## 1 Introduction
(2) The OFDM system has reconfigurable bandwidth and spectrum allocation [31]. In addition, the communication signal includes various channels (such as synchronization, broadcast, and reference signals), and numerous signal components can be used for navigation service. These NR and receiver configurations significantly influence their tracking accuracy. But no study systematically evaluated the impact of different configurations and signal components on tracking accuracy. (3) Many works research opportunity navigation based on actual signals from the LEO constellations like Starlink, and the experiment systems are complicated [30; 38; 39; 40; 41; 42; 43; 44]. These studies also lack quantitative analyses of error sources, such as clock bias and ionospheric and tropospheric delays. Providing simple, quantitative, and low-cost analysis for LEO navigation research is essential. This paper builds a simulation system of OFDM opportunity navigation to overcome these limitations. The 5G new radio (NR) is an open communication standard based on OFDM, and it is used as an OFDM signal in the simulation. A novel zero-padding correlation (ZPC) is proposed for the navigation receiver to eliminate interference from cyclic prefixes (CP) and inter-carriers (including communication and reference signals). We derive the power spectral density of NR reference signals and comprehensively analyze how different NR configurations and signal components affect tracking accuracy. Moreover, an extended Kalman filter (EKF) is designed for the LEO position. The experimental results demonstrate an 80% improvement in tracking precision and a 88.3% enhancement in positioning accuracy compared to existing NR receivers. This paper has three contributions:  
1. A system architecture for LEO NR opportunity navigation is presented in detail. We design an NR navigation receiver, and the zero-padding correlator (ZPC) is proposed to address the influence of OFDM CP and inter-carrier interference on navigation performance. For the proposed ZPC receiver, all the reference signals in NR can be utilized to provide navigation service. 2. A experiment validates that ZPC eliminates the influence caused by CP and inter-carriers and significantly enhances tracking accuracy. Compared with other works, the ZPC receiver achieves higher tracking accuracy. Moreover, the relationship between the tracking accuracy and NR configurations, including bandwidth, spectrum location, and signal components combination, is rigorously investigated. 3. We discuss the positioning performance of LEO NR based on an EKF, and simulation results show it can achieve centimeter-level accuracy. Additionally, the clock bias and ionospheric and tropospheric effects on positioning performance are quantitatively analyzed. The remainder of this paper is organized as follows. Section 2 introduces related works. Section 3 details the NR signal model, OFDM modulation, and power spectral density (PSD). Section 4 introduces the LEO NR navigation system and proposes the ZPC receiver and EKF algorithm. Section 5 discusses the advantages of ZPC in tracking accuracy. Section 6 analyzes ZPC's tracking performance under varying NR and receiver configurations. Section 7 evaluates positioning accuracy via simulations. Section 8 summarize this paper.