Campuses:

Reception and Poster Session

Monday, June 27, 2005 - 5:00pm - 6:30pm
Lind 400
  • Reduction of Complexity for Systems Involving A Discrete-time Markov Chain: Time-scale Separation
    George Yin (Wayne State University)Qing Zhang (University of Georgia)
    Many problems in wireless communications involve a
    discrete-time Markov chain. Often, the state space of the Markov
    chain is inevitably large. To reduce the computation complexity
    becomes a practical concern. This poster presents a brief summary on
    recent developments for such systems. To achieve the goal of complexity
    reduction, time-scale separation and singular perturbation techniques are
    used in the modeling and analysis. Asymptotic expansions of probability
    vectors and structural properties of the Markov chain are provided
    together with near optimality in related control problem and Markov
    decision processes.
  • Temporal Properties of Congestion Events in Networks with

    Fractional Brownian Traffic

    Yasong Jin (University of Kansas)
    In packet networks congestion events tend to persist, producing large
    delays and long bursts of consecutive packet loss resulting in perceived
    performance degradations. The length and rate of these events have a
    significant effect on network quality of service (QoS). The packet delay
    resulting from these congestion events also influences QoS. A technique
    for predicting these properties of congestion events, such as, the
    inter-congestion events time and the congestion duration, is developed in
    the presence of fractional Brownian Motion (fBM) traffic.
  • Particle Filtering in Wireless Communications
    Alain Tchagang (University of Minnesota, Twin Cities)
    With the increase use of wireless communication systems, the demand for
    fast and reliable filtering algorithm capable of coping with difficult
    transmission conditions is becoming more and more prevalent. Physical
    limitations and impairments of wireless channels, including multi-access
    and co-channel interference, time-variation and frequency selectivity,
    present a major technical challenge to the reliable transmission over a
    wireless link. The task can be greatly facilitated by the use of an
    efficient signal processing technique. In this poster, we present an
    overview and the application of particle filtering to the problems
    associated with transmission in wireless communications.
  • High-Throughput Random Access Via PHY-Layer Opportunism and Interference

    Cancellation

    Yingqun Yu
    We consider two cross-layer design examples of high-throughput random
    access schemes via PHY-layer opportunism and interference cancellation.
    The first example is the so-called channel-aware slotted Aloha, which
    can exploit fading by effecting decentralized multi-user diversity. For
    continuous channels with analog amplitude, we prove the optimality of
    binary scheduling in terms of sum-throughput for homogeneous systems and
    in terms of sum-log-throughput for heterogeneous systems. For finite
    state Markov chain (FSMC) channels, we provide a convex formulation of
    the corresponding throughput optimization problem, and derive a simple
    binary-like access strategy.

    The second example is SICTA, a contention tree algorithm with
    successive interference cancellation (SIC). The conventional random
    access algorithms, including tree algorithms (TAs), have relatively low
    throughput, since collided packets are typically discarded when packet
    collisions happen. We develop a novel protocol exploiting successive
    interference cancellation in a tree algorithm, where collided packets
    are reserved for reuse. We show that SICTA with binary splitting and
    gated access can achieve a throughput of 0.693, which represents about
    40% increase in throughput over the renowned 0.487
    first-come-first-serve (FCFS) tree algorithm.
  • Effective capacity approach to providing statistical

    quality-of-service guarantees in wireless networks

    Dapeng Wu (University of Florida)
    The next-generation wireless networks are targeted at supporting
    various applications such as voice, data, and multimedia with diverse
    quality of service (QoS) requirements. To provide explicit QoS
    guarantees such as a data rate, delay bound, and delay-bound violation
    probability triplet, it is necessary to analyze a QoS provisioning
    system in terms of these QoS measures. This task requires
    characterization of the service (channel modeling), and queueing
    analysis of the system. However, the existing channel models such as
    finite-state Markov chain models, do not explicitly characterize a
    wireless channel in terms of these QoS measures. This leads to high
    complexity in characterizing the relation between the control
    parameters of QoS provisioning and the calculated QoS measures.

    Recognizing that the above difficulty is the lack of a channel model
    that can easily relate the control parameters of a QoS provisioning
    system to the QoS measures, we propose and develop a link-layer
    channel model termed the effective capacity (EC) model. The EC model
    captures the effect of channel fading on the queueing behavior of the
    link, using a computationally simple yet accurate model, and thus, is
    a critical tool for designing efficient QoS provisioning mechanisms.
    Such an approach to channel modeling and QoS provisioning, is called
    effective capacity approach. In this poster, I will present our
    effective capacity approach to channel modeling.
  • A Charged Van der Waals Equation of State and Order-Decreasing Lattice-Path Mappings
    Dov Chelst (DeVry University)
    One can successfully modify a standard derivation of a van der Waals
    equation of state (see Lebowitz and Penrose, Journal of Math. Phys.
    1966) to accomodate a system of charged particles. Along the way,
    significant modifications to the original arguments must be made to
    accomodate the long-range nature of the Coulomb potential. Particularly,
    in a one-dimension two-component plasma, a purely combinatorial result
    regarding lattice path mappings proves useful. I will define the term
    order-decreasing mapping, to explain the nature of the combinatorial
    result and its connection to the original statistical mechanical
    problem. In addition, I will discuss attempts at generalizing the
    mathematical result in order to accomodate a wider class of physical
    systems.
  • Wireless Local Area Network Simulation
    Martin Eiger (Telcordia)
    We describe a software system that simulates wireless local area networks supporting heterogeneous services and multiple
    protocols. We present applications of this system in three areas: analysis of voice capacity, maximization of data throughput while
    protecting voice quality of service, and the design and evaluation of scheduling algorithms in a polling-based system.
  • Bandwidth Guaranteed Provisioning in Network-Based Mobile VPNs
    Katherine Guo (Alcatel-Lucent Technologies Bell Laboratories)
    Provision of VPN services to mobile customers is a revenue
    generating opportunity for Network Service Providers (NSPs). To
    provide network-based Mobile-VPN services, the NSPs terminate the
    VPN sessions from remote mobile users within the NSP network and
    aggregate VPN traffic destined to the same enterprise intranet
    onto one or a few VPN sessions from within the network to the
    enterprise VPN gateway. In between, value-added services are
    provided for this customer traffic.

    We propose the use of a hierarchical network
    architecture to efficiently realize network-based Mobile VPNs. The
    hierarchical architecture consists of three main components:
    a) the Mobile Access Point (MAP), b) the IP Services
    Gateway (IPSG), and c) the enterprise VPN gateway or the
    Customer Premise Equipment (CPE). We address the problem of
    provisioning customers on the IP Service Gateways (IPSGs) in a
    bandwidth constrained network such that the profit realized by the
    NSP by delivering Mobile-VPN services is maximized. The parameters
    considered in the optimization problem include the cost of
    provisioning customers on the IPSGs, the bandwidth capacity of
    links on the network, the bandwidth cost and the revenue that a
    NSP realizes from a customer.

    We derive an integer programming formulation for the problem and
    provide solutions for a few practical cases. The results provide
    insights into the design of Mobile-VPN service architectures and
    illustrates the different trade-offs that are involved.
  • Capacity-approaching LDPC Codes Based on Markov Chain Monte Carlo MIMO Detection
    Rong-Rong Chen (The University of Utah)
    We study joint code design and MIMO (multiple-input multiple-output)
    detection based on Markov Chain Monte Carlo (MCMC) approach. The MCMC
    detector is highly effective for large antenna systems because it has a
    much lower complexity than traditional MIMO detectors including the sphere
    decoding detector. We apply the extrinsic information transfer (EXIT)
    technique to find optimal irregular LDPC codes that are matched to the
    characteristics of the MCMC detector. For a large system of 8 transmit and
    8 receive antennas and 16 QAM modulation, the optimized LDPC code achieves
    within 1.4 dB of the channel capacity. This result improves best published
    results by 2.3 dB, where 1.3 dB is due to the MCMC detection and 1 dB is
    due to code optimization.
  • Capacity-approaching LDPC Codes Based on Markov Chain Monte Carlo MIMO Detection
    Rong-Rong Chen (The University of Utah)
    We study joint code design and MIMO (multiple-input multiple-output)
    detection based on Markov Chain Monte Carlo (MCMC) approach. The MCMC
    detector is highly effective for large antenna systems because it has a
    much lower complexity than traditional MIMO detectors including the sphere
    decoding detector. We apply the extrinsic information transfer (EXIT)
    technique to find optimal irregular LDPC codes that are matched to the
    characteristics of the MCMC detector. For a large system of 8 transmit and
    8 receive antennas and 16 QAM modulation, the optimized LDPC code achieves
    within 1.4 dB of the channel capacity. This result improves best published
    results by 2.3 dB, where 1.3 dB is due to the MCMC detection and 1 dB is
    due to code optimization.
  • On the optimum power allocation in interference-free cooperative systems
    Paul Anghel (University of Minnesota, Twin Cities)
    We consider an interference-free fixed wireless cooperative system where
    transmissions from different terminals are orthogonal. In the proposed
    system the idled terminals help a source by relaying its information signal
    to the destination. We consider both regenerative and non-regenerative idled
    terminals (relays). For the inference-free system with non-regenerative
    relays, we show that maximizing mutual information for each user under total
    power constraint is a strictly quasi-concave maximization problem whose
    global optimal solution can be found efficiently. In fact, we provide a
    simple analytic formula for the optimum power allocation strategy, which is
    reminiscent of the water-filling principle. We also illustrate how the setup
    can be extended in order to allow for terminal mobility. For the
    regenerative system we consider two cases - full collaboration between
    relays and no-collaboration between relays - and show that in both cases the
    maximum mutual information under total power constraint can be found in
    polynomial-time.
  • Optimizing Performance Metrics for Cellular Networks
    John Hobby (Alcatel-Lucent Technologies Bell Laboratories)
    We have developed an interactive tool for modeling and optimizing
    various types of cellular networks including CDMA, GSM, UMTS, EV-DO.
    Modeling network coverage and capacity as smooth, differentiable
    functions of parameters such as antenna tilts and azimuths
    facilitates efficient optimization even for large networks.

    The model involves explicit probability computations for effects
    such as shadow fading, and it includes steady-state approximations
    to dynamic processes such as the effect of the add/drop timer.
    Reverse-link power control and power amplifier sharing lead to
    highly-coupled systems that are nontrivial to solve and make the
    analytical derivative functions especially challenging.
  • Reducing energy consumption for power-constrained mobiles
    Eric van den Berg (Telcordia)
    We present a new method to increase the lifetime of energy constrained
    mobile devices. Each mobile node powers off its radio interface during
    time periods where it does nog expect to originate, receive or relay
    traffic. Nodes make autonomous decisions on whether and when to power down
    and wake up, without signaling messages to/from other nodes.
    We present results to show that the proposed method can significantly
    increase the lifetime of energy constrained nodes.
  • Cooperation vs. compression for sensor networks
    Chulhan Lee (The University of Texas at Austin)
    In a sensor network, nodes share information about their
    observations, and the amount of
    shared information can often be substantial. This paper compares two
    different strategies
    that exploit this redundant information - compression and cooperation. It
    finds compression
    to be the winning strategy when energy savings is the most important
    objective, but finds cooperation to be the throughput maximizing strategy. A
    weighted optimization problem
    is formulated to obtain intermediate schemes that allow a critical level of
    cooperation in the system, thereafter compressing all other redundant
    information.
  • High SNR analysis of MIMO broadcast channels
    Nihar Jindal (University of Minnesota, Twin Cities)
    The behavior of the multiple antenna
    broadcast channel at high SNR is investigated.
    The sum rate capacity (achievable by dirty paper coding),
    the sum rate achievable using transmitter beamforming,
    and an upper bound to the sum rate capacity are studied.
    Though these three terms are equivalent in the sense of
    the multiplexing gain, i.e. in terms of first order growth, there
    is an absolute difference between the corresponding rates.
    These difference terms are calculated and
    simple and intuitive geometrical interpretations are given.
  • Power Requirements in CDMA Networks with Multiple Classes

    of Traffic

    Komandur Krishnan (Telcordia)Arnie Neidhardt (Telcordia)
    We propose methods for calculating downlink power-requirements in
    a CDMA network that supports multiple classes of traffic. In
    providing for fluctuations of transmitter-power requirements in
    response to traffic-rate fluctuations, we make use of the notion
    of an effective power of a transmitter, analogous to the notion
    of an effective bandwidth of a traffic source. The methods
    consist of perturbation analysis by means of an expansion about
    approximate average values of transmitter-powers.
  • Random multi-access protocols - A mean field analysis
    Alexandre Proutiere (France Telecom R&D, LLC)
    Joint work with Charles Bordenave (ENS, Paris) and David McDonald (University of Ottawa, Canada).

    Although random multi-access protocols, such as the Decentralized
    Coordination Function (DCF) in IEEE 802.11-based networks, are widely
    used, their performance remains largely unknown. This is due to the
    fact that the inherent interactions between competing sources have
    proven to be extremely complex to model and analyze. A very popular
    approach to circumvent this difficulty consists in decoupling the
    source behaviors; i.e. assuming that the evolutions of the back-off
    processes of the different sources are mutually independent. This
    assumption allows one to derive explicit estimates of
    the performance. This approach was applied by Bianchi (IEEE trans. on
    Wireless Comm. 2000) to analyze the DCF protocol and since then has
    been widely used to accurately predict the performance of similar
    protocols. In this work, using mean field techniques, we prove that,
    for a wide range of random multi-access protocols, the decoupling
    assumption is asymptotically exact as the number of competing sources
    grows. In the specific case of the DCF, the mean field analysis
    provides the transient and the stationary distributions of the backoff
    processes.
  • Achieving Wireline Random Access Throughput in Wireless Networking via User Cooperation
    Georgios Giannakis (University of Minnesota, Twin Cities)
    Well appreciated at the physical layer, user cooperation is introduced here
    as a diversity enabler for wireless random access (RA) at the medium access
    control sub-layer. This is accomplished through a two-phase protocol in
    which active users start with a low power transmission attempting to reach
    nearby users, and follow up with a high power transmission in cooperation
    with the users recruited in the first phase. We show that such a
    cooperative protocol yields a significant increase in throughput.
    Specifically, we prove that for networks with a large number of users, the
    throughput of a cooperative wireless RA network operating over Rayleigh
    fading links approaches the throughput of a RA network operating over
    additive white Gaussian noise (AWGN) links. As a result, user cooperation
    migrates diversity benefits to the wireless RA regime, thus bridging the
    gap to wireline RA networks, without incurring a bandwidth or energy
    penalty.