Research On The Method Of Wireless Multi-Channel Precision Measurement In Tunnel

Perfect wireless communication system is very important in limited space of tunnel.The positioning system with high precision and strong stability can guarantee the safety of the personnel and equipment in roadway, improving work efficiency.Considering cost, wireless precise positioning is more related to the distance in tunnel; Ranging first, and then positioning.So ranging precision and accuracy will directly affect the accuracy of positioning.The environment of tunnel is a special wireless transmission.The environment space is long and narrow.The wall of tunnel and surrounding objects will cause some special phenomenon of wireless signal, such as reflection, scattering and diffraction.Significant multi-path effect results in unstable amplitude of electromagnetic wave and much deep decline in some areas when reaching the receiver.RSSI(received signal strength) ranging accuracy has great deviation and the traditional positioning method based on RSSI is limited in the tunnel due to the above reasons. Aiming at the problem of large deviation of RSSI ranging in tunnel, multi-channel RSSI ranging accuracy compensation method is presented in this paper.First of all, the deep fading characteristics of wireless signal of the short and long tunnel are analyzed respectively in paper. The characteristics of short distance is analyzed by ray tracing method and long distance is analyzed by wave mode theory. The location and amplitude of deep fading are related to of the antenna position, the size of the roadway, and signal frequency and other factors.The signal frequency drift causing the deep fading area location change is proved through the theoretical simulation. According to the findings, CC2530 Zig Bee wireless module is used to experiment in the lab building corridor simulation tunnel in paper.The experimental results also prove that the location deep decline of different channel of Zig Bee has a smaller degree of deviation.Finally, the multi-channel compensation precision ranging method is proposed by using the above conclusions in paper. Paper adopts RSSI data of three channels to compensate deep fading area.Firstly using the Gaussian filter to deal with each channel, and then determining the channel needed to compensate by derivative method, then using Kalman to pre-process the channel.Finally the channel is compensated by calculating mean. By simulation and practical experiments, distance measurement error of single channel and three channel compensation are analyzed.The results show that ranging error of the multi-channel compensation algorithm is smaller than single channel and ranging error from 4m down 2m.