|WiNGS Group's Research Snapshot (Oct 2011)
|Understanding wireless interference
|Understanding wireless interference
Airshark + WiFiNet: How can we detect the existence of non-WiFi transmitters
in the unlicensed spectrum, using only off-the-shelf WiFi cards?
Examples of non-WiFi transmitters are Bluetooth gadgets, ZigBee units,
various game controllers (PS2, Xbox, etc.), analog phones, frequency
hopping phones, and even microwave ovens. Past work
and various commercial products do this but often use more sophisticated
spectrum sensing chips or specialized embedded hardware (e.g., WiSpy).
If we do this without using any such additional hardware, then every
WiFi Access Point (AP) and client can do this in software we can build great
interference awareness in WiFi APs and clients.
We designed a technique, called Airshark, for doing this using Atheros 9280 WiFi chipsets,
all in software.
[IMC 2011 paper], [YouTube video]
Media coverage: Network World, Slashdot, CRA Highlight of the week, PC Magazine, The Register, BoingBoing, ...
|Many wireless devices occupy spectrum.
Our continued work in this domain, called WiFiNet, provides even deeper analysis of non-WiFi transmitters
in two ways still using off-the-shelf WiFi cards: (i) it can now quantify the impact
each individual non-WiFi interferer has on WiFi traffic, including when there are
multiple devices of the same or different type For example, there may be two Bluetooth headsets
in operation and one analog phone, WiFiNet tries to separate the contribution of each
such device on how much it impacts specific WiFi users (maybe 10%, 12%, and 25% respectively);
(ii) it can localize the position of this non-WiFi interferer.
The core challenge we have solved in both these cases is how to meet both these goals
using only WiFi cards, and hence with the constraint that our system cannot decode the
transmissions from these non-WiFi devices in the air.
Paper and video coming soon.
|Locate Non-WiFi devices in space.
FLUID: This work shows efficient ways to assign flexible channels
(channels with arbitrary center frequencies and widths) in a multi-link scenario.
We show that even in a simple two link scenario, and with two width choices
(say, 20 MHz and 40 MHz) and a single center frequency, the best width
assignment varies significantly based on the scenario. This is because
altering channel widths alter interference significantly. Some links become
hidden terminals and others can be exposed terminals simply due to change
in a channel width. The work proposes a systematic model for that can
be used to efficiently reason how different flexible channels can be
assigned to multiple WiFi transmitters in range, and how such choices
[MobiCom 2011 paper]
This paper was a best paper nominee at MobiCom 2011, and was one of three papers fast-tracked to the Transactions of Mobile Computing.
|WiScape: Monitoring Wide-area Cellular Networks through Client Assistance
A large number of clients can collaboratively provide a unique view of
performance across space and time for wide-area wireless (cellular) networks.
The naive approach would require a measurement server requesting each
client to collect a lot of measurements. Clearly, this is inefficient and
resource intensive. The WiScape system maps out the wireless landscape of
a cellular network by figuring out what is a small amount of measurement
needed to get a good, coarse-grained understanding of the network's overall
user experience. We partition required measurements into time and space
and collect a small number of measurements to gain some statistical
insights about multiple large wide-area cellular networks, covering
60 sq. miles in and around Madison, WI, and along more than 120 miles of
highways between Madison and Chicago.
[IMC 2011 paper], [Datasets coming soon]
|Snapshot of one cellular network's performance in Madison.
|WiRover: High Bandwidth Internet Connectivity to Moving Vehicles
WiRover provides high bandwidth connectivity to moving vehicles. Our targeted
applications are to provide Internet connectivity to passengers of
public transit buses, trains, limousines, taxis, as well
as emergency services including ambulances, police, and fire vehicles.
We have provided this as an experimental service since April 2010 to upto 12
vehicles in the Madison area, including multiple Madison Metro Transit buses
(the local public transit operator) and Van Galder buses (a long-distance
bus operator). The WiRover system aggregates data striping across multiple
wireless cellular (3G or 4G) and WiFi networks simultaneously. Core innovations
in WiRover lie purely in algorithms that efficiently handles transient
failures of each network and provides significant improved performance,
reliability, and overall user experience.
We are always interested in trialing the WiRover system with various
vehicle operators (or in other non-vehicular scenarios). If you
have a fleet of vehicles (taxis, buses, trains, or other rental cars)
that you want to provide Internet connectivity too, we can make WiRover
available to you for use. Similarly, if you have a non-vehicular
application that requires high-bandwidth
connectivity (e.g., high-bandwidth video) in any arbitrary
location, you can use WiRover for that as well.
Please email Prof. Suman Banerjee.
|WiRover exploits wireless diversity for improved performance.
|Apex: Cross-layer design for improving wireless media delivery through Value-aware Networking
In many media delivery systems are bits are not created equal. Some bits are
created to be more important (at the time when the media is encoded). The
simplest example is found in MPEG streams where the relative importance of I, P, B-frames
vary to the receiver. Apex (which stands for APproximate Communication for media
EXchange) is a proposed wireless communication model in which we observe received
symbols, when in error are typically a good approximation of the transmitted symbols.
We exploit this property to provide the abstraction that more important bits (such as
I-frames) can be better protected by the wireless channel natively than the
less important bits. This design allows for an improved media experience. The system
was implemented using the WARP software radio platform.
[Sigcomm 2010 paper]
|Approximate communication exploits the fact that symbol errors are typically localized around the transmitted symbol.
|Last updated on Oct 2011