What is Spread spectrum?
'''Spread spectrum''' is a method in [[radio]] and other kinds of [[telecommunication]]. Its purpose is to overcome [[interference]], [[noise (electronics)|noise]] and [[radio jamming|jamming]] of signals. Sending radio wave signals through the air became possible in the later 19th century with wireless [[telegraphy]]. The fact that signals were affected by natural interference was soon discovered. By the early 1900s, wireless telegraphy could cross the [[Atlantic]]. Intercepting the enemy's radio communications and interfering with their transmission was important in [[World War II]]. Messages in [[code]] were intercepted and recorded for [[decryption]] and [[translation]].<ref>Debag-Montefiore, Hugh 2000. ''Enigma: the battle for the code''. London: Phoenix. {{ISBN|0-75381-130-8}}</ref> Not only can radio signals be detected, but those listening can be detected, since radio receivers also emit a signal. Above all, since [[radio direction-finding]] is widely used in civil and military aviation, ways are needed to reduce interference with these transmissions. The main method is spread spectrum. Spread spectrum systems transmit the message using a bandwidth that is wider than the bandwidth actually needed by the message signal. This spreading of the transmitted signal over a large bandwidth make the resulting wideband signal appear as a noise signal. This resists intentional and unintentional interference with the transmitted signal.<ref>Rappaport, Theodore 2010. ''Wireless communications principles and practice''. 2nd ed, Prentice-Hall, p. 458.</ref> #'''[[Direct-sequence spread spectrum]]''' transmits the messages and adds chips of noise to the message. The sequence of chips produced by the transmitter is already known by the receiver. The receiver uses the same pseudonoise (PN) sequence to reconstruct the information signal. Benefits: ##It resists intended or unintended jamming ##It shares a single channel among multiple users ##It reduces the signal/background-noise level: this hampers [[signals intelligen