On the effect of the physical layer on VoIP Quality of user Experience in wireless networks

Thanks to the expansion of wireless networks, Voice over IP (VoIP) is becoming widespread. Because of the particular characteristics of the physical layer of wireless scenarios, providing good levels of quality has become a new challenge for multimedia services. The current trend is to measure the Quality of user Experience (QoE), instead of only assessing network metrics (Quality of Service, QoS). This paper evaluates, via simulation, the effect of the fading channels on VoIP traffic for IEEE 802.11 systems and its influence over QoE. Moreover, we evaluate the effect of fading over system coverage range and VoIP capacity, using different codecs and different bandwidths. We employ two statistical propagation models, namely, Rice and Rayleigh, in order to represent different fading environments. The Free Space model is also used to evaluate the system performance under non-fading situations. From the results achieved, we observe that i) fading channels have a noticeable negative effect over VoIP communication QoE, mainly affecting low bit-rate codecs, and ii) fading also has a severe impact on the network coverage range and VoIP capacity, represented by a reduction of the maximum number of valid VoIP calls accepted by the system.