Prevailing over Wires in Healthcare

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?