Prevailing over Wires in Healthcare

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21 Νοε 2013 (πριν από 3 χρόνια και 4 μήνες)

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Prevailing over Wires in Healthcare
Environments: Benefits and

Authors: David
, Nicolas
, and Nada

Presentation by: Mohamad Chaarawi

COSC 7388 Advanced Distributed Computing


Wireless technologies spreading in healthcare

Need a reliable connection especially in this
kind of environment

Cost effectiveness

Universal interface for wireless

Wireless over Wires?

Cost and time of Wiring



Patient comfort

Ubiquitous connectivity



Healthcare applications

User case:

Wireless technologies



Moving between APs


Universal Standard

Development of a specification for wireless
universal and interoperable interface


Easy to use



Not starting from scratch

IEEE 802 Local Area Network/Metro Area Network
standards organization

Healthcare Applications (I)


Reliable connectivity

Timeliness and integrity of information

BW, delay, loss

Different medical applications will use
different wireless technologies

Healthcare Applications (II)

Medical Data


Wireless Technologies

Standards developed by IEEE 802.

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

with many different
physical layers (a/b).

WPAN: each defines its MAC

physical layers.

IEEE 802.15.1: includes layers of the Bluetooth

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

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


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
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

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

ands for medical usage include (ISM):




Those bands are shared however with other

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

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.

> mains

> batteries

Wireless to remove wires!! So ECG is battery

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

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


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

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

of the low
level WPAN monitor is measured for

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

Noncollaborative Techniques

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

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

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

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

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

Handle interference effects and mobility

Handover Management

Changing the point of attachment to the

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

Layer 3

Need to discover the information of the link


Router Advertisement

Update location of the node with the link


Surveyed several wireless technologies

Used ECG as a user case for choosing the right

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