1,564 research outputs found
Implementing and Evaluating a Wireless Body Sensor System for Automated Physiological Data Acquisition at Home
Advances in embedded devices and wireless sensor networks have resulted in
new and inexpensive health care solutions. This paper describes the
implementation and the evaluation of a wireless body sensor system that
monitors human physiological data at home. Specifically, a waist-mounted
triaxial accelerometer unit is used to record human movements. Sampled data are
transmitted using an IEEE 802.15.4 wireless transceiver to a data logger unit.
The wearable sensor unit is light, small, and consumes low energy, which allows
for inexpensive and unobtrusive monitoring during normal daily activities at
home. The acceleration measurement tests show that it is possible to classify
different human motion through the acceleration reading. The 802.15.4 wireless
signal quality is also tested in typical home scenarios. Measurement results
show that even with interference from nearby IEEE 802.11 signals and microwave
ovens, the data delivery performance is satisfactory and can be improved by
selecting an appropriate channel. Moreover, we found that the wireless signal
can be attenuated by housing materials, home appliances, and even plants.
Therefore, the deployment of wireless body sensor systems at home needs to take
all these factors into consideration.Comment: 15 page
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
Evaluation of IEEE 802.11 coexistence in WLAN deployments
This is a pre-print of an article published in Wireless Networks. The final authenticated version is available online at: https://doi.org/10.1007/s11276-017-1540-z.Wi-Fi has become a successful technology since the publication of its first WLAN standard due to continuous advances and updates while remaining always backwards compatible. Backwards compatibility among subsequent standards is an important feature in order to take advantage of previous equipment when publishing a new amendment. At present, IEEE 802.11b support is still mandatory to obtain the Wi-Fi certification. However, there are several harmful effects of allowing old legacy IEEE 802.11b transmissions in modern WLAN deployments. Lower throughput per device is obtained at slow rates, but also the effect known as performance anomaly, which nearly leads to starvation of fast stations, has to be taken into account. Finally, backwards compatibility mechanisms pose an important penalty in throughput performance for newer specifications. This paper presents a thorough analysis of the current state of IEEE 802.11, comparing coverage range and throughput performance among subsequent amendments, and focusing on the drawbacks and benefits of including protection mechanisms.Peer ReviewedPostprint (author's final draft
Cooperative performance bounds of Wireless Local Area Networks
In a Wireless Local Area Network (WLAN), capacity gain and delay reduction play a crucial role in system performance. In this paper, we focus on performance improvements when WLANs exploit the concept of cooperation among nodes. We propose a geometrical model to determine the potential location area of relay nodes. The analytical results are validated by simulation. Performance bounds and average of capacity gain and delay ratio are studied for different IEEE 802.11 standards
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