| Due to the specific environment characteristics of underground coalmine in terms of long narrow tunnel,high humidity,high risk of explosions and collapses,etc.it is desirable to establish a precise and efficient wireless communication systems to be able to find hidden dangers timely and ensure safety production and accident relief.Therefore,it is of great significance to study the propagation characteristics of electromagnetic wave in the aspect of emergency wireless communication system and personnel localization.In this dissertation,the propagation law and influence factors of radio wave in mine tunnel are analyzed.Moreover,the attenuation model of underground electromagnetic wave propagation is established,and a fingerprint database is established based on the model,providing data support for subsequent fingerprint positioning algorithms.The main research work of this dissertation are summarized as follows:(1)The modeling method of wireless channel is analyzed and studied.Particularly,the principle of ray tracing and its application in the modeling of wireless channel are introduced.Four basic transmission modes and propagation characteristics of electromagnetic wave in mine tunnel are analyzed.Formulas for calculating the field intensity of direct rays,reflected rays,diffracted rays and transmitted rays are given.(2)The electromagnetic wave propagation model based on the SBR algorithm belongs to ray tracing method in underground tunnel is established.The modeling process includes ray generation,ray tracing,and ray reception.The path of each effective ray is obtained,that is to say,propagation path of electromagnetic waves in underground tunnel is obtained.The field strength of each effective path is calculated,and then summed to obtain the total field strength,received power,path loss,and delay spread of the signal at the receiving point.The obtained propagation model is simulated and analysis.The simulation results show different influences on the electromagnetic wave propagation in terms of tunnel cross section,frequency,antenna position,polarization mode,tunnel wall roughness and tunnel electrical parameters.(3)An accurate fingerprint database based on the established electromagnetic wave propagation model is set up.The process of fingerprint localization algorithm is briefly introduced.The fingerprint localization algorithm mainly includes the off-line acquisition stage and the online positioning stage,and the work of this paper is mainly to complete the data collection and the establishment of the fingerprint database.Several evenly reference points are selected and three fixed APs are set up in underground tunnel.According to the radio propagation model,the signal propagation path from three APs to each reference point is determined,and the received power of each path is calculated.Then the fingerprint database is established with the power intensity of each ray and its corresponding location information as the fingerprint sample. |
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