Tunnel high-precision positioning system based on fusion of leaky coaxial cable and pseudo-satellite

Abstract

The invention belongs to the technical field of tunnel positioning, and discloses a tunnel high-precision positioning system based on fusion of leaky coaxial cables and pseudo satellites, and the system comprises a conduction unit which generates BDS / GPS dual-system navigation signals; the main control clock unit is configured with a dual-mode clock taming module and generates a local carrier signal homologous with a main clock; the leaky coaxial cable is made of a radiation type low-smoke halogen-free flame-retardant polyolefin sheath material; the indoor and outdoor integrated positioning terminal realizes indoor and outdoor positioning by combining the signal transmission characteristics of the leaky coaxial cable; and the comprehensive management platform supports real-time trajectory tracking, electronic fence alarm and multi-dimensional data analysis, and provides real-time monitoring and safety management. According to the tunnel high-precision positioning system based on fusion of the leaky coaxial cables and the pseudo satellites, random errors caused by asymmetric paths in traditional Ethernet synchronization are overcome through the deterministic time delay characteristic of a physical transmission medium, and therefore the synchronization precision superior to that of a traditional industrial Ethernet is achieved.

Description

Technical Field

[0001] This invention relates to the field of tunnel positioning technology, and in particular to a high-precision tunnel positioning system based on the fusion of leaky cable and pseudo-satellite. Background Technology

[0002] During the construction and operation phases of tunnel engineering, accurate positioning of personnel and equipment is a core requirement for ensuring construction safety and improving operational management efficiency. With the continuous expansion of tunnel construction scale and the ongoing improvement of construction safety standards, higher demands are placed on the accuracy, signal coverage integrity, deployment convenience, and equipment compatibility of tunnel positioning technology. However, the current state of tunnel positioning technology still falls short of meeting the high-precision, high-reliability positioning requirements of practical applications, and many technical shortcomings urgently need to be addressed.

[0003] Currently, in tunnel positioning scenarios, mainstream technologies still rely on wireless communication positioning technologies such as WiFi, Bluetooth, and Ultra-Wideband (UWB). Related research shows that the positioning accuracy of these technologies is typically within the range of 1-5 meters (Zhang et al., IEEE Trans. Veh. Technol., 2020). However, because tunnels are enclosed or semi-enclosed spaces, these technologies generally suffer from severe signal attenuation and significant multipath effects in tunnel environments, resulting in poor positioning accuracy stability and making it difficult to meet the stringent positioning accuracy requirements of scenarios such as tunnel construction safety.

[0004] To overcome the limitations of wireless communication positioning technology, some studies have attempted to apply satellite positioning signals to positioning within tunnels. However, due to the obstruction effect of the tunnel's main structure, satellite signals cannot effectively penetrate the tunnel walls to achieve full coverage, resulting in the inability to perform positioning functions normally (Wang et al., IEEE Trans. Intell. Transp. Syst., 2021), making it difficult to apply to the special enclosed environment of tunnels.

[0005] Pseudo-satellite positioning technology is considered a potential solution to compensate for insufficient satellite signal coverage, but its existing technical solutions still have significant shortcomings. Most current mainstream pseudo-satellite systems adopt a point-to-point deployment mode, which easily leads to uneven signal coverage areas within tunnels, resulting in a large number of positioning blind spots and making it impossible to achieve continuous positioning throughout the tunnel (Chen et al., J. Navig., 2022).

[0006] In summary, existing tunnel positioning technologies have the following core defects and shortcomings: First, the positioning accuracy is too low. The positioning accuracy of mainstream technologies such as traditional WiFi and Bluetooth is generally maintained at 2-5 meters, while core application scenarios such as tunnel construction safety clearly require a positioning accuracy of better than 1 meter. The accuracy level of existing technologies is far from meeting this high-precision positioning requirement.

[0007] Second, uneven signal coverage. Improved solutions, such as pseudosatellite positioning technology, cannot achieve uniform signal coverage throughout the tunnel due to their point-to-point deployment mode. The existence of positioning blind spots seriously affects the reliability and practicality of the positioning system.

[0008] Third, the system deployment is complex. Most existing tunnel positioning technologies require the additional laying of power and communication lines, which not only increases the difficulty of system deployment but also significantly increases the overall cost of equipment purchase, construction, installation, and subsequent maintenance, hindering the large-scale promotion and application of the technology.

[0009] Fourth, poor device compatibility. Existing positioning systems typically require dedicated positioning terminal equipment, which is incompatible with existing mobile terminals such as smartphones. Users need to purchase additional dedicated equipment, which not only raises the barrier to entry but also limits the scope of widespread application of the technology.

[0010] In summary, existing tunnel positioning technologies generally suffer from problems such as low positioning accuracy, uneven signal coverage, complex deployment, and poor compatibility, failing to meet the actual needs of tunnel construction safety and operation management for high-precision, high-reliability, and convenient positioning. Therefore, developing a tunnel positioning technology that can overcome the above-mentioned defects has become an urgent technical problem to be solved in this field. Summary of the Invention

[0011] The purpose of this invention is to provide a high-precision tunnel positioning system based on the fusion of leaky cable and pseudo-satellite, which aims to solve the positioning failure problem caused by the obstruction of traditional satellite signals in tunnels.

[0012] To achieve the above objectives, the present invention provides a tunnel high-precision positioning system based on the fusion of leaky cable and pseudo-satellite, including a communication and navigation unit, a main control clock unit, a leaky cable, an indoor and outdoor integrated positioning terminal, and a comprehensive management platform; The communication and navigation unit generates BDS / GPS dual-system navigation signals and achieves uniform signal coverage through a radial leaky cable. The master clock unit sends PTP synchronization messages through the leaky cable network. Each pseudo-satellite signal transmitting node obtains the synchronization signal through the IEEE1588 PTP hardware timestamp processing unit and generates a local carrier signal that is of the same origin as the master clock. Leaky cable, radial type, low smoke halogen-free flame-retardant polyolefin sheath material; The indoor and outdoor integrated positioning terminal integrates a four-arm spiral antenna and an A-GNSS+ indoor Beidou positioning algorithm, and combines the characteristics of leaky cable signal transmission to achieve indoor and outdoor positioning. The integrated management platform supports real-time trajectory tracking, electronic fence alarms, and multi-dimensional data analysis, providing real-time monitoring and security management.

[0013] Preferably, the source device receives real satellite signals and generates BDS / GPS dual-system navigation signals through the communication and navigation unit, specifically including: The pseudo-satellite base station is fixedly deployed at a known coordinate point inside the tunnel, and it transmits navigation messages and ranging codes simulating BeiDou / GPS satellites, equipped with a highly stable atomic clock or synchronized with the main station clock; The communication and navigation unit receives the original signals from the BDS / GPS dual system, reconstructs the navigation message through the FPGA, and generates pseudo-satellite radio frequency signals that are synchronized with the real satellite time and frequency. Doppler frequency shift compensation technology is adopted, and dynamic signal compensation is achieved through phase-locked loop and digitally controlled oscillator to ensure the signal acquisition stability of the vehicle terminal when it moves at high speed. All pseudo-satellite reference stations are synchronized by the central master station through the IEEE 1588 PTP hardware timestamp synchronization mechanism to meet the coherent accumulation requirements of pseudo-satellite signals in multipath interference environments, ensure the continuity of the carrier phase of the positioning signal, and achieve time alignment between the leaky cable signal and the pseudo-satellite signal. The conduction unit embeds a time stamp unit (TMU) to inject timestamps at specific locations; the user terminal uses the known leaky cable topology to inversely calculate the local clock deviation through a signal propagation delay model. Assisted synchronization, as shown below: ; in, This represents the distance from TMU; This represents the speed at which the signal propagates in the leaky cable.

[0014] Preferably, the main control clock unit is distributed within the tunnel as pseudo-satellite signal transmission nodes and a leaky cable transmission network; both the main control clock unit and each pseudo-satellite signal transmission node are equipped with a dual-mode clock discipline module; The dual-mode clock discipline module includes an IEEE 1588 PTP hardware timestamp processing unit, a high-stability temperature-controlled crystal oscillator (OCXO), and a GNSS receiver. The master clock unit sends PTP synchronization messages through the leaky cable network. Each pseudo-satellite signal transmitting node obtains the synchronization signal through the IEEE1588 PTP hardware timestamp processing unit and uses a high-stability constant temperature crystal oscillator for phase smoothing to generate a local carrier signal that is the same as the master clock. The dual-mode clock discipline module also includes a clock hold algorithm unit. When a network interruption or PTP synchronization signal abnormality is detected, the clock hold algorithm unit controls the high-stability constant-temperature crystal oscillator to enter hold mode based on the frequency deviation and phase difference before the disconnection. In hold mode, the pseudo-satellite signal transmitting node uses local GNSS discipline historical data to compensate for the crystal oscillator aging rate and maintain carrier phase continuity.

[0015] Preferably, the signal transmission unit couples the signal to the radial leaky cable transmission unit, which then uniformly radiates the signal into the tunnel. Specifically, this includes: Leaky cable transmission units are uniformly deployed on the tunnel sidewalls with a slotting period of λ / 4, supporting bidirectional communication and achieving signal field uniformity within the tunnel; the characteristic impedance of the leaky cable is 50Ω, the voltage standing wave ratio (VSWR) is less than 1.5, and the operating frequency covers 1.1GHz-1.6GHz. The leaky cable transmission unit transmits continuous wave or OFDM pilot signals for signal coverage and coarse ranging; integrated optical fiber enables long-distance power supply and data backhaul. The leaky cable transmission unit uses a low-smoke, halogen-free, flame-retardant polyolefin sheath, with an operating temperature range of -40℃ to 80℃. A repeater amplifier is installed every 300m to compensate for transmission loss. During the system initialization phase, the physical length and time delay difference of the leaky cable at each node are measured by a frequency sweeper, and the fixed time delay value is written into the correction register of the IEEE 1588 PTP hardware timestamp processing unit.

[0016] Preferably, the integrated indoor and outdoor positioning terminal receives the radiated signal from the leaky cable transmission unit and combines it with A-GNSS and indoor BeiDou positioning algorithms to achieve multi-source fusion positioning, specifically including: The indoor and outdoor integrated positioning terminal has a multi-channel radio frequency front-end, a baseband demodulation module, and a fusion positioning calculation engine; based on dynamic switching of carrier-to-noise ratio, it fuses A-GNSS and pseudo-satellite TOA / TDOA data, and outputs the position through Kalman filtering. Leaky cable location depends on the distance along the cable, while pseudo-satellites provide three-dimensional coordinates. Before fusion, the leaky cable TDOA results are converted into two-dimensional / three-dimensional coordinate estimates. A spatial reference line is established based on the leaky cable deployment path, and the TDOA difference is mapped to the mileage along the line and the lateral offset. Multiple leaky cables are used for cross-location, and the coordinates are unified with the pseudo-satellite coordinates to the same geodetic coordinate system. The indoor and outdoor integrated positioning terminal separately calculates the TDOA observations from the leaky cable and the pseudorange / carrier phase observations from the pseudosatellite; under a unified time reference, observation-level fusion is adopted, and the two types of observations are input into the extended Kalman filter or factor graph optimization for joint estimation; among them, the accuracy of observation-level fusion is higher than that of decision-level fusion, and the real-time performance is better than that of data-level fusion. Among them, the indoor BeiDou positioning algorithm includes signal reception and preprocessing, observation value conversion and unification, and multi-source fusion positioning solution; Signal reception and preprocessing are used to achieve signal acquisition and tracking and observation extraction; The observation conversion and unification process involves first converting the exposed cable TDOA into a geometric observation model, then establishing a three-dimensional spatial reference line based on the physical layout path of the leaking cable, and finally obtaining two-dimensional or three-dimensional coordinates through least squares fitting and cross-positioning of multiple non-parallel leaking cables, and converting them to a local geodetic coordinate system consistent with the pseudo-satellite system. Multi-source fusion positioning solution is used to construct fusion positioning state equation and observation equation, and joint estimation is performed using extended Kalman filtering or factor graph optimization to obtain the optimal state trajectory estimate.

[0017] Preferably, adaptive covariance estimation is introduced to dynamically adjust the observation noise covariance matrix according to the signal quality; In signal blind spots, inertial measurement units are introduced to perform short-term dead reckoning to compensate for signal blockage blind spots, and zero-velocity detection is used to correct accumulated errors; when the signal is restored, the IMU state is reset with the fused positioning results. It adopts a four-arm helical antenna structure, which has wide bandwidth and circular polarization gain characteristics, and improves the signal reception capability in the tunnel.

[0018] Preferably, A-GNSS is used to collect outdoor data; pseudosatellite TOA / TDOA is used to collect indoor data.

[0019] Preferably, the integrated management platform obtains the coordinates of the indoor and outdoor integrated positioning terminal through the location data interface, providing real-time monitoring and security management, specifically including: The integrated management platform performs real-time electronic fence comparison and trajectory anomaly detection on location data, triggers security alarms, and realizes multi-source data fusion, error modeling, coordinate unification, trajectory smoothing and visual monitoring. By employing GeoHash combined with time window indexing technology, it supports efficient querying of hundreds of millions of trajectory points, enabling real-time monitoring and safety management of tunnel construction personnel and equipment.

[0020] Preferably, the specific implementation process of a tunnel high-precision positioning system based on leaky cable and pseudo-satellite fusion is as follows: Step S1: Deployment of the communication unit and signal generation; First, a dual-frequency GNSS receiver is deployed at the tunnel entrance to receive BDS B1I / B2a and GPS L1 / L5 signals; Then, satellite ephemeris, clock bias, and ionospheric parameters are extracted using FPGA; Finally, the navigation message is reconstructed using direct digital frequency synthesis technology to generate pseudo-satellite signals; the pseudo-satellite signals are then injected into the radial leaky cable via a signal isolator. Step S2, Leaky cable laying and signal radiation; First, lay low-smoke halogen-free flame-retardant polyolefin sheathed leaky cables along the top or sidewalls of the tunnel. Then, repeater amplifiers are installed every 300m of the leaky cable to compensate for transmission loss; Finally, after the leaky cable is laid, the standing wave ratio (VSWR) is measured using a vector network analyzer (VNA) to ensure that VSWR < 1.5. Step S3: Indoor and outdoor integrated positioning terminal environment identification and positioning mode switching; Firstly, after the indoor and outdoor integrated positioning terminal is powered on, the four-arm spiral antenna monitors the signal quality in real time; Then, based on the environment discrimination algorithm, when a transition area between inside and outside the tunnel is detected, a smooth transition algorithm is activated to ensure the continuity of positioning; Step S4: Indoor positioning calculation; First, the indoor and outdoor integrated positioning terminal receives pseudo-satellite signals radiated by the leaky cable and extracts the pseudorange and carrier phase; Then, based on the coordinates of the leaky cable layout, a database of pseudo-satellite equivalent radiation centers was established; Finally, the least squares method was used to solve for the location of the integrated indoor and outdoor positioning terminal; Step S5: Multi-source fusion and positioning output; Step S6: Data interaction and alarm management with the integrated management platform; First, the location results are uploaded to the integrated management platform via the LoRa / Cat.1 communication module; Then, the integrated management platform uses CesiumJS / WebGL technology to realize the 3D real-scene reconstruction of the tunnel, supporting 2D plan view and 3D perspective. Figure 1 Key toggle; Step S7: System calibration and maintenance; First, periodically correct the leaky cable phase delay using known control points; Then, a spectrum analyzer is deployed to monitor the VSWR of the leaky cable, and an alarm is triggered when the VSWR is >1.8.

[0021] Preferably, the integrated management platform uses CesiumJS / WebGL technology to realize 3D real-scene reconstruction of the tunnel, supporting 2D plan view and 3D perspective. Figure 1 Key switching, specifically including: (1) Electronic fence settings: Draw a polygonal area on the map and set the entry and exit alarm thresholds; (2) Real-time trajectory display: sampling rate of 1Hz, supporting visualization of trajectory point density; (3) Historical trajectory playback: Based on GeoHash encoding, fast retrieval of trajectory points is achieved; (4) Emergency event handling: Supports SOS alarm triggering work order process to achieve closed-loop handling.

[0022] Therefore, this invention employs a tunnel high-precision positioning system based on the fusion of leaky cable and pseudo-satellite technology. It achieves uniform signal coverage through a radial leaky cable and solves the signal obstruction problem within the tunnel by combining pseudo-satellite technology. The A-GNSS + indoor BeiDou positioning algorithm achieves high-precision positioning of 0.1-1m within the tunnel, far exceeding traditional WiFi / Bluetooth positioning technology (1-5 meters). Based on time synchronization mechanisms and signal simulation technology, it achieves seamless switching between navigation and positioning inside and outside the tunnel, with a switching time of only 1-3 seconds. The system proposed in this invention requires only one leaky cable, eliminating the need for additional power supply, simplifying deployment processes, and reducing construction costs. It supports ordinary smartphones, vehicle navigation systems, and other devices, requiring no dedicated equipment. This invention overcomes the random errors caused by asymmetric paths in traditional Ethernet synchronization by utilizing the deterministic delay characteristics of the physical transmission medium (leaky cable), thereby achieving synchronization accuracy superior to that of traditional industrial Ethernet.

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0024] Figure 1 This is an overall architecture diagram of a tunnel high-precision positioning system based on the fusion of leaky cable and pseudo-satellite. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0026] like Figure 1 As shown, the present invention discloses a tunnel high-precision positioning system based on the fusion of leaky cable and pseudo-satellite, including a communication and navigation unit, a main control clock unit, a leaky cable, an indoor and outdoor integrated positioning terminal, and a comprehensive management platform.

[0027] The communication and navigation unit generates BDS / GPS dual-system navigation signals, and achieves uniform signal coverage through a radial leaky cable.

[0028] The master clock unit sends PTP synchronization messages through the leaky cable network. Each pseudo-satellite signal transmitting node obtains the synchronization signal through the IEEE1588 PTP hardware timestamp processing unit and generates a local carrier signal that is of the same origin as the master clock.

[0029] Leaky cable, radial type, low smoke halogen-free flame retardant polyolefin sheath material, operating temperature -40℃~80℃.

[0030] The integrated indoor and outdoor positioning terminal integrates a quad-helical antenna and an A-GNSS+ indoor BeiDou positioning algorithm. Combined with the characteristics of leaky cable signal transmission, it achieves high-precision positioning of 0.1-1m indoors and 0.01-0.3m outdoors (RTK mode).

[0031] The integrated management platform supports real-time trajectory tracking, electronic fence alarms, and multi-dimensional data analysis, and is suitable for real-time monitoring and safety management of tunnel construction personnel and equipment.

[0032] Example 1 This invention constructs a four-layer technical architecture system consisting of "synchronous generation of communication and navigation signals - uniform radiation from leaky cables - multi-source positioning fusion - closed-loop control of integrated management platform", which solves the problem that traditional satellite positioning completely fails in tunnels.

[0033] 1. The source device receives real satellite signals and generates BDS / GPS dual-system navigation signals through the communication and navigation unit.

[0034] The pseudo-satellite base station is fixedly deployed at known coordinate points inside the tunnel (e.g., one every 200 meters), and transmits navigation messages and ranging codes simulating BeiDou / GPS satellites. It is equipped with a highly stable atomic clock or synchronized with the main station clock.

[0035] The communication and navigation unit receives the original signals from the BDS / GPS dual system, reconstructs the navigation message through the FPGA, and generates pseudo-satellite radio frequency signals that are synchronized with the real satellite time and frequency (±0.1ppm).

[0036] Doppler frequency shift compensation technology is adopted, and dynamic signal compensation is achieved through phase-locked loop (PLL) and numerically controlled oscillator (NCO) to ensure the signal acquisition stability of the vehicle terminal when moving at high speed (>60km / h).

[0037] To ensure the effectiveness of signal fusion, all pseudo-satellite reference stations are synchronized by the central master station through the IEEE 1588 PTP hardware timestamp mechanism to meet the coherent accumulation requirements of pseudo-satellite signals in multipath interference environments, ensure the continuity of the carrier phase of the positioning signal, and achieve time alignment between the leaky cable signal and the pseudo-satellite signal.

[0038] The conduction unit embeds a time stamp unit (TMU) to inject timestamps at specific locations; the user terminal uses the known leaky cable topology to inversely calculate the local clock deviation through a signal propagation delay model. Assisted synchronization, as shown below: ; in, This represents the distance from TMU; This represents the speed at which the signal propagates in the leaky cable.

[0039] 2. The master clock unit sends PTP synchronization messages through the leaky cable network. Each pseudo-satellite signal transmitting node obtains the synchronization signal through the IEEE 1588 PTP hardware timestamp processing unit and generates a local carrier signal with the same source as the master clock.

[0040] The main control clock unit is distributed throughout the tunnel, including pseudo-satellite signal transmission nodes and the leaky cable transmission network. Both the main control clock unit and each pseudo-satellite signal transmission node are equipped with a dual-mode clock discipline module. The dual-mode clock discipline module includes an IEEE 1588 PTP hardware timestamp processing unit, a high-stability, temperature-controlled crystal oscillator (OCXO), and a GNSS receiver.

[0041] The master clock unit sends PTP synchronization messages through the leaky cable network. Each pseudo-satellite signal transmitting node obtains the synchronization signal through the IEEE1588 PTP hardware timestamp processing unit and uses a high-stability constant temperature crystal oscillator for phase smoothing to generate a local carrier signal that is the same as the master clock. The dual-mode clock discipline module also includes a clock holdover algorithm unit. When a network interruption or PTP synchronization signal anomaly is detected, the clock holdover algorithm unit controls the high-stability, temperature-controlled crystal oscillator to enter holdover mode based on the frequency deviation and phase difference before the disconnection. In holdover mode, the pseudo-satellite signal transmitting node uses historical data from local GNSS discipline to compensate for the crystal oscillator aging rate and maintain carrier phase continuity.

[0042] The high-stability temperature-controlled crystal oscillator (OCXO) of this invention has a daily aging rate better than ±0.5ppb and a phase noise better than -150dBc / Hz at a 1kHz offset. During brief unlocking periods of the PTP protocol, this crystal oscillator can utilize its excellent short-term stability to maintain the phase difference between the local clock and the master clock within a controllable range (e.g., within one carrier cycle).

[0043] Third, the signal is coupled to the radial leaky cable transmission unit and radiated evenly into the tunnel through the leaky cable transmission unit.

[0044] The leaky cable transmission unit (LCX-50-22 model) is uniformly deployed on the tunnel sidewall with a slotting period of λ / 4 (≈5cm@1.575GHz), supporting bidirectional communication and achieving signal field uniformity (field strength fluctuation ≤3dB) within the tunnel. The leaky cable has a characteristic impedance of 50Ω, a voltage standing wave ratio (VSWR) of less than 1.5, and an operating frequency range of 1.1GHz-1.6GHz.

[0045] Leaky cable transmission units transmit continuous wave or OFDM pilot signals for signal coverage and coarse ranging (based on signal attenuation or TDOA); they can be integrated with optical fibers to achieve long-distance power supply and data backhaul.

[0046] The leaky cable transmission unit uses a low-smoke, halogen-free, flame-retardant polyolefin sheath, with an operating temperature range of -40℃ to 80℃. A repeater amplifier (gain 10dB) is installed every 300m to compensate for transmission loss (less than or equal to 0.2dB / m@1.5GHz).

[0047] This invention utilizes the deterministic latency characteristic of leaky coaxial cable transmission. Compared to ordinary wireless networks, leaky coaxial cable, as a transmission medium, exhibits extremely low signal propagation delay jitter (typically in the picosecond range). During system initialization, this invention measures the physical length and latency difference of the leaky coaxial cable at each node using a frequency sweeper, and writes this fixed latency value into the correction register of the PTP algorithm. This eliminates the random jitter caused by queuing and forwarding in traditional wireless networks, significantly improving the synchronization accuracy of the IEEE 1588 PTP hardware timestamp synchronization mechanism.

[0048] IV. The indoor and outdoor integrated positioning terminal receives the radiated signal from the leaky cable transmission unit and combines it with A-GNSS and indoor Beidou positioning algorithms to achieve high-precision multi-source fusion positioning.

[0049] This integrated indoor / outdoor positioning terminal features a multi-channel RF front-end, a baseband demodulation module, and a fusion positioning calculation engine. Based on dynamic switching of carrier-to-noise ratio (C / N0), it fuses A-GNSS (outdoor) and pseudosatellite TOA / TDOA (indoor) data, outputting the position via Kalman filtering (KF). Employing a four-arm helical antenna structure, it boasts wide bandwidth (1.1-1.6GHz) and circular polarization gain (≥5dBi), enhancing signal reception capabilities within tunnels.

[0050] Leaky cable positioning relies on the distance along the cable (one-dimensional), while pseudo-satellites provide three-dimensional coordinates. Before fusion, the leaky cable TDOA results need to be converted into two-dimensional / three-dimensional coordinate estimates. A spatial reference line is established based on the leaky cable deployment path, and the TDOA difference is mapped to the mileage along the line and the lateral offset. Through cross-positioning of multiple leaky cables, the coordinates are unified with the pseudo-satellite coordinates to the same geodetic coordinate system.

[0051] The integrated indoor and outdoor positioning terminal separately calculates TDOA observations from leaky cables and pseudorange / carrier phase observations from pseudosatellites. Under a unified time reference, observation-level fusion is employed, inputting the two types of observations into an extended Kalman filter (EKF) or factor graph optimization (FGO) for joint estimation. Observation-level fusion demonstrates higher accuracy than decision-level fusion and better real-time performance than data-level fusion.

[0052] The indoor BeiDou positioning algorithm includes signal reception and preprocessing, observation value conversion and unification, and multi-source fusion positioning solution.

[0053] Signal reception and preprocessing are used to achieve signal acquisition and tracking and observation extraction; The observation conversion and unification process involves first converting the exposed cable TDOA into a geometric observation model, then establishing a three-dimensional spatial reference line based on the physical layout path of the leaking cable, and finally obtaining two-dimensional or three-dimensional coordinates through least squares fitting and cross-positioning of multiple non-parallel leaking cables, and converting them to a local geodetic coordinate system consistent with the pseudo-satellite system. Multi-source fusion positioning solution is used to construct fusion positioning state equation and observation equation, and joint estimation is performed using extended Kalman filtering or factor graph optimization to obtain the optimal state trajectory estimate.

[0054] Leaky cable signals are susceptible to multipath propagation and vehicle obstruction; pseudo-satellites exhibit clock drift and multipath propagation. Adaptive covariance estimation is introduced to dynamically adjust the observation noise covariance matrix based on signal quality (e.g., SNR, residuals); in Kalman filtering, high signal-to-noise ratio sources are given higher gain.

[0055] For example, when a pseudo-satellite signal carrier-to-noise ratio is detected to be below 35dB-Hz, the system automatically increases the variance weight of its observations by 30% and enhances its reliance on leaky cable TDOA observations.

[0056] In signal blind spots (such as construction areas and curves), inertial measurement units (IMUs) are introduced to perform short-time dead reckoning (DR) to compensate for signal blockage blind spots, and zero-velocity detection (ZUPT) is used to correct accumulated errors; when the signal is restored, the IMU state is reset with the fused positioning results.

[0057] V. The integrated management platform obtains the coordinates of indoor and outdoor integrated positioning terminals through the location data interface, providing real-time monitoring and security management.

[0058] The integrated management platform performs real-time comparison of location data with electronic fences and detects trajectory anomalies, triggering security alarms and achieving multi-source data fusion, error modeling, coordinate unification, trajectory smoothing, and visual monitoring.

[0059] By employing GeoHash combined with time window indexing technology, it supports efficient querying of hundreds of millions of trajectory points, enabling real-time monitoring and safety management of tunnel construction personnel and equipment.

[0060] This system breaks through the bottleneck of high deployment cost (≥500 yuan / m) of traditional UWB positioning in long tunnels, and achieves high-precision seamless positioning service with continuous coverage of 0.1-1m in the tunnel and a positioning switching time of <1 second between the inside and outside of the tunnel. The positioning stability reaches the decimeter level, providing reliable technical support for tunnel construction safety and operational efficiency.

[0061] Example 2 This embodiment is based on a tunnel high-precision positioning system based on leaky cable and pseudo-satellite fusion proposed in this invention. The specific implementation process is described in detail below: Step S1: Deployment of the communication unit and signal generation.

[0062] First, a dual-frequency GNSS receiver is deployed at the tunnel entrance to receive BDS B1I / B2a and GPS L1 / L5 signals; Then, satellite ephemeris, clock bias, and ionospheric parameters are extracted using FPGA; Finally, the navigation message is reconstructed using direct digital frequency synthesis (DDS) technology to generate pseudo-satellite signals; the pseudo-satellite signals are then injected into the radial leaky cable via a signal isolator.

[0063] The phase accumulator has a 32-bit width and a clock frequency of 100MHz to ensure signal synchronization accuracy; the pseudo-satellite signal power is controlled between -60 and -80dBm / m to avoid self-interference.

[0064] Step S2: Leaky cable laying and signal radiation.

[0065] First, lay low-smoke halogen-free flame-retardant polyolefin sheathed leaky cables along the top or sidewalls of the tunnel. Then, repeater amplifiers are installed every 300m of the leaky cable to compensate for transmission loss; Finally, after the leaky cable is laid, the standing wave ratio (VSWR) is measured using a vector network analyzer (VNA) to ensure that VSWR < 1.5.

[0066] The slotting period of the leaky cable is designed to be λ / 4=5cm (λ=19cm@1.575GHz) to ensure radiation uniformity; the leaky cable adopts a 45° cross-polarization slot design to support independent transmission of 5G and Beidou signals, with an isolation of >30dB.

[0067] Step S3: Indoor and outdoor integrated positioning terminal environment identification and positioning mode switching.

[0068] Firstly, after the indoor and outdoor integrated positioning terminal is powered on, the four-arm spiral antenna monitors the signal quality in real time; Then, based on the environment discrimination algorithm, when a transition area between inside and outside the tunnel is detected, a smooth transition algorithm is activated to ensure positioning continuity.

[0069] Step S4: Indoor positioning calculation (pseudo-satellite mode).

[0070] First, the indoor and outdoor integrated positioning terminal receives pseudo-satellite signals radiated by the leaky cable and extracts the pseudorange and carrier phase; Then, based on the coordinates of the leaky cable layout, a database of pseudo-satellite equivalent radiation centers was established; Finally, the least squares method is used to solve for the position of the integrated indoor and outdoor positioning terminal. And combined with IMU DR to compensate for signal dead zones: in, Let k be the position at time k. For speed, It is acceleration.

[0071] Step S5: Multi-source fusion and localization output. Construct a state vector, perform measurement updates, state updates, and covariance updates based on Kalman filter fusion, and output the final localization result. Outdoor RTK mode: Positioning accuracy 0.01-0.3m (95% confidence level); In-tunnel mode: Positioning accuracy 0.1-1m (95% confidence level).

[0072] Step S6: Data interaction and alarm management on the integrated management platform.

[0073] First, the location results are uploaded to the integrated management platform via the LoRa / Cat.1 communication module; Then, the integrated management platform uses CesiumJS / WebGL technology to realize the 3D real-scene reconstruction of the tunnel, supporting 2D plan view and 3D perspective. Figure 1 Key switching, specifically including: (1) Electronic fence settings: Draw a polygonal area on the map and set the entry and exit alarm thresholds; (2) Real-time trajectory display: sampling rate of 1Hz, supporting visualization of trajectory point density; (3) Historical trajectory playback: Based on GeoHash encoding (precision 50cm), the trajectory point can be quickly retrieved; (4) Emergency event handling: Supports SOS alarm triggering work order process to achieve closed-loop handling.

[0074] Step S7: System calibration and maintenance.

[0075] First, periodically correct the leaky cable phase delay using known control points (such as tunnel mileage markers); Then, a spectrum analyzer is deployed to monitor the leakage cable standing wave ratio (VSWR), and an alarm is triggered when VSWR > 1.8.

[0076] In this embodiment, the leaky cable fault prediction based on machine learning constructs a fault prediction model by collecting parameters such as the leaky cable's radiation field strength and temperature, achieving an accuracy rate of >85%. An application case in a city's East Sixth Ring Road tunnel shows that the system's indoor positioning accuracy is 0.3m (95% confidence level), system availability is 99.6%, and it exhibits good compatibility with vehicle / mobile terminals, meeting the requirements for construction safety supervision.

[0077] Therefore, this invention employs a tunnel high-precision positioning system based on the fusion of leaky cable and pseudo-satellite technology. It achieves uniform signal coverage through a radial leaky cable and solves the signal obstruction problem within the tunnel by combining pseudo-satellite technology. The A-GNSS + indoor BeiDou positioning algorithm achieves high-precision positioning of 0.1-1m within the tunnel, far exceeding traditional WiFi / Bluetooth positioning technology (1-5 meters). Based on time synchronization mechanisms and signal simulation technology, it achieves seamless switching between navigation and positioning inside and outside the tunnel, with a switching time of only 1-3 seconds. The system proposed in this invention requires only one leaky cable, eliminating the need for additional power supply, simplifying deployment processes, and reducing construction costs. It supports ordinary smartphones, vehicle navigation systems, and other devices, requiring no dedicated equipment.

[0078] This invention overcomes the random errors caused by asymmetric paths in traditional Ethernet synchronization by utilizing the deterministic delay characteristics of the physical transmission medium (leaky cable), thereby achieving synchronization accuracy superior to that of traditional industrial Ethernet.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high-precision tunnel positioning system based on leaky cable and pseudo-satellite fusion, characterized in that: Includes a communication and control unit, a main control clock unit, a leaky cable, an indoor and outdoor integrated positioning terminal, and a comprehensive management platform; The communication and navigation unit generates BDS / GPS dual-system navigation signals and achieves uniform signal coverage through a radial leaky cable. The master clock unit sends PTP synchronization messages through the leaky cable network. Each pseudo-satellite signal transmitting node obtains the synchronization signal through the IEEE1588 PTP hardware timestamp processing unit and generates a local carrier signal that is of the same origin as the master clock. Leaky cable, radial type, low smoke halogen-free flame-retardant polyolefin sheath material; The indoor and outdoor integrated positioning terminal integrates a four-arm spiral antenna and A-GNSS+ indoor Beidou positioning algorithm, and combines the characteristics of leaky cable signal transmission to achieve indoor and outdoor positioning. The integrated management platform supports real-time trajectory tracking, electronic fence alarms, and multi-dimensional data analysis, providing real-time monitoring and security management.

2. The tunnel high-precision positioning system based on leaky cable and pseudo-satellite fusion as described in claim 1, characterized in that: The source device receives real satellite signals and generates BDS / GPS dual-system navigation signals through the communication and navigation unit, specifically including: The pseudo-satellite base station is fixedly deployed at a known coordinate point inside the tunnel, and it transmits navigation messages and ranging codes simulating BeiDou / GPS satellites, equipped with a highly stable atomic clock or synchronized with the main station clock; The communication and navigation unit receives the original signals from the BDS / GPS dual system, reconstructs the navigation message through the FPGA, and generates pseudo-satellite radio frequency signals that are synchronized with the real satellite time and frequency. Doppler frequency shift compensation technology is adopted, and dynamic signal compensation is achieved through phase-locked loop and digitally controlled oscillator to ensure the signal acquisition stability of the vehicle terminal when it moves at high speed. All pseudo-satellite reference stations are synchronized by the central master station through the IEEE 1588 PTP hardware timestamp synchronization mechanism to meet the coherent accumulation requirements of pseudo-satellite signals in multipath interference environments, ensure the continuity of the carrier phase of the positioning signal, and achieve time alignment between the leaky cable signal and the pseudo-satellite signal. The conduction unit embeds a time stamp unit (TMU) to inject timestamps at specific locations; the user terminal uses the known leaky cable topology to inversely calculate the local clock deviation through a signal propagation delay model. Assisted synchronization, as shown below: ； in, This represents the distance from TMU; This represents the speed at which the signal propagates in the leaky cable.

3. The tunnel high-precision positioning system based on leaky cable and pseudo-satellite fusion according to claim 1, characterized in that: The main control clock unit is distributed among pseudo-satellite signal transmission nodes and leaky cable transmission networks within the tunnel; both the main control clock unit and each pseudo-satellite signal transmission node are equipped with a dual-mode clock discipline module. The dual-mode clock discipline module includes an IEEE 1588 PTP hardware timestamp processing unit, a high-stability temperature-controlled crystal oscillator (OCXO), and a GNSS receiver. The master clock unit sends PTP synchronization messages through the leaky cable network. Each pseudo-satellite signal transmitting node obtains the synchronization signal through the IEEE 1588PTP hardware timestamp processing unit and uses a high-stability constant temperature crystal oscillator for phase smoothing to generate a local carrier signal that is the same as the master clock. The dual-mode clock discipline module also includes a clock hold algorithm unit. When a network interruption or PTP synchronization signal abnormality is detected, the clock hold algorithm unit controls the high-stability constant-temperature crystal oscillator to enter hold mode based on the frequency deviation and phase difference before the disconnection. In hold mode, the pseudo-satellite signal transmitting node uses local GNSS discipline historical data to compensate for the crystal oscillator aging rate and maintain carrier phase continuity.

4. The tunnel high-precision positioning system based on leaky cable and pseudo-satellite fusion as described in claim 1, characterized in that: The signal transmission unit couples the signal to the radial leaky cable transmission unit, which then radiates the signal evenly into the tunnel. Specifically, this includes: Leaky cable transmission units are uniformly deployed on the tunnel sidewalls with a slotting period of λ / 4, supporting bidirectional communication and achieving signal field uniformity within the tunnel; the characteristic impedance of the leaky cable is 50Ω, the voltage standing wave ratio (VSWR) is less than 1.5, and the operating frequency covers 1.1GHz-1.6GHz. The leaky cable transmission unit transmits continuous wave or OFDM pilot signals for signal coverage and coarse ranging; integrated optical fiber enables long-distance power supply and data backhaul. The leaky cable transmission unit uses a low-smoke, halogen-free, flame-retardant polyolefin sheath, with an operating temperature range of -40℃ to 80℃. A repeater amplifier is installed every 300m to compensate for transmission loss. During the system initialization phase, the physical length and time delay difference of the leaky cable at each node are measured by a frequency sweeper, and the fixed time delay value is written into the correction register of the IEEE 1588 PTP hardware timestamp processing unit.

5. A tunnel high-precision positioning system based on leaky cable and pseudo-satellite fusion as described in claim 1, characterized in that: The integrated indoor and outdoor positioning terminal receives the radiated signal from the leaky cable transmission unit and combines it with A-GNSS and indoor BeiDou positioning algorithms to achieve multi-source fusion positioning, specifically including: The indoor and outdoor integrated positioning terminal has a multi-channel radio frequency front-end, a baseband demodulation module, and a fusion positioning calculation engine; based on dynamic switching of carrier-to-noise ratio, it integrates A-GNSS and pseudo-satellite TOA / TDOA data, and outputs the position through Kalman filtering. Leaky cable location depends on the distance along the cable, while pseudo-satellites provide three-dimensional coordinates. Before fusion, the leaky cable TDOA results are converted into two-dimensional / three-dimensional coordinate estimates. A spatial reference line is established based on the leaky cable deployment path, and the TDOA difference is mapped to the mileage along the line and the lateral offset. Multiple leaky cables are used for cross-location, and the coordinates are unified with the pseudo-satellite coordinates to the same geodetic coordinate system. The indoor and outdoor integrated positioning terminal separately calculates the TDOA observations from the leaky cable and the pseudorange / carrier phase observations from the pseudosatellite; under a unified time reference, observation-level fusion is adopted, and the two types of observations are input into the extended Kalman filter or factor graph optimization for joint estimation; among them, the accuracy of observation-level fusion is higher than that of decision-level fusion, and the real-time performance is better than that of data-level fusion. Among them, the indoor BeiDou positioning algorithm includes signal reception and preprocessing, observation value conversion and unification, and multi-source fusion positioning solution; Signal reception and preprocessing are used to achieve signal acquisition and tracking and observation extraction; The observation conversion and unification process involves first converting the exposed cable TDOA into a geometric observation model, then establishing a three-dimensional spatial reference line based on the physical layout path of the leaking cable, and finally obtaining two-dimensional or three-dimensional coordinates through least squares fitting and cross-positioning of multiple non-parallel leaking cables, and converting them to a local geodetic coordinate system consistent with the pseudo-satellite system. Multi-source fusion positioning solution is used to construct fusion positioning state equation and observation equation, and joint estimation is performed using extended Kalman filtering or factor graph optimization to obtain the optimal state trajectory estimate.

6. A tunnel high-precision positioning system based on leaky cable and pseudo-satellite fusion as described in claim 5, characterized in that: Adaptive covariance estimation is introduced to dynamically adjust the observation noise covariance matrix based on signal quality. In signal blind spots, inertial measurement units are introduced to perform short-term dead reckoning to compensate for signal blockage blind spots, and zero-velocity detection is used to correct accumulated errors; when the signal is restored, the IMU state is reset with the fused positioning results. It adopts a four-arm helical antenna structure, which has wide bandwidth and circular polarization gain characteristics, and improves the signal reception capability in the tunnel.

7. A tunnel high-precision positioning system based on leaky cable and pseudo-satellite fusion as described in claim 5, characterized in that: A-GNSS collects outdoor data; pseudosatellites TOA / TDOA collect indoor data.

8. A tunnel high-precision positioning system based on leaky cable and pseudo-satellite fusion as described in claim 1, characterized in that: The integrated management platform obtains the coordinates of indoor and outdoor integrated positioning terminals through a location data interface, providing real-time monitoring and security management, specifically including: The integrated management platform performs real-time electronic fence comparison and trajectory anomaly detection on location data, triggers security alarms, and realizes multi-source data fusion, error modeling, coordinate unification, trajectory smoothing and visual monitoring. By employing GeoHash combined with time window indexing technology, it supports efficient querying of hundreds of millions of trajectory points, enabling real-time monitoring and safety management of tunnel construction personnel and equipment.

9. A tunnel high-precision positioning system based on leaky cable and pseudo-satellite fusion according to any one of claims 1-8, characterized in that, The specific implementation process is as follows: Step S1: Deployment of the communication unit and signal generation; First, a dual-frequency GNSS receiver is deployed at the tunnel entrance to receive BDS B1I / B2a and GPS L1 / L5 signals; Then, satellite ephemeris, clock bias, and ionospheric parameters are extracted using FPGA; Finally, the navigation message is reconstructed using direct digital frequency synthesis technology to generate pseudo-satellite signals; the pseudo-satellite signals are then injected into the radial leaky cable via a signal isolator. Step S2, Leaky cable laying and signal radiation; First, lay low-smoke halogen-free flame-retardant polyolefin sheathed leaky cables along the top or sidewalls of the tunnel. Then, repeater amplifiers are installed every 300m of the leaky cable to compensate for transmission loss; Finally, after the leaky cable is laid, the standing wave ratio (VSWR) is measured using a vector network analyzer (VNA) to ensure that VSWR < 1.

5. Step S3: Indoor and outdoor integrated positioning terminal environment identification and positioning mode switching; Firstly, after the indoor and outdoor integrated positioning terminal is powered on, the four-arm spiral antenna monitors the signal quality in real time; Then, based on the environment discrimination algorithm, when a transition area between inside and outside the tunnel is detected, a smooth transition algorithm is activated to ensure the continuity of positioning; Step S4: Indoor positioning calculation; First, the indoor and outdoor integrated positioning terminal receives pseudo-satellite signals radiated by the leaky cable and extracts the pseudorange and carrier phase; Then, based on the coordinates of the leaky cable layout, a database of pseudo-satellite equivalent radiation centers was established; Finally, the least squares method was used to solve for the location of the integrated indoor and outdoor positioning terminal; Step S5: Multi-source fusion and positioning output; Step S6: Data interaction and alarm management with the integrated management platform; First, the location results are uploaded to the integrated management platform via the LoRa / Cat.1 communication module; Then, the integrated management platform uses CesiumJS / WebGL technology to realize the three-dimensional real-scene reconstruction of the tunnel and supports one-click switching between 2D plan view and 3D perspective view; Step S7: System calibration and maintenance; First, periodically correct the leaky cable phase delay using known control points; Then, a spectrum analyzer is deployed to monitor the VSWR of the leaky cable, and an alarm is triggered when the VSWR is >1.

8.

10. A tunnel high-precision positioning system based on leaky cable and pseudo-satellite fusion as described in claim 9, characterized in that, The integrated management platform uses CesiumJS / WebGL technology to achieve 3D real-scene reconstruction of the tunnel, supporting one-click switching between 2D plan views and 3D perspective views, specifically including: (1) Electronic fence settings: Draw a polygonal area on the map and set the entry and exit alarm thresholds; (2) Real-time trajectory display: sampling rate of 1Hz, supporting visualization of trajectory point density; (3) Historical trajectory playback: Based on GeoHash encoding, fast retrieval of trajectory points is achieved; (4) Emergency event handling: Supports SOS alarm triggering work order process to achieve closed-loop handling.

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