HSDPA dual streaming approach for improving VoIP speech quality in forensic applications

Today, the mobile HD-VoIP (High Definition Voice over IP) transmission represents one of the most appropriate communication techniques for the environmental wiretap applications. The perceived speech quality, which is the crucial aspect of a forensic scenario, depends on the QoS guaranteed by the wireless data service of a specific telephone operator and it is mainly due to the radio link quality, packet delay/loss, and guaranteed bandwidth. In particular, the paper presents the architecture and the performance evaluation of a dual stream approach to mobile VoIP applications (DualVoIP) over 3G/HSPA access networks. Test results, obtained via a real-time implementation of DualVoIP algorithms adopted in a practical test bed, demonstrate an average packet loss reduction of 85% and an average improvement of speech quality of about 0,8 MOS. Finally, the paper highlights the significant reduction of the audio signal clipping at all levels: phoneme, word, sentence and conversation.