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I N D U S T R Y T R E N D S

Pu b l i sh e d by th e IEEE Co mpu te r So c ie ty

As wireless-sensor technologyimproves, an increasing num-ber of organizations are usingit for a wide range of pur-poses. Users are working

with the technology to monitor andautomate home, building, industrial,and agricultural systems, includingthermostats and security products,said Mareca Hatler, director ofresearch for ON World, a marketresearch firm.

In addition, they are working with

sensor networks for checking on envi-ronmental quality and the integrityof bridges and other structures, auto-mated meter reading, and even inhome healthcare, national security, andmilitary networks, she added.

ON World forecasts 127 milliondeployed wireless sensing networknodes in 2010, up from 1.2 million in2005, she noted.

To achieve technological and mar-ketplace success, the low-power, inex-pensive sensor networks need an eco-

nomical, low-latency, robust, energy-efficient, wireless connectivity infra-structure. With this in mind, users areincreasingly working with ZigBee tech-nology.

Other prominent wireless technolo-gies, such as Bluetooth, dont fit the billbecause, for example, they are tooexpensive or use too much energy.Bluetooth is designed to connect high-volume, packet-based devices such aslaptops, phones, and major peripher-

als. ZigBee, on the other hand, con-nects low-volume devices such as sen-sors and works with simpler, lessexpensive, easy-to-use technology.

The ZigBee Alliance (www.zigbee.org) promotes use of the technology,and its 200 members are currently con-ducting interoperability tests and releas-ing products. Specification-compliantproducts receive a ZigBee Alliance logo,noted Nick Dutton, director of businessdevelopment for Integration Associates,a semiconductor design company andalliance member.

However, ZigBee faces competitionfrom other technologies, as well asmarketplace confusion.

INSIDE ZIGBEEIn 1999, the Firefly Working Group,

no longer in existence, originated thetechnology that would become ZigBee.

Todays ZigBee is built on the IEEE802.15.4 low-rate, wireless, personal-area-network standard, adopted in2003. The ZigBee Alliance ratified thefirst ZigBee standard in December2004 and released it to the public in

June of this year.

TechnologyAlthough IEEE 802.15.4 supports

mesh and other network technologies,the specification itself operates peer topeer. However, adding network-layerspecifications can introduce othercapabilities. For example, addingZigBee atop the 802.15.4 stack lets thetechnology work directly with othernetwork topologies such as mesh,explained Dutton. ZigBee also addssecurity to the IEEE standard, asFigure 1 shows.

ZigBee additionally defines the natureof its data communications and routing

within networks, as well as the waynodes discover one another.ZigBee uses IEEE 802.15.4s bea-

coning techniquein which a nodecontinuously transmits small packetsto advertise its presence to othermobile units, which then try to estab-lish a connectionto start networksand let other devices join in, addedPhilip Orlik, principal technical staffmember with the Mitsubishi ElectricResearch Laboratories (MERL).

The technology also works withthe routing discovery approach that

ad hoc on-demand networks use,explained Orlik. When a sending nodeneeds a route to a destination, it broad-casts a route-request packet across thenetwork. Nodes then set up backwardpointers to the source node in the routetables. The system then builds routesbetween nodes and maintains them aslong as they are needed.

Spectrum and transmission range.

ZigBee uses the same unlicensed 2.4-GHz (worldwide), 868-MHz (inEurope), and 915-MHz (in the

Americas) radio bands as many cord-less telephones. These bands work wellfor low-cost sensor networks becauseusers dont have to obtain licenses andthe spectrum is widely available.

The technologys transmissionranges are 10 meters indoors and 200meters outdoors for devices using the2.4-GHz band, and 30 meters indoorsand 1,000 meters outdoors for devicesusing the other bands, according toDutton.

Users Make aBeeline for ZigBeeSensor TechnologyDavid Geer

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development director at semiconduc-tor vendor Chipcon.

And because each node can take careof the necessary switching and routing,ZigBee networks dont need separateequipment such as hubs and routers,

and thus they can handle network traf-fic economically.

ImplementationZigBee is implemented in a device or

other node via chips. Currently, ZigBeedevices need only an 8-bit controllerchip that includes some networkingand security functionality; a trans-ceiver chip, which has the radio func-tionality; a power source; and a fewpassive components.

Chip makers such as Chipcon and

Ember are beginning to combine thecontroller and transceiver circuitryonto one piece of silicon.

ZigBees simplicity and plug-and-play capabilities make implementingthe technology inexpensive and easy,particularly because it requires little orno network engineering.

And organizations can use gatewaysto easily integrate ZigBee technologywith their back-end maintenance,building automation, automated meter

Data rates. ZigBee transmits data ata relatively slow 250 Kbits per second

at 2.4 GHz, 40 Kbps at 915 MHz, and20 Kbps at 868 MHz, which workswell for simple sensor systems thattransmit only small amounts of dataoccasionally, said Orlik. This is con-siderably slower than other wirelessconnectivity technologies such asBluetooth and far too slow for otherwireless purposes such as transmittingreal-time video.

Security. For security, ZigBee uses128-bit Advanced Encryption Standardcryptography and trust-center-based

authentication, according to DavidMcCartney, vice president of sales andmarketing for software vendor AirbeeWireless. A trust center admits devicesto a network and hands out ZigBeedevice and network authenticationkeys, he explained.

Nodes. Theoretically, ZigBee cansupport up to 65,536 nodes. However,supporting this many nodes makesnetwork administration unmanage-able. To avoid this problem, Duttonsaid, ZigBee networks should have nomore than 3,000 nodes. For situations

requiring more nodes, he explained,multiple subnets would work betterthan trying to make a single large net-work even bigger.

Low latency. ZigBee is optimized fortime-critical applications that wonttolerate latency, such as lighting andpower-management controls. ZigBeedevices dont have to synchronize withother nodes on a network before join-ing and beginning communications.Thus, devices require only 30 mil-liseconds to join a network and 15

milliseconds to access and start com-municating with other nodes.

Energy efficiency. Because ZigBee per-forms just a few specific, simple tasks,the protocol stack can be as small as 28Kbytes. Thus, system controllers needless memory and consume less power.

In addition, ZigBee devices transmitsmall amounts of simple data, likethose from sensors, which minimizesthe amount of energy the systems use,Dutton noted.

Also, he said, ZigBee activates de-vices only when theyre needed to passor act on data, which also contributesto power efficiency.

ZigBee can thus let batteries indevices run for a long time, which is

critical for install-and-forget sensor-related tasks such as wireless monitor-ing and control systems.

Mesh networkingZigBee uses a full mesh topology,

in which all nodes connect to andcommunicate directly with othernodes within range. Only the in-tended recipient acts on the transmit-ted data.

This approach avoids problemsexperienced by nonmesh networks

that require clear lines of sight betweennodesin which obstacles block radiosignals. This is an important consider-ation in factories or warehouses full ofequipment and shelves.

Mesh networking also lets commu-nications pass through any set of nodesbetween the sender and receiver, whichis helpful if a node breaks down or isremoved from service. This makesZigBee networks self-healing, notedGraham Martin, ZigBee business

December 2005 17

Applications

Application profiles

Application framework

Network and securitylayers

Media access control

Layer

Physical layer

Silicon ZigBee stack Application

Source: ZigBee Alliance

User

ZigBee application profiles

IEEE 802.15.4

ZigBee-compliantplatform

Figure 1. ZigBee is built on the robust physical and media-access-control layers defined by

the IEEE 802.15.4 standard. Above these layers, ZigBee defines a mesh network topology

with security features and interoperable application profiles.

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writing profiles that will work only withtheir own applications.

ZigBee could have many other poten-tial uses, such as transmitting tempera-ture readings from thermostats; on andoff requests for wireless light switches,which could eliminate the expensiveand time-consuming wiring that tradi-

tional switches require; or keystrokesfrom a wireless keyboard.

Because of its low cost, easy installa-tion, and many potential uses, ZigBeewould particularly appeal to buildersand homeowners, said ChipconsMartin.

ZigBee-based monitors could tracksenior citizens living alone and warnmedical personnel about changes thatcould indicate health or safety prob-lems. ZigBee-powered sprinkler systemscould use just enough water to keep

plants green. The technology could evenenable fleet-management systems toreport on vehicle maintenance status,tire conditions, and mileage.

ZIGZAGGING AROUND OBSTACLESWidespread ZigBee adoption faces

several challenges.

CompetitionZigBee must cope with marketplace

competition from technologies such as

reading, energy management, andother systems.

Integrating wireless sensor net-works with other systems is essentialto the end user in enabling them to notonly collect sensor information butalso translate it into useful informationfor data analytics, remote control, and

monitoring applications, explainedON Worlds Hatler. Wireless sensornetworks connected to gateways thatare in turn connected to wide area net-works enable the sensor informationto be transmitted many miles away forprocessing in a faraway office.

UsesThe ZigBee Alliance is devising

application profiles, which let pro-grammers use application-specificcommands when setting up ZigBee

controllers for related sets of tasks.The first profile, recently completed,

addresses lighting applications andincludes information needed to enabledimmers, switches, and lights to com-municate with one another, accordingto ZigBee Alliance chair Bob Heile.

The Alliance will soon release profilesfor heating, ventilation, and air condi-tioning; industrial process control; andbuilding automation, he noted. Andsome companies like Honeywell are

Zensyss Z-Wave and SmarthomesInsteon, which perform many of the

same functions.Z-Wave (www.z-wavealliance.com)

and Insteon (www.insteon.net) areproprietary wireless technologiesdesigned mainly for home control andautomation.

Z-Wave uses low-power mesh-net-worked transmitters and repeaters.

Insteon uses radio technology and ahomes existing electrical wiring. Itworks on a peer-to-peer basis and isnot routed, like ZigBee and Z-Wave.Insteon thus doesnt require network

controllers.Proponents of the two technologiesclaim they are better than ZigBee forthe residential uses for which they weredesigned.

For example, because ZigBee wasdesigned to work with many applica-tions in both home and industrial set-tings, the technologys radios willrequire more memory and thus will costmore, said Raoul Wijgergangs, Zensyssvice president of business development.Also, the chips will be bigger and moreexpensive and, therefore, less practical

for home use, he added.

Confused marketplaceDue to the wide range of applica-

tions and types of end users, there aremany proprietary solutions today thatconfuse the marketplace by callingthemselves ZigBee-ready, noted ONWorlds Hatler.

However, she predicted that userswho want ZigBee functionality even-tually will support only products thatuse technology based on the standard.

MOVING AHEADThe ZigBee Alliance is looking at

ways to bridge its technology withother types of wireless and wired net-works, such as those based on Wi-Fi.Interacting with other types of net-works would broaden their usefulness,according to Heile.

For example, bridging could takeadvantage of both ZigBees and othernetworks capabilities and eliminate

I n d u s t r y T r e n d s

Source: Gartner Dataquest

0

20

40

60

80

Units(millions)

100

120

140

160

2006 2007 2008 20092005 2010

Figure 2. Gartner Dataquest, a market research firm, predicts rapidly growing ZigBee

adoption during the next five years.

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the need for users to base all theirdesired functionality on ZigBee.

Also, Heile explained, it would beeasier to link two ZigBee networks onseparate floors of a building via a wiredbackbone than via a wireless connec-tion.

ZigBee proponents say widespreadadoption will require consumer aware-ness. They are, therefore, focusing onglobal promotion and marketing suchas worldwide open houses with practi-cal demonstrations of devices and appli-cations, Heile noted.

Research indicates the demand for

having security systems at home willdrive the adoption of ZigBee. Theincreasing human dependence onmachines to take control of the house-hold will also drive the need for ZigBeein home automation. In fact, by 2006-07, many homes are expected to havea minimum of 100 to 150 ZigBee chipsin various appliances, said DeepaDoraiswamy, an analyst for Frost &Sullivan, a market research firm.

According to Chipcons Martin,energy conservation will motivate Zig-

Bee use in Asia and Europe. For exam-ple, he said, in some countries, running

washing machines at night is either pro-hibited or incurs higher energy costs.Owners thus may want to use ZigBee torun the machines remotely during theday, when they are not at home.

Stan Bruederle, research vice presi-dent at Gartner Dataquest, a marketresearch firm, projects that the numberof devices worldwide connected viaZigBee will increase from 400,000this year to 150 million in 2010, asFigure 2 shows.

Once ZigBee proves itself in its ini-tial implementation with lightingand control systems, it will then

play a major role in product tracking,medical monitoring, and industrialsensor networks, said Martin.

Eventually, ZigBee could enable sen-sor networks to undertake suchadvanced and promising applicationsas checking environmental conditionsin large industrial complexes, trackingagricultural parameters such as soil

moisture and temperature, overseeingwastewater processing, and even mon-

itoring a city for bioterror hazards, saidFrost & Sullivan analyst Amit Jain.

The technology has proven to besound, many companies have sup-ported the ZigBee Alliance, and manypeople have downloaded the specifica-tion or bought development kits, so theissue is when, not if, the technologywill take off, stated Martin.

The market opportunity for ZigBeeis huge, said ON Worlds Hatler.However, in order for it to reach itsfull potential, there needs to be more

development and investment in net-working software, middleware, andsensor applications.

David Geeris a freelance technologywriter based in Ashtabula, Ohio. Con-tact him at david@geercom.com.

December 2005 19

Editor: Lee Garber, Computer,

l.garber@computer.org