# Effect of AQM-Based RLC Buffer Management on the eNB Scheduling Algorithm in LTE Network +
## 6 Simulation Result and Performance Evaluation  
In this section, we first demonstrate the effectiveness of different versions of SmRED as compared to the original RED algorithm. With the topology in Figure 6, we have simulated different versions of SmRED where the Guaranteed Bit Rate (GBR) video traffic is downloaded from the source to the target UEs. The number of UEs is varied from 2 to 10 to demonstrate different traffic-loads. We set 15 resource blocks in eNB to serve the UEs. This means that the channel bandwidth is 3 MHz (Other values for resource blocks are 6, 25, 50, 75, 100. We set the value 15 in order to create a bottleneck in the LTE wireless access part. So, even with 10 parallel TCP connections, i.e., 10 UE, the traffic load is considered high when the application is sending packets at a rate of 100 Mbps). The results are shown in Figures 8 and 9. \begin{table}
\begin{tabular}{c c} \hline \hline
**Simulation Parameter** & **Value** \\ \hline Radio Link Control (RLC) Buffer Size & 100\(\sim\)200 \\ Number of Traffic Source & 2\(\sim\)10 \\ Pkt Size & 1000 Bytes \\ Number of Resource Block & \\ Application Data Rate & 100 Mbps (i.e., 1250 Packets/s) \\ Wired Link Capacity & 10 Mbps \\ Wired Link Delay & 50 ms \\ eNB Transmission Mode & SISO \\ Transmission Control Protocol (TCP) Traffic Type & Cubic \\ Handover Algorithm & A3 Rsrp \\ Mobility & Random Walk 2D \\ Node Movement Speed & 20 m/s \\ Total Simulation Time & 100 s \\ Application Start Time & From 0.1 s \\ Application Stop Time & 100 s \\ Simulation Area & Single and multi cell with 5 Km Radius \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Different Simulation Parameters in ns3. From the results, we can see that, in a low traffic-load condition, a higher value of \(i\) gives higher throughput and lower delay. In fact, \(i=5\) behaves like Droptail. This is because, when the traffic-load is low, higher values of \(i\) result in lower dropping probability and even no dropping occurs for some cases. However, as the traffic-load is increasing, higher values of \(i\) such as \(i=5\) failed to provide the optimal performance. This is because, for the high traffic-load condition, if the dropping probability is set too low (before the Target), then the AQM algorithm failed to inform the TCP source about the possible congestion more in advance. As a result, the queue becomes full and packet dropping as well as TCP timeout occurs and the TCP window size enters into the slow start phase, which results in lower throughput and higher delay. On the other hand, the dropping probability should not be set too high (after the Target), so that unnecessary dropping can be avoided. From the result, we can see that SmRED with \(i=4\) achieves a better balance between the throughput and the delay as compared to other versions. To understand the performance of RED as compared to SmRED-4, we varied the RLC buffer size as the input parameter and calculated the average packet loss rate in percentage with the high traffic load scenario (10 parallel TCP connections) and moderate traffic load scenario (4 parallel TCP connections). The buffer size was varied from 100 packets to 200 packets with a granularity of 25 packets. The simulation results are shown in Tables 2 and 3 for high load and moderate load respectively. As can be seen from the table, the packet loss rate of SmRED-4 is lower than that of RED  
Figure 8: End-to-end average throughput of different versions of Smart RED (SmRED). Figure 9: End-to-end average delay of different versions of SmRED. with buffer size changed throughout the whole range. With the high traffic load scenario, the reduction rates of the packet loss rates of SmRED-4 compared with RED increased from 3.05 to 14.05. On the other hand, when the traffic load is moderate, the reduction rate is increased from 17.99 to 34.19. This is because, when the traffic load is low, the dropping probability of SmRED-4 is low. So, unnecessary packet dropping is avoided.