Frequency hopping spread spectrum (FHSS), patented in 1942 by Hedy Lamarr and George Antheil as a “Secret Communication System,” is a method of transmitting radio signals by rapidly switching frequencies according to a predetermined pattern. Though invented to prevent torpedo jamming during World War II, this technology became the foundation for Wi-Fi, Bluetooth, GPS, and modern cellular communications.
Background
During World War II, radio-controlled torpedoes were vulnerable to jamming—enemies could broadcast interference on the control frequency, causing torpedoes to miss their targets. The Allied forces needed a way to make wireless communications unjammable.
Hedy Lamarr, an Austrian-American actress with knowledge of weapons systems from her first marriage to an arms manufacturer, conceived a solution: rapidly changing the transmission frequency so that jamming any single frequency would be ineffective[1].
The Invention
Lamarr partnered with George Antheil, an avant-garde composer known for “Ballet Mécanique,” which used synchronized player pianos. Together, they developed a system where both transmitter and receiver would hop between frequencies in a synchronized pattern.
Their key insight: if sender and receiver changed frequencies at the same time according to the same random-seeming pattern, the communication would appear as brief noise bursts on any single frequency—impossible to jam effectively.
To synchronize the frequency hops, they proposed using paper rolls similar to player piano rolls—the transmitter and receiver would each have identical rolls dictating the sequence of frequency changes[2].
The Patent
On August 11, 1942, U.S. Patent 2,292,387 was granted for their “Secret Communication System.” The patent was filed under Lamarr’s married name, Hedy Kiesler Markey.
The patent described:
- 88 frequencies (matching piano keys)
- Synchronized hopping using mechanical coordination
- Jamming resistance through rapid frequency changes
Military Interest and Delay
The Navy expressed interest but considered the mechanical implementation impractical for torpedoes of that era. The technology was classified and not implemented during World War II.
The patent expired in 1959 without commercial use.
Revival and Implementation
Electronic technology eventually caught up with the concept:
- 1962: Ships during the Cuban Missile Crisis used frequency hopping
- 1985: FCC allocated spectrum for spread-spectrum technologies
- 1997: IEEE 802.11 (original Wi-Fi standard) incorporated FHSS
Modern Applications
FHSS and its variants are now fundamental to wireless communication[3]:
Bluetooth
Classic Bluetooth uses FHSS, hopping between 79 frequencies in the 2.4 GHz band 1,600 times per second.
Wi-Fi
The original 802.11 standard used FHSS. Modern Wi-Fi uses related spread-spectrum techniques including OFDM.
GPS
GPS signals use spread-spectrum coding for accuracy and interference resistance.
Cellular Networks
CDMA (Code Division Multiple Access) cellular networks use spread-spectrum principles derived from FHSS.
Military Communications
Modern military radios continue to use frequency hopping for secure, jam-resistant communication.
Recognition
For decades, Lamarr and Antheil received no credit for their invention. Recognition came only in the 1990s:
- 1997: Electronic Frontier Foundation Pioneer Award
- 2014: Lamarr inducted into National Inventors Hall of Fame (posthumously)
Legacy
The Lamarr-Antheil patent demonstrated that frequency agility could provide security and robustness to wireless communications. Though their mechanical implementation was never built, the concept proved foundational. Today, billions of devices—phones, laptops, wireless earbuds, GPS receivers—rely on spread-spectrum techniques that trace their lineage to a Hollywood actress and an avant-garde composer imagining how to protect torpedoes from enemy jamming.
Sources
- Wikipedia. “Hedy Lamarr.” Background and motivation for the invention.
- IEEE Standards Association. “Actress/Inventor Hedy Lamarr.” Technical details of the patent.
- National Inventors Hall of Fame. “Hedy Lamarr.” Modern applications.