Multiplexing of digital information in VHF maritime radiotelephony

The complex system for covered transmission of digital information in standard VHF maritime radiotelephone channels is designed on the basis of digital watermarking (DWM) technology. Audio imperceptibility and interference stability of multiplexed digital data are provided with application of OFDM and ISS algorithms in cooperation with new methods of normalized distribution of introduced distortions and data block detection using hash functions. It is based on OFDM modulation and ISS method with new methods of insertion interferences distribution and data packet detection with a hash function. Experiments are carried out for signal transmission in the real VHF radio channel using SAILOR RT-2048 radio station and USB-module E14-140M L-CARD for off-line MatLab processing. The designed DWM system provides data transmission rate of 60 bit/sec at 4 dB from additive noise in a standard VHF radio channel maintaining resistance to intersymbol and amplitude distortions. The design method is intended for implementation of radiotelephone transmissions automatic identification in maritime communication without standard radio equipment replacing, additional frequency-time resources allocation and altering the adopted radio communication procedures.