Bluetooth and ZigBee: Their similarities and differences

* ZigBee challenges Bluetooth for mindshare

Bluetooth and ZigBee have much in common. Both are types of IEEE 802.15 "wireless personal-area networks," or WPANs. Both run in the 2.4-GHz unlicensed frequency band, and both use small form factors and low power.

At the Wireless Communications Alliance's February meeting in Silicon Valley, Bhupender Virk, president and CEO of WPAN components maker CompXs, sorted out the application and technical differences between Bluetooth (IEEE 802.15.1) and the ZigBee specification (based on IEEE 802.15.4), which was ratified in December.

ZigBee protocols define a type of sensor network for residential and commercial applications such as heating, air conditioning and lighting control. It combines IEEE 802.15.4, which defines the physical and MAC protocol layers, with network, security and application software layers as specified by the ZigBee Alliance, a consortium of technology companies.

Imagine the freedom if light switches were to become wireless, eliminating the electrical cabling through your walls, for example.

Bluetooth, as you likely know, eliminates cabling between electronic products and accessories, such as between computers and printers or between phones and headsets. Bluetooth users with handhelds or laptops can exchange files, business cards and calendar appointments. Bluetooth is more oriented toward user mobility and eliminating short-distance cabling; ZigBee aims more for grand-scale automation and remote control.

The first ZigBee products are now in interoperability testing through April, says Virk, who expects alliance-certified products to be available in the third quarter (when he says CompXs will ship a ZigBee protocol analyzer). Industry reports imply that, eventually, ZigBee might be built into mobile phones via dual-function ZigBee-Bluetooth chips for remote control of nearly anything you can think of and for buying items from vending machines.

Finally, for the geeks among us, Virk pointed out some technical differences between the two protocols:

* Modulation technique

Bluetooth: Frequency Hopping Spread Spectrum (FHSS)

ZigBee: Direct Sequence Spread Spectrum (DSSS)

* Protocol stack size

Bluetooth: 250K bytes

ZigBee: 28K bytes

* Battery

Bluetooth: Intended for frequent recharging

ZigBee: Not rechargeable (one reason batteries will last for up to 10 years)

* Maximum network speed:

Bluetooth: 1M bit/sec

ZigBee:  250K bit/sec

* Network range:

Bluetooth: 1 or 100 meters, depending on radio class

ZigBee: Up to 70 meters

* Typical network join time

Bluetooth: 3 seconds

ZigBee: 30 milliseconds

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