## 6 NR Tracking Performance Analysis for Different NR and Receiver Configuration
### Impact of NR Signal Configuration on Tracking Accuracy  
As described in Section 4, NELP is used as a code tracking loop and its theoretical tracking accuracy is as follows [76]:  
\[ \begin{split}\sigma_{\text{NELP}}=&\sqrt{\frac{B_{ \text{LDLL}}(1-0.5B_{L}T_{\text{coh}})\int_{-\beta_{r}/2}^{\beta_{r}/2}G(f) \sin^{2}(\pi f\Delta)df}{\left(\frac{C_{\text{env}}}{N_{0}}\right)\left(2\pi \int_{-\beta_{r}/2}^{\beta_{r}/2}fG(f)\sin(\pi f\Delta)df\right)^{2}}}\\ &\times\sqrt{1+\frac{\int_{-\beta_{r}/2}^{\beta_{r}/2}G(f)\cos^{2 }(\pi f\Delta)df}{T_{\text{coh}}\left(\frac{C_{\text{env}}}{N_{0}}\right) \left(\int_{-\beta_{r}/2}^{\beta_{r}/2}G(f)\cos(\pi f\Delta)df\right)^{2}}}\end{split}  \tag{38}\]  
where \(G(f)\) denotes the normalized PSD of the navigation signal, and \(\beta_{r}\) represents the receiver front-end bandwidth. \(\Delta=2d\) is the time interval between the early and late branches, and \(B_{\text{LDLL}}\) is the bandwidth of DLL. \(C_{\text{env}}/N_{0}\) is the carrier-to-noise ratio, which can be determined by LEO transmit power (Appendix A). Unless otherwise specified, all NR signals follow default configurations listed in Table 1. This section only utilizes PDSCH DMRS as a local replica signal to evaluate the impact of NR configurations on tracking accuracy. The NR's PDSCH contains 10 resource blocks (RBs), each comprising 12 subcarriers with a 15 kHz spacing. Hence, the default NR signal contains 120 subcarriers, and its bandwidth is 1.8 MHz. The center frequency of PDSCH is located at zero frequency. The DLL tracking accuracy significantly depends on three key configurations: _signal bandwidth_, _spectral distribution_, and the _proportion_ of NR reference signal. The base station flexibly configures these parameters according to the communication scenario. First, we discuss the relationship between tracking accuracy and signal bandwidth. The experiment chooses three signal bandwidths: 1.8 MHz, 3.6 MHz, and 5.4 MHz. Their corresponding reference signal PSD and DLL standard deviation (STD) are depicted in Figure 8. The comparison results reveal that expanded NR bandwidth significantly enhances the DLL tracking accuracy. At a fixed transmitting power of 60 dBm, the DLL tracking accuracy improves from 0.1187 m (1.8 MHz) to 0.0605 m (3.2 MHz) and 0.0506 m (5.4 MHz), respectively, by 49.03% and 65.80%. When the NR bandwidth increases, its spectral redistribution moves to higher frequencies. This spectral redistribution leads to higher tracking accuracy. Moreover, the tracking accuracy increases with transmitting power. Each five dBm power increment generates approximately 44% improvement in DLL tracking accuracy. The spectral location of the NR signal constitutes another critical factor affecting tracking performance. For a fixed bandwidth NR signal, its center frequencies are placed at 0, 130\(\Delta f\), and 260\(\Delta f\), respectively. The receiver front-end bandwidth is 15.36 MHz to ensure complete signal reception. The relationship of NR signal spectral location and tracking accuracy is shown in Figure 9. We can find that the tracking accuracy increases with the center frequency of the NR signal. Under 60 dBm transmitting power, the tracking accuracy achieves 86.35% enhancement when the center frequency shifts from zero frequency to 260\(\Delta f\). Moving the NR spectral to a higher frequency is conducive to improving tracking accuracy. Notably, the NR spectral should be within the receiver front bandwidth to ensure the integrity of the received NR signal. Figure 8: Relationship between NR signal bandwidth and tracking accuracy. (**a**) PSD of NR reference signal; (**b**) DLL STD with different bandwidth NR signal. At 60 dBm transmitting power, the DLL has 65.8% accuracy gain at 5.4 MHz compared to 1.8 MHz. Figure 9: Relationship between signal frequency location and tracking accuracy. (**a**) PSD of NR reference signal; (**b**) DLL STD with different NR frequency location.