| As the subway has gradually become the first choice for relieving urban traffic pressure,the safety issues in the construction of subway tunnels have also received attention,so it is of great significance to locate the personnel in the tunnel in real time.Ultra-wideband(UWB)technology can realize high-precision ranging and positioning functions,and is widely used in indoor positioning and other occasions.However,the current UWB positioning technology generally has a series of problems such as non-line of sight(NLOS)interference,poor dynamic tracking and positioning performance,and insufficient coverage of the positioning base station.At present,there are few researches on the propagation characteristics of UWB electromagnetic waves in tunnels.Therefore,this paper studies the propagation characteristics and positioning methods of UWB electromagnetic waves in tunnels.The main research contents are as follows:(1)By comparing several classical positioning methods,the Symmetrical Double-Sided Two Way Ranging(SDS-TWR)algorithm based on Time of Arrival(TOA)is used as the ranging implementation method to reduce the system error.(2)The ray tracing method is used to simulate the propagation characteristics of the 3.997 GHz UWB electromagnetic wave in the tunnel.It is found that the UWB signal receiving power is attenuated close to the tunnel wall.Through the simulation results of delay parameters,it is found that the delay spread is higher due to more effective reflection paths within 50 m in the tunnel,reaching about 9 ns,and gradually decaying in the range of 50 m to 75 m.When the distance reaches 75 m,the delay spread is reduced to 2 ns and tends to be stable,so the pulse interval should be greater than 9 ns.By simulating the channel path loss parameters of the antenna at different positions and polarization directions,it is found that when the distance is 0.15 m from the tunnel wall,the antenna is on the side wall of the tunnel and is vertically polarized or at the top of the tunnel and horizontally polarized to obtain lower loss.Based on this,two-dimensional positioning and one-dimensional positioning schemes are proposed for different tunnel environments.(3)Through the simulation of common positioning algorithms,it is found that the ranging error is the key factor affecting the positioning accuracy.Considering that the NLOS error in the tunnel is the main source of ranging error,and has the characteristics of independence and positive value,the traditional Kalman algorithm is improved,and the simulation results show that the improved Kalman filter algorithm can suppress the NLOS error well.In order to realize the dynamic tracking and positioning of moving targets,combined with the dynamic and efficient characteristics of particle swarm,a hybrid tunnel localization algorithm based on improved Kalman and error constraint function is proposed.The simulation results show that in the LOS environment,the hybrid positioning algorithm can obtain the positioning result close to the real trajectory,and the positioning error is less than 0.2 m,which is relatively stable.The simulation results in the NLOS environment show that the NLOS error causes the positioning error to increase.However,compared with the traditional positioning algorithm,the positioning result after using the hybrid positioning algorithm still floats around the real trajectory,and the positioning error is stable within 0.4 m.(4)The UWB tunnel positioning platform is built to verify the method of this paper and tested from three aspects: ranging error,positioning accuracy and power consumption of mobile tag.The results show that the UWB tunnel positioning platform based on the hybrid tunneling positioning algorithm proposed in this paper can effectively suppress the NLOS error,and improve the positioning accuracy,and enables the real-time positioning of the operators in the tunnel. |
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