计算机专业时文选读之二十七

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 recent 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

时文选读

Bluetooth与ZigBee的异同

Bluetooth(蓝牙)与ZigBee有很多相同之处。两者都属于IEEE 802.15“无线个人局域网”(WPAN)类型，都运行在无需许可证的2.4GHz频段，都只有很小的外形尺寸和消耗很低的电力。

最近在硅谷召开的无线通信联盟会议上，WPAN部件制造商CompXs公司的总裁兼CEO Bhupender Virk指出了蓝牙 (IEEE 802.15.1) 和今年(2004年)12月被批准的ZigBee 规范(基于IEEE 802.15.4)之间在应用和技术上的不同点。

ZigBee协议定义了家居和商业应用(如供热、空调以及灯光控制)的传感器网络的类型。它将定义物理和MAC协议层的IEEE 802.15.4与网络、安全和应用软件层结合在起来，这是由ZigBee联盟(一个由技术公司组成的团体)制定的。

想象一下，如果电灯开关变成无线的，消除了墙内的连接电线，将带来多大的自由度。

Bluetooth如同你可能了解的那样，消除了电子产品与附件之间的连线，如计算机与打印机或者电话机与话筒之间的连线。拥有手持式或便携式计算机的蓝牙用户就能交换文件、名片和约会时间。Bluetooth更多地面向用户的移动性和消除短距离的连线，而ZigBee更多地瞄准大范围的自动化和远程控制。

Virk称，第一批ZigBee产品现正在进行互用性测试，他预计获得联盟鉴定的展品将于今年第三季度问世(届时，CompXs将交付ZigBee协议分析仪)。业界的报告暗示，最终 ZigBee将通过双功能的ZigBee-Bluetooth芯片做进移动电话，用于你能想象出的任何设备的遥控以及从售货机买东西等等。

最后，Virk为我们中间的极客(技术迷)们指出了这两个协议之间的技术差异:

● 调制技术

Bluetooth：调频扩频

ZigBee：直接序列扩频

● 协议堆栈大小

Bluetooth:：250K字节

ZigBee：28K字节

● 电池

Bluetooth：需要经常充电

ZigBee：不能充电(原因之一，电池寿命高达10年之久)

● 最大网络速度

Bluetooth: 1M bit/sec

ZigBee: 250K bit/sec

● 网络范围

Bluetooth： 1米或100米，视无线电的级别而定

ZigBee：较高达70米

● 典型的网络连接时间

Bluetooth: 3 秒

ZigBee: 30 毫秒