524 research outputs found
Throughput optimization strategies for large-scale wireless LANs
Thanks to the active development of IEEE 802.11, the performance of wireless local area networks (WLANs) is improving by every new edition of the standard facilitating large enterprises to rely on Wi-Fi for more demanding applications. The limited number of channels in the unlicensed industrial scientific medical frequency band however is one of the key bottlenecks of Wi-Fi when scalability and robustness are points of concern. In this paper we propose two strategies for the optimization of throughput in wireless LANs: a heuristic derived from a theoretical model and a surrogate model based decision engine
Performance modelling of fairness in IEEE 802.11 wireless LAN protocols
PhD ThesisWireless communication has become a key technology in the modern world, allowing network
services to be delivered in almost any environment, without the need for potentially expensive
and invasive fixed cable solutions. However, the level of performance experienced by wireless
devices varies tremendously on location and time. Understanding the factors which can cause
variability of service is therefore of clear practical and theoretical interest.
In this thesis we explore the performance of the IEEE 802.11 family of wireless protocols,
which have become the de facto standard for Wireless Local Area Networks (WLANs). The
specific performance issue which is investigated is the unfairness which can arise due to the
spatial position of nodes in the network. In this work we characterise unfairness in terms of the
difference in performance (e.g. throughput) experienced by different pairs of communicating
nodes within a network. Models are presented using the Markovian process algebra PEPA which
depict different scenarios with three of the main protocols, IEEE 802.11b, IEEE 802.11g and
IEEE 802.11n. The analysis shows that performance is affected by the presence of other nodes
(including in the well-known hidden node case), by the speed of data and the size of the frames
being transmitted.
The collection of models and analysis in this thesis collectively provides not only an insight
into fairness in IEEE 802.11 networks, but it also represents a significant use case in modelling
network protocols using PEPA. PEPA and other stochastic process algebra are extremely powerful
tools for efficiently specifying models which might be very complex to study using conventional
simulation approaches. Furthermore the tool support for PEPA facilitates the rapid solution of
models to derive key metrics which enable the modeller to gain an understanding of the network
behaviour across a wide range of operating conditions.
From the results we can see that short frames promote a greater fairness due to the more
frequent spaces between frames allowing other senders to transmit. An interesting consequence
of these findings is the observation that varying frame length can play a role in addressing
topological unfairness, which leads to the analysis of a novel model of IEEE 802.11g with
variable frame lengths. While varying frame lengths might not always be practically possible, as
frames need to be long enough for collisions to be detected, IEEE 802.11n supports a number of
mechanisms for frame aggregation, where successive frames may be sent in series with little
or no delay between them. We therefore present a novel model of IEEE 802.11n with frame
aggregation to explore how this approach affects fairness and, potentially, can be used to address
unfairness by allowing affected nodes to transmit longer frame bursts.Kurdistan Region Government of Iraq
(KRG) sponso
A particle system in interaction with a rapidly varying environment: Mean field limits and applications
We study an interacting particle system whose dynamics depends on an
interacting random environment. As the number of particles grows large, the
transition rate of the particles slows down (perhaps because they share a
common resource of fixed capacity). The transition rate of a particle is
determined by its state, by the empirical distribution of all the particles and
by a rapidly varying environment. The transitions of the environment are
determined by the empirical distribution of the particles. We prove the
propagation of chaos on the path space of the particles and establish that the
limiting trajectory of the empirical measure of the states of the particles
satisfies a deterministic differential equation. This deterministic
differential equation involves the time averages of the environment process.
We apply our results to analyze the performance of communication networks
where users access some resources using random distributed multi-access
algorithms. For these networks, we show that the environment process
corresponds to a process describing the number of clients in a certain loss
network, which allows us provide simple and explicit expressions of the network
performance.Comment: 31 pages, 2 figure
The analysis of achieving TCP fairness in IEEE 802.11 infrastructure WLAN
This paper raising the TCP fairness issues that reviewed from three aspects; per-flow, per-station, and per-rate based on the IEEE 802.11 Wireless Local Area Networks (WLANs) environment.Due to the strong drive towards wireless Internet access via mobile devices, these issues must be carefully handled in order to build improved systems. We succinctly review and categorize the TCP fairness characteristic and then outline the problems and solutions from previous works through comparative table.Finally, we considered the future direction for solving these problems.Overall this paper summarizes current state of knowledge of the WLAN TCP fairness
Rigorous and Practical Proportional-fair Allocation for Multi-rate Wi-Fi
Recent experimental studies confirm the prevalence of the widely known performance anomaly
problem in current Wi-Fi networks, and report on the severe network utility degradation caused by
this phenomenon. Although a large body of work addressed this issue, we attribute the refusal of
prior solutions to their poor implementation feasibility with off-the-shelf hardware and their impre-
cise modelling of the 802.11 protocol. Their applicability is further challenged today by very high
throughput enhancements (802.11n/ac) whereby link speeds can vary by two orders of magnitude.
Unlike earlier approaches, in this paper we introduce the first rigorous analytical model of 802.11
stations’ throughput and airtime in multi-rate settings, without sacrificing accuracy for tractability.
We use the proportional-fair allocation criterion to formulate network utility maximisation as a con-
vex optimisation problem for which we give a closed-form solution. We present a fully functional
light-weight implementation of our scheme on commodity access points and evaluate this extensively
via experiments in a real deployment, over a broad range of network conditions. Results demonstrate
that our proposal achieves up to 100% utility gains, can double video streaming goodput and reduces
TCP download times by 8x
Cooperative Jamming in Wireless Networks - Turning Attacks into Privacy Protection
Generally, collisions between packets are undesired in wireless networks. We design this scheme, Cooperative Jamming in Wireless Networks (CJWN), to make use of collision to protect secret DATA packets from being sniffed by a nearby eavesdropper. We are intending to greatly increase the Packet Error Rate (PER) at the eavesdropper when the PER at the receiver is maintained at an acceptable level. This scheme is not intended to completely take the place of various encryption/decryption schemes which are working based on successfully received packets. Adding CJWN to the popular CSMA/CA adopted in IEEE 802.11 will add more security even the key for encryption/decryption is already exposed. Because the overhead of CJWN is very big, we do not suggest using it on every transmission. When some secret packets have a high requirement of confidentiality, CJWN is worth trying at the cost of throughput performance and power
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