16,488 research outputs found
The Sensing Capacity of Sensor Networks
This paper demonstrates fundamental limits of sensor networks for detection
problems where the number of hypotheses is exponentially large. Such problems
characterize many important applications including detection and classification
of targets in a geographical area using a network of sensors, and detecting
complex substances with a chemical sensor array. We refer to such applications
as largescale detection problems. Using the insight that these problems share
fundamental similarities with the problem of communicating over a noisy
channel, we define a quantity called the sensing capacity and lower bound it
for a number of sensor network models. The sensing capacity expression differs
significantly from the channel capacity due to the fact that a fixed sensor
configuration encodes all states of the environment. As a result, codewords are
dependent and non-identically distributed. The sensing capacity provides a
bound on the minimal number of sensors required to detect the state of an
environment to within a desired accuracy. The results differ significantly from
classical detection theory, and provide an ntriguing connection between sensor
networks and communications. In addition, we discuss the insight that sensing
capacity provides for the problem of sensor selection.Comment: Submitted to IEEE Transactions on Information Theory, November 200
Adaptive fair channel allocation for QoS enhancement in IEEE 802.11 wireless LANs
The emerging widespread use of real-time multimedia applications over wireless networks makes the support of quality of service (QoS) a key problem. In this paper, we focus on QoS support mechanisms for IEEE 802.11 wireless ad-hoc networks. First, we review limitations of the upcoming IEEE 802.11e enhanced DCF (EDCF) and other enhanced MAC schemes that have been proposed to support QoS for 802.11 ad-hoc networks. Then, we describe a new scheme called adaptive fair EDCF that extends EDCF, by increasing the contention window during deferring periods when the channel is busy, and by using an adaptive fast backoff mechanism when the channel is idle. Our scheme computes an adaptive backoff threshold for each priority level by taking into account the channel load. The new scheme significantly improves the quality of multimedia applications. Moreover, it increases the overall throughput obtained both in medium and high load cases. Simulution results show that our new scheme outperforms EDCF and other enhanced schemes. Finally, we show that the adaptive fair EDCF scheme achieves a high degree of fairness among applications of the same priority level
Effective Capacity of Cognitive Radio Links: Accessing Primary Feedback Erroneously
We study the performance of a cognitive system modeled by one secondary and
one primary link and operating under statistical quality of service (QoS) delay
constraints. We analyze the effective capacity (EC) to quantify the secondary
user (SU) performance under delay constraints. The SU intends to maximize the
benefit of the feedback messages on the primary link to reduce SU interference
for primary user (PU) and makes opportunistic use of the channel to transmit
his packets. We assume that SU has erroneous access to feedback information of
PU. We propose a three power level scheme and study the tradeoff between
degradation in EC of SU and reliability of PU defined as the success rate of
the transmitted packets. Our analysis shows that increase in error in feedback
access causes more interference to PU and packet success rate decreases
correspondingly.Comment: Accepted for publication in International Symposium on Wireless
Communication Systems (ISWCS) 201
Extending the Energy Framework for Network Simulator 3 (ns-3)
The problem of designing and simulating optimal transmission protocols for
energy harvesting wireless networks has recently received considerable
attention, thus requiring for an accurate modeling of the energy harvesting
process and a consequent redesign of the simulation framework to include it.
While the current ns-3 energy framework allows the definition of new energy
sources that incorporate the contribution of an energy harvester, the
integration of an energy harvester component into an existing energy source is
not straightforward using the existing energy framework. In this poster, we
propose an extension of the energy framework currently released with ns-3 in
order to explicitly introduce the concept of an energy harvester. Starting from
the definition of the general interface, we then provide the implementation of
two simple models for the energy harvester. In addition, we extend the set of
implementations of the current energy framework to include a model for a
supercapacitor energy source and a device energy model for the energy
consumption of a sensor. Finally, we introduce the concept of an energy
predictor, that gathers information from the energy source and harvester and
use this information to predict the amount of energy that will be available in
the future, and we provide an example implementation. As a result of these
efforts, we believe that our contributions to the ns-3 energy framework will
provide a useful tool to enhance the quality of simulations of energy-aware
wireless networks.Comment: 2 pages, 4 figures. Poster presented at WNS3 2014, Atlanta, G
Coordinated Dynamic Spectrum Management of LTE-U and Wi-Fi Networks
This paper investigates the co-existence of Wi-Fi and LTE in emerging
unlicensed frequency bands which are intended to accommodate multiple radio
access technologies. Wi-Fi and LTE are the two most prominent access
technologies being deployed today, motivating further study of the inter-system
interference arising in such shared spectrum scenarios as well as possible
techniques for enabling improved co-existence. An analytical model for
evaluating the baseline performance of co-existing Wi-Fi and LTE is developed
and used to obtain baseline performance measures. The results show that both
Wi-Fi and LTE networks cause significant interference to each other and that
the degradation is dependent on a number of factors such as power levels and
physical topology. The model-based results are partially validated via
experimental evaluations using USRP based SDR platforms on the ORBIT testbed.
Further, inter-network coordination with logically centralized radio resource
management across Wi-Fi and LTE systems is proposed as a possible solution for
improved co-existence. Numerical results are presented showing significant
gains in both Wi-Fi and LTE performance with the proposed inter-network
coordination approach.Comment: Accepted paper at IEEE DySPAN 201
Joint Cooperative Spectrum Sensing and MAC Protocol Design for Multi-channel Cognitive Radio Networks
In this paper, we propose a semi-distributed cooperative spectrum sen sing
(SDCSS) and channel access framework for multi-channel cognitive radio networks
(CRNs). In particular, we c onsider a SDCSS scheme where secondary users (SUs)
perform sensing and exchange sensing outcomes with ea ch other to locate
spectrum holes. In addition, we devise the p -persistent CSMA-based cognitive
MAC protocol integrating the SDCSS to enable efficient spectrum sharing among
SUs. We then perform throughput analysis and develop an algorithm to determine
the spectrum sensing and access parameters to maximize the throughput for a
given allocation of channel sensing sets. Moreover, we consider the spectrum
sensing set optimization problem for SUs to maxim ize the overall system
throughput. We present both exhaustive search and low-complexity greedy
algorithms to determine the sensing sets for SUs and analyze their complexity.
We also show how our design and analysis can be extended to consider reporting
errors. Finally, extensive numerical results are presented to demonstrate the
sig nificant performance gain of our optimized design framework with respect to
non-optimized designs as well as the imp acts of different protocol parameters
on the throughput performance.Comment: accepted for publication EURASIP Journal on Wireless Communications
and Networking, 201
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