Patent ID: 6044119
Filing Date: 2000-03-28
Classification: H04B

Abstract:
A method of controlling a frequency of a local oscillator at a first station that uses the local oscillator to demodulate a signal received from a second station, the signal carrying a stream of information symbols, with reference symbols having predetermined values inserted at predetermined locations among the information symbols, said method comprising:demodulating the signal to obtain, for each reference symbol and for each information symbol, a received symbol value equal to a symbol value transmitted by the second station, altered by transmission channel effects and by a frequency offset of the local oscillator;determining a data value represented by each received symbol value, by making a hard decision based on the received symbol value of each information symbol, and by setting the data value represented by each reference symbol equal to the predetermined value of the reference symbol;removing the data value from the received symbol value, thereby obtaining a channel estimation value representing the transmission channel effects and the frequency offset;delaying the channel estimation value by a predetermined duration, during which a plurality of symbol values are received, thereby obtaining a delayed channel estimation value;multiplying the channel estimation value by a complex conjugate of the delayed channel estimation value, thereby obtaining a complex product; andcalculating, from an imaginary part of the complex product, a frequency adjustment to be applied to the local oscillator.