VoIP Voice and Fax Signal Processing

5.5 PLC TECHNIQUES DESCRIPTION

In this section, the G.711 pitch-based technique, the T1.521a LP technique, and an overview on hybrid techniques are presented for performing a PLC operation.

5.5.1 PLC Based on G.711 Appendix-I

The PLC scheme as per G.711 Appendix-I recommendation [ITU-T-G.711 (1999)] is the most popular packet loss concealment scheme to use with G.711 and G.726 waveform-based codecs. The G.711 Appendix-I PLC is known as the PLC scheme based on Annex A. The G.711 Appendix-I scheme gives reasonably better and acceptable quality at low complexity of computation. Unlike CELP-based coders such as G.729, G.723.1, and G.728, the codec G.711 has no model of speech production. With CELP-based coders, the decoder's state variables take time to recover after an erasure. PLC in G.711 has the ability to recover rapidly to the original signal after an erasure is over. This PLC scheme is well characterized and widely used in deployments. The results are available in the published literature for different conditions [Britt (2007), ITU-T-G.107 (2005), ITU-T-G.113 (2002), ITU-T-G.113 (2007), TIA-EIA-810A (2000), TIA-EIA-116A (2006)].

The G.711 Appendix-I scheme is shown in Fig. 5.4. This figure is a simplified version to represent the principle of the scheme. In this decoder path, the jitter buffer provides voice packets to the decoder. The packet type information is analyzed by the control block. This block generates required control and timing information to various internal blocks ...