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1、外文文献A Coal Mine Environmental Monitor System with Localization I.RESEARCH STATUSAs an important energy, coal plays a pivotal role in the economic development. Coal mine monitoring system, is the important guarantee for coal mine safety and high efficiency production. In order to ensure the safe oper
2、ation, the installation of environment monitoring node in tunnels to real-time detection is very important. However, commonly used traditional monitoring node wired connection to obtain communication with the control system, this node exist wiring difficulties, expensive and other shortcomings. In c
3、ontrast, wireless sensor node can be easily with current mine monitoring network connection, and good compatibility, facilitate constituted mine gas monitoring network, to suit various size of mine applications. Since wireless nodes are battery powered, so completely out of the shackles of the cable
4、, shorten the construction period can be arranged at any time where the need to use.The Zigbee wireless communication technology is used in this coal mine environmental monitor system. This is a new short-range, low complexity, low power, low data rate, low-cost two-way wireless communication techno
5、logy. Now, wireless sensor network product based on Zigbee technology are quantity and variety, but the real product can be applied in underground environments of special sensor node is very few. The sensor node that we designed in the system is truly able to apply to in-well environment, it through
6、 the wireless sensor node security certification. At the same time, due to the special nature of the wireless network is that it can spread the wireless signal, we can easily locate staff for coal mine safety monitoring provides more protection.II. SYSTEM ARCHITECTUREThis system is a comprehensive m
7、onitoring system which is combined with software and hardware. Hardware part includes wireless mobile nodes and fixed nodes which were deployed in the underground tunnel, the main function of them is to collect coal mine environment data and require persons location. Software part refers to the PC m
8、onitoring software which is designed in VC+ is used to summarize and display the data of each node. Monitoring node is divided into mobile nodes and fixed nodes; they are using Zigbee protocol for wireless transmission of data. Because the fixed node is also using wireless data transmission method,
9、so its deployed in the underground roadway becomes very convenient. As the mobile node is carried by the miner, it must be using wireless transmission method. This allows the mine to form a topology of Zigbee wireless sensor network. The fixed node in wireless sensor network is router device and the
10、 mobile node carried by miner is the end device. Normally, the router of Zigbee network has no sensor equipment; it is only responsible for data forwarding. But considering the practical application, we believe that add sensor devices on the router will be better on monitoring underground coal mine
11、environment. So in our design, the router also has an environment monitoring function which is usually designed in end device.Fixed node will sent received data from mobile node to the gateway, then the gateway transmits data to monitor computer through RS232 or optical fiber. The PC monitor softwar
12、e in the computer will process all data and display them in a visualization window. The PC software also calculates each mobile nodes real-time location through the specific localization algorithm, according to the received signal strength (RSSI) obtained from mobile nodes.III. NODE DESIGNSince the
13、Zigbee wireless network platform sold on present market was designed for the general environment, for special underground so they are not suitable for the environment. Therefore, we need to customize the system for underground environment whit a special hardware circuit. Node photo are shown in Fig.
14、 1Then wireless microcontroller CC2530 chip is the core processor of the node device, it can constitute a Zigbee network with very few peripheral circuits. The CC2530 is an IEEE 802.15.4 compliant true System-on-Chip, supporting the proprietary 802.15.4 market as well as the Zigbee, Zigbee PRO, and
15、Zigbee RF4CE standards. Unlike other wireless chip, CC2530 built-in 8051 monolithic integrated circuits kernel, therefore we no longer need to use a single MCU to control the circuit, and this save us a lot of cost.A. Mobile NodeThe mobile node is the end device of a Zigbee network that can be carri
16、ed by miner; it should be a portable and low power consumption node. So the mobile node we designed is only as small as a mobile phone, and it is by built-in lithium ion battery power supply. In power loss, the core processor CC2530 is a low power consumption chip, when it is in the sleep mode, it o
17、nly need to use less then 1uA work current. In order to reduce power consumption as much as possible on the display, a 100*32 pixel matrix with no backlighting LCD screen was used. The batterys capacity of the mobile node is 1500mAh, so it is enough to meet the miners long hour works in the undergro
18、und. The battery charge management chip is TP4057, the maximum charge current can up to 500Ma.The mobile node circuit includes the gas concentration sensor MJ4.0 and temperature sensor PT-1000. As far as we know, many wireless sensor platforms use the digital type sensor. The communication between t
19、he digital sensor and the MCU need strict timing requirements. But considering the actual application, the wireless MCU usually has a real-time operating system in general, if we use the microcomputer to simulate the strict timing, it will affect the real-time of whole operating system. These two se
20、nsors output analog signals not digital signals. Only input this signal into a differential amplifier, can we get an appropriate signal that can be converted to a digital signal by an ADC mode within the CC2530 chip. In order to facilitate the carrying, external antenna was not used in our mobile no
21、de, instead of using a 2.4GHz patch antenna. And we customize a shell like a cell phone size; it is enough to put all PCBs, sensors and battery in it. Taking into account the small shell of the explosive performance is not very good, the design of PCBs and the selection of component are all carried
22、out the safety assessment.B. Fixed NodeFixed node is installed in the wall of the underground tunnel. Because it is big than the mobile node, it is not appropriate to carry around. The circuit of the fixed node is almost same with the mobile node, it also use a CC2530 chip as core processor. Because
23、 of underground tunnels generally deploy with power cable, fixed nodes can use cable power-supply modes. At the same time, because we use wireless signal transmission, the deployment of new fixed nodes become very convenient, which also resolves the problem of the signal lines deployment.As a fixed
24、node, the minor who is doing work may far from it, in order to facilitate the miners observed environmental data around the fixed nodes, it uses LED digital display. At the same time, the large current LED lights and buzzer are designed in the circuit; it makes the fixed node with the function of so
25、und-light alarm. Considering that it may occur the emergency of without electricity, fixed node also built-in a lithium-ion battery. Under normal conditions, lithium-ion battery is in charging status, when external cable disconnect, fixed node is automatic switched to battery power, which can ensure
26、 the mobile node can deliver the information through fixed nodes in underground.Without regarding to fixed nodes portability, we have a customized shell that has excellent explosion properties, and the internal space is enough to hold down the 2.4 GHz antenna. To ensure safety, all cables and the lo
27、cation of sensors are placed with particular glue sealed, so that it has a good seal.IV. POSITIONING FUNCTION One of the important functions of the wireless sensor networks is localization, especially in the underground tunnel, it relates to the safe of the miners life. Currently most widely used or
28、ientation method is GPS satellite positioning, it is a high precision, all-weather and global multifunctional system with the function of radio navigation, positioning and timing. But the GPS positioning method is not suitable for the underground work environment of coal mine, once you enter the und
29、erground, it cannot receive satellite signal, thus unable to achieve targeting. We need to consider how to use wireless network to realize positioning function, means using wireless signal between the communications of devices for positioning. The existing distance measuring technology between the w
30、ireless-devices basically is the following kinds of methods: TOA, TDOA, AOA and RSSI. About the TOA method, the distance between the two devices is determined by the product of the speed of light and transmission time. Although the precision of this method is accurate, but it require a precise time
31、synchronization, so it demand hardware is higher.TDOA technology need ultrasonic signal，which is setting on a node with receive and transmit function. When measure the distance, it can sent ultrasonic wave and wireless signals together. By measuring the difference between two signals arrival time, w
32、e can calculate the distance between two devices. Using this method can also obtain accurate result, but the method need to increase ultrasonic sending and receiving device on the node circuit, it will increase cost.AOA technology needs to install multiple antennas through the nodes so it can obtain
33、 adjacent nodes signals on deferent directions. With this it can determine the location information from number of adjacent nodes and calculate its own position. This method not only need to add additional hardware, but also its still very vulnerable to external disturbance, therefore its not suitab
34、le for utilize.RSSI ranging is a cheap and easy technology. By using this method, we dont need to add additional hardware design. We also do not need very precise time requirements. This technique is about with measuring the wireless signals strength in the propagation of the loss, to measure the di
35、stance between two nodes. Because of this method requires hardware equipment is less, algorithm is simple, so it has been using in many wireless communication field. Comprehensive all conditions, positioning on the use of RSSI ranging technique.A. Hardware Location EngineThe CC2431 wireless microcon
36、troller chip produced by TI Company has a hardware location engine. From the softwares point of view, CC2431s hardware location engine has a very simple API interface, as long as writing the necessary parameters and waiting for calculation, it can read the location results.The hardware location engi
37、ne is also based on RSSI technology. The localization system includes reference nodes and blind nodes. The reference node is a fixed node that located in a known position, the node know their place and send a packet notify to other nodes. The blind node receives packets from reference nodes, which c
38、an obtains reference nodes location and the corresponding RSSI value and put them into the hardware location engine, and then the blind nodes location can be read from the engine. On the surface, using the CC2431 hardware location engine targeting the program as a good choice, but considering the pr
39、actical application, it will encounter the following problems. First of all, we have choose the CC2530 as the main chip of fixed nodes of the system, its internal programs is running in Zigbee2007 protocol, but CC2431 as a early chip, it applies only to Zigbee2006 protocol. In the communications bet
40、ween CC2431 and CC2530 that will have compatibility problems. Secondly, CC2431 hardware location engine use the distributed computing, all mobile nodes location are calculated by themselves, and then they upload information to the gateway node, this will not only occupy the mobile node processing ti
41、me, still it can take up more network resources. For this reason, we have to shelve this approach, consider how to implement location by using CC2530 chip.B. Software Location Engine If we want to use CC2530 to implement location function, that we must write software location engine by ourselves. Be
42、cause that chip do not have a hardware location engine inside of it. This software location engine is still used RSSI technology; meanwhile mobile node position is calculated by the PC software, so as to reduce the burden of mobile node computing. To calculate the mobile node location, there must be
43、 at least three reference nodes. We will regard router nodes as reference nodes in network, and record the X, Y coordinates of every reference node. Then we let the mobile node send signal to each reference node, so that each reference node can obtain a RSSI values, with these parameters, we can use
44、 trilateral measurement method to calculate the specified location of the mobile node. The simpler way give the mobile node to broadcast way to send data, then around it every router node would receive the data from the mobile node, thus obtains RSSI values. Once the mobile node number increasing ne
45、twork, this method will make router nodes more burden, because the every radio message that the router node receives will transmit from the low layer to the top layer. Finally the application layer will analyze data packets. In fact, the mobile node need not to broadcast transmitted data, other rout
46、ing node can also receive the mobile node packets. Only child mobile nodes of the router node will continue to transmit the packet forwarding upward, the other router nodes will shield out the packet in the bottom of the protocol. In order to let all router nodes can receive the packet which sending
47、 by mobile nodes, and send its RSSI values up to the gateway node, we need to modify the relevant function in Z- Stack protocol which is provided by TI. First we find the function named afIncomingData, it deals with the received data from the bottom of protocol, in which we add some code that can ob
48、tain packets RSSI value. Then through the osal_set_event function to add and send an event MY_RSSI_REPORT_EVT of RSSI value task to OSAL polling system. This events corresponding function will be executed in the task of OSAL interrupt-driven function, thus the mobile node corresponding RSSI values w
49、ill be sent to gateway node. Through this method, the packet will only be processed by bottom function of the protocol. According to this method we can obtain corresponding RSSI value and save the computation time of mobile nodes. In fact, this software location engine is not implementing with a single mobile node, but through the operation of the whole system to achieve. By which the mobile node is only responsible for sending unicast packets. The mobile nodes parent router node is responsible to forwar