Measurement and analysis of extra propagation loss of tunnel curve

Wave propagation experiences extra loss in curved tunnels, which is highly desired for network planning. Extensive narrow-band propagation measurements are made in two types of Madrid subway tunnels (different cross sections and curvatures) with various configurations (different frequencies and polarizations). A ray tracer validated by the straight and curved parts of the measuring tunnels is employed to simulate the reference received signal power by assuming the curved tunnel to be straight. By subtracting the measured received power in the curved tunnels from the simulated reference power, the extra loss resulting from the tunnel curve is extracted. Finally, this paper presents the figures and tables quantitatively reflecting the correlations between the extra loss and radius of curvature, frequency, polarization, and cross section, respectively. The results are valuable for statistical modeling and the involvement of the extra loss in the design and network planning of communication systems in subway tunnels

Experimental characterization of non-stationary V2I radio channel in tunnels

The fading process in vehicular communications is inherently non-stationary. In this paper, vehicle-to-infrastructure (V2I) radio channel measurements are performed inside a tunnel for low and medium traffic conditions to estimate the stationarity time, in addition to the time-varying RMS delay and Doppler spreads. Furthermore, we show the good fit of the spreads to a lognormal distribution, as well as for the Rician K-factor of the fading amplitude. From our analysis we conclude that the traffic density has an impact on the large-scale parameters as it increases delay and Doppler spreads, while reducing the correlation between them as well as the average K-factor. Larger traffic densities may be required to impact the stationarity time

Transmission-Based Signaling Systems

In this chapter, we describe the principal communication systems applied to the transmission-based signaling (TBS) systems for railways. Typical examples are communication-based train control (CBTC), European Rail Traffic Management System (ERTMS), and distance to go (DTG). Moreover, to properly address some of the challenges that need to face these systems, we will provide a deep insight on propagation issues related to all the environments (urban, suburban, rural, tunnel, etc.). We will highlight all the communication-related issues and the operational as well. Finally, a detailed survey on the directions of research on all these topics is provided, in order to properly cover this interesting subject. In this research, hot topics like virtual coupling are explained as well

Experimental study on the impact of antenna characteristics on non-stationary V2I channel parameters in tunnels

This paper analyses the experimentally-assessed dual-polarized (DP) mobile channel in a tunnel environment at 1.35 GHz under traffic conditions. We investigate the impact of antenna polarization and radiation pattern on the non-stationary vehicle-to-infrastructure (V2I) channel. Basic channel evaluation metrics are examined including path gain, co-polarization ratio (CPR), and cross-polarization discrimination (XPD). In addition, the stationarity region is estimated using the channel correlation function approach, and used to calculate the time-varying delay and Doppler power profiles. Statistical models are presented for parameters like CPR, XPD, RMS delay and Doppler spreads, where the lognormal distribution provides the best fit. The polarization and the opening angle of the antennas into the propagation channel are found to strongly influence the observed non-stationarity of the channel. They impact the degree of multipath richness that is captured, thus providing different path gain, delay and Doppler spreads. Based on our analysis, the directional antenna with vertical polarization provides the longest stationarity time of 400 ms at 90 km/h, as well as the highest path gain and lowest dispersion. Furthermore, the DP channel capacity is calculated and its dependence on different normalization approaches is investigated. We propose a more accurate normalization for the DP channels that takes the conservation of energy into account. Moreover, the subchannels correlation coefficients are determined. While the condition number is found to be low on average, the correlation results show high correlation among the DP subchannels. As conclusion, we show how the CPR and XPD play the main role in providing multiplexing gain for DP tunnel channels

Time-Domain Electromagnetic Wave Propagation in Confined Environments

International audienceConfined environments like tunnels are electrically large structures for guided wave propagation. They can have arbitrary cross sections, and the design and optimization of antenna for communication system requires the knowledge of a "full-wave" solution in nearby zones. Current models based on asymptotic approaches do not describe adequately the wave propagation under the above conditions. In addition, a complete "full-wave" analysis of the tunnel propagation performances is not feasible in terms of computer expenditure. After a survey of the most commonly used techniques for propagation in tunnels, some investigation regarding an appropriate approach to find the fields is proposed. It is based on a modal decomposition of the wave propagation that allows an optimization of the coupling with the antenna. To find the mode characteristic for arbitrary cross section, a full-wave method, namely, the transmission-line matrix (TLM), is modified to a so-called 2.5-dimensional TLM algorithm and presented in details. This approach is validated for a canonical structure. Then, it is applied to study the wave propagation in a realistic rectangular tunnel. The concept of surface impedance boundary condition (SIBC) is introduced to reduce the TLM computational domain and model the tunnel walls that can be considered as lossy dielectric. Results show that guided structures with lossy dielectric walls of arbitrary cross section can be studied with this approach