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Application prospect of 5G technology in coal mine intelligence (II)
2. The necessity and feasibility of intelligent application of 5G technology in coal mine
Intellectualization is the only way for the development of coal and the key core technology to support the high-quality development of coal. Coal mine intelligence is inseparable from the efficient interconnection of data and information, and the data characteristics and transmission needs of different coal mine application scenarios vary greatly. The traditional 4G + WiFi data transmission technology is difficult to meet the differentiated needs, resulting in the mutual influence and restriction of various application scenarios in coal mine, which can not support the needs of the development of coal mine intelligence. The characteristics of 5G large bandwidth, low delay and wide connection, micro base station, slicing technology and end-to-end connection provide the core technology support for breaking through the bottleneck of data transmission and processing in intelligent coal mining.
2.1 Necessity of intelligent application of 5G technology in coal mine
At the beginning of 5g design, three application scenarios were identified, namely Enhanced Mobile Broadband (eMBB), Ultra Reliable Low Latency Communications (urLLC) and Massive Machine Type Communications, (mMTC). Its technical support ability for eMBB scene can effectively meet the business requirements of large bandwidth such as ultra high definition video transmission in coal mine; its technical support ability for urLLC scene can effectively meet the communication requirements between unmanned mining vehicles, unmanned excavators and other intelligent devices in unmanned mines; The technical support ability of mMTC scene can better support a variety of coal mine safety monitoring and other sensor data acquisition needs. Therefore, the application of 5G communication technology in intelligent coal mining (Fig. 2) is the only way for future coal mining, which will effectively promote the process of intelligent coal mining and pave the way of "network communication" for fully opening intelligent coal mining.
Fig. 2 Support of 5G for intelligent mining of coal mine
At the same time, the existing mainstream coal mine wireless communication technologies, such as 4G and WiFi, are difficult to support the data transmission and processing needs of intelligent coal mining.
Disadvantages of 4G Technology: it can provide the peak rate of users with downlink exceeding 100 Mbps and uplink exceeding 50 Mbps, but in the process of intelligent production, a large number of scenes such as machine vision need high-definition video return, 1080p single channel needs 20 Mbps uplink bandwidth, 4K even needs 75 Mbps uplink bandwidth (The bandwidth affects the accuracy, the accuracy affects the recognition, and the real-time determines whether it can be controlled remotely and in time). Obviously, 4G can't cope with the above industrial application requirements.
WiFi networking pain points:
(1) Poor mobility. The delay of cross AP handoff is more than 100 ms, which causes AGV and other mobile devices to break the chain easily and is limited by the movement within AP.
(2) Poor coverage. WiFi signal is easy to form multipath interference after reflection and diffraction.
(3) Frequency band interference. WiFi uses the common frequency band, which has interference and affects the demodulation ability.
(4) Limited bandwidth. Vision based applications need a large uplink bandwidth (100 megabytes).
2.1.1 Perception demand of intelligent mining
Intelligent mining first needs the support of a large number of sensor data, which has the following characteristics (Fig. 3)
Fig. 3 Diversity of coal mine data
(1) Data types are diversified. The relevant data include video, voice, vibration, pressure, temperature, speed, gas concentration and other data of various types and transmission requirements.
(2) fast data generation. 5G application scenarios are mostly based on the real-time support of a large amount of data. At the same time, the instant data output of the Internet of things supported by 5G will be tens or even hundreds of times more than the previous data, and the data generation speed will be greatly improved.
(3) the volume of data is growing rapidly. The data in unit time increases exponentially, and the data volume accumulated over time develops towards PB or even ZB level, which lays the foundation for big data application analysis.
2.1.2 Intelligent mining transmission requirements
In the past, in order to solve the problem of timely transmission and isolation of coal mine control data, video monitoring data and safety data, the independent construction scheme of control communication ring network, video ring network and safety ring network was mostly adopted. Although the problem of data mutual occupation channel and safety data isolation was solved to a certain extent, the problems of large investment, low-level IOT and high-level integration were also prominent. 5g technology adopts slice management technology, customized network on demand, isolated private networks and interconnected bottom end-to-end, providing dedicated channels and security solutions for transmission requirements of different scenarios (Figure 4).
Fig. 4 Data transfer mode change
2.1.3 Demand of intelligent mining decision control
There are many underground intelligent fully mechanized face equipment, including high-precision positioning equipment, inertial autonomous navigation system, intelligent coordinated control system, high-density sensor access system, intelligent robot inspection system, high-definition video return system, etc. (Fig. 5) The equipment group composed of these devices needs to be unified coordinated processing and fast feedback control through the central control system, which puts forward higher requirements for the reliability and real-time performance of the communication network.
Fig. 5 Demand scenarios for diversification of mining decisions
2.1.4 Application requirements of new intelligent mining technology and new scenarios
With the improvement of the intelligent degree of coal mine production, underground UAV, intelligent VR / AR and other equipment will be widely used, so as to timely patrol the scene and remote consultation for equipment failure, no matter it is UAV flight control, UAV inspection video return, or remote diagnosis Fault diagnosis and maintenance of VR / AR intelligent remote equipment not only need to consume network bandwidth resources, but also need fast information feedback and real-time state control.
The requirements of typical business scenarios of intelligent production in coal mine for wireless transmission network are shown in Table 1
Table 1 Requirements for wireless transmission network in typical application scenarios of intelligent coal mine
The time delay of the mainstream WiFi technology, 4glte technology, Zig Bee, Lora and other wireless transmission technologies (the typical 4G delay is about 100 ms) can not support the demand of intelligent production technology; The bandwidth (4G uplink stable bandwidth is about 20 Mbps, which can only meet 2-3 UHD video image transmission) is also unable to carry the mobile broadband services such as Ultra HD industrial image processing, production robot control and intelligent remote maintenance (VR/ AR). The delay (typical) of 5g network is about 10 ms [15], the uplink stable bandwidth is about 150 Mbps, the number of connections is 106 /km2, and the quality of service (QoS) of the network can reach 99.999 9%. Through the comparison in Table 1, 5g network provides a strong support for the realization of various business scenarios of intelligent production in coal mines.
2.1.5 Interconnection requirements of heterogeneous IOT equipment
At present, there are many wireless communication protocols used in the field of coal mine production, each of which has its own shortcomings and is relatively closed. It is difficult to interconnect industrial equipment, and the user experience is poor. It is urgent to build a new generation of wireless technology system that can be compatible with a variety of protocols. 5g network has the ability to integrate multiple types of existing or future wireless access transmission technologies and functional networks, and is controlled through a unified core network to provide ultra-high rate and ultra-low delay user experience and consistent seamless services in multiple scenarios.
2.2 Feasibility of intelligent application of 5G technology in coal mine
When 5g technology is applied to intelligent coal mining, it is necessary to analyze the feasibility of 5G system deployment in underground special wireless communication environment.
Compared with the ground, the actual environmental factors of underground wireless transmission mainly have the following characteristics: ① the spatial characteristics of long and narrow underground and multibranches; ② the rough coal wall which is easy to absorb or interfere with radio wave transmission; ③ the complex equipment layout and strong magnetic interference; ④ the mining environment with more dust and gas.
When 5G wireless transmission technology is applied underground, there are mainly phenomena such as rapid attenuation of high-frequency wireless signal, enhancement of directional transmission ability and decline of diffraction ability, which lead to short transmission distance and limited coverage. These problems faced by 5G technology were tackled as major problems at the early stage of 5g technology development, so there are ultra dense networking technology and massive MIMO (Large scale antenna array technology) and micro base station technology, etc. these breakthroughs form the 5G core technology system, and support the commercialization of 5G technology.
From the perspective of network deployment, the current underground 4G network is a 4G + WiFi architecture, and the 4G coverage distance (based on the long and narrow space characteristics of the underground without the concept of coverage radius) is about 1500 m. 5G has two types: Acer station and micro base station. The large-scale equipment capacity and high transmitting power of the base station are not suitable for large-scale underground applications. Although the equipment capacity of the micro base station is small, the transmission power is low, and the effective coverage distance is about 500 m. Therefore, the control scope of the original 4G network can be completely covered by more than 3 5G micro base stations from the technical point of view, and the bandwidth and speed can be greatly improved and the delay will be reduced. In addition, the power consumption and volume of a single 5G micro base station is smaller than that of the existing 4G base station, which is more conducive to the safety of long-term underground use. The layout of 5G micro base station is shown in Fig. 6.
Fig. 6 Schematic diagram of 5G layout of fully mechanized mining face
For other adverse environmental factors faced by coal mine, reasonable use and planning of 5G technology can solve the problem of underground practical application. The key to success or failure is to design different 5g layout schemes for different application scenarios and application environments. For example, for the long and narrow multi branch underground space, the mode of wired optical fiber trunk + dense 5G micro base station should be adopted, the key is to control the power consumption and optimize the site; for the problem of synchronous transmission of video monitoring and control signals, the key is to reasonably slice the network, and do security isolation.
Therefore, the development of intelligent coal mining must establish a 5g network as the infrastructure of data transmission and distribution platform, build 5g + coal mine application scenarios, and provide the basic platform and application guarantee for the realization of intelligent coal mining.
To be continued......
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