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?
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