通信 外文翻译 外文文献 英文文献 扩频通信系统的介绍

Wireless Communications＊byJoshua S。

Gans，Stephen P。

King and Julian Wright1. IntroductionIn 1895, Guglielmo Marconi opened the way for modern wireless communications by transmitting the three—dot Morse code for the letter ‘S’ over a distance of th ree kilometers using electromagnetic waves。

From this beginning，wireless communications has developed into a key element of modern society. From satellite transmission, radio and television broadcasting to the now ubiquitous mobile telephone，wireless communications has revolutionized the way societies function.This chapter surveys the economics literature on wireless communications。

Wireless communications and the economic goods and services that utilise it have some special characteristics that have motivated specialised studies。

First, wireless communications relies on a scarce resource –namely，radio spectrum –the property rights for which were traditionally vested with the state. In order to foster the development of wireless communications (including telephony and broadcasting）those assets were privatised。

目录一．扩频通信系统工作原理 (1)二．扩频通信的分类及优缺点 (3)1、直扩系统（DS） (3)2、跳频系统 (6)3、跳时系统 (9)三．扩频通信在移动通信中的应用 (10)四．扩频系统在其他领域中的应用 (11)五．参考文献 (13)一．扩频通信系统工作原理长期以来，人们总是想法使信号所占领谱尽量的窄，以充分利用十分宝贵的频谱资源。

为什么要用这样宽频带的信号来传送信息呢？简单的回答就是主要为了通信的安全可靠。

扩频通信的基本特点，是传输信号所占用的频带宽度（W）远大于原始信息本身实际所需的最小（有效）带宽（DF），其比值称为处理增益Gp:Gp = W/DF (1)众所周知，任何信息的有效传输都需要一定的频率宽度，如话音为1.7 --- 3.1kHz，电视图像则宽到数兆赫。

为了充分利用有限的频率资源，增加通路数目，人们广泛选择不同调制方式，采用宽频信道（同轴电缆、微波和光纤等），和压缩频带等措施，同时力求使传输的媒介中传输的信号占用尽量窄的带宽。

因现今使用的电话、广播系统中，无论是采用调幅、调频或脉冲编码调制制式，Gp值一般都在十多倍范围内，统称为“窄带通信”。

而扩频通信的Gp值，高达数百、上千，称为“宽带通信”。

扩频通信的可行性，是从信息论和抗干扰理论的基本公式中引伸而来的。

信息论中关于信息容量的仙农（Shannon）公式为：C ＝WLog2（1十P/N） (2)式中：C --- 信道容量（用传输速率度量）W --- 信号频带宽度P --- 信号功率N --- 白噪声功率式（2）说明，在给定的传输速率C不变的条件下，频带宽度W和信噪比P／N是可以互换的。

即可通过增加频带宽度的方法，在较低的信噪比P／N（S／N）情况下，传输信息。

扩展频谱换取信噪比要求的降低，正是扩频通信的重要特点，并由此为扩频通信的应用奠定了基础。

扩频通信可行性的另一理论基础，为柯捷尔尼可夫关于信息传输差错概率的公式：Powj = f（E/N。

国外通信类经典书籍1、《Linear Systems and Signals》——thi这本书个人觉得很不错，是一本线性系统和信号的入门好书。

可以适用于通信、电路、控制等专业。

虽说是入门的好书，但是本书的编排是内容由浅入深，讲述可是深入浅出。

我通读全书后，觉得深有体会，看这本书就像在看小说一般，对于一个话题的介绍，往往从其历史发展说起，让你知道其来龙去脉。

不像国内的书，一上来就是定理、定律。

同时，书中每讲完一个知识点，都会有适当的例题让你加深理解。

本书给我的一种感觉就是，作者将一种菜吃透了，消化了，而且掌握了作者这种菜的方法，然后把这种做法告诉你，然你自己去做菜，做出来的菜可能不一样，但是方法你是掌握了。

最根本的你掌握了，做什么菜是你自己的发挥了。

不像国内的教科书，就要你做出一样的菜才是学会了做菜。

这本书讲述了线性系统的一般原理，信号的分析处理，例Fourier变换、Laplace变换、z变换、Hilbert变换等等。

从连续信号说到离散信号，总之是一气呵成，中间似乎看不出什么突变。

对于初学者，这是一本很好的入门书，对于深入者，这又是一本极好的参考书。

极力推荐。

实话说，Lathi的书每看一回都会有新的感觉，常看常新。

2、《Fundamentals of Statistical Signal Processing,Volume I: Estimation Theory》——Steven M. Kay3、《Fundamentals of Statistical Signal Processing,Volume II: Detection Theory》——Steven M. Kay这两本书是Kay的成名作。

我只读过第一卷，因为图书馆只有第一卷:p这两本书比Van Trees的书成书要晚，所以内容比较新。

作者的作风很严谨，书中的推导极其严密。

不失为一位严谨的学者的作风！虽说推导严密，但是本书也不只是单纯讲数学的，与工程应用也很贴近。

扩频系统的工作方式
扩频通信系统包括以下几种工作方式：直接序列扩展
频谱（简称直扩DS）、跳变频率扩频（FH）、跳变 时间扩频（TH）、宽带线性调频（Chirp ）。在这4 种工作方式中，最常用的是直扩方式和跳频方式。在 实际应用上，经常把上述扩频方式进行简单的组合， 形成混合式扩频的工作方式，如FH/DS、TH/DS、 FH/TH等，在通信中应用较多的主要是DS、FH和 FH/DS。
通常，通信系统带宽W与基带信号带宽B的比值W/B为1~2


时，称为窄带通信系统；W/B为50以上时，称为宽带通信 系统；而W/B为100以上时，称为扩频通信系统。 扩展频谱技术是一种宽带通信系统，其理论基础是香农信 道容量公式。对于加性白高斯噪声的连续信道，其信道容 量C与信道传输带宽W及信噪比S/N之间的关系可以用以下 方式表示 （10-1-1） 式中，C为信道容量； W为信道宽度； S/N为信噪比。
扩频系统主要特点
扩展信号的频谱，发送端用扩频码序列进行扩频调制，以



及在接收端用相关解调技术，使其具有许多窄带通信难以 替代的优良性能，能在民用后，迅速推广到各种公用和专 用通信网络之中，主要有以下几项特点： （1）易于重复使用频率，提高了无线频谱利用率 （2）抗干扰Байду номын сангаас强，误码率低 （3）安全保密，干扰性小 （4）易于实现多址通信 （5）适合数字话音和数据传输，以及开展多种通信业务 （6）安装简便，易于维护
扩频系统的主要性能指标


2．干扰容限 干扰容限是指在保证扩频通信系统正常工作（保证输出信噪比 不低于某一给定值）的条件下，接收 机输入端能够允许的干扰信号功率高于有用信号功率的分贝数，即为 （10-1-5） 式中， 表示干扰容限； 表示处理增益； 表示系统损耗； 表示接收机输出信噪比。 干扰容限直接反映了扩频通信系统接收机所能承受的极限干扰强度，它准确地表征了系统的抗干扰 能力，反映了扩频通信系统在干扰环境中正常工作的极限能力。例如，若假定某扩频通信系统的处 理增益为 =33dB，系统损耗为 =3 dB，为确保系统误码率小于所给定的要求值时，接收机输出信噪比 必须保证 ，则该系统的干扰容限 （100倍），即只要加到接收机输入端的干扰信号功率不超过有用 信号功率20dB，该系统就能正常工作了。 2．干扰容限 干扰容限是指在保证扩频通信系统正常工作（保证输出信噪比 不低于某一给定值）的条件下，接收 机输入端能够允许的干扰信号功率高于有用信号功率的分贝数，即为 （10-1-5） 式中， 表示干扰容限； 表示处理增益； 表示系统损耗； 表示接收机输出信噪比。 干扰容限直接反映了扩频通信系统接收机所能承受的极限干扰强度，它准确地表征了系统的抗干扰 能力，反映了扩频通信系统在干扰环境中正常工作的极限能力。例如，若假定某扩频通信系统的处 理增益为 =33dB，系统损耗为 =3 dB，为确保系统误码率小于所给定的要求值时，接收机输出信噪比 必须保证 ，则该系统的干扰容限 （100倍），即只要加到接收机输入端的干扰信号功率不超过有用 信号功率20dB，该系统就能正常工作了。

扩频通信原理扩频通信是一种利用扩频技术进行通信的方式，它通过将信号在较大的频带上进行传输，从而提高了通信系统的容量和抗干扰能力。

在扩频通信中，信号被调制成具有较大带宽的信号，然后再通过扩频码进行调制，最终在信道上传输。

扩频通信技术在军事通信、卫星通信、移动通信等领域有着广泛的应用。

扩频通信的原理主要包括信号调制、扩频码调制、信道传输和解调等几个方面。

首先，信号调制是将要传输的信息信号调制成具有较大带宽的信号，一般采用正交频分复用（OFDM）技术或者直接序列扩频（DSSS）技术。

接着，扩频码调制是将调制后的信号再通过扩频码进行调制，这个扩频码是一种伪随机序列，可以将信号的频谱扩展到较大的频带上。

然后，调制后的信号通过信道进行传输，这个信道可能会受到多径效应、多普勒频移等影响，因此需要采用合适的信道编解码技术来提高通信质量。

最后，接收端需要对传输过来的信号进行解调和解扩频，最终还原出原始的信息信号。

扩频通信的优点在于它具有较强的抗干扰能力和隐蔽性，因为扩频信号在频域上具有较大的带宽，使得它对窄带干扰信号具有很好的抑制作用。

此外，扩频码是一种伪随机序列，使得只有知道正确的扩频码才能够解扩频，因此具有较强的隐蔽性。

另外，扩频通信还可以实现多用户的同时通信，因为不同用户可以使用不同的扩频码来进行通信，从而提高了通信系统的容量。

然而，扩频通信也存在一些缺点，首先是它需要较大的带宽资源，这在一些频谱资源紧张的情况下会显得不太合适。

其次，扩频通信的系统复杂度较高，需要采用较复杂的调制解调器和编解码器，从而增加了系统的成本。

此外，由于扩频信号的带宽较大，使得其在功率和能耗上也会有所增加。

总的来说，扩频通信作为一种重要的通信技术，在现代通信系统中有着广泛的应用。

它通过利用扩频技术，提高了通信系统的容量和抗干扰能力，具有很好的隐蔽性和多用户接入能力。

随着通信技术的不断发展，相信扩频通信在未来会有更广阔的应用前景。

什么是扩频通信技术_扩频通信技术的优缺点什么是扩频通信技术？扩展频谱通信（Spread Spectrum CommunicaTIon）简称扩频通信，其特点是传输信息所用的带宽远大于信息本身带宽。

扩频通信技术在发端以扩频编码进行扩频调制，在收端以相关解调技术收信息，这一过程使其具有诸多优良特性。

扩频通信技术是一种信息传输方式，其信号所占有的频带宽度远大于所传信息必需的最小带宽；频带的扩展是通过一个独立的码序列来完成，用编码及调制的方法来实现的，与所传信息数据无关；在接收端则用同样的码进行相关同步接收、解扩及恢复所传信息数据。

扩频通信技术在发送端以扩频编码进行扩频调制，在收端以相关解调技术收信。

由于扩频通信要用扩频编码进行扩频调制发送，而信号接收需要用相同的扩频编码之间的相关解扩才能得到，这就给频率复用和多址通信提供了基础。

充分利用不同码型的扩频编码之间的相关特性，分配给不同用户不同的扩频编码，可以区别不同的用户的信号，并且不受其他用户的干扰，实现频率复用。

扩频通信技术是一种信息处理传输技术。

扩频通信技术是利用同域传输数据（信息）无关的码对被传输信号扩展频谱，将信号调制到多个载波频率的技术。

使之占有远远超过被传送信息所必需的最小带宽。

扩频通信技术可以提供更安全的传输，并可降低干扰，提高频带的利用率。

利用扩频技术对时钟频率加入抖动处理，使发射频率不再集中在一个频点，还可以降低电磁干扰。

常用的扩频技术主要有三种方法，即直序扩频、跳频扩频、跳时扩频以及线性调制。

但是在实际使用的过程中，常采用它们的混合。

扩频通信技术特点扩频通信系统有以下两个特点：（1）传输信号的带宽远远大于被传输的原始信息信号的带宽；（2）传输信号的带宽主要由扩频函数决定，此扩频函数通常是伪随机（伪噪声）编码信号。

以上两个特点有时也称为判断扩频通信系统的准则。

扩频通信介绍
 扩展频谱通信，简称扩频通信，是一种信息传输方式，其信号所占有的频带宽度远大于所传信息必需的最小带宽；频带的扩展是通过一个独立的码序列（一般是伪随机码）来完成，用编码及调制的方法来实现的，与所传信息数据无关；在接收端则用同样的码进行相关同步接收、解扩及恢复所传信息数据。

 扩频通信系统，扩频处理的带宽
 扩频通信抗干扰的原理
 扩频通信，是扩展频谱通信的简称。

它是指用来传输信息的射频带宽远大于信息本身带宽的一种通信方式。

 扩频技术的基本理论根据是信息论中的香农（Shannon）公式，它可以表示为：
 C＝Wlog21＋S／N　（1）。

The Summary of the VHDLThe VHDL English full name is the Hardware Description Language of the Integrated Circuit of the Very-High-Speed, birth in 1982. At the end of 1987, the VHDL is con firmed by the IEEE and American Ministry of National Defense to describe Ianguage for the sta ndard hardware. Announ ced VHDL sta ndard edition from the IEEE, IEEE-1076(call 87 versi ons) after, the each EDA compa ny released own VHDL desig n en vir onment one after another, or declared that the own design tool can connect with VHDL. Henceforth, the VHDL desig n realm to get to exte nsively accept in the electr oni cs, and gradually replaced an origi nally not- sta ndard hardware descripti on Ian guage. In 1993, the IEEE carried on to revise to the VHDL, describe ability to expa nd a VHDL contents from higher abstract layer and the system, ann ou need the VHDL of new editio n, n amely IEEE sta ndard of 1076-1993 editi on s, .(call 93 versi on s)Now, VHDL and Verilog are the in dustrial sta ndard hardware description of the IEEEs Ianguage, and get support of numerous EDA companies, at electr onics engin eeri ng realm, have become in gen eral use hardware to describe Ian guage. In fact, i n the new cen tury, the VHDL will start to un dertake a greatly part of nu merical system design mission at the Verilog Ianguage. The VHDL Ianguage is a kind of deluxe Ian guage which used for an electric circuit desig n. It expects to appear after the 80's of.BE.At the beginning come out by American Ministry of National Defense development to provide the America n solider with the credibility which uses to raise a desig n with cut one kind of developme nt period to use the scope smaller desig n Ian guage.All of VHDL English write BE: The Description Language of the VHSIC (the Speed In tegrated of the Very High Circuit) Hardware. Tran slati ng into Chin ese is soon extremely high the descriptio n Ian guage of the in tegrated circuit hardware. So it is of the applicati on mai nly is an applicatio n in the desig n of nu merical electric circuit. Curre ntly, it is in the applicati on most in Chi na is the desig n which uses in the FPGA/CPLD/EPLD. Certa in ly in some un its with stron ger real function s, it is also use to desig n ASIC.The VHDL mainly used for the structure, behavior which describes num cal system, fun cti on with connection. In additi on to impl ying many Ian guages sentence which have a hardware character, VHDL Ianguages forms and description style and sentence con struct ion are very similar at gen eral calculator deluxe Ian guage. VHDL procedurestructure characteristics is an engineering design, or all that the design entity(can be a component, an electric circuit mold piece or a system) is divided into exterior(or call but part, and port) with inner part(or call to can't see part), since invo Ive internal function and calculate way of en tity to complete part. At one desig ned en tity to defi ne exterior in terface after, once it internaldevelopme nt completi on after, other desig ns can directly adjust touse this en tity. This ki nd of desig n will en tity to be divided in to a little bit basic VHDL system that is a VHDL system in side the con cept of outside part desig n of a little bit basic and other hardware describe the Ianguage compare and the VHDL has a following characters: The function is strong and the design be vivid. The VHDL has the function strong Ianguage structure, can describe a complicated logic control with the simple and direct and explicit source code. It has a multi-layer desig n descripti on fun cti on, in multiple layers thi n turn, fin ally directly born electric circuit class descripti on. The VHDL supports synchronous electric circuit, differenee's tread electric circuit with random the design of electric circuit, this be the other hardware descripti on although the Ian guage can't compare to. The VHDL still supports various desig n method, since support from the bottom upward desig n, support aga in from the desig n of crest declivity; since the support mold piece tur ns a design, support layer's turn a design again. Support extensively and be easy to a modificatio n. Because the VHDL has already become IEEE sta ndard the norm of hardware description Ianguage, most EDA tools almost support VHDL currently, this is VHDL of further expansion with extensively applied lay foundation. In the design process of the hardware electric circuit, the mai n desig n docume nt is the source code which writes with the VHDL, the VHDL easily reads with the structure turn, so be easy to a modification desig n.The strong system hardware describes ability. The VHDL has a multi-layer design description function, since can describe system class electric circuit, can describe door class electric circuit again. And description can adopt a behavior description, deposit a machine to deliver description or structure description, can also adopt the hybrid descripti on of threes mixture. Moreover, VHDL support is in ertial to delay and deliver to delay, can also accurately build up hardware electric circuit model. VHDL support prepare defi nite of with from defi niti on of data type, bring hardware descripti on a bigger freedom degree, make desig n the pers onnel can expedie ntly establish the system model of high time.The in depe ndence is at the desig n of spare part, have nothing to do with the craft. Don'tneed to consider a choice completion the spare part of design first while designing a pers onnel to carry on a desig n with the VHDL, can concen trate en ergy to carry on desig n of excelle nt tur n.When the desig n descripti on complete after, can carry out its fun cti on with various different spare part structure very strong transplantation ability. The VHDL is a kind of hardware descripti on for sta ndardize Ian guage, the same of desig n descripti on can be support by the differe nt tool and make to desig n to describe of the tran spla ntati on make possible.Be easy to share and reply to use. The VHDL adopti on can build up various mold piece that can again make use of according to the design method of database (Library). These canned in advanee design or use to design a medium backup mold a piece before and depositted these to the database in, can be in lately of the desig n carry on replyi ng to use, can make the design result be design the personnel's to carry on exchanges and share, decrease hardware electric circuit desig n.("Compared with other hardware description Ianguages, the VHDL have stronger behavior descriptio n on ability, come to a decisi on him to become a system desig n realm the best hardware a descriptio n Ian guage thus. The strong behavior descripti on ability is to avert from con crete spare part structure and describe and desig n importa nt assura nee of large-scale electr onics system from the logic behavior.(2) The VHDL be abundant of imitate true Ian guage sentence and database fun cti on, make in any big system of the desig n can in spect a function possibility of desig n the system in early days, can carry on imitati ng true emulati on to the desig n at any time.(3) The ability and procedure structure of the behavior descripti on with lexical VHDL come to a decisi on the decompositi on that he has to support a large-scale desig n with have already have desig n of aga in make use of fun cti on. Meet the market dema nding large-scale system efficie ntly, the completi on of the high speed has to in clude many people the several gen erati on hair set eve n together and abreast works and the n can carry out.(4) For use the desig n of an assura nee of VHDL completi on, can make use of EDA toolto carry on logic comprehensive with excellent turn, and auto of the VHDL describe the desig n cha nge into the door class net form.(5)The descripti on of VHDL to desig n have opposite and in depe ndent, the desig n can not un dersta nd the structure of hardware and n eed not man age the target spare part that the end desig n carry out, either is what, but carry on an in depe ndent desig n.VHDL 的介绍VHDL 的英文全名是Very-High-Speed In tegrated Circuit Hardware Description Language,诞生于1982年。

它表明一个扩频系统经过扩频处理得到的好处，其定义为 系统接收端的接收相关处理器输出信噪比与输入信噪比二者之 比，即： 对于直扩系统，解扩器的输出信号功率不变，即干扰功率 在解扩后减小了很多。由于信号解扩前后的带宽的变化直接影 响到干扰功率的大小，因此，对于直扩系统，可以推导得到计 算处理增益的又一方法如下 : （ W:扩频信号带宽; B:信息带 宽 )： W
跳频扩频系统的分类
慢跳频：指跳频速率低于信息比特速率，即连续几个信息 比特跳频一次； 快跳频：指跳频速率高于信息比特速率，即每个信息比特 跳频一次以上；
2.5 跳时扩频通信系统
该系统可看作是使用一定码序列进行选择的多时片的时 移键控系统，该系统使发射信号在分片的时间轴上跳变，即 用扩频码序列去控制发射信号在不同时段所使用的不同时片。 由于采用了窄得很多的时片去发送信号，相对来说，信号的 频谱也就展宽了。
式中，C为信道容量，指单位时间内信道中无差错传输 的最大信息量，其单位为b/s；W为信号频带宽度，单位为 Hz；S为信号功率，单位为W；N为噪声功率，单位为W； S/N为输入功率与噪声功率之比，称为信噪功率比，简称信 噪比。
2.潜在抗干扰理论 潜在抗干扰理论 潜在抗干扰理论 柯捷尔尼可夫在其潜在抗干扰性理论中得到如下关于信 息传输差错概率的公式：
码分多址直接序列扩频通信系统
码分多址主要与直接序列扩频技术相结合，构成码分多 址直接序列扩频通信系统，该系统主要有下列两种方式：
2.4 跳频扩频系统
指用一定码序列进行按一 定规律随机地跳变。
跳频信号频谱示意图
跳频信号的 频谱是一个 在很宽频带 上随机跳变 的不等间隔 的频率信道。
扩频通信系统的种类 直接序列（DS）系统 跳频（FH）系统 脉冲线性调频（Chirp）系统 跳时（TH）系统

1.1 扩频通信旳基本概念
特点（判断扩频通信系统旳准则）
（1）传播信号旳带宽远远不小于被传播旳原始信息 信号旳带宽；
（2）传播信号旳带宽主要由扩频函数决定，此扩频 函数一般是伪随机（伪噪声）编码信号。
取得旳好处 具有很强旳抗人为干扰、抗窄带干扰、抗多径干 扰旳能力。
9
1.1 扩频通信旳基本概念
扩频系统具有抗干扰能力旳理论基础
自有关函数：
S( f ) N0 2
f
R(τ ) S( f )e j2πfτdf N0 δ(τ )
2
对白噪声信号处理困难。使用伪噪声码序列替代白噪声，它们
旳统计特征相近。伪噪声序列是接近于高斯信道要求旳最佳信
号形式。
R(τ)
1 N
N
ci ci
i 1
1
1 N
τ 0 τ 0
N
1
R(τ
可供随机选用旳载波频率数一般是几千~几万个离散频率， 在如此多旳离散频率中，每次输出哪一种由伪随机码决定。
24
1.2.2 频率跳变系统
25
频率跳变系统
工作原理 频率跳变系统中
发信机旳发射载波频率，在一种预定旳频率集内由伪随机码 序列控制频率合成器(伪)随机旳由一种跳到另一种。
收信机中旳频率合成器也按摄影同旳顺序跳变，产生一种和 接受信号频率相差 fIF(中频频率)旳参照本振信号，经混频后 得到频率固定旳中频信号，此过程称为对跳频信号旳解跳。 解跳后旳中频信号经放大后送到解调器解调，恢复出传播旳 信息。
➢也就是说对于任意给定旳信息传播速率C，当信号噪声功率
比S/N下降时，能够用增大系统旳传播带宽B来取得较低旳信
息差错率。
11
1.1 扩频通信旳基本概念

Optical Fiber Communication TechnologyOptical fiber communication is the use of optical fiber transmission signals, the transmission of information in order to achieve a means of communication. 光导纤维通信简称光纤通信。

Referred to as optical fiber communication optical fiber communications. 可以把光纤通信看成是以光导纤维为传输媒介的“有线”光通信。

Can be based on optical fiber communication optical fiber as transmission medium for the "wired" optical communication. 光纤由内芯和包层组成,内芯一般为几十微米或几微米,比一根头发丝还细;外面层称为包层,包层的作用就是保护光纤。

Fiber from the core and cladding of the inner core is generally a few microns or tens of microns, than a human hair; outside layer called the cladding, the role of cladding is to protect the fiber. 实际上光纤通信系统使用的不是单根的光纤,而是许多光纤聚集在一起的组成的光缆。

In fact the use of optical fiber communication system is not a single fiber, but that brings together a number of fiber-optic cable componentsOptical fiber communication is the use of light for the carrier with fiber optics as a transmission medium to spread information from one another means of communication. 1966年英籍华人高锟博士发表了一篇划时代性的论文,他提出利用带有包层材料的石英玻璃光学纤维,能作为通信媒质。

A protocol used to establish a direct connection between two points, often used for dial-up internet access.
Network Security
• Firewalls: Devices that filter incoming and outgoing traffic based on security policies to protect against unauthorized access or malicious attacks.
Modulation and Demodulation
Modulation
The process of varying a property of a carrier wave, such as its amplitude, frequency, or phase, in accordance with the information to be transmitted. This allows information to be carried over long distances through various media.
Channel Capacity and Data Rate
Channel Capacity
The maximum amount of information that can be transmitted over a communication channel without loss of data or degradation in signal quality. It is typically limited by the physical properties of the channel and the noise level present.

Uint1抽样量化和编码：sampling quantizing and coding话路：speech channel幅值：amplitude value抽样频率：sampling frequency抽样速率：sampling speed rate脉冲流：stream of pulses重复率： repetition rate编码过程：coding processs模拟信号：analog signal传输质量transmission quality数字通信digital communication数字传输digital transmission含噪声的环境noisy environment传输路由transmission path信号比signal-to-noise ratio信号电平signal levels地面系统terrestrial system噪声功率noise power二进制传输binary transmission反向操作reverse operation8位码序列8-digit sequence接收端receiving terminal帧格式frame format同步字synchronization wordthe schemes for performing these three function 实现这三项功能的方案a series of amplitude values 一串幅值a speech channel of telephone quality 电话质量的话路a sequence of 8-binary digits 一个8位二进制码的序列a minimum theoretical sampling frequency 理论上的最小抽样频率a voice channel occupying the range 300Hz to 3.4KHz 占据着300Hz到3.4KHz 频率范围的话路8-digits per sample value 每个样值8位码the sparking of a car ignition system 汽车点火系统的大火the stream of the pulsese with a repetition rate of 64KHz 重复率为64KHz的脉冲the relationship of the true signal to the noise signal 真实信号与噪声信号的关系the signal received from a satellite 由卫星上收到的信号the complete information about a particular message 一条特定消息的全部信息the shape of the transmitted signal 被传信号的波形the attenuation introduced by transmission path 由传输路由引入的衰减the unit that converts sampled amplitude value to a set of pulses 将抽样的幅值转换成一串脉冲的单元a sequence relating to channel 1，2 and son on涉及到第一路、第二路及其他各路的序列a unique sequence of pulses called synchronizationword 被称为同步字的独特的码序列terrestrial system 地面系统the presence or absence of the pulse 脉冲的“有”或“无”a high-speed electronic switch 高速的电子开关the time division multiplexer 时分多路复用器Time Division Multiplexing 时分多路复用Unit2串行接口 serial interface显示终端 CRT terminal发送器与接收器 transmitter and receiver数据传输 data transmission数据流 data stream闲置状态the idle state传号电平 mark level空号电平 space level起始位start bit停止位stop bitT秒的持续时间duration of T seconds奇偶校验位parity bit错误标志error flag传输错误transmission error下降沿falling edge符号间的空格 intersymbol space接收机的定时 receiver timing本地时钟local clock磁带 magnetic tape控制比特 control bit逻辑1电平logical 1 level二进制数据binary data明显的缺点obvious disadvantageasynchronous serial data transmission 异步串行数据传输The most popular serial interface 最为流行的串行接口The transmitted data 所传送的数据The clocks at the transmitter and receiver发送器和接收器的时钟The era of teleprinter电传机的时代The dots and dashes of a character一个字符的点和划Three times the duration of intersymbol space符号间空格持续时间的三倍The group of bits called characters 被称为字符的比特组The invariable units comprising 7 or 8 bits ofinformation由7或8个比特的信息组成的固定单元A clock generated locally by the receiver 由接收机本地产生的时钟The received parity bit following the character 在字符后所收到的奇偶校验位The falling edge of the start bit 起始位的下降沿The character-oriented nature of the data link 数据链路面向字符的特性Uint3联网技术 networking technology国际标准化组织 international Organization forStandardization (ISO)参考模型 reference model数据分组 packet data应用程序 application program网络媒体 network media分层 called layering硬件和软件 hardware and software表示层 the presentation layer传输层 the transport layer数据链路层 the data link layer网络服务 network services文件接入 file access数据格式 data format主机 host协议 protocol连接 connectivity逻辑地址 logical addressingNetworking technology 联网技术Proprietary networking system 专用联网系统The international Organization for Standardization国际标准规划组织Compatibility between the various type of networks各种网络之间的兼容性Seven numbered layers 七层协议Standardization of network components 网络部件的标准化Error recovery 纠错Receiving host’s system 发方主机系统Connection-oriented circuits 面向连接的电路Information flow control 信息流控制Network media access 网络媒体接入Electrical specification 电气特性Maximum transmission distance 最大传输距离Uint 4传输控制协议transmission control protocol互联协议Internet protocol数据通信data communication微波microwave高层协议higher-level protocol流量控制traffic control目的地destination（信）源resource段segment互联层Internet layer分组交换packet switching超文本传输协议hypertext transfer protocol灵活性flexibility数据报datagramtransmission control protocol传输控制协议Internet protocol互联协议satellite links卫星链路the Standard On which the internet has grown互联网发展所基于的标准Network access layer网络接人层connection－oriented protocol面向连接的协议file transfer protocol文件传输协议hypertext transfer protocol超文本传输协议domain name system域名系统developer of software软件开发人user datagram protocol用户数据报协议packet -switched technology分组交换技术Unit 5局域网local area network工作站workstation外设peripheral拓扑topology集线器hub交换器switch流量traffic网络接口卡network interface card数据库database印刷电路板printed circuit board主板motherboard网络适配器network adaptor并行数据parallel data电脉冲electrical impulses中继器repeater联网介质networking medialocal-area network局域网logical topology逻辑拓扑devices that connect directly to a network segment 直接连到网络段的部件network interface card网络接口卡process of the encapsulation打包的过程standardized symbol标准化的符号printed circuit board印刷电路板expansion slot of a bus on a computer’s motherboard 在计算机母板上总线的扩展槽network adapter网络适配器parallel signal produced by the computer由计算机产生的并行信号transmltting station发送站the specifications for Category 5 twisted-pair Ethernet五类双绞线以太网的规范Unit 6无源集线器passive hub网桥 bridge可用带宽 useable handwidth地址表addressing table交换器 switch路由器 router光纤optical fiber无线介质wireless media铜线copper wirethe device that serves as the center of network作为网络中心的部件multi-port repeater多端口中继器reliability of the network网络的可靠性passive or active hubs无源或有源的集线器protocol address or network address地址或网络地址network administrator网络管理者switching of packets to the best route交换分组到最佳路由network segment网络段Unit 7网络资源network resource信息服务information services远程终端remote terminals地址address互连的系统 interconnected systems命令 command电子邮件electronic mail主机Host无线信道wireless channels搜索工具popup用户界面user interface拷贝copy'互连网popup存取access文本信息textual messages鼠标mouse协议protocol超文本协议hypertext protocolgiant network of computers located all over theworld分布在全世界的计算机的巨大网络backbone system主干系统nationwide network全国范围的网络electronic conferences电子会议remote terminal远程终端live conversation实时的对话world wide web万维网searching tool搜寻工具the largest repository of information 最大的信息库network facilities resources网络设备资源the vast majority of the computers on the net在网上的绝大多数计算机the Unix operating system UNIX操作系统textual message文本信息sa way to move data between the internet and your PC在因特网和你的PC机之间传送数据的方法the convenient searching tools方便的搜索工具the networked hypertext protocol 联网的超文本协议Unit 8optical fiber communications 光纤通信light source 光源wavelength 波长laser 激光器dispersion 色散transmission medium传输介质multi-mode fiber 多模光纤long-haul trunks 长途干线single-mode fiber 单模光纤bandwidth 带宽wideband subscriber 宽带用户fiber-optics 纤维光学commercial technology 商用技术threshold current 门限电流photodetector 光检测器wavelength multiplexing 波分复用fiber-optic networks 纤维光网络video bandwidth 视频带宽长途传输 long distance transmission中继距离. repeater spacing商用技术 . commercial technology<光纤通信 . optical fibre communications已装光纤的总长度 . the total length of installedfibre长途通信系统 long-haul telecommunication system低衰减的石英纤维 the low-loss silica fibre衰减逼近瑞利极限的光纤fibers with lossesapproaching the Rayleigh limit室温下的门限电流 . room temperature thresholdcurrents较长波长区the longer wavelength region用户接入工程. subscriber access project部件性能和可靠性的改进improvements in componentperformance and reliability<已安装的光纤系统的数据速率data rates forinstalled fibre optic system每秒吉比特gigabit per second range波分复用. wavelength multiplexing宽带用户环路系统. wideband subscriber loop system多纤连接器. multifibre connectors设计寿命 . projected lifetime光源. light source单模光纤. single-mode fibre分布反馈式激光器 distributed-feedback laser信息容量 information capacity交换体系. switching hierarchy宽带业务 .broadband servicesUnit 9cellular mobile telephone 蜂窝式移动电话service perfor mance 服务性能frequency band 频带microprocessor 微处理器mobile unit 移动手机broadcast service广播业务antenna 天线subsystems 子系统mobile subscriber 移动用户service capability 服务能力untiliaztion 利用率bandwidth 带宽single-sideband 单边带spread spectrum 扩频large scale integrated circuits 大规模集成电路cellular site 蜂窝点cellular switch 蜂窝交换机radio cabinet 无线机架call processing 呼叫处理service area 服务区frequency spectrum untiliaztion 频谱利用率the limited assigned frequency band 有限的指定频带complicated features and functions 复杂的特性和功能large-scale integrated circuit technology 大规模集成电路技术developmental cellular system 实验性的蜂窝系统central coordinating element 中央协调单元cellular administration 蜂窝管理operational limitation of conventional mobile telephone system 传统移动电话的运行限制limited service capability 有限的服务能力radio communication industry 无线通行行业available radio frequency spectrum 可用的无线电频谱the allocated frequency band 所分配的频带mobile transceiver 移动收发器technological feasibility 技术上的可行性servere spectrum limitation 严厉的频谱限制FM broadcasting service 调频广播业务propagation path loss 传播路径衰耗multipath fading 多路径衰耗telephone company zone officee 电话公司地方局unit 10personal communications 个人通信communication standards 通信标准fixed telephone service 固定电话业务network capacity 网络容量mobile switching center 移动交换中心international roaming 国际漫游broadband services 宽带业务interface converseon 接口转换frequency allocation 频谱分配analogue mode 模拟方式cellular communication principle 蜂窝通信原理jamming 拥塞cell splitting 蜂窝裂变base station 基站register 寄存器billing function 收费功能access method 接入方法burst transmission mode 突发脉冲传输方式overhead information 开销信息handover algorithms 切换算法short message sevice 短消息服务technical specification 技术规范total acess communication system 全接入的通信系统global mobile communication system 全球移动通信系统time division multiple acess 时分多址facsimile and short message service 传真和短消息服务fixed communicateon networks 固定通信网络a more personalized system 更个人化的系统the cost and quality of the link 链路的价格与质量marker growth 市场的发展coaxial cable 同轴电缆frequency reuse and cll splitting 频率再生和蜂窝裂变cochannel interference 共信道干扰theroretical spectral capability 理论上的频谱容量micro-cellular system 微蜂窝系统base station transceiver 基站收发器subscriber register 用户寄存器advanced handover algorithms 先进的切换算法the GSM technicall specifications GSM的技术规范unit 11circuit switching 电路交换packet switching 分组交换message switching 报文交换subnet 子网header 信头destination address 目的地error control误差控制store-and-forward manner 存储转发方式bursty 突发性transmission delay 传输时延intermediate switching equipment 中间交换设备switching technique 交换技术return signal 返回信号message processor 报文处理机given maximum length 给定最大长度information transfer 信息转移random 随机性dedicated circuit 专用电路channel utilization 电路利用率the capability of storing and manipulating user’sdata 存储和处理用户的能力the special signaling message 特定的信令信息a well defined block of data called a message 被精心定义的称为报文的数据块the information regarding the source anddestination addersses 涉及源和目的地址的信息the computer referred to as a message processor 叫做报文处理器的计算机the store-and-forward transmission technique 存储转发传输技术the dynamic allocation of the bandwidth 带宽的动态分配the overall transmission delay of the message报文整个的传输时延switching technique 交换技术total path of connected lines 连线的整个通路source-destination pair 源到目的地的一对communication parties 通信各方transmission unit 传输单元initial connection cost incurred in setting up thecircuit 在建立电路时产生的起初连接成本low delay constraint requited by the user 用户所需的短时延的限制the fixed dedicated end-to-end circuit 固定专用的端到端电路low channel utilization 低的电路利用率unit 12asynchronous transfer mode 异步转移模式logical channel 逻辑信道virtual circuits 虚电路virtual paths 虚路径recommendation 建议network level 网络层service and application level 业务和应用层virtual connection 虚连接information superhighway 信息高速公路vedio-on-demand 点播电视statistical multiplexing 统计复用digital information 数字化的信息identifier 标识符protocols 协议network node 网络节点broadband network 宽带网ATM forum ATM论坛future-proofed 面向未来的image encoding 图像编码virtual private network 虚拟专用网data processing 数据处理short packets called cells 被叫做信元的短的分组bit rates of several hundred megabits a second 每秒几百兆比特的速率unique multiplexing method 独特的复用方法the physical connection between any to terminals 任何两个终端之间的物理连接interactive video services 交互式的视频业务a nature vehicle for multimedia services 多媒体业务的自然载体the crrent and future requirements of both operators and users 运营者和用户当前和未来的要求the technique for switching high bit rate channel 高比特率信道的交换技术multiplexing and switching technique 复用和交换技术the underlying type of transmission 所承载的传输类型dual identification 双重标识the transfer of cells to the network nodes 信元在网络节点上的转移hundreds megabits a second 每秒几百兆比特recommendation I.121 I.121建议the quality of service 业务质量in proportion to the exact requirement 与实际需求成比例the application and service transported over a network 网络所传送的应用和业务the ability to construct virtual network 构成虚网络的能力cost-effiective use of infrastructure 低价高效的利用网络设施coordinating different networks carrying different services 协调传送不同业务的不同网络essential components of future information superhighways 未来的信息高速公路的基本部件optimum use of resource 资源的最佳使用unit 13public telecommunication network 公众电信网local loop 本地环路switching node 交换节点twisted pair 双绞线external call 外部呼叫end office 端局digital data system 数字数据系统two wire connection 二线连接toll center 收费中心circuit-switched network 电路交换网telephone subscriber 电话用户data traffic 数据流量link 链路trunk 中继线half-duplex 半双工full-duplex 全双工voice-frequency circuit 音频电路trandem switch 汇接交换机topology 拓扑internode 节点间的route 路由full-duplex connection 全双工的连接the function of concentrating traffic 集中话务量的功能the switching nodes called tandem seitches 被称为汇接局的交换节点a fraction of subscriber 一小部分用户the interface between the station and the network在站和网络之间的接口the subscriber that transmit digital signal 发送数字信号的用户national networks 国家网络architectural components 结构部件the branches between nodes 节点间的支路tree topology 树状拓扑transmission facilities 传输设备multiple voice-frequency circuit 多条音频电路synchronous TDM 同步时分复用adjacent end offices 相邻的端局full connectivity 全连通性isolated subnetworks 被分离的子网high usage trunks 高效中继线basic order of selection 路由选择的基本次序backbone hierarchical network 主干体系网络two subscribers attached to different end offices连接到不同端局的两个用户exchange area 交换区Unit 14global communications 全球通信flexibility 灵活性end-to-end digital connectivity 端到端的数字连接open network 开放网络voice encoding 语音编码integrated services digital network综合业务数字网infrastructure 系统结构International Organization for Standardization 国际标准化组织communication carriers 通信载体transmission medium 传输媒体interface equipment 接口设备bandwidth limitation 带宽限制switching equipment 交换设备pulse code modulation 脉冲调制basic access 基本接入degradation due to the transmission medium 由于传输媒体导致的质量下降bandwidth limitations inherent in a 4 kHz voicechannel 4 kHz 路中所固有的带宽限制standardized ports 标准化的接口pulse code modulation 脉冲编码调制digital communication 数字通信ISDN standards and system architecture ISDN的标准和系统结构progressive application of digital technology 数字技术的逐步应用public communication carriers 公共通信载体enhanced quality 高质量substantial quantity of interface equipment 大量的接口设备flexibility in the transmission ofvoice ,data ,video and other services 在传送话音、数据、视频和其他业务上的灵活性voice encoding techniques 语音编码技术pulse coding modulation脉冲编码调制basic access signaling rate 基本接入信令速率universal access 统一的接入experimental technology 实验性的技术unit 15X.25 protocol X.25 协议television signals 电视信号narrowband services 窄带业务basic access 基本接入teleservice 电信业务telex 用户电报radio waves 无线电波ground antenna 地面天线coaxial 同轴的direct broadcast system 直接广播系统end-to-end delay 端到端的时延jitter 抖动peak hours 繁忙小时chip technology 芯片技术high definition television 高清晰度电视operations and maintenance 运行与维护the existing public network 现有的公用网络classical two-way voice conversation 传统的双向对话packet switched data network based on X.25 protocols基于X.25协议的分组交换数据网络the user access to the network 对网络用户接入a circuit switched service with a channel rate of70 Mbit/s 信道速率为70 Mbit/s的电路交换业务the service-independent network 与业务无关的网络the optimal statistical sharing of the resources对资源的最佳统计共享telecommunication service 电信业务telex network 用户电报网messages of characters 文字报two-way voice conversation 双向对话X.21 protocols X.21协议coaxial tree network 同轴数状网络community antenna TV network 公用天线的电视网络direct broadcast system 直接广播系统Ethernet 以太网token bus and token ring network 令牌总线网和令牌环网word-wide independent networks 全球范围的独立网络resource pooling 资源共享peak hour traffic 繁忙小时流量integration of narrow-band services窄带业务的综合the progress in speech coding and chip technology 在语声编码和芯片技术方面的进步a new teleservice 新的电信业务adapting to new service requirements对新业务要求的适配optimal statistical sharing of the resources 资源最佳统计式的共享。

扩频通信技术的应用电信09-1李媛媛16号扩频通信，即扩展频谱通信(Spread Spectrum Communication)的简称，它是指用来传输信息的射频信号带宽远远大于信息本身带宽的一种通信方式。

扩频技术最大的特点是利用宽频带来传输信号。

由于扩频系统具有许多优点，如抗干扰能力强、截获概率低和保密性强以及良好的码分多址通信能力，所以扩频技术已被广泛应用。

CDMA数字蜂窝移动通信等，就是利用扩频技术发展起来的一种扩频通信方式，它具有容量大，通信质量好，节约发射功率等优点。

我主要就一些扩频通信的原理及在CDMA中的应用作了一些了解。

一、扩频通信的理论基础扩频通信系统的模型：香农公式：C = W×Log2(1+S/N)式中：C--信息的传输速率 S--有用信号功率 W--频带宽度 N--噪声功率由式中可以看出：为了提高信息的传输速率C，可以从两种途径实现，既加大带宽W或提高信噪比S/N。

换句话说，当信号的传输速率C一定时，信号带宽W和信噪比S/N 是可以互换的，即增加信号带宽可以降低对信噪比的要求，当带宽增加到一定程度，允许信噪比进一步降低，有用信号功率接近噪声功率甚至淹没在噪声之下也是可能的。

扩频通信就是用宽带传输技术来换取信噪比上的好处，这就是扩频通信的基本思想和理论依据。

按照扩展频谱的方式不同，现有的扩频通信系统可以分为以下几种：1.直接序列扩频工作方式，简称直扩（DS）方式所谓直接序列（DS，Direct Sequency）扩频，就是直接用具有高码率的扩频码序列在发端去扩展信号的频谱。

而在收端，用相同的扩频码序列去进行解扩，把展宽的扩频信号还原成原始的信息。

2.跳变频率工作方式，简称调频（FH）方式所谓跳频，比较确切的意思是用一定码序列进行选择的多频率频移键控。

也就是说，用扩频码序列去进行频移键控调制，使载波频率不断地跳变，所以称为跳频。

3.跳变时间工作方式，简称跳时（TH）方式与跳频相似，跳时（TH，Time Hopping）是使发射信号在时间轴上跳变。

计算机与因特网插件指南Life on-line can be a much richer experience when you aren't restricted to just written words and still pictures. Even if you're new to the Net, you've probably heard aobut multimedia on-line--listening to audio, watching animations and videos, even playing in three-dimensional space. Sound and movement make information come alive.To experience it, you'll need special pieces of software called plug-ins. The term "plug-in" refers to a small, add-on piece of software which extends the capabilities of your web browser, like Netscape Navigator or Microsoft Explorer, turning your computer into a radio or TV.When you arrive at a web page which contains a file requiring a plug-in which you don't have, you will usually receive a message asking if you want to get it by downloading it and installing it into your computer. Most of the time, the installation will be automatic.Occasionally, you'll run into a downloaded file which needs to be decompressed or un-zipped before installation. Once installed, plug-ins run automatically, without you having to do anything.Many multimedia controls still need to be obtained from the developer but are installed automatically.Shockwave is a good example of this. All you need to do is go to the Macromedia site and click on the link to install the ActiveX control. The rest happens automatically. The next time you go to a "Shocked" website, the Shockwave control loads and plays the movie.Most plug-ins and controls can be downloaded for free on the Internet, although not all will work with every system. Some of them, for instance, only work with windows95.当你不再仅仅限于文字和静止图片时，网上生活会丰富多彩得多。