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Introduction to Wireless Sensor Networks

ZigBee Overview

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What is ZigBee?• “Internet Everything”

– Your toaster gets an IP address• Wireless standard formed by an

alliance of industry leaders• Motorola, Phillips, Samsung, Cisco…

over 100 companies!!

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Why ZigBee?• Reliable and self healing• Supports large number of nodes• Easy to deploy• Very long battery life• Secure• Low cost• Can be used globally

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Applications

ZigBeeWireless Control that

Simply Works

RESIDENTIAL/LIGHT

COMMERCIAL CONTROL

CONSUMER ELECTRONICS

TVVCRDVD/CDremote

securityHVAClighting controlaccess controllawn & garden irrigation

PC & PERIPHERALS

INDUSTRIALCONTROL

asset mgtprocess control

environmentalenergy mgt

PERSONAL HEALTH CARE

BUILDING AUTOMATION

securityHVACAMR

lighting controlaccess control

mousekeyboardjoystick

patient monitoring

fitness monitoring

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– “the software” – Network, Security &

Application layers– Brand management

IEEE 802.15.4– “the hardware” – Physical & Media

Access Control layers

PHY868MHz / 915MHz / 2.4GHz

MAC

NetworkStar / Mesh / Cluster-Tree

Security32- / 64- / 128-bit encryption

Application

API

ZigBeeAlliance

IEEE 802.15.4

Customer

Silicon Stack App

IEEE 802.15.4 & ZigBee In Context

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Why IEEE 802.15.4?

• Ultra Low complexity• Ultra Low cost• Ultra Low power consumption• Data reliability• Low data rate

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802.15.4 General Characteristics

• Data rates of 20 kbps and up to 250 kbps• Star or Peer-to-Peer network topologies• Support for Low Latency Devices• CDMA-CA Channel Access• Handshaking• Low Power Usage consumption• 3 Frequencies bands with 27 channels• Extremely low duty-cycle (<0.1%)

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802.15.4 Frequency Bands

BAND COVERAGE DATA RATE CHANNELS

2.4 GHz ISM Worldwide 250 kbps 16

915 MHz ISM Americas 40 kbps 10

868 MHz Europe 20 kbps 1

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Channel Division

868MHz/915MHz PHY

2.4 GHz

868.3 MHz

Channel 0 Channels 1-10

Channels 11-26

2.4835 GHz

928 MHz902 MHz

5 MHz

2 MHz

2.4 GHz PHY

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Modulation & Spreading• Direct Sequence Spread Spectrum

(DSSS)– Chipping Sequences

• 2.4 GHz– 32-chip PN codes– Chip modulation is MSK at 2.0 Mchips/s

• 868/915 MHz– 15-chip m-sequence– Chip modulation is BPSK at 0.3 Mchips/s

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Media Access Control• Code Division Media Access w/

Collision Avoidance (CDMA-CA)• Bi-Directional Communications

(Duplex)• Dynamic Device Addressing• Fully Handshaked Protocol• Optional Guaranteed Time Slots• 2.4 GHz - 16-ary orthogonal• 868/915 MHz - differential encoding

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Packet Structure• Packet Fields

– Preamble (32 bits) - synchronization– Start of Packet Delimiter (8 bits) - specifies one of

3 packet types– PHY Header (8 bits) - Sync Burst flag, PSDU

length– PSDU (0 to 127 bytes) - Data

PreambleStart ofPacket

Delimiter

PHYHeader

PHY ServiceData Unit (PSDU)

6 Bytes 0-127 Bytes

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Transceiver Characteristics• Transmit Power

– Capable of at least 1 mW– Power reductions capability required if > 16 dBm

(reduce to < 4dBm in a single step)• Receiver Sensitivity

– -85 dBm (1 % Packet Error Rate)• RSSI measurements

– Packet Strength indication– Clear channel assessment– Dynamic channel selection

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PHY Layer Primitives• PHY Data Service

– PD-DATA - exchange data packets between MAC and PHY

• PHY Management Service– PLME-CCA - clear channel assessment– PLME-GET - retrieve PHY parameters– PLME-RX-ENABLE - enable/disable

receiver– PLME-SET - set PHY parameters

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Basic Network Characteristics

• 65,536 network (client) nodes

• Optimized for timing-critical applications– Network join time:

30 ms (typ)– Sleeping slave changing to

active: 15 ms (typ)– Active slave channel access

time: 15 ms (typ)

Network coordinatorFull Function nodeReduced Function node

Communications flowVirtual links

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Topology Models (cont)

• Star Networks (Personal Area Network)– Home automation– PC Peripherals– Personal Health Care

• Peer-to-Peer (ad hoc, self organizing & healing)– Industrial control and monitoring– Wireless Sensor Networks– Intelligent Agriculture

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Topology Models

PAN coordinatorFull Function DeviceReduced Function Device

Star

Mesh

Cluster Tree

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Device Classes

• Full function device (FFD)– Any topology– Network coordinator capable– Talks to any other device

• Reduced function device (RFD)– Limited to star topology– Cannot become a network coordinator– Talks only to a network coordinator– Very simple implementation

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Comparison of complimentary protocols

Feature(s) IEEE 802.11b Bluetooth ZigBeePower Profile Hours Days YearsComplexity Very Complex Complex Simple

Nodes/Master 32 7 64000

Latency Enumeration upto 3 seconds Enumeration upto 10 seconds

Enumeration 30ms

Range 100 m 10m 70m-300mExtendability Roaming possible No YESData Rate 11Mbps 1Mbps 250Kbps

Security Authentication Service Set ID (SSID)

64 bit, 128 bit 128 bit AES and Application Layer user defined

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Bluetooth 30 days (park mode @ 1.28s)

802.15.4/ZigBee more battery-effective at all beacon intervals greater than 0.246s

At beacon interval ~1s, 15.4/ZigBee battery life 85

days

At beacon interval ~15.4/ZigBee battery

approx 416 days

802.15.4/ZigBee vs Bluetooth

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Device Addressing• All devices have IEEE addresses• Short addresses can be allocated• Addressing modes:

– Network + device identifier (star)– Source/destination identifier (peer-peer)– Source/destination cluster tree + device

identifier (cluster tree)

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General Data Packet Structure

PRE SPD LEN PC CRCLink Layer PDUADDRESSING

Preamble sequence

Start of Packet Delimiter

Length for decoding simplicity

Flags specify addressing mode

Data sequence numberCRC-16

DSN

Addresses according to specified mode

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Optional Frame Structure

15ms * 2n

where 0 n 14Networkbeacon

Contentionperiod

Beaconextension

period

Transmitted by network coordinator. Contains network information,frame structure and notification of pending node messages.

Space reserved for beacon growth due to pending node messages

Access by any node using CSMA-CA

GTS 3 GTS 2

GuaranteedTime Slot

Reserved for nodes requiring guaranteed bandwidth [n = 0].

GTS 1

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Traffic Types

• Periodic data– Application defined rate (e.g. sensors)

• Intermittent data– Application/external stimulus defined

rate (e.g. light switch)• Repetitive low latency data

– Allocation of time slots (e.g. mouse)

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Development Boards• Atmel

– AT86RF210 Z-Link™ Transceiver is an 868/915 MHz direct sequence spread spectrum BPSK transceiver designed for IEEE 802.15.4/ZigBee™-based systems; supports data rates of 20 kbps and 40 kbps, respectively.

– AT86ZL3201 Z-Link™ Controller is an 8-bit AVR® Microcontroller customized for IEEE 802.15.4/ZigBee™ for wireless monitor and control applications; supports the 868/915 MHz and 2.4 GHz bands with data rates of 20 kbps, 40 kbps, and 250 kbps, respectively.

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Development Boards (cont.)• MicroChip PICDEM Z Demonstration

kit – Features:

• ZigBee software stack supporting RFD (Reduced Function Device), FFD (Full Function Device) and Coordinator

• PIC18LF4620 MCU featuring nanoWatt Technology, 64 KB Flash memory and robust integrated peripherals

• RF transceiver and antenna interface via daughter card for flexibility

• Supports 2.4 GHz frequency band via Chipcon CC2420 RF transceiver

• Temperature sensor (Microchip TC77), LEDs and button switches to support demonstration

– Package Contents• Two PICDEM Z demonstration boards each

with an RF transceiver daughter card • ZigBee protocol stack source code (on CD

ROM)

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Development Boards (cont.)

• Motorola/FreeScale 13192DSK– Two 2.4 GHz wireless nodes

compatible with the IEEE 802.15.4 standard

• MC13192 2.4 GHz RF data modem • MC9S08GT60 low-voltage, low-power 8-bit

MCU for baseband operations • Integrated sensors

– MMA6261Q 1.5g X-Y-axis accelerometer – MMA1260D 1.5g Z-axis accelerometer

• Printed transmit-and-receive antennae • Onboard expansion capabilities for

external application-specific development activities

• Onboard BDM port for MCU Flash reprogramming and in-circuit hardware debugging

• RS-232 port for monitoring and Flash programming

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Development Boards (cont.)

• Emulator Development Kits– Ember– CompXs– Helicomm

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Mote• “Tiny piece of anything”• Low-power (RF) transceiver• Microcontroller

• Operating system

Crossbow mote with battery

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Mote• Transceiver 400 MHz and up

– Line-of-sight– Short range– Unlicensed operation

• Microcontroller– ATmega 128 - 16 MHz, 128KB Flash, 4 KB

RAM– Low power, sleep modes

• TinyOS– Makes programming much, much easier

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Operating Systems• MSDOS, Windows, Linux, TinyOS• NOT the interface, but• The program that manages all other

software and the hardware resources• Provide services to other programs

“applications” (encapsulate common tasks)

For example, a simple task such as writing a few bytes to a disk without an OS is a significant task

• Isolate programmer from hardware

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Sensor Network

Interface electronics, radio

and microcontroller

Soil moisture probe Mote

Antenna

Gateway

Server

Internet

Communications barrier

Sensor field

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Sensor Network

Gateway

Server

Internet

Sensor fieldWatershed

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Low Data Rate Wireless Evolution

Proprietary Fades

ZigBee Emerges

Semiconductor Focus

Early Adopter OEMs

$1 - $10B Industry

$100 - $10 Unit Cost

Second Stage2004 2005 2006

Standards Dominate

IEEE 1451.5 Emerges

OEM Focus

Wireless Ubiquitous

$10 - $100B+ Industry

$10 - $1 Unit Cost

Third Stage2007 2008 2009+

First Stage……… 2002 2003

Proprietary Dominates

IEEE 802.15.4 Emerges

System Integrator Focus

Leading Edge OEMs

$.1 - $1B Industry

$1,000 - $100 Unit Cost

Mapping Your Future: From Data to ValueAMRA 2003 International Symposium

Mom’s House September 2004

• Son installs a retail two-pack ZigBee lamp controller and lamp module

• Mom likes it, allows her to stay warm in bed without having to get up to turn out lamp

Mom’s House October 2004

• Son worried about her health, so adds wearable panic button and phone line connection

• New PAN coordinator assumes coordination master function from lamp module; network auto-reconfigures for star topology

Mom’s House December 2004

• Mom likes it, son worried about her neighborhood, so adds door and window security sensor

• PAN Coordinator locates these new devices and adds them• PAN Coordinator offers to alert police via phone line if window

sensor is tripped, turns on lamp by bed

Mom’s House December 2005

• Mom now worries about mail being stolen from roadside box, so wants to know when mailman delivers mail

• • Son buys ZigBee Mailbox Alert– finds that range is exceeded, purchases ZigBee Range Extender, finds it

also allows her Panic Button to work outside in the garden

Mom’s House September 2004

• For Christmas, Mom gets new computer with ZigBee Human Interface Devices (HID)

• Comes with software to allow her to automate her house via ZigBee

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References• The ZigBee Alliance web site

– http://www.zigbee.org– Bob Heile, ZigBee Alliance Chairman bheile@ieee.org

• Helicomm, Inc.• Atmel, Inc.• Microchip, Inc.• Motorola, Inc.• www.engineering.uiowa.edu/~ece195/2005/