Authors: David Cypher, Nicolas Chevrollier,
Nicolas Montavont, and Nada Golmie
Presentation by: Mohamad Chaarawi
COSC 7388 Advanced Distributed Computing

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

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

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

• 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

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

Medical Data General purpose

• 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

• 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

• 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

• 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)

• 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.

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

• 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 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 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.

• 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.

• 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.

• 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?

• Need to configure the channels to avoid or reduce interference by avoiding overlapping channels.
• Channel configuration can be done statically or dynamically.

• 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

• 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.

• 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?

• 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.

• 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.

• 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.

• 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.

• 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.

• 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

• 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

• Discovery Phase:
– Passive: waits for a beacon message sent periodically by the AP
– Active: send probe request messages, in which inrange 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

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

• 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