Research Of Weak Signal Extraction And Transmission Technology Based On Low Voltage Power Line In Underground Coal Mine

Nowadays there are many coal mines in our country. The automation of coal mine production is getting more and more important. While the development of signal extraction and transmission technology (SETT) underground coal mining is lagged. Communication network which can overcast the whole coal mine is difficult to establish, so the information sharing cannot work better because of different technique protocol used in different communication equipments. So the coal mine automation development is restricted badly. And even more, it could make large numbers of coal mine accidents, which could take a heavy number of casualties and national property loss. At present, there is not effective technology to solve this problem. SETT based on low voltage power line underground coal mine (LVPLUCM) is deeply researching in this work. Not only is the study theoretic meaning, but it has practical value. First of all, the theory and algorithm are built by researching SETT of special environments similar as underground coal mine. Second, the results of this research can be applied to production and safety of special environments and can resolve practical problem of underground coal mine.The research emphases of the high-speed digital network construction based on LVPLUCM is the channel modeling and the communication technique. The key SETT based on LVPLUCM were studied deeply, such as the methods of LVPLUCM characteristics testing, channel modeling and the technique of digital communications. The main research work and contributions are as follows:1. The channel model of LVPLUCM based on the expansion of wavelet matrix is built in the paper. Now, the researches of channel modeling based on LVPLUCM are concentrated on the channel of over ground low voltage power line. The most typical techniques of channel modeling are the method of modeling based on multi-path and transmission matrix. Both are difficult when they are carried out on the channel modeling underground coal mine due to the disadvantage of property of real time adjustment. The experiments show that the model is exact and the real time property of the model is excellent. The model can meet the requirement of real time property of digital signal extraction and transmission.2. In this paper the technique of LVPLUCM based wavelet-OFDM is proposed. The construct and arithmetic of the synthesis filter based on Daubechies wavelet-OFDM was built in this work. This technology can solve low efficiency and bad spectrum features of the OFDM. The communication performance can be improved through this technology.3. Capacity of resisting disturbance is not good enough and the PAPR is high when the technique of traditional OFDM was used on LVPLUCM to transmit digital signal. The technique based on CLUSTER-OFDM was proposed and cluster distribution mechanism was built in this paper. The simulation results verify the effectiveness of the proposed algorithm. The complexity was reduced efficiently, PAPR was improved and the system reliability was increased by using the technique of CLUSTER-OFDM.4. The bit error rate at some frequency is extremely high when the traditional OFDM technique was used in LVPLUCM, which effects the communication of signal information badly. The underground low voltage power line communication technique based on PRECODED-OFDM was built in this paper. The technique is different to the pre-coding technique in the field of wireless communication, so it is very important to build a simple structure and an easy coding process of the pre-coding technique. The conclusion of simulation shows that the problem of bad null-spectrum can be solved using the technique built in this work with a little increment of calculation. And the efficiency of communication can be improved observably.