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ECE 5900 Computer Engineering Seminar
Instructor: Dr. Chigan
Analysis of the Performance of IEEE
802.15.4 for Medical Sensor Body
Area Networking
Huaming Li
Outline
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Introduction
802.15.4 Overview
Analysis assumptions
Average transmission time with csma/ca
Network scenarios and power analysis
Results
Conclusion
Introduction
One promising kind of sensor network:
Wireless Body Area Network (WPAN)
 Medical sensing and control
 Wearable computing
 Location awareness and identification
 Implanted medical sensors (Focus)
Coronary care
Diabetes
Optical aids
Drug delivery
Introduction (Cont)
Implanted medical sensors (Focus)
Advantages
Spread the memory load,
processing load and improving the
access to data
Pains
Power! (battery lifetime)
Replacing or charging batteries
means a serious medical procedure
Introduction (Cont)
Implanted medical sensors (Main concern)
Objective
Make Batteries work 10-15 years
Method
Ensure that all sensors are powered
down or in sleep mode when not in
active use
Tradeoff
Battery life VS. latency
Introduction (Cont)
Our options
Market Name
Standard
Application
Focus
GPRS/GSM
1xRTT/CDMA
Wi-Fi™
802.11b
Bluetooth™
802.15.1
ZigBee™
802.15.4
Wide Area
Voice & Data
Web, Email,
Video
Cable
Replacement
Monitoring &
Control
System
Resources
16MB+
1MB+
250KB+
4KB - 32KB
Battery Life
(days)
1-7
.5 - 5
1-7
100 - 1,000+
Network Size
1
32
7
255 / 65,000
Bandwidth
(KB/s)
64 - 128+
11,000+
720
20 - 250
Transmission
Range (meters)
1,000+
1 - 100
1 - 10+
1 - 100+
Success
Metrics
Reach,
Quality
Speed,
Flexibility
Cost,
Convenience
Reliability,
Power, Cost
Outline
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Introduction
802.15.4 Overview
Analysis assumptions
Average transmission time with csma/ca
Network scenarios and power analysis
Results
Conclusion
802.15.4 (LR-WPAN) Overview
Architecture
Upper Layers
Other LLC
IEEE 802.2 LLC
IEEE 802.15.4 MAC
IEEE 802.15.4
868/915 MHz
PHY
IEEE 802.15.4
2400 MHz
PHY
Physical Medium
802.15.4 (LR-WPAN) Overview
Physical Layer (use 2.4G here)
802.15.4 (LR-WPAN) Overview
MAC Layer (use star topology here)
Why star topology here?
802.15.4 (LR-WPAN) Overview
Why star topology here?
Coordinator is external to the body
PDA, mobile phone or bedside monitor
station
Easy to replace of charge batteries
Easy to communicate with other networks
Coordinator defines the start and end of a
superframe and is charge of the association
and disassociation of the other nodes
802.15.4 (LR-WPAN) Overview
IEEE 802.15.4 superframe structure
802.15.4 (LR-WPAN) Overview
Two Communication methods
Beacon mode
Pros: Coordinator can communicate at will
Cons: Listeners have to keep awake
Non-beacon mode
Pros: Nodes can sleep more
Cons: Communication latency
Outline
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Introduction
802.15.4 Overview
Analysis assumptions
Average transmission time with csma/ca
Network scenarios and power analysis
Results
Conclusion
Analysis Assumptions
Sensor specification
Hardware assumption
Implanted sensor link budget
Description of network
Analysis Assumptions
Sensor specification
Analysis Assumptions
Hardware assumption
Transceiver parameters (Chipcon CC2420)
Microcontroller: Motorola MC9508RE8 4.5uA 700nA
Battery: Lithium 560mAh at 3.0V
Analysis Assumptions
Implanted sensor link budget
A 0 dBm 2.45 GHz transmitter will operate with
a 5.6 dB margin
Description of network
A star network consists of the coordinator and
10 body implanted sensors
Steady state network (no consideration about
association or disassociation) to or from network
Outline
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Introduction
802.15.4 Overview
Analysis assumptions
Average transmission time with csma/ca
Network scenarios and power analysis
Results
Conclusion
Average transmission time
with CSMA/CA
Three variables maintained by each node for each
transmission attempt (CSMA/CA):
NB: Number of back-offs permitted before
declaring channel access failure (0-5);
CW: contention window length, only used in
slotted CSMA/CA (Set to 2)
BE: back-off exponent, back-off periods in the
(0-5)
range 0 to 2BE  1
If BE is set to 0, CSMA/CA is switched off
Average transmission time
with CSMA/CA
Back-off periods
The average number of back-off periods for each range is
Average transmission time
with CSMA/CA
The total transmission time
The average number of back-off periods for each range is
Average transmission time
with CSMA/CA
The total transmission time
The average number of back-off periods for each range
is
P is the probability of a clear channel after the first back-off interval
(n sensors)
Q is the probability of a sensor transmits in a CCA period
Average transmission time
with CSMA/CA
The total transmission time
The average number of back-off periods for each range is
How to calculate
For example when R=2.5
The average back-off time for each back-off interval
Outline
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Introduction
802.15.4 Overview
Analysis assumptions
Average transmission time with csma/ca
Network scenarios and power analysis
Results
Conclusion
Network scenarios and power analysis
Sensor power consumption with beacon reception
Problem: The sensor devices within a beacon network
have to wake up to receive the beacon from the
coordinator (Power consuming)
Timebase Tolerances
Warm-up time
Network scenarios and power analysis
Data Transfer Mechanisms (Beacon)
Data transfer to a coordinator (upload)
Is the upload period
Network scenarios and power analysis
Data Transfer Mechanisms (Beacon)
Data transfer from a coordinator (download)
Is the download period
Network scenarios and power analysis
Data Transfer Mechanisms (Non-beacon)
Data transfer to a coordinator (upload)
Is the upload period
Network scenarios and power analysis
Data Transfer Mechanisms (Non-beacon)
Data transfer from a coordinator (upload)
Results
Outline
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Introduction
802.15.4 Overview
Analysis assumptions
Average transmission time with csma/ca
Network scenarios and power analysis
Results
Conclusion
Results
Average Back-off
Results
Average Back-off
Results
Average Back-off
With a small number of sensors that are
effectively off most of the time, the probability of
a channel being free is greater than 99 %.
Therefore, for the relatively small number of
sensors used in the WBAN networks explored
here, it would be more economical to keep
the CSMA/CA switched off.
This is to ensure that the automatic initial
back-off is avoided.
Results
Node Lifetime in Beacon Networks
Results
Node Lifetime in Beacon Networks
Results
Node Lifetime in Beacon Networks
15-year lifetime may only be obtained for
very low upload rates.
It is under very limited data rate conditions
and a tight tolerance crystal, which typically
must be better than 25 ppm.
Results
GTS Option
Results
GTS Option
The main drawback of using GTS is that the receiver
in the sensor remains on for the duration of the
timeslot regardless of the size of the data packet.
Results
Non-Beacon Networks
Results
Non-Beacon Networks
Outline
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Introduction
802.15.4 Overview
Analysis assumptions
Average transmission time with csma/ca
Network scenarios and power analysis
Results
Conclusion
Conclusion
As a solution to the challenge of the body
area network, the IEEE 802.15.4 standard
would provide a limited answer in its nonbeacon form.
Sensors that do not have large amounts of
data to transfer could be used, i.e., small
packets of data several times per hour.
Questions And Comments
Thank You！