Patent ID: 7778357

Claim:
A COFDM demodulator comprising: a fast Fourier transform circuit receiving a signal on an information channel, the received signal corresponding to a sequence of symbols comprising a series of symbols and a current symbol, each symbol of the sequence of symbols conveying several carriers, some of which are pilots, each of the pilots having been modulated in phase and in amplitude by a complex coefficient, said fast Fourier transform circuit extracting from each pilot a complex coefficient so that complex coefficients are extracted from a series of pilots and a current pilot, wherein the series of pilots and the current pilot correspond to a same portion of the information channel for different symbols in the sequence of symbols; a circuit for determining at least a portion of a frequency response of the information channel by calculating a time average of real or imaginary parts of the complex coefficients extracted from the series of pilots and the current pilot to provide, for each pilot of a symbol of the sequence of symbols, an estimated complex coefficient, wherein the circuit for determining at least the portion of the frequency response comprises a circuit for providing, for each pilot of the symbol, a differential complex coefficient obtained based on a difference between the complex coefficient extracted from the current pilot and the estimated complex coefficient; and a circuit for calculating a time variation of the frequency response of the information channel based on the estimated complex coefficient and the differential complex coefficient associated with the current pilot, wherein the circuit for calculating the time variation of the frequency response of the information channel comprises: a circuit for providing a first value representative of a modulus of the estimated complex coefficient associated with the current pilot; a circuit for providing a second value representative of a modulus of the differential complex coefficient associated with the current pilot; and a circuit for providing an instantaneous indicator of the time variation of the frequency response of the information channel for the current pilot, corresponding to a ratio between the second value and the first value.