Цифровые водяные знаки для радиотелефонных каналов с межсимвольной интерференцией
Journal Title: Цифрові технології - Year 2018, Vol 1, Issue 23
Abstract
Abstract. A method for embedding additional data in the form of digital watermarks (DWM) in the voice messages transmitted via analog radiotelephone channels of the maritime mobile service has been designed. Data embedding is carried out in the frequency domain of the discrete Fourier transform (DFT) coefficients in a scheme with an informed encoder. In order to increase the resistance of digital watermarks againstintersymbolinterferences, a multi-channel algorithm for the digital watermarks data transmission in a narrow-band frequency channels according to the orthogonal frequency multiplexing (OFDM) principle has been proposed. The basic single-channel algorithm for the DWM formation is based on the modulation of the correlation coefficient (CC) of the DFT coefficients vector and a certain random vector. As a result of the modulation, a new vector of coefficients is calculated, which has the same Euclidean norm, a CC with a given quantized value and has the smallest mean square root deviation from the original vector. This allows to preserve the physical power of the signal in a narrow frequency band for the auditory immunity of the introduced distortion of the signal and to ensure the robustness of DWM to amplitude distortion. Under fixing the distortion level the possible types of CC modulation amplitude, phase and quadrature-amplitude, the best robustness of the DWM is provided for amplitude modulation. The off-line tests were carried out using the Sailor maritime VHF radio stations showed the possibility of realizing the DWM data transfer rate R = 125 bit/sec in the standard 3 kHz radiotelephony frequency band with the watermark-to-signal ratio WSR = –12.4 dB and signal-to-noise ratio SNR = 14 dB. The practical implementation of the automatic identification of voice transmissions using DWM in the VHF maritime radio channels can be carried out without replacing the existing radio equipment. Only a handset with a built-in microchip and a DWM decryption circuit should be connected to the VHF transceiver.
Authors and Affiliations
А. В. Шишкин, В. М. Кошевой
Keywords
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