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Spread spectrum is a technique used for transmitting radio or telecommunications signals. The term refers to the practice of spreading the transmitted signal to occupy the frequency spectrum available for transmission.
The advantages of spectrum spreading include noise reduction, security and resistance to jamming and interception.
One way in which spread spectrum is implemented is through frequency hopping, a technique in which a signal is transmitted in short bursts, "hopping" between frequencies in a pseudo-random sequence. Both the transmitting device and the receiving device must be aware of the frequency sequence.
Frequency hopping was used by the German military as early as World War I in an attempt to prevent the British from listening in on transmissions. Spread spectrum technology saw further development and deployment during World War II.
Probably the most famous developer of spread spectrum technology was the actress Hedy Lamarr, who co-patented a frequency hopping technique in 1942 to prevent radio-controlled torpedoes from being detected and jammed.
Today, spread spectrum is an important component of code division multiple access (CDMA) technology, which used in cellular telecommunications. In CDMA, a pseudo-random spreading code is used to spread the signal within the available bandwidth.