Performance evaluation of QoE in VoIP traffic under fading channels

Voice over IP (VoIP) and wireless networks are technologies that are receiving an increasing interest by both, the research community and the final users. For instance, the effect of layer two handoffs, delay constraints, channels with constant bit error rates, packet size, UDP traffic, TCP traffic, overheads from different layers, etc., have been exhaustively evaluated for VoIP over wireless networks. Surprisingly, the effect of the physical layer has been barely addressed in the related literature. This paper evaluates, via computer simulation, the effect of fading channels on VoIP traffic for IEEE 802.11 systems and its influence on the Quality of user Experience (QoE). We use the Nakagami-m propagation model in order to represent different physical radio propagation environments. A complete study about the effect of fading over system capacity, coverage range, and QoE is provided. To this end, we simulate several scenarios, with different codecs, different packetization time intervals, and different bandwidths. From the results achieved, we observe that fading channels have i) a severe impact on the network capacity, represented by a reduction in the maximum number of valid VoIP supported calls, ii) a reduction of the network coverage accepting VoIP calls, and iii) a degradation of the QoE evidenced by a reduction of the assessed Mean Opinion Score.