Transcript Autonomous Networks Research Group: Vision and Plans

Performance Evaluation of
IEEE 802.15.4 MAC
for Low Rate Low Power
Wireless networks
Gang Lu
Bhaskar Krishnamachari
Cauligi S. Raghavendra
Department of Electrical Engineering-Systems
April 9, 2004
http://ceng.usc.edu/~anrg/
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Outline
• Overview of IEEE 802.15.4TM/ZigBeeTM
• Physical Layer
• MAC Layer
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Super frame Structure
CSMA and polling
GTS in CFP
Synchronization
• Simulation
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Introduction to LR-WPAN
• Low-Rate Low-Power Wireless Networks
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Wireless sensor networks
Industrial Control and Monitoring
Environmental and Health Monitoring
Home Automation, Entertainment and Toys
Security, Location and Asset Tracking
Emergency and Disaster Response
• IEEE 802.15.4
– A new MAC for LR-WPAN
– IEEE 802.11: an “overkill technology”
– Bluetooth: high data rate for multimedia applications,
small size network, high power consumption
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Features of IEEE 802.15.4
• 16 channels in the 2450 MHz band, 10 channels in the
915 MHz band, and 1 channel in the 868 MHz band
• Over-the-air data rates of 250 kb/s, 40 kb/s, and 20 kb/s
• Star or peer-to-peer operation
• Allocated 16 bit short or 64 bit extended addresses
• Allocation of guaranteed time slots (GTSs)
• Carrier sense multiple access with collision avoidance
(CSMA-CA) channel access
• Fully acknowledged protocol for transfer reliability
• Low power consumption
• Energy detection (ED)
• Link quality indication (LQI)
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Network Topologies
IEEE 802.11 only describes the MAC and PHY layer.
Upper layers are designed by ZigBee which has not be
released.
April 9, 2004
From ``Home Networking with IEEE 802.15.4: A Developing Standard for Low-Rate Wireless
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Personal Area Networks", Ed Callaway, Paul Gorday and Lance Hester, IEEE
Communications Magazine Aug. 2002
PHY: Channel Structure
From ``Home Networking with IEEE 802.15.4: A Developing Standard for Low-Rate Wireless
Personal Area Networks", Ed Callaway, Paul Gorday and Lance Hester, IEEE
April 9, 2004 Communications Magazine Aug. 2002
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PHY Features
Power feature of CC2420
Rx
Tx
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19.7mA
P=-25dBm 8.5mA
P=-15dBm 9.9mA
P=-10dBm 11mA
P=-5dBm 14mA
P=0dBm 17,4mA
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•
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Both PHYs are based on DSSS
2.4GHz PHY provides 250kbps
868/915 MHz PHY provides
20kbps and 40kbps respectively
Sensitivity: -85dBm for 2.4GHz
and -92dBm for 868/915MHz
Range: 10-20m
From ``Home Networking with IEEE 802.15.4: A Developing Standard for Low-Rate Wireless
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Personal Area Networks", Ed Callaway, Paul Gorday and Lance Hester, IEEE
Communications Magazine Aug. 2002
MAC: Super frame
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Beacon Mode:
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PAN coordinator broadcasts a beacon which tells the superframe structure
CAP: Contention Access Period
CFP: Contention Free Period
GTS: Guaranteed Time Slot
Turn off radio in inactive period to save energy
Beaconless mode
–
Just CSMA-CA
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Collision Access Period
• Transaction
– either the coordinator needs to indicate in its beacon when
messages are pending for devices
– or the devices themselves need to poll the coordinator to
determine whether they have any messages pending.
• CSMA-CA
– Power consumption during the backoff period
– IEEE 802.15.4 provides a “Battery Life Extension” (BLE)
mode which limited the backoff exponent to 0-2.
– Reduced the idle listening period
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GTS in CFP
• A device can request dedicated bandwidth to
achieve low latency
• Used only for communication between PAN
coordinator and devices
• PAN coordinator maintain and assign the GTS
slots used by devices
• A device enables its radio at a time prior to the
start of the GTS and transmit during GTS
without CSMA-CA
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Synchronization
• PAN coordinator transmits beacon frames
periodically to announce the superframe
structure
• A device need to know the superframe before
any data transmission
• Synchronization methods:
– Tracking
• Enable its radio periodically to receive the beacon
– Non-tracking
• Enable its radio when necessary and search for the next
beacon
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Simulation
• Only evaluate the
beacon mode on star
topology
• Radio parameters in
table 1
• 7X7 grid with 49 node
• 4m distance between
adjacent node
• CBR traffic with 50%
randomization
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CSMA-CA
4
4
x 10
3.5
Throughput (bps)
3
2.5
2
1.5
1
1 source
20 sources
40 sources
0.5
0
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0
20
40
60
80
100
120
Traffic Load (kbps)
140
160
180
200
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Duty Cycle-Energy
3.5
4
macSuperframe=0
macSuperframe=1
macSuperframe=2
3
3
2.5
2.5
2
Delay (s)
Energy (Joule)
macSuperframeOrder=0
macSuperframeOrder=1
macSuperframeOrder=2
3.5
1.5
2
1.5
1
1
0.5
0
0.5
0
0.1
0.2
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0.3
0.4
0.5
0.6
Duty Cycle
0.7
0.8
0.9
1
0
0
0.1
0.2
0.3
0.4
0.5
0.6
Duty Cycle
0.7
0.8
0.9
1
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GTS in CFP
2
36
1.8
34
1.6
32
CAP
CFP
1.4
30
1.2
Delay (ms)
Energy (J)
CAP
CFP
1
0.8
28
26
24
22
0.6
20
0.4
18
0.2
5
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15
20
Background Traffic (kbps)
25
30
16
5
10
15
20
Background Traffic (kbps)
25
30
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Synchronization
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2
Energy (J)
Enegy (J)
1.5
1
0.5
4
2
0
600
0
0
2
macBeaconOrder
600
400
200
4
0
Tracking
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Rate (bps)
6
400
Rate (bps) 200
4
0
0
2
macBeaconOrder
Non-tracking
Tracking: Enable radio periodically to receive the beacon
Non-tracking: Enable radio when necessary and search for the next beacon 16
Synchronization
Crossover curve
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Analysis & Simulation result
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Conclusion
• An overview of IEEE 802.15.4
• Evaluation of MAC
– CSMA-CA in CAP
– Energy Latency Tradeoff of Duty Cycle
– Energy Latency Tradeoff of GTS in CFP
– Tradeoff between tracking and non-tracking
synchronization
• Plan to make NS-2 model available online
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