网络工程 英文 毕业 设计 论文 文献翻译 无线技术.docx

1、网络工程 英文 毕业 设计 论文 文献翻译 无线技术单位代码 01 学 号_080114601_分 类 号_ TN92 _ 密 级_文献翻译无线技术，低功耗传感器网络 无线技术，低功耗传感器网络译文正文：加里莱格在发掘无线传感器的潜在应用方面我们几乎没遇见任何困难。比如说在家庭安全系统方面，无线传感器比有线传感器更易安装。而无线传感器的安装费用通常只占有线传感器安装费用的80%，这一点用于工业环境方面同样合适。并且相对于有线传感器而言，无线传感器应用性更强。虽然，无线传感器需要消耗更多能量，也就是说所需电池的数量会随之增加或更换过于频繁。再加上对无线传感器由空气传送的数据可靠性的怀疑论，所以无

2、线传感器看起来并不是那么吸引人。一个被称为ZigBee的低功率无线技术，它是无线传感器方程重写，但是，通过的IEEE 802.15.4无线标准（图1），ZigBee承诺，把无线传感器的一切，从工厂自动化系统延伸到家庭安全系统，消费电子产品中。与802.15.4的合作下，ZigBee提供的电池寿命可比普通小型电池长几年。 ZigBee设备预计也便宜，有人估计销售价格最终不到3美元每节点，。由于价格低，他们应该也能适用于无线交换机，无线自动调温器，烟雾探测器等产品。图1：ZigBee将网络安全和应用服务层添加到PHY和IEEE811.15.4网络通信的MAC层虽然还没有正式规范的ZigBee存在，

3、但ZigBee的前景似乎一片光明。技术研究公司In-Stat/MDR在它所谓的“谨慎进取”的预测中预测，802.15.4节点和芯片销售将从今天基本上为零，增加到2010年的165万台。不是所有这些单位都将与ZigBee结合，但大多数可能会。世界研究公司预测，到2010年射频模块无线传感器出货量4.65亿美量，其中77是与ZigBee相关的。从某种意义上说，ZigBee的光明前途在很大程度上是由于其较低的数据速率（20 kbps到250 kbps），而这些数据率则取决于频段频率（图2）。但ZigBee不能发送电子邮件和大型文件，如Wi - Fi功能，或文件和音频，蓝牙一样。对于发送传感器的读数，

4、这是典型的数万字节数，高带宽是没有必要，ZigBee低带宽有助于它实现其低功耗，低成本。图2：zigbee的数据传输速率为20kbps到250kbps的，这取决于使用频率由于ZigBee带宽要求低，ZigBee节点大部分时间可以是睡眠模式，从而节省电池电源，然后醒来，快速发送数据，再回去睡眠模式。而且，由于ZigBee可以从睡眠模式过渡到15毫秒或更少主动模式下，即使是睡眠节点也可以达到适当的低延迟。一个ZigBee的功耗节省很大一部分来自802.15.4无线电技术，它本身就是为低功耗而设计的。802.15.4采用DSSS（直接序列扩频）技术。ZigBee节点使用802.15.4，是几个不同的

5、沟通方式之一。然而，它在某些方面比别人拥有更多的使用权力。但是，ZigBee用户却不能够实现传感器网络上所有方式的选择。事实上，即使ZigBee的电池需求很大，一些技术专家还是打算用小型无线传感器创建大的网络。一个ZigBee网络节点可能会消耗额外的功率，例如，如果它试图避免与其他节点的传输或与其他无线电源传输重叠的传输。那么在ZigBee 802.15.4无线电使用实现CSMA / CA（载波侦听多址接入冲突避免）技术，与ZigBee节点使用CSMA / CA是基本上采取了听先于谈话的方式，看是否有无线电通信已经展开。为了尽可能省电ZigBee采用一种简单交际策略，talk-when-rea

6、dy发送数据时,数据准备派遣然后就等着自动确认。根据鲍勃Heile,ZigBee联盟主席和电子802.15,talk-when-ready的“开门见山”计划,这将使电力的使用更加有效。当面策略导致RF干扰非常小。这主要是因为ZigBee节点具有非常低的占空比，只偶尔传输发送少量的数据。其他的ZigBee节点，以及Wi - Fi和蓝牙模块，可以轻松应付这么小，这么频繁的爆发。ZigBee的通话就绪计划并不适合所有的目的。例如，在成千上万的微型传感器网络进入战区监视敌方部队调动，提供的支持仍可能是不够的。每个网络节点周期性地发送和反复通过网状网络配置中的其他节点到达网络，控制器的大碰撞和重发的数据

7、包数量可能会浪费功率，并明显缩短传感器节点的电池寿命。如果传感器电池非常小，功率有限，这将成为极大的局限。ZigBee已经注册了更省电的技巧。例如，除了更强大能为ZigBee元件提供电力消耗的全功能设备（FFDs），其他设备都被减少。每个ZigBee网络至少需要一个控制器作为一个发展筹资，但大多数网络节点可以RFDs（图3）。RFDs只有FFDs可以谈，而不是其他RFDs，它们含有较少的电路，比FFDs少或者干脆就没有功率消耗内存。图3：zigbee网络可以包含在多种配置，如许多节点，65536ZigBee节省、减少了相关处理，但仍然需要更多权力。简单的8位像8051处理器可以处理家务，简单的

8、ZigBee和ZigBee协议栈占用很少的内存。而发展筹资一个堆栈，大概需要32字节，例如一个RFD的堆栈只需要4字节。这些数字是比250蓝牙技术更复杂的字节。ZigBee实现起来比较简单，节约成本。其简单的8位处理器和小协议栈能帮助保持系统成本。通常，一个应用程序的主处理器可以很容易地承担ZigBee的额外处理负载，使得ZigBee不必要单独的处理器。保持ZigBee低价格的主要策略是大市场和高容量。ZigBee联盟，通过一个开放的标准，大力推进ZigBee设备之间的互操作性，使得ZigBee的预期应用非常大，如家庭与楼宇自动化应用。目前该联盟正在为这些特殊应用努力，它预计将在今年较迟时与Z

9、igBee规范1.0的互操作性程序一起完成。ZigBee网络还可以自行在商业和工业形式中转换，但专业安装人员将需要特别的安全工具并提供额外的控制才行。ZigBee是安全灵活的，它可能是缓慢渗透到无线传感器的工业市场。但是，据对世界市场研究后发现，它需要五至七年来说服客户相信他在工业上的可靠性，耐用性，以及无线传感器系统的安全性。并预测在整个世界中ZigBee将在工业制造上有长期的增长。因此，到2010年，公司项目，射频模块，应用于工业监控和控制的将达到1.65亿台，同比增长190万元，在世界性预测中，2004年，大约75将基于ZigBee和802.15.4。最终，ZigBee可进入各种广泛的应

10、用。在家用电器中，它可以帮助监测和控制能源消耗。在汽车应用中，它可以提供轮胎压力监测和远程无钥匙进入系统。也可用于医疗设备中，甚至计算机外围设备，如无线键盘或鼠标。值得关注的是越来越多，虽然ZigBee可能变成一种适合所有技术的尺寸，但它并不是适合任何应用程序。例如，企图使ZigBee无所不包，就可能导致ZigBee协议栈太大，ZigBee的双重目标是非常低功耗和非常低的成本。如果出现这种情况，那么ZigBee将是低功耗和低数据速率。这样，将被证明是过于宽泛的。然后，也许我们会需要另一种无线标准，以适应我们蓬勃发展的需求。 文献原文正文：Wireless Technology for Low-

11、Power Sensor Networks. Gary LeggWe have never had trouble coming up with potential applications for wireless sensors. In a home security system, for example, wireless sensors would be much easier to install than sensors that need wiring. The same is true in industrial environments, where wiring typi

12、cally accounts for 80% of the cost of sensor installations. And then there are applications for sensors where wiring isnt practical or even possible.The problem, though, is that most wireless sensors use too much power, which means that their batteries either have to be very large or get changed far

13、 too often. Add to that some skepticism about the reliability of sensor data thats sent through the air, and wireless sensors simply havent looked very appealing.A low-power wireless technology called ZigBee is rewriting the wireless sensor equation, however. A secure network technology that rides o

14、n 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 batter

15、ies. 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. Figure 1: ZigBee adds network, sec

16、urity, and application-services layers to the PHY and MAC layers of the IEEE 811.15.4 radio Although no formal specification for ZigBee yet exists, the outlook for ZigBee appears bright. Technology research firm In-Stat/MDR, in what it calls a cautious aggressive forecast, predicts that sales of 802

17、.15.4 nodes and chipsets will increase from essentially zero today to 165 million units by 2010. Not all of these units will be coupled with ZigBee, but most probably will be. Research firm ON World predicts shipments of 465 million wireless sensor RF modules by 2010, with 77% of them being ZigBee-r

18、elated.In a sense, ZigBees bright future is largely due to its low data rates20 kbps to 250 kbps, depending on the frequency band used (Figure 2). But ZigBee wont be sending email and large documents, as Wi-Fi does, or documents and audio, as Bluetooth does. For sending sensor readings, which are ty

19、pically a few tens of bytes, high bandwidth isnt necessary, and ZigBees low bandwidth helps it fulfill its goals of low power, low cost, and robustness.Figure 2: ZigBees data rates range from 20 kbps to 250 kbps, depending on the frequency used Because of ZigBee applications low bandwidth requiremen

20、ts, 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. A big part of ZigBees power

21、 savings come from the radio technology of 802.15.4, which itself was designed for low power. 802.15.4 uses DSSS (direct-sequence spread spectrum) technology, for example, because the alternative FHSS (frequency-hopping spread spectrum) would have used too much power just in keeping its frequency ho

22、ps synchronized.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 cant necessarily implement a sensor network any way they choose and still expect the multiple-year battery life that is ZigBee

23、s hallmark. 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

24、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. To save as much power as possible, ZigBee employs a talk-when-ready communication strategy, simply sending data when it has data ready to se

25、nd and then waiting for an automatic acknowledgement. According to Bob Heile, who is chairman of both the ZigBee Alliance and IEEE 802.15, talk-when-ready is an in-your-face scheme, but one thats very power efficient. We did an extensive analysis that led to the best power-saving strategy in various

26、 kinds of environments from quiet to noisy, Heile says.Fortunately, this in-your-face strategy leads to very little RF interference. Thats largely because ZigBee nodes have very low duty cycles, transmitting only occasionally and sending only small amounts of data. Other ZigBee nodes, as well as Wi-

27、Fi and Bluetooth modules, can easily deal with such small, infrequent bursts.ZigBees talk-when-ready scheme doesnt suit all purposes, however. For example, in a network of thousands of tiny sensors dropped into a war zone to monitor enemy troop movements, the power savings provided still might not b

28、e enough. With each network node sending data periodicallyand with transmissions repeated numerous times through other nearby nodes of a mesh network configuration in order to reach a network controllerlarge numbers of packet collisions and retransmissions could waste power and significantly shorten

29、 sensor node battery life. If the sensor batteries are very small and power-limited, thats especially problematic.ZigBee has still more power-saving tricks up its sleeve, however. For example, it reduces power consumption in ZigBee components by providing for power-saving reduced-function devices (R

30、FDs) in addition to more capable full-function devices (FFDs). Each ZigBee network needs at least one FFD as a controller, but most network 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 power-consuming memor

31、y. Figure3:ZigBeenetworkscancontainasmanyas65,536nodesinavarietyofconfigurations ZigBee conserves still more power by reducing the need for associated processing. Simple 8-bit processors like an 8051 can handle ZigBee chores easily, and ZigBee protocol stacks occupy very little memory. An FFD stack,

32、 for example, needs about 32 kbytes, and an RFD stack needs only about 4 kbytes. Those numbers compare with about 250 kbytes for the far more complex Bluetooth technology.From ZigBees 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 applications main processor can easily bear the small additional