Prevailing over Wires in Healthcare

illnurturedtownvilleMobile - Wireless

Nov 21, 2013 (3 years and 10 months ago)

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Prevailing over Wires in Healthcare
Environments: Benefits and
Challenges

Authors: David
Cypher
, Nicolas
Chevrollier
,
Nicolas
Montavont
, and Nada
Golmie

Presentation by: Mohamad Chaarawi

COSC 7388 Advanced Distributed Computing

Introduction


Wireless technologies spreading in healthcare
environments


Need a reliable connection especially in this
kind of environment


Cost effectiveness


Universal interface for wireless
communication

Wireless over Wires?


Cost and time of Wiring


Mobility


Interoperability


Patient comfort


Ubiquitous connectivity


Topology

Outline


Healthcare applications


User case:


Wireless technologies


Deployment


Interference


Moving between APs


Summary

Universal Standard


Development of a specification for wireless
universal and interoperable interface
communication:


Transparent


Easy to use


Quicky

(re)configurable


Not starting from scratch


IEEE 802 Local Area Network/Metro Area Network
standards organization

Healthcare Applications (I)


Requirements:


Reliable connectivity


Timeliness and integrity of information


BW, delay, loss


Different medical applications will use
different wireless technologies

Healthcare Applications (II)

Medical Data

General
purpose

Wireless Technologies


Standards developed by IEEE 802.


WLAN (IEEE 802.11): uses a single media access
control (MAC)
sublayer

with many different
physical layers (a/b).


WPAN: each defines its MAC
sublayer

and
physical layers.


IEEE 802.15.1: includes layers of the Bluetooth
specification


IEEE 802.15.4: designed for low data rates, low power
consumption, and low usage applications

Electrocardiogram (ECG)


Records electrical signals from the heart


Continuous signals


Must be sampled to be digitized (important
for choosing the traffic characteristics of the
transport)


For Example: we have 500 samples/s and
sample size is 8 bits, this means that the data
traffic requirement is 4000 bits/s

Heart to Digital

Wireless Technologies

Packetization


The pairing focuses on packetization (framing
and the sample accumulation delay).


Considering just the data traffic requirement,
the 802.15.4 is the most appropriate


Medium Access


Need to consider the method that contributes
to the end
-
to
-
end delay:


802.15.4 uses CSMA/CA which produces a random
access delay for each frame.


Analysis of the ECG shows that the medium access
delay ranges from 1.024 to 5.216 ms, as the
number of samples per frame varies from 1 to 118
(max payload)


Data Service


ECG application is more sensitive to time
delays than to packet loss.


IEEE 802.15.4 offers both unacknowledged
and acknowledged which contribute to delay
and overhead, so unacknowledged data
service is used in our case.

Deployment issues (I)


Several issues need to be considered for
deployment:


Coverage Area


Network Architecture


Frequency Allocation


Output power

Deployment issues (II)


ECG leads on the patient’s body collect the
medical data that is displayed on a monitor
nearby. This data also is transmitted to a
remote station.


Movement of the patient between rooms
should not break the communication.

Coverage Area (I)


Coverage areas vary between:


Body area (< 1m)


Personal area (< 10m)


Local area (< 100m)


Wide area (> 100m)


802.15 designed for personal area and 802.11
for local area.


Coverage Area (II)


Coverage areas vary widely based on radio
frequency used and the physical environment.


For the personal area, the signal can be
constrained within a limited area, while for local
area larger distances need to be covered.


Since the ECGs communication devices are close
to each other, a personal area network (802.15.4)
can be used.


But to communicate with remote stations, a local
area network is needed.

Network Architecture


Wireless technologies are designed with:


Infrastructure mode: assumes a fixed AP, which
attaches to the established network and thus provides
a communication portal for stations in the AP’s range.


Ad hoc mode: permits devices to communicate with
other peer devices dynamically (802.15). Quick
deployment is an advantage but Radio Frequency
management can be a problem.


For the ECG, Ad hoc mode is more appropriate.


Frequency Allocations (I)


Radio frequency (RF) spectrum: (3 kHz


300 GHz)


In the US, the Federal Communications
Commission (FCC) divides it into many usage
bands.


B
ands for medical usage include (ISM):


Industry


Scientific


Medical


Those bands are shared however with other
users.

Frequency Allocations (II)


Need to select first which ISM band to use.


All three wireless technologies use the 2400
MHz band. 802.11a and 802.15.4 have other
channels in some bands that can be used in
case the 2400 MHz band is overcrowded.


Next step: How the band is used?

Frequency Allocations (III)


Need to configure the channels to avoid or
reduce interference by avoiding overlapping
channels.


Channel configuration can be done statically
or dynamically.

Frequency Allocations (IV)

Output Power


Power used to generate the signal affects the
coverage area and the power consumption of
the device.


WLANS
-
> mains


WPANS
-
> batteries


Wireless to remove wires!! So ECG is battery
powered

Pairing ECG and Wireless Technologies


After looking at the deployment issues
discusses, the IEEE 802.15.4 can support the
needs for the ECG.


A WLAN can support the communication
between the monitor device and remote
station.


RF frequencies can be selected for peaceful
coexistence of different wireless technologies.

Interference


In the wireless world, anticipation of devices is
very low, since any device can appear anytime
anywhere.


How serious will the interference be?


How will devices maintain communication?

Interference in the 2400 MHz Band


Usage scenario is extended by adding an
individual that enters the patient’s room using
a Bluetooth device.


The Bluetooth device spans the entire
frequency band. Overlap is inevitable with the
WLAN or WPAN channels.

Walk in Usage Scenario


The simulation consists of the WPAN sensors
carrying ECG traffic, which is collected and
transmitted via the WLAN to a remote location.


When the walk in Bluetooth device is activated,
the packet loss at the MAC
sublayer

of the low
level WPAN monitor is measured for
performance.


The loss came up to 60% at close range (0.5m)


Interference mitigation techniques are needed to
tackle this issue.

Interference Mitigation Techniques


Two main categories:


Collaborative: require communication between
heterogeneous protocol stacks.


Noncollaborative: no direct communication
between devices, rely on channel or network
measurements to detect presence of other
devices.

Noncollaborative Techniques


Two strategies are used to avoid usage of the
same frequency:


Time
-
Division Multiplexing (TDM): postpone
transmissions till a channel is clear (reduce packet loss
but increase delay)


Frequency
-
Division Multiplexing (FDM): allocate
different portions of the frequency band to a specific
group of communicating devices.


Neither of these can eradicate interference, and
these techniques are triggered after the
communication is impacted.

Mobility of Wireless Networks (I)


Main advantage of using wireless in
healthcare is the ability to move those devices
around.


Wireless technologies have to handle the
movement of devices even when there is an
ongoing communication.


In a hospital environment, the assumption is
that the movement is in the hospital and at
walking speed.

Mobility of Wireless Networks (II)


Two wireless devices are communicating
directly (Cell phone and
earset

or ECG sensors
and monitor)


Wireless devices are communicating through
an AP (the patient’s bed moving out of the
current coverage area of the current WLAN
AP)


Handle interference effects and mobility
management

Handover Management


Changing the point of attachment to the
infrastructure


Layer 2 handover: old and new APs share the
same subnet.


Layer 3 handover: the APs are connected to a
different subnet

Layer 2


Discovery Phase:


Passive: waits for a beacon message sent periodically
by the AP


Active: send probe request messages, in which in
-
range APs reply to by a probe response message


Authentication Phase: mobile nodes and APs
exchange identities.


Association Phase: exchange two frames to
allocate an association identifier to the mobile
node

Layer 3


Need to discover the information of the link


IPv6:


Router Advertisement


Update location of the node with the link

Summary


Surveyed several wireless technologies


Used ECG as a user case for choosing the right
technology


Deployment issues


Need to fully investigate the requirements of the
medical application, and the functions of the
wireless technology


Continuous evaluation


Trade offs for wireless networks

Questions?