METHOD FOR SYNCHRONISING OFDM SYMBOLS DURING RADIO TRANSMISSIONS

摘要

The invention relates to a method for synchronising OFDM symbols during radio transmissions, said method being used to facilitate strong and efficient frame and frequency synchronisation. Additional pilots are added to the OFDM symbols by the transmitter in order to form pilot pairs. A sequence is modulated on said pilot pairs and then extracted by the receiver in order to produce a measure for each OFDM symbol by comparing the extracted sequence and a stored sequence. The OFDM symbol with the largest measure is recognised as being the first OFDM symbol in a frame. The sequence is modulated using a differential modulation, QPSK or BPSK. A first rough time synchronisation is determined by correlation in the receiver using protective intervals. A non-integer frequency error can also be determined in this way in order to correct the received OFDM symbols of said non-integer frequency error. The extracted sequence and the stored sequence are compared by means of cross correlation, said cross correlation providing the measure. The integer frequency error can thus also be determined. Frame synchronisation is improved by averaging the frame synchronisation results of groups of OFDM symbols.