Communications engineering. A multi-carrier modulation scheme, i.e. the user data is distributed onto several carriers. These sub-carriers are orthogonal to each other, i.e. at the maximum of one sub-carrier in the amplitude spectrum, all other sub-carriers have their zero crossing. Therefore there is no cross-talking between the sub-carriers and so there is no need for a guard band between them. This leads to a smaller bandwidth requirement than for FDM. OFDM is used for example for WiMAx, WLANs or terrestrial digital TV. OFDM is similar to COFDM (coded orthogonal frequency division multiplex) and DMT (discrete multi-tone modulation).