Establishment Of MIMO Channel Model Of Semicircular Arch Mine Tunnel And Analysis Of Channel Capacity

Coal occupies the dominant position of the energy of our country.The mining operations have higher safety risks.Thus,it is necessary to improve the wireless communication system in the mine and ensure the fluency of information in the mine tunnel.And mastering the channel characteristics of the mine tunnel is key to it.At present,most of the research objects of mine tunnels are rectangular cross-sections,which are not completely in line with the real situation.Therefore,this thesis chooses the more representative arched cross-sections as the research object,and then established a mine tunnel MIMO channel model that can predict the propagation characteristics of electromagnetic waves based on the mirror image method,and analyzed the channel characteristics of the model.Finally,this thesis gave specific solutions that can improve the channel capacity of the MIMO communication system in the mine tunnel.The main research results of this thesis include:(1)To solve the problem that the mirror image method is not suitable for mine tunnels with the arched roof surface,this thesis proposed a novel method.It predicts the electromagnetic wave propagation field strength of semicircular arch mine tunnels,which combines splitting arched roof surface and the mirror image method,and established the SISO channel model of the mine tunnel.This method obtains several effective reflection planes by dividing the arched surface and uses the mirror image principle to reversely find the effective propagation path of electromagnetic waves.The simulation results show that the algorithm proposed in this thesis can effectively count the number of reflected rays and predict the field strength at the receiving point.The field strength distribution curve is consistent with the general law of electromagnetic wave propagation along the mine tunnel.The curve first drops quickly and then drops slowly after passing the ‘breakpoint’.The results also show that the position of the‘breakpoint’ is affected by the signal frequency,the horizontal position,and the vertical position of the transmitting and receiving points.(2)In order to analyze the channel characteristics of the MIMO communication system in the mine,this thesis combined the principle of antenna array pattern synthesis and the mirror image method and established a MIMO channel model of mine tunnels.Then the calculation formulas of antenna array factors of different shapes and the calculation method of field strength vector sum are given.The simulation results show that the model can effectively simulate the field strength fading changes of the electromagnetic waves emitted by the antenna arrays of different shapes in the mine.And the radiation direction of the linear antenna array is consistent with the direction of the receiving antenna array,so the electromagnetic wave it emits reaches the receiving antenna array with greater field strength.In order to improve the reliability of the MIMO communication system in the mine,this thesis proposed a statistical algorithm for the angle spread and delay spread of the discrete arrival angle.And draw conclusions that the antenna array should be kept in the center of the tunnel as much as possible by analyzing delay spread and angle spread.Because in this case,the angle spread is larger,which can reduce the correlation between antennas;the delay spread is smaller and the received power is larger.(3)In order to improve the channel capacity of the MIMO communication system in the mine,in an unknown CSI scenario,reducing the correlation between antennas can increase channel capacity which can be achieved by increasing antenna spacing or using cross-polarized antennas.Because the propagation space of electromagnetic waves in the tunnel is limited,the effect of using cross-polarized antennas is more obvious.In a known CSI scenario,a water injection allocation algorithm based on the number of weighted reflection lines is used to allocate the transmit power to maximize the channel capacity when the transmit power is fixed.Comparing the channel capacity obtained by the algorithm proposed in this paper with the channel capacity obtained by the equal allocation method and the channel gain-based water injection allocation method by simulation,the results show that the proposed algorithm can improve the channel capacity,and it is consistent with the channel capacity obtained based on the channel gain matrix.