zigbee相關(guān)外文翻譯---無(wú)線技術(shù)，低功耗傳感器網(wǎng)絡(luò)-其他專業(yè)-文庫(kù)吧資料
2025-01-27 06:55本頁(yè)面
【正文】 e, 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 plete later this year along with ZigBee Specification . One reason for optimism about ZigBee adoption for home automation and security is its ease of use. ZigBee works are selfforming, making it easy even for consumers to set them up. In the residential space, there39。s more plex and less powerefficient than TDMA. ZigBee has still more powersaving tricks up its sleeve, however. For example, it reduces power consumption in ZigBee ponents by providing for powersaving reducedfunction devices (RFDs) in addition to more capable fullfunction devices (FFDs). Each ZigBee work needs at least one FFD as a controller, but most work nodes can be RFDs (Figure 3). RFDs can talk only with FFDs, not to other RFDs, but they contain less circuitry than FFDs, and little or no powerconsuming memory. Figure 3: ZigBee works can contain as many as 65,536 nodes in a variety of configurations ZigBee conserves still more power by reducing the need for associated processing. Simple 8bit processors like an 8051 can handle ZigBee chores easily, and ZigBee protocol stacks occupy very little memory. An FFD stack, for example, needs about 32 kbytes, and an RFD stack needs only about 4 kbytes. Those numbers pare with about 250 kbytes for the far more plex Bluetooth technology. From ZigBee39。s inevitably some contention and some inefficiency. To avoid ZigBee39。s especially problematic. Although contention for airwave access isn39。s talkwhenready scheme doesn39。s quiet before you talk. Fortunately, this inyourface strategy leads to very little RF interference. That39。s very power efficient. We did an extensive analysis that led to the best powersaving strategy in various kinds of environments from quiet to noisy, Heile says. We discovered that, hands down, we were better off just sending the packet and acknowledging it. If you don39。t like to do that. Another ZigBee and munications option is the beacon mode, in which normally sleeping work slave nodes wake up periodically to receive a synchronizing beacon from the work39。 transmissions or with transmissions from other radio sources. The 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 listenbeforetalk approach to see if any radio traffic is already underway. But, as noted by Venkat Bahl, marketing vice president for sensor pany Ember Corp. and vice chairman of the ZigBee Alliance, that39。t necessarily implement a sensor work any way they choose and still expect the multipleyear battery life that is ZigBee39。 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 ZigBeeenabled wireless light switch, for example, would not be aware of a wakeup delay before the light turns on. In contrast, wakeup delays for Bluetooth are typically around three seconds. A big part of ZigBee39。s low bandwidth helps it fulfill its goals of low power, low cost, and robustness. Figure 2: ZigBee39。t be sending and large documents, as WiFi does, or documents and audio, as Bluetooth does. For sending sensor readings, which are typically a few tens of bytes, high bandwidth isn39。s bright future is largely due to its low data rates—20 kbps to 25
醫(yī)療健康相關(guān)推薦
鄂ICP備17016276號(hào)-1