|
Extracting a Cryptographic Key from the
Wireless Channel:
In this
talk, I will describe a simple protocol that allows two parties,
Alice and Bob, communicating on a point-to-point wireless link, to
establish a common secret cryptographic key using fundamental
properties of the wireless medium, without letting an adversary
infer any information about the key. The established key can then be
used to encrypt communication between Alice and Bob using standard
symmetric key algorithms such as Rijndael, DES, etc. The protocol
allows Alice and Bob to regularly refresh their keys. It resists
cryptanalysis of the generated key by an eavesdropping adversary Eve
and unlike key-agreement schemes that have been proposed in prior
literature, does not require that Alice and Bob share an
authenticated channel. The presence of a man-in-the-middle adversary
can be detected much as in quantum key distribution systems. We are
currently numerically evaluating the performance of our algorithm
while conducting a measurement based study using the GNUradio
platform & a network analyzer. For those interested, an open
mathematical problem that we are trying to solve as part of this
work will also be described.
Power-Modulated Challenge-Response Schemes
for Verifying Location Claims:
Location
information should be verifiable in order to support new computing
and information services. In this work, we adapt the classical
challenge-response method for authentication to the task of
verifying an entity's location. Our scheme utilizes a collection of
transmitters, and adapts their power allocations to verify a user's
claimed location. This strategy, which we call power-modulated
challenge response, is able to be used with existing wireless sensor
networks, and we present three variations. First, we propose a
direct method, where some transmitters are selected to send
``challenges" that the claimant node should be able to witness based
on its claimed location, and for which the claimant node must
correctly respond in order to prove its location. Second, we reverse
the strategy by presenting an indirect method, where some
transmitters send challenges that the claimant node should not be
able to witness. Finally, we present a signal strength based method,
where the node responds with its received signal strength and
thereby provides improved location verification. To evaluate our
schemes, we examine different adversarial models for the claimant,
and characterize the performance of our power-modulated challenge
response schemes under these adversarial models.
Virtual Trip Lines for
Distributed Privacy-Preserving Traffic Monitoring:
Automotive traffic monitoring
through probe vehicles with Global Positioning System receivers
promises significant improvements in cost, coverage, and accuracy.
Current approaches, however, raise privacy concerns because they
require participants to reveal their positions to an external
traffic monitoring server. To address this challenge, we propose a
system based on virtual trip lines and an associated cloaking
technique. Virtual trip lines are geographic markers that indicate
where vehicles should provide location updates. These markers can be
placed to avoid particularly privacy sensitive locations. They also
allow aggregating and cloaking several location updates based on
trip line identifiers, without knowing the actual geographic
locations of these trip lines. Thus they facilitate the design of a
distributed architecture, where no single entity has a complete
knowledge of probe identities and fine-grained location
information. We have implemented the system with GPS smartphone
clients and conducted a controlled experiment with 20 phone-equipped
drivers circling a highway segment. Results show that even with this
low number of probe vehicles, travel time estimates can be provided
with less than 15% error, and applying the cloaking techniques
reduces travel time estimation accuracy by less than 5% compared to
a standard periodic sampling approach.
Robust Sentry-based Schemes:
Towards Long-lived, Fault-Tolerant Wireless Sensor Networks:
Recent advances in MEMS technology,
wireless communication and networking have enabled the development
of low-cost yet capable wireless micro-sensors, thus bringing up a
new class of applications involving remote surveillance and date
collection. However, there are still barriers to overcome to deploy
these applications in large scale, one of which is the limited
network lifetime. Extending network lifetime is challenging because
the network is built out of short-lived sensor nodes. The lifetime
of a sensor node is limited by its battery capacity; and due to
limitations of cost and size, the sensor hardware is rather
unreliable. Additionally, sensor networks are often deployed in
harsh environments
and left unattended in operation, which further contributes to
frequent node failures.
In order to extend the lifetime of the networked system beyond the
lifetime of the individual sensor node, a common practice is to
deploy a large array of sensor nodes, and at any instance, have only
a minimal set of nodes active performing duties while others stay in
sleep mode to conserve energy. With this rationale, random node
failures, either from active nodes or from redundant nodes, can
seriously disrupt system operations. To address this issue, a node
scheduling algorithm is proposed: R-Sentry, a gang-based scheduling
algorithm that attempts to bound the service loss duration due to
node failures
by coordinating the schedules among redundant nodes. Intensive
simulations clearly show R-Sentry's superiority over existing
schemes, like PEAS.
A Physical-Layer Technique to
Enhance Authentication for Mobile Terminals:
We propose an enhanced
physical-layer authentication scheme for multi-carrier wireless
systems, where transmission bursts consist of multiple frames. More
specifically, it is based on the spatial variability characteristic
of wireless channels, and able to work with moderate terminal
mobility. For the authentication of the first frame in each data
burst, the legal transmitter uses the saved channel response from
the previous burst as the key for authentication of the first frame
in the next burst. The key is obtained either via feedback from the
receiver, or using the
symmetric channel property of a TDD system. Then the authentication
of the following frames in the burst is performed either by a Neyman-Pearson
hypothesis test, or a least-squares adaptive channel estimator.
Simulations in a typical indoor building show that both methods work
efficiently, if the speed of
transmitters is no more than typical pedestrian velocities.
Interference-assisted Secret
Communication:
Wireless communication is
susceptible to adversarial eavesdropping due to the broadcast nature
of the wireless medium. In this talk, we illustrate how
eavesdropping can be alleviated by exploiting the superposition
property of the wireless medium. A wiretap channel with a helping
interferer (WT-HI), in which a transmitter sends a confidential
message to its intended receiver in the presence of a passive
eavesdropper, and with the help of an independent interferer, is
considered. The interferer, who does not know the confidential
message, helps in ensuring the secrecy of the message by sending
independent signals. An achievable secrecy rate for the WT-HI is
given. The results show that interference, which seldom offers any
advantage for problems not involving secrecy, can be exploited to
assist secrecy in wireless communication. An important example of
Gaussian channels is the case when the interferer has a better
channel to the intended receiver than to the eavesdropper. Here, the
interferer can send a (random) codeword at a rate which ensures that
it can be decoded and subtracted from the received signal by the
intended receiver and not decoded by the eavesdropper. Hence, only
the eavesdropper is interfered upon and the secrecy level of the
confidential message is increased.
Secure Wireless Communications Utilizing Physical Layer
Characteristics:
In
this talk, we will give a brief summary of our researches in Japan.
We are developing some wireless communication systems utilizing
physical layer property. Most of them make use of key extraction
techniques from the reciprocal channel response. We also have some
concern about secret communication and analysis of radio propagation
which ensures the security of our secure wireless communication
schemes. After the presentation, we will make a demonstration of key
extraction by a simple prototype system.
Bio:
Shimpei
Yasukawa and Takayuki SHIMIZU are two Japanese
exchange students. They come from Communication System Lab,
Doshisha University, Japan. Both of their advisors are
Professor Hisato IWAI and Professor
Hideichi SASAOKA. Currently, they are under the
guidance of Professor Trappe.
Radio Scene Analysis using Trilinear Decomposition:
We consider a
scenario with multiple radio sources performing packet based
transmissions. The sources belong to heterogeneous networks and
their signals may overlap in time and frequency. Each source is
characterized by its power spectral density and on/off activity
sequence. A network of sensors performs measurements, where each
sensor computes spectrogram of the received signal with certain time
and frequency resolution. Spectrograms from different sensors are
collected and arraigned in a three-way array, whose three dimensions
correspond to space, time, and frequency indices. We show that,
under certain rank conditions of the three-way array, it is possible
to recover sources to sensors channel gain coefficients, power
spectral densities and on/off activity sequences of the sources by
decomposing the three-way array into rank-one components. The
recovery process is illustrated with simulation examples involving
802.11b/g and Bluetooth sources whose signals overlap in time and
frequency.
Bandwidth Exchange as an
Incentive for Relaying:
Relay cooperation
has been recognized as an important mechanism to enhance
connectivity and throughput in multi-hop wireless
networks,especially under varying channel conditions. One major
problem of relay cooperation is that relaying always incurs energy
and possibly delay costs. To a rational and selfish node these costs
are worth incurring only if it receives at least comparable returns
in the long term. In light of this, we propose a new incentive
mechanism called bandwidth exchange where a node can delegate a
portion of its bandwidth to another node in exchange for relay
cooperation. In this talk we specifically discuss bandwidth exchange
in the simple form of exchanging orthogonal frequency bands to
provide incentives for relaying in a wireless network. Other forms
of exchanging bandwidth such as delegation of time-slots or using
spreading codes of different lengths are also possible. Using a Nash
Bargaining framework, we explore the advantage of bandwidth exchange
in both static and fading channels.
Locating a Non-interactive
Transmitter Based on Dynamic Signal Strength Mapping:
In the
new paradigm of the spectrum access driven by cognitive radios, the
location awareness has its special importance to issues such as
spectrum etiquette enforcement and spectrum hole discovery. Because
of the nature of the cognitive radios, the most accessible
information at a receiver is the received signal strength (RSS).
This motivates us to revisit the RSS based localizations in a
cognitive radio framework. Given the radio propagation law in
nature, the RSS usually corresponds to the direct link distance
between a transmitter and a receiver, with random distortions by
obstructions, multipath and noises. By making use of such
correlations, it is possible to recover more RSS data without actual
measuring them.
We
present two range-free localization algorithms based on dynamic
mapping of received signal strength. The schemes are designed for a
non-interactive location system that does not require the
cooperation from the device to be located. A detailed signal
strength map across the surveillance area is constructed by
interpolation. By making use of this signal map, the proposed
schemes achieve better accuracy of location estimation than existing
non-interactive and RSS based methods in most channel variation
conditions.
Fiber Assisted Wireless for
Broadband Access Networks:
With the
advent of broadband wireless systems operating at microwave
frequency bands, and with the entailed shrinkage of cell coverage
for high capacity wireless access, the simplification of the antenna
stations becomes crucial to reduce access infrastructure cost.
For this purpose, radio-over-fiber (RoF) distribution antenna
systems are an attractive option for the transparent delivery of
wireless data signals from a central office location to remote
antenna sites via optical fiber. In this way, the complicated and
costly (in particular for high RF frequencies) wireless signal
processing can be placed in the central office.
This
presentation will give an overview of the Fiber Assisted Wireless
for Broadband Access Networks. The approach is based on passive
optical network architectures that can support the generation,
transmission and delivery of high frequency signals required in
wireless links. In addition these architectures allow the sharing
of a single central office and provide additional direct
interconnectivity of the antenna station so dynamic bandwidth
allocation can be addressed as mobile customers enter or leave the
coverage area of different cell coverage.
Bio:
Professor Nicholas Madamopoulos is currently an Associate Professor
in Department of Electrical Engineering, City College of CUNY, New
York. He got his Ph.D. in Optical Science and Engineering, The
School of Optics, University of Central Florida, Orlando, FL. 1998,
M.S. in Optical Science and Engineering, The School of Optics and
Department of Electrical and Computer Engineering, Univ. of Central
Florida, Orlando, FL. 1996, and B.S. in Physics, University of
Patras, Patras, Greece. 1993. His research interests include Optical
communications, passive optical networks, analog photonics, photonic
sensors, photonic systems for telecom and non-telecom applications.
Email:
nmadamopoulos@ccny.cuny.edu
Experimental Study of Interference Models for Low-Power Wireless
Networks:
Practical approaches for modeling interference on wireless links are
critical for understanding wireless network behavior. This is
because the MAC layer protocol must fundamentally be able to
schedule transmissions on links in an interference-free fashion.
While many algorithmic studies have used
protocol interference
models based on network
topology or physical node distance, focus has recently shifted
toward more realistic,
physical interference
models, based on signal-to
interference-and-noise ratio (SINR). Essentially, in SINR model,
success of a packet reception depends on the ratio of the signal
power and the aggregated interference and noise power. Here,
interference is considered in an aggregated form as the sum of all
interference powers from all interfering links. Prior work, has
reported interesting observations that refute the additive
interference assumption for low power radios used in previous
generation sensor motes, indicating that the SINR model may not be
useful in designing higher layer protocols. In our work, we perform
a careful set of measurements on 802.15.4 compatible, CC2420 radio
which is used in the new generation low power sensor networks. We
find that, in contrast to the observations in prior work, additive
model works quite well in practice.
We
then perform extensive experimentation to model the SINR vs. PRR
relationship for this
physical interference model,
as well as several common
protocol interference models
typically considered in literature for scheduling studies, such as
hop-based, range based, distance ratio-based, etc. We observe that
the physical
model is significantly more
accurate than the protocol models considered for evaluation.
We then look closely into the physical interference model itself,
and consider its two incarnations --- thresholded (overly
conservative, but typically considered in literature) and graded
(more realistic). We show via solving the one shot scheduling
problem, that the graded version can significantly improve expected
throughput over the thresholded version by scheduling imperfect
links.
BIO
Shweta
Jain: I graduated with a PhD in Computer Science from Stony Brook
University in August 2007. I also have a MS degree in Computer
Science from Stony Brook University and a BE in Electronics and
Telecommunication Engineering from Bengal Engineering and Science
University (Shibpore). My research interests are in wireless
embedded systems, medium access protocols and experimental systems
research. I have experience in designing embedded systems solutions
through several exciting projects in small and medium size startup
companies. I currently work as Senior Engineer at Staccato
Communications where I am developing embedded wireless USB solutions
for next generation cameras and cell phones. Further information
about my research and work experiences is available at
http://www.wings.cs.sunysb.edu/~shweta
Exploiting Environmental Properties
for Wireless Localization and Location Aware Applications:
Wireless sensor
networks monitor phenomena that vary over the spatial region the
sensor network covers. The sensor readings may also be dual-used for
additional purposes. We propose to use the inherent spatial
variability in physical phenomena to support localization and
position verification. In this talk, we first present the problem of
localization using general spatial information fields, and then
propose a theory for exploiting this spatial variability for
localization. Our Spatio-Correlation Weighting Mechanism (SCWM) uses
spatial relationships of measured physical phenomena to determine an
appropriate subset of environmental parameters for better location
accuracy. We next present the Flex-EP algorithm, which supports our
theoretical model for performing localization. Finally, we provide
an experimental evaluation of our approach by using a collection of
physical phenomena measured across one hundred locations inside a
building. Our results provide strong evidence of the viability of
using general sensor readings for location applications.
Feedback-assisted belief propagation
decoder for Fountain codes and application for minimum-delay data
collection:
Our research
analyzes the benefits of an automatic repeat request (ARQ) scheme
employed in doped belief-propagation decoding for increasing the
throughput of Fountain encoded data transmissions. Both Ideal and
Robust Soliton code symbol degree distributions are studied. The
proposed doping mechanism selects doping symbols randomly from the
set of input symbols contributing to degree-two output symbols. Here
an output symbol is the encoded symbol whose code-graph links to
input symbols decoded thus far have been severed. This doping
approach always ensures releasing of at least one output symbol,
thus increasing the number of degree-one output symbols (the
ripple). Using a random walk analysis, we study the belief
propagation decoding with degree-two random doping for a fountain
code with symbols drawn from an Ideal Soliton distribution. We show
that the decoding process is a renewal process whereas the process
starts all over afresh after each doping. The asymptotic interdoping
process analysis revolves around a random walk model for the ripple
size. We show that the sequence of the ripple size increments (due
to doping and/or decoding) can be modeled as an iid sequence of
shifted Poisson random variables (with unit mean), regardless of the
number of input symbols. This model furnishes the final cost
analysis with a prediction on the number of required doping symbols.
In particular, the cost analysis is given for various decentralized
strategies used to facilitate
data collection in circular wireless sensor networks, which rely on
the stochastic diversity of data storage. The goal is to allow for a
reduced delay collection by a mobile data collector (MDC) who
accesses the network at a random position and random time.
A Hybrid
Satellite & Terrestrial Mobile TV System is Launched:
Emerging mobile
Television (MTV) systems such as the DVB family, complement 3G
wireless telephony in both service and in technology. For example,
technologically advanced digital radio concepts including Turbo and
LDPC coding, OFMD, and physical and link layer interleaver are now
being used in broadcast television to mobile terminals. Satellite
broadcast to mobile terminals are also now about to launch. On April
14th, a satellite is to be launched from Cape Canaveral to become
the first to provide hybrid satellite plus terrestrial transmission
of mobile TV on a Single Frequency Network (SFN). This will utilize
the new Digital Video Broadcast - Satellite to Handset (DVB-SH)
standard.
Synchronizing the
satellite and terrestrial repeaters in this network present some
fascinating challenges in architecture and RF network design. This
talk will highlight the DVB-SH standard, the implementation of the
trial system and the challenges ahead for deploying and integrating
wireless broadcasting with wireless broadband.
BIO
The talk will be
presented by Stephen Wilkus of Alcatel-Lucent Bell Labs, who has
been the solutions architect for this first North American
application of the DVB-SH standard. He graduated with his MSEE and
Physics degrees from the University of Illinois in 1981. He has been
22 years at Bell Laboratories and a long time supporter of the
industrial affiliation with Rutgers' WINLAB.
|
