跳频扩频技术中文资料与外文翻译(编辑修改稿)

跳频扩频技术中文资料与外文翻译(编辑修改稿)内容摘要：

uld easily be jammed. The Antheil–Lamarr 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 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 research on radar systems and a technologically similar concept called phase coding also had an impact on spreadspectrum development. Military use Spreadspectrum signals are highly resistant to deliberate jamming , unless the adversary has knowledge of the spreading characteristics. Military radios use cryptographic techniques to generate the channel sequence under the control of a secret Transmission Security Key ( TRANSEC ) that the sender and receiver share in advance. By itself, frequency hopping provides only limited protection against eavesdropping and jamming. There is a simple algorithm that effectively discovers the sequence of frequencies. To get around this weakness most modern military frequency hopping radios employ separate encryption devices such as the KY57 . US military radios that use frequency hopping include the JTIDS/MIDS family, HAVE QUICK and SINCGARS . Civilian use Since the Federal Communications Commission (FCC) amended rules to allow frequency hopping spread spectrum systems in the unregulated GHz band, many consumer devices in that band have employed various spreadspectrum modes. Some walkietalkies that employ frequencyhopping spread spectrum technology have been developed for unlicensed use on the 900 MHz band. Several such radios are marketed under the name eXtreme Radio Service (eXRS). Despite the name39。 s similarity to the FRS allocation, the system is a proprietary design, rather than an official US Federal Communications Commission (FCC) allocated service. Commercial use The 1976 publication of Spread Spectrum Systems by Robert Dixon, ISBN 0471216291 , was a significant milestone in the mercialization of this 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 syste m for newspaper newswire services, Del Norte Technology39。 s radio navigation system for navigation of aircraft for crop dusting and similar applications, and Qualm 39。 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 permitted WiFi , Bluetooth , and many other products including cordless telephones. These rules were then copied in many other was incorporated within 2 months after the decision to mercialize CDMA. Technical considerations The 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 only on a small portion of this bandwidth at any given time, the effective interference bandwidth is really the same. Whilst providing no extra protection against wideband thermal noise , the frequencyhopping approach does reduce the degradation caused by narrowband interferers.。