# Evaluation of 5G Positioning Based on Uplink SRS and Downlink PRS Under LOS and NLOS Environments
## 3 Simulation Results
The statistical metrics, including the mean error and standard deviation (SD), were computed across 100 Monte Carlo trials  
Figure 10: Ranging error of the UL-SRS and DL-PRS. Figure 9: SRS correlation detection at the UE. for both UL-SRS and DL-PRS. At a gNB separation of 100 m, DL-PRS exhibited notably lower positioning errors under LOS scenarios. For instance, with Comb Size 2 (C2), the mean positioning error was 1.943 m (SD = 0.304 m), increasing to 10.435 m (SD = 0.983 m) under NLOS. Similarly, for Comb Sizes 4 and 6, LOS mean errors exhibited a modest increase with comb size (2.531 m for C4 and 3.064 m for C6), whereas NLOS conditions led to significantly higher errors of 11.281 m and 11.313 m, respectively. In comparison, UL-SRS under the 100-m spacing also demonstrated strong LOS performance, with slightly higher mean errors than DL-PRS. The mean error for UL-SRS LOS at C2 was 2.055 m (SD = 0.303 m), which increased to 3.414 m at C8. As the distance between gNBs was augmented to 150 m, both UL-SRS and DL-PRS exhibited an anticipated escalation in error. DL-PRS LOS positioning errors grew from 2.222 m at C2 to 3.472 m at C6, while NLOS errors increased from 11.592 m to 13.139 m, with standard deviations consistently above 0.98 m. For UL-SRS, LOS performance remained competitive (e.g., 2.447 m at C2, 3.602 m at C8), while NLOS errors ranged from 9.694 m to 10.446 m, reinforcing the signal stability. Therefore, the numerical results presented in Tables 3 and 4, along with the graphical representations in Figure 11 show strong alignment. This validates the accuracy and robustness of the positioning error analysis under the LOS and NLOS conditions. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Comb Size**} & \multicolumn{3}{c}{**UL-SRS**} & \multicolumn{2}{c}{**DL-PRS**} \\ \cline{2-5}  & **LOS [m]** & **NLOS [m]** & **LOS [m]** & **NLOS [m]** \\ \hline
2 & 2.06 & 8.48 & 1.94 & 10.47 \\ \hline
4 & 2.64 & 8.85 & 2.52 & 11.16 \\ \hline
6 & — & — & 3.09 & 11.30 \\ \hline
8 & 3.41 & 9.20 & — & — \\ \hline \end{tabular}
\end{table} 
Table 3: Positioning error at BS–BS distance of 100 m.  
Figure 11: CDF of UE positioning error at BS-BS distance of: (**a**) 100 m; (**b**) 150 m.  
As illustrated in Figure 12, the positioning error performance of UL-SRS and DL-PRS signals varies with both LOS and NLOS conditions, depending on the comb sizes (2, 4, 6 and 8), and the site distance of BS-BS. According to 3 GPP specifications, PRS supports comb size 6 but not comb size 8, whereas SRS supports comb size 8 but not comb size 6. It has been observed that DL-PRS under LOS consistently achieves the lowest positioning error, measured at 1.94 m, compared to UL-SRS. Conversely, UL-SRS performs better under NLOS conditions, exhibiting a positioning error of 10.37 m, while DL-PRS under NLOS exhibits a higher error of 13.20 m. The results emphasize the importance of selecting the appropriate signal and comb size based on environmental conditions to optimize positioning accuracy. These findings clearly demonstrate that DL-PRS performs better in LOS environments, whereas UL-SRS exhibits superior resilience in NLOS scenarios. This analysis confirms that exploiting the respective strengths of each signal type, DL-PRS under LOS conditions and UL-SRS in NLOS environments, facilitates a more context-aware and accurate UE localization strategy. Figure 13 illustrates the trilateration principle for determining the UE position using the known locations of the gNBs as estimated through UL-SRS. The gNBs are represented by blue triangles, with their respective distances to the UE as shown by circles. The actual position of the UE is marked by a red star. The estimated position of the UE, determined by the intersection of the circles, is indicated by a black \"x\". The deviation between the estimated and actual positions indicates potential inaccuracies in the trilateration.