Prevailing over Wires in Healthcare Environments: Benefits and

ChallengesAuthors: David Cypher, Nicolas Chevrollier,

Nicolas Montavont, and Nada GolmiePresentation 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.

• Bands 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?