Application Of MIMO-OFDM In Mine Wireless Communication System

Different from the subaerial wireless communication environment,the mine tunnel is a non-free propagation space in limited space.The electromagnetic wave propagation characteristics are very complicated,and the multipath fading is serious,which may easily cause Inter-Symbol Interference(ISI),as well as seriously affects the communication quality of the mine wireless communication system.The Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing(MIMO-OFDM)technology as a core technology of 4G not only eliminates ISI,effectively combats multipath fading,but also increases the capacity of the channel without increasing emission power and extra bandwidth,and increases the information transmission rate of the wireless communication system,and has broad application prospects in realizing the high-speed transmission of mine wireless communication in the future.For the complicated and varied characteristics and the serious multipath fading characteristics of mine tunnel,this thesis applies MIMO-OFDM technology to the mine wireless communication system.The specific research contents are as follows:Firstly,the Maxwell equation,electromagnetic field boundary conditions and Marcatili approximate analysis method are used to study the electromagnetic wave propagation characteristics of an ideal rectangular mine tunnel according to the theory of the electromagnetic wave propagation.It is verified that the best electromagnetic wave transmission frequency band in the mine is about 900 MHz through simulation analysis,and this frequency is used as the carrier frequency of mine MIMO-OFDM communication system.Secondly,the basic principle and system model of MIMO-OFDM system are introduced,and the simulation verify that the MIMO channel capacity increases with the increase of the number of transceiver antennas.The MIMO-OFDM system combines the advantages of MIMO and OFDM technologies.It not only combats frequency selective fading,but also increases channel capacity and improves spectrum efficiency.Then,the fading characteristics of mine wireless channel are analyzed in detail.A spatial correlation MIMO channel model based on the Nakagami fading is established by using the Kronecker product,and the spatial correlation and channel capacity of the channel model are analyzed.The simulation results show that compared with the MIMO channel model based on Rayleigh fading,this model can fit different distributions by changing the parameter m,so it is more suitable for the complex mine tunnel environment;it can increase the channel capacity by reducing the correlation of the channel and increasing the number of antennas or increasing the multipath number of the channel,so that verify the rationality of the model.Finally,the STBC-OFDM and SFBC-OFDM coding techniques are studied,the coded and uncoded OFDM systems are analyzed and compared based on the MIMO channel model established in this thesis.The simulation results show that both STBC-OFDM and SFBC-OFDM codes have a better anti-fading performance than uncoded OFDM systems;STBC-OFDM codes perform better than SFBC-OFDM codes in mine tunnels that without considering Doppler effect.The spatial correlation of the channel will seriously affect the coding performance,in order to ensure the coding performance,the channel correlation coefficient should be less than 0.4.