Browsing by Author "Steger, Christopher"

Now showing 1 - 7 of 7
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    802.11b Operating in a Mobile Channel: Performance and Challenges
    (2003-09-20) Steger, Christopher; Radosavljevic, Predrag; Frantz, Patrick; Center for Multimedia Communications (http://cmc.rice.edu/)
    In the past, the worlds of wireless voice and data transmission have been largely disjoint. Voice traffic has been carried over circuit-switched cellular links, and data has been largely restricted to packet-switched wireless LANs. Now, as consumers demand higher bandwidth connections without sacrificing mobility and traffic transitions from primarily voice to data, service providers must produce what is essentially a ubiquitous wireless LAN. To this end, we have studied the effects of a mobile channel on current generation 802.11 A, B, and G wireless LAN cards to see how readily they can be applied to more challenging environments. Not surprisingly, current WLAN technology suffers from significantly degraded performance when subjected to the rigors of a mobile channel. We created emulated bi-directional peer-to-peer links in which we were able to manipulate individual channel parameters. By isolating individual propagation effects and testing several different implementations of the standards, we have discovered which channel parameters have the most significant impact on performance. For instance, the large delay spreads typical of an outdoor channel seem to produce the most deleterious effect on throughput in 802.11b. We use our observations to evaluate the viability of direct-sequence spread-spectrum systems (similar to 802.11b) versus that of OFDM systems (like 802.11a and 802.11g). Then we offer suggestions for how future systems should be adapted in order to manage these effects, and we project the ultimate limitations and possibilities for subsequent 802.11-like systems.
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    Measurement Driven Deployment of a Two-Tier Urban Mesh Access Network
    (ACM Press, 2006-06-01) Camp, Joseph; Robinson, Joshua; Steger, Christopher; Knightly, Edward; Center for Multimedia Communications (http://cmc.rice.edu/)
    Multihop wireless mesh networks can provide Internet access over a wide area with minimal infrastructure expenditure. In this work, we present a measurement driven deployment strategy and a data-driven model to study the impact of design and topology decisions on network-wide performance and cost. We perform extensive measurements in a two-tier urban scenario to characterize the propagation environment and correlate received signal strength with application layer throughput. We find that well-known estimates for pathloss produce either heavily overprovisioned networks resulting in an order of magnitude increase in cost for high pathloss estimates or completely disconnected networks for low pathloss estimates. Modeling throughput with wireless interface manufacturer specifications similarly results in severely underprovisioned networks. Further, we measure competing, multihop flow traffic matrices to empirically define achievable throughputs of fully backlogged, rate limited, and web-emulated traffic. We find that while fully backlogged flows produce starving nodes, rate-controlling flows to a fixed value yields fairness and high aggregate throughput. Likewise, transmission gaps occurring in statistically multiplexed web traffic, even under high offered load, remove starvation and yield high performance. In comparison, we find that well-known noncompeting flow models for mesh networks over-estimate network-wide throughput by a factor of 2. Finally, our placement study shows that a regular grid topology achieves up to 50 percent greater throughput than random node placement.
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    Performance of IEEE 802.11b Wireless LAN in an Emulated Mobile Channel
    (2003-04-20) Steger, Christopher; Radosavljevic, Predrag; Frantz, Patrick; Center for Multimedia Communications (http://cmc.rice.edu/)
    The performance of 802.11b wireless LANs is well understood for indoor environments. However, their behavior in outdoor and mobile environments has remained largely unexplored. We have performed experiments to bridge this knowledge gap by empirically measuring the performance of an 802.11b system in a broad spectrum of emulated environments. The goal of our work is to contribute to the evolution of currently existing wireless standards by measuring the effects of different channel phenomena on 802.11b. Our results show that current implementations of the 802.11b standard may not be well suited to use in a mobile environment, but that they could conceivably be modified to have better performance in such situations.
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    TAP Channel Measurement: Fundamentals, Goals, and Plans
    (2004-05-01) Steger, Christopher; Center for Multimedia Communications (http://cmc.rice.edu/)
    Before we can realize the potential of the TAP (Transit Access Point) project, we must first understand the channel in which we will operate. Specifically, very little information exists on the characteristics of elevated MIMO wireless channels at 2.4 GHz. Thus, we have chosen to produce our own measurement equipment and conduct a measurement campaign. In addition, we hope to gain insights into the tools and techniques that will be necessary for the eventual implementation of a high-speed MIMO OFDM data system.
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    White Paper on IEEE 802.11b Mobile Channel Modeling
    (2002-04-20) Steger, Christopher; Radosavljevic, Predrag; Frantz, Patrick; Center for Multimedia Communications (http://cmc.rice.edu/)
    Researchers from Rice Universityâ s Center for Multimedia Communications (CMC) recently conducted experiments with the goal of understanding and quantifying the effects of various channel effects on an 802.11b link. In order to manipulate the channel effects, the CMC group used a TAS 4500 channel emulator to connect two specially modified wireless LAN cards mounted in laptop PCâ s.
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    Wireless @ Wired Speeds
    (2004-12-01) Steger, Christopher; Chakrabarti, Arnab; Center for Multimedia Communications (http://cmc.rice.edu/)
    This is a poster from the first 100x100 project meeting. It outlines some basic concepts in MIMO algorithm and system design at a relatively high, accessible level.
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    Wireless Downlink Schemes in a Class of Frequency Selective Channels with Uncertain Channel State Information
    (2004-04-01) Steger, Christopher; Center for Multimedia Communications (http://cmc.rice.edu/)
    The fourth generation of cellular wireless technology will be called upon to perform at data rates far exceeding those of any existing system. The most fundamental decision in the design of the physical layer of 4G wireless systems is the choice of downlink channel allocation scheme. The four prospective technologies are OFDM, TDMA, MC-CDMA, and DS-CDMA. We contend that spectral efficiency is an essential metric with which to compare the performance of the different schemes. In this thesis, we contribute in three essential areas to the analysis of broadcast spectral efficiency by accounting for the cost of channel estimation, the uncertainty of channel estimates, and the effects of a variety of frequency-selective channels. We begin by analyzing two path channels. Then we extend our analytical results to create a more versatile and practical simulation technique that serves as a useful tool for making 4G design decisions.