Subjective Audio Quality over Secure IEEE 802.11 Wireless Local Area Networks

This paper presents the results of experiments to measure subjective G.711 audio quality resulting from wireless transmission over encrypted IEEE 802.11b, IEEE 802.11g, and IEEE 802.11n draft 2.0 wireless local area networks (WLANs). Following ITU-T Recommendation P. 800, forty-two human subjects rate audio recordings taken during 12 network conditions. WLAN encryption is alternated between WPA2 and WPA2 with transport mode 3DES IPsec, and simultaneous call volume is alternated between 6 or 10 simultaneous calls. Results indicate that a previous E-model calculation for 802.11b accurately predicts the subjective Mean Opinion Score (MOS). The upper bound for the decline in MOS due to 3DES IPsec is found to be less than 0.65 (90% CI) for all scenarios examined. Additionally, the subjective data suggest that the combination of G.711 encoding and 802.11 transmission makes toll quality (MOS > 4.0) calls over an encrypted 802.11 WLAN impractical.