致谢
本次毕业设计顺利完成，在毕业设计的这个精细的过程中，让我学到很多的东西，感受到很到。我要感谢给我支持和帮助的老师和朋友。首先，我要感谢我的导师魏志刚老师，在我撰写的过程中，是他给了我很大的支持与帮助。
在写论文的初期，我对于论文的结构以及文献选取等方面存在很多问题，我主动找到魏老师。虽然，我们是在开始毕业设计时才初次认识，但是，老师的随和热情，认真负责，就给了我很大的鼓励，他细心而富有耐心的对我本次的毕业设计的内容做了详尽的讲解，帮助我开拓研究思路，精心点拨，热忱鼓励，使我对整个毕业设计的思路有了总体的把握，让我的内心得到了很大的鼓励与支持。在设计的这个过程中，我学习、研究，魏老师的指导与帮助，使得我顺利完成，在此表示深深的感谢。
大学四年的学习生活即将画上句号，毕业设计是我大学里完成的最后一份作业，是我们自己对整个四年学习能力的总结与考验 。在这个过程的体验中，我提取、应用、总结着这四年以来所学习到的知识，搜集查询、学习知识、积累知识、设计完成。看到自己最终顺利完成的论文，心里充满着无限的喜悦。
回首四年，我的每一步成长和取得的进步，有快乐也有艰辛。感谢四年以来给我悉心教导、给我支持和鼓励的老师和朋友。感谢我的母校—重庆邮电大学移通学院，给我提供良好的学习环境，感谢我的辅导员皮老师的精心教导。在这个如今以熟悉不过的校园里让我学到了太多太多的东西。
即将离开大学的校园，走向工作岗位，这对我的人生来说，又将是踏上一个新的征程，再次，衷心的感谢与我一起走过四年的大学生活的老师、朋友们，感感谢我的父母的关心与支持，感谢有你们，使我变得更加坚强与自信。
我对自己的未来充满着信心与希望。 祝各位老师朋友：身体健康，工作顺利！
27
参考文献
[1] 啜钢，移动通信原理与系统[M]，北京邮电大学出版社，2005.9. [2 田日才，扩频通信[M]，清华大学出版社，2007.4.
[3] 查光明．熊贤祚，扩频通信[M]，西安：西安电子科技大学出版社．1990 [4] 吴海红，CDMA扩频通信中m序列与Gold序列的比较及应用[N]，喀什师范学院,学 报，2010.3.
[5] 林可祥，汪一飞 伪随机码的原理与应用[M]，人民邮电出版社，1978 [6] 王会华，李宝平，m序列发生器的设计与实现[J]，北京电子科技学院学报，2007.6
[7] 吴明捷，伪随机码及计算机的产生[J],辽宁工程技术大学学报（自然科学版），2002
[8] 吴先用，邹学玉，一种m序列伪码发生器的产生方法[J]，测控技术，2003,22（9）
[9] 王哲.伪随机序列的Matlab实现与分析[J].科技创新导报，2008. 23 [10] 刘新永，蔡凤丽，MATLAB的m序列的产生及相关特性仿真[J]，安徽电子信息职业技术学院学报，2009.5，44（8）
[11] 王立宁，matlab与通信仿真[M]，人民邮电出版社，2000.1.
[12] 陈海龙，李宏，基于MATLAB的伪随机序列的产生和分析[J]，计算机仿真，2005,22（5）:
[13] R· C·Dixon Spread Spectrum System. John Wiley & Sons, 1986
[14] Rodger E.Ziemer,Roger L.Peterson, David E.Borth, Introduction to Spread Spectrum Communications , 电子工业出版社,2006,7
[15] M· K· Simon Spread Spectrum Communications Handbook,人民邮电出版社
28
附 录
一、英文原文
spread spectrum communication
Rodger E.Ziemer
Abstract:
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).
【key words】Spread spectrum communication Direct sequence Frequency hopping
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 world's first radio-controlled submersible boat in 1898, when it became apparent the wireless signals controlling the boat needed to be secure from \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 Telefunken 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 Polish engineer, Leonard Danilewicz, came up with the idea in 1929.Several other patents were taken out in the 1930s, including
29
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, SIGSALY's 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 received U.S. Patent 2,292,387 for their \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 when ITT Corporation and other private 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 \Spread-spectrum telecommunications
This 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.
30
Notes
? Techniques known since 1940s and used in military communication system since 1950s
? \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, 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 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 \the signal and reduces the chance of an adversary's making sense of it. What's 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 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; %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. Theoretical Justification for Spread Spectrum
Spread-spectrum is apparent in the Shannon and Hartley channel-capacity theorem:
C=B×log2(1+S/N) (Eq.1)
In this equation,C is the channel capacity in bits per second(bps),which is the
31