Wireless Networks

Lecture 41
IEEE 802.15.4/ZigBee
Dr. Ghalib A. Shah

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Outlines
 Overview of ZigBee
► Whats is ZigBee, Zigbee in Wireless World,
Architecture, Characteristics

 IEEE 802.15.4
►
►
►
►

Basics, Type of Devices
Topology, Addressing
Phy Layer
Channel Access Mechanisms
• Slotted/Unslotted CSMA/CA

► Data Transfer Model
► Superframe Structure
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Last Lecture






IP Over Bluetooth
Bluetooth Security
WPAN Standards
IEEE 802.15.3 Overview
802.15.3
►
►

Topology
Coordination
•
•
•
•
•

►
►
►
►

Starting a Piconet
Handing over control of piconet

Creating child piconet
Ending a Piconent
Association/Disassociation

Medium Access (Superframe)
Channel Time Management
Power management
MAC Frame format
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What is ZigBee Alliance?
 An organization with a mission to define
reliable, cost effective, low-power, wirelessly
networked, monitoring and control products
based on an open global standard
 The alliance provides interoperability,
certification testing, and branding.

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IEEE 802.15.4: What is ZigBee?


A standard for mesh networking
►




Designed for low power applications
►



20-250Kb/sec (depending on band)

Very Secure
►



Very long battery life

Low data rate
►



Reliability through meshed connectivity

AES-128 encryption available

Self configuring
►
►

Allows ad hoc networks
Ease of installation and configuration


5


ZigBee in the wireless world

Chart Copyright ZigBee Alliance 2004

6


ZigBee/IEEE 802.15.4 Market Feature







Low power consumption
Low cost
Low offered message throughput
Supports large network orders (<=65k nodes)
Low to no QoS guarantees
Flexible protocol design suitable for many
applications

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ZigBee Target Markets

Security
HVAC

TV

AMR

VCR

Lighting Control

DVD/CD

Access Control

BUILDING
AUTOMATION

CONSUMER
ELECTRONICS

Patient
monitoring

ZigBee

Fitness
monitoring

Wireless Control that

Simply Works

PERSONAL
HEALTH CARE

RF Remotes

PC &
PERIPHERALS
Security

Asset Mgt
Process
Control

INDUSTRIAL
CONTROL

RESIDENTIAL/
LIGHT
COMMERCIAL
CONTROL

Environmental
Energy Mgt

HVAC
Lighting Control
Access Control
Lawn & Garden

Irrigation
Chart Copyright ZigBee Alliance 2004

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ZigBee/802.15.4 Architecture

9


ZigBee/802.15.4 Technology: General
Characteristics







Data rates of 250 kbps , 20 kbps and 40kpbs.
Star or Peer-to-Peer operation.
Support for low latency devices.
CSMA-CA channel access.
Dynamic device addressing.
16 channels in the 2.4GHz ISM band, 10
channels in the 915MHz ISM band and one
channel in the European 868MHz band.

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IEEE 802.15.4 Basics
 802.15.4 is a simple packet data protocol for
lightweight wireless networks
► Channel Access is via Carrier Sense Multiple
Access with collision avoidance and optional time
slotting

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IEEE 802.15.4 Device Types
 There are two different device types :
► A full function device (FFD)
► A reduced function device (RFD)

 The FFD can operate in three modes serving
► Device
► Coordinator
► PAN coordinator

 The RFD can only operate in a mode serving:
► Device
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FFD vs RFD
 Full function device (FFD)
► Any topology

► Network coordinator capable
► Talks to any other device

 Reduced function device (RFD)

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Star Topology

Network
coordinator
Master/slave

Full Function Device (FFD)
Reduced Function Device (RFD)
Communications Flow
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Peer-Peer Topology

Point to point

Tree

Full Function Device (FFD)
Communications Flow
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Combined Topology

Full Function Device (FFD)
Reduced Function Device (RFD)
Communications Flow
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Extending ZigBee Networks


ZED (Zig Be e  Exte ns io n De vic e )
►




J oins two or more radio disjoint PANs
Provides a “wormhole” within a single
PAN
►



A ZigBee router with a wire interface

A low cost, high reliability link within the
radio network


ZED

ZED

PAN  A

PAN  A

Coordinator A

“Extends” the ZigBee network layer

ZED

Coordinator B

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PAN  B

ZED


Device Addressing
 Each independent PAN will select a unique
PAN identifier
 Addressing modes:
► star: Network (64 bits) +device identifier (16 bits)
► peer-to-peer: Source/destination identifier (64 bits)


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IEEE 802.15.4 PHY Overview
 PHY functionalities:
►
►
►
►
►
►

Activation and deactivation of the radio transceiver
Energy detection within the current channel
Link quality indication for received packets
Clear channel assessment for CSMA-CA
Channel frequency selection
Data transmission and reception

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IEEE 802.15.4 PHY Overview
 Operating Frequency Bands
868MHz/
915MHz
PHY

Channel 0


868.3 MHz

2.4 GHz
PHY

Channels 1-10

902 MHz

Channels 11-26

2 MHz

928 MHz

5 MHz

2.4 GHz

2.4835 GHz

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Frequency Bands and Data Rates
 The standard specifies two PHYs :
► 868 MHz/915 MHz direct sequence spread spectrum
(DSSS) PHY (11 channels)
• 1 channel (20Kb/s) in European 868MHz band
• 10 channels (40Kb/s) in 915 (902-928)MHz ISM band


► 2450 MHz direct sequence spread spectrum (DSSS)
PHY (16 channels)
• 16 channels (250Kb/s) in 2.4GHz band

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General Radio Specifications
 Transmit Power
► Capable of at least –3dBm

 Receiver Sensitivity
► -85 dBm (2.4GHz) / -91dBm (868/915MHz)

 Link quality indication
► The measurement may be implemented using
• Signal to noise ratio estimation
• Receiver energy detection

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Channel Access Mechanism
 Two type channel access mechanism, based
on the network configuration:
► In non-beacon-enabled networks  unslotted
CSMA/CA channel access mechanism
► In beacon-enabled networks  slotted CSMA/CA
channel access mechanism

• The super frame structure will be used.

23


CSMA/CA Algorithm
 Each device shall maintain three variables for
each transmission attempt
► NB: number of slots the CSMA/CA algorithm is
required to backoff while attempting the current
transmission.
► BE: the backoff exponent which is related to how
many backoff periods a device shall wait before
attempting to assess a channel
► CW: (a special design)

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Data Transfer Model
 Data transferred from device to coordinator

Network
Device

Coordinator

Beacon

Data

Acknowledgement

Network
Device

Coordinator

Data

Acknowledgement
(Optional)

(Optional)

Communication to a coordinator
In a beacon-enabled network

Communication to a coordinator
In a non beacon-enabled network

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