外文翻譯ad_hoc網(wǎng)絡(luò)的一個(gè)簡(jiǎn)要概述挑戰(zhàn)與研究方向

1、<p><b>　　附 錄</b></p><p><b>　　英文原文</b></p><p>　　A Brief Overview of ad hoc Networks:</p><p>　　Challenges and Directions</p><p>　　One of the

2、 most vibrant and active “new” fields today is that of ad hoc networks. Significant research in this area has been ongoing for nearly 30 years, also under the names packet radio or multi-hop networks. </p><p&g

3、t;　　ad hoc network is a (possibly mobile) collection of communications devices (nodes) that wish to communicate, but have no fixed infrastructure available, and have no pre-determined organization of available links. Ind

4、ividual nodes are responsible for dynamically discovering which other nodes they can directly communicate with. </p><p>　　Ad hoc networking is a multi-layer problem. The physical layer must adapt to rapid ch

5、anges in link characteristics. The multiple access control (MAC) layer needs to minimize collisions, allow fair access, and semi-reliably transport data over the shared wireless links in the presence of rapid changes and

6、 hidden or exposed terminals. The network layer needs to determine and distribute information used to calculate paths in a way that maintains efficiency when links change often and bandwidth is a</p><p>　　Ad

7、 hoc networks are suited for use in situations where infrastructure is either not available, not trusted, or should not be relied on in times of emergency. A few examples include: military solders in the field; sensors s

8、cattered throughout a city for biological detection; an infrastructureless network of notebook computers in a conference or campus setting; the forestry or lumber industry; rare animal tracking; space exploration; unders

9、ea operations; and temporary offices such as campaign head</p><p><b>　　History</b></p><p>　　The history of ad hoc networks can be traced back to 1972 and the DoD-sponsored Packet Rad

10、io Network (PRNET), which evolved into the Survivable Adaptive Radio Networks(SURAN) program in the early 1980s [l]. The goal of these programs was to provide packetswitched networking to mobile battlefield elements in a

11、n infrastructureless, hostile environment (soldiers, tanks, aircraft, etc., forming the nodes in the network).</p><p>　　In the early 1990s a spate of new developments signaled a new phase in ad hoc networkin

12、g. Notebook computers became popular, as did open-source software, and viable communications equipment based on RF and infrared. The idea of an infrstructureless collection of mobile hosts was proposed in two conference

13、papers [2,3], and the IEEE 802.11 subcommittee adopted the term “ad hoc networks.” The concept of commercial (non-military) ad hoc networking had arrived. Other novel non-military possibilities</p><p>　　At a

14、round the same time, the DoD continued from where it left off, funding programs such as the Global Mobile Information Systems(GloMo), and the Near-term Digital Radio(NTDR). The goal of GloMo was to provide office-environ

15、ment Ethernet-type multimedia connectivity anytime, anywhere, in handheld devices. Channel access approaches were now in the CSMA/CA and TDMA molds, and several novel routing and topology control schemes were developed.

16、The NTDR used clustering and linkstate routing, and self</p><p>　　Spurred by the growing interest in ad hoc networking, a number of standards activities and commercial standards evolved in the mid to late’90

17、s.Within the IETF, the Mobile Ad hoc Networking(MANET) working group was horn, and sought to standardize routing protocols for ad hoc networks. The development of routing within the MANET working group and the larger com

18、munity forked into reactive (routes ondemand) and proactive (routes ready-to-use) routing protocols [4]. The 802.11 subcommittee standardiz</p><p>　　Open Problems</p><p>　　Despite the long histo

19、ry of ad hoc networking, there are still quite a number of problems that are open. Since ad hoc networks do not assume the availability of a fixed infrastructure, it follows that individual nodes may have to rely on port

20、able, limited power sources. The idea of energy-efficiency therefore becomes an important problem in ad hoc networks. Surprisingly,there has been little published work in the area of energy-efficiency of ad hoc networks

21、until fairly recently. Most existing s</p><p>　　The ability of fixed, wireless networks to satisfy quality of service (QoS) requirements is another open problem. Ad hoc networks further complicate the known

22、QoS challenges in wireline networks with RF channel characteristics that often change unpredictably, along with the difficulty of sharing the channel medium with many neighbors, each with its own set of potentially chang

23、ing QoS requirements. Reflecting the multi-layer nature of ad hoc networks, there are numerous attempts to improve the Qo</p><p>　　A similar multi-layer issue is that of security in ad hoc networks [10]. Sin

24、ce nodes use the shared radio medium in a potentially insecure environment, they are susceptible to denial of service (DoS) attacks that are harder to track down than in wired networks. Also, since a large portion of the

25、 network nodes will be dynamically reorganizing and forwarding packets on behalf of others, ad hoc networks are particularly susceptible to the injection of bogus network control traffic. Finally, ad hoc </p><

26、p>　　Robots and sensors also provide new hardware capabilities ripe for new methods of enhancing ad hoc efficiency. Robots, for example,have a tight integration between the processes of movement, decision-making, and n

27、etworking that allow them to modify their actions while taking into account the effects on many different system aspects [12]. Similarly,sensors are often deployed in a way that makes their roles and capabilities redunda

28、nt, suggesting new ways of combining application knowledge of deliv</p><p>　　Finally, a problem that overarches all these others is the lack of well defined and widely accepted models for RF path attenuation

29、, mobility, and traffic. These tightly interrelated models are needed for quantifying and comparing ad hoc system performance to a common baseline.The physical processes of refraction, reflection, and scattering of RF ra

30、diation is moderately well understood but difficult to quantify in detail when including a large number of complex objects such as foliage, cars, or b</p><p>　　The Future</p><p>　　Imagine the fo

31、llowing scenarios: a wireless mesh of rooftop-mounted ad hoc routers; an ad hoc network of cars for instant traffic and other information; sensors and robots forming a multimedia network that allows remote visualization

32、and control; multiple airborne routers (from tiny robots to blimps) automatically providing connectivity and capacity where needed (e.g., at a football game); an ad hoc network of spacecraft around and in transit between

33、 the Earth and Mars. </p><p>　　These may seem like science fiction, but are in fact ideas pursued seriously by the ad hoc research community. While only time can tell which of these imagined scenarios will b

34、ecome real, the above offers a glimpse into both the technological potential and the evolving state of the art. We discuss in this section the forces at play that are likely to shape the future of ad hoc networking, and

35、discuss the directions in which it may evolve.</p><p>　　To appreciate the role ad hoc networks are likely to play in the future, consider this: bandwidth-hungry applications and the laws of physics drive wir

36、eless architectures away from cellular toward ad hoc. This is because more capacity implies the need for a higher communications bandwidth and better spatial spectral reuse.Higher bandwidth is found at higher frequencies

37、,where the propagation is dismal. Further, mobile devices have to be power-thrifty. Propagation,spectral reuse, and energy issues</p><p>　　The other main impetus to ad hoc networks comes from the rapidly imp

38、roving communications technologies.Wireless communication devices are getting smaller, cheaper, more sophisticated, and hence more ubiquitous.Exploitation of these technologies for better ad hoc networking gives rise to

39、new problems that point to new research. For instance, the use of smart antennas in ad hoc networking requires new medium access and neighbor discovery protocols.The ability to dynamically alter spread spectrum c</p&g

40、t;<p>　　How are ad hoc networks likely to evolve? It is likely that the nodes themselves will be smaller,cheaper, more capable and probably conformal,and come in all forms. Indoor ad hoc networks (perhaps based on

41、 Bluetooth, Wireless LAN, or similar technologies) will probably be used to connect smart appliances to the Internet. Mesh-based last-mile solutions will increase in popularity and may even be the dominant solution.Milit

42、ary ad hoc networks will have higher capacities and support multimedia appl</p><p>　　Finally, there is the utopian idea of a "global infosphere" where all network elements form a gigantic ad hoc wi

43、reless network using unlicensed spectrum, bypassing the existing infrastructure.While fascinating from a research viewpoint, the realization of this vision will depend not only on overcoming the capacity and other hurdle

44、s, but also the pragmatics of a "cooperative" network. Notwithstanding our predictions,however, like the Internet, which existed for more than 20 years before the World</p><p><b>　　二、英文翻譯<

45、/b></p><p>　　ad hoc網(wǎng)絡(luò)的一個(gè)簡(jiǎn)要概述：挑戰(zhàn)與研究方向 </p><p>　　ad hoc網(wǎng)絡(luò)已成為當(dāng)今最為鮮明活躍的一個(gè)新的領(lǐng)域，在這個(gè)領(lǐng)域已經(jīng)將近有30年的重點(diǎn)研究下命名為“分組無(wú)線網(wǎng)”或“多跳網(wǎng)絡(luò)”。</p><p>　　ad hoc網(wǎng)絡(luò)是一個(gè)（可能是移動(dòng)的）希望相互通信的沒有固定基礎(chǔ)設(shè)施的沒有預(yù)先組織有效連接的通信設(shè)備（點(diǎn)）的集合。

46、各個(gè)節(jié)點(diǎn)負(fù)責(zé)動(dòng)態(tài)地發(fā)現(xiàn)其他的節(jié)點(diǎn)中哪些是可以與自己直接進(jìn)行通信。</p><p>　　ad hoc網(wǎng)絡(luò)是一個(gè)多層問題。物理層必須與快速變化的鏈路特性相適應(yīng)，媒體介質(zhì)接入控制（MAC）層盡量減少碰撞，允許公平接入，在共享無(wú)線鏈路快速變化和存在隱藏或暴露終端條件下進(jìn)行較可靠的傳輸數(shù)據(jù)，網(wǎng)絡(luò)層需要確定和傳輸用于計(jì)算在鏈路質(zhì)量時(shí)變和帶寬有限條件下保持高效路由的信息，它也需要與傳統(tǒng)的無(wú)線ad hoc互聯(lián)網(wǎng)和執(zhí)行功能（比如在

47、不斷變化的環(huán)境中自動(dòng)配置）順利的融合在一起，傳輸層需要處理與有線網(wǎng)絡(luò)差別很大的延遲和分組數(shù)據(jù)丟失統(tǒng)計(jì)分析；最后，應(yīng)用層需要處理與對(duì)等應(yīng)用之間頻繁的斷連和重連以及變化范圍較大的延遲和分組數(shù)據(jù)丟失特性。</p><p>　　ad hoc網(wǎng)絡(luò)適合在以下情況下使用，要么是沒有固定的基礎(chǔ)設(shè)施可用的場(chǎng)合，要么在緊急情況下沒有依賴的場(chǎng)合，一些應(yīng)用的例子包括：在野戰(zhàn)軍用通信應(yīng)用方面；散布在一個(gè)城市的生物的傳感器檢測(cè)；在會(huì)議或校園

48、內(nèi)的一個(gè)無(wú)筆記本計(jì)算機(jī)的通信設(shè)施的網(wǎng)絡(luò)；林業(yè)和木材工業(yè)；稀有動(dòng)物跟蹤；太空探索；海底作業(yè)；臨時(shí)辦公，比如總統(tǒng)的競(jìng)選。</p><p><b>　　歷史</b></p><p>　　ad hoc網(wǎng)絡(luò)技術(shù)的起源可以追溯到1972年的美國(guó)國(guó)防部高級(jí)研究計(jì)劃局資助研究的戰(zhàn)場(chǎng)環(huán)境中的無(wú)線分組數(shù)據(jù)網(wǎng)（PRNET）[1]，在20世紀(jì)80年代初發(fā)展成為具有抗毀性和自適應(yīng)能力的網(wǎng)絡(luò)（S

49、URNAN）項(xiàng)目。該項(xiàng)目的目標(biāo)是在沒有現(xiàn)成基礎(chǔ)設(shè)施可以利用、敵意環(huán)境中為移動(dòng)戰(zhàn)場(chǎng)節(jié)點(diǎn)（戰(zhàn)士、坦克、飛機(jī)等）提供基于分組交換的網(wǎng)絡(luò)。</p><p>　　在20世紀(jì)90年代初一連串的新發(fā)展標(biāo)志著ad hoc網(wǎng)絡(luò)化進(jìn)入一個(gè)新的階段。筆記本計(jì)算機(jī)的流行和基于無(wú)線和紅外技術(shù)通信設(shè)備的廣泛出現(xiàn)，產(chǎn)生了計(jì)算機(jī)互聯(lián)的要求，為無(wú)線ad hoc網(wǎng)絡(luò)的應(yīng)用提供了廣闊的空間。在文獻(xiàn)[2][3]中提到，IEEE 802.11委員會(huì)將這種

50、無(wú)基礎(chǔ)設(shè)施的移動(dòng)主機(jī)網(wǎng)絡(luò)采用術(shù)語(yǔ)“ad hoc 網(wǎng)絡(luò)”一詞，已經(jīng)形成了商業(yè) (非軍事）ad hoc網(wǎng)絡(luò)的概念，此外許多新型的非軍事發(fā)展可能（簡(jiǎn)介中已經(jīng)提到）也有了增長(zhǎng)利益。</p><p>　　大約在同一時(shí)間，美國(guó)國(guó)防部繼續(xù)資助曾停止過(guò)的項(xiàng)目，諸如全球移動(dòng)信息系統(tǒng)GloMo和近期數(shù)字化無(wú)線電(NTDR)。GloMo的目標(biāo)是用手持設(shè)備為辦公環(huán)境提供任何時(shí)間、任何地點(diǎn)的以太網(wǎng)類型的多媒體鏈接，采用CSMA/CA和TD

51、MA作為信道接入方式，并開發(fā)了幾種新的路由協(xié)議和拓?fù)淇刂品桨浮TDR采用分群和鏈路狀態(tài)路由，并自組為兩層結(jié)構(gòu)的ad hoc網(wǎng)絡(luò)。NTDR是美國(guó)軍方正在使用的實(shí)用網(wǎng)絡(luò)，也是當(dāng)今惟一的實(shí)用（非原型）網(wǎng)絡(luò)。</p><p>　　到了20世紀(jì)90年代中期，隨著ad hoc組網(wǎng)熱潮的到來(lái)，涌現(xiàn)了一系列標(biāo)準(zhǔn)活動(dòng)和商業(yè)標(biāo)準(zhǔn)。在IETF成立了一個(gè)專門的移動(dòng)ad hoc網(wǎng)絡(luò)MANET工作組，專門負(fù)責(zé)研究和開發(fā)具有數(shù)百個(gè)節(jié)點(diǎn)的移動(dòng)

52、ad hoc網(wǎng)絡(luò)的路由算法，并制定相應(yīng)的標(biāo)準(zhǔn)，其開發(fā)的路由協(xié)議派生為先應(yīng)式和反應(yīng)式路由協(xié)議[4]。IEEE 802.11委員會(huì)對(duì)基于CA和容許隱藏終端的MAC協(xié)議進(jìn)行了標(biāo)準(zhǔn)化，雖然不是最優(yōu)，但可用于構(gòu)建ad hoc網(wǎng)絡(luò)原型。HIPERLAN和藍(lán)牙技術(shù)也為ad hoc組網(wǎng)提供了一些技術(shù)設(shè)備。</p><p><b>　　面臨的挑戰(zhàn)</b></p><p>　　盡管ad

53、hoc網(wǎng)絡(luò)的歷史悠久，仍然存在很多問題。由于ad hoc網(wǎng)絡(luò)無(wú)法利用固定基礎(chǔ)設(shè)施，因此，單個(gè)節(jié)點(diǎn)必須依靠可攜帶的有限電源。這種節(jié)能的想法在ad hoc網(wǎng)絡(luò)已成為一個(gè)重要的問題。令人驚訝的是直到最近才有一些有關(guān)ad hoc網(wǎng)絡(luò)的能源效率方面的發(fā)表著作?，F(xiàn)有ad hoc 網(wǎng)絡(luò)大多數(shù)節(jié)能解決方案圍繞減少電臺(tái)收發(fā)功率進(jìn)行。在MAC及以上層可以選擇將收信機(jī)設(shè)置為睡眠狀態(tài)，或通過(guò)可變的發(fā)射機(jī)輸出功率和選擇需要更多短距離跳數(shù)取代少的長(zhǎng)距離跳數(shù)的路由[

54、8]實(shí)現(xiàn)。</p><p>　　固定無(wú)線網(wǎng)絡(luò)滿足服務(wù)質(zhì)量(QoS)能力要求是另一個(gè)要面對(duì)的問題。有線網(wǎng)絡(luò)的已知服務(wù)質(zhì)量QoS的挑戰(zhàn)和RF信道特性的變化的不可預(yù)見性使得ad hoc網(wǎng)絡(luò)進(jìn)一步復(fù)雜化，同時(shí)與許多鄰居共享信道也存在著困難，它們都有自己的隨時(shí)設(shè)置和變化所需求的服務(wù)質(zhì)量?？紤]到ad hoc網(wǎng)絡(luò)的多層特性，對(duì)MAC層的服務(wù)協(xié)議[9]作了很多改善服務(wù)質(zhì)量問題的嘗試。為了滿足 QoS 要求的有效方式是一個(gè)更統(tǒng)一的

55、跨層設(shè)計(jì)和分層設(shè)計(jì)結(jié)合，這個(gè)想法違反了各種允許不同地區(qū)的堆棧來(lái)適應(yīng)環(huán)境的傳統(tǒng)分層法，在某種程度上，考慮在其他層上的適應(yīng)性和可利用的信息。</p><p>　　在ad hoc網(wǎng)絡(luò)中類似多層問題的論點(diǎn)是安全問題[10]。共享無(wú)線環(huán)境的潛在的不安全因素使得節(jié)點(diǎn)比有線網(wǎng)的更容易受到拒絕服務(wù) (DoS) 攻擊，更難追蹤。此外，由于很大一部分網(wǎng)絡(luò)節(jié)點(diǎn)的動(dòng)態(tài)重配置和鄰居分組轉(zhuǎn)發(fā)容易被注入偽網(wǎng)絡(luò)控制業(yè)務(wù)中。最后，ad hoc網(wǎng)絡(luò)

56、可能受到各種特定的安全攻擊的受害者，如不停發(fā)射直至消耗完節(jié)點(diǎn)的電源。</p><p>　　機(jī)器人與傳感器網(wǎng)絡(luò)已具有采用新方法提高網(wǎng)絡(luò)效率的新硬件能力，這為提高ad hoc性能做好準(zhǔn)備。機(jī)器人，舉例來(lái)說(shuō)，有一間緊密結(jié)合的過(guò)程中，決策、網(wǎng)絡(luò)化等動(dòng)作，讓他們改變他們的行為而考慮到許多不同的系統(tǒng)方面[12]的影響。同樣，傳感器常常在某種程度上針對(duì)他們的角色與功能提出冗余信息的應(yīng)用知識(shí)與交付路由層[13]相結(jié)合的新方法。&

57、lt;/p><p>　　最后，跨層切換設(shè)計(jì)是所有這些其他的問題中的一個(gè)，缺乏明確和通用模型的靈活性、射頻路徑衰減和通信。為量化需要特別的系統(tǒng)性能，我們對(duì)這些緊密相關(guān)的模型進(jìn)行了分析比較，一個(gè)常見的諸如反射、折射、射頻輻射和散射的基本的物理過(guò)程的理解是相當(dāng)容易的,但卻很難量化,包括大量的復(fù)雜的對(duì)象，如樹葉、汽車、建筑。相比之下，與移動(dòng)節(jié)點(diǎn)的通信流模式可以肯定很容易進(jìn)行詳細(xì)描述，但依賴于目標(biāo)程序，缺乏現(xiàn)有系統(tǒng)的有效研究，

58、連接性、 移動(dòng)性和應(yīng)用程序之間的可能相互作用，將導(dǎo)致現(xiàn)有模型的含糊不清。</p><p><b>　　展望</b></p><p>　　想象一下以下情況：一個(gè)無(wú)線網(wǎng)格的天臺(tái)安裝ad hoc路由器；ad hoc網(wǎng)絡(luò)的汽車提供即時(shí)交通和其他信息；傳感器和機(jī)器人形成網(wǎng)絡(luò)多媒體，允許遠(yuǎn)程可視化和遠(yuǎn)程控制；多個(gè)（來(lái)自微小機(jī)器人)機(jī)載路由器在有需要時(shí)自動(dòng)提供連接和容量（例如，在一

59、場(chǎng)足球比賽中)；航天器周圍的ad hoc網(wǎng)絡(luò)和在地球和火星之間的運(yùn)輸途中。</p><p>　　這些可能看起來(lái)像是科幻小說(shuō)，但事實(shí)上是ad hoc研究委員會(huì)的一個(gè)嚴(yán)謹(jǐn)?shù)目茖W(xué)追求思想，只有時(shí)間能告訴那些想象的場(chǎng)景變成現(xiàn)實(shí)，而上述提供具有技術(shù)潛力和不斷發(fā)展的現(xiàn)狀的一種展望。在本節(jié)中我們討論未來(lái)的ad hoc網(wǎng)絡(luò)，并討論了它在方向演進(jìn)。</p><p>　　鑒于ad hoc網(wǎng)絡(luò)在未來(lái)可能扮演的角

60、色，我們有如下考慮：帶寬需求的應(yīng)用和物理性質(zhì)使得移動(dòng)單元對(duì)ad hoc無(wú)線體系結(jié)構(gòu)分離。這是因?yàn)楦蟮娜萘啃枨笠馕吨枰粋€(gè)更高的通信帶寬和更好的空間譜復(fù)用，高頻率建立高帶寬的傳播是很難實(shí)現(xiàn)的，此外移動(dòng)設(shè)備還要節(jié)省電源。光譜的重用和能源問題支持從單長(zhǎng)無(wú)線鏈接（如小區(qū)）轉(zhuǎn)為短鏈接（如在ad hoc網(wǎng)絡(luò)）網(wǎng)傳播。未來(lái)可能的潮流是由新興的初創(chuàng)企業(yè)證明，諸如屋頂通訊（現(xiàn)在諾基亞的一部分），網(wǎng)狀網(wǎng)絡(luò)、輻射網(wǎng)絡(luò)，用基于多徑網(wǎng)格技術(shù)取代傳統(tǒng)的3G架構(gòu)

61、。</p><p>　　ad hoc網(wǎng)絡(luò)其他主要?jiǎng)恿?lái)自于迅速提高的通信技術(shù)。無(wú)線通信設(shè)備變得更小、更廉價(jià)、更精細(xì)，因此更為普遍。這些技術(shù)開發(fā)為更好地ad hoc網(wǎng)絡(luò)指出新的問題，引發(fā)新的研究。比如，利用智能天線在ad hoc組網(wǎng)需要新的媒體訪問和鄰居查找協(xié)議。動(dòng)態(tài)地改變擴(kuò)頻碼、調(diào)制方案和波形的功能需要在更高層次的相應(yīng)創(chuàng)新。代表著一種無(wú)線電體系結(jié)構(gòu)中的重要變化的軟件無(wú)線電提供更佳的靈活性，它適合移動(dòng)自組網(wǎng)。<

62、;/p><p>　　ad hoc網(wǎng)絡(luò)容易發(fā)展嗎？在所有的網(wǎng)絡(luò)形式中，ad hoc網(wǎng)絡(luò)自身的節(jié)點(diǎn)更小、更廉價(jià)、更能勝任和可能形成。室內(nèi)ad hoc網(wǎng)絡(luò)(也許是基于藍(lán)牙技術(shù)的無(wú)線局域網(wǎng)或類似的技術(shù))可能會(huì)被用于智能電器到互聯(lián)網(wǎng)上的連接?；诰W(wǎng)格的最后一英里解決方案將會(huì)增加受歡迎程度，甚至可能是占主導(dǎo)地位的解決方案。軍事ad hoc網(wǎng)絡(luò)將會(huì)有更高的能力，會(huì)支持多媒體應(yīng)用，會(huì)更有自適應(yīng)性、隱身技術(shù)，與進(jìn)化系統(tǒng)，這些都是對(duì)所有

63、戰(zhàn)場(chǎng)元素、移動(dòng)或固定的多媒體網(wǎng)絡(luò)。 </p><p>　　最后，存在一個(gè)“烏托邦”思想是形成一個(gè)全部采用巨大無(wú)線ad hoc網(wǎng)絡(luò)的頻譜，繞過(guò)現(xiàn)有的基礎(chǔ)結(jié)構(gòu)的全球信息網(wǎng)絡(luò)。同時(shí)吸引人的地方是，從研究角度來(lái)看，這個(gè)想象的實(shí)現(xiàn)將不僅取決于容量和其他障礙克服，而且取決于“協(xié)作”網(wǎng)絡(luò)的因果研究法。盡管我們的預(yù)測(cè)是像互聯(lián)網(wǎng)一樣在萬(wàn)維網(wǎng)出現(xiàn)之前存在的時(shí)間超過(guò)20年，它可能是一個(gè)令人驚訝的“殺手應(yīng)用程序”式的ad hoc網(wǎng)絡(luò)的未

64、來(lái)。</p><p><b>　　三、源程序</b></p><p><b>　　（1）隨機(jī)運(yùn)動(dòng)軌跡</b></p><p>　　function b1</p><p><b>　　n=50</b></p><p>　　x=rand(n,1)*120;&

65、lt;/p><p>　　y=rand(n,1)*120; </p><p>　　plot(x,y);</p><p>　?。?）L3，L2切換</p><p><b>　　clear;</b></p><p>　　counter2=0; counter3=0;</p><p&g

66、t;　　a(1:j)=[];</p><p>　　b(1:j)=[];</p><p>　　d1(1:j)=[];</p><p>　　for i=1:100</p><p><b>　　x=0;</b></p><p><b>　　y=0; </b></p>

67、<p><b>　　j=1;</b></p><p><b>　　a(1:j)=x;</b></p><p><b>　　b(1:j)=y;</b></p><p><b>　　j=j+1;</b></p><p>　　dir=rand(1)*

68、2*pi; </p><p>　　v=rand(1)*5+10; </p><p>　　for t=0:0.1:30</p><p><b>　　T=t/5;</b></p><p>　　T1=floor(T);</p><p&

69、gt;<b>　　if T==T1</b></p><p>　　dir=rand(1)*2*pi; </p><p>　　v=rand(1)*5+10; </p><p>　　end </p>

70、;<p>　　x=x+v*t*cos(dir);</p><p>　　y=y+v*t*sin(dir);</p><p><b>　　a(1:j)=x;</b></p><p><b>　　b(1:j)=y;</b></p><p>　　d=sqrt(a(1:j).*a(1:j)+b(

71、1:j).*b(1:j));</p><p>　　d1(1:j)=d;</p><p>　　if (d1(1:j)>=107)&(d1(1:j)<=120)</p><p>　　counter3=counter3+1; </p><p><b>　　j=j+1;</b></p>&

72、lt;p><b>　　break</b></p><p><b>　　end</b></p><p><b>　　t=t+0.1;</b></p><p><b>　　T=t/5;</b></p><p>　　T1=floor(T);</p&g

73、t;<p><b>　　if T==T1</b></p><p>　　dir=rand(1)*2*pi; </p><p>　　v=rand(1)*5+10; </p><p>　　end

74、 </p><p>　　x=x+v*t*cos(dir);</p><p>　　y=y+v*t*sin(dir);</p><p><b>　　a(1:j)=x;</b></p><p><b>　　b(1:j)=y;</b></p><p>　　d=sqrt(a(1:j).

75、*a(1:j)+b(1:j).*b(1:j));</p><p>　　d1(1:j)=d;</p><p>　　if ( d1(1:j)>=120)</p><p>　　counter2=counter2+1;</p><p><b>　　j=j+1;</b></p><p>　　brea

76、k </p><p><b>　　end</b></p><p><b>　　end </b></p><p>　　end </p><p>　　m=counter3/counter2;</p><p>