It has been developed that transforms an audio signal corresponding to a time-domain signal into a frequency-domain signal based on a modified complex lapped transform (MCLT), and that inserts synchronization data by changing a phase of a frequency coefficient.
The synchronization data may be a predetermined value which is shared with a receiver, and may consist of ‘0’ and ‘1’. In the process of inserting the synchronization data, a phase of a MCLT coefficient may be changed to be ‘0’ or ‘π’ based on whether the data to be inserted is ‘0’ or ‘1’.
According to the MCLT, each frame is overlapped half with adjacent ones and interference may occur among frames and thus, phases at a transmitter are changed at a receiver. To enable the phase of the MCLT to be accurately ‘0’ or ‘π’ at the receiver, a coefficient may be changed by taking into consideration interference among frames at the transmitter.
To perform synchronization, the receiver may transform a received audio signal into a frequency-domain signal based on the MCLT, and may calculate a correlation with predetermined synchronization data. A process of synchronization may calculate an MCLT coefficient for each sample, calculate a correlation from each coefficient, and determine a location where a correlation is greater than a threshold.
However, the receiver may be required to perform a large amount of calculation to calculate the MCLT coefficient for each sample. Although a fast Fourier transform (FFT) may be used to reduce the amount of calculation, this method still requires a large amount of calculation since a coefficient should be calculated for each sample.
Also, a method of calculating an approximate correlation may be utilized to reduce an amount of calculation, but the method has a drawback in that performance of synchronization is deteriorated.