Optimization Of Joint Communication And Sensing System Assisted By RIS In Coal Mine Scenario

In coal mines,sensing and communication are two essential functions,the devices underground need to communicate with ground devices while monitoring the safe information.However,in underground coal mines,tunnels are mostly zigzag,and the line-of-sight（Lo S）links are blocked frequently,contributing to the difficulty of communicating.The cost of reconfigurable intelligent surface（RIS）is low,and the wireless signal can be reflected intelligently by RIS.Thus,RIS becomes the essential choice to solve the non-line-of-sight（NLo S）propagation problem.In addition,the monitoring devices underground is powered by battery,and energy efficiency must be considered.Above all,this thesis investigates the resource allocation of RIS-assisted joint communication and sensing systems in coal mines.The specifical research works as follows:In the JCAS system,aiming at the propagation problem of（NLo S）links,this thesis places RIS in the corner of the tunnel to indirectly establish Lo S communication links to improve the wireless communication environment.Moreover,a small battery-powered intelligent base station（BS）is deployed deep in the coal mine to sense multiple target areas（TA）while providing internet of things（Io T）and communication services for coal mine users.On this basis,the data center（DC）is placed on the ground to analyze the sensed data and send control information such as sensing priority.This thesis proposed a joint optimization problem of the RIS phase shift matrix,and area sensing times.It aims to maximize the amount of data successfully sensed under the constraints of the total data update time T and the maximum transmission power P_max.To this end,this paper divides this problem into three sub-problems:BS-RIS-DC channel gain maximization problem,sensing time optimization problem,and 3D-RIS optimization problem.The iterative method based on successive convex approximation（SCA）is used to solve the optimization sub-problem of the RIS phase shift matrix.For the sensing time optimization problem,an iterative algorithm based on quadratic approximation is proposed to solve the sensing times of the TA.In addition,under the premise of variable sensing signal transmission power,this thesis uses dichotomy to obtain the optimal BS transmission power,uses greedy algorithm to obtain the optimal sensing transmission power,and uses coordinate descent method to obtain the optimal RIS component switch sequence.The simulation results show that the optimal RIS phase-shift matrix can be quickly found by the iterative method based on SCA in the coal mine scenario.That is,the RIS-assisted communication in the coal mine is feasible;The optimal interval of the sensing process can also be obtained by Taylor quadratic approximation method,time-division JCAS system is feasible in real-time.Moreover,when the number of RIS elements is abundant,the optimal switches can be obtained by utilizing the coordinate descent method.Thus the energy efficiency of the JCAS system is improved further.