無(wú)線傳感器網(wǎng)絡(luò)SMAC協(xié)議的分析與算法改進(jìn)

1、無(wú)線傳感器網(wǎng)絡(luò)smac協(xié)議的分析與算法改進(jìn)the analysis of smac protocol for wireless sensor networks and its algortithm improvement摘要：無(wú)線傳感器網(wǎng)絡(luò)（wsn）使用靈活，移動(dòng)性強(qiáng)，架設(shè)便捷，應(yīng)用范圍非 常廣泛。abstract: nowadays wireless sensor networking（wsn） has been widely used because of its adaptivity, mobility and scalability （假設(shè)便捷）。媒體訪問(wèn)控制（mac沏議是保證無(wú)線傳感

2、器網(wǎng)絡(luò)高效通信的關(guān)鍵網(wǎng)絡(luò)協(xié)議之一。mac protocol is one of the most important network protocol which guarantees the efficiency of wsn communication.重點(diǎn)分析了 wsn中基于競(jìng)爭(zhēng)的典型mac協(xié)議smac協(xié)議。our major concern is the typical contentionbased mac protocol in wsn smac protocol.針對(duì)smac協(xié)議中采用的退避算法不能良好地解決節(jié)點(diǎn)通信公平性等問(wèn)題，提 出了 qrdb退避算法。仿真結(jié)果表明，該算法可

3、以使節(jié)點(diǎn)在發(fā)送失敗時(shí)快速逃離擁擠競(jìng)爭(zhēng)窗口，在發(fā)送 成功后能保持最優(yōu)發(fā)送窗口，并能定位和解決網(wǎng)絡(luò)擁堵區(qū)域問(wèn)題，從而有效地提 高了節(jié)點(diǎn)通信公平性，降低了信道的碰撞，延長(zhǎng)了網(wǎng)絡(luò)的生命周期。the results dem on strate that by using this algorithm, the no des can promptly escape （擁擠競(jìng)爭(zhēng)窗口）when transmission is failed關(guān)鍵詞：無(wú)線傳感器網(wǎng)絡(luò)，媒體訪問(wèn)控制，退避算法keyword: wireless sensor networks（wsn）, medium access control（ma

4、c）, avoidance algorithm0引言introduction無(wú)線傳感器網(wǎng)絡(luò)（wsn）以其獨(dú)特的優(yōu)勢(shì)，廣泛應(yīng)用于氣象和地理研究、 洪水、火災(zāi)檢測(cè)，監(jiān)視農(nóng)作物灌溉悄況、土壤參數(shù)變化、牲畜和家禽的環(huán)境狀況 以及人血積的地表檢測(cè)等4, 6owsn has a wide range of application including 氣象 and geography researches, detection of floods and fire with its unique advantages,無(wú)線傳感器網(wǎng)絡(luò)綜合了現(xiàn)代傳感器技術(shù)、微電子技術(shù)、通信技術(shù)、嵌入式計(jì) 算技術(shù)和分布式信息處理

5、技術(shù)等多個(gè)學(xué)科3 4owsn synthesizes many modern sensor technology, micro electronic tech no logy而在無(wú)線傳感器網(wǎng)絡(luò)屮，媒體訪問(wèn)控制（mac）協(xié)議決定無(wú)線信道的使用 方式8,主要作用是為無(wú)線節(jié)點(diǎn)合理分配通信資源，避免眾多節(jié)點(diǎn)在同一時(shí)間 發(fā)射信號(hào)時(shí)產(chǎn)生碰撞沖突。無(wú)線信道的使用方式 in wsn is determined by mac protocol.the main function of mac protocol is distributi ng communication sources reas on ably

6、 , avoiding collision from interfering nodes對(duì)大多數(shù)傳感器硬件平臺(tái)而言，無(wú)線通信模塊是傳感器節(jié)點(diǎn)能量的主要消耗 者。as for most of sen sor hardware platforms, the wireless comm unication module is the primary consumer of the sensor nodes energy.由圖1所示可見，通信過(guò)程屮發(fā)生、接收、空閑狀態(tài)消耗了大部分的能量門。as shown in the figure 1, transmitting, receiving and idl

7、ing dominate the total energy consumption.而mac子層直接與物理層連接，即mac協(xié)議直接控制著無(wú)線射頻收發(fā)器 的活動(dòng)，決定何時(shí)發(fā)送數(shù)據(jù)或接收數(shù)據(jù)，所以mac協(xié)議節(jié)能效率的好壞將嚴(yán)重 影響網(wǎng)絡(luò)的生命周期9。however mac layer links to physical layer directly, which means that mac protocol controls the無(wú)線射頻收發(fā)器，通信圖1 wsn節(jié)點(diǎn)能量消耗圖1 smac協(xié)議分析the analysis of smac protocol無(wú)線傳感器網(wǎng)絡(luò)應(yīng)用的范圍非常廣泛，不同應(yīng)用

8、場(chǎng)合對(duì)網(wǎng)絡(luò)的要求都是不盡相同的。wsn has a wide range of applications, whereas the demanding of networks are varied from different circumstances.因此，對(duì)于無(wú)線傳感器網(wǎng)絡(luò)的mac協(xié)議來(lái)說(shuō)，并不存在一種適用于所有無(wú)線傳感器 網(wǎng)絡(luò)應(yīng)用的mac協(xié)議，也不能說(shuō)某種mac協(xié)議相對(duì)其他mac協(xié)議在所有方面都有 明顯優(yōu)勢(shì)。各種mac協(xié)議均有各自的性能特點(diǎn)，或者傾向于提能量有效性方面，或者傾向于提高 網(wǎng)絡(luò)延遲方面，或者傾向于提高網(wǎng)絡(luò)吞吐量方面等，在這些性能之間都存在不同程度的矛盾 性，且受到多方面因素

9、的制約rio0every mac protocol has its own characteristics因此，應(yīng)根據(jù)具體應(yīng)用環(huán)境來(lái)決定無(wú)線傳感器網(wǎng)絡(luò)的mac協(xié)議。therefore the mac protocols of wsn should be used accordingly by the certain circumstance.1.1 smac工作機(jī)制the smac operation mechanism無(wú)線傳感器網(wǎng)絡(luò)與應(yīng)用高度相關(guān)，研究人員從不同的方面出發(fā)提出了多種mac協(xié)議。根據(jù)信道訪問(wèn)策略，mac協(xié)議可分為競(jìng)爭(zhēng)協(xié)議、調(diào)度協(xié)議和混合mac協(xié)議。according to th

10、e channel access scheme, mac protocol can be sorted ass-mac(sensor-mac)是基于競(jìng)爭(zhēng)機(jī)制的典型mac協(xié)議 它是wei ye等人在ieee802. 11 協(xié)議的基礎(chǔ)上，針對(duì)傳感器網(wǎng)絡(luò)的節(jié)省能量的需求而設(shè)計(jì)的1。s-mac is a typical protocol based on the contention mechanismsmac的主要工作機(jī)制如下：smac main operation mechanisms are as follows:(1 ) 周期性睡眠/偵聽機(jī)制periodic sleep /listen mec

11、hanism 周期性的偵聽/睡眠機(jī)制是smac協(xié)議最主要的運(yùn)行機(jī)制。periodic sleep /listen mechanism is the most primary operation mechanism該機(jī)制把節(jié)點(diǎn)、的工作周期分為偵聽時(shí)間(listen)和睡岷時(shí)間(sleep )兩個(gè)大幀,the mechanism divides the node operation cycle into two frame, listening and sleeping perio cl.在保證正常工作的條件下，通過(guò)使節(jié)點(diǎn)進(jìn)入的睡眠時(shí)間，利用低占空比盡量地降低 節(jié)點(diǎn)的能量消耗?？梢哉f(shuō)smac提出的

12、這種周期性的偵聽/睡眠機(jī)制，是整個(gè)協(xié)議運(yùn)行的核 心內(nèi)容。listensleeplistensleep圖1周期性睡眠/偵聽機(jī)制(2)虛擬簇機(jī)制the virtual cluster mechanism在同步策略方面，smac采用了一種非常聰明的虛擬簇機(jī)制。from the aspect of synchronize schedule, smac exploits a very smart virtual cluster mechanism節(jié)點(diǎn)每隔n個(gè)偵聽周期廣播一次同步幀，相鄰節(jié)點(diǎn)通過(guò)同步幀采取相同的偵聽/睡眠策 略，從而形成了 一個(gè)同步的小網(wǎng)絡(luò)，這些小網(wǎng)絡(luò)s-mac稱之為虛擬簇。every s

13、everal listen period, the node broadcasts a synchronize frame. the neighboring nodes adopt the same listen/sleep schedule with the synchronize frame. therefore they form a micro network which is called virtual cluste匚這樣整個(gè)無(wú)線傳感器網(wǎng)絡(luò)就形成了若干個(gè)采用不同偵聽/睡眠策咯的虛擬簇，thus the whole wsn consists of several virtual cl

14、usters by listen/sleep schedules.如圖2所示。虛擬簇之間通過(guò)邊緣節(jié)點(diǎn)來(lái)進(jìn)行數(shù)據(jù)傳輸。as figure 2shown, data is sent and received between the virtual cluster through the cluster edge node通過(guò)虛擬簇機(jī)制，新的節(jié)點(diǎn)也可以很容易地加入到網(wǎng)絡(luò)當(dāng)中。with the virtual cluster mechanism, the new nodes can be easily implemented into the networks.the collision overhe

15、aring avoidance mechanisms-mac協(xié)議采用與802. 11mac協(xié)議類似的虛擬和物理載波偵聽機(jī)制，以及rts/cts的通 告機(jī)制，以此較好地解決了隱藏終端問(wèn)題和暴露終端問(wèn)題。s-mac adopts similar virtual/physical csma, and rts/cts 的通告機(jī)制 as 802.11 mac protocola b； c圖3隱藏終端問(wèn)題和暴露終端問(wèn)題(4 ) 退避發(fā)送機(jī)制為進(jìn)一步減低數(shù)據(jù)發(fā)送碰撞幾率，節(jié)點(diǎn)在信道空閑要傳送數(shù)據(jù)的時(shí)候，將利用退避算法 退避一個(gè)時(shí)間來(lái)競(jìng)爭(zhēng)信道。in order to reduce the possibilit

16、y of collision, the node strives for idle channel by using avoidance algorithm when it wants to transmit data一個(gè)好的退避算法，可大大降低節(jié)點(diǎn)間碰撞的概率，提高信道的利用效率。(5 ) 流量自適應(yīng)偵聽機(jī)制traffic adaptive overhearing mechanism節(jié)點(diǎn)根據(jù)偷聽到的鄰居節(jié)點(diǎn)發(fā)送的rts幀或者cts幀，轉(zhuǎn)入睡眠一定時(shí)間，并由此判 斷自己是否為下一跳目標(biāo)節(jié)點(diǎn)。若為目標(biāo)節(jié)點(diǎn)，當(dāng)鄰居節(jié)點(diǎn)發(fā)送結(jié)束后，即可喚醒自己立即 進(jìn)行接收。according to the rts

17、 frame or cts frame from neighboring nodes, the node itself switches to sleep mode for a time.。(6)消息傳遞機(jī)制網(wǎng)絡(luò)傳輸中，長(zhǎng)消息傳輸成功率相對(duì)不高。因此，smac協(xié)議為提高數(shù)據(jù)發(fā)送成功率， 采用了消息傳遞機(jī)制，即把長(zhǎng)消息分割為若干段消息，并集中突發(fā)傳送減少協(xié)議控制消息的 開銷。ris21data19data17data1cts20ack18ack16?ck0圖4消息傳遞機(jī)制1.2smac協(xié)議缺點(diǎn)、分析the analysis of smac protocol disadvantagessmac協(xié)議

18、利用周期性的睡眠/偵聽減少了空閑監(jiān)聽所造成的能量浪費(fèi)，并采用物理和 虛擬載波偵聽機(jī)制以提高數(shù)據(jù)發(fā)送的成功率，是無(wú)線傳感器網(wǎng)絡(luò)中應(yīng)用較廣的mac協(xié)議。smac protocol use periodic sleeping/listerling to reduce energy waste from idle overhearing.,但是，smac協(xié)議也存在著一定的缺點(diǎn)。but smac protocol also has some disadvantages.一方面，當(dāng)網(wǎng)絡(luò)負(fù)載較低的時(shí)候，由于smac協(xié)議采用固定的周期性偵聽/睡眠機(jī)制， 節(jié)能效果并不理想；on one hand, owing

19、to using the fixed periodic listen/sleep schedule, the smac protocol for energy savings is less effective when the network overloading is low另一方面，當(dāng)網(wǎng)絡(luò)比較繁忙時(shí)，smac協(xié)議數(shù)據(jù)收發(fā)的延時(shí)和信道碰撞的幾率都急劇 增大，并非常容易導(dǎo)致網(wǎng)絡(luò)堵塞和節(jié)點(diǎn)的“餓死”和“早死”現(xiàn)象。on the other hand, latency and the contingency of collision increase drastically which eas

20、ily leads towhen the networking is busy在第二個(gè)方面中，smac協(xié)議所采用的退避算法機(jī)制過(guò)于簡(jiǎn)單和原始是一個(gè)突出原因。as the second aspect shows, smac因此，本文提出一種全新的退避算法，采用新算法的smac協(xié)議在無(wú)線傳感器網(wǎng)絡(luò)中 的吞吐量、時(shí)延、能耗等方面均得到一定的提高。therefore, this paper proposes a novel avoidance algorithm2改進(jìn)方案the improvement scheme2.1 smac采用的退避算法smac avoidance algorithm首先，我們

21、來(lái)看一下smac所采用的退避算法的原理：first, let5s see the principle of avoidance algorithm adopted by smacbtime = random。* slottime;( 1 )(1) 式中,btime代表節(jié)點(diǎn)的退避時(shí)間,slottim是由物理層決定大小的時(shí)隙,random() 是均勻分布于0, cw啲隨機(jī)整數(shù)，在smac中，cw是一個(gè)固定值。in equation ( 1 )> btime represents the avoidance time of node. slottime is the slot which si

22、ze is determined by the physical laye匚 random() is ainteger.cwis a constant in smac從（1）式中，我們可以看到無(wú)論節(jié)點(diǎn)發(fā)送成功與否，節(jié)點(diǎn)的退避時(shí)間都是在固定的競(jìng)爭(zhēng) 窗口里隨機(jī)選取的，as shown above, we know that whether it successes or not, the avoidance time of node is picked up randomly from the fixed contention window.節(jié)點(diǎn)的競(jìng)爭(zhēng)發(fā)送完全不能反映出網(wǎng)絡(luò)實(shí)際情況。退避算法對(duì)數(shù)據(jù)

23、收發(fā)的公平以及對(duì)信道 的分配都不能起到很好的改善作用。because the contention of nodes transmission is not able to reveal the actual condition of networks, so the avoidance algorithm cannot achieve the goal of improving per-node fairness and channel assignment2.2改進(jìn)的退避算法the improving avoidance algorithm本文針對(duì)smac原先采用的退避算法的缺陷，提出了一

24、種改進(jìn)的退避算法。considering the drawback of former smac avoidance algorithm, this paper proposes a improving one.為了便于敘述，本文將改進(jìn)后的退避算法協(xié)議稱為qrdb,改進(jìn)后的s-mac協(xié)議稱為 qs-mac 協(xié)議。qrdb首先對(duì)競(jìng)爭(zhēng)窗口設(shè)定最小值cwmin和最大值cwmax,即cw是在cwmin, cw max區(qū)間動(dòng)態(tài)調(diào)整。然后為了判斷節(jié)點(diǎn)的發(fā)送意愿，添加一個(gè)數(shù)據(jù)發(fā)送失敗計(jì)數(shù)器fcourter0通過(guò)統(tǒng)計(jì)該節(jié) 點(diǎn)發(fā)送失敗的次數(shù)，來(lái)判斷節(jié)點(diǎn)發(fā)送數(shù)據(jù)意愿的是否強(qiáng)烈。為判斷節(jié)點(diǎn)是否繁忙，添加一個(gè)變量q統(tǒng)

25、計(jì)節(jié)點(diǎn)的數(shù)據(jù)包隊(duì)列數(shù)，以此判斷該節(jié)點(diǎn)是否處于 無(wú)線傳感器網(wǎng)絡(luò)中的繁忙區(qū)域。最后設(shè)定一個(gè)退避窗口的分隔閥值cwm,通過(guò)cwm把競(jìng) 爭(zhēng)窗口區(qū)間分隔成如圖5,以此判斷當(dāng)前網(wǎng)絡(luò)流量的高低情況。1iii0minmmax圖5以下是在四種不同的情況的時(shí)候，qrdb對(duì)競(jìng)爭(zhēng)窗口作出不同調(diào)整策略的描述：(1 ) 發(fā)送失敗未超過(guò)規(guī)定次數(shù)x時(shí)(fcourtcr<x ),cw =min ( z ( f*cw ), cwmax ); f=fl.5, 2.0, z 代表取整；(2) 發(fā)送失敗超過(guò)規(guī)定次數(shù)x時(shí)(fcourter>=x),若cw在cwmin, cwm區(qū)間，則將cw降至cwmin; 若cw在cwm,

26、cwmax區(qū)間，則將cw降至cwm;(3) 發(fā)送成功時(shí)，cw =max ( z ( s*cw), cwmin); s二0.7, 0.9 , z 代表取整；(4 ) 節(jié)點(diǎn)傳輸?shù)臄?shù)據(jù)包隊(duì)列數(shù)q超過(guò)n個(gè)時(shí)，cw立即降至cwmin。每個(gè)節(jié)點(diǎn)的初始退避窗口 cw均為cwmin.當(dāng)節(jié)點(diǎn)發(fā)送數(shù)據(jù)失敗時(shí)，數(shù)據(jù)發(fā)送失敗計(jì) 數(shù)器fcourter統(tǒng)計(jì)發(fā)送的次數(shù)。當(dāng)fcourter 卜于規(guī)定的失敗次數(shù)時(shí)，cw乘以一個(gè)參數(shù)f(f 根據(jù)實(shí)際情況可取1.5-2.0),以盡快逃離擁擠的競(jìng)爭(zhēng)窗口；當(dāng)fcourter等于或大于規(guī)定的失 敗次數(shù)時(shí)，表明節(jié)點(diǎn)非?！翱释卑l(fā)送數(shù)據(jù)但是自身?yè)屨夹诺赖哪芰s較低，為了公平地分 配信道，這時(shí)

27、如果節(jié)點(diǎn)的cw在cwmin, cwm區(qū)間，則將cw馬上降低到cwmin,如果 cw在cwm, cwmax區(qū)間，則將cw馬上降低到cwm,通過(guò)跳躍式調(diào)節(jié)節(jié)點(diǎn)cw的取 值，有效提高節(jié)點(diǎn)搶占信道的能力。當(dāng)節(jié)點(diǎn)發(fā)送數(shù)據(jù)成功后，cw乘以一個(gè)參數(shù)s (s根據(jù) 實(shí)際情況可取0.7-0.9 ),以盡量保持當(dāng)前對(duì)節(jié)點(diǎn)自身和整個(gè)網(wǎng)絡(luò)都是適當(dāng)?shù)母?jìng)爭(zhēng)窗口，解決“餓死”和“早死”現(xiàn)象。變量q是用來(lái)統(tǒng)計(jì)節(jié)點(diǎn)的數(shù)據(jù)包隊(duì)列數(shù)的，通過(guò)該值我們可以定 位無(wú)線傳感器網(wǎng)絡(luò)中的擁堵區(qū)域，為了盡快均衡網(wǎng)絡(luò)的傳輸，當(dāng)q等于大于n時(shí)候，當(dāng)前 cw將無(wú)條件降低到cwmin。2.3 qbeb流程圖節(jié)點(diǎn)競(jìng)爭(zhēng)信道攤爭(zhēng)先敗次cw-cw m7d<cw>cw masv1ac退避機(jī)制算法f龜 1 asmac backoffm echanisn algorithm3仿真驗(yàn)證本文選用了目前使用相當(dāng)廣泛的網(wǎng)絡(luò)仿真軟件ns-2來(lái)