ZigBee: Wireless Technology for Low-Power Sensor Networks A low-power wireless technology called ZigBee is rewriting the wireless sensor equation, however. A secure network technology that rides on top of the recently ratified IEEE 802.15.4 radio standard , ZigBee promises to put wireless sensors in everything from factory automation systems to home security systems to consumer electronics. In conjunction with 802.15.4, ZigBee offers battery life of up to several years for common small batteries. ZigBee devices are also expected to be cheap, eventually selling for less than $3 per node by some estimates. With prices that low, they should be a natural fit even in household products like wireless light switches, wireless thermostats, and smoke detectors.39683
Because of ZigBee applications' low bandwidth requirements, a ZigBee node can sleep most of the time, thus saving battery power, and then wake up, send data quickly, and go back to sleep. And, because ZigBee can transition from sleep mode to active mode in 15 msec or less, even a sleeping node can achieve suitably low latency. Someone flipping a ZigBee-enabled wireless light switch, for example, would not be aware of a wake-up delay before the light turns on. In contrast, wake-up delays for Bluetooth are typically around three seconds.
ZigBee nodes, using 802.15.4, can communicate in any of several different ways, however, and some ways use more power than others. Consequently, ZigBee users can't necessarily implement a sensor network any way they choose and still expect the multiple-year battery life that is ZigBee's hallmark. In fact, some technologists who are planning very large networks of very small wireless sensors say that even ZigBee is too power hungry for their uses.
A ZigBee network node can consume extra power, for example, if it tries to keep its transmissions from overlapping with other nodes' transmissions or with transmissions from other radio sources. The 802.15.4 radio used by ZigBee implements CSMA/CA (carrier sense multiple access collision avoidance) technology, and a ZigBee node that uses CSMA/CA is essentially taking a listen-before-talk approach to see if any radio traffic is already underway. But, as noted by Venkat Bahl, marketing vice president for sensor company Ember Corp. and vice chairman of the ZigBee Alliance, that's not a preferred approach. "Having to listen burns power," says Bahl, "and we don't like to do that."
Another ZigBee and 802.15.4 communications option is the beacon mode, in which normally sleeping network slave nodes wake up periodically to receive a synchronizing "beacon" from the network's control node. But listening for a beacon wastes power, too, particularly because timing uncertainties force nodes to turn on early to avoid missing a beacon.
From ZigBee's relatively simple implementations, cost savings naturally accrue. RFDs, of course, reduce ZigBee component costs by omitting memory and other circuitry, and simple 8-bit processors and small protocol stacks help keep system costs down. Often, an application's main processor can easily bear the small additional load of ZigBee processing, making a separate processor for ZigBee functions unnecessary.
But the main strategy for keeping ZigBee prices low is to have big markets and high volumes. The ZigBee Alliance, by making ZigBee an open standard and by vigorously promoting interoperability among ZigBee devices, expects that ZigBee will be very big in applications such as home and building automation. The alliance is currently working on interoperability procedures for those particular applications, which it expects to complete later this year along with ZigBee Specification 1.0.
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ZigBee：无线技术，低功耗传感器网络
低功耗无线无线个域网技术是无线传感器方程改写,然而。一个安全的网络技术,骑在最近批准内部IEEE 802.15.4无线标准提供服务,无线个域网承诺将无线传感器从工厂自动化系统向消费电子家庭安全系统。内部结合802.15.4,提供服务无线个域网提供数年的电池寿命常见的小型电池。无线个域网设备也将被便宜,最终售价不到3美元每节点根据一些估计。价格低,他们应该是一个自然的健康甚至在家用无线电灯开关等产品,无线恒温器,和烟雾探测器论文网 ZigBee无线技术英文文献和中文翻译:http://www.youerw.com/fanyi/lunwen_40067.html