) pricing. Based on this decentralized coordination, autonomous power and precoder update decision rules are considered, leading to algorithms with different characteristics in terms of user data rates, signaling load, and convergence speed. Simulation results in a practical setting show that the proposed pricing-based self-organization can achieve up to 100% improvement in cell-edge data rates when compared to baseline optimization strategies. Furthermore, the convergence of the proposed algorithms is also proved theoretically.

  • 144.
    Ahmed, Haroon
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Sund, Gabriel
    KTH, School of Information and Communication Technology (ICT).
    Security challenges within Software Defined Networks2014Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    A large amount of today's communication occurs within data centers where a large number of virtual servers (running one or more virtual machines) provide service providers with the infrastructure needed for their applications and services. In this thesis, we will look at the next step in the virtualization revolution, the virtualized network. Software-defined networking (SDN) is a relatively new concept that is moving the field towards a more software-based solution to networking. Today when a packet is forwarded through a network of routers, decisions are made at each router as to which router is the next hop destination for the packet. With SDN these decisions are made by a centralized SDN controller that decides upon the best path and instructs the devices along this path as to what action each should perform. Taking SDN to its extreme minimizes the physical network components and increases the number of virtualized components. The reasons behind this trend are several, although the most prominent are simplified processing and network administration, a greater degree of automation, increased flexibility, and shorter provisioning times. This in turn leads to a reduction in operating expenditures and capital expenditures for data center owners, which both drive the further development of this technology.

    Virtualization has been gaining ground in the last decade. However, the initial introduction of virtualization began in the 1970s with server virtualization offering the ability to create several virtual server instances on one physical server. Today we already have taken small steps towards a virtualized network by virtualization of network equipment such as switches, routers, and firewalls. Common to virtualization is that it is in early stages all of the technologies have encountered trust issues and general concerns related to whether software-based solutions are as rugged and reliable as hardwarebased solutions. SDN has also encountered these issues, and discussion of these issues continues among both believers and skeptics. Concerns about trust remain a problem for the growing number of cloud-based services where multitenant deployments may lead to loss of personal integrity and other security risks. As a relatively new technology, SDN is still immature and has a number of vulnerabilities. As with most software-based solutions, the potential for security risks increases. This thesis investigates how denial-of-service (DoS) attacks affect an SDN environment and a singlethreaded controller, described by text and via simulations.

    The results of our investigations concerning trust in a multi-tenancy environment in SDN suggest that standardization and clear service level agreements are necessary to consolidate customers’ confidence. Attracting small groups of customers to participate in user cases in the initial stages of implementation can generate valuable support for a broader implementation of SDN in the underlying infrastructure. With regard to denial-of-service attacks, our conclusion is that hackers can by target the centralized SDN controller, thus negatively affect most of the network infrastructure (because the entire infrastructure directly depends upon a functioning SDN controller). SDN introduces new vulnerabilities, which is natural as SDN is a relatively new technology. Therefore, SDN needs to be thoroughly tested and examined before making a widespread deployment.

  • 145.
    Ahmed, J
    et al.
    KTH.
    Monti, Paolo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Spadaro, S
    Enhancing restoration performance using service relocation in PCE-based resilient optical clouds2014In: Conference on Optical Fiber Communication, Technical Digest Series, 2014Conference paper (Refereed)
    Abstract [en]

    This paper investigates the benefits of dynamic restoration with service relocation in resilient optical clouds. Results from the proposed optimization model show that service availability can be significantly improved by allowing a few service relocations.

  • 146.
    Ahmed, Jawwad
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Dynamic Resource Provisioning and Survivability Strategies in Optical Networks2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Optical networks based on Wavelength Division Multiplexing (WDM) technology show many clear benefits in terms of high capacity, flexibility and low power consumption. All these benefits make WDM networks the preferred choice for today’s and future transports solutions which are strongly driven by a plethora of emerging online services.

    In such a scenario, capability to provide high capacity during the service provisioning phase is of course very important, but it is not the only requirement that plays a central role. Traffic dynamicity is another essential aspect to consider because in many scenarios, e.g., in the case of real time multimedia services, the connections are expected to be provisioned and torn down quickly and relatively frequently. High traffic dynamicity may put a strain on the network control and management operations (i.e., the overhead due to control message exchange can grow rapidly) that coordinate any provisioning mechanisms. Furthermore, survivability, in the presence of new failure scenarios that goes beyond the single failure assumption, is still of the utmost importance to minimize the network disruptions and data losses. In other words, protection against any possible future failure scenario where multiple faults may struck simultaneously, asks for highly reliable provisioning solutions.

    The above consideration have a general validity i.e., can be equally applied to any network segment and not just limited to the core part. So, we also address the problem of service provisioning in the access paradigm. Long reach Passive Optical Networks (PONs) are gaining popularity due to their cost, reach, and bandwidth advantages in the access region. In PON, the design of an efficient bandwidth sharing mechanism between multiple subscribers in the upstream direction is crucial. In addition, Long Reach PONs (LR-PONs) introduces additional challenges in terms of packet delay and network throughput, due to their extended reach. It becomes apparent that effective solutions to the connection provisioning problem in both the core and access optical networks with respect to the considerations made above can ensure a truly optimal end-to-end connectivity while making an efficient usage of resources.

    The first part of this thesis focuses on a control and management framework specifically designed for concurrent resource optimization in WDM-based optical networks in a highly dynamic traffic scenario. The framework and the proposed provisioning strategies are specifically designed with the objective of: (i) allowing for a reduction of the blocking probability and the control overhead in a Path Computation Element (PCE)-based network architecture, (ii)  optimizing resource utilization for a traffic scenario that require services with diverse survivability requirements which are achieved by means of  dedicated and shared path-protection, and (iii) designing provisioning mechanism that guarantees high connection availability levels in Double Link Failures (DLF) scenarios. The presented results show that the proposed dynamic provisioning approach can significantly improve the network blocking performance while making an efficient use of primary/backup resources whenever protection is required by the provisioned services. Furthermore, the proposed DLF schemes show good performance in terms of minimizing disruption periods, and allowing for enhanced network robustness when specific services require high connection availability levels.

    In the second part of this thesis, we propose efficient resource provisioning strategies for LR-PON. The objective is to optimize the bandwidth allocation in LR-PONs, in particular to: (i) identify the performance limitations associated with traditional (short reach) TDM-PON based Dynamic Bandwidth Allocation (DBA) algorithms when employed in long reach scenarios, and (ii) devise efficient DBA algorithms that can mitigate the performance limitations imposed by an extended reach. Our proposed schemes show noticeable performance gains when compared with conventional DBA algorithms for short-reach PON as well as specifically devised approaches for long reach.

  • 147.
    Ahmed, Jawwad
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Cavdar, Cicek
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Monti, Paolo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    A Dynamic Bulk Provisioning Framework for Concurrent Optimization in PCE-Based WDM Networks2012In: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 30, no 14, p. 2229-2239Article in journal (Refereed)
    Abstract [en]

    A centralized network control and management plane, such as the one based on a path computation element (PCE), is highly beneficial in terms of resource optimization in wavelength division multiplexing optical networks. Benefits of centralized provisioning are even more evident when connection requests are provisioned in batches, i.e., they allow a better use of network resources via concurrent optimization. In this study, a dynamic bulk provisioning framework is presented with the objective of optimizing the use of network resources that also presents, as an additional benefit, the ability to yield a reduction of the control plane overhead. The rationale behind the proposed framework is based on a mechanism in which the PCE client is allowed to bundle and simultaneously send multiple labeled switch path (LSP) requests to the PCE where, in turn, several bundles can be concurrently processed together as a single bulk. From the network deployment perspective, a PCE-based network architecture is proposed to practically realize this approach. For dynamic bulk provisioning of optical LSP requests, a time-efficient integer linear programming (ILP) model (LSP BP ILP) is presented to minimize the request blocking, the network resource consumption, and the network congestion. In addition, a heuristic based on a greedy randomized adaptive search procedure (GRASP), namely LSP_BP_GRASP, is also proposed as a scalable alternative. The presented results demonstrate significant advantages of the proposed PCE bulk provisioning framework based on concurrent optimization in terms of reduced blocking probability and control overhead when compared with conventional dynamic connection provisioning approaches processing a single connection request at a time.

  • 148.
    Ahmed, Jawwad
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Photonics (Closed 20120101).
    Cavdar, Cicek
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Photonics (Closed 20120101).
    Monti, Paolo
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Photonics (Closed 20120101).
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Photonics (Closed 20120101).
    An Optimal Model for LSP Bundle Provisioning in PCE-based WDM Networks2011In: 2011 Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference, OFC/NFOEC 2011, Washington: Optical Society of America , 2011Conference paper (Refereed)
    Abstract [en]

    A time-efficient resource optimization model for dynamic concurrent provisioning of connection requests at PCE is proposed. It is shown that a significant performance improvement can be achieved without noticeable increase in connection setup-time.

  • 149.
    Ahmed, Jawwad
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Photonics (Closed 20120101).
    Cavdar, Cicek
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Photonics (Closed 20120101).
    Monti, Paolo
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Photonics (Closed 20120101).
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Photonics (Closed 20120101).
    Bulk provisioning of LSP requests with shared path protection in a PCE-based WDM network2011In: ONDM 2011 - 15th Conference on Optical Network Design and Modeling, 2011Conference paper (Refereed)
    Abstract [en]

    The Path Computation Element (PCE) is a network entity utilized for network path computation operations, especially useful in optical networks based on wavelength division multiplexing (WDM). In the PCE paradigm, the communication between a node and the PCE is specified by the Path Computation Element Communication Protocol (PCEP). According to PCEP protocol, multiple LSP (Label Switched Path) requests can be bundled together before being sent to the PCE in order to reduce the control overhead. Multiple bundles received by the PCE can then be provisioned at once as a single bulk. Enabling bulk provisioning of LSP requests at the PCE in a concurrent manner can bring significant improvements in terms of higher network resource utilization and control plane overhead reduction. However, these advantages come at a cost of a longer connection setup-time and of an instantaneous increase in the network load, which may lead to a degradation of the network performance, e.g. blocking probability. In this study pros and cons of bulk provisioning are explored in shared path protection (SPP) by comparing sequential and concurrent path computation strategies. An efficient meta-heuristic named GRASP-SPP-BP (Greedy Random Adoptive Search Procedure for Shared Path Protection with Bulk Provisioning) is proposed for concurrent provisioning of primary and shared backup path pairs. GRASP-SPP-BP minimizes the backup resource consumption while requiring minimal path computation time. The presented results demonstrate that, in a SPP network scenario, a significant reduction in the PCEP control overhead, network blocking probability and backup resource consumption can be achieved via LSP bulk provisioning at the PCE with the proposed GRASP-SPP-BP approach.

  • 150.
    Ahmed, Jawwad
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Cavdar, Cicek
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Monti, Paolo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Hybrid Survivability Schemes Achieving High Connection Availability With a Reduced Amount of Backup Resources2013In: Journal of Optical Communications and Networking, ISSN 1943-0620, E-ISSN 1943-0639, Vol. 5, no 10, p. A152-A161Article in journal (Refereed)
    Abstract [en]

    Maximizing connection availability in WDM networks is critical because even small disruptions can cause huge data losses. However, there is a trade-off between the level of network survivability and the cost related to the backup resources to be provided. The 100% survivability can be achieved by dedicated path protection with multiple pre-reserved protection paths for each provisioned connection, i.e., DPP (1:N). Unfortunately, the blocking probability performance of DPP (1:N) is negatively affected by the large number of pre-reserved backup wavelengths standing-by unutilized. On the other hand, path restoration (PR)-based solutions ensure good blocking performance at the expense of lower connection availability.

    The work in this paper aims at finding hybrid network survivability strategies that combine the benefits of both techniques (i.e., high availability with low blocking rate). More specifically, the paper focuses on a double link failure scenario and proposes two strategies. The first one, couples dedicated path protection DPP (1:1) with path restoration (referred to as DPP + PR) to minimize the number of dropped connections. The second scheme adds up the concept of backup reprovisioning (BR), referred to as DPP + BR + PR, in order to further increase the connection availability achieved by DPP + PR. Integer Linear Programming (ILP) models for the implementation of the proposed schemes are formulated. Extensive performance evaluation conducted in a PCE-based WDM network scenario shows that DPP + BR + PR and DPP + PR can significantly lower the blocking probability value compared to DPP (1:2) without compromising too much in terms of connection availability.

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