3 research outputs found
Performance evaluation tools for QoS MAC Protocol for Wireless Sensor Networks
International audienc
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