# QoE Optimization in a Live Cellular Network through RLC Parameter Tuning
## 6 Proof of Concept
### Real Network
#### 6.2.2 Results and Discussion  
Like the tests carried out in the simulated environment, the parameters or factors selected to configure the TM-based controller were the RLC AM timers t-StatusProhibit and t-PollRetransmit. As the initial ranges of values to be evaluated for these two parameters, the ranges of values allowed in the network were selected, which in the case of t-StatusProhibit ranged from 0 ms to 500 ms and in the case of t-PollRetransmit spanned from 5 ms to 500 ms. For each configuration parameter, three levels were defined. The TM  
\begin{table}
\begin{tabular}{c c} \hline \hline  & 2 Terminals \\ Scenario & (A MONROE Node and a Smartphone) \\  & Each Connected to a Picocell \\ \hline System bandwidth & 20 MHz \\ \hline Serving cell & \\ reference signal & \(-\)7.6 dBm \\ transmission power & \\ \hline Interfering cell & \\ reference signal & \(-\)14.9 dBm \\ transmission power & \\ \hline RLC mode & AM \\ \hline RLC parameters & t-StatusProhibit: 0–500 ms \\  & t-PollRetransmit: 5–500 ms \\ \hline Mobility & Static user \\ \hline Transmission direction & Download \\ \hline Service & File transfer service (file size: 20 MB) \\ \hline e-NodeB (Picocell) & Omnidirectional antennas \\  & MIMO \\ \hline Scheduler & Enhanced proportional fair \\ \hline TTI & 1 ms \\ \hline \hline \end{tabular}
\end{table}
Table 2: Configuration of the UMAHetNet network.  
stop criterion was set to 0.2. The response metric to be maximized in this case was the E2E throughput obtained in file transfer experiments.  
Figures 9 and 10 show the adjustment of t-PollRetransmit and t-StatusProhibit, respectively. Thus, the values adopted for each of these parameters in the experiments performed during the optimization process are shown. In these figures, the functioning of the optimization algorithm can be observed. The TM-based controller progressively reduced the search range to find the combination of t-PollRetransmit and t-StatusProhibit that maximized the E2E throughput. For the tested scenario, this combination of parameters matched a t-PollRetransmit value of 9.53 ms and a t-StatusProhibit value of 162.4 ms.  
Finally, Figure 11 shows the E2E throughput obtained in each of the experiments performed during the optimization process (in blue) and its moving average (in red). It can be seen that the maximum throughput value was obtained for those values of the timers selected by the TM-based controller. As in the tests carried out in the simulator for the file transfer service, QoE optimization was achieved by reaching a tradeoff between excessively small and large values of the t-StatusProhibit and t-PollRetransmit timers. If the timers were set to very small values, there would be excessive control traffic, and the delay in sending the information would increase. Excessively large timer values would lead to the lack of acknowledgment of received packets and therefore the collapse of the transmission window and the loss of packets. The optimal values obtained in the t-StatusProhibit and t-PollRetransmit test are specific to this scenario and may vary depending on the environment conditions in which the algorithm is applied.  
Figure 10: Real environment—t-StatusProhibit adjustment.  
Figure 9: Real environment—t-PollRetransmit adjustment.