Leaky Coaxial Cable (LCX) or leaky cable is basically the same structure as common coaxial cable. It consists of three parts: inner conductor, insulating medium and outer conductor with periodic grooves. The signal transmits in the leaky cable while radiating the electromagnetic wave to the outside through the grooves. The external electromagnetic field can also be induced into the leaky cable through the grooves and transmitted to the receiving end. At present, the frequency band of leaky cable covers are 90MHz-3.2 GHz or above, which are adapted to various existing wireless communication systems. The application scenarios include subway, railway tunnel, highway tunnel, underground mine, etc.
With the development of information technology, people have higher and higher requirements for signal coverage and signal quality. In subway tunnel, leaky coaxial cable is used as wireless signal coverage, and the field strength coverage of leaky coaxial cable has obvious advantages, which is an important means to improve transportation efficiency and management level, improve service quality, etc. At present, in Metro Communication, leaky cable carries the following tasks:

In the normal operation of subway, cable leakage is not only responsible for the transmission of wireless information for train dispatching, fire command and other services, but also for the public network signal transmission task closely related to passenger information. For technical reasons, leaky cable is the only key equipment not included in the scope of online monitoring in Metro communication dispatching system. In the current Metro practice, the conventional cable leakage laying structure is output by the station base station, and the signal is distributed in the upstream and downstream sections of the adjacent two sides of the station through the 4-power divider, a total of four sections. At present, the detection method of cable leakage in operation company is mainly to detect standing wave. The detection method adopted is: the base station has its own standing wave detection and alarm function at the signal output position. If the standing wave parameter is abnormal, the signal of the base station will alarm, and then the operator will carry out four sections of troubleshooting according to the standing wave alarm of the base station. The troubleshooting sequence is the station base station - jumper - arrester - power divider - cable leakage in each section. The troubleshooting focuses on each joint. The troubleshooting instruments are generally Standing wave instrument. After the alarm, the fault types and locations of the four sections need to be manually checked by the operators. The inspection method is time-consuming, laborious and untimely. The following figure shows the scene of workers patrolling the line.

In order to meet the demand of rail transit system for signal security and stability, the launch of IL guard online comprehensive diagnosis system for leaky cable can conduct all-weather online monitoring for leaky cable in real time and realize centralized management and control of information. The system adopts pulse compression technology, which has the best characteristics of traditional pulse and FMCW radar system, and realizes the perfect fusion of long and short detection distance and high precision fault location; the perfect fusion of fault location, diagnosis and evaluation; the perfect fusion of leaky cable health monitoring and base station signal strength monitoring. The equipment is mainly composed of leaky cable health online diagnosis unit and data transmission unit And monitoring center.

IL Guarder LCX online diagnosis system adopts pulse compression technology, which has the best characteristics of traditional pulse and FMCW radar system, and realizes the perfect fusion of long and short detection distance and high precision fault location; the perfect fusion of fault location, diagnosis and evaluation; the perfect fusion of cable leakage monitoring and base station signal strength monitoring
The hardware design of the system is based on SDR, which greatly simplifies the hardware design and improves the reliability. Its upgrade, operation and maintenance are realized through software as much as possible, which greatly improves work efficiency and greatly reduces maintenance workload. The algorithm is based on FPGA. It breaks the sequential execution mode, completes more processing tasks in each clock cycle, and surpasses the operation ability of DSP. Based on the powerful calculation energy, the system can locate multiple fault points at the same time (up to 10 points), and a single test unit can monitor multiple leaky cables at the same time.

System features mainly include：
1)Fault location at the same time (up to 10 points)
2)Multiple leaky cables can be monitored at the same terminal at the same time (up to 6 can be upgraded)
3)The fault diagnosis and location are completed at the hardware end. The hardware equipment is set with redundancy to improve the system reliability
4)Full platform digitalization, easy to produce and maintain, as well as future upgrade and function expansion
5)Based on Linux operating system, there is a strong possibility of in-depth development in software development
6)Various network protocols and software interfaces can be realized according to user requirements
7)The system can provide high confidentiality and intellectual property protection through hardware and software cooperation
8)Seismic resistance, strong magnetic interference resistance, compact structure, easy to install, and can adapt to harsh conditions