扩频技术外文翻译

毕业设计（论文）外文资料翻译学院 专业 学生姓名 班级学号通信与信息工程学院通信工程外文出处Robert Clyde Dixon.Spread Spectrum TechniquesM.IEEEPress,1976附件：1.外文资料翻译译文；2.外文原文指导教师评价:1 翻译内容与课题的结合度：优良中差2.翻译内容的准确、流畅：优良中差3.专业词汇翻译的准确性：优良中差4.翻译字符数是否符合规定要求：符合口不符合指导教师签名：年 月 日附件 1：外文资料翻译译文扩频技术摘要扩频技术是信号（例如一个电气、电磁，或声信号）生成的特定带宽频率域中特 意传播，从而导致更大带宽的信号的方法。这些技术用于各种原因包括增加抗自然干 扰和干扰，以防止检测，并限制功率流密度（如在卫星下行链路）的安全通信设立的。 跳频的历史：跳频的概念最早是归档在 1903 年美国专利 723188 和美国专利 725605 由尼古拉 特斯拉在 1900 年 7 月提出的。特斯拉想出了这个想法后，在 1898 年时展示了世界上 第一个无线电遥控潜水船，却从 “受到干扰，拦截，或者以任何方式干涉 ”发现无线信 号控制船是安全的需要。他的专利涉及两个实现抗干扰能力根本不同的技术，实现这 两个功能通过改变载波频率或其他专用特征的干扰免疫。第一次在为使控制电路发射 机的工作，同时在两个或多个独立的频率和一个接收器，其中的每一个人发送频率调 整，必须在作出回应。第二个技术使用由预定的方式更改传输的频率的一个编码轮控 制的变频发送器。这些专利描述频率跳变和频分多路复用，以及电子与门逻辑电路的 基本原则。跳频在无线电报中也被无线电先驱约翰内斯 Zenneck 提及（1908 ，德语，英语翻 译麦克劳希尔， 1915 年），虽然 Zenneck 自己指出德律风根在早几年已经试过它。 Zenneck 的书是当时领先的文本，很可能后来的许多工程师已经注意到这个问题。一 名波兰的工程师 （Leonard Danilewicz） ，在 1929 年提出了这个想法。其他几个专利被 带到了 20 世纪 30 年代包括威廉贝尔特耶斯（德国 1929 年，美国专利 1869695 ，1932） 在第二次世界大战中， 美国陆军通信兵发明一种称为 SIGSALY 的通信系统，使得罗斯 福和丘吉尔之间能相互通信，这种系统称为扩频，但由于其高的机密性， SIGSALY 的 存在直到 20 世纪 80 年代才知道。最著名的跳频发明是女演员海蒂拉玛和作曲家乔治安太尔，他们的 “秘密通信系 统”1942 年获美国第 2,292,387 专利。拉玛与前夫弗里德里希汀曼德这位奥地利武器制 造商在国防会议上了解到这一问题。安太尔 -拉马尔版本的跳频用钢琴卷 88 个频率发 生变化，其旨在使无线电导向鱼雷，让敌人很难来检测或干扰。该专利来自五零年代 ITT公司和其他私人公司开始时发展码分多址（CDMA）, 个民间形式扩频，尽管拉马 尔专利有没对后续技术有直接影响。它其实是在麻省理工学院林肯实验室、乐华政府 和电子工业公司、国际电话电报公司及万年电子系统导致早期扩频技术在 20 世纪 50 年代的长期军事研究。雷达系统的并行研究和一个称为 “相位编码 ”的技术类似概念对 扩频发展造成影响。扩频通信 这是一种在其(电信)信号传输一个带宽远远多于原始信息的频率内容的技术。 扩频通信是构建技术，它采用直接序列、调频，或多个访问 /多种功能可用这些的 混合信号。这种技术减少了对其他接收机的潜在干扰，同时实现隐私。扩频通常会使 用噪声的连续的信号传播结构，通常使用窄带上的信息信号分散一个相对宽带(单选) 的波段的频率。 接收器接收信号的相关性检索原始的信息信号。要么努力抵御敌人的 通信干扰(防堵塞，或简称AJ),或隐瞒事实，沟通，甚至发生，有时也称为低截获 概率(LPI)的。跳频扩频(FHSS),直接序列扩频(DSSS)、时间跳频扩频(THSS)、线性扩频(CSS), 和这些技术的组合都是扩频的形式。每种方法采用了伪随机数字序列使用的伪随机数 字生成器创建一一以确定与控制信号通过分配带宽的传播模式。 超宽带(UWB)是另一 种调制技术，实现了基于传输短时间内脉冲相同的目的。 无线以太网标准 IEEE 802.11 在其无线接口使用跳频扩频或直接序列扩频。备注自20世纪40年代以来已知和自20世纪50年代以来在军事通信系统中使用的技 术。 “传播”的无线电信号较宽的频率范围内若干程度高于最低要求。扩频的核心原则 就是波载波噪声样，使用和作为名称意味着比相同的数据速率在简单的点对点通 信所需更多的带宽。 两种主要的方法：1. 直接序列(DS)2. 跳频 (FH) 耐干扰。直接序列在抵御连续时间窄带干扰更好，而跳频抗脉冲干扰是更好。在 直接序列系统中，窄带干扰会影响检测性能如干扰功率量蔓延了整个信号的带宽 时，通常检测性能不会比更强背景噪声。相比之下，在那些低带宽的窄带信号系 统，如果干扰功率恰巧集中在信号带宽那么接收的信号质量将会严重降低。 抗窃听。扩频代码(在直接序列系统)或跳频模式(在跳频系统)通常任何一方都 不知道谁的信号是未定义的，在这种情况下 “加密”信号，并降低对方的对其的判 断意识。更重要的是，有一个给定的噪声功率谱密度(PSD)，扩频系统需要在每 比特相同数量的能源之前传播窄带系统因此同样的功率，如果比特率在扩展前是 相同的，但由于每比特能量信号功率扩散超过一个大带宽的扩散，则信号 PSD 的 要低得多，而往往大大低于噪声 PSD 的，因此对手可能无法确定是否存在于所有 的信号。不过，对于关键任务的应用尤其是雇用商用无线电通讯设备，扩频无线 电本质上没有提供足够的安全 “只用扩频无线电通信本身是不足够的安全。 ”抗衰落。扩频信号所占用的高带宽提供某些频率的多样性，也就是说，即是不可 能的信号也会遇到整个带宽的严重多径衰落，而在其他情况下信号可以被检测到 使用，例如 Rake 接收机。 多种接入能力。多个用户可以同时传输相同的频率（范围），只要他们使用不同的 扩频码。请参阅 CDMA。主要技术：一、直接序列扩频在电信中，直接序列扩频（DSSS ）是一种调制技术。与其他扩频技术一样传输的 信号比被调制的信息信号的占用更多带宽。扩频名称来自一个事实，即载波信号在整 个带宽（谱设备的发射频率）发生。功能1. 与它相调制正弦波伪随机地与伪连续的字符串（PN）的代码符号称为“芯片”， 各自有一个比信息比特更短的时间。也就是说每个信息位是由一个更快的芯片序列调 制，因此芯片速率远高于信息信号的比特率。2. 它使用的信号接收器的众所周知的先验结构，其中是由发射机生产的芯片序 列。接收器就可以使用相同的伪随机码序列，以抵消对接收信号的伪随机码序列的影 响，以重建信息信号。传输方法直接序列扩频传输数据乘以由一个 “噪音”信号传送。这种噪声信号是 1 和-1 伪随 机序列值，其频率比原始信号为高，从而带能量延伸到更广泛的原信号。产生的信号类似于白噪声，像 “静态”的音频录音。不过，这个类似噪声的信号可 用于乘以相同的伪随机序列完全重建接收端的原始数据（因为1 x 1 = 1，-1 x-1 = 1）。 这个过程称为 “解扩”的过程在数学上构成传播的 PN 序列，接收方认为使用发射器 PN 序列的相关性。对于解扩的正常运行，发送和接收序列必须同步。这需要通过某种形式的时间搜 索过程使发射器的序列与接收器序列同步。但是，这种明显的缺点可以是一个重要好 处：如果多个发射器的序列是相互同步的，那么相对的同步接收器必须使它们之间可 以用来确定相对时间，而反过来，如果已知发射器的位置，可用于计算接收器的位置。 这是许多卫星导航系统的基础。调用过程中加强对通道信噪比造成的影响被称为处理增益。这种影响可通过采用 较大较长 PN 序列和每比特更多的芯片，但用来生成 PN 序列的物理设备的多个芯片上 可达到的处理增益实际限制。如果在同一信道发送器发送同一频道，但使用不同的 PN 序列（或根本没有序列） 解扩过程导致该信号没有获得处理。这种效果是码分多址（CDMA ）属性的直接序列 扩频，它允许多个发射机内共享他们的伪码序列的互相关特性来限制相同的频道。由于这说明表明，一个传输的波形图有一个大致的钟形信封的载波频率为中心， 就像 AM 传播, 除了增加的传输噪音导致的分配要大大高于一个 AM 信号的更广泛的 传播。相比之下，跳频扩频伪随机重新调整载波信号，而不是添加伪随机噪声数据，结 果导致在一个统一的频率分布，其宽度是由伪随机数发生器的输出范围决定。 优点对预期的或非预期抗干扰共享多个用户间的单信道 减少信号 /背景噪声级别包装截取（隐身） 发射器与接收器之间的相对时间的测定 使用 美国全球定位系统和欧洲伽利略卫星导航系统 基于直接序列扩频系统（直接序列码分多址）是一种在扩频多址接入方案的基 础上，从信号的传播，到不同的用户有不同的代码。这是 CDMA 的最广泛使用的类 型。 无绳电话在 900 兆赫， 2.4 吉赫和 5.8 吉赫频带操作 电气和电子工程师协会 802.11b 2.4 GHz 无线网络和其前身 802.11-1999 。 （正 交频分复用技术继任 802.11g 技术） 自动抄表 电气和电子工程师协会 802.15.4 标准（例如用作物理层和链路层的紫蜂 ） 二、跳频扩频跳频扩频（FHSS）通过很多渠道快速切换频率，其中一个运载体发射无线电信号的 一种方法是，使用一个发射机和接收机已知的伪随机序列。它被利用作为多个访问方 法中跳频码分多址（FH-CDMA）计划。扩频传输通过三个主要优点提供了固定频率传输：1. 扩频信号高度抗窄带干扰。再收集传播信号传播出了干扰信号的过程，导致其 退到背景的干扰信号。2.扩频信号难以进行拦截。一个跳频扩频信号显示为一个简单的背景噪声增加至 窄带接收机。如果窃听者知道了伪随机序列，他们只能够拦截传输。3. 扩频传输可以与许多类型的最小干扰的常规传输共享一个频带。扩频信号添加 最小噪声窄频的通信，反之亦然。这样一来可以更有效地利用带宽。基本的算法通常，一个调频通信的启动是如下所示1. 发起方发送请求通过预定义的频率或控制通道。2.接收方发送一个数字，像已知的种子。3. 发起方作为变量的计算顺序，必须使用的频率的一个预定义算法中使用该号 码。最经常的频率变化的时期是预定义的，以允许一个基站，服务多个连接。4. 发起方通过第一次发送同步信号的频率计算，从而为接受确认它有正确的计算 顺序。5. 在通信开始，发送方和接收沿该计算的顺序在同一点开始的时间更改其频率。 技术的几点思考所需频率跳变的整体带宽是比需要来传输仅一个相同信息使用载波频率更大。不 过，由于在任何给定时间只能在此带宽的一小部分上发生传播，实在是一样有效的干 扰带宽是。虽然没有提供额外的热噪声对宽带的保护，跳频方法确实降低窄带干扰造 成的退化。对跳频系统的挑战之一是如何同步发射器和接收器。一种方法是有将保证的发射 机使用在固定时间内的所有渠道。接收器随机选择一个频道就可以找到发送器，该频 道提供有效的数据倾听变送器。发送器的数据都是通过一个特殊的数据序列不像发生 在这个渠道为数据段和段可以有一个完整的校验和进一步鉴定。发射器和接收器可以 使用固定的渠道序列表，以便他们按照表中的能保持同步。每个通道段上发射器表中， 可以将其当前位置的进行发送。在美国的通信委员会第 15部分无牌系统 900兆赫兹和 2.4兆赫兹频带上允许更多 非扩频系统功率。调频和直接序列系统可以在 1瓦传输。该限制从 1毫瓦增加到 1瓦 或增加一千倍。美国联邦通讯委员会（FCC）规定了渠道的最低数目和每个通道的最 大驻留时间。在实际的多点式无线电系统，空间允许的多个相同频率的传输，在一个地理区域 内可能使用多个无线电设备。这将创建系统数据速率高于香农极限的单通道的可能性 扩频系统没有违反香农极限。扩频系统过多的依赖信号信噪比的频谱共享。多输入多 输出和直接序列扩频系统中也看到此属性。电波传导和定向天线也通过提供远程无线 电通讯设备之间的隔离提高系统的性能。附件 2：外文原文Spread Spectrum TechniquesAbstract:Spread-spectrum techniques are methods by which a signal (e.g. an electrical, electromagnetic, or acoustic signal ) generated in a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth. These techniques are used for a variety of reasons, including the establishment of secure communications, increasing resistance to natural interference and jamming, to prevent detection, and to limit power flux density (e.g. in satellite downlinks).History Frequency hopping:The concept of frequency hopping was first alluded to in the 1903 U.S. Patent 723,188 and U.S. Patent 725,605 filed by Nikola Tesla in July 1900. Tesla came up with the idea after demonstrating the worlds first radio-controlled submersible boat in 1898, when it became apparent the wireless signals controlling the boat needed to be secure from being disturbed, intercepted, or interfered with in any way. His patents covered two fundamentally different techniques for achieving immunity to interference, both of which functioned by altering the carrier frequency or other exclusive characteristic. The first had a transmitter that worked simultaneously at two or more separate frequencies and a receiver in which each of the individual transmitted frequencies had to be tuned in, in order for the control circuitry to respond. The second technique used a variable-frequency transmitter controlled by an encoding wheel that altered the transmitted frequency in a predetermined manner. These patents describe the basic principles of frequency hopping and frequency-division multiplexing, and also the electronic AND-gate logic circuit.Frequency hopping is also mentioned in radio pioneer Johannes Zennecks book Wireless Telegraphy (German, 1908, English translation McGraw Hill, 1915), although Zenneck himself states that Telefunken had already tried it several years earlier. Zennecks book was a leading text of the time, and it is likely that many later engineers were aware of it. A Polish engineer, Leonard Danilewicz, came up with the idea in 1929.Several other patents were taken out in the 1930s, including one by Willem Broertjes (Germany 1929, U.S. Patent 1,869,695, 1932). During World War II, the US Army Signal Corps was inventing a communication system called SIGSALY for communication between Roosevelt and Churchill, which incorporated spread spectrum, but due to its top secret nature, SIGSALYs existence did not become known until the 1980s.The most celebrated invention of frequency hopping was that of actress Hedy Lamarr and composer George Antheil, who in 1942 receivedU.S. Patent 2,292,387for their Secret Communications System. Lamarr had learned about the problem at defense meetings she had attended with her former husband Friedrich Mandl, who was an Austrian arms manufacturer. The Antheil-Lamarr version of frequency hopping used a piano-roll to change among 88 frequencies, and was intended to make radio-guided torpedoes harder for enemies to detect or to jam. The patent came to light during patent searches in the 1950s whenITT Corporation and otherprivate firms began to develop Code Division Multiple Access (CDMA), a civilian form of spread spectrum, though the Lamarr patent had no direct impact on subsequent technology. It was in fact ongoing military research at MIT Lincoln Laboratory, Magnavox Government & Industrial Electronics Corporation, ITT and Sylvania Electronic Systems that led to early spread-spectrum technology in the 1950s. Parallel research on radar systems and a technologically similar concept called phase coding also had an impact on spread-spectrum development. Spread-spectrum telecommunicationsThis is a technique in which a (telecommunication) signal is transmitted on a bandwidth considerably larger than the frequency content of the original information.Spread-spectrum telecommunications is a signal structuring technique that employs direct sequence, frequency hopping, or a hybrid of these, which can be used for multiple access and/or multiple functions. This technique decreases the potential interference to other receivers while achieving privacy. Spread spectrum generally makes use of a sequential noise-like signal structure to spread the normally narrowband information signal over a relatively wideband (radio) band of frequencies. The receiver correlates the received signals to retrieve the original information signal. Originally there were two motivations: either to resist enemy efforts to jam the communications (anti-jam, or AJ), or to hide the fact that communication was even taking place, sometimes called low probability of intercept (LPI).Frequency-hopping spread spectrum (FHSS), direct-sequence spread spectrum (DSSS), time-hopping spread spectrum (THSS), chirp spread spectrum (CSS), and combinations of these techniques are forms of spread spectrum. Each of these techniques employs pseudorandom number sequences created using pseudorandom number generators to determine and control the spreading pattern of the signal across the alloted bandwidth. Ultra-wideband (UWB) is another modulation technique that accomplishes the same purpose, based on transmitting short duration pulses. Wireless Ethernet standard IEEE 802.11 uses either FHSS or DSSS in its radio interface.Notes Techniques known since 1940s and used in military communication system since 1950s Spread radio signal over a wide frequency range several magnitudes higher than minimum requirement. The core principle of spread spectrum is the use of noise-like carrier waves, and, as the name implies, bandwidths much wider than that required for simple point-to-point communication at the same data rate. Two main techniques:1. Direct sequence (DS)2. Frequency hopping (FH) Resistance to jamming (interference). DS is better at resisting continuous-time narrowband jamming, while FH is better at resisting pulse jamming. In DS systems, narrowband jamming affects detection performance about as much as if the amount of jamming power is spread over the whole signal bandwidth, whenit will often not be much stronger than background noise. By contrast, in narrowband systems where the signal bandwidth is low, the received signal quality will be severely lowered if the jamming power happens to be concentrated on the signal bandwidth. Resistance to eavesdropping. The spreading code (in DS systems) or the frequency-hopping pattern (in FH systems) is often unknown by anyone for whom the signal is unintended, in which case it encrypts the signal and reduces the chance of an adversarys making sense of it. Whats more, for a given noise power spectral density (PSD), spread-spectrum systems require the same amount of energy per bit before spreading as narrowband systems and therefore the same amount of power if the bitrate before spreading is the same, but sincethe signal power is spread over a large bandwidth, the signal PSD is much lower, often significantly lower than the noise PSD, therefore the adversary may be unable to determine if the signal exists at all. However, for mission-critical applications, particularly those employing commercially available radios, spread-spectrum radios do not intrinsically provide adequate security; .just using spread-spectrum radio itself is not sufficient for communications security Resistance to fading. The high bandwidth occupied by spread-spectrum signals offer some frequency diversity, i.e. it is unlikely that the signal would encounter severe multipath fading over its whole bandwidth, and in other cases the signal can be detected using e.g. a Rake receiver. Multiple access capability. Multiple users can transmit simultaneously on the same frequency (range) as long as they use different spreading codes. See CDMA.Main techniques:1、Direct-sequence spread spectrumIn telecommunications, direct-sequence spread spectrum (DSSS) is a modulation technique. As with other spread spectrum technologies, the transmitted signal takes up more bandwidth than the information signal that is being modulated. The name spread spectrum comes from the fact that the carrier signals occur over the full bandwidth (spectrum) of a devices transmitting frequency.Features1.It phase-modulates a sine wave pseudorandomly with a continuous string of pseudonoise (PN) code symbols called chips, each of which has a much shorter duration than an information bit. That is, each information bit is modulated by a sequence of much faster chips. Therefore, the chip rate is much higher than the information signal bit rate.2. It uses a signal structure in which the sequence of chips produced by the transmitter is known a priori by the receiver. The receiver can then use the same PN sequence to counteract the effect of the PN sequence on the received signal in order to reconstruct the information signal.Transmission methodDirect-sequence spread-spectrum transmissions multiply the data being transmitted by a noise signal. This noise signal is a pseudorandom sequence of 1 and 1 values, at a frequency much higher than that of the original signal, thereby spreading the energy of the original signal into a much wider band.The resulting signal resembles white noise, like an audio recording of static. However, this noise-like signal can be used to exactly reconstruct the original data at the receiving end, by multiplying it by the same pseudorandom sequence (because 1x1 = 1, and -1 x -1 = 1). This process, known as de -spreading, mathematically constitutes a correlation of the transmitted PN sequence with the PN sequence that the receiver believes the transmitter is using.For de-spreading to work correctly, the transmit and receive sequences must be synchronized. This requires the receiver to synchronize its sequence with the transmitters sequence via some sort of timing search process. However, this apparent drawback can be a significant benefit: if the sequences of multiple transmitters are synchronized with each other, the relative synchronizations the receiver must make between them can be used to determine relative timing, which, in turn, can be used to calculate the receivers position if the transmitters positions are known. This is the basis for many satellite navigation systems.The resulting effect of enhancing signal to noise ratio on the channel is called process gain. This effect can be made larger by employing a longer PN sequence and more chips per bit, but physical devices used to generate the PN sequence impose practical limits on attainable processing gain.If an undesired transmitter transmits on the same channel but with a different PN sequence (or no sequence at all), the de-spreading process results in no processing gain for that signal. This effect is the basis for the code division multiple access (CDMA) property of DSSS, which allows multiple transmitters to share the same channel within the limits of the cross-correlation properties of their PN sequences.As this description suggests, a plot of the transmitted waveform has a roughly bell-shaped envelope centered on the carrier frequency, just like a normal AM transmission, except that the added noise causes the distribution to be much wider than that of an AM transmission.In contrast, frequency-hopping spread spectrum pseudo-randomly re-tunes the carrier, instead of adding pseudo-random noise to the data, which results in a uniform frequency distribution whose width is determined by the output range of the pseudo-random number generator.Benefits Resistance to intended or unintended jamming Sharing of a single channel among multiple users Reduced signal/background-noise level hampers interception (stealth) Determination of relative timing between transmitter and receiverUses The United States GPS and European Galileo satellite navigation systems DS-CDMA (Direct-Sequence Code Division Multiple Access) is a multiple access scheme based on DSSS, by spreading the signals from/to different users with different codes. It is the most widely used type of CDMA. Cordless phones operating in the 900 MHz, 2.4 GHz and 5.8 GHz bands IEEE 802.11b 2.4 GHz Wi-Fi, and its predecessor 802.11-1999. (Their successor 802.11g uses OFDM instead) Automatic meter reading IEEE 802.15.4 (used e.g. as PHY and MAC layer for ZigBee) 2、Frequency-hopping spread spectrumFrequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. It is utilized as a multiple access method in the frequency-hopping code division multiple access (FH-CDMA) scheme.A spread-spectrum transmission offers three main advantages over a fixed-frequency transmission:1. Spread-spectrum signals are highly resistant to narrowband interference. The process of re-collecting a spread signal spreads out the interfering signal, causing it to recede into the background.2. Spread-spectrum signals are difficult to intercept. An FHSS signal simply appears as an increase in the background noise to a narrowband receiver. An eavesdropper would only be able to intercept the transmission if they knewthe pseudorandom sequence.3. Spread-spectrum transmissions can share a frequency band with many typesof conventional transmissions with minimal interference. The spread-spectrum signals add minimal noise to the narrow-frequency communications, and vice versa. As a result, bandwidth can be utilized more efficiently.Basic algorithmTypically, the initiation of an FHSS communication is as follows1. The initiating party sends a request via a predefined frequency or control channel.2. The receiving party sends a number, known as a seed.3. The initiating party uses the number as a variable in a predefined algorithm, which calculates the sequence of frequencies that must be used. Most often the period of the frequency change is predefined, as to allow a single base station to serve multiple connections.4. The initiating party sends a synchronization signal via the first frequency in the calculated sequence, thus acknowledging to the receiving party it has correctly calculated the sequence.5. The communication begins, and both the receiving and the sending party change their frequencies along the calculated order, starting at the same point in time.Technical considerationsThe overall bandwidth required for frequency hopping is much wider than that required to transmit the same information using only one carrier frequency. However, because transmission occurs on