Abstract: Receiver and transmission system for orthogonal frequency-division multiplexing signals comprising a frequency synchronization circuit (116) which has a local oscillator (214) whose frequency is controlled by a correction signal .epsilon.. The latter is generated by a frequency detector (213) which operates in the time domain, by utilizing the redundant information contained in such signals. The performance of the invention is particularly of interest for transmissions on multipath channels which occur in mobile radio, digital television, and so on.

Abstract: A carrier recovery circuit includes a correction circuit for correcting phase differences which appear betwen a complex input signal and a local carrier supplied by a local oscillator. The correction circuit defines zones in a plane defined by in-phase components and quadrature components of the complex signal. Each zone includes a respective state of a constellation that is used for encoding the signal during transmission. When a point representing the signal in the I/Q plane is subjected to a decision, the correction circuit produces a correction signal proportional to a measured phase difference. When the point lies outside the zones, the correction circuit produces a correction signal that varies as a function of the measured phase difference to which a weighting factor, dependent on the distance from the point to the nearest zone, is applied. In a first mode the correction circuit corrects either the local oscillator phase or frequency; or in a second mode, corrects the signal phase.

Abstract: A carrier synchronization device determines and compensates for differences in synchronization between a local carrier and a received modulated signal to be demodulated by the local carder. The device includes an apparatus determining an error signal .epsilon.(t) representative of synchronization errors. This error signal may be filtered, with different loop bandwidths, either by a first low-pass filter (Hf.sub.1 or by a second low-pass filter (Hf.sub.2) in order to generate a control signal u(t) for control of a local oscillator. A lock mode detector compares the control signal with a delayed replica of this control signal and selects one of the filters depending on whether the device operates in the lock-in mode or in the capturing mode. The lock mode detector is programmed to switch automatically from one mode to the other. The device can be used for the synchronization of symbol-block format OFDM signals.

Abstract: Receiver (105) for signals transmitted according to an orthogonal frequency division multiplexing technique with carriers distributed symmetrically around a centre frequency f.sub.e, said receiver comprising a frequency synchronizer (116) for the local oscillator (214). The synchronizer (116) utilizes the fact that part of the side carriers are not transmitted to ensure in the lock-on mode a frequency synchronization having a wide lock-on range. It may also be used in the permanent mode with very little jitter. The receiver can be used in digital television for receiving signals transmitted according to an orthogonal frequency division multiplexing technique.