Patent ID: 8411531

Claim:
An acoustic signal transmission method comprising: selecting, by a selection unit of a modulation device, a carrier frequency of a data signal and a PN sequence corresponding to the carrier frequency; modulating, by a modulation unit of the modulation device, the carrier frequency selected by the selecting with the data signal; generating, by a generation unit of the modulation device, a symbol synchronization signal according to the PN sequence selected by the selecting; superposing, by a superimposition unit of the modulation device, the symbol synchronization signal generated by the generating and the data signal modulated by the modulating onto the acoustic signal and transmitting thus obtained signal; receiving, by an input unit of a demodulation device, the acoustic signal superposed with the modulated data signal; calculating, by a calculation unit of the demodulation device, correlations between the acoustic signal received by the receiving and a plurality of PN sequences; determining, by a determination unit of the demodulation device, the PN sequence having the highest maximum correlation value with the received acoustic signal in the plurality of PN sequences according to a result of the calculating; deciding, by a synchronization processing unit of the demodulation device, a synchronization point by using the PN sequence determined by the determining and synchronizing the modulated data signal superposed on the acoustic signal according to the synchronization point; and demodulating, by a demodulation unit of the demodulation device, the modulated data signal subjected to the synchronizing.