Prevailing over Wires in Healthcare Environments: Benefits and Challenges

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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

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Introduction

• Wireless technologies spreading in healthcare
  environments
• Need a reliable connection especially in this
  kind of environment
• Cost effectiveness
• Universal interface for wireless communication

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Wireless over Wires?

• Cost and time of Wiring
• Mobility
• Interoperability
• Patient comfort
• Ubiquitous connectivity

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Topology
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Outline

• Healthcare applications
• User case
• Wireless technologies
• Deployment
• Interference
• Moving between APs
• Summary

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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

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Healthcare Applications (I)

• Requirements
• Reliable connectivity
• Timeliness and integrity of information
• BW, delay, loss
• Different medical applications will use different
  wireless technologies

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Healthcare Applications (II)
Medical Data
General purpose
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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

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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

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Heart to Digital
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Wireless Technologies
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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

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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)

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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.

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Deployment issues (I)

• Several issues need to be considered for
  deployment
• Coverage Area
• Network Architecture
• Frequency Allocation
• Output power

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Deployment issues (II)

• ECG leads on the patients 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.

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Coverage Area (I)

• Coverage areas vary between
• Body area (lt 1m)
• Personal area (lt 10m)
• Local area (lt 100m)
• Wide area (gt 100m)
• 802.15 designed for personal area and 802.11 for
  local area.

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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.

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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 APs 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.

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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.

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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?

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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.

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Frequency Allocations (IV)
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Output Power

• Power used to generate the signal affects the
  coverage area and the power consumption of the
  device.
• WLANS -gt mains
• WPANS -gt batteries
• Wireless to remove wires!! So ECG is battery
  powered

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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.

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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?

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Interference in the 2400 MHz Band

• Usage scenario is extended by adding an
  individual that enters the patients room using a
  Bluetooth device.
• The Bluetooth device spans the entire frequency
  band. Overlap is inevitable with the WLAN or WPAN
  channels.

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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.

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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.

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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.

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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.

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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 patients bed moving out of the current
  coverage area of the current WLAN AP)
• Handle interference effects and mobility
  management

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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

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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

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Layer 3

• Need to discover the information of the link
• IPv6
• Router Advertisement
• Update location of the node with the link

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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

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Questions?