A Transmission Scheme for Encrypted Speech over GSM Network

With the widely applications of mobile communication networks, end-to-end secure voice has become a very important research issue and has attracted many people¿s interests. A simple and effective method for end-to-end secure communication is to encrypt speech signal at user ends. But the use of encryption techniques leads to a hard problem that encrypted speech data can not be directly transmitted on mobile voice channel. In this paper, we propose a scheme for encrypted speech transmitting on GSM voice channel. Not only does this scheme offer a good method for encrypted speech accessing mobile voice channel by using a proposed special modem called smodem based on linear predictive coding (LPC) technique, but also it can ensure the encrypted data transmitting through GSM networks with sufficient accuracy so that the received data can be decrypted correctly at the receiver. Moreover, the proposed scheme has advantages of no change to the existing clear voice communication procedure, short time of call establishment and propagation delay, good interoperability over heterogeneous networks, and favorableness to encryption information hidden. The results of experiment show that the proposed scheme is feasible.