Packet Loss Recovery and Control for VoIP

Abstract

Technology is growing rapidly which results in the rise of the VoIP technology. VoIP is a technology to transfer voice signal communication over the internet (Network). The transmission of audio data over packet switched networks faces lots of difficulties by a variety of network impairments such as packet loss, delay, echo, network security and throughput. To minimize the effect of packet loss a Packet Loss Concealment (PLC) technique is introduced in VoIP communications. Voice is a real time application and the biggest problem it faces is the loss of packets due to network congestion, delay, jitter and other network factors. The internet services implements protocols to detect and retransmit the lost packets to overcome the packet loss. However, for a real time application it is too late before a lost intermediate packet is retransmitted. This causes a need for reconstruction of the lost packets. Therefore, good reconstruction techniques must be in action to minimize the effect of packet loss during voice communication. In this thesis a concealment algorithm to reconstruct lost voice packets is reported. The algorithm is receiver based and its functionality is based on Time Scale Modifications of speech and autocorrelation of a speech signal. The technique used is Average Magnitude Difference Function (AMDF) to estimate pitch (fundamental frequency of data sample) along with Overlap and Add (OLA) technique. Method of PLC can be implemented as artificial regeneration of the packet received prior to the lost one, followed by insertion of the duplicated packet into the gap. Also lost packet can be estimated by interpolation on the basis of previously received voice packet. PLC algorithm is an end-to-end bidirectional transmission control scheme. PLC also monitor VoIP communication at both end the sender and the receiver side. Implementation of PLC minimize the effect of data loss in voice communication and overall sound quality is improved.