Single-sideband modulation
refinement of amplitude modulation
In radio communications, single-sideband modulation (SSB) or single-sideband suppressed-carrier modulation (SSB-SC) is a type of signal modulation used to transmit information, such as an audio signal, by radio waves. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. Amplitude modulation produces an output signal the bandwidth of which is twice the maximum frequency of the original baseband signal. Single-sideband modulation avoids this bandwidth increase, and the power wasted on a carrier, at the cost of increased device complexity and more difficult tuning at the receiver.
Basic concept
In conventional amplitude modulation (AM), an audio signal controls the amplitude of a radio-frequency carrier, producing a carrier plus two mirror-image sidebands. Each sideband contains a complete copy of the original information, while the carrier itself conveys none. Consequently, an AM signal occupies a bandwidth equal to twice the highest audio frequency and expends a large fraction of the transmitted power on the carrier and redundant sideband. This spectral structure of AM is described in classic radio texts, including Everitt's treatments of modulation theory.
Single-sideband modulation (SSB) is derived directly from AM by removing this redundancy. Since either sideband alone contains the entire modulating signal, SSB transmits only one sideband and usually suppresses the carrier.
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