# High-Precision Ranging Method of 5G NR Co-Band PRS in Industrial Internet Scenarios
### Related Work  
In this section, we first investigate the high-precision ranging methods that currently exist and then elaborate on their inability to adequately meet the high-precision positioning requirements for commercial mobile communication networks. Facing industrial internet scenarios, the multipath distribution of signals is the main cause of ranging errors [12]. The methods to address multipath are primarily categorized into identification and suppression. Among them, high-resolution ranging algorithms based on multiple signal classification (MUSIC) [13], estimation of signal parameters by rotational invariance (ESPRIT) [14], and a series of variants of EKAT (ESPRIT and Kalman filter) [15] are popular for their ability to effectively discriminate channel spatial multipath. In [16], the MUSIC algorithm is used to enhance the time of arrival (TOA) measurement performance by stitching sounding reference signals (SRSs) of multiple frequency bands. Test evaluations have shown that the device can reach an accuracy of 0.3 m@90%. However, the performance of the high-resolution algorithm is limited by the number of samples and therefore requires a very high sampling rate for the terminal. Recently, timing recovery methods based on the pilot signal have become a popular research topic. Timing recovery schemes for orthogonal frequency division multiplexing (OFDM) systems, which include symbol synchronization and sample clock synchronization, were systematically introduced in [17]. By employing a path delay estimation method to enhance the performance of correlation-based symbol synchronization and a delayed phase-locked loop to improve the synchronization of the sampling clock, the timing estimation error can be reduced by several orders of magnitude. However, the system requires a uniform distribution of the pilot signals across the subcarriers. The authors in [18] used pilot symbols in the Digital Video Broadcasting-Terrestrial (DVB-T) signal to measure pseudorange in AWGN, multipath, and SFN channel environments, with an average pseudorange error of less than 20m. In an urban environment, the authors in [19] utilized LTE cell-specific reference signal (CRS) as the pilot signal and employed a phase-locked loop-aided DLL to achieve timing recovery with a root mean square error (RMSE) of 3.17 m. In [20], the author proposed a timing recovery method for the 5G standard-compliant PRS signal, which achieves a loop tracking accuracy of better than 0.13 samples, corresponding to a ranging error of less than 1.27 m.  
However, none of the above schemes consider the occupation of communication signal resources by the positioning signal. In order to achieve better ranging accuracy, it usually requires a significant amount of communication resources. For this reason, the Multi-Scale Non-Orthogonal Multiple Access (MS-NOMA) scheme has been proposed in [21], which superimposes an extremely low-power positioning signal on the communication signal and uses pseudo-random sequence codes to obtain spread spectrum gain. Experiments have demonstrated that the quality of service (QoS) of the communication signal is not affected when the positioning signal is more than 18 dB lower than the communication signal [22]. In this paper, we superimpose a low-power PRS signal close to the noise power level on the communication signal, called the Co-Band PRS signal, and design a high-precision ranging method for this signal. Compared to the methods mentioned above, Co-Band PRS offers the following three advantages. (1) Performance: The ranging performance of the proposed method in this paper is comparable to that of the super-resolution method. (2) Cost: By utilizing the time-frequency resources of communication signals and broadcasting low-power positioning signals, there is no need for operators to allocate additional communication resources or provide extra hardware support for the positioning service.