A Flexible Sender-Based Packet Loss Recovery Method

Project Type: Master/Diploma Thesis
Project Status: Finished


 Voice communication over packet networks, often referred to as voice over IP (VoIP), has become commonplace. Such packet switching networks cause both varying transmission delays and loss. Methods to address packet loss can be divided into sender-based and receiver-based methods. Recently Ch. Feldbauer and B. Kleijn developed a new adaptive, sender-based packet loss recovery method that uses a bit rate-scalable secondary encoding as redundancy. The aim of this thesis is to develop a prototype in Matlab, which uses this system to provide redundancy in a robust and efficient way for an improved packet loss concealment (PLC) method for the speech coder iLBC. Using the secondary encoding, the waveform of the lost packets is reconstructed by performing pitch-synchronous overlap-and-add (PSOLA) and adding modulated noise. For different loss scenarios, including single and burst losses, performance analyses of the packet loss recovery method are presented. The new PLC approach and the PLC implemented in the iLBC codec are compared. The quality is evaluated using perceptual evaluation of speech quality (PESQ) scores. It turns out that the new invention always performs better than the iLBC codec. Especially at higher loss rates the performance gain can be increased.