423 research outputs found
On the Behavior of the Distributed Coordination Function of IEEE 802.11 with Multirate Capability under General Transmission Conditions
The aim of this paper is threefold. First, it presents a multi-dimensional
Markovian state transition model characterizing the behavior of the IEEE 802.11
protocol at the Medium Access Control layer which accounts for packet
transmission failures due to channel errors modeling both saturated and
non-saturated traffic conditions. Second, it provides a throughput analysis of
the IEEE 802.11 protocol at the data link layer in both saturated and
non-saturated traffic conditions taking into account the impact of both the
physical propagation channel and multirate transmission in Rayleigh fading
environment. The general traffic model assumed is M/M/1/K. Finally, it shows
that the behavior of the throughput in non-saturated traffic conditions is a
linear combination of two system parameters; the payload size and the packet
rates, , of each contending station. The validity interval of
the proposed model is also derived.
Simulation results closely match the theoretical derivations, confirming the
effectiveness of the proposed models.Comment: Submitted to IEEE Transactions on Wireless Communications, October
21, 200
On The Linear Behaviour of the Throughput of IEEE 802.11 DCF in Non-Saturated Conditions
We propose a linear model of the throughput of the IEEE 802.11 Distributed
Coordination Function (DCF) protocol at the data link layer in non-saturated
traffic conditions. We show that the throughput is a linear function of the
packet arrival rate (PAR) with a slope depending on both the number
of contending stations and the average payload length. We also derive the
interval of validity of the proposed model by showing the presence of a
critical , above which the station begins operating in saturated
traffic conditions.
The analysis is based on the multi-dimensional Markovian state transition
model proposed by Liaw \textit{et al.} with the aim of describing the behaviour
of the MAC layer in unsaturated traffic conditions. Simulation results closely
match the theoretical derivations, confirming the effectiveness of the proposed
linear model.Comment: To appear on IEEE Communications Letters, November 200
On Efficiency and Validity of Previous Homeplug MAC Performance Analysis
The Medium Access Control protocol of Power Line Communication networks
(defined in Homeplug and IEEE 1901 standards) has received relatively modest
attention from the research community. As a consequence, there is only one
analytic model that complies with the standardised MAC procedures and considers
unsaturated conditions. We identify two important limitations of the existing
analytic model: high computational expense and predicted results just prior to
the predicted saturation point do not correspond to long-term network
performance. In this work, we present a simplification of the previously
defined analytic model of Homeplug MAC able to substantially reduce its
complexity and demonstrate that the previous performance results just before
predicted saturation correspond to a transitory phase. We determine that the
causes of previous misprediction are common analytical assumptions and the
potential occurrence of a transitory phase, that we show to be of extremely
long duration under certain circumstances. We also provide techniques, both
analytical and experimental, to correctly predict long-term behaviour and
analyse the effect of specific Homeplug/IEEE 1901 features on the magnitude of
misprediction errors
Investigating the validity of IEEE 802.11 MAC modeling hypotheses
As WLANs employing IEEE 802.11 have become pervasive, many analytic models for predicting their performance have been developed in recent years. Due to the complicated nature of the 802.11 MAC operation, approximations must be made to enable tractable mathematical models. In this article, through simulation we investigate the veracity of the approximations shared by many models that have been developed starting with the fundamental hypotheses in Bianchipsilas (1998 and 2000) seminal papers. We find that even for small numbers of station these assumptions that hold true for saturated stations (those that always have a packet to send) and for unsaturated stations with small buffers. However, despite their widespread adoption, we find that the commonly adopted assumptions that are used to incorporate station buffers are not appropriate. This raises questions about the predictive power of models based on these hypotheses
How CSMA/CA With Deferral Affects Performance and Dynamics in Power-Line Communications
Power-line communications (PLC) are becoming a key component in home
networking, because they provide easy and high-throughput connectivity. The
dominant MAC protocol for high data-rate PLC, the IEEE 1901, employs a CSMA/CA
mechanism similar to the backoff process of 802.11. Existing performance
evaluation studies of this protocol assume that the backoff processes of the
stations are independent (the so-called decoupling assumption). However, in
contrast to 802.11, 1901 stations can change their state after sensing the
medium busy, which is regulated by the so-called deferral counter. This
mechanism introduces strong coupling between the stations and, as a result,
makes existing analyses inaccurate. In this paper, we propose a performance
model for 1901, which does not rely on the decoupling assumption. We prove that
our model admits a unique solution for a wide range of configurations and
confirm the accuracy of the model using simulations. Our results show that we
outperform current models based on the decoupling assumption. In addition to
evaluating the performance in steady state, we further study the transient
dynamics of 1901, which is also affected by the deferral counter.Comment: To appear, IEEE/ACM Transactions on Networking 201
An Approximate Inner Bound to the QoS Aware Throughput Region of a Tree Network under IEEE 802.15.4 CSMA/CA and Application to Wireless Sensor Network Design
We consider a tree network spanning a set of source nodes that generate
measurement packets, a set of additional relay nodes that only forward packets
from the sources, and a data sink. We assume that the paths from the sources to
the sink have bounded hop count. We assume that the nodes use the IEEE 802.15.4
CSMA/CA for medium access control, and that there are no hidden terminals. In
this setting, starting with a set of simple fixed point equations, we derive
sufficient conditions for the tree network to approximately satisfy certain
given QoS targets such as end-to-end delivery probability and delay under a
given rate of generation of measurement packets at the sources (arrival rates
vector). The structures of our sufficient conditions provide insight on the
dependence of the network performance on the arrival rate vector, and the
topological properties of the network. Furthermore, for the special case of
equal arrival rates, default backoff parameters, and for a range of values of
target QoS, we show that among all path-length-bounded trees (spanning a given
set of sources and BS) that meet the sufficient conditions, a shortest path
tree achieves the maximum throughput
A Non-Parametric Approach to Estimating Ambient Noise Levels in the Presence of Bursty Interference
We propose a new transmitter-side approach for
estimating the contribution to the packet error rate that is
due to background noise, distinct from the contribution due to
interference bursts. The technique relies solely on an existing
data-ack handshake and the transmitters ability to adjust or
monitor the packet size. One immediate application of this
information is in rate adaptation. Experimental measurements
with microwave oven interference are presented to demonstrate
the practical utility of the proposed technique
Detection and control of small civilian UAVs
With the increasing proliferation of small civilian Unmanned Aerial Vehicles (UAVs), the threat to critical infrastructure (CI) security and privacy is now widely recognised and must be addressed. These devices are easily available at a low cost, with their usage largely unrestricted allowing users to have no accountability. Further, current implementations of UAVs have little to no security measures applied to their control interfaces. To combat the threat raised by small UAVs, being aware of their presence is required, a task that can be challenging and often requires customised hardware.
This thesis aimed to address the threats posed by the Parrot AR Drone v2, by presenting a data link signature detection method which provides the characteristics needed to implement a mitigation method, capable of stopping a UAVs movement and video stream. These methods were developed using an experimental procedure and are packaged as a group of Python scripts.
A suitable detection method was developed, capable of detecting and identifying a Parrot AR Drone v2 within WiFi operational range. A successful method of disabling the controls and video of a Parrot AR Drone in the air was implemented, with collection of video and control commands also achieved, for after-the-event reconstruction of the video stream.
Real-time video monitoring is achievable, however it is deemed detrimental to the flight stability of the Parrot, reducing the effectiveness of monitoring the behaviour of an unidentified Parrot AR Drone v2. Additionally, implementing a range of mitigations for continued monitoring of Parrot AR Drones proved ineffectual, given that the mitigations applied were found to be non-persistent, with the mitigations reverting after control is returned to the controller. While the ability to actively monitor and manipulate Parrot AR Drones was successful, it was not to the degree believed possible during initial research
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