[CPCC] Performace Anomalies in Outdoor WLAN

[Ender Ayanoglu]

                                   TALK

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.

Speaker's Biography:
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.

Host: Athina Markopoulou, athina at uci.edu.