Wireless Sensor Networks in

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21 Νοε 2013 (πριν από 3 χρόνια και 7 μήνες)

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Wireless Sensor Networks in
Healthcare

Potential and Challenges


?
integrate available specialized medical tech.
with wireless networks (ex: wearable
accelerometers with integrated wireless cards
for patient monitoring)


Benefits: save on medical expenses, time
(less face
-
to
-
face appointments required),
allows more participants in clinical trials

Requirements


Interoperability between biomedical devices
required


Event ordering, timestamps, synchronization,
quick response in emergencies required


Reliability and robustness for making
accurate diagnoses and proper functioning in
uncontrolled environments


Integration of many types of sensors
demands new node architecture

Requirements (cont.)


Operation in buildings results in further
interference due to walls, etc. decreasing
reliability


Multi
-
modal collaboration and energy
conservation


Multi
-
tiered data management


Privacy of records: ownership of information
not always clear


Priority override must be carefully designed


Data available during emergencies


Realtime role
-
based access control

Acceptance of WSNs by
patients


Especially important for elderly patients:


Tendency to reject technology


Must be intuitive and easy to operate


A study in which elderly residents of Sydney
participated in an open
-
ended discussion found:


Overall positive view of WSNs due to implications
for independence


Ashamed of visible sensors (design as
unobtrusive as possible)


Adherence issues due to forgetfulness


Distrust of technology


Privacy

Implementation


Sensors: various types of wearable biomedical sensors with
integrated radio transceivers (ex: accelerometer in bracelet to
detect hand tremors)


Ad hoc network using Zigbee protocol?


Low power consumption of protocol makes it desirable for this
application


Radio signal received by cell phone and transmitted to server


Analysis of raw data performed via wavelet analysis


Decision tree or artificial neural network used to decide
appropriate action (data is within normal range, outside normal
range and either does or does not require emergency action,
etc.)


Data stored in server side database and report is generated to
send to healthcare professional



Monitoring and Data
Transmission


Monitoring and transmission can occur continuously,
periodically or be alert
-
driven (case
-
dependent)


Transmit differential data to decrease energy
consumption/traffic


Priority
-
based transmission: path of transmission
determined by nature of data, with emergency signals
receiving highest priority


Sensors (and potentially other wireless devices in the
area) form an ad hoc network


If cell phone fails to transmit data, data can be
transmitted over multiple hops in ad hoc network
to travel within range

Data Transmission (cont.)


ZigBee could be appropriate
specification for networking biomedical
devices


Significantly lower wake up time than
Bluetooth (15 ms or less vs. 3 s) > low
power consumption, long battery life


Inexpensive transceivers


Capable of establishing self
-
forming, self
-
healing mesh networks

Motion Detection: Wavelet
Analysis


Continuous Wavelet Transform (CWT)
-

similar to Fourier Transform, but with a variety
of probing functions






b translates function across x(t) and a varies time scale



(t), when b=0 and a=1, represents mother wavelet of a


family of wavelets



problem with CWT
-

overly redundant and extremely difficult

to recover original signal

Discrete Wavelet Transform


To limit redundancy, DWT restricts variations
in translation and scale (often to powers of
two)


Recovery tranformation:


Where a=2
k
, b = l * 2
k
, and d(k,l) is a sample of
W(a,b) at discrete points


Scaling function:



c(n) is a series of scalars defining specific
function


Wavelet:



d(n) is a series of scalars related to x(t)

Filter Banks


Most basic filter bank: x(n) is divided
into two
-

y
lp
(n) and y
hp
(n), using a
digital lowpass filter H
0

and highpass
filter H
1

respectively

Filter Banks (cont.)


Using this method, twice the points of original
function must be generated


Compensate by downsampling


Signal smoothed by series of low pass filters


Original signal broken down into frequency
bands > useful information about signal can
be determined