zigbee report

8/3/2019 ZigBee Report

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CONTENTS

1. Introduction .................................................................................................2

2. What is Wireless technology? .....................................................................4

3. Need of Zigbee ...................................................................9

4. What is Zigbee/802.15.4 ........................................ 11

5. Benefits of zigbee .................................................................................... 15

6.Technology behind zigbee ..................................................................... 17

7. Applications .........21

8. Conclusion .......22

9. References 23

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1.INTRODUCTION

ZigBee is a communication standard that provides a short-range cost effective

networking capability. It has been developed with the emphasis on low-cost battery

powered application such as building automation industrial and commercial control

etc. Zigbee has been introduced by the IEEE and the zigbee alliance to provide a first

general standard for these applications. The IEEE is the Institute of Electrical and

Electronics Engineers. They are a non-profit organization dedicated to furthering

technology involving electronics and electronic devices. The 802 group is the section

of the IEEE involved in network operations and technologies, including mid-sizednetworks and local networks. Group 15 deals specifically with wireless networking

technologies, and includes the now ubiquitous 802.15.1 working group, which is also

known as Bluetooth.

The name "ZigBee" is derived from the erratic zigging patterns many bees make

between flowers when collecting pollen. This is evocative of the invisible webs of

connections existing in a fully wireless environment. The standard itself is regulated by

a group known as theZigBee Alliance, with over 150 members worldwide.

While Bluetooth focuses on connectivity between large packet user devices, such

as laptops, phones, and major peripherals, ZigBee is designed to provide highly

efficient connectivity between small packet devices. As a result of its simplified

operations, which are one to two full orders of magnitude less complex than a

comparable Bluetooth device, pricing for ZigBee devices is extremely competitive,

with full nodes available for a fraction of the cost of a Bluetooth node.

ZigBee devices are actively limited to a through-rate of 250Kbps, compared to

Bluetooths much larger pipeline of 1Mbps, operating on the 2.4 GHz ISM band,

which is available throughout most of the world.

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ZigBee has been developed to meet the growing demand for capable wireless

networking between numerous low-power devices. In industry ZigBee is being used

for next generation automated manufacturing, with small transmitters in every device

on the floor, allowing for communication between devices to a central computer. Thisnew level of communication permits finely-tuned remote monitoring and manipulation.

In the consumer market ZigBee is being explored for everything from linking low-

power household devices such as smoke alarms to a central housing control unit, to

centralized light controls.

The specified maximum range of operation for ZigBee devices is 250 feet (76m),

substantially further than that used by Bluetooth capable devices, although security

concerns raised over sniping Bluetooth devices remotely, may prove to hold true for

ZigBee devices as well.

Due to its low power output, ZigBee devices can sustain themselves on a small

battery for many months, or even years, making them ideal for install-and-forget

purposes, such as most small household systems. Predictions of ZigBee installation for

the future, most based on the explosive use of ZigBee in automated household tasks in

China, look to a near future when upwards of sixty ZigBee devices may be found in an

average American home, all communicating with one another freely and regulating

common tasks seamlessly.

2. WHAT IS WIRELESS TECHNOLOGY?

Wireless networks are becoming more pervasive, accelerated by new wireless

communications techno logies, inexpensive wireless equipment, and broader Internet

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access availability. These networksare transforming theway people use computers and

other personal electronics devices at work, home, andwhen traveling.

There are many wireless communicationstechnologies that can be different iated

by frequency, bandwidth, range, and applications. In this white paper, we survey thesetechnologies, which can be broadly organized into the four categories depicted in

Figure below. These categories range from wireless wide area networks (WWANs),

which coverthe widest geographic area, to wireless personalareanetworks (WPANs),

which cover less than 10meters.

Bluetooth wireless technology is the prevalent WPAN technology today. It

operatesin the 2.4-GHz unlicensed frequency band. Figure 2 shows its evolution from

version 1.1 at a datarate of 1Mbpsto version1.2, which improves the signaling and

frequency band coexistence mechanisms.The 3-Mbps Bluetooth 2.0+ Enhanced Data

Rate (EDR) was ratified in November 2004 andproducts are beginning to appear on the

market.

Over the next three years, WPAN applications that require higher data rates may

adopt the emerging hig h bandwidth Ultrawideband (UWB) technology. UWB

provides high bandwidth by transmitting at very low power across a broadfrequency

spectrum. The UWB physical interface (or PHY) specification802.15.3a is

under developmentin theIEEE,and a competing specification is under development

by an industry working group called the Multi Band Orthogonal Frequency Division

Multiplexing (OFDM) Alliance (MBOA). Initial UWB products with data rates of

100-480 Mbps are anticipated in early 2006. Future versions are expected to have data

rates of up to 1 Gbps. Failure to resolve the issue of competing standards may stall the

market opportunity for UWB technology. In addition, although the U.S. Federal

Communications Commission (FCC) has approved a large amount of spectrum for

UWBin the U.S., there are regulatory and regional policy issues outside the U.S.

An additional wireless technology that fits roughly in the WPAN category

ZigBee (802.15.4)is optimized for low-bandwidth niche applications such as

instrumentation and home automation. Zigbee is notdepicted in Figure 2 because it is

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unlikely that it will be deployed outside these specialized applications.

Fig1 : Various Network Ranges

Fig2:Bluetooth Range

Wireless Local Area Networks (WLANs):

In contrast to WPANs, WLANs provide robust wireless network connectivity overa

local areaofapproximately100 meters between the access point and associated clients.

Today's WLANs are based on the IEEE 802.11 standard and are referred to as Wi-Fi

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networks. 802.11b was the first commercially successful WLAN technology. It

operates in the 2.4-GHz frequency band at 11Mbps. By implementing adifferent data

transmission method, data rates were increased to 54 Mbpsin2003with 802.11g in the

2.4-GHz band and 802.11a in the 5-Ghz band.Today, dual-band Wi-Fi access pointsand client network adaptersthat supportvariouscombinations of 802.11a, b, and g are

common. Highly integrated, single-chip solutions that are smaller and require less

power have enabled new designs and applications.

In addition, new standards address Wi-Fi network security. Wi-Fi Protected Access

(WPA) and 802.11i (orWPA2) focus on user authentication and encryption. WPA2

employs next-generation Advanced Encryption Security (AES) encryption. A

component of WPA and WPA2the IEEE 802.1X standardprovidesa port-level

authentication framework.Finally, the upcoming 802.11e standard addresses quality of

service (QoS).QoS enables the prioritization of latency-sensitive applications such as

voice and multimedia. The Wi-Fi Alliance, an industry group responsible for

certification and interoperability testing, has developed the Wi-Fi Multi- media

(WMM) test specificationto certifyproduct compliance with t he 802.11e standard.

The next-generation WLAN standard is IEEE 802.11n, which is currentlybeing

defined.802.11n will bebackward-compatible with 802.11a, b, and g, and will provide

data ratesin excess of 100 Mbps. The 802.11nperformance increases stem from new

Multiple-Input, Multiple-Output (MIMO) radio technology, wider radio frequency

(RF) channels, and improvements to the protocol stack. MIMO enables higher data

rates by increasingthe number of radios and antennas in a wireless device. 802.11nis

scheduled forIEEE ratification in mid-2006. Dell is leading an initiative in the Wi-Fi

Alliance to launch a productcertification program concurrent with ratification of the

IEEE 802.11n standard.

Wi reless Metr o Are aNet works (WMANs) :

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A WMANis awireless communications network that covers a large geographic area

such as a city or suburb. Traditionally, long-distance wireless technologiesproviding

T1 or T3 data rates have been proprietary owned and operated by major telephonecompanies, in dependent local exchange carriers (ILECs), and otherproviders to link

remote sites or large campuses. The IEEE has standardized a new set of WMAN

technologies that operate in licensed and license exempt frequency bands. The best

known of these technologies IEEE 802.16d or WiMaxwill operate in the 2-

to11-GHz frequency range. (In the U.S., it will operate in the 2.5-, 3.5-, and 5.8-GHz

frequencybands.) Its maximum data rate when operated within line of sight and under

idealconditions is 70Mbps over 50 kilometers. Initial deployments will require an

external antenna at the customer premises. A mobile version802.16eisplanned in

2007. It is not yet clear when (or whether) telecommunicationsand Internet service

providers willbroadly deploy the requiredinfrastructure tosupport either thefixed or

mobile versions of Wi-Max. However, it is widely expected thatWiMax deployments

will leverage existing and emerging towe r infrastructures and installations.

Wireless Wide Area Networks (WWANs):

WWANs are digital cellular networks used for mobile phone and data service and

operated by carriers such as Cingular Wireless, Vodafone, and Verizon Wireless

WWANsprovide connectivity over a wide geographical area, but, until recently, data

rates have been relatively low115 Kbpscompared to othermore localized wireless

technologies.

Two WWAN technologies Global System for Mobile Communications (GSM) and

Code Division Multiple Access (CDMA)dominate WWAN deployments

worldwide. These two technologies are expected to evolve on parallel paths for the

foreseeable future.pe standardized early on GSM. Today, GSM and its associated

wireless data capability, General Packet RadioService (GPRS) and next-generation

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Enhanced Data GSM Evolution (EDGE), have about two thirds of the worldwide

market. These technologies have been deployed in North America, Europe, andAsia.

Next-generation EDGE boosts GPRS data rates by 34 times. Other GSM operators,

especially those that have acquired new 3G frequency spectrum, are commercializingWideband CDMA (WCDMA), which is expected to have data rates of 2 Mbps. An

extension called High-Speed Downlink Packet Access (HSDPA) is expected to be

deployed starting in 2006. HSDPA will further increase these data rates to 3.6 Mbps

and beyond.

CDMA technology dominates in the U.S. The CDMA2000 WWAN technology has

seen strong deploymentsin NorthAmerica, Japan, Korea, and China. TheCDMA2000

single-carrier radio transmission technology (1xRTT) version has been widely deployed.

The next-generation 1xEvolution-Data Optimized (1xEV-DO) is currently being

aggressively deployed by Verizon Wire- less and Sprint PCS in the U.S. andwill support

a data rate of 2.4 Mbps. Carriers will bui ld on EV-DO with version A of the

specification, which w ill support even higher data rates and Voice over Internet

Protocol(VoIP)calls.

3. NEED OF ZIGBEE

Wireless sensor networking is one of the most exciting technology markets today. They say

that over the next five to ten years, wireless sensors will have a significant impact on almost

all major industries as well as our home lives. Broadly, this technology market includes

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application segments such as automated meter reading, home automation, building

automation, container security/tracking, and many others.

Although products that span these application segments are diverse and different in howthey operate and what they do, their requirements from a wireless communication

technology are very similar. For example, these applications generally require low data rates

and are battery powered.

The main motivations for migrating these products to wireless communications are three-

fold:

1. Installation cost The cost of running wires in a typical building automation project

in an existing facility can be as high as 80% of the total project cost

2. Maintenance It is easier to configure a hot-water heater controller with a hand-held

remote than a keypad in the closet.

3. New markets Eliminating the wire opens new markets that were

previously unavailable to wired products.

In the wireless worlds of WiFi and BlueTooth, market growth was fueled by standards

development that ultimately brought down the cost of the technology and ensured excellent

value to the user. In that spirit, a number of companies forged an alliance to create a

wireless standard for the embedded wireless market space, also called personal area

networking (PAN); this standard is now called Zigbee. The list of promoting members is

prominent and includes names like Honeywell, Phillips, Motorola, Freescale, Invensys, and

many others.

Technically, Zigbee is a protocol standard that defines network, security, and application

framework protocol software. Zigbee is designed to work on top of the IEEE 802.15.4

PHY/MAC layer standard. The IEEE 802.15.4 standard was ratified in May of 2003; to our

knowledge the Zigbee standard is not at the time of this writing ratified, though we

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understand that it is very close.

4. WHAT IS ZIGBEE

The IEEE 802.15.4 standard defines the PHY and MAC layers, which are used by

Zigbee.

PHY description :

Three frequency bands are specified, though an implementation need only operate on

one of the three, the bands are:

868 MHz - for European applications

902-928 MHz - for North American applications

2.450 GHz -for world wide application

In all bands, the modulation scheme is direct sequence spread spectrum. In the 868 and

902-928 MHz bands, the transmitter is modulated using BPSK. In the 2.450 GHz band, the

transmitter is modulated using offset-QPSK, which is more bandwidth efficient than BPSK.

Direct sequence spread spectrum is a technique that essentially spreads the narrow band of

data over a much broader bandwidth by using a pseudo-random chipping sequence. This

process provides gain at the receiver because of the correlating effect of de-spreading the

data. The amount of gain is determined by the ratio of the chipping rate to the data rate.

The higher the ratio, the higher the gain. This gain also provides proportional rejection of

on channel interference. As the wanted signal is correlated and de-spread, the interferer is

spread, increasing the level of the wanted signal and decreasing the level of the interfering

carrier. The amount of rejection is determined by the spreading gain.

In the 2.450 GHz band, an 802.15.4 radio spreads the data using an 8 bit chipping

sequence. Actually, the chipping sequence is 32 bits, but the data being spread is actually

4 bits, thus the 8:1 chipping ratio. The process gain in dB is calculated by multiplying ten

times the log of the chipping ratio; in this case the gain is 9dB. Receiver sensitivity is

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specified at 85dBm; adjacent channel rejection is 0dB minimum.

In the 868 and 902-928 MHz band, an 802.15.4 radio spreads the data using a 15 bit

chipping sequence. In this case, chipping ratio is 15 and spreading gain is12dB. Receiver sensitivity is specified at -92dBm; adjacent channel rejection is 0dB

minimum.

MAC Description:

The 802.15.4 specification defines a very complicated MAC layer, and I will not attempt

to give a detailed explanation here.802.15.4 defines two classes of implementations: full

function devices (FFD) and reduced function devices (RFD).

An FFD can operate in three modes serving as a PAN coordinator, a coordinator, or a

device. FFDs contain all of the features of 802.15.4 and can talk to both RFDs and

FFDs. A PAN coordinator is the primary controller of the network, and it must be a

FFD. There can be only one PAN controller per network. A PAN controller is required

for an 802.15.4 network. A coordinator is a FFd that provides synchronization Services

by transmitting beacons.

A RFD can operate only as a device. RFDs contain a subset of the features of 802.15.4

and are intended to be high-volume, low cost devices. They can be duty-cycled to reduce

power consumption. RFD devices can talk only to FFDs. This means that RFDs have no

routing capability, so they must be on the perimeters of a mesh network. A device is a

simple end-point. A device can be a RFD or FFD. Conceptually, each network would have

one FFD that acted as the PAN coordinator and several more FFDs that formed the mesh

network. The majority of the nodes in the network would be low-cost RFDs. The number

and position of FFDs in the network would determine the coverage of the network.

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Fig3 : Zigbee Network Configuration

The illustration on the above shows an example Zigbee network configuration. There is one

PAN coordinator, six FFD devices, and nine RFD devices. The actual mesh network is

formed by the FFDdevices and the PAN coordinator. The RFD devices form a point to

multipoint network with FFD devices that are in range Node 8 is not connected to the

network. Although it is in range of nodes 7 and 9, it cannot connect to them because all three

are RFD devices. An additional FFD device would be required to connect node 8 to the

network.

There in lies an inherent limitation of the Zigbee model. The number of FFD devices in the

network determines the coverage area; the more FFD devices, the larger the coverage area.

It is probable, given the current 802.15.4 specification, that a real-world application of

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Zigbee would require a high ratio of FFD devices to RFD devices to attain the required

coverage, which will adversely affect the pricing model.

This also has implications in system deployment. The primary factor driving the marketneed is lower installation cost . Using the example just given, it is easy to see how the

installation will be complicated. If a device (node 8) is installed in a location that is not in

range of an FFD device, it will not be connected to the network. The installer would then be

required to place an additional FFD device to serve as an intermediate router. This would

have to be done by trial and error, increasing both labor and materials cost.

If this all sounds complicated, that is because it is. The 802.15.4 specification alone

consumes 670 printed pages. A typical implementation requires nearly 32K of flash, and

that is just for the MAC layer.

The Zigbee specification is likely to be just as large and the software

implementation requires another 32K or more of flash memory.

The important aspects of the 802.15.4 standard are listed below :

82-89 dB link budget

0 dB adjacent channel rejection

10 channels @ 900 MHz, 16 channels at 2.450 GHz MHz

40kbps @ 900 MHz, 250 kbps @ 2.450 GHz

RFD devices are not a part of the mesh network

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Every network requires a PAN coordinator The coverage area is determined by both the 802.15.4 link budget and the number of

FFD devices deployed

5. BENEFITS OF ZIGBEE

In all of its uses, ZigBeeoffers four inherent characteristics that are highly beneficial:

Low cost

The typicalZigBee radio is extremely cost-effective. Chipset prices canbe as low as $12

each in quantities as few as 100 pieces (while the 802.15.4 and ZigBee stacks are

typically included in thiscost, crystals and otherdiscrete components are not). Design-in

modules fallin the neighborhood of $25 in similar quantities. This pricingprovides an

economic justification for extending wireless networking to even the simplest ofdevices.

Range and obstruction issues avoidance:

ZigBee routers double as input devices and repeaters to create a form of mesh network.

If two network points are unable to communicate as intended, transmission is

dynamically routed from the blockednode to a router with a clear path to the datas

destination. This happens automatically, so that communications continue even when a

link fails unexpectedly. The use of low-cost routers can also extend the networks

effective reach; when the distance between the base station anda remote node exceeds

the devicesrange, an intermediate node or nodes canrelay transmission, eliminating the

need for separate repeaters

Multi-source products:

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As an open standard, ZigBee provides customers with the ability to choose among

vendors. ZigBee Alliance working groups define interoperability profiles to which

ZigBee-certified devices must adhere, and certified radio will interoperate with any other

ZigBee-certified radio adhering to the same profile, promoting compatibility and theassociated competition that allows the end users to choose the best device for each

particular network node, regardless of manufacturer.

Low powerconsumption :

Basic ZigBee radios operate at 1 mW RF power, and can sleep when not involved in

transmission (higher RF power ZigBee radios for applications needing greater range also

provide the sleep function). As this makes battery-powered radios more practicalthan

ever, wireless devices are free to be placed without power cable runs in addition to

eliminating datacable runs.

6. TECHNOLOGY BEHIND ZIGBEE

IEEE 802.15.4 :

The IEEE workgroup 802.15.4 has standardized the PHY and MAC, layer within

WPAN (Wireless Personal Area Network) area. The primary goal for the working

group within IEEE was to define the standard to meet requirements on low

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complexity, low cost and low power consumption.

802.15.4 MAC :

The MAC sublayer provides interfaces towards the PHY and higher (Zigbee) layers.

The MAC is responsible for several functions, such as: generation of

acknowledgment frames, association, disassociation, security control, and some

optional services such as: beacon generation and guaranteed time slot

management. One aim when defining the MAC was to make the scheduling engine

simple, thus improving the overall power consumption.

Channel Access:

For all types of deployed networks the Carrier Sense Multiple Access Collision

Avoidance (CSMA-CA) protocol is used. This method is useful to avoid unnecessary

collision over the radio channel. CSMA-CA is used for all traffic except beacons,

ACK frames and transmissions within a GTS.

Beacon signaling:

Only a FFD has the capability of generating beacon frames in a true peer-to-peer

network topology there can only be FFDs operating. One exception is when a RFD

operates as a peripheral device without routing capability.

Guaranteed Time Slot (GTS):

By using GTS scheduling at the MAC level two important attributes can be

achieved over the channel.

Low latency: For specific applications sensitive for delays such as alarms, PC mice,

lamp switches or QoS differentiation based on application software. It is possible to

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reach response times down to 15 msec in GTS mode.

Bandwidth allocation:

Useful for applications that requires to generate a known data traffic rate. The higherlayer protocol is responsible for assigning the traffic rate and the MAC level will

grant the request.

802.15.4 PHY:

The physical layer provides the interface to the wireless medium and is

responsible for low-level control for link quality, energy detection,

activation/deactivation of the radio transceiver etc. The PHY in 802.15.4 has three

different modes of operation depending of geographically region.

The IEEE 802.15.4 PHY uses Direct Sequence Spread Spectrum (DSSS) as the

transmission distances ranges from 10-100 meter (approx), depending on output

power, radio environment and antenna solution.

Network Topologies:

In general there exist three different network topologies:

Star

Cluster Tree

Mesh

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In this mode the PAN Coordinator is responsible for updating routing tables,

transmit beacons, maintaining synchronization, routing of messages between nodes

etc. within the network.

Antenna Considerations:

The antenna design is often very crucial for the overall product. One requirement

is often to minimize the size of the antenna, which is needed in many embedded

applications for short range wireless communications. However, a small antenna

may be inefficient unless attention is paid to the design of both the antenna and

its placement in the product.

Choice of antenna:

There are several design choices in the case of an internal antenna.

The obvious and cheapest choice is to use a substrate antenna, by using a piece of

circuit board trace. One disadvantage with this solution is the relative resistive loss

and the possible cross interference with components on the board and nearby

ground planes.

Another choice is wire antennas where the antenna can be placed away from the

board, which improves the performance. One drawback is that this solution may

require tuning, due to mechanical differences and size variations. A third choice is to

use ceramic antennas which offers smaller physical size than the above

mentioned solutions but with a substantially higher cost.

ZigBee Alliance :

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The ZigBee alliance was founded in order to develop a common standard for Short

Range Devices (SRD) with focus on low power consumption, ad-hoc behavior, low

latency, self configurable radio nodes. The ZigBee alliance is today an association

with over 50 member companies. The main focus within ZigBee is to define therouting mechanisms that together with IEEE802.15.4 will form the total solution.

General Characteristics :

Data rates from 20 to 250 kbps

Star Topology/Peer to Peer (mesh)

255 devices / network

CSMA-CA Access Scheme

Enumeration (new node) ~ 15-30 ms

Dual PHY (868/915 MHz, 2.4 GHz), DSSS

Range: 10-100 m

Low Duty Cycle (< 0 .1%, TX)

Low Power Cons, +1 year battery life time

Complexity: 4 -32 kB (protocol)

7. APPLICATIONS

Water level sensing:

Zigbee can be installed in remote location where conventional GSM modems would be outof their network coverage area, such as inside water tanks. Zigbee transceiver can be

hermetically sealed with batteries and co-located with sensors. Each transceiver transmits

periodically to another unit installed above ground. A GSM modem transmits the data to

base.

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In building control:

Zigbee-enabled switches and lights can be reduce installation costs in new building by

eliminating the need to route light control through the walls, and remove the need to call inqualified electrician when switches need to be relocated. Thermostats and air-conditioning

placed anywhere, free of any wiring constraints.

8. CONCLUSION

The Zigbee solution will be available soon. It will not hit the $10 price point until 2009.

The 802.15.4 radio specification has a very poor link budget; 89dB. A Zigbee based

solution is not scalable; it will not work reliably with only two end-points separated by

the length of a house. It is complicated and requires a significant learning curve from the

engineer and significant resources from the protocol controller. The customer must

form three supplier relationships; the chip vendor, the software vendor, and the

microcontroller vendor.

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In addition to cost, reliability, and scalability, Zigbee purports to offer other

advantages over proprietary solutions such as Interoperability, Vendor independence

and Common platform.

There are three separate frequency bands specified for Zigbee. If one manufacturer of

heating controls chooses the 900 MHz band, and another chooses the 2.4 GHz band, the

products will not operate together. Additionally, it is likely that IC vendors will add

proprietary features to their 802.15.4 implementations in an effort to differentiate their

product; if the OEM uses these proprietary features, the benefit of interoperability will be

negated. In the end, the only way to guarantee interoperability using Zigbee is to design only

2.4GHz products using only Zigbee standard features.

9. REFERENCES

Chipcon, CC2420 2.4 GHz IEEE 802.15.4 RF Transceiver Data Sheet

On World, October 2004, Wireless AMR and submetering: A market

dynamics study on fixed wireless technologies

Electronic Design, The Zigbee buzz is growing: New low- power wireless

standard opens powerful possibilities

On World, Wireless Sensor Networks: Mass Market Opportunities

IEEE, 802.15.4 Part 15.4: Wireless Medium Access control

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(MAC) & Physical (PHY) Layer Specifications for Low Rate Wireless Personal

Area Networks

ZigBee Open House Oslo.htm

Zigbee Alliance -- Home Page.htmZigbee Tutorial.htm

zigbee report

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