Radio channel measurement and characterization for wireless communications in tunnels

There is an increasing demand on wireless communications in subway tunnels to provide video surveillance and sensory data for security, maintenance and train control, and to offer various communication or entertainment services (e.g., Internet, etc.) to passengers as well. The wireless channel in tunnels is quite unique due to the confined space and the waveguide effects. Modeling the channel characteristics in tunnels is critically important to design or optimize subway wireless communication systems. This paper investigates the key radio channel characteristics of a subway tunnel in Beijing, China, such as the path loss, root mean square (RMS) delay spread, K-factor, channel stationarity, RMS Doppler spread, and channel capacity. Our field measurements show that channel characteristics in tunnels are highly location-dependent and there exists a dominant path in line-of-sight (LOS) scenarios as well as in non-line-of-sight (NLOS) scenarios, which is quite different from that in the land mobile communications. In the straight section of the subway tunnel, the measured path loss exponents at 2.45 GHz and 5.7GHz are 1.58 and 1.62, respectively.