Orthogonal Frequency-Division Multiplexing (OFDM) is a digital multi-carrier modulation scheme commonly used for wideband digital communications which uses a large number of closely-spaced orthogonal sub-carriers. Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation) at a low symbol rate, maintaining data rates similar to conventional single-carrier modulation schemes in the same bandwidth. In practice, OFDM signals are generated using the Fast Fourier transform algorithm.

The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions. Some examples of OFDM for wideband digital communications include ADSL, SDSL and VDSL broadband access and certain Wi-Fi (IEEE 802.11a/g) Wireless LANs.

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