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The development and deployment of mobile communication systems, personnel and vehicle positioning systems in mines require an analysis of wireless transmission characteristics, the selection of preferred working frequency bands, and the optimization of wireless communication base stations and positioning substations. In this study, wireless transmission tests were conducted in a large frequency range from 350 MHz to 6 GHz in mine environments such as curved tunnels, branch tunnels, main transportation tunnels, excavation tunnels, and fully mechanized mining faces. The test results were analyzed, revealing the characteristics of wireless transmission in mines: ① In curved tunnels, the lower the wireless transmission frequency, the smaller the attenuation, with the least attenuation in the 350 MHz to 900 MHz frequency band. ② In branch tunnels, the lower the frequency, the smaller the attenuation, with the least attenuation in the 350 MHz to 900 MHz frequency band. ③ In main transportation tunnels, the least wireless transmission attenuation was found in the 700 MHz to 900 MHz frequency band. ④ In excavation tunnels, the least attenuation was in the 700 MHz to 900 MHz frequency band. ⑤ In fully mechanized mining faces, the least attenuation was observed in the 433 MHz to 1 300 MHz frequency band. ⑥ With the same cross-sectional area of the tunnels, wireless transmission attenuation in curved tunnels was smaller than in branch tunnels, and the attenuation in branch tunnels emitted from branch sources was smaller than that emitted from main tunnels. Curves and branches in tunnels increased wireless transmission attenuation. Furthermore, this paper proposed the preferred working frequency bands and the best arrangement of antennas for wireless communication systems in underground coal mines, specifically in curved and branch tunnels: ① The working frequency bands for underground wireless communication systems should preferably be in the 700 MHz to 900 MHz range. ② To minimize the impact of curves and branches in tunnels on wireless transmission, wireless communication base stations, positioning substations, and their antennas should be set at the turning points of curved tunnels and at the branch points of branch tunnels. The research results have been applied to the People's Republic of China energy industry standards NB/T 11546-2024 General specification of 5G communication system for coal mines, NB/T 11523-2024 5G communication base station for coal mines, and NB/T 11547-2024 5G communication baseband controller for coal mines.

In order to meet the different requirements of coal mine monitoring, positioning, video, audio, remote control, 5G and other services for latency, reliability, bandwidth and other indicators, the coal mine information comprehensive bearer network should have the following functions. ① The network slicing function supports FlexE interface technology or channelized sub interface technology, and divides port bandwidth resources into different network slices. The services between different network slices are isolated and carried by each other without affecting each other. ② The online bandwidth expansion function of network slicing ensures that there is no packet loss during the bandwidth adjustment process. ③ Network slices set the power-off protection function. ④ The network complies with IEEE 802.3 and TCP/IP protocols, supports IPv6 protocol and IPv6 service bearer, and supports both IPv4 and IPv6 services simultaneously. ⑤ The network supports 10GE optical interface, 1GE optical interface, 10/100/1000 Mbit/s adaptive interface. The core and aggregation nodes should support optical interfaces of 50GE or above. ⑥ It is advisable to use a circular or double ring structure. ⑦ The real time monitoring function for business quality, monitors the delay, jitter, and packet loss rate of specified services in real time. ⑧ 1588v2 clock synchronization function supports 5G base station service access. The main technical indicators of the coal mine information comprehensive bearer network should meet the following requirements. ① The optical port transmission distance should be ≥ 20 km. The transmission distance of the electrical port should be ≥ 100 meters. ② The transmission rate of the backbone network should be ≥ 10 Gbit/s. The transmission rate of the access network should be ≥ 1 Gbit/s. ③ The packet loss rate for different frame lengths is ≤ 0.01% (under 70% network traffic load conditions). ④ The single node transmission delay should be ≤ 1 ms (when the Ethernet frame length is 1518 bytes). ⑤ Node forwarding jitter should be ≤100 μs. ⑥ The number of slices supported by a single interface should be ≥ 5. ⑦ The minimum bandwidth of FlexE interface technology should be ≤1 Gbit/s. The minimum bandwidth of channelized sub interface technology should be ≤ 2 Mbit/s. ⑧ The self-healing time of network reconstruction should be ≤ 50 ms. ⑨ After a power outage in the power grid, the continuous working time of the bearer network equipment under standby power supply should be ≥ 4 hours.

High power radio waves emitted by mobile communication systems such as 5G, 5.5G, WiFi6, WiFi7, UWB, ZigBee, as well as personnel and vehicle positioning systems in mines, pose a risk of igniting gas and coal dust. Therefore, it is necessary to set a reasonable threshold for the explosion-proof safe power of radio waves emitted by explosion-proof radio equipment, and limit the power of radio waves emitted by explosion-proof radio equipment. The European standard CLC/TR 50427:2004 Assessment of inadvertent ignition of flammable atmospheres by radio-frequency radiation-Guide specifies a threshold for the safe reception and ignition power of radio waves in explosive gas environments. But it lacks content on the threshold for the safe transmission power of radio waves. Although the national standard GB/T 3836.1-2021 Explosive atmospheres-Part 1:Equipment-General requirements and the international standard IEC 60079-0:2017 Explosive atmospheres-Part 0:Equipment-General requirements have relevant provisions on the safe transmission power threshold for radio wave explosion protection, they mistakenly modify the safe reception ignition power threshold for radio wave explosion protection in the European standard CLC/TR 50427:2004 to the safe transmission power threshold for radio wave explosion protection. It greatly reduces the maximum transmission power allowed by radio equipment in explosive atmospheres. There’s a lack of slender structural objects such as cranes that can serve as receiving antennas in coal mines. The existing radio communication and positioning systems in mines operate at frequencies far greater than 30 MHz. Therefore, the threshold for the safe reception and ignition power of radio waves should be 8 W, instead of the radio wave explosion-proof safe transmission power threshold of 6 W specified in the national standard GB/T 3836.1-2021 and the international standard IEC 60079-0:2017. When the energy of the radio waves emitted by the transmitting antenna is fully absorbed by the equivalent antenna, which is the most unfavorable for wireless explosion-proof transmission and coupling, and the operating frequency of the radio equipment is the equivalent antenna resonance frequency, the reception and ignition power reaches its maximum. It is half of the total power received by the equivalent antenna, that is, half of the transmission power. In practical engineering, both radio transmission efficiency and coupling efficiency are not equal to 1. Therefore, the threshold for safe transmission power of radio waves should be more than twice the threshold for safe reception and ignition power of radio waves. The threshold for the safe reception and ignition power of underground radio waves in coal mines is 8 W. Therefore, the threshold for the safe transmission power of underground radio waves in coal mines should be greater than 16 W.

The current national standard GB/T 3836.1-2021 Explosive atmospheres-Part 1: Equipment-General requirements and the international standard IEC 60079-0:2017 Explosive atmospheres-Part 0: Equipment-General requirements stipulate that the threshold power of a radio transmitter is the product of the effective output power of the radio transmitter and the antenna gain. Under the condition of a certain threshold for the safe transmission power of radio wave explosion-proof, the larger the antenna gain, the smaller the effective output power of the radio transmitter. This will limit the improvement of wireless transmission distance by increasing the antenna gain. Therefore, it is necessary to study the correctness of the threshold power specified in the national standard GB/T 3836.1-2021 and the international standard IEC 60079-0:2017, and propose reasonable explosion-proof requirements and detection methods for radio wave transmission power. It has been proposed that the safe transmission power of radio waves is independent of antenna gain, and the threshold power of radio transmitters specified in the national standard GB/T 3836.1-2021 and the international standard IEC 60079-0:2017 is incorrect. It is proposed that the threshold for the safe transmission power of underground wireless radio waves in coal mines should be greater than 16 W and independent of antenna gain. The national standard GB/T 3836.1-2021 and the international standard IEC 60079-0:2017 stipulate that the threshold power shall not exceed 6 W, which is incorrect. A method for detecting the explosion-proof safety performance of wireless radio waves has been proposed. The method detects the output power of wireless transmitters. This not only ensures the explosion-proof safety of the detected wireless equipment, but also simplifies the detection method. The method improves the wireless radio wave transmission power of the wireless equipment, removes the limitation on antenna gain, and greatly improves the wireless transmission distance of wireless explosion-proof equipment in coal mines.

The automatic perception and alarm method for coal mine rock burst and coal and gas outburst is an effective measure to timely detect accidents and emergency rescue, reduce casualties, avoid or reduce secondary accidents such as gas and coal dust explosions, and curb delayed, missed, and concealed reporting of accidents. It is difficult to perceive coal mine rock burst accidents, and there is currently no automatic detection and alarm method for coal mine rock burst accidents. Coal mine rock burst accidents are mainly discovered manually. At present, there are only automatic alarm methods for coal and gas outbursts based on methane, wind speed, and direction sensors. There are problems such as slow response speed and inability to detect significant increases in methane concentration before methane sensor damage. A method for image perception and alarm of coal mine rock burst and coal and gas outburst has been proposed. Based on the image features of coal mine rock burst and coal and gas outburst temperature, color, depth, burial, etc., the method recognizes coal mine rock burst and coal and gas outburst. Based on the changes in gas concentration in the roadway space and mining face, the method distinguishes between rock burst and coal and gas outburst. If the gas concentration rapidly increases over a large area, it is judged as coal and gas outburst, otherwise it is judged as rock burst. This method has the advantages of intuitiveness, fast response speed, non-contact, wide monitoring range, simplicity and reliability, and can intuitively record the real situation of coal mine rock burst and coal and gas outburst. When the coal mine rock burst and coal and gas outburst accidents are alarmed, the personnel on duty in the control room can immediately confirm the accident through video recording and carry out emergency rescue in a timely manner. A method has been proposed to reduce the impact of coal mine rock burst and coal and gas outbursts on image perception, including multi point arrangement of cameras, setting of cameras at higher positions, timely transmission of video data, and multi-point arrangement of methane sensors.

In order to meet the needs of remote monitoring, video monitoring, data acquisition, and voice communication in coal mines, the 5G communication system used in coal mines should have the following functions. ① The system has different service-bearing functions such as remote control, monitoring, positioning, surveillance, and voice. ② The system has remote control functions such as coal mining machines, roadheaders, electric shovels, excavators, trackless rubber wheeled vehicles, and electric locomotives. ③ The system has an emergency remote takeover function for mining transportation vehicles. ④ The system has a remote real-time transmission function of camera audio and video. ⑤ The system has data collection functions such as monitoring equipment, sensors, and vehicle-assisted driving. ⑥ The system has a voice call function. ⑦ The system has an end-to-end slicing function that meets the differentiated business performance requirements of remote control, monitoring, video, and voice. ⑧ The system supports SA networking and 5G NR communication system. ⑨ The system supports 5G LAN Ethernet communication. ⑩ The system has an emergency inertia operation function. In case of disconnection between the mining area's private network and the communication operator's public network, local businesses can continue to operate online. ⑪ The system has a device level redundancy protection function that ensures uninterrupted data service in the event of a single physical port failure. ⑫ The system has a dual device redundancy protection function of the core network that allows for the switching of backup devices to continue providing services when the main device fails. ⑬ The system has the core network control surface transmits confidentiality and integrity protection functions to ensure the security of the core network control surface. ⑭ The system has terminal authentication, checking, and restricting access to unauthorized terminals in the system, supporting the authentication of terminals by coal mining enterprise security servers. ⑮ The system has functions that prevent terminal attacks on the system and legitimate terminal. ⑯ The system has the integrated management function of the core network, transmission equipment, base station controller, base station, and terminal. ⑰ The system has a centralized monitoring function for network performance and business service performance. ⑱ The system has an abnormal visual alarm and fault location function. ⑲ The system has the evaluation function of mining 5G network resources. The system can evaluate the utilization rate of 5G network resources and provide a report on whether new services can be accessed when the coal mine adds new services or more terminals are connected to the 5G network. ⑳ The system has backup power supply. The main technical indicators of the 5G communication system used in coal mines should meet the following requirements. ① When the uplink rate is 20 Mbit/s and the wireless working frequency band is 700-900 MHz, the wireless coverage radius (unobstructed) of the base station in the underground coal mine should be ≥ 500 meters. When the wireless working frequency band is other working frequency bands, the wireless coverage radius (unobstructed) of the base station in the underground coal mine is ≥ 150 m. When the uplink rate is 30 Mbit/s, the wireless coverage radius (unobstructed) of the base station in the open-pit coal mine is ≥ 400 m. ② The wired transmission distance from the base station to the base station controller is ≥ 10 km. ③ The maximum number of access terminals in the system is ≥ 20000. ④ The wireless transmission power of the base station and terminal of the underground coal mine is ≤ 6 W. The transmission power of the base station in the open-pit coal mine is ≤ 320 W. The wireless transmission power of the terminal in the open-pit coal mine is ≤ 6 W. ⑤ The base station wireless reception sensitivity is ≤ −95 dBm. The terminal wireless reception sensitivity is ≤ −85 dBm. ⑥ The wireless working frequency should be selected from the frequency bands of 700 MHz, 800 MHz, 900 MHz, 1.9/2.1 GHz, 2.6 GHz, 3.3 GHz, 3.5 GHz, 4.9 GHz, 6 GHz, etc. (preferably 700 to 900 MHz for underground coal mine). ⑦ When the format is TDD and the frame structure is 1D3U1S, the average uplink throughput rate of multiple users accessed by the base station is ≥ 600 Mbit/s, and the average downlink throughput rate is ≥ 250 Mbit/s. ⑧ For underground coal mines, when operating upstream services at 1 Mbit/s and 20 Mbit/s, the average system delay should be less than 20 ms, and the probability of end-to-end delay stability being less than 100 ms should not be less than 99.99%. For open-pit coal mines, when operating upstream services at 1 Mbit/s and 30 Mbit/s, the average system delay should be less than 20 ms, and the probability of end-to-end delay stability being less than 100 ms should not be less than 99.9%. ⑨ The packet loss rate of a single user is ≤ 0.01%. ⑩ The handover delay for a single user from cell A of the base station to cell B of the base station is ≤ 100 ms. ⑪ The continuous working time of the mobile station battery should not be less than 11 hours, among which the call time should not be less than 2 hours. ⑫ After a power outage in the power grid, the backup power supply continuously provides power to the base station, base station controller, and transmission equipment for ≥ 4 hours.

Early detection of mine electric sparks and alarm can prevent or reduce gas and coal dust explosions and mine fire accidents. There are no natural light sources such as sunlight, moonlight, and starlight underground. The main factor affecting the recognition of mine electric sparks is the mine light source. By adjusting the installation position and angle of the camera, the impact of fixed mine light sources on electric spark recognition can be avoided or reduced. But it cannot solve the impact of mobile mine light sources on electric spark recognition. The discharge cycle of electric sparks generated by different forms of circuits is different, but the discharge time of electric sparks is less than 4 ms. The minimum bright duration of the flash light source is 240 ms. Therefore, the features of the short emission time of electric sparks and longer exposure time of mine moving light sources to cameras can be utilized to eliminate the impact of mine moving light sources on camera exposure. The camera shoots at a high frame rate, and the electric spark image has a feature of 1 frame dark -1 frame bright -1 frame dark, that is, a 'dark light dark' frame feature. The 'bright' frames with sparks have a large sum of pixel grayscales in a single frame. The 'dark' frames without sparks have a small sum of pixel grayscales in a single frame. The illumination of a moving light source on the camera is variable, going through a process of no light, light, and no light. In the absence of electric sparks, the camera also shoots at a high frame rate. The images of both moving constant bright light sources and moving flashing light sources do not exhibit the 'dark bright dark' frame feature. Based on the unique 'dark bright dark' frame feature of electric spark images, a mine electric spark recognition and alarm method based on the sum of adjacent frame pixel grayscale is proposed. The method collects monitoring area video images in real time. According to the set frame rate, the method preprocesses the video image into frames and calculates the pixel grayscale of a single frame image separately. If the difference between the current frame image pixel grayscale and the previous frame image pixel grayscale is less than the pre-set threshold, the method continues to collect the video image. Otherwise, the method calculates the difference between the current frame image pixel grayscale and the subsequent frame image pixel grayscale. If the difference is less than the pre-set threshold, the method continues to collect video images. Otherwise, the method issues a mine electric spark alarm signal. After the mine electric spark alarm, if the emergency response is not activated manually, the mine electric spark alarm will continue. Otherwise, the method exits the current alarm state and continues to collect video images. This method can effectively eliminate the interference of moving constant light sources and flashing light sources.

This paper analyzes the technologies of mine ranging and positioning, such as ultrasound, laser, video, inertial navigation, pedometer, and radio. Among them, radio ranging and positioning have the advantages of long positioning distance, small positioning error, no impact from light, little impact from dust, easy identification, and low system cos. They are suitable for positioning mine personnel and precise positioning of mine personnel. The paper analyzes radio ranging and positioning technologies such as UWB, ZigBee, RFID, 5G and WiFi6. Mining UWB has the advantages of long positioning distance, small positioning error, and low cost. It is suitable for precise positioning systems for mine personnel. Mining ZigBee has the advantages of long positioning distance, small positioning error, and low cost. It is suitable for mine personnel positioning systems. Mining RFID has the advantage of having the lowest system cost. It is suitable for coal mine underground personnel management systems. The positioning precision of mine 5G and WiFi6 is lower than UWB, and the system cost is higher than ZigBee. It is unsuitable for mine personnel positioning and precise positioning systems. The received signal strength indication (RSSI), time of arrival (TOA), time differences of arrival (TDOA), two-way ranging (TWR), symmetrical double-sided two way ranging (SDS-TWR), angle of arrival (AOA) and other mine personnel positioning algorithms are analyzed. The RSSI positioning method has a large positioning error, making it difficult to meet the needs of mine personnel positioning and precise positioning. The TOA positioning method requires accurate and synchronized timing between the positioning card and the substation clock. The positioning card and substation have high costs. It is unsuitable for mine personnel positioning and precise positioning. The TDOA positioning method does not require synchronization between the positioning card and the positioning sub-station clock. It has low requirements for the precision of the positioning card clock and low cost of the positioning card. However, it requires accurate timing of the positioning sub-station clock and synchronization between the positioning sub-stations. The positioning substation cost is high. It can be used for mine personnel positioning and precise positioning. The TWR positioning method and SDS-TWR positioning method do not require clock synchronization between the positioning substation and the positioning card, nor do they require clock synchronization between the positioning substations, nor do they require clock synchronization between the positioning cards. This reduces the complexity and cost of the positioning card and the positioning substation. It is suitable for mine personnel positioning and precise positioning. The AOA positioning method system is complex, costly, with large long-distance positioning errors and dead angles. It can only be used for straight-line obstacle-free positioning. The positioning antenna and positioning precision are greatly affected by mechanical vibration. It is not suitable for the independent positioning of mine personnel and precise positioning. However, it can be used in conjunction with other mine positioning methods.

The application of technologies such as 5G, UWB, ZigBee and WiFi6 in coal mine mobile communication, personnel and vehicle positioning, and wireless transmission has promoted coal mine safety production and intelligent construction. However, due to the limitations of electrical explosion-proof measures, the wireless transmission power underground in coal mines is not greater than 6 W, which restricts the wireless transmission distance in the mine, and increases the usage of base stations and system costs. It is not convenient for system use and maintenance. Under the condition that the wireless transmission power is limited by electrical explosion-proof measures, selecting a wireless operating frequency band with smaller transmission attenuation can effectively increase the wireless transmission distance, reduce the usage of base stations, and reduce system costs. In order to meet the needs of selecting and optimizing the working frequency band of wireless transmission in mines, wireless transmission tests in the 700 MHz to 6 GHz frequency band are conducted in the auxiliary transportation roadway and fully mechanized working face of the Sandaogou Coal Mine of the National Energy Group. The test results are analyzed and the optimal frequency band for wireless transmission in mines is proposed. ① The optimal operating frequency band for wireless transmission in auxiliary transportation roadways is 700 to 910 MHz. ② The optimal working frequency band for wireless transmission in fully mechanized working faces is 700 to 1 710 MHz. ③ The wireless transmission attenuation of the auxiliary transportation roadway is smaller than that of the fully mechanized working face. As the frequency increases, the difference in wireless transmission attenuation between the auxiliary transportation roadway and the fully mechanized working face decreases. ④ The optimal working frequency band for wireless transmission in mines is 700 to 1 710 MHz.

In order to improve the detection accuracy of coal mine gas and coal dust explosion, recognition method of coal mine gas and coal dust explosion based on the sound spectrogram and SVM was proposed: installing mining pickups in key monitoring areas of underground coal mines, monitoring of working sounds of underground coal mine equipment and environmental sound in real-time. The collected sound was extracted from the sound spectrogram composed of MFCC, and the energy, entropy, contrast, and correlation of 0°, 45°, 90°, and 135° were obtained by calculating the gray co-generation matrix of the sound spectrogram. Calculated their mean and standard deviation as the texture features of the sound spectrogram image, which constituted the feature quantity of the sound, which brought to SVM to establish the sound recognition model of coal mine gas and coal dust explosion. For the sound to be tested, the texture features were also extracted and input to the trained recognition model for sound recognition and classification, which has passed the test verification. Firstly, the MFCC feature values of different sounds, such as mining equipment operation, gas and coal dust explosion were extracted, and the distribution of MFCC feature values of different sounds was analyzed; the sound spectrograms of different sounds were extracted, and the mean and standard deviation of the sound spectrograms of different sounds were analyzed by analyzing the feature parameters of energy, entropy, contrast, and correlation, and the grayscale co-generation matrix feature parameters of the sound spectrograms constitute the feature quantities that can effectively characterize the sound signals. Secondly, the sound to be measured was input into the recognition model established to complete the recognition and classification. The results show that the recognition rate of the proposed method reaches 95%, and the overall recognition performance is higher than others models. Finally, the experimental results of Bayesian parameter optimization show that the recall rate and recognition rate of the optimized SVM recognition model increased by 10% and 3% respectively. It was better than the recognition model before optimization, which can meet the needs of coal mine gas and coal dust explosion sensing and alarming.

The powerful radio waves can ignite explosive gases. Therefore, it is necessary to reasonably set the radio wave explosion-proof safety power and energy threshold emitted by the radio transmitter to limit the radio wave power and energy emitted by the radio transmitter. The radio wave explosion-proof safety power and energy thresholds specified in European Standard CLC/TR 50427:2004 Assessment of inadvertent ignition of flammable atmospheres by radio-frequency radiation-Guide are the ignition power and energy threshold. The national standard GB/T 3836.1-2021 Explosive atmospheres-Part 1: Equipment-General requirements and the international standard IEC 60079-0:2017 Explosive atmospheres-Part 0: Equipment-General requirements directly cite the radio wave explosion-proof safe power and energy threshold specified in the European standard CLC/TR 50427:2004. But the continuous radio wave explosion-proof safe ignition power threshold is incorrectly modified as the product of the effective output power of the transmitter and the antenna gain. This leads to the reduction of the continuous radio wave explosion-proof safe transmission power threshold. Under certain transmission attenuation and reception sensitivity conditions, the wireless transmission distance is reduced. This is not conducive to the promotion and application of mine wireless communication system and personnel positioning system. Therefore, the safe power threshold for continuous radio wave explosion-proof specified in national standard GB/T 3836.1-2021 and international standard IEC 60079-0:2017 should be the ignition power threshold, not the product of the effective output power of the transmitter and the antenna gain.

At present, there are some problems in the construction of the intelligent mine, such as the non-uniform interface protocol and the formation of new 'information island'. They lead to the difficulty of data fusion and sharing in mines and the difficulty of realizing the high-quality development of intelligent mine. It is pointed out that the key problem of mine intelligent construction lies in the lack of standardized and unified data acquisition, transmission and sharing standards. According to the core specification, application specification, and operation and maintenance specification, the technology system of intelligent mine communication interface and protocol is designed. The communication interface and protocol model of intelligent mine is proposed. The perception layer, transmission layer and application layer of the model are defined. The model of intelligent mining equipment is constructed, and the communication interface is described formally. The intelligent mine data is divided into perception data, text data and audio-visual data. The message structures of the three kinds of data are defined. According to the current mining equipment, technology application and development direction, the intelligent mine data acquisition modes are divided into equipment direct acquisition, protocol conversion acquisition, and system transfer acquisition. The application scenarios of three data acquisition modes are pointed out. The acquisition and transmission process of perception data, text data, and audio-visual data are described. The technical specification of intelligent mine communication interface and protocol covers the whole process of mine data fusion communication. It provides unified interface mode and communication protocol specification for intelligent mine data acquisition, transmission, fusion and sharing. And it realizes interconnection and intercommunication among various systems of the mine.

The paper analyzes the image characteristics of the thrown coal and rock when rock burst and coal and gas outburst occur. ① The coal and rock thrown out during rock burst and coal and gas outburst are mainly black, but the underground equipment of the coal mine is generally not black. Therefore, nonblack mining equipment can be used as the background and color cameras can be used to identify coal and rock. ② The normal coal falling speed, the moving speed of shearer, roadheader, and the moving speed of underground personnel and vehicles are far less than the speed of coal and rock thrown out in the event of rock burst and coal and gas outburst. Therefore, according to the speed characteristics, the interference from normal coal falling, movement of equipment such as shearer and roadheader, and movement of underground personnel and vehicles can be eliminated. ③ The explosion of gas and coal dust will also cause the objects in the roadway to have a high speed in a short time, accompanied by high brightness. But the rock burst and coal and gas outburst will not produce high brightness. Therefore, according to the average image brightness, the interference of gas and coal dust explosion can be eliminated. The paper proposes a color camera set method. The camera of the heading face should be set at the roof of the heading roadway or near the roof on both sides of the heading roadway. The camera of the working face should be set on the top of the hydraulic support. The paper puts forward a coal mine rock burst and coal and gas outburst perception alarm method based on color image. ① The color camera with fill light shall be set at the roof of the heading roadway or near the roof on both sides of the heading roadway, and at the top of the hydraulic support of the working face. The nonblack mining equipment is used as the background. ② The method monitors and identifies whether the color of the color image has changed greatly. ③ If the image color changes significantly, the average brightness of the image is identified, otherwise the monitoring of the identified image color change continues. ④ If the average brightness of the image is less than the set brightness threshold, the movement speed of the object causing a large change in the image color is identified, otherwise the monitoring of the identified image color change continues. ⑤ If the movement speed of the object is greater than the set speed threshold value, the methane concentration in the monitoring area is identified, otherwise the monitoring of the identified image color change continues. ⑥ If the methane concentration rises rapidly or reaches the alarm value, the coal and gas outburst alarm will be given. Otherwise, the rock burst alarm will be given. The method has the advantages of non-contact, wide monitoring range, low cost, convenient use and maintenance.

The burial image features of a large amount of black coal rock thrown out during rock burst and coal and gas outburst are analyzed. The features include changes in the area of the monitoring area's color and corresponding graphics, changes in the number of colors and corresponding graphics, changes in the shape of colors and corresponding graphics, and anomalies in burial positions. When a disaster occurs, it will result in a reduction in the area of non-black areas within the monitoring area, with a significant reduction in speed and acceleration. Based on the above feature, a perception alarm method for rock burst and coal and gas outburst is proposed based on the features of color and its corresponding graphic area changes. When a disaster occurs, it will result in a reduction in the number of non-black areas within the monitoring area, with a significant reduction in speed and acceleration. Based on the above feature, a perception alarm method for rock burst and coal and gas outburst is proposed based on the features of colour and its correspoding graphic number changes. When a disaster occurs, it will cause a decrease in the circularity, rectangularity, and area-to-perimeter ratio of non-black graphics within the monitoring area, with a significant reduction in speed and acceleration. Based on the above feature, a perception alarm method for rock burst and coal and gas outburst is proposed based on the features of color and its corresponding graphic shape changes. When a disaster occurs, it can lead to underground coal mine personnel, hydraulic support at the top and near the top being buried by coal and rock. Based on the above feature, a perception alarm method for rock burst and coal and gas outburst is proposed based on the features of abnormal burial position. The above perception alarm method for rock burst and coal and gas outburst based on burial image features has the advantages of fast response speed, non-contact, wide monitoring range, low cost, and convenient use and maintenance.

The paper puts forward a perception and alarm method of rock burst and coal and gas outburst based on temperature. The infrared thermal imager is used to monitor the temperature of objects, and the methane sensor is used to monitor the concentration of ambient methane. When the temperature of the objects is higher than the ambient temperature of the coal mine and the temperature of the exposed coal rock, and the number, volume and area of objects that are higher than the ambient temperature and the temperature of the exposed coal rock are large, it is determined that rock burst, coal and gas outburst, mine fire or gas and coal dust explosion accidents have occurred. The temperature of the high temperature object is further determine. If it is greater than the set threshold, it is determined that a mine fire or a gas and coal dust explosion accident has occurred. Otherwise, it is determined that a rock burst or a coal and gas outburst accident has occurred. The change of methane concentration is further analyzed. If the methane concentration rises rapidly, it is determined that a coal and gas outburst accident has occurred. Otherwise, it is determined that a rock burst accident has occurred. The paper puts forward a perception and alarm method of rock burst and coal and gas outburst based on velocity. The lidar, millimeter-wave radar, ultrasonic radar, binocular vision camera are used to monitor the moving speed of objects. The methane sensors are applied to monitor the concentration of ambient methane. When the moving speed of the object is not less than the set threshold, it is determined that rock burst, coal and gas outburst or gas and coal dust explosion accident have occurred. The number, volume and area of objects with abnormal velocity is further determined. If the number of objects with abnormal velocity is small, the volume and area are small, it is determined that a gas and coal dust explosion accident has occurred. If the number of objects with abnormal velocity is large, the volume and area are large, it is determined that a rock burst or a coal and gas outburst accident has occurred. The changes of methane concentration are further analyzed. If the methane concentration increases rapidly, it is determined that a coal and gas outburst accident has occurred. Otherwise, it is determined that a rock burst accident has occurred. A multi-information fusion method for perception, alarming and judging disaster source of rock burst and coal and gas outburst is proposed. The method monitors and integrates various information such as temperature, speed, acceleration, burial depth, sound, air pressure, wind speed, wind direction, dust, methane concentration, equipment status, micro-seismic, geosound, stress, infrared radiation, electromagnetic radiation and images so as to monitor the pressure and coal and gas outbursts. The source of the disaster is determined through the magnitude of parameter changes at different locations, the sequence relationship and sensor damage.

The characteristics of coal mine gas and coal dust explosion are analyzed. The gas concentration changes suddenly. The ambient temperature rises rapidly. The air pressure rises suddenly. It produces fireballs and smoke. It produces strong infrared and ultraviolet radiation. It generates explosion shock waves and flame waves. It produces explosive sound. The coal mine gas and coal dust explosion perception based on explosion sound has the following advantages. ① Explosion shock waves and flame waves attenuate quickly and travel close distances. Sound waves attenuate slowly and travel over long distances. The mine sound pickup equipment far away from the explosion source can be used for the perception of coal mine gas and coal dust explosion. ② Compared with the coal mine gas and coal dust explosion perception method based on gas concentration and temperature sensors, the proposed method has the advantage of fast response. ③ Compared with the coal mine gas and coal dust explosion perception method based on video images, the proposed method has the advantages of not being affected by dust, light, shelter, etc. ④ Mine sound pickup equipment has low cost and is easy to install. ⑤ The sound travels over a long distance and it is less affected by roadways and branches. ⑥ The sound processing speed is fast. The gas and coal dust explosion sound can be quickly recognized from various sound signals in a short time. A perception method of coal mine gas and coal dust explosion based on explosion sound recognition is proposed. The sound signals in the monitoring area are collected using microphone array pickups. After preprocessing such as normalization, framing, and adding category labels, the sound signal features are extracted. The features are input into a statistical classifier for training. The sound recognition model for coal mine gas and coal dust explosion is established. The sound signal of the monitoring area is collected in real-time. The extracted sound signal features are input into the trained coal mine gas and coal dust explosion sound recognition model. Whether it is the coal mine gas and coal dust explosion sound can be determined. If so, an alarm will be given.

In order to prevent gas explosion caused by radio waves emitted by wireless equipment in the coal mine, the power and energy of radio waves in coal mines should be limited. This paper introduces the safety power threshold of continuous radio wave explosion-proof specified in different standards. ① GB/T 3836.1-2021 Explosive atmospheres-Part 1: Equipment-General requirements and the international standard IEC 60079-0:2017 Explosive atmospheres-Part 0: Equipment-General requirements refer to the European standard CLC/TR 50427:2004 Assessment of inadvertent ignition of flammable atmospheres by radio-frequency radiation-Guide. When there is no slender structure object (such as a crane) that can be used as a receiving antenna in an explosive environment, the clause that the explosion-proof safety power threshold of continuous radio wave in Class I environment (representative gas is methane) is 8 W is omitted. It is indiscriminately stipulated that the safe power threshold of continuous radio wave explosion-proof in Class I environment is 6 W. ② The British Standard BS 6656:1991 Guide to prevention of inadvertent ignition of flammable atmospheres by radio-frequency radiation specifies that for continuous radio-wave operating frequencies greater than 30 MHz in a Class I environment, the safe power threshold for continuous radio-wave explosion-proof is 8 W, Whether there is a crane or other slender annular structure object. ③ The British Standard BS 6656:2002 Assessment of inadvertent ignition of flammable atmospheres by radio-frequency radiation - Guide and the European Standard CLC/TR 50427:2004 both specify a safety power threshold of 8 W for continuous radio-wave explosion-proof in Class I environments without slender annular structures such as cranes. The safe power threshold of continuous radio wave explosion-proof in Class I environment with slender annular structures such as cranes is 6 W. The characteristic of the underground environment and equipment in the coal mine are analyzed. Generally, there is no crane underground. The underground coal mine is a confined space, with a long roadway but a small roadway section. Cable, water pipe, rail, steel wire rope, overhead line, tape rack and other axial conductors laid along the roadway axis are thin and long, but will not form a ring antenna conducive to radio wave reception. Transverse conductors such as roadway I-beam support can form a ring antenna conducive to radio wave reception. However, the section of the I-steel conductor is large, which does not meet the characteristics of slender structure. The hydraulic support in the fully mechanized working face can form an annular structure. However, the hydraulic support jack divides it into multiple annular structures. The support conductor section is large, which does not meet the characteristics of slender structure. It is pointed out that before the explosion-proof safety power threshold of continuous radio wave in coal mine is implemented to 6 W, the mine wireless communication systems such as leakage, induction, through-the-ground and multi-base stations have been widely used in the coal mine. And there is no case of gas and coal dust explosion accident. Therefore, the threshold of explosion-proof safety power of radio wave in the coal mine is set as 6 W without distinction, which lacks of theoretical analysis and experimental verification. In particular, 5G, WiFi 6, UWB, ZigBee and other mining mobile communication systems and personnel and vehicle positioning system working frequency is higher. Therefore, the coal mine continuous radio wave explosion-proof safety power threshold should be 8 W.

In order to reduce the number of operators in the working face of coal mines, an unmanned 5G ground remote control method for working face is proposed. The industrial cameras and sensors are set up in the working face, which transmit video, audio and sensor signals to the ground through the 5G network. The ground operator operates the equipment remotely, which transmits control commands to the working face through the 5G network, and controls the actions of the mine equipment. The wireless transmission distance and transmission bandwidth calculation method are proposed for unmanned ground remote control of the fully mechanized working face. The wireless transmission distance between the base stations at the two ends of the fully mechanized working face should not be less than 1/2 of the length of the fully mechanized working face. The total uplink transmission bandwidth required for unmanned ground remote control of the fully mechanized working face is proportional to the length of the fully mechanized working face, inversely proportional to the center distance of the hydraulic support, inversely proportional to the number of supports and cameras, and proportional to the transmission bandwidth required for the compressed video of a single camera. In order to reduce the demand for uplink transmission bandwidth for unmanned ground remote control of fully mechanized working face, it is possible to only transmit the camera videos of the adjacent shearers. The minimum bandwidth of uplink transmission required for unmanned ground remote control the fully mechanized working face is proportional to the number of cameras of the adjacent shearers, and proportional to the required transmission bandwidth of a single camera after video compression. The wireless transmission distance test method for the unmanned ground remote control system of the fully mechanized working face is proposed. The method is applied for the wireless transmission system such as 5G for the unmanned ground remote control system of the fully mechanized working face. Under the premise of ensuring transmission bandwidth, time delay and reliability, the wireless transmission distance is tested. The test shows that the uplink wireless transmission bandwidth of the base station shall not be less than 20 Mbit/s, and the wireless transmission distance shall not be less than 150 m. This study proposes the all-mine integrated information transmission network based on network hard slicing. Through network hard slicing, different channels are allocated for coal mine safety monitoring, mine monitoring, personnel and vehicle and equipment positioning, video monitoring, voice communication, 5G communication, etc. This method guarantees the high reliability and low time delay requirements of coal mine safety monitoring and mine monitoring, and unifies the underground information transmission network of coal mines. Moreover, it integrates multiple networks such as coal mine safety monitoring network, mine industrial Ethernet and mine 5G communication network.

In order to solve the problem that most of the current mine external fire monitoring methods do not have fire source positioning function, a binocular vision-based perception and positioning method of mine external fire is proposed. Firstly, the method sets up mine visible binocular cameras or near-infrared binocular cameras at multiple points in roadways, chambers and working faces with cables, tapes and electromechanical equipment to capture images of the monitoring area. Then, the adopted images are preprocessed and binarized images are obtained by threshold segmentation. The roundness, rectangularity and number of sharp corners in the image are calculated, and the images are identified by flames according to the roundness, rectangularity and number of sharp corners. If there is flame in the image detection area, a fire alarm signal will be issued and the temperature, smoke, carbon dioxide, carbon monoxide, oxygen and infrared sensor information are taken into consideration to improve the accuracy of alarms. Finally, the method uses mine visible binocular cameras or near-infrared binocular cameras to measure the distance of the fire source, locates the fire source based on the camera position, and outputs the fire source location information to control the fire extinguishing device near the fire source. Far-infrared binocular cameras can also be used for fire perception and fire source positioning, but the cost is high. The binocular vision-based perception and positioning method of mine external fire can sense and locate the fire source. This method has the advantages of wide monitoring range, low cost, fast response and visualization, and solves the problem of locating the fire source of mine external fire.

The characteristics of the mine wireless relay emergency communication system are analyzed in this study. The wireless transmission power is limited by explosion-proof, the mine wireless transmission attenuation is large, and the wireless transmission distance is short. The working frequency band is not limited on the premise that the wireless communication equipment working underground does not interfere with each other and does not affect the normal operation of the wireless equipment on the ground when being taken out of the mine. The relay links are distributed in a chain in the roadway, and the overall network is in a tree topology. In order to solve the impact of the broken cable (cable or optical cable) caused by the coal mine accident on the mine emergency communication system, the implementation method of mine wireless relay emergency communication system is proposed. This method separates the data transmission link from the protocol control link to improve the flexibility of link control and the transmission efficiency of routing protocol signaling. The receiving/transmitting frequency bands and sub-channel frequencies of each base station in the link are set according to the physical sequence of base stations, which solves the problem of mutual interference between relay stations at all levels. In data link relay transmission, each relay station in the link can exchange data continuously with the front and back nodes, which solves the problems of bandwidth loss, relay delay and system stability caused by multi-level relay. The frequency molecular channel mode of the relay station with spatial multiplexing of zones solves the problem of limited frequency division channel resources. The fixed node-based transparent routing strategy simplifies the level-by-level route addressing and route discovery process and improves data forwarding efficiency. The redundant base station down-link routing strategy of normal link avoids the channel interference problem caused by the mixed transmission of primary and redundant nodes. The link breakpoint recovery method of redundant base stations, mobile terminal bridging and local access coordination improves the anti-fault ability of the link.

In order to solve the problem that visible light images are greatly interfered by mine lights, car lights, roadway lights, dust and red object in mines, the mine external fire sensing method based on near-infrared and visible light images is proposed. The near-infrared images and visible light images are fused to bring into play the advantages of obvious early flame characteristics in near-infrared images and obvious mid-term flame characteristics in visible light images so as to improve the recognition rate of mine external fire. This paper proposes a mine external fire sensing method based on multiple information fusion of near-infrared image, visible light image, temperature sensor, gas sensor and smoke sensor. The method fuses near-infrared image, visible image and sensor information. The sensor does not need no blind area coverage. Only a certain number of gas sensors, temperature sensors and smoke sensors need to be set up, which has the advantages of being timely, reliable and low-cost.The fire alarms are divided into four categories, including the image, temperature, smoke and gas fire alarms. The image fire alarm information includes near-infrared image and visible light image information. When the fire is detected by near-infrared image or visible light image, the image fire alarm signal is issued.When the temperature exceeds the limit, the temperature alarm signal is issued. When the smoke exceeds the limit, the smoke alarm signal is issued. The gas fire alarm information includes CO, CO2, O2, etc. When CO, CO2 or O2 exceeds the limit, the gas alarm signal is issued. The fire alarms are divided into four levels, including blue, yellow, orange and red, with red being the highest level.When one of the four alarm signals of image, temperature, smoke and gas issued, the blue alarm signal is issued. When two of the four alarm signals of image, temperature, smoke and gas issued, the yellow alarm signal is issued. When three of the four alarm signals of image, temperature, smoke and gas issued,the orange alarm signal is issued. When all four alarm signals of image, temperature, smoke and gas issued, the red alarm signal is issued.

Coal mine gas and coal dust explosion will produce explosive sound. Coal and gas outburst will produce the sound of coal cannon and the supports will produce squeaking and cracking sound. Rock burst will produce huge rock breaking sound and vibrations. Coal mine water inrush will produce 'hissing' water sound, and a large amount of water inrush will produce water flow sound. Coal mine roof fall will produce roof cracking sound, coal rock hitting the ground sound and support damage sound. According to the characteristics of the sound of extraordinary accidents in coal mines, the alarm methods of accidents of mine gas and coal dust explosion, coal and gas outburst, rock burst, water inrush and roof fall are proposed. The characteristics of the time domain and frequency domain of each accident sound are different from the characteristics of other sounds, and the sound can be monitored in real time by mine explosion-proof sound pickup equipment and system. Therefore, accidents can be sensed and alarmed through the intelligent analysis of the sound and the analysis of the characteristic parameters of the sound frequency, amplitude and short-term energy. By monitoring and analyzing the sound intensity and other characteristics of different monitoring locations, the sequence of occurrence and the damage sequence of explosion-proof sound pickup equipment, the accident location is able to be determined. Based on the characteristics of each accident, the accident identification method of multi-information fusion analysis is proposed to reduce the sound interference of coal fall from the working face, blasting operations, coal mining equipment, excavation equipment, transportation and lifting equipment, power supply equipment, emulsion pumps, water pumps and local ventilators. The paper discusses the advantages and disadvantages of different sound pickup equipment and proposes that the microphone arrays should be used for mine sound pickup equipment. Furthermore, the paper proposes a sound recognition classifier applicable to coal mine extraordinary accidents.

Mine unmanned vehicles are needed to reduce the number of coal mine underground operating personnel and to build safe, efficient, green and intelligent mines. The characteristics of mine unmanned vehicles are summarized as following points. The positions of underground operating personnel in coal mine are comprehensively identified. All mine vehicles are controlled. Mine track transportation equipment only needs one-dimensional positioning. The lighting condition is poor. The wireless transmission attenuation is large. There is no satellite signal. The electromagnetic environment is complex. The characteristics also include electrical explosion-proof, humid environment and water spray and dust. This paper analyzes the technical characteristics of mine vehicle positioning, such as ultrasonic positioning, laser position, radio positioning(including RFID, ZigBee, UWB, WiFi6, 5G), inertial navigation, simultaneous localization and mapping(SLAM), odometer and so on. This study puts forward a joint positioning method of mine vehicle, which is based on UWB and supplemented by inertial navigation, odometer and SLAM. This paper analyzes the technical characteristics of obstacle identification and distance measurement of mine unmanned vehicle, such as laser radar, millimeter wave radar, infrared camera, visible light camera, visible light binocular vision camera and so on. This study puts forward a multi-information fusion method of obstacle identification and distance measurement of mine unmanned vehicle. The method is mainly based on laser radar, supplemented by millimeter wave radar, infrared camera, visible light camera, visible light binocular vision camera and ultrasonic radar. When the road condition is complex and the automatic driving can not make decisions, the mine unmanned vehicle needs to automatically switch to the ground remote control mode. In view of the above situation, it is pointed out that the mine unmanned vehicle ground remote control technology based on 5G is the preferred scheme. However, the mine 5G wireless communication system has the problems of small wireless coverage radius and high cost. Therefore, it is suggested to study the application of WiFi7 in the mine vehicle ground remote control.

The electric leakage of underground cables and electrical equipment in coal mine, electromotive force discharge induced by high-power radio transmission on metal support and electromechanical equipment metal will generate electric spark, which will then lead to mine fire, gas and coal dust explosion. The early perception of mine electric spark and taking preventive measures can avoid or reduce mine fire, gas and coal dust explosion. The early perception of mine fire, gas and coal dust explosion and timely emergency rescue can reduce casualties and property losses. The ultraviolet image perception method of mine electric spark and thermal power disaster is proposed. The ultraviolet camera, pickup and air pressure sensor are set in coal working face, heading face and roadway to collect mine ultraviolet image, sound and air pressure in real time. The ultraviolet images are preprocessed. The interference of fluorescent lamps, incandescent lamps and LED lamps is eliminated. If there was an electric spark ultraviolet image, the electric spark alarm would be given. If there was a fire ultraviolet image, the fire alarm would be given. If the ultraviolet image was not an electric spark image nor a fire ultraviolet image, and if the pickup detected an explosion sound or the air pressure sensor detected a sudden increase in air pressure, the gas and coal dust explosion alarm would be given. The ultraviolet image is greatly interfered by incandescent lamps and fluorescent lamps, and is less interfered by LED lamps. With LED lamp replacing incandescent lamp and fluorescent lamp in coal mine, various lighting and signal equipment in coal mine have little interference to ultraviolet image in coal mine. Therefore, the ultraviolet image perception method of mine electric spark and thermal power disaster has the advantages of small external interference, high reliability and simultaneously perception of electric spark, external fire, gas and coal dust explosion disasters.

Aiming at characteristics of electrical explosion-proof and large wireless transmission attenuation in underground coal mine, 5G technology and its application scope were analyzed.Mine-used 5G should adopt intrinsically safe explosion-proof. Mine-used 5G for control should have strong anti-interference ability. Mine-used 5G should be used for remote control of coal mining face and tunneling face. Mine-used 5G should be used for ground remote control of unmanned vehicle in underground coal mine. Mine-used 5G that has not been developed for characteristics of mine mobile communication is less cost-effective than mine-used WiFi mobile communication system. It is strictly forbidden to replace mine-used wired dispatching communication system with mine-used 5G mobile communication system. Mine-used 5G that is not developed for coal mine safety monitoring characteristics cannot replace coal mine safety monitoring system. Positioning accuracy of mine-used 5G that has not been developed for precise positioning characteristics of mine moving target is lower than that of mine-used UWB precision positioning system. Transmission rate of mine-used 5G in frequency range of 450-6 000 MHz is lower than that of mine-used WiFi6. Reliability of mine-used 5G that is not developed for monitoring characteristics of fixed equipment in underground coal mine is lower than that of mine-used wired monitoring system. It is urgent to research and develop mine-used 5G based on characteristics of safe production in coal mine, not just for explosion-proof transformation of existing ground 5G products.

Characteristics of coal mine gas and coal dust explosion are analyzed: Concentration of O2 in air decreases rapidly, while concentrations of CO2, CO and other toxic and harmful gases increase rapidly; Ambient temperature rises rapidly, and air pressure increases rapidly and then falls; Stronger infrared and ultraviolet radiation are generated; High-temperature, high-pressure, high-speed explosion shock wave and flame front are generated; Explosion sound and vibration are generated; A large amount of smoke and dust are generated; Wind speed increases rapidly and then falls, and wind flow reverses; Roadway collapses, electromechanical equipment is moved and damaged; A large number of casualties are caused. A coal mine gas and coal dust explosion perception alarm and explosion source judgment method based on multi-information fusion of gas (O2, CO2, CO)concentration, temperature, sound, vibration, air pressure, wind speed, wind direction, smoke, dust, infrared, ultraviolet and image is proposed: Gas and coal dust explosion can be identified through change of multi-parameters; Explosion source can be determined according to change range, change sequence of the parameters and sensor damage at different positions. Protection and setting methods of sensor are proposed: Sensor should be equipped with a streamlined or arc-shaped shell, and the sensor shell should use high-temperature resistant, fireproof and heat-insulating material; Sensor should be installed in center of roadway top; Sensor should be installed on mining face and heading face, and the sensor should be located 10-15 m away from the working face; Sensor should be installed in the middle of each roadway(without branches).Protection and setting methods of cable and optical cable are proposed: Armored cable and optical cable should be adopted, and the cable and optical cable should have properties of flame retardant, high-temperature resistance and impact resistance; Cable and optical cable should be buried at the angle between roadway side wall and floor; Cable and optical cable can also be protected by introducing into compressed air duct.

Mine wireless communication and mine-used 5G mobile communication technology is one of the key technologies of coal mine intelligence.In order to improve wireless transmission distance and diffraction ability as well as stability and reliability of wireless communication system in underground coal mine, reduce base station consumption, networking cost and maintenance workload, the effect of mine-used 5G working frequency band and antenna position of base stations on wireless transmission loss and transmission distance is studied.The major conclusions are as follows: ① Wireless transmitting power in underground coal mine is limited by intrinsically safe explosion-proof, receiving sensitivity is limited by electromagnetic noise, and antenna gain is limited by intrinsically safe explosion-proof and tunnel space.Therefore, under the conditions of limited wireless transmitting power, receiving sensitivity and antenna gain in coal mine, it is necessary to increase wireless transmission distance and diffraction ability, improve stability and reliability of wireless communication system, and reduce base station consumption, networking cost and maintenance workload by optimizing wireless working frequency band and antenna location setting.② 700 MHz is recommended as mine-used 5G working frequency band. Compared with other 5G frequency bands such as 2.6 GHz, 3.5 GHz and 4.9 GHz, 700 MHz frequency band in underground coal mine has the advantages of low wireless transmission loss, long wireless transmission distance, strong diffraction ability, less base station consumption, low networking cost and maintenance workload and so on.③ Analysis method of transmission loss/position change rate is put forward, which is convenient to analyze the change of transmission loss caused by position change in different transversal areas of tunnel.④ The antennas of wireless base stations should be set close to tunnel side, not less than 0.01 m away from tunnel side, and the height of antennas should be about 2/5 of tunnel height.This is convenient for installation and maintenance, not only does not affect pedestrians and driving but also can satisfy the requirements of low transmission loss and long transmission distance. ⑤ In order to improve wireless transmission distance, wireless terminals used in underground coal mine, such as mobile phones, personnel positioning cards, portable wireless methane detection alarms, multi-functional wireless lamps, portable wireless cameras, portable wireless instruments and equipments, wearable wireless devices, vehicle positioning cards, vehicle wireless devices, wireless cameras, wireless sensors, Internet of things devices and so on, should be closer to the tunnel center as much as possible under the condition of not affecting normal use.

At present, the information carrier network used in coal mine is mainly 100 Megabit, Gigabit and 10 Gigabit mining Ethernet ring network. The time delay and reliability of the network are uncontrollable. Therefore, it is difficult to meet the needs of few people or unmanned operation in underground coal mine and remote control on the ground. Quality of service (QoS) can guarantee the real-time performance and reliability of the highest priority application. However, the real-time performance and reliability of the highest priority application can not be guaranteed when multiple interface signals are imported at the same time and the data volume is large, or when the previous data packet is being sent. In order to solve the above problems, the technical requirements of coal mine intelligent information comprehensive carrier network are proposed. The requirements include wide transmission bandwidth, short transmission delay, high reliability, long transmission distance, strong anti-interference capability, intrinsically safe explosion-proof, strong adaptability to grid voltage fluctuation, strong anti-fault capability, good protection performance, multi-service comprehensive carrying, etc. Based on the above requirements, a coal mine intelligent information comprehensive bearing network based on flexible Ethernet (FlexE) is proposed. This network allocates different channels according to the requirements of different services on bandwidth, time delay and reliability. The businesses include time sensitive and time insensitive video, time sensitive and time insensitive audio, personnel positioning, vehicle positioning, equipment positioning, safety monitoring, power supply monitoring, transportation monitoring, drainage monitoring, coal working face monitoring and heading face monitoring. The network integrates coal mine monitoring, positioning, video and audio into one network. The coal mine intelligent information comprehensive carrier network based on FlexE not only meets the requirements of different services such as ground remote control, personnel positioning and safety monitoring for bandwidth, delay and reliability, but also realizes the coal mine intelligent information comprehensive carrier network, reducing the maintenance difficulty and workload.

Broadband wireless communication is foundation and key of smart mine construction. Special requirements for mine broadband wireless communication were proposed. Wireless signal is required to cover roadway more than 10 kilometers coal mine underground. Wireless transmission must be intrinsically safe. Wireless working frequency band should not be too high. Wireless transmission should have certain diffraction ability. Anti-interference ability is strong. Mobility requirements are not high. Mine-used 5G and WiFi6 were researched. Both 5G and WiFi6 can be used for broadband wireless communication in smart mine. Mine-used 5G has advantages of high transmission rate, small transmission delay and high call quality, but the system is complex and cost is high.Mine-used WiFi6 has advantages of high transmission rate, simple system and low cost, but transmission delay is large and call quality is poor.

The characteristics of mine flood video images were analyzed. The mine flood identification and trend prediction methods based on video images were proposed, including flood video dynamic identification, region segmentation, area estimation and trend prediction. The results were verified by experiments. The main conclusions are as follows: ① Both threshold pixel grayscale statistical method and pixel grayscale statistical method can monitor and identify floods. The threshold pixel grayscale statistical method not only can suppresses noise below the grayscale threshold and improve the accuracy of recognition, but also can reduce the pixel grayscale statistics, enhance contrast of a particular pixel grayscale range. ② Both the threshold segmentation method and the video differential segmentation method can segment the image of the flood area, the former is better overall and the latter is more detailed.③ The area of the water inrush area can be estimated and the trend can be forecast based on the segmented flood area image.

Mine exogenous fire monitoring methods were analyzed, and a mine exogenous fire identification method based on visible light and infrared image was proposed. ① Mine exogenous fire monitoring methods based on sensors for temperature, smoke and others need to arrange multiple points, so cost is high, and maintenance workload is large. ② Mine exogenous fire monitoring method based on visible light image has advantages of large monitoring range, simple use, low cost, small influence by distance, high resolution ratio, rich color information, clear edge texture information, easy extraction of flame structure information, etc. But it is influenced greatly by cap-lamp lights, roadway lights and red objects. ③ Mine exogenous fire monitoring method based on infrared image has advantages of large monitoring range and simple use, and can monitor fire in case of low visibility with smoke or others. But monitoring distance, mine dust, ambient temperature or humidity and emissivity of object surface all affect temperature measurement. Close-range workers, incandescent lamps and electromechanical equipment will affect fire monitoring. ④ The mine exogenous fire identification method based on visible light and infrared image improves accuracy of fire identification. When both visible light image and infrared image identify fire, it is determined to be a fire, and a fire alarm signal is issued. When there is only a single visible light image or infrared image to identify fire, it is not determined to be a fire, and a suspected fire alarm signal is issued. ⑤ The feasibility of the mine exogenous fire identification method based on visible light and infrared image is verified by experiments.

Based on analysis of principle and characteristics of mine flood perception methods such as water quality monitoring method, water inflow monitoring method, water temperature monitoring method, temperature monitoring method, humidity monitoring method, water level monitoring method, resistivity monitoring method, stress monitoring method, microseismic monitoring method and hydrological drilling method, mine flood perception method based on image monitoring and image-based big data mine flood perception and water source determination method were proposed. Conclusions were got as following: ① The water quality monitoring method can not only perceive flood, but also determine water source that causes flood, which has high perception accuracy of mine flood caused by surface water and goaf water. ② Time-based water inflow monitoring method has high accuracy, but complex deployment and poor real-time performance. The water inflow monitoring method based on flow velocity has advantages of simple operation and good real-time performance, but large measurement error. ③ The water temperature monitoring method can not only perceive mine flood, but also determine water source that causes flood, but it is not applicable to the flood perception that difference between mine flood water source temperature and normal mine water inflow temperature is small. ④ The temperature monitoring method has advantages of simplicity and convenience, but it is affected by mine fire such as coal spontaneous combustion, explosion of gas and coal dust, surface air temperature, mine ventilation quantity, underground equipments starting and stopping, and number of underground workers. The temperature monitoring method is not applicable to the flood perception that difference between mine flood water source temperature and normal mine water inflow temperature is small. ⑤ The humidity monitoring method has advantages of simplicity and convenience, but it is affected by humidity and temperature of surface air, mine ventilation quantity, and mine fire such as coal spontaneous combustion. ⑥ Change of surface water and groundwater source can be timely grasped by the water level monitoring method, but location of goaf water needs to be proved. ⑦ The resistivity monitoring method has advantages of fast response and high sensitivity, but accuracy is greatly affected by mining environment, and electrode arrangement is difficult. ⑧ The stress monitoring method and the microseismic monitoring method have advantages of good real-time performance, but due to impact of coal and gas outburst and rock burst pressure, the methods need to be used together with other mine flood perception methods. ⑨ The hydrological drilling method has advantage of large amount of information, but it needs to be used together with other mine flood perception methods. ⑩ The mine flood perception method based on image monitoring has advantages of non-contact, real-time and rapid, wide monitoring range, simple deployment and installation, low cost and convenient use and maintenance. Image-based big data mine flood perception and water source determination method simultaneously monitors mine water, water conducted channel and water source, which can not only perceive mine flood, but also determine water source that causes flood, and has advantage of high reliability.

Based on analysis of principle and characteristics of mine fire monitoring methods such as temperature monitoring method, gas monitoring method, smoke monitoring method, visible light image monitoring method and infrared image monitoring method, a mine fire monitoring and trend prediction method based on multi-parameter fusion was proposed. Conclusions were got as following:① Thermocouple temperature measurement method and semiconductor temperature measurement method have advantages of high accuracy, strong real-time performance and early detection of early fire, but there are disadvantages such as large sensor consumption and large maintenance workload; Infrared temperature measurement method has advantages of wide monitoring range and easy sensor arrangement, but shielding and coal dust between sensor and measured object will affect monitoring result; Fiber distributed temperature measurement method has advantages of multi-point temperature monitoring and small amount of cable consumption, but there are disadvantages such as easy damage, complicated installation and difficult maintenance of optical fiber. ② Gas monitoring method and smoke monitoring method have advantages of wide monitoring range, convenient use and maintenance, but there are disadvantages such as cannot monitor early fire with low concentration of index gas and less smoke. ③ Visible light image monitoring method has advantages of wide monitoring range, convenient use and maintenance, low cost, but interference sources such as roadway light, miner's lamp, vehicle lamp and red clothes and smoke will affect monitoring effect, and the method cannot monitor early fire with no flame and less smoke.④ Infrared image monitoring method has advantages of wide monitoring range, convenient use and maintenance, but cost is high, and shielding and coal dust between infrared camera and measured object will affect monitoring effect. ⑤ Mine fire monitoring and trend prediction method based on multi-parameter fusion of temperature, smoke, gas concentration, odor, wind direction, wind speed, air volume, visible light image and infrared image can not only detect fire in time, but also locate fire source and predict fire development trend.

Video image characteristics of gas and coal dust explosion are analyzed: Explosive fireball is usually red with high brightness, high temperature and strong radiation of infrared and ultraviolet rays, and area of the fireballs expands rapidly; Area, brightness, color, shape and radiation intensity of flame front are constantly changing; Area, color and shape of smoke and dust are constantly changing; There are objects that move or deform rapidly. Based on visible light video image, near infrared video image, far infrared video image and ultraviolet video image, a method of gas and coal dust explosion perception alarm and explosion source judgment is proposed: According to brightness and change rate of highlight area, area and change rate of highlight area, image shape and its change, image color and its change, gas and coal dust explosion are identified; Explosion source is determined according to image changes and time sequence of the changes and camera damage at different positions. A gas and coal dust explosion perception alarm and explosion source judgment method is proposed based on multi-information fusion of visible light video image, near infrared video image, far infrared video image, ultraviolet video image, O2, CO2, CO, temperature, sound, vibration, air pressure, wind speed, wind direction, smoke, dust, etc. The method reduces impact of fire, roadway lamp, miner's lamp, car lamp, red clothing, electromechanical equipment heat, fault discharge of electrical equipment and cable, coal and gas outburst, rock burst, large area roof fall, flood, blasting operation, coal falling on working face, coal transfer and transportation on gas and coal dust explosion identification.

For problems of low illumination intensity, uneven illumination and high coal dust concentration in working face, a visual tracking method of shearer based on compressive sensing was proposed. The image is normalized by use of rectangular filter firstly to get feature vectors. Then compressed Haar-like feature vectors of target samples and background samples are gotten according to compressive sensing theory for building target model and training naive Bayes classifier. The target image and background image are identified by the naive Bayes classifier finally, so as to realize dynamic tracking of shearer. The experimental result shows that the method can track shearer effectively when the shearer is moving or covered in environment of uneven and varied illumination, and average tracking frame rate is 22 frames per second.

Alpha‐linolenic acid and antioxidant substances (such as tocopherols and polyphenols) are abundant in chia seed oil, which may prevent certain chronic diseases. This study compared the physicochemical parameters, chemical composition and antioxidant properties of black and white chia seed oil extracted by solvent extraction, pressing and supercritical CO2 extraction. Chia seed oil contained higher levels of polyunsaturated fatty acids, including linoleic acid (18.68%–20.15%) and α‐linolenic acid (60.47%–63.68%). Black and white chia seeds and processing methods had significant effects on minor components (tocopherols, total phenols, phytosterols and squalene), oxidative stability and free radical scavenging ability. Compared with other methods, the contents of tocopherols (512.72–603.04 mg/kg), total phenols (35.21–57.75 mgGAE/kg) and phytosterols (5536.69–5956.65 mg/kg) were higher in the pressing method. In addition, 17 individual polyphenols were identified and quantified, among which genistein and gallic acid had higher contents, which were significantly affected by varieties and processing methods. In general, the pressing process may be the best processing method to improve minor components and antioxidant capacity. This study can provide a valuable reference for producing functional foods supplemented with α‐linolenic acid. [ABSTRACT FROM AUTHOR]

Introduction: High serum phosphorus level has been reported to be a risk factor for disease progression in patients with chronic kidney disease, whereas, its role in IgA nephropathy (IgAN) still remains uncertain. This study aimed to investigate the association between serum phosphorus and progression of IgAN. Methods: A total of 247 patients diagnosed with IgAN from 2016.11 to 2019.12 at the First Affiliated Hospital of Xi'an Jiaotong University were retrospectively enrolled in this study. The association between serum phosphorus and kidney disease progression events, defined as 30% estimated glomerular filtration rate (eGFR) decline or kidney failure, was evaluated using Cox models. Results: Serum phosphorus was an independent risk factor for poor renal outcome after adjusting for age, gender, urine protein, MAP, eGFR, hemoglobin, Oxford S and T scores (HR, 2.586; 95% CI, 1.238–5.400, p = 0.011). The addition of serum phosphorus to the reference model containing clinical and pathological variables significantly improved the risk prediction of IgAN progression (C statistic, 0.836; 95% CI, 0.783–0.889) as compared with the reference model (C statistic, 0.821; 95% CI, 0.756–0.886). The ability of serum phosphorus level to predict progression was much stronger in IgAN patients without use of immunosuppression (HR 5.173; 95% CI, 1.791–14.944; p = 0.002). Conclusion: Higher serum phosphorus levels were independently associated with kidney disease progression in patients with IgAN, especially in those without immunosuppression. The addition of serum phosphorus to clinical and pathological data at the time of biopsy significantly improved risk prediction of IgAN progression. [ABSTRACT FROM AUTHOR]

TOA ranging method requests high precision time measurement while existing mine WiFi systems can not provide high temporal resolution timer. In order to resolve the above technical problems, a TOA ranging method using re-spread spectrum technology to WiFi signal to obtain high resolution was proposed. Multi-carrier spread spectrum modulator is integrated into WiFi mobile station which is used to spread spectrum for ranging WiFi signal. Correspondingly, multi-carrier spread spectrum demodulator is integrated into WiFi base station, and a spread spectrum code capture algorithm with high speed digital matched filter designed by FPGA is used to capture ranging signal sent by the WiFi mobile station in sub-chip level, thus, the signal propagation delay time with high resolution is obtained. The test results show that the proposed method can provide reliable ranging data with mean-error of 1.92 m for TOA positioning of WiFi communication system.

The standard stipulates product classification, general requirements, environmental conditions, power supply, system design requirements, basic functions, software functions, main technical indexes, transmission performance, power fluctuation adaptability, working stability, anti-interference ability and explosion-proof performance of coal mine safety monitoring system. The standard is applicable to coal mine safety monitoring system used in coal mine.