# Maximum Transmit Power for UE in an LTE Small Cell Uplink
## 4 Performance Evaluation
### HetNet Deployment with Small Cells near Macro Cell Edge  
In this section, the performance analysis for the third HetNet deployment scenario is presented. The uniform macro/small cell deployment was considered as the reference case here as well. From Figure 4, there was only one interfering ring of small cells around the central small cell. However, the interfering ring was at the macro cell edge and at a distance \(4R\) from the central small cell eNodeB. The \(P_{\max}\) value varied for the small cell uplink from 16 dBm to 23 dBm. The target was to find the \(P_{\max}\) value which resulted in the same SIR value as compared to the uniform macro cell deployment with \(P_{\max}\) = 23 dBm and a uniform small cell deployment with \(P_{\max}\) = 18 dBm.  
The interference offered to the central small cell is presented in Figure 17 using Equation (25). Compared to Figure 8, Figure 11, and Figure 14, the interference level was lower by 6.5 dB, 6.6 dB, and 5.1 dB, respectively. In Figure 17, it can be seen clearly that for the small cells, \(P_{\max}\) = 21.29 dBm corresponded to the same interference level as compared to the reference cases with \(P_{\max}\) = 23 dBm and \(P_{\max}\) = 18 dBm in the uniformly distributed macro and small cell deployments, respectively.  
Figure 16: Spectral efficiency for the small cell as a function of distance and \(\alpha_{\text{small}}\) in the HetNet deployment with small cells near the macro cell eNodeB.  
Figure 17: Interference comparison as a function of \(P_{\max}\) in the uniform macro cell and HetNet deployments.  
The impact of increased \(P_{\rm max}\) and decreased interference was observed by plotting the received SIR in Figure 18 using Equation (26). The trend with an increase in \(\alpha_{\rm small}\) can clearly be observed for the UE near the eNodeB (i.e., UE with the index 1); the received SIR decreased from 11.71 dB to 5.4 dB. Compared to Figure 5, the received SIR gain was 1.01 dB and 1.2 dB for \(\alpha_{\rm small}\) = 0.7 and \(\alpha_{\rm small}\) = 1, respectively. Similarly, compared to Figure 9, the received SIR gain was 1.21 dB and 0.8 dB for \(\alpha_{\rm small}\) = 0.7 and \(\alpha_{\rm small}\) = 1, respectively. Meanwhile, for the UE near the cell edge (i.e., UE with the index 6), the received SIR improved from 3.7 dB to 5.4 dB. The received SIR gains as compared to Figure 5 were 0.5 dB and 1.2 dB, while the gain compared to Figure 9 were 0.6 dB and 0.8 dB. The results for the spectral efficiency presented in Figure 19 further validate our argument, where a significant gain in the system performance can be observed by revisiting the \(P_{\rm max}\) limit. This HetNet deployment scenario shows significant gain in system performance, as the interfering ring of the small cell was far away from the central small cell, and the increased \(P_{\rm max}\) value resulted in higher received SIR for all the UE. The \(P_{\rm max}\) limits for the considered network deployments are summarized in Table 2.  
Figure 19: Spectral efficiency for the small cell as a function of distance and \(\alpha_{\rm small}\) in the HetNet deployment with small cells near the macro cell edge.  
Figure 18: SIR as a function of \(\alpha_{\rm small}\) in the HetNet deployment.  
As expected earlier, such a HetNet deployment with \(P_{\text{max}}\) = 21.29 dBm offers advantages in terms of received SIR by adopting FPC instead of full compensation. The further optimization of the \(P_{\text{max}}\) value by considering various energy efficient deployment strategies such as small cell on/off, non-uniform, and mobile small cell deployment in the macro cell, and other cell-specific features will be continued in future work.