Unformatted text preview: 25Year Old Hollywood Star Hedy Lamarr
Frequency Hopping "Not Just a Pretty Face" Ramie Barghouti 6/9/2004 Quick Bio
1914-2000 Hedwid Eva Maria Kiesler was born in Vienna, Austria on November 9, 1914. Her father, Emil, was a bank director, and her mother, Gertrud, was a pianist. Hedwig grew up a self-described "enfant terrible." She was schooled privately, and in her late teens, was schooled at Max Reinhardt's famous acting school in Berlin. Afterwards, she returned to Vienna and worked in the film industry as a script girl in the early 1930's, and shortly thereafter began to get small acting parts. Her Story The year: 1940. Viennese actress Hedy Lamarr, one of the great sex symbols of all time, was making small talk with American film-score composer George Antheil. Antheil. Lamarr and Antheil discussed the Nazi domination of Europe. Lamarr spoke from firsthand knowledge. Three years earlier she had fled Austria, largely out of dislike of her wealthy munitions tycoon husband, Friedrich (Fritz) Mandl. Lamarr thought up an interesting scheme to control armed torpedoes over long distances without the enemy detecting them or jamming their transmissions. As Lamarr spoke that evening Antheil lay sprawled out on her living room floor diagramming her ideas in a spiral notebook. Two years later Lamarr and Antheil were awarded a U.S. patent for a 'secret communication system.' Her Story Cont. Lamarr designed a new kind of guidance system for torpedos. Eventhough her formal education consisted of private schools without technical training, she had absorbed quite a bit about weaponry during her marriage to the arms merchant, Mandl. Hedy knew that "guided" torpedos were much more effective hitting a target, a ship at sea for example. The problem was that radio-controlled torpedos could easily be jammed by the enemy. Neither she nor Antheil were scientists, but one afternoon she realized "we're talking and changing frequencies" all the time. At that moment, the concept of frequency-hopping was born. Antheil gave Lamarr most of the credit, but he supplied the player piano technique. Using a modified piano roll in both the torpedo and the transmitter, the changing frequencies would always be in synch. A constantly changing frequency cannot be jammed. How it Works A signal is broadcast over a seemingly random series of radio frequencies, hopping from frequency to frequency at split-second intervals. The signal could carry spoken words or commands for a torpedo. A receiver, hopping between frequencies in synchrony with the transmitter, picks up the message. Would- be eavesdroppers hear only unintelligible blips. Attempts to jam the signal succeed only at knocking out a few small bits of it. So effective is the concept that it is now the principal antijamming device used in the U.S. government's $25 billion Milstar defense communications satellite system. Spread Spectrum Narrow Band How it Works Cont. Transmitter and torpedo are equipped with identically perforated paper rolls which run synchronously. In this way, the change of frequency takes place continuously and simultaneously, and proceeds so rapidly that the enemy has no chance to disrupt the signal. In order to be able to jam the radio contact, the enemy would also have to be in possession of an identically perforated paper roll. Spread Spectrum vs. Narrow Band
Narrow Band data Modulation
The energy of the transmitted signal is concentrated close to the carrier frequency. High energy in a part of the band The actual power density is determined by the data signal (to be transmitted) Concentration of energy => High energy level => Greater coverage Small BW AM=4kHz FMw=15kHz FMn=8kHz TV=5MHZ Archived by frequency allocation. There's a limit of system for a given BW and band Archived by increasing the power of the carrier Spread Spectrum Data Modulation
The energy of the signal is distributed (spread) in all the frequencies. Low Energy in all the band Actual Power Density Geographical Coverage Approx. Bandwidth The actual power density is determined by the data and a specific code Spread Energy => Low Power density => Small coverage Large BW 902-928 MHz 2.400 2.485 GHz 5.720 5.850 GHz Archived by using different codes (CDMA) There's in any case a limit System Collocation Noise Immunity The information is present all over the band in a redundant way. The system use the code to look for its partners. Example of Use No Profit They offered their patented device to the U.S. military then at war with Germany and Japan. Their only goal was to stop the Nazis. Unfortunately or predictably, the military establishment did not take them or their novel invention seriously. Their device was never put to use during World War II. Lamarr wanted to continue working at the National Inventors Council, but she was persuaded to raise money for war bonds back in Hollywood, selling kisses for $50,000 a smack. No Profit Cont. By the 1950's, the patent on the device had expired when engineers at Sylvania "re-discovered" frequency-hopping. They called it "spread spectrum." These electronic devices were designed for use during the Cuban Missile crisis in the sixties. Hedy's film career was winding down. She had turned down the lead in Casablanca and made a few other bad career decisions. In one interview, she estimated that she went through about 30 million dollars. She never made a dime on her and Antheil's invention; though it is cited as the basis for most spread spectrum technology in use today. Nor did they receive widespread recognition for their invention until the 1990's Advances Today, spread spectrum devices using micro-chips, make pagers, cellular phones, and, yes, communication on the internet possible. Many units can operate at once using the same frequencies.
Most important, spread spectrum is the key element in anti-jamming devices used in the government's 25 billion Milstar system. Milstar controls all the intercontinental missiles in U.S. weapons arsenal. Fifty-five years and five marriages later, Lamarr was recently given the EFF (Electronic Frontier Foundation) Award for their invention. Antheil was also honored; he died in the sixties. Hedy's son accepted the award for her since she no longer makes public appearances.
From her Florida apartment where she lived on a pension from the Screen Actor's Guild, Lamarr responded, "It's about time." ...
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This note was uploaded on 04/28/2008 for the course ECE 4607 taught by Professor Akyldiz during the Spring '08 term at Georgia Tech.
- Spring '08