Effects of the wireless channel, signal compression and network architecture on speech quality in VOIP networks

摘要

Voice over Internet Protocol (VoIP) telephony is an emerging technology slowly finding its way into military applications. It provides several advantages over PSTN but comes short on performance, quality of service and availability. The purpose of this thesis is to measure the quality of voice in VoIP communications. More specifically it investigates the effects of wireless channel conditions as well as channel coding and compression on the received speech quality. Both simulation and experimentation are conducted using Matlab code and Speex software and across commercial VoIP networks. Simulation shows that fading channel parameters can heavily affect the quality of received speech. Speech compression results in bit rate gain, but, on the other hand, the signal becomes more sensitive to errors. The performance of an outdoor wireless network is better than that of an indoor network. The VoIP network architecture can affect the received speech quality on a long-distance connection.