基于m序列的扩频通信系统的仿真设计外文翻译(共12页).doc

精选优质文档-倾情为你奉上扩频技术摘 要扩频技术是（例如一个电气、电磁，或声）生成的特定中特意传播，从而导致更大的的方法。这些技术用于各种原因包括增加抗自然和，以防止检测，并限制（如在）的安全通信设立的。频率跳变的历史：跳频的概念最早是归档在1903年美国专利和美国专利由尼古拉特斯拉在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。一名的工程师()，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，1932）。在中，美国陆军通信兵发明一种称为的通信系统，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。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88个频率发生变化，其旨在使无线电导向，让敌人很难来检测或干扰。该专利来自五零年代和其他私人公司开始时发展(CDMA)，一个民间形式扩频，尽管拉马尔专利有没对后续技术有直接影响。它其实是在、乐华政府和电子工业公司、国际电话电报公司及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（）信号传输一个远远多于原始信息的内容的技术。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。扩频通常会使用的连续的信号传播结构，通常使用上的信息信号分散一个相对（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。(FHSS)，（DSSS）、(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创建以确定与控制信号通过分配带宽的传播模式。 (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。无线以太网标准在其无线接口使用或直接序列扩频。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： 1.2.· 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。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 (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。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 。主要技术：一、直接序列扩频在，直接序列扩频（DSSS）是一种技术。与其他技术一样传输的信号比被调制的信息信号的占用更多。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，因此远高于信号的。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，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 × 1 = 1，1 ×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。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（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，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 · 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· 美国和欧洲卫星导航系统· 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· 2.4 GHz和其前身。(继任技术)·· 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)通过很多快速切换频率，其中一个发射无线电信号的一种方法是，使用一个和已知的序列。它被利用作为中跳频(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。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使用更大。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。和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。Spread Spectrum Techniques Abstract:Spread-spectrum techniques are methods by which a (e.g. an electrical, electromagnetic, or acoustic ) generated in a particular is deliberately spread in the , resulting in a with a wider . These techniques are used for a variety of reasons, including the establishment of secure communications, increasing resistance to natural and , to prevent detection, and to limit (e.g. in ).History Frequency hopping:The concept of was first alluded to in the 1903 U.S. Patent 723,188 and filed by in July 1900. Tesla came up with the idea after demonstrating the world's 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 Zenneck's book Wireless Telegraphy (German, 1908, English translation McGraw Hill, 1915), although Zenneck himself states that had already tried it several years earlier. Zenneck's book was a leading text of the time, and it is likely that many later engineers were aware of it. A engineer, , came up with the idea in 1929.Several other patents were taken out in the 1930s, including one by Willem Broertjes (Germany 1929, , 1932). During , the US Army Signal Corps was inventing a communication system called for communication between Roosevelt and Churchill, which incorporated spread spectrum, but due to its top secret nature, SIGSALY's existence did not become known until the 1980s.The most celebrated invention of frequency hopping was that of actress and composer , who in 1942 received for their "Secret Communications System". Lamarr had learned about the problem at defense meetings she had attended with her former husband , who was an Austrian arms manufacturer. The Antheil-Lamarr version of frequency hopping used a to change among 88 frequencies, and was intended to make radio-guided harder for enemies to detect or to jam. The patent came to light during patent searches in the 1950s when and other private firms began to develop (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 , Government & Industrial Electronics Corporation, ITT and 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 () signal is transmitted on a considerably larger than the 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 -like signal structure to spread the normally information signal over a relatively (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 (). (FHSS), (DSSS), (THSS), (CSS), and combinations of these techniques are forms of spread spectrum. Each of these techniques employs pseudorandom number sequences created using to determine and control the spreading pattern of the signal across the alloted bandwidth. (UWB) is another modulation technique that accomplishes the same purpose, based on transmitting short duration pulses. Wireless Ethernet standard 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. 2.· 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, when it 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 . 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 adversary's making sense of it. What's more, for a given noise (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 since the 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 . The high bandwidth occupied by spread-spectrum signals offer some frequency diversity, i.e. it is unlikely that the signal would encounter severe fading over its whole bandwidth, and in other cases the signal can be detected using e.g. a .· Multiple access capability. Multiple users can transmit simultaneously on the same frequency (range) as long as they use different spreading codes. See .Main techniques:1、Direct-sequence spread spectrumIn , direct-sequence spread spectrum (DSSS) is a technique. As with other technologies, the transmitted signal takes up more 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 device's transmitting frequency.Features1.It a with a continuous of (PN) symbols called "chips", each of which has a much shorter duration than an information . That is, each information bit is modulated by a sequence of much faster chips. Therefore, the is much higher than the signal .2. It uses a 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 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 , 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 1 × 1 = 1, and 1 × 1 = 1). This process, known as "de-spreading", mathematically constitutes a 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 transmitter's 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 receiver's position if the transmitters' positions are known. This is the basis for many .The resulting effect of enhancing on the channel is called . 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 (CDMA) property of DSSS, which allows multiple transmitters to share the same channel within the limits of the 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 transmission, except that the added noise causes the distribution to be much wider than that of an AM transmission.In contrast, 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-