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Zigbee: another standard for wireless links
Posted on 2-Aug-2003 18:24. | Tags Filed under: Articles.

Zigbee: another standard for wireless links
Lots of talks about a new wireless protocol, even a few articles on Slashdot. This article explains what it is and how it compares with other standards.

ZigBee is one implementation of the logical layer needed to implement the standard IEEE 802.15.4 ractified in May 2003. The standard intends to be a simple packet data protocol, with a low power requirement and narrow bandwidth requirements. Its maximum speed is 250kbps, compared to Bluetooth at 720kbps and wi-fi from 11mbps (although we all know real life applications will have different performance).

The new standard provides Quality of Service through packet acknowledgement, and it is focused in data collection (sensors) and control. This includes assembly lines and remote data collectors. The RFID (Radio Frequency Identification) is the most direct competition for ZigBee.
Because of its limited bandwidth it's not intended to be a wire replacement like Bluetooth, or a wireless network adapter like wi-fi.

The ZigBee technology is well suited to a wide range of applications in every industry. Essentially, any application that could benefit from interoperability, or that matches the fundamental RF characteristics of the IEEE 802.15.4 standard would benefit from a ZigBee solution. Examples include:

  • Wireless home security
  • Remote thermostats for air conditioner
  • Remote lighting, drape controller
  • Call button for elderly and disabled
  • Universal remote controller to TV and radio
  • Wireless keyboard, mouse and game pads
  • Wireless smoke, CO detectors
  • Industrial and building automation and control (lighting, etc.)

    According to the official ZigBee website the logical size of a ZigBee network depends on which frequency is selected, how often each device on the network needs to communicate, and how much data loss or retransmissions can be tolerated by the application. ZigBee's addressing scheme supports 255 active nodes per 'network coordinator', and multiple network coordinators can be linked together to support extremely large networks. With support for 16 channels in the 2.4GHz band, and 255 nodes per network coordinator, ZigBee networks can contain over 4,000 unique nodes in a single network with high system reliability.

    The site also lists a comparisson between ZigBee and Bluetooth. The main differences are:

  • The ZigBee stack is small (28Kbytes) compared to the Bluetooth stack (250K). This relates to lower cost and lower power consumption.
  • Ultra-low power consumption is a key system design aspect of the ZigBee technology to allow long lifetime non-rechargeable battery powered devices versus rechargeable devices for Bluetooth. As an example the transition from sleep mode to data transition is much faster in ZigBee than for Bluetooth.
  • ZigBee networking capabilities include 255 devices per network, compared to 8 for Bluetooth networks.
  • The data rate for ZigBee technology is 250kbps (peak information rate 128kbps) compared to 720kbps for Bluetooth wireless technology.
  • Range for ZigBee products is expected to be ~30 meters in a typical home, compared to ~10 meters for Bluetooth products (without power amplifier).

    A complete comparison between these two technologies is in the donwload .pdf file linked below.

    Because the duty cycles are low in ZigBee networks the probability of interference and packet loss in Bluetooth networks is very low. If the Bluetooth network causes the loss of a ZigBee packet, the ZigBee sender is able to resend if it does not see the acknowledgement packet come back from the destination.

    The site also cites the Bluetooth focus on voice and high data rate application as the main differential between standards and puts emphasys on ZigBee suitability for control applications, which do not require high data rates, but must have low power, low costs and ease of use (remote controls, home automation, etc.).

  • More information:

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