Harvard Bits 1

Spread Spectrum

Technology is forever

April 19,2011

Harvard Bits 2

National Broadcasting Co. v. U. S.,319 U.S. 190 (1943)

… the radio spectrum simply is not large enough to accommodate everybody. There is a fixed natural limitation upon the number of stations that can operate without interfering with one another.

Unlike other modes of expression, radio inherently is not available to all. That is its unique characteristic, and that is why, unlike other modes of expression, it is subject to governmental regulation. …

- Justice Felix Frankfurter

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Thomas, J., Concurring

April 19,2011

This deep intrusion into the First Amendment rights of broadcasters, which the Court has justified based only on the nature of the medium, is problematic … [D]ramatic technological advances have eviscerated the factual assumptions …. Broadcast spectrum is significantly less scarce than it was 40 years ago … The extant facts that drove this Court to subject broadcasters to unique disfavor under the First Amendment simply do not exist today … For all these reasons, I am open to reconsideration … in the proper case.

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Thomas, J., Concurring

April 19,2011

This deep intrusion into the First Amendment rights of broadcasters, which the Court has justified based only on the nature of the medium, is problematic … [D]ramatic technological advances have eviscerated the factual assumptions …. Broadcast spectrum is significantly less scarce than it was 40 years ago … The extant facts that drove this Court to subject broadcasters to unique disfavor under the First Amendment simply do not exist today … For all these reasons, I am open to reconsideration … in the proper case.

Harvard Bits 7

Shannon-Hartley, once again

C = B lg (1+S/N)where C = channel capacityB = bandwidthS = signal powerN = noise powerWhat happens to C if B = 0?What happens to C if S = 0?What happens to C if S = N?

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Noise is InevitableC = B lg (1+S/N): What happens if N = 0?Infinite channel capacity!!!Noise is like friction: it’s always going to be with usOr sin! Wonderful things would happen without itE.g. moving any amount of information in fixed time

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011011000101…01

One long bit string

011011000101…01

Perfectly duplicated bit string

Imaginary noiseless channel

One short pulse with amplitude equal to the number represented by the bit string

Perfectly received pulse of very precise amplitude

All the books in Widener

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Spread Spectrum Tradeoff:Lower Power <==> Larger Bandwidth

C = B lg (1+S/N)

April 19,2011http://sss-mag.com/primer.html#ds

Noise

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How to Use Bandwidth?

Simple idea: Treat multiple frequencies as multiple Shannon channels, like radio stations.

More bandwidth <=> More channels <=> More information flow

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103.3MHz 96.9 MHz

freq1 freq2

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Spread Spectrum I:Frequency Division Multiple Access (FDMA)

• Several communications in the same bandwidth range, each in a separate “channel”

• If phones are spatially far enough apart, signals fade and frequencies can be re-used

• Old analog cell phones used this technology• Handoffs awkward when moving from cell to adjacent cell if

same frequency channel is in use

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123456

123456

123456

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Security Issue

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123456

123456

123456

• Big risk: Eavesdropper can just tune in the right frequency and listen

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Spread Spectrum II: Code Division Multiple Access (CDMA)

• Have all communications share the same bandwidth but give data from each a unique key so that it can be disentangled from the others

• Divide the bandwidth into channels but have each conversation jump rapidly between frequencies according to a unique sequence known only to the tower and cell phone

• This is Frequency Hopping Spread Spectrum (FH/SS)• Smoother handoffs since key can be maintained across cells

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123456

4,2,5,6,1,3,4,5,2,… 4,2,5,6,1,3,4,5,2,…

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Spread Spectrum for Security

• Instead of using just one frequency, hop rapidly from one frequency to another

• The source and the destination must agree on the values and sequencing of frequencies

• The sequence is an encryption key • Must appear random and unpredictable to an eavesdropper:

pseudo-noise• Eavesdropper on any one frequency hears only “noise”

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123456

4,2,5,6,1,3,4,5,2,…

4,2,5,6,1,3,4,5,2,…

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The Strange History of Frequency Hopping

• World War II: Torpedoes could be guided by radio control, but the radio transmission could also be jammed by the enemy, confusing the torpedo

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1942

Torpedoes caused enormous losses to both Allied and Axis fleets

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Hedy Lamarr

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Hedy Lamarr

• ~1914: Born Hedwig Eva Maria Kiesler in Vienna• First woman to appear nude in a feature film, Ecstasy

(1933), when she was age 19

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After release of film, married wealthy industrialist Fritz Mandl, who tried to buy up and burn all the prints

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Hedy Lamarr

Hostess for Mandl’s parties in Vienna, where they entertained his business friends

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“Any girl can be glamorous.

All she has to do is stand still and look stupid.”

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Louis Mayer and America

• Kiesler became increasingly hostile both to the Nazis and to her husband Mandl

• In 1937 she hired a maid who looked like her, then drugged the maid and escaped to Paris in the maid’s uniform

• She met movie mogul Louis Mayer, who gave her a movie contract and the name Hedy Lamarr

• Divorced Mandl on grounds of desertion• Emigrated to America and settled in Hollywood

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George Antheil

• Born 1900 in New Jersey, of Prussian parents• Studied music in Philadelphia, became concert pianist in

Berlin and Paris• Avant-garde composer of “mechanistic” pieces such as

Airplane Sonata and Death of Machines• Ballet Mécanique was scored for 16 player pianos,

xylophone, and percussion; one production had electric bells, airplane propellers, and siren

• Ezra Pound: “Antheil is supremely sensitive to the existence of music in time-space”

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Antheil in the US

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• By 1933, Antheil’s music was out of fashion and he was broke and moved to California

• Invented the “See Note” system of musical notation, read down the page with each column representing one note, like a player piano roll - also a commercial failure

Man R

ay photo

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Antheil and Endocrinology

• 1936, Esquire: Glandbook for the Questing Male and The Glandbook for Practical Use

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The Glandbook in Practical Use (Esquire, June 1936)

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Lamarr and Antheil

• In 1940 Lamarr arranges to meet Antheil in Hollywood• She knows about Antheil’s applied endocrinology and wants

to know how to enlarge her nnnnnnn• The next night they talk again and Lamarr says she is thinking

of quitting MGM and offering her services to the National Inventor’s Council

• “They could just have me around, and ask me questions”

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What Hedy Lamarr Knew

Lamarr learned a lot while standing around and looking stupid at parties

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Fritz Mandl was a munitions maker and his regular dinner guests included:

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The Invention

• Lamarr understands major problems in weapons design • She has some ideas about unjammable torpedo guidance

systems• She explains to Antheil the idea of spread spectrum

frequency hopping to prevent interception and jamming• She does not know how to control the sequencing of

frequencies

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Antheil:“With a Player Piano Roll!”

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The Fate of the Invention

• Out of patriotism, Lamarr and Antheil give the patent to the Navy and never receive any royalties

• She helps the war effort by selling kisses at $50,000 each, raising $7M in War Bonds in one night

• The Navy classifies but does not implement the invention, reluctant to put player pianos into torpedoes

• In the 1950s electronic control became possible, and frequency hopping became the basis for all secret military communications

• First heavily used for secret communications in the Cuban Missile Crisis in 1962

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The Curious End of Hedy Lamarr

• Antheil dies in 1959, never seeing the fruit of his labors• Lamarr runs through six husbands, several fortunes, and two

shoplifting arrests• She develops a habit of suing almost anyone who mentions

her name in public, but wins few of the lawsuits• In 1997, with spread spectrum technology now being used to

secure millions of cell phone conversations, Lamarr, 84, is awarded the Electronic Frontier Foundation Pioneers Award

• “It’s About Time”

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Lamarr on Telephone with her Sonat the EFF Award Ceremony

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• … the number of available broadcasting frequencies is limited. (KFKB v. FRC, 1930)

• … the radio spectrum simply is not large enough to accommodate everybody. There is a fixed natural limitation upon the number of stations that can operate without interfering with one another. (NBC v. U.S., 1943)

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The Broadcast Spectrum is Not a Limited Resource!

• Spread spectrum passed from military to commercial use• Spread spectrum makes it possible to have essentially

unlimited numbers of cell phone calls • Spread spectrum makes possible multiple low power, spatially

limited, encrypted digital signals• If radio stations can broadcast and rebroadcast at low power

over limited areas using spread spectrum, there can be essentially unlimited numbers of stations

• The legal justification for FCC control of content has been rendered irrelevant by technological advances that started with Lamarr and Antheil!

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The most beautiful woman in the world - Louis Mayer

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Coda

• In 1996, Corel Corporation, producer of drawing software Corel Draw8, awards a prize to the draftsman of this image of Lamarr as the best picture drawn using their program

• Thinking Lamarr is dead, Corel puts the image on its box and startup screen

• Lamarr sues Corel for $15M, eventually settles, and lives out her last years in comfort

• 1999: “Films have a certain place in a certain time period. Technology is forever.”

Hedy Lamarr died January 19, 2000, at the age of 86

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