In an orthogonal frequency division modulation (OFDM) apparatus and method, a transmitter produces a clock and a reference signal to provide an accurate phase in modulation of a carrier. A receiver is thus able to reproduce the reference signal, even if the signal-to-noise (S/N) ratio of the carrier...http://www.google.de/patents/US5956318?utm_source=gb-gplus-sharePatent US5956318 - Orthogonal frequency division multiplexing
