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Tuesday, 20 July 2010

Zigbee - Emerging Simple Wireless System

Introduction To Zigbee

In the wireless world, the name Bluetooth and WIFI have become a household name in recent years. They quickly find applications amongst others in mobile computing and mobile phones.

Zigbee is the result of the demand from industry and consumer for wireless applications that demand for lower data rate, longer battery life, simple design, shorter range and low cost solutions.

Introduction To IEEE 802.15.4

IEEE 802.15.4 is a simple standard that specifies the Media Access Controller (MAC) and Physical (PHY) networking layers for packet data protocol. Its license free frequency bands are:

2.4 GHz (16 channels with baud rate of 250 kps)
902 MHz - 928 MHz (10 channels with baud rate of 40 kps)
868 MHz - 870 MHz (1 channel with baud rate of 20 kps)

North America, Europe, Australia and New Zealand use the sub 1 GHz bands whereas the rest of the world uses 2.4 GHz bands.

It uses Carrier Sense Multiple Access with Collison Avoidance for Channel Access.

The security method used is AES-128.

Has message acknowledgement and a host of other features.

Zigbee Applications

Zigbee technology is based on IEEE 802.15.4 industry standard. It incorporates the standard, adding the logical network, security and software to it. It supports up to 3 network topologies namely STAR, MESH and CLUSTER tree. Developers need only have to focus on application while the MCU/Microprocessor/RF Transceiver makers and Zigbee Alliance take care of the RF Transmitter, RF Receiver, RF Channel and its protocol.

There are 3 types of traffics that can be used.

a) Periodic data

An example of this traffic is a wireless sensor to read the water meter. The sensor is programmed to wake up at certain interval to transmit the information needed and goes back to sleep after this is done.

b) Intermittent data

An example of this traffic is a wireless light switch to ON or OFF a light manually. It is triggered only by external input and hence wakes up to transmit the message to the network. When done, it is disconnected to the network and hence save energy.

c) Repetitive data

An example of this traffic is the security system monitoring. The devices are time multiplex to return its status to the network. This type uses more energy.

There are numerous applications that can be implemented using Zigbee. Amongst others are in the industry and home applications.

In the industry, the applications include utility and metering where gas/water/electricity meter readings are automated and send back to utility headquarter for further action. This saves the time it takes for their personnel to come to the premises to take its reading. In the area of warehousing/inventory management , the wireless technology will enable accurate and hassle free management of goods. Security and access control, building management system and lighting control are among the applications that can be implemented with ease.

In the home, a total home automation system to control lightings, blinds, air conditioning, security system, remote control and appliances can be implemented.

A good reference source and solution on Zigbee can be obtained from Microchip Website.

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