Introduction  

With the rapid development of urban rail transit, subways have become an efficient and convenient mode of transportation, carrying a huge passenger flow. At the same time, the importance of subway security inspections has become increasingly prominent, as they are related to the travel safety of every passenger. Traditional security inspection technologies have gradually exposed some limitations when dealing with complex and changeable security scenarios. As an emerging wireless communication technology, Ultra-Wideband (UWB) technology is gradually making its mark in the field of subway security inspections due to its unique technical advantages, bringing new possibilities to improve the efficiency and accuracy of subway security inspections.  

Overview of UWB Technology  

Technical Principle  

UWB technology transmits data using nanosecond to picosecond-level non-sinusoidal narrow pulses. Instead of using traditional sinusoidal carriers, it achieves communication and positioning by sending and receiving strictly controlled Gaussian single-cycle ultra-short pulses with precise intervals. This ultra-short single-cycle pulse gives the signal an extremely wide bandwidth. In terms of positioning, UWB systems typically use positioning algorithms such as Time Difference of Arrival (TDOA). Taking TDOA as an example, a tag sends data packets to an area covered by anchors, and all nearby anchors receive the tag's wireless signals. Due to the different distances between the anchors and the tag, the messages arrive at each anchor at different times. These time differences are multiplied by the constant speed of light in space to obtain the distance differences between the tag and the anchors, forming the basis for multi-point positioning calculations to ultimately determine the tag's relative coordinates.  

Technical Advantages  

- High-Precision Positioning: UWB signals have pulse widths in the nanosecond range, corresponding to a distance resolution capability of up to centimeter level. For example, in practical application scenarios, positioning accuracy of 10–35 cm can be achieved, which is difficult for other narrowband systems to match, providing a strong guarantee for accurately tracking the positions of personnel and objects.  

- Strong Anti-Interference and Penetration Capability: In complex subway environments, there is a large amount of electromagnetic interference and signal blockage by obstacles such as metal and concrete. Using Time of Flight (ToF) and Angle of Arrival (AoA) ranging technologies, UWB can maintain stable positioning signals even in complex environments similar to mine tunnels (up to 10 km long) with rock obstructions and equipment electromagnetic interference. In subway platform layers, its pulse signals have strong penetrability, capable of penetrating concrete walls to achieve full coverage of the station hall and platform.  

- Low Power Consumption: Taking the UWB positioning tag worn by miners as an example, its battery life can exceed 6 months. In subway security inspection applications, the low-power consumption feature eliminates the need for frequent battery replacement or charging, reducing maintenance costs while ensuring long-term stable operation of the equipment.  

- High Capacity: UWB positioning systems can support large-scale terminal concurrent positioning. For example, in coal mine scenarios, they can meet the needs of overcrowding monitoring and attendance management; in subway construction personnel positioning systems, they can track more than 2,000 terminals simultaneously, uploading trajectory data in real time to meet the needs of monitoring and managing a large number of personnel and equipment in subway security inspections.  

Application Scenarios of UWB Technology in Subway Security Inspections  

Positioning and Tracking of Personnel and Luggage  

- Real-Time Location Monitoring: In subway security inspection areas, UWB tags are worn by security personnel and passengers, while UWB base stations are deployed at key positions in security checkpoints and surrounding areas. Through the UWB positioning system, real-time location information of security personnel can be obtained, allowing managers to clearly grasp the work dynamics of each security officer, such as whether they are on duty at their designated posts or responding promptly to passenger needs. For passengers, their movement trajectories in the security inspection area can be tracked in real time. If abnormal situations occur, such as passengers staying in the security area for an extended period or moving against the flow, the system can issue timely warnings. In luggage security inspections, UWB tags attached to luggage carts or luggage itself can track the real-time location of luggage during the security inspection process, preventing cases of misplaced or lost luggage.  

- Rapid (Crowd Control) and Emergency Response: During peak hours with high passenger flow, such as morning and evening rushes, security inspection areas are prone to congestion. With the real-time monitoring of personnel positions via UWB technology, intelligent analysis systems can promptly plan optimal crowd control routes to guide passengers through security checks quickly and orderly, improving security inspection efficiency and alleviating congestion. In emergency situations such as fires or explosions, rescue personnel can quickly determine the precise locations of trapped personnel and security staff through the UWB positioning system, formulate optimal rescue plans, and improve rescue success rates.  

Assistance in Prohibited Items Detection  

- Precise Positioning of Suspicious Items: When traditional security inspection equipment such as X-ray security machines detect suspected prohibited items, UWB technology can play a crucial role. UWB base stations deployed beside X-ray security machines enable real-time positioning of luggage passing through the machines. Once a suspicious item is detected, the system can quickly determine the precise location of the luggage and feedback the information to security personnel, who can then quickly locate the corresponding luggage for further manual inspection, significantly improving the efficiency of prohibited items screening.  

- Assisted Multi-Modal Detection: Combining UWB technology with other advanced prohibited items detection technologies, such as millimeter-wave imaging detection, UWB is responsible for precise positioning of luggage and personnel, while millimeter-wave imaging technology performs detailed imaging detection of objects. Through their collaborative operation, more comprehensive and accurate detection of prohibited items can be achieved. For example, millimeter-wave imaging technology can obtain detailed image information of prohibited items hidden deep in luggage or obscured by other objects, while UWB technology ensures that detection equipment can accurately target the intended luggage or items, enhancing the pertinence and accuracy of detection.  

Optimization of Safety Management  

- Employee Attendance and Workflow Management: The UWB positioning system enables automatic attendance management for security personnel. When security personnel enter the work area, the system automatically identifies their UWB tags and records attendance information, avoiding issues such as proxy attendance in traditional attendance methods. Meanwhile, by recording and analyzing the work trajectories of security personnel, security inspection workflows can be optimized. For example, if unnecessary walking or waiting time is found in certain posts, workflow adjustments can be made to improve overall work efficiency.  

- Zonal Permission Management: In subway security inspection areas, different permission zones are set up, such as security equipment operation areas and prohibited items temporary storage areas. Personnel with different responsibilities are equipped with UWB tags corresponding to their permissions. When personnel enter areas beyond their authority, the UWB positioning system immediately issues an alarm to remind managers, preventing unauthorized personnel from entering sensitive areas and ensuring the safety management order of security inspection areas.  

With its high-precision positioning, strong anti-interference capabilities, and other features, UWB technology has demonstrated great value in multiple subway security inspection scenarios, providing key technical support for the intelligent and efficient upgrading of subway security inspections. It is expected to become an important component of the future subway safety protection system.