通信专业毕业论文外文翻译---扩频技术

通信专业毕业论文外文翻译---扩频技术内容摘要：

hopping is also mentioned in radio pioneer Johannes Zenneck39。 s book Wireless Telegraphy (German, 1908, English translation McGraw Hill, 1915), although Zenneck himself states that Telefunken had already tried it several years earlier. Zenneck39。 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 other patents were taken out in the 1930s, including one by Willem Broertjes (Germany 1929, . Patent 1,869,695, 1932). During World War II, the US Army Signal Corps was inventing a munication system called SIGSALY for munication between Roosevelt and Churchill, which incorporated spread spectrum, but due to its top secret nature, SIGSALY39。 s existence did not bee known until the 1980s. The most celebrated invention of frequency hopping was that of actress Hedy Lamarr and poser Gee Antheil, who in 1942 received . Patent 2,292,387 for their Secret 11 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 AntheilLamarr version of frequency hopping used a pianoroll to change among 88 frequencies, and was intended to make radioguided 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 amp。 Industrial Electronics Corporation, ITT and Sylvania Electronic Systems that led to early spreadspectrum technology in the 1950s. Parallel research on radar systems and a technologically similar concept called phase coding also had an impact on spreadspectrum development. Commercial use The 1976 publication of Spread Spectrum Systems by Robert Dixon, ISBN 0471216291, was a significant milestone in the mercialization of this technology. Previous publications were either classified military reports or academic papers on narrow subtopics. Dixon39。 s book was the first prehensive unclassified review of the technology and set the stage for increasing research into mercial applications. Initial mercial use of spread spectrum began in the 1980s in the US with three systems: Equatorial Communications System39。 s very small aperture (VSAT) satellite terminal system for newspaper newswire services, Del Norte Technology39。 s radio navigation system for navigation of aircraft for crop dusting and similar applications, and Qualm39。 s OmniTRACS system for munications to trucks. In the Qualm and Equatorial systems, spread spectrum enabled small antennas that viewed more than one satellite to be used since the processing gain of spread spectrum eliminated interference. The Del Norte system used the high bandwidth of spread spectrum to improve location accuracy. In 1981, the Federal Communications Commission started exploring ways to permit more general civil uses of spread spectrum in a Notice of Inquiry docket. This docket was proposed to FCC and then directed by Michael Marcus of the FCC staff. The proposals in the docket were generally opposed by spectrum users and radio equipment manufacturers, although they were supported by the then HewlettPackard Corp. The laboratory group supporting the proposal would later bee part of Agilent. The May 1985 decision in this docket permitted unlicensed use of spread spectrum in 3 bands at powers up to 1 Watt. FCC said at the time that it would wele additional requests for spread spectrum in other resulting rules, now codified as 47 CFR 12 permitted WiFi, Bluetooth, and many other products including cordless telephones. These rules were then copied in many other countries. Qualm was incorporated within 2 months after the decision to mercialize CDMA. Spreadspectrum telemunications This is a technique in which a (telemunication) signal is transmitted on a bandwidth considerably larger than the frequency content of the original information. Spreadspectrum telemunications 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 noiselike 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 munications (antijam, or AJ), or to hide the fact that munication was even taking place, sometimes called low probability of intercept (LPI). Frequencyhopping spread spectrum (FHSS), directsequence spread spectrum (DSSS), timehopping spread spectrum (THSS), chirp spread spectrum (CSS), and binations 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. Ultrawideband (UWB) is another modulation technique that acplishes the same purpose, based on transmitting short duration pulses. Wireless Ether standard IEEE uses either FHSS or DSSS in its radio interface. Notes  Techniques known since 1940s and used in military munication system since 1950s  Spread radio signal over a wide frequency range several magnitudes higher than minimum requirement. The core principle of spread sp。