Multipath characteristics of through-the-earth stratified medium channel of elastic wave signal communiaction

Abstract：By analyzing the interface reflecting and power attenuation characteristics of elastic wave during propagating in parallel stratified earth medium,the multipath channel model of longitudinal elastic wave propagating in homogeneous stratified medium was achieved,and the relationship between multipath delay,medium layer thickness and longitudinal wave velocity was derived,as well as multipath/direct signal ratio approximate calculation.Meanwhile,the multipath fading caused by layer reflecting was studied.Based on the drill column data of adjacent rock in Shangwan Coal Mine of Shenhua Group,the channel model was established.Simulation results show：if direct signal is normal,the amplitude of multipath signal is lower than the direct signal＇s of 20 dB,so the interference of multipath signal caused by layer interface reflection can be neglected,and it proved that even the transmission bandwidth of signal is wider than channel correlation bandwidth Bc,the multipath fading is still a approximately flat fading.If the direct signal is shadowed（-20 dB to normal）,the stratified earth media channel is a frequency selective fading channel,and the fading depth is up to about 15 dB.Also,it illuminates that in spread spectrum communication,high chip rate is benefit for multipath interference rejection.