Identification of radiotelephony transmissions in VHF band of maritime radio communications

Application of orthogonal frequency division multiplexing (OFDM) is suggested for digital watermarking (DWM) in VHF radiotelephony of maritime mobile service. Algorithm of normalized spreading of DWM energy in the method of improved spread spectrum (ISS) considering information on carrier signal and DWM detection method based on hash function are designed. The OFDM–ISS method allows for achieving the DWM rate of 60–268 bit/sec in the conditions of their acoustic stealthiness in the problem of automatic radiotelephone transmissions identification using existing radio communications equipment