## 3 MOS-Aware Measurement Scheme in Mobile Networks
### Video Conference MOS Measurement  
The real-time video conferencing MOS values were calculated based on the experimental results in [25]. The tool used to test video conferencing was Skype. Since Skype supports variable video bit rates, it is often used for real-time video processing by adjusting the video resolution and FPS. Table 2 lists the video-related parameters used by Skype. Skype can support up to 640 \(\times\) 480 resolution, 30 FPS and 950 Kbps bit rate, and it can be reduced to 160 \(\times\) 120 resolution, 5 FPS and 5 Kbps bit rate when the network conditions are not sufficient to support it. According to the test experiments in [26], video transmission in video conferencing relies mainly on the UDP protocol. The factors affecting the quality of video conference are packet loss rate, video bitrate and frame rate. The video bitrate is calculated as shown in Equation (1), which represents the amount of data that can be received during a video conference. When the packet loss rate is less than 10%, the amount of received data \begin{table}
\begin{tabular}{c c c} \hline \hline MOS & Quality & Impairment \\ \hline
5 & Excellent & Imperceptible \\
4 & Good & Perceptible but not annoying \\
3 & Fair & Slightly annoying \\
2 & Poor & Annoying \\
1 & Bad & Very Annoying \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The relationship between MOS and VoIP. \begin{table}
\begin{tabular}{c c} \hline \hline Video resolution & 640 \(\times\) 480, 320 \(\times\)240, 160 \(\times\) 120 \\ \hline Frame rate per second & 5–30 fps \\ \hline Video bitrate & 5–950 Kbps \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Skype video codec parameters. depends on the current available throughput, and when the available throughput is more than 1 Mbps, the amount of received data is sufficient for the video conference. When the packet loss rate is greater than 10%, due to the continuous loss of packets, it is difficult to meet the requirement of video conference, and then the first priority will be to ensure the transmission quality of sound, thus the BW value will be fixed at 21 Kbps. \[\mathrm{R_{v}}\ =\ \left\{ \begin{array}{cc}(1-0.15-4.5\mathrm{PL})(0.77\mathrm{ BW}-10.8)&\mathrm{PL}<10\%\\ (1-0.15-4.5\mathrm{PL})\times 21&\mathrm{PL}\geq 10\%\end{array} \right. \tag{1}\]  
Equation (2) represents the relationship between the amount of received data and the frame rate. The measurement results are shown in Figure 4, which illustrates that the fps (frame per second) can achieve 28 fps when the video bit rate is greater than 200 kbps and can only maintain 5 fps when the bitrate is less than 20 kbps. \[f(\mathrm{R_{v}})\ =\ \left\{ \begin{array}{cc}5&\mathrm{R_{v}}\leq 20\\ 10&20<\mathrm{R_{v}}\leq 80\\ 15&80<\mathrm{R_{v}}\leq 200\\ 28&200<\mathrm{R_{v}}\end{array} \right. \tag{2}\]  
The video bitrate and frame rate obtained from Equations (1) and (2) can be used to calculate the current MOS for the video conference service, defined in [21]. In Equation (3), where \(\mathrm{I_{coding}}\) represents the video quality under the influence of video bitrate and frame rate and PL represents the packet loss rate, \(\mathrm{D_{PL}}\) indicates the extent to which the robustness of the video quality is affected by packet loss. \[\mathrm{MOS}\ =\ 1+\mathrm{I_{coding}}\exp\left(-\frac{\mathrm{PL}}{\mathrm{D_{ PL}}}\right) \tag{3}\]  
The \(\mathrm{I_{coding}}\) is shown in Equation (4), where \(\mathrm{I_{off}}\) represents the ideal video quality that can be achieved at the current video bitrate, \(\mathrm{f(R_{v})}\) represents the current fps, \(\mathrm{O_{fr}}\) represents the ideal frame rate that can be achieved at the current video bitrate, and \(\mathrm{D_{fr}}\) represents the extent to which the robustness of the video quality is affected by the frame rate. \[\mathrm{I_{coding}}\ =\ \mathrm{I_{O_{fr}}}\times\exp\left\{-\frac{\left[ \mathrm{ln(f(R_{v}))-\mathrm{ln(O_{fr})}}\right]^{2}}{2\mathrm{D_{fr}}^{2}}\right\} \tag{4}\]  
Figure 4: The relationship between the amount of data received and the frame rate.