The Simulative Investigation of Zigbee/IEEE 802.15.4

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Thesis Defense on
The Simulative Investigation of Zigbee/IEEE
802.15.4
By, Vaddina Prakash Rao Under the Guidance
of, Dipl.-Ing. Dimitri Marandin (TUD) Dipl.-Ing.
Falk Hofmann (ZMD AG)
13th December 2005
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Contents

• Introduction to Zigbee
• Simulation Environment
• Performance Metrics
• Performance Analysis
• Adaptive Backoff Exponent (ABE)
• Performance Analysis of ABE
• Conclusions and Future Work

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1. Introduction to Zigbee

• Address Low Data Rate Applications
• Very Simple
• Just about 14 PHY and 35 MAC Primitives
• Low Data Rate
• 868MHz 20Kbps (Europe)
• 914MHz 40Kbps (USA)
• 2.4GHz 250Kbps (World Wide)
• Very Low Power Consumption
• 6 months 2 years of battery use
• Low Cost
• Avg. Module Cost 5 6 Euro

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1.1 Zigbee Basics

• Device Classes
• Full Function Device (FFD)
• Reduced Function Device (RFD)
• Supported Modes
• Beacon Enabled
• Non beacon
• Network Topologies
• Star
• Peer-to-Peer

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Star Topology
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Peer-to-Peer Topology
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1.2 Superframe Structure
BI aBaseSuperFrameDuration x 2 BO
SD aBaseSuperFrameDuration x 2 SO
Beacon
CAP
CFP
Beacon
(GTS)
BO/SO Beacon/Superframe Order BI Beacon
Interval SD Superframe Duration
CAP Contension Access Period CFP Contension
Free Period GTS Guaranteed Time Slots
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1.3 Data Transmission

• Network Device ? Coordinator

1. Coord Beacon Transmission
2. Node Synchronizes to the Super frame structure
3. Node Waits for its turn of transmission using
CSMA-CA
PAN coord
Node
0
1
4. Node On its turn, transmits data
5. Coord (Optional) Acknowledges the data
reception
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2. Simulation Environment

• Simulator NS-2
• Zigbee Parameters
• Frequency Band 868Mhz
• Scan Channels 0, 1 and 2
• Transmitting Power (Pt_) 1mW
• RXThresh_ -97dBm (1.9952e-13 W)
• CSThresh_ -97dBm (1.9952e-13 W)
• CPThresh_ 10
• Antenna Height 0.0864m
• Physical Parameters
• Propagation Model TwoRay Ground
• Antenna Type Omni Antenna

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• Traffic Parameters
• Traffic Type CBR (Constant Bit Rate)
• Number of Flows 8
• Packet Size 70 Bytes
• Traffic Direction node ? Coordinator

• Queue Parameters
• Queue Type Drop Tail
• Queue Length 150 packets
• General
• Simulation Time 1000 Secs
• Initial Energy 13000 Joules
• Number of Nodes 15
• Confidence Intervals 95

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3. Performance Metrics

• Throughput
• Total data bits received by all the nodes per
  second.
• Average Delay
• Flight time of a data packet to reach the
  destination.
• Delivery Ratio
• Percentage of successfully received packets.
• Energy Consumed
• Energy consumed to achieve throughput.

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4. Performance Analysis

• 4.1 Throughput Analysis

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4.2 Delivery Ratio
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4.3 Energy Consumption
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4.4 Packet Drops - Link Quality Indication
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4.5. Backoff Exponent Management
Backoff Exponent (BE) Determines number of
backoff periods ( 2BE-1) the device waits
before checking the channel
The Problem !!

• To conserve energy Zigbee uses very small
  BEs.
• gt devices tend to choose identical backoff
  exponents (identical backoff) periods.
• gt frequent collisions

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5. Adaptive Backoff Exponent (ABE)
1
8
2
node
Pkts Recv
27 31 35 39
28 32 36 40
29 33 37 41
30 34 38 42
31 35 39 43
32 36 40 44
33 37 41 45
6 8 5 7
34 38 42 46
End of Analyzing Cycle !!
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0
7
Coord calculates contribution by each node
4
6
Start of Analyzing Cycle
5, 6, 7 and 8 transmit to Coordinator
5
Beacon enabled PAN
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At the coordinator
5
7
8
7
5
6
8
6
Node
Contribution to n/w traffic (num of pkts)
5
7
8
6
46
38
34
42
34
38
42
46
42
38
46
34
Group-1
Group-2
-

PKT_DIFFERENCE
Coordinator has Information about each nodes
contribution to network traffic
Arranging their contribution in ascending order
PKT_DIFFERENCE 7
Check if it is time to implement ABE
Arranging into Groups
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At the coordinator
Beacon Construction
5
8
7
6
Coordinator decides Decrement BE of 5, 7
Increment BE of 6, 8
During the beacon construction ...
Inserting the number of increments and decrements
Inserting the addresses
5
8
7
6
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At the Nodes
5
8
7
6
macMinBE --
macMinBE
Receive the beacon
Read the ABE fields
If their address listed, change BE
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6. Performance Analysis of ABE
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7. Conclusions

• Applicability of Zigbee as an ideal automation
  technology for low data rate applications is
  investigated
• General Performance Analysis
• Maximum achievable data bandwidth 5.3Kbps
• Achievable Data Bandwidth _at_ 99 delivery ratio
  5.25kbps
• A device transmitting _at_ 10.07 Kbytes/day 4
  months
• Performance Analysis with ABE
• Maximum achievable data bandwidth 6.73kbps
• 27 Improvement of maximum throughput
• Achievable Data Bandwidth _at_ 99 delivery ratio
  6.554kbps
• 25 Improvement of maximum throughput _at_ 99
  delivery ratio

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Future Work

• Development of the software modules for the GTS
  implementation to investigate topics like
• efficient bandwidth utilization with GTS and CAP,
  
• reliable data transfer under these conditions
• Development of software modules for accurate
  energy consumption analysis
• Routing in complex mesh topologies
• Applying the Adaptive backoff exponent algorithm
• At congestion situations for 2.4Ghz.
• For mixed traffic scenarios

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Thank you !!