## 1 Introduction
Reference [17] achieves vehicle positioning in tunnels through the dense deployment of pseudolites, combined with laser ranging and a digital elevation model (DEM) [17]. This system requires a large number of anchor nodes inside the tunnel, increasing deployment costs and system complexity, and positioning accuracy is susceptible to interference from parallel vehicles. Reference [18] combines GNSS, INS, and odometry (OD) and uses LiDAR lateral distance measurements and lane constraints for precise positioning [18]. This method relies on LiDAR lateral distance measurements and lane constraints to eliminate INS-accumulated errors, but increased traffic inside the tunnel can affect positioning accuracy. Reference [19] establishes a high-precision external geographic mapping network using GNSS technology by deploying measurement points outside the tunnel to achieve positioning during tunnel construction [19]. This method relies on GNSS technology outside the tunnel, but GNSS signals cannot cover the tunnel's interior, limiting its application deep within. Although this method reduces errors through the external network, errors may accumulate progressively as the measurement distance increases deep inside the tunnel. Reference [20] achieves positioning in tunnels without GNSS signals by integrating V2X communication technology, UWB, INS, and map matching techniques [20]. However, the algorithm does not address the elimination of accumulated INS errors, making it unsuitable for long-duration vehicle positioning. Reference [21] uses Doppler shift and ToA measurements, combined with V2I communication signals, applying extended Kalman filters (EKFs) and KFs to correct signal propagation errors to achieve vehicle positioning in tunnels [21]. Although this method uses filtering techniques to correct propagation errors, severe multipath effects in tunnels still impact the accuracy of Doppler shift and TOA measurements. Compared to traditional antennas, the LCX cable demonstrate superior performance in mobile communication within enclosed environments such as tunnels [22]. The uniform signal coverage characteristic of the LCX cable ensures consistent signal strength distribution throughout the space, avoiding the signal blind areas that are often present with traditional antennas in certain areas [23; 24]. Additionally, the LCX cable emits signals continuously along its length, reducing the number of reflected signal paths and mitigating the multipath effect during signal transmission [25]. Currently, several researchers are leveraging LCX cables to address positioning challenges, with most approaches combining LCX cables with non-GNSS signals. Reference [26] implements RF fingerprinting and signal power intensity difference analysis in conjunction with high-loss and step-attenuation LCX cables to achieve indoor positioning [26]. However, the positioning accuracy of the system is compromised due to the effects of multipath propagation and multi-point coupling. Reference [27] explores a positioning method utilizing LCX cables and Time-Code Division Multiplexing Orthogonal Frequency Division Multiplexing (TC-OFDM) signals [27]. This method demonstrates strong positioning performance in low-signal-to-noise ratio (SNR) environments. However, its accuracy is reduced in high-SNR conditions. Reference [28] proposes a two-dimensional measurement method using LCX cables for wide-area monitoring. This method achieves two-dimensional target position detection through multi-frequency measurement techniques and employs propagation delay and beamforming technology to estimate the precise location of the target [28]. At present, GNSS enables high-precision positioning in open environments. While many studies have achieved positioning within indoor or tunnel environments, they are often unable to utilize existing GNSS receivers and require significant initial infrastructure deployment or the creation of detailed databases, leading to high system deployment costs.