VoIP Voice and Fax Signal Processing

5

PACKET LOSS CONCEALMENT TECHNIQUES

In VoIP network packet drops, packet delay, delay variations, errors, and fragmentation are very common and may degrade voice quality significantly. Packet loss concealment (PLC), also known as packet erasure concealment, synthesizes the missing voice samples during the packet erasures without creating the noticeable artifacts. This chapter on PLC is presented for improving the voice quality in the presence of packet drops. PLC techniques are categorized as transmitter–receiver- and receiver-only based.

Transmitter–receiver-based techniques are simply referred to as transmitter-based techniques and as encoder–decoder-based techniques. In this method, receiver support is required and both transmitter and receiver use the same technique. Transmitter-based techniques are commonly applicable to all compression codecs. These techniques are based on standard methods of redundancy and forward error correction. Receiver-only methods are known as decoder-based techniques. Receiver-based techniques are based on the selected codec and can accommodate nonstandard and proprietary techniques. In this chapter, generic transmitter-based methods and waveform-coding-based receiver methods are given.