[UCI-Calit2] Lecture: Performace Anomalies in Outdoor WLAN Deployments

Anna Lynn Spitzer aspitzer at calit2.uci.edu
Tue Apr 15 15:16:49 PDT 2008


Title:
Unexpected Performance Anomalies in Outdoor IEEE 802.11 WLAN Deployments

Speaker:
Luca Scalia, University of Palermo

Time:
4-5 p.m.

Date:
Wednesday, April 16, 2008 

Location:
Calit2 Building, Room 4355

Abstract:
The IEEE 802.11 standard is largely recognized as the "de-facto"
technology for deploying local area networks. The incredible flexibility
of its design, the cheapness of the devices and the easiness of
installation have allowed it to be employed for providing Internet
connectivity to a majority of metropolitan areas.
This potential to access a very appealing market slice at very low costs
has increased interest both from industrial companies and service
providers to search for proprietary and optimized solutions for such
environments. In this direction, not only new MAC-layer enhancements
have been introduced to provide mesh-based operations, but also QoS
support and QoS-aware routing solutions have been accounted for
providing very remunerative voice and high-data-rates application
services.
However, enhancing the MAC layer functionalities sometimes may not be
enough. In this talk Scalia shows how new unexpected as well as critical
impairments may occur in practical scenarios. In particular, by means of
simple measurements developed in controlled experimental environments,
he noticed that different-brand IEEE 802.11 commercially available cards
not only experience misaligned performance behaviors when accessing the
wireless medium, but also, when deployed in outdoor environments,
experience performance figures that are strongly affected by unexpected
drawbacks deriving from manufacturers' proprietary solutions.
Scalia presents the experimental evidence that proprietary
antenna-transmit diversity algorithms as well as interference mitigation
operations implemented in many commercial cards, may cause very low
link-level performance either for 802.11b and 802.11g outdoor mesh
deployments. By focusing on a specific and widely adopted card/driver
pair (Atheros/Madwifi), he observed how transmit antenna diversity
mechanisms remain enabled by default even when the available antennas
are not homogeneous in terms of gain or polarization or, in the worst
case, when only a single antenna is physically supported. In addition,
results found how the proprietary Interference Mitigation algorithm,
enabled by default and implemented in the card firmware, severely
affects link performance up to reducing the Packet Delivery Probability
(PDR) to 2%, whereas by disabling them causes a PDR around 75%.
Although the impact of these solutions is not evident in indoor
scenarios, it causes considerable performance impairments (large
frame-loss ratio) in outdoor scenarios, the typical 802.11 mesh ones,
where multi-path and interference phenomena become more critical.

Short bio:
Dr. Luca Scalia obtained the "Laurea" degree (summa cum laude) in
electronic engineering and the Ph.D. in computer science, respectively
in November 2002 and April 2007, from the University of Palermo, Italy.
Since May 2007 he has been research collaborator at the University of
Palermo. His main research interests regard 802.11 wireless networks,
and specifically, performance analysis and optimization, MAC-layer
design, radio resource allocation, QoS support and optimization of
multi-hop delivery mechanisms.

For more information: Athina Markopoulou, athina at uci.edu




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