HEDY LAMARR & GEORGE ANTHEIL, THE ORIGIN OF WI-FI

Today, The Grandma has been reading about Hedy Lamarr and George Antheil's patent for a frequency-hopping spread spectrum communication system that later became the basis for modern technologies in wireless telephones, two-way radio communications, and Wi-Fi, and that was received on a day like today in 1942.

Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly changing the carrier frequency among many distinct frequencies occupying a large spectral band. 

The changes are controlled by a code known to both transmitter and receiver.  

FHSS is used to avoid interference, to prevent eavesdropping, and to enable code-division multiple access (CDMA) communications.

The available frequency band is divided into smaller sub-bands. Signals rapidly change (hop) their carrier frequencies among the centre frequencies of these sub-bands in a predetermined order. Interference at a specific frequency will affect the signal only during a short interval.

FHSS offers four main advantages over a fixed-frequency transmission:

-FHSS signals are highly resistant to narrowband interference because the signal hops to a different frequency band.

-Signals are difficult to intercept if the frequency-hopping pattern is not known.

-Jamming is also difficult if the pattern is unknown; the signal can be jammed only for a single hopping period if the spreading sequence is unknown.

-FHSS transmissions can share a frequency band with many types of conventional transmissions with minimal mutual interference. FHSS signals add minimal interference to narrowband communications, and vice versa.

More information: Geeks for Geeks

In 1899 Guglielmo Marconi experimented with frequency-selective reception in an attempt to minimize interference.

The earliest mentions of frequency hopping in open literature are in US patent 725,605, awarded to Nikola Tesla on March 17, 1903, and in radio pioneer Jonathan Zenneck's book Wireless Telegraphy (German, 1908, English translation McGraw Hill, 1915), although Zenneck writes that Telefunken had already tried it. Nikola Tesla doesn't mention the phrase frequency hopping directly, but certainly alludes to it.

Entitled Method of Signaling, the patent describes a system that would enable radio communication without any danger of the signals or messages being disturbed, intercepted, interfered with in any way.

The German military made limited use of frequency hopping for communication between fixed command points in World War I to prevent eavesdropping by British forces, who did not have the technology to follow the sequence.

Jonathan Zenneck's book Wireless Telegraphy was originally published in German in 1908, but was translated into English in 1915 as the enemy started using frequency hopping on the front line. Zenneck was a German physicist and electrical engineer who had become interested in radio by attending Tesla's lectures on wireless sciences. 

Wireless Telegraphy includes a section on frequency hopping, and, as it became a standard text for many years, it probably introduced the technology to a generation of engineers.

A Polish engineer and inventor, Leonard Danilewicz, came up with the idea in 1929. Several other patents were taken out in the 1930s, including one by Willem Broertjes (U.S. Patent 1,869,659, issued Aug. 2, 1932).

During World War II, the US Army Signal Corps was inventing a communication system called SIGSALY, which incorporated spread spectrum in a single frequency context. But SIGSALY was a top-secret communications system, so its existence was not known until the 1980s.

In 1942, actress Hedy Lamarr and composer George Antheil received U.S. Patent 2,292,387 for their Secret Communications System, an early version of frequency hopping using a piano-roll to switch among 88 frequencies to make radio-guided torpedoes harder for enemies to detect or jam. The U.S. Navy rejected the idea, then seized it as alien property in 1942 (Lamarr was Austrian) but filed it away with no record of a working device being produced.

 More information: National Air and Space Museum

Lamarr's and Antheil's idea was rediscovered in the 1950s during patent searches when private companies were independently developing direct-sequence Code Division Multiple Access, a non-frequency-hopping form of spread-spectrum, and has been cited numerous times since.

In 1957, engineers at Sylvania Electronic Systems Division adopted the patented concept, combined with the recently invented transistor.

In 1962, the US Navy finally utilized the technology during the Cuban Missile Crisis; Lamarr's and Antheil's patent had expired.

A practical application of frequency hopping was developed by Ray Zinn, co-founder of Micrel Corporation. 

Zinn developed a method allowing radio devices to operate without the need to synchronize a receiver with a transmitter. Using frequency hopping and sweep modes, Zinn's method is primarily applied in low data rate wireless applications such as utility metering, machine and equipment monitoring and metering, and remote control. 

In 2006 Zinn received U.S. Patent 6,996,399 for his Wireless device and method using frequency hopping and sweep modes.

More information: Forbes

The world isn't getting any easier.

With all these new inventions, I believe that people are hurried more and pushed more...

The hurried way is not the right way; 

you need time for everything 

-time to work, time to play, time to rest.

Hedy Lamarr