Unequal Protection Mechanism for Digital Speech Transmission Based on Turbo Codes

In this paper, the Turbo-based unequal protection mechanism for reliable transmission of speech signal is studied. In order to obtain the hierarchical importance regularity of information bits for each sampling point, the changing value caused by the variation of each bit in 8-bit folded code of pulse-code modulation is first calculated. According to the obtained hierarchical importance of information bits, two unequal error protection (UEP) schemes of 3-level and 8-level are proposed based on Turbo codes. In order to achieve the satisfactory error protection capability for the global speech signal, the nonuniform puncturing is utilized in these two schemes, which can adaptively assign more parity bits for error protection to more important information bits. Compared with the traditional equal error protection (EEP) scheme, our schemes not only have greater coding rate, but also have generally better quality of the decoded speech signal on the receiver side, especially in poor channel condition. Experimental results demonstrate the effectiveness of the proposed schemes.