# Evaluation of 5G Positioning Based on Uplink SRS and Downlink PRS Under LOS and NLOS Environments
## 4 Discussion  
The performance analysis of UL-SRS and DL-PRS reveals distinct behaviors under both LOS and NLOS conditions. Initially, the correlation results of UL-SRS and DL-PRS are examined, where each gNB selects a unique SRS and PRS ID to ensure the transmission of orthogonal sequences. Figure 10 illustrates the ranging error, emphasizing the discrepancy in estimating the distance between the UE and the gNB under varying comb sizes. The positioning error performance and its accuracy are further evaluated through CDF and bar charts, depicted in Figures 11 and 12, respectively. Tables 3 and 4 present a summary of the final results, including positioning errors (in meters) for UL-SRS and DL-PRS across various comb sizes and inter-site distances. These results highlight the respective strengths and limitations of UL-SRS and DL-PRS, shaped by their distinct transmission structures and processing mechanisms. According to 3 GPP TS 138.211 V16.2.0, clause 7.4.1.7.3 PRS supports comb sizes of 2, 4, and 6, while SRS supports comb sizes of 2, 4, and 8, as per 3 GPP TS 138.211 V17.1.0, clause 6.4.1.4.2. In LOS scenarios, DL-PRS consistently outperforms UL-SRS, achieving lower positioning errors. For example, at a comb-2 and BS-BS distance of 100 m, DL-PRS achieves a positioning accuracy of 1.94 m, which is slightly better than UL-SRS at 2.06 m. This advantage arises because, in LOS conditions, the UE receives a strong, direct signal from the gNB, enabling accurate TOA estimation. An increase in the BS-BS distance to 150 m has been shown to result in substantial alterations. In the LOS scenario, the DL-PRS positioning error increased to 2.25 m while the UL-SRS exhibited a positioning error of 2.44 m. However, DL-PRS performance significantly deteriorates in NLOS environments, with positioning errors increasing from 10.47 m to 11.30 m. This degradation highlights the UE's limited ability to process weak or reflected signals in the absence of a direct path, making TOA estimation more susceptible to errors caused by obstacles. In contrast, UL-SRS exhibits enhanced robustness in NLOS conditions, with a BS-BS distance of 100 m, maintaining lower positioning errors as compared to DL-PRS. The range of positioning errors, from 8.48 m at comb-2 to 9.20 m at comb-8, reflects the system's adaptability to urban environments. It has been demonstrated that a significant change occurs when the BS-BS distance is increased to 150 m. The UL-SRS positioning error under NLOS ranges from 9.62 m to 10.37 m, a significant improvement over the DL-PRS. The DL-PRS positioning error under NLOS ranges from 11.64 m to 13.20 m. This resilience stems from the uplink transmission approach, where the signal is transmitted from the UE to the gNB. The gNB is equipped with advanced signal processing capabilities, higher  
Figure 14: UE position through DL-PRS under: (**a**) LOS; (**b**) NLOS. precision, and better time synchronization, which can effectively mitigate errors. Uplink transmissions are enhanced by timing advance adjustments, where the gNB tightly controls the UE transmission timing to compensate for propagation delays. In contrast, DL-PRS relies on UE-based processing, where the presence of obstacles in NLOS conditions leads to positioning errors. Tables 3 and 4 present the final positioning results for both UL-SRS and DL-PRS. It is important to note that the entries marked with a \"--\" indicate configurations that are not applicable in this context. According to 3 GPP specifications, PRS supports comb size 6 but not comb-8, whereas SRS supports comb size 8 and does not include comb-6. The findings highlight the efficacy of DL-PRS in high-accuracy positioning within LOS environments, where the transmission of a robust, direct signal facilitates precise UE estimation. In contrast, UL-SRS demonstrates superior performance in NLOS scenarios due to the advanced processing capabilities of the gNB.