Fiber optic network-based remote sensing of rail systemsvehicles

Abstract

In recent years, the need for precise positioning of moving vehicles has become increasingly important, especially in smart cities. Accurate positioning is critical for an efficient and safe transportation system. However, the existing positioning systems are often limited because they are point-based, and the error margin for non-point-based systems is usually more than one meter, sometimes even exceeding ten meters. This limitation significantly reduces the potential use of these positioning technologies, particularly in urban metro systems. To address the accuracy problem in fast positioning, a new hybrid system utilizing Fiber Bragg Gratings (FBG) technology is proposed within the scope of this thesis. One unique feature of this designed model is the ability to encode the transmitted signal. Another essential feature is the correlation between the reference and reflected signals. This allows for precise positioning, even at high noise levels. With the help of the coding of transmitter signal 1, 2, 4, 8, 16, 32, 64, 128, 256-bit pulse sequences have been created for the transmission side, and the localization errors were 118.4, 68.1, 4.8, 0.4, 0.3, 0.3, 0.2, and 0.1 m respectively for 50 km track line under high Gaussian noise. Additionally, the hybrid system can determine the speed and direction of a moving object by interpreting two consecutive or just a single transmitted signal. Speed and direction estimation can also be achieved by examining the frequency shift of the signal. This approach contributes to speed, position, and direction determination without analyzing multiple signals, providing higher accuracy and protection against erroneous data. The research aims to address four main questions: 1. Which should be chosen between FBG and Distributed Acoustic Sensing (DAS) methodologies for sensor applications? 2. What technical specifications are essential for implementing the hybrid FBG and DAS system to position mobile vehicles in railway applications precisely? 3. How do the hybrid system's performance, speed, and direction determination capabilities compare to existing systems, and what are the optimal configurations and parameters of the proposed system? 4. What are the hybrid system's potential uses, advantages, and limitations in various transportation types, and how can it enhance the efficiency and safety of urban transportation systems? The literature review has indicated the positioning capabilities, technical specifications, and limitations of FBG and DAS systems. Using fiber optic sensors, these systems expose external stimuli to measure stress and temperature changes in optical fibers. These changes cause a shift in the Bragg wavelength of FBG, which can be detected by measuring the reflected signal from the fiber. Furthermore, DAS, another sensing system, is used to detect the position and movement of an object by utilizing acoustic waves originating from external stimuli. However, the random nature of the backscattered signal limits the mathematical modeling to randomness. Development studies are ongoing in this scope. An advanced simulation software, using Optiwave's OptiSystem, was conducted for a newly developed and tested design to evaluate the hybrid system's performance. The software can simulate FBG sensors based on a mathematical model with a limited randomness of the reflected and transmitted signals. The effect of train on FBG expressed related to IEEE 1698 std. which defines air resistance force at the surface of the train which is directly effects the FBG sensor. This model was developed and verified with field tests to provide the highest accuracy and reliability during simulation. The behavior of FBG sensors calibrated and optimized related to field results. Also, the proper FBG working frequencies selected related to the FS Community channels guide. The performance of the proposed hybrid system was carefully evaluated and compared to existing systems. The most suitable configurations and parameters for the designed model were determined. The design and implementation of the system were evaluated considering the provided accuracy, speed, direction determination, and potential applications in various transportation contexts. To showcase the system's capabilities, a cleaning train cleaning operation in clearing the track was modeled and demonstrated using the hybrid system. Various measures against foreign objects on the track could also be provided. The proposed hybrid sensing system fills a gap in the literature by analyzing potential applications in the railway transportation sector. It could contribute significantly to the knowledge of high-precision positioning for detecting moving vehicles. This thesis extensively researches the implementation of a hybrid system for high-precision positioning in urban transportation. Addressing the research questions above demonstrates this model's feasibility and potential to revolutionize the urban transportation sector. The published articles from this thesis have significantly contributed to the knowledge of high-precision positioning systems and their applications in the transportation sector. The proposed hybrid system has several potential uses, advantages, and limitations in various transportation types. For instance, the system can be used in railway transportation to track trains and ensure their safe and efficient operation. The system can also be used in road transportation to track vehicles and optimize traffic flow. Additionally, the system can be used in air transportation to track airplanes and ensure their safe and efficient operation. One of the significant advantages of the hybrid system is its high accuracy in positioning, speed, and direction determination. The system can provide accurate positioning even at high noise levels, making it suitable for use in busy urban environments. The system is also robust and can withstand harsh environmental conditions, making it suitable for use in various transportation contexts. However, the hybrid system has certain limitations that need to be considered. For instance, the system requires a network of sensors to provide accurate positioning, which can be costly to implement. In conclusion, the proposed hybrid system utilizing Fiber Bragg Gratings (FBG) technology is a promising solution to the accuracy problem in real-time positioning. The system can provide high-precision positioning, speed, and direction determination, making it suitable for use in various transportation contexts. The system has several potential uses, advantages, and limitations that need to be considered when implementing it. Overall, the system has the potential to revolutionize the urban transportation sector by ensuring safe and efficient operation.