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WLAN propagation measurements in Railway tunnels. Case study: Madrid metro
Predicting Train Derailments Using Vibration Sensors And Wireless Transmitters
Redundancy techniques based on the combination of multiple diverse communication channels are an established countermeasure to improve performance characteristics of wireless communication systems. Besides parallel redundancy in the space and frequency domain, serial redundancy in the time domain can be utilized. It is known that the parallel approaches can significantly improve performance characteristics like jitter and reliability, when applied for wireless packet-based data transmission. In this work, an investigation on the performance impact of additional time diversity on top of the parallel redundancy approaches is performed. An OPNET simulation model is created and analysed for its performance characteristics.
The propagation characteristics of electromagnetic (EM) waves in tunnels are significantly different from those in terrestrial environment. However, the current tunnel channel models cannot provide an analytical solution for both near and far region of the sources. In this paper, the Multimode model is proposed to completely characterize the wireless channel of tunnels in roads/subways as well as underground mines. The new model provides an analytical expression for the path loss and delay spread at any position in a tunnel. This theoretical model is validated by comparing results with experiment measurements. Our channel model reveals that: the mode attenuation is mostly determined by the tunnel size and operating frequency, while the mode intensity is governed by the position of the transmission antenna. Physical factors, such as, humidity, pressure and temperature of the tunnel air, as well as the material of tunnel walls have little influence on the signal propagation in tunnels.
This paper first presents an application of the modal theory for interpreting experimental results of the electromagnetic field variation along a tunnel. The transmitting frequency is assumed to be high enough so that the tunnel behaves as an oversized waveguide. Then, for a Multiple-Input Multiple-Output channel, theoretical results of the channel capacity are given. To explain the decrease of the capacity at large distance from the transmitter, even by assuming a constant signal to noise ratio, an approach based on the calculation of the eigenvalues of the transfer matrix in a reference scenario is described.