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Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks and Workshops, 2008. WiOPT 2008. 6th International Symposium on

Date 1-3 April 2008

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Displaying Results 1 - 25 of 149
  • Proceedings of the 6th intl. symposium on modeling and optimization Wiopt 2008

    Publication Year: 2008 , Page(s): i
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  • WiOpt 2008 — Message from the general chairs

    Publication Year: 2008 , Page(s): ii
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    Freely Available from IEEE
  • [Copyright notice]

    Publication Year: 2008
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    Freely Available from IEEE
  • Steering Committee

    Publication Year: 2008 , Page(s): iv
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  • Organizing Committee

    Publication Year: 2008 , Page(s): v
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  • Technical Program Committee

    Publication Year: 2008 , Page(s): vi
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  • Table of contents

    Publication Year: 2008 , Page(s): vii - xiv
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  • Wiopt 2008 Paper track — Session 1

    Publication Year: 2008 , Page(s): 1
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  • Programmable active emulation of wireless systems — A DVB-RCS example

    Publication Year: 2008 , Page(s): 2 - 7
    Cited by:  Papers (1)
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    This paper presents a DVB-RCS satellite emulation system built using the NPBox programmable network emulation system. NPBox allows system components to be modeled both at a higher abstraction level using a finite-state-machine like abstraction, and also at a lower level using customized event guards and actions. Comparison experiments show that the emulated performance is similar to that of a complex low-level emulator. View full abstract»

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  • An experimental investigation of VoIP and video streaming over fixed WiMAX

    Publication Year: 2008 , Page(s): 8 - 15
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    Despite the significant interest in WiMAX technology and deployment, there are very few publicly reported measurements from testbeds and field trials. As such, most WiMAX studies employ simulation and modeling. This paper contributes to our understanding of what is realistically possible using off-the-shelf fixed WiMAX equipment today. We employ multiple competing traffic sources over a point-to-multipoint WiMAX topology and measure the capacity of the WiMAX equipment to handle a multitude of VoIP flows between subscriber stations while delivering a variable number of video streams. We measure throughput, packet loss, and one-way delay for both line-of-sight (LOS) and non-line-of-sight (NLOS) conditions. For the one-way delay measurements we synchronize the clocks of all testbed hosts with a software-only, open source implementation of the IEEE 1588 Precision Time Protocol. We compare these one-way delay measurements with those obtained when GPS-based synchronization is used. View full abstract»

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  • Effect of 802.11 adaptive exponential backoffs on the fluidity of downlink flows in mesh networks

    Publication Year: 2008 , Page(s): 16 - 22
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (481 KB) |  | HTML iconHTML  

    Efficient multihop traffic management is a need for successful Wireless Mesh Networks (WMNs) deployment. Using an analogy with fluid mechanism, we classify a flow as laminar if the packets flow smoothly from the Wired Access Point (WAP) over the mesh network, and as turbulent otherwise. We identify a particular but frequent collision scenario, which sets the flow to be turbulent, resulting in a strongly reduced downlink end-to-end throughput. We show that the exponential backoff mechanism in an 802.11 WMN is responsible for this problem and suggest a modification of the current exponential backoff policy of 802.11 for WMNs. We support these findings both with simulations and real measurements on a testbed infrastructure. View full abstract»

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  • Wiopt 2008 Paper track - Session 2

    Publication Year: 2008 , Page(s): 23
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  • The effect of using directional antennas on adjacent channel interference in 802.11a: Modeling and experience with an outdoors testbed

    Publication Year: 2008 , Page(s): 24 - 29
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (878 KB) |  | HTML iconHTML  

    We present an outdoors 802.11a testbed based on off-the-shelf components that we used for multi-radio node experimentation. This is the first such testbed, to our knowledge, equipped with directional antennas. With it we conducted a thorough and systematic set of measurements, in medium range outdoors links, to examine how the physical separation of the antennas, the output power of the interfaces, and the channel separation of the links affect throughput. For the setup of the testbed and to estimate the induced ACI we utilized a theoretical model, already verified on an in-lab wireless testbed emulator [Angelakis, 2008]. We discuss how the model needs to adapt and propose to create a tool for the design of large scale multi-radio wireless networks. View full abstract»

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  • Collecting broken frames: Error statistics in IEEE 802.11b/g links

    Publication Year: 2008 , Page(s): 30 - 35
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (324 KB) |  | HTML iconHTML  

    We present a measurement method that allows to capture the complete set of all PSDU (PLCP Service Data Unit) transmissions and receptions in live IEEE 802.11b/g links with very high timing resolution. This tool provides an in-depth view of the statistics of frame-losses as it makes it possible to distinguish between different loss types such as complete miss, partial corruption and physical-layer capture. Getting access to this low-level statistics on nodes that actively participate in transmissions themselves is a challenging task since the software-interface provided to the network layer needs to remain untouched and cannot be used for tracing. In this contribution we describe in detail how to non-intrusively circumvent these restrictions and also present initial results. View full abstract»

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  • Energy and link measurements for mobile phones using IEEE802.11b/g

    Publication Year: 2008 , Page(s): 36
    Cited by:  Papers (4)
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    The document that should appear here is not currently available. View full abstract»

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  • Wiopt 2008 Paper track - Session 3

    Publication Year: 2008 , Page(s): 36a
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  • Analysis and detection of bottlenecks via TCP footprints in live 3G networks

    Publication Year: 2008 , Page(s): 37 - 42
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (270 KB) |  | HTML iconHTML  

    In this paper we evaluate four different metrics for non intrusive bottleneck detection based on TCP counters. This work is based on the full TCP statistics recorded on five days spread over the last one and a half year within the core network of a mobile network operator in Austria. Scatterplots, so called ldquofootprintsrdquo, were generated counting the number of packets and the number of retransmission for each user during the peak hours. Two of the datasets had a known capacity bottleneck in place. Based on those datasets we benchmarked the different metrics for the detection of a bottleneck event. We preprocessed the traces in order to remove the traffic increase. After this step all metrics were able to detect the special bottleneck case. Even traces separated for more than one year deliver a clear result. The performance of a PSNR metric was similar to the other metrics based on more sophisticated functions. View full abstract»

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  • Spurious TCP timeouts in 802.11 networks

    Publication Year: 2008 , Page(s): 43 - 49
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1886 KB) |  | HTML iconHTML  

    In this paper, we investigate spurious TCP timeouts in 802.11 wireless networks. Though timeouts can be a problem for uploads from an 802.11 network, these timeouts are not spurious but are caused by a bottleneck at the access point. Once this bottleneck is removed, we find that spurious timeouts are rare, even in the face of large changes in numbers of active stations or PHY rate. View full abstract»

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  • Wiopt 2008 The worst-case capacity of wireless networks - Roger Wattenhofer (ETHZ)

    Publication Year: 2008 , Page(s): 50
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  • Wiopt 2008 Paper track - Session 1

    Publication Year: 2008 , Page(s): 51
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  • Node Interaction in 802.11 based networks with boolean interference

    Publication Year: 2008 , Page(s): 52 - 57
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (154 KB) |  | HTML iconHTML  

    Wireless local area networks (WLANs) have been extensively studied over the past several years. So far, research has primarily focussed on scenarios where all nodes in the network can hear each other. The present paper discusses interaction between nodes in a more complex setting, where nodes may only hear parts of the network. The analysis relies on a Markov process that keeps track of the activity of nodes. Return times and hitting probabilities in this process are related to interaction phenomena in the wireless network and examples are given to illustrate how these can be used to predict network performance. The approximations are validated through simulations. View full abstract»

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  • Efficient quantization for feedback controlled networks with type II hybrid ARQ

    Publication Year: 2008 , Page(s): 58 - 63
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    This paper addresses feedback design issues in ad hoc networks with simultaneous access of multiple users, when type II HARQ exploits a constrained capacity reverse channel. In such networks, communications performance is limited by interference and nodes operate in a distributed fashion; thus, efficient resource allocation relies on proper feedback signaling, which on the other hand can use only a limited amount of network resources. For this reason, we investigate how to determine a finite set of feedback messages, which accounts for the underlying type II HARQ error control and jointly regulates power allocation and medium access in an optimal manner. View full abstract»

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  • Wiopt 2008 Paper track - Session 2

    Publication Year: 2008 , Page(s): 64
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  • A closed power allocation solution for outage restricted distributed MIMO multi-hop networks

    Publication Year: 2008 , Page(s): 65 - 70
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (152 KB) |  | HTML iconHTML  

    Power consumption and Quality-of-Service are the critical factors when developing resource allocation strategies for wireless networks. In order to minimize total transmission power while meeting the end-to-end outage probability requirement in a distributed MIMO multi-hop network, we will formulate the power allocation task as a convex optimization problem. By using some approximations to the optimization problem, we derive a novel near-optimal power allocation solution with lower complexity for distributed MIMO multi-hop networks. For the network with a large number of relaying nodes per virtual antenna array even a simple closed-form solution can be obtained. The simulation results show that our solution achieves a near-optimal performance. View full abstract»

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  • QoS provisioning in wireless data networks under non-continuously backlogged users

    Publication Year: 2008 , Page(s): 71 - 76
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (495 KB) |  | HTML iconHTML  

    This paper addresses the problem of efficient resource allocation in CDMA wireless networks, supporting non-real-time services with various long-term QoS requirements, by exploiting the advantages of opportunistic scheduling. Most of the existing work covers the analysis of the system under the assumption of infinite backlogs. In this paper, we remove this assumption and analyze the behavior of the system with respect to its overall achievable performance and its ability to gratify userspsila individual QoS requirements under different fundamental opportunistic scheduling policies, for the more realistic case of non-continuously backlogged users. Motivated by the corresponding results that indicate the unsatisfactory performance of these schedulers when considering finite backlogs, and in order to overcome these inefficiencies, a new non-work-conserving opportunistic scheduling framework is proposed which is seamlessly integrated within the operation of the various schedulers. The corresponding results demonstrate that the proposed approach results in the fulfillment of userspsila QoS prerequisites while still maintaining the opportunistic nature of the schedulers and thus achieving high system throughput. View full abstract»

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