Characterization of UHF radio propagation channels in tunnel environments for microcellular and personal communications

Narrowband and wideband propagation measurements have been conducted in five tunnels. The effects of pedestrians, vehicles, and curvature on propagation are included in the characterization. The narrowband propagation is characterized in terms of power distance law, slow fading, and fast fading statistics: wideband propagation, rms delay spread, and its statistics. The results show that the power distance law is insensitive to the location of the transmit antenna in the cross section of a tunnel, but not to the antenna insertion loss. The lognormal distribution basically fits the slow variation of the received signals, whereas the Rician distribution, the fast fading in the straight empty sections of the tunnels. In the curved tunnel sections, the Rayleigh distribution does not fit the fast fading variation as is expected. Tunnel radio propagation channels are dependent strongly upon frequency. Higher frequency signals exhibit more severe fluctuations and larger rms delay spread. The rms delay spreads are found to be generally less than 25 and 103 ns for the emptied and occupied tunnel conditions, respectively. One can conclude that the tunnel channels have a broad coherent bandwidth and can support the data rate up to 1 Mb per second without equalization.