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Modified 2D Finite-Difference Time-Domain Based Tunnel Path Loss Prediction for Wireless Sensor Network Applications

To effectively deploy wireless sensor networks (WSNs) for monitoring and assessing the condition of tunnels, a Propagation Path Loss (PL) Model, which describes the power loss versus distance between the transmitter and the receiver for the tunnel environment is required. For most of the existing propagation measurements that have been conducted in tunnels, the antennas have been positioned along the central axis of a tunnel. However this is not representative of most infrastructure monitoring applications where the wireless sensor nodes will be mounted on the walls of the tunnel. In this paper, the results obtained from conducting close-to-wall measurements at 868MHz and 2.45GHz in curved arched-shaped tunnels are presented along with predictions made using a newly proposed Modified 2D Finite-Difference Time-Domain (FDTD) method. Since most currently available wireless sensor nodes have a communication range less than about 100m, we will focus on path loss measurement and modelling up to a maximum range of several hundred metres. During our measurements, the antennas are always maintained at a height of 2m, however the antenna distance to the tunnel wall is varied. By having the PL model as a guideline, we are able to determine the critical parameters for wireless communication in a tunnel, such as maximum communication distance, transmit power and receiver sensitivity.