# Congestion Analysis of Transport Layer in a Multicell 5G DL Communication System
## 4 Discussion  
This section presents the simulation results and discussion according to the simulation environment using the scenarios defined in Table 3.  
**Single-cell environment:**  
Figure 4 shows the impact of the number of users on the utilization of the downlink PRBs. After the PRB utilization rate reached approximately 70% with 80 UE devices, its variation became nonlinear and, at approximately 140 UE devices, it began to level off with a 100% PRB utilization rate. The data volume, which, in this context, refers to the data waiting in the buffer to be sent, was relatively stable up to approximately 80-90% PRB utilization, as presented in Figure 5. After that point, it started to rapidly increase because, as the number of UE devices increased, the amount of data that had to be delivered by the gNB also increased; however, there were no free PRBs. The charts in Figures 6 and 7 show how the cell throughput shifts when the number of users in the cell and the PRB utilization both increase. The cell throughput in the downlink direction shows linear growth. In Figure 6, we can observe that the maximum throughput for a cell is 1.2 Gbps. The throughput achieved is extremely high because of additional  
Figure 4: DL PRB utilization vs. number of users. Figure 5: DL data volume vs. PRB utilization. capabilities, such as 4x4 MIMO and 256 QAM modulation. The cell throughput is 800 Mbps when there are 100 UE devices. When the number of users in a cell doubles, the throughput of the cell increases by approximately 50%, reaching a maximum of 1.2 Gbps (see Figure 7). The changes in the cell edge user throughput in response to the number of PRBs and the total number of cell users are emphasized in Figures 8 and 9, respectively. As the number of UE devices in the cell increases, the cell edge user throughput available decreases due to the increase in PRB utilization. An average throughput of 20 Mbps at the cell edge can be observed with approximately 40% PRB utilization, which is equivalent to approximately 70 UE devices in the cell. After this point, the cell edge user throughput is extremely low. User throughput decreases with the increase in PRB utilization as there are more UE devices in the cell. This trend can be seen in Figures 10 and 11, which present how the relationship between the two variables evolves over time. Between 10 and 50% PRB utilization, the user throughput is between 650 Mbps and 500 Mbps, respectively. The decline in user throughput follows a linear pattern, with a more noticeable incline after 50% load in the cell. A maximum user throughput of 650 Mbps is achieved when there are 20 UE devices. This value drastically falls to half (i.e., 375 Mbps) when there are 100 UE devices. From 160 UE devices onward, the user throughput is at its lowest. Figure 6: DL cell throughput vs. PRB utilization. Figure 7: DL cell throughput vs. number of users. Figure 8: DL cell edge user throughput vs. PRB utilization. Figure 10: DL user throughput vs. PRB utilization. Figure 9: DL cell edge user throughput vs. number of users. Figures 12 and 13 indicate how latency in the downlink changes as the number of UE devices in the cell and the use of PRBs increase. The delay gradually increases up to roughly 98% PRB utilization in the cell, at which point it begins to increase exponentially, reaching a maximum of 45 ms at 100% PRB utilization. The delay begins to increase when the cell has approximately 140 UE devices, which indicates that, with that number of UE devices, there is already a load that is close to 100% PRB utilization. **Multicell environment:**  
This section presents the results obtained with the multicell scenario, where we simulated three cells. Figure 14 presents the PRB utilization according to the number of users. It can be observed that, at 45 UE devices, the PRB utilization is 50%, and it increases linearly until there are approximately 100 UE devices, at which point it saturates at around 100% PRB usage. Data volume represents the data waiting to be transmitted in the buffer.