Secure communications through speech dedicated channels using digital modulations

The usage of networkspsila speech channels for secure communications or data transmission could be interesting in the case of lack of data channels. In this paper, a scheme for secure communications over voice-dedicated channels of mobile networks, using digital modulations, is proposed. When transmitted over speech channels, the secure communication signal transmission could be subjected to a high damage, especially in mobile networks, due to the presence of speech coders. The technical reasons behind the signalpsilas degradation are discussed. The performances of the transmission of digital modulated signals through speech coders are presented for QAM and OFDM modulations, after optimization of their parameters. The voice activity detector sharpens the signal degradation. Its role is detailed in this paper, and a method to eliminate its negative effect is introduced. Simulation results, in terms of binary error rate, will give prominence to the possibility of establishing a communication at a bit rate high enough to transmit voice, coded at low bit rates and ciphered. The type of the low bit rate coder that could be used is studied, considering the coding bit rate, and the influence of the binary error rate on the quality of the coded speech.