1. CS526 Wireless Sensor Networks
ZigBee/IEEE Overview
KD Kang
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CS526 Wireless Sensor Networks

2. WPAN (Wireless Personal Area Network)
Cellular networks
A cell covers a large area (1-2 km)
A smaller coverage is needed for higher user densities and emergent data traffic
IEEE
Ethernet matching speed,
Long range (100m)
High data rate
WPAN
Wireless network around a person (10m)
Low-cost, low-power, short range, very small size
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CS526 Wireless Sensor Networks

3. CS526 Wireless Sensor Networks
WPAN classes
High data rate WPAN
20 Mbps or higher
Multimedia applications with high QoS needs
Medium rate WPAN
IEEE /Bluetooth
Cell phones – PDA communication
Voice communication: 1 – 3 Mbps
Low rate WPAN (LR-WPAN)  IEEE /ZigBee
Industrial, residential, and medical applications
Low-power, low-cost
Relaxed need for data rate and QoS: 20kbps – 250kbps
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4. CS526 Wireless Sensor Networks
ZigBee vs. Bluetooth
ZigBee
Can implement mesh networks larger than is possible with Bluetooth
ZigBee compliant device transmit 10 – 75 meters (Bluetooth device can transmit 10m)
Low data rate in unlicensed RF worldwide
2.4GHz global: 250kbps
915MHz in Americas: 40kbps
868MHz in Europe: 20kbps
Low frequency provides longer range due to lower propagation losses
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5. CS526 Wireless Sensor Networks
IEEE /ZigBee
ZigBee is a low data rate, low power, low cost wireless networking protocol targeted towards automation and remote control applications
IEEE committee started working on a low data rate standard a short while later
ZigBee alliance and IEEE joined forces
ZigBee is the commercial name
IEEE standard more focused on Physical and MAC layers
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6. CS526 Wireless Sensor Networks
ZigBee devices
Full function device (FFD)
A network has at least one FFD operating as the PAN coordinator
Can operate as a PAN coordinator, router, or device
Only one coordinator in a PAN
Can communicate with RFDs and FFDs
Reduced function device (RFD)
End device
Can only talk to FFD
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7. CS526 Wireless Sensor Networks
Network Topologies
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8. CS526 Wireless Sensor Networks
Star topology
Communication is established between devices and a single PAN coordinator
Applications: home automation, personal computer peripherals, toys & games
After an FFD is activated for the first time, it may establish its own network and become the PAN coordinator
Each star network has a unique PAN ID
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9. Mesh/P2P (peer-to-peer) topology
Unlike a star PAN, FFDs can directly talk with each other as long as they are in a communication range of one another
Applications: industrial control and monitoring, WSNs, …
Multipath routing is possible for reliability
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10. Cluster-tree topology
A special case of a P2P network
Most devices are FFDs
Any FFD can be a coordinator, but only one of them is the PAN coordinator
The PAN coordinator forms the first cluster by establishing itself as the cluster head (CLH) with cluster ID (CID) 0, choose an unused CID and broadcast beacon frames to neighboring devices
A device receiving the beacon may request to join the network at the CLH
The coordinator may instruct a device to become the CLS of a new cluster
Increased coverage at the cost of increased message latency
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11. CS526 Wireless Sensor Networks
IEEE MAC
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12. CS526 Wireless Sensor Networks
Superframe structure
Superframe bounded by network beacons from the coordinator
Divided into 16 equally sized slots: Structure defined by coordinator
Beacon sent in the first slot of each superframe to synchronize devices, to identify PAN, and describe superframe structure
Optional: Coordinator can turn off beacon transmissions, if it doesn’t want superframe structure
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13. Optional Frame Structure
Inactive Period
15ms * 2SO
where 0  SO  14
Active Period
15ms * 2BO
where SO  BO  14
Beacon Interval
SO = Superframe order
BO = Beacon order
Superframe may have inactive period
If superframe structure is not used, coordinator does not transmit a beacon and set BO = SO = 15  All transmissions except ACK will use unslotted CSMA-CA
Source: Marco Naeve.

14. Optional Superframe Structure: Active portion = CAP + CFP with Guaranteed Time Slots
GTS 1
GTS 2
GTS 3
Contention Access Period
Contention Free Period
Slot
15ms * 2n
where 0  n  14
Network beacon
Transmitted by PAN coordinator. Contains network information,
frame structure and notification of pending node messages.
Beacon
extension
period
Space reserved for beacon growth due to pending node messages
Contention
Access by any node using slotted CSMA-CA
Guaranteed
Time Slot
Reserved for nodes requiring guaranteed bandwidth [n = 0].
Source: Marco Naeve, Eaton Corp.

15. CS526 Wireless Sensor Networks
CSMA-CA
CSMA-CA is not used in two cases:
Channel access during CFP
If a device requests data from the coordinator, the coordinator immediately send ACK followed by data
If superframe structure is used, use slotted CSMA-CA: similar to CSMA-CA in
Else, use unslotted CSMA-CA: more aggressive than slotted CSMA-CA
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16. Slotted CSMA Procedure
Used in beacon enabled networks.
Source: Marco Naeve

17. Un-slotted CSMA Procedure
Used in non-beacon networks.
Source: Marco Naeve

18. CS526 Wireless Sensor Networks
Routing: AODV
RREQ
RREP
RERR
Hop count
Sequence number
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19. Routing: Single cluster network
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20. Routing: Single cluster network – Multihop cluster setup
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21. Routing: Multiple cluster network
Designated deivce (DD)
Assign a unique cluster ID to each cluster head
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22. CS526 Wireless Sensor Networks
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23. CS526 Wireless Sensor Networks
More information
S. C. Ergen, ZigBee/IEEE Summary, Sept. 10, 2004.
IEEE Working Group for WPAN
ZigBee Allicance
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24. CS526 Wireless Sensor Networks
Questions?
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CS526 Wireless Sensor Networks