Channel measurements and models for high-speed train wireless communication systems in tunnel scenarios: a survey
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paper_title: Cellular architecture and key technologies for 5G wireless communication networks

paper_content:

The fourth generation wireless communication systems have been deployed or are soon to be deployed in many countries. However, with an explosion of wireless mobile devices and services, there are still some challenges that cannot be accommodated even by 4G, such as the spectrum crisis and high energy consumption. Wireless system designers have been facing the continuously increasing demand for high data rates and mobility required by new wireless applications and therefore have started research on fifth generation wireless systems that are expected to be deployed beyond 2020. In this article, we propose a potential cellular architecture that separates indoor and outdoor scenarios, and discuss various promising technologies for 5G wireless communication systems, such as massive MIMO, energy-efficient communications, cognitive radio networks, and visible light communications. Future challenges facing these potential technologies are also discussed.
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paper_title: Measurements and Modeling of Distributed Antenna Systems in Railway Tunnels

paper_content:

This paper covers some of the work carried out in the planning of the global system for mobile communication for railway (GSM-R) of the tunnels on the new high-speed trains in Spain. Solutions based on distributed antenna systems have been tested by installing several 900-MHz transmitters inside and outside of a 4000-m tunnel and measuring the propagation in different conditions. The measurements have been used to model the effects of tunnel propagation, including curves, trains passing from the outside to the inside, and the effect of two trains passing inside the tunnel. All cases have been tested by comparing solutions using isofrequency and multifrequency distributed transmitters inside the tunnel. The improvements of signal-to-noise ratio and the reduction of the blocking effects of two trains passing have demonstrated the advantages of using isofrequency distributed antenna systems in tunnels. Finally, a complete propagation model combining both modal analysis and ray tracing has been applied to predict the propagation loss inside and outside these tunnels, and results have been compared with the measurements. The model has proven to be very useful for radio planning in new railway networks.
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paper_title: Radio channel measurements and analysis at 2.4/5GHz in subway tunnels

paper_content:

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. Therefore, modeling the radio channel characteristics in tunnels is critically important for communication systems design or optimization. This paper investigates the key radio channel characteristics of a subway tunnel at 2.4 GHz and 5 GHz, such as the path loss, root mean square (RMS) delay spread, channel stationarity, Doppler shift, and channel capacity. The field measurements show that channel characteristics in tunnels are highly location-dependent and there exist abundant components in Doppler shift domain. In the straight section of the subway tunnel, the measured path loss exponents are close to 1.6, lower than that in free space.
---
paper_title: Investigation on MIMO channels in subway tunnels

paper_content:

The purpose of this paper is to examine the possibilities of increasing the channel capacity in tunnels, and particularly in railway tunnels, due to the use of multiple-input-multiple-output techniques. Many measurement campaigns have been carried out, considering the complicated geometric structure of these tunnels. We determine the channel characteristics by making a statistical analysis of correlation matrices between antennas and singular values of the channel transfer matrix. A comparison between the theoretical and experimental results is also presented. A stochastic channel model is then proposed and validated.
---
paper_title: Wideband radio channel measurements for train tunnels

paper_content:

We present and analyse the results of wideband radio channel measurements performed in tunnels. Both a high speed train tunnel and a smaller test tunnel have been investigated with both antennas and leaky feeders as fixed radiators. The results show typical features of the tunnel radio channel with typically low delay spread combined to significant slow fading of the LOS signal due to interferences. The delay spread may increase substantially during the fading dips.
---
paper_title: Wideband analysis of large scale and small scale fading in tunnels

paper_content:

In this contribution, the analysis and the modeling of the large scale and small scale fading statistics in a semicircular tunnel is presented. The results are based on experimental data obtained during an extensive measurement campaign in the 2.8 - 5 GHz frequency range. Lastly, a simple model to characterize the statistics of the received signal in tunnels is presented.
---
paper_title: An Empirical Random-Cluster Model for Subway Channels Based on Passive Measurements in UMTS

paper_content:

Recently, a measurement campaign for characterizing the channels in underground subway environments was conducted in Shanghai, China. Downlink signals transmitted by 46 universal mobile telecommunication system cells deployed along a 34-km-long subway were collected. Channel impulse responses are extracted from the data received in the common pilot channels, based on which parameters of multipath components are estimated by using a high-resolution parameter algorithm derived using the space-alternating generalized expectation-maximization principle. Multiple time-evolving clusters are obtained, each representing the channel from a remote-radio-unit of a base station to the receiver. Based on a total of 98 time-evolving clusters, channels observed in the station scenario and the tunnel scenario are modeled separately for their distinctive behaviors in many aspects, particularly in the variations of clusters’ trajectories. Intracluster characteristics parameterized by cluster delay and Doppler frequency spreads, $K$ -factor, and dependences among these parameters are investigated. Intercluster parameters, including coexisting cluster number, delay offset, power offset, and cross correlations, are investigated for the station scenario. A path loss model is established for the tunnel scenario.
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paper_title: Characterization of Angular Spread in Underground Tunnels Based on the Multimode Waveguide Model

paper_content:

One of the biggest challenges facing wireless designers is determining how to configure multiple-input–multiple-output (MIMO) antennas in underground-environments, such as mines, so that they deliver best performance. Here, we showed that angular dispersion of the signal, a phenomenon that greatly impacts channel capacity, can be accurately predicted in both near-field and far-field of underground tunnels using a multimode waveguide. Not only this analytical model is much faster than other methods, but also it does not have other shortcomings of measurement-based modeling (e.g., poor resolution for far distances in the tunnel). Further, we characterized angular-spread for different tunnel sizes and showed that the power-azimuth-spectrum can be modeled by a zero-mean Gaussian distribution whose standard-deviation (angular-spread) is dependent on the tunnel dimension and the transmitter-receiver distance. Angular-spread is found to be a decreasing function of axial distance. After a certain distance, it becomes very small (about 4 $^{\circ}$ ) and independent of tunnel transverse dimension. Our results are useful for design of MIMO systems in underground tunnels and sufficient to permit the correlation-matrix required to extend the IEEE 802.11n MIMO channel model to underground environments.
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paper_title: Effect of Antenna Position and Polarization on UWB Propagation Channel in Underground Mines and Tunnels

paper_content:

Radio propagation in confined spaces is consequent upon reflections by the boundaries. In such cases, the relative position and polarization of antennas becomes important. This paper investigates the effect of antenna position and polarization on ultra-wideband radio propagation in underground mines and tunnels. Analysis is based on channel measurements, over 2.4 to 4 GHz frequency band, in three tunnels of varying cross-sectional dimensions and lengths. Effects of mounting antennas on ceiling versus walls and horizontal versus vertical polarization are compared in terms of path loss and time dispersion. Results show that average path loss is more sensitive to antenna position and polarization, than is time dispersion. The effect of polarization is found to be dependent upon antenna position. Horizontal polarization results in less average path loss when the antennas are mounted close to the ceiling, whereas vertical polarization results in less average loss when mounted close to a side wall. It is demonstrated that carefully considering antenna position and polarization can result in more efficient and cost-effective deployment of UWB systems in underground environments.
---
paper_title: Broadband radio communications in subway stations and tunnels

paper_content:

Broadband radio communication systems are very important for railway traffic control systems and passengers network services. Nowadays, even though 4G LTE (Long Term Evolution) has deployed for commercial use with excellent results in open areas, it is still lack of knowledge regarding to how such broadband signals propagate inside complex environments with many complex structures that affect propagation such as subway tunnels and stations. For this reason, the aim of the presented measurements in this paper is to model the response of the broadband channel at 1000 MHz and 2450 MHz in the subway environments. These measurements focus on three types of scenarios: subway stations, straight tunnels and a train effect the signal. The results provide detailed information about the propagation channel, which can be useful to develop a broadband propagation model for underground communication systems.
---
paper_title: Measurement and statistical analysis of 1.89GHz radio propagation in a realistic mountain tunnel

paper_content:

Accurate characterization of the radio channel in tunnels is of great importance for vehicle control communications systems. For the purpose of modeling characterizations of this special environment, actual measurements have been carried out at 1.89GHz in Shidao Mountain Highway Tunnel environment. During the measurements, a base station transmitters and a mobile receiver was installed in the tunnel and on a testing car respectively. With an optimum antenna configuration, main propagation characteristics of a complex mountain tunnel environment, including path loss, shadow fading, fast fading, level crossing rate (LCR) and average fade duration (AFD), have been measured and computed. All analysis results have been shown in a complete table for deepening the insight into the propagation mechanism within tunnel environments.
---
paper_title: Measurements of the propagation of UHF radio waves on an underground railway train

paper_content:

Measurements of the natural propagation of UHF radio waves on an underground train are reported. Of prime interest are the natural propagation attenuation and the median signal level behavior. The propagation attenuation rates or the median signal level behaviors are found to correlate with the train carriages and frequency. On the front carriage, the propagation attenuation rate is 54 dB/100 m at 465 MHz and reduced to 21 dB/100 m at 820 MHz. However, on the rear carriage, it becomes 14.8 dB/100 m at 465 MHz and 7.8 dB/100 m at 820 MHz. It is shown that higher frequency is beneficial to the natural propagation and the train body greatly affects the natural propagation. Furthermore, the values of the path loss exponent are also given.
---
paper_title: Broadband Channel Long Delay Cluster Measurements and Analysis at 2.4GHz in Subway Tunnels

paper_content:

The delay caused by the reflected ray in broadband communication has a great influence on the communications in subway tunnel. This paper presents measurements taken in subway tunnels at 2.4 GHz, with 5 MHz bandwidth. According to propagation characteristics of tunnel, the measurements were carried out with a frequency domain channel sounding technique, in three typical scenarios: line of sight (LOS), Non-line-of-sight (NLOS) and far line of sight (FLOS), which lead to different delay distributions. Firstly IFFT was chosen to get channel impulse response (CIR) h(t) from measured three-dimensional transfer functions. Power delay profile (PDP) was investigated to give an overview of broadband channel model. Thereafter, a long delay caused by the obturation of tunnel is observed and investigated in all the scenarios. The measurements show that the reflection can be greatly remained by the tunnel, which leads to long delay cluster where the reflection, but direct ray, makes the main contribution for radio wave propagation. Four important parameters: distribution of whole PDP power, first peak arriving time, reflection cluster duration and PDP power distribution of reflection cluster were studied to give a detailed description of long delay characteristic in tunnel. This can be used to ensure high capacity communication in tunnels.
---
paper_title: Measurement of Distributed Antenna Systems at 2.4 GHz in a Realistic Subway Tunnel Environment

paper_content:

Accurate characterization of the radio channel in tunnels is of great importance for new signaling and train control communications systems. To model this environment, measurements have been taken at 2.4 GHz in a real environment in Madrid subway. The measurements were carried out with four base station transmitters installed in a 2-km tunnel and using a mobile receiver installed on a standard train. First, with an optimum antenna configuration, all the propagation characteristics of a complex subway environment, including near shadowing, path loss, shadow fading, fast fading, level crossing rate (LCR), and average fade duration (AFD), have been measured and computed. Thereafter, comparisons of propagation characteristics in a double-track tunnel (9.8-m width) and a single-track tunnel (4.8-m width) have been made. Finally, all the measurement results have been shown in a complete table for accurate statistical modeling.
---
paper_title: On the Possibility of Interpreting Field Variations and Polarization in Arched Tunnels Using a Model for Propagation in Rectangular or Circular Tunnels

paper_content:

We investigate the possibility of using the modal theory of the electromagnetic propagation in rectangular or circular tunnels, to satisfactorily interpret experimental results, including polarization, in arched tunnels. This study is based on extensive measurement campaigns carried out in the 450 MHz-5 GHz frequency range.
---
paper_title: Analysis of radio wave propagation characteristics in rectangular road tunnel at 800 MHz and 2.4 GHz

paper_content:

We analyze radio wave propagation characteristics in tunnel using simulations by ray-tracing method and measurements for a newly constructed tunnel in Korea. As the simulation results using direct wave and 25 reflected waves and the measurement ones against the 14.7 meters wide, and 6.15 meters high, and 365 meters long tunnel is similar to each other, the radio wave propagation model for predicting received power in the tunnel can be applied to the other tunnels.
---
paper_title: Measurements and Modeling of Distributed Antenna Systems in Railway Tunnels

paper_content:

This paper covers some of the work carried out in the planning of the global system for mobile communication for railway (GSM-R) of the tunnels on the new high-speed trains in Spain. Solutions based on distributed antenna systems have been tested by installing several 900-MHz transmitters inside and outside of a 4000-m tunnel and measuring the propagation in different conditions. The measurements have been used to model the effects of tunnel propagation, including curves, trains passing from the outside to the inside, and the effect of two trains passing inside the tunnel. All cases have been tested by comparing solutions using isofrequency and multifrequency distributed transmitters inside the tunnel. The improvements of signal-to-noise ratio and the reduction of the blocking effects of two trains passing have demonstrated the advantages of using isofrequency distributed antenna systems in tunnels. Finally, a complete propagation model combining both modal analysis and ray tracing has been applied to predict the propagation loss inside and outside these tunnels, and results have been compared with the measurements. The model has proven to be very useful for radio planning in new railway networks.
---
paper_title: Investigation on MIMO channels in subway tunnels

paper_content:

The purpose of this paper is to examine the possibilities of increasing the channel capacity in tunnels, and particularly in railway tunnels, due to the use of multiple-input-multiple-output techniques. Many measurement campaigns have been carried out, considering the complicated geometric structure of these tunnels. We determine the channel characteristics by making a statistical analysis of correlation matrices between antennas and singular values of the channel transfer matrix. A comparison between the theoretical and experimental results is also presented. A stochastic channel model is then proposed and validated.
---
paper_title: Wideband analysis of large scale and small scale fading in tunnels

paper_content:

In this contribution, the analysis and the modeling of the large scale and small scale fading statistics in a semicircular tunnel is presented. The results are based on experimental data obtained during an extensive measurement campaign in the 2.8 - 5 GHz frequency range. Lastly, a simple model to characterize the statistics of the received signal in tunnels is presented.
---
paper_title: An Empirical Random-Cluster Model for Subway Channels Based on Passive Measurements in UMTS

paper_content:

Recently, a measurement campaign for characterizing the channels in underground subway environments was conducted in Shanghai, China. Downlink signals transmitted by 46 universal mobile telecommunication system cells deployed along a 34-km-long subway were collected. Channel impulse responses are extracted from the data received in the common pilot channels, based on which parameters of multipath components are estimated by using a high-resolution parameter algorithm derived using the space-alternating generalized expectation-maximization principle. Multiple time-evolving clusters are obtained, each representing the channel from a remote-radio-unit of a base station to the receiver. Based on a total of 98 time-evolving clusters, channels observed in the station scenario and the tunnel scenario are modeled separately for their distinctive behaviors in many aspects, particularly in the variations of clusters’ trajectories. Intracluster characteristics parameterized by cluster delay and Doppler frequency spreads, $K$ -factor, and dependences among these parameters are investigated. Intercluster parameters, including coexisting cluster number, delay offset, power offset, and cross correlations, are investigated for the station scenario. A path loss model is established for the tunnel scenario.
---
paper_title: Broadband radio communications in subway stations and tunnels

paper_content:

Broadband radio communication systems are very important for railway traffic control systems and passengers network services. Nowadays, even though 4G LTE (Long Term Evolution) has deployed for commercial use with excellent results in open areas, it is still lack of knowledge regarding to how such broadband signals propagate inside complex environments with many complex structures that affect propagation such as subway tunnels and stations. For this reason, the aim of the presented measurements in this paper is to model the response of the broadband channel at 1000 MHz and 2450 MHz in the subway environments. These measurements focus on three types of scenarios: subway stations, straight tunnels and a train effect the signal. The results provide detailed information about the propagation channel, which can be useful to develop a broadband propagation model for underground communication systems.
---
paper_title: Measurement and statistical analysis of 1.89GHz radio propagation in a realistic mountain tunnel

paper_content:

Accurate characterization of the radio channel in tunnels is of great importance for vehicle control communications systems. For the purpose of modeling characterizations of this special environment, actual measurements have been carried out at 1.89GHz in Shidao Mountain Highway Tunnel environment. During the measurements, a base station transmitters and a mobile receiver was installed in the tunnel and on a testing car respectively. With an optimum antenna configuration, main propagation characteristics of a complex mountain tunnel environment, including path loss, shadow fading, fast fading, level crossing rate (LCR) and average fade duration (AFD), have been measured and computed. All analysis results have been shown in a complete table for deepening the insight into the propagation mechanism within tunnel environments.
---
paper_title: Broadband Channel Long Delay Cluster Measurements and Analysis at 2.4GHz in Subway Tunnels

paper_content:

The delay caused by the reflected ray in broadband communication has a great influence on the communications in subway tunnel. This paper presents measurements taken in subway tunnels at 2.4 GHz, with 5 MHz bandwidth. According to propagation characteristics of tunnel, the measurements were carried out with a frequency domain channel sounding technique, in three typical scenarios: line of sight (LOS), Non-line-of-sight (NLOS) and far line of sight (FLOS), which lead to different delay distributions. Firstly IFFT was chosen to get channel impulse response (CIR) h(t) from measured three-dimensional transfer functions. Power delay profile (PDP) was investigated to give an overview of broadband channel model. Thereafter, a long delay caused by the obturation of tunnel is observed and investigated in all the scenarios. The measurements show that the reflection can be greatly remained by the tunnel, which leads to long delay cluster where the reflection, but direct ray, makes the main contribution for radio wave propagation. Four important parameters: distribution of whole PDP power, first peak arriving time, reflection cluster duration and PDP power distribution of reflection cluster were studied to give a detailed description of long delay characteristic in tunnel. This can be used to ensure high capacity communication in tunnels.
---
paper_title: Measurement of Distributed Antenna Systems at 2.4 GHz in a Realistic Subway Tunnel Environment

paper_content:

Accurate characterization of the radio channel in tunnels is of great importance for new signaling and train control communications systems. To model this environment, measurements have been taken at 2.4 GHz in a real environment in Madrid subway. The measurements were carried out with four base station transmitters installed in a 2-km tunnel and using a mobile receiver installed on a standard train. First, with an optimum antenna configuration, all the propagation characteristics of a complex subway environment, including near shadowing, path loss, shadow fading, fast fading, level crossing rate (LCR), and average fade duration (AFD), have been measured and computed. Thereafter, comparisons of propagation characteristics in a double-track tunnel (9.8-m width) and a single-track tunnel (4.8-m width) have been made. Finally, all the measurement results have been shown in a complete table for accurate statistical modeling.
---
paper_title: Four-slope channel model for path loss prediction in tunnels at 400 MHz

paper_content:

The present study analyses radio propagation at the 400 MHz frequency band inside road and railway tunnels. It proposes, on the basis of field measurements, a path loss model consisting of four segments, namely: the free space segment, the high path loss segment, the waveguide segment and, in the furthest region, the free space propagation segment. Free space propagation is characteristic in a region close to an antenna. In the next region, the near region, only a few reflected rays reach the receiver resulting in high path loss. Further away, in the far region, the waveguide effect occurs because of a set of waves reflected from the tunnel walls resulting in low path loss. In the extreme far region, the waveguide effect vanishes because of attenuation of reflected rays. The points separating the individual segments are analytically defined. Model applicability and accuracy are checked by calculating the mean error and standard deviation. The results indicate reasonable agreement between measurements and the model. This four-slope path loss channel model can be applied for rapid and simple coverage prediction of direct mode operation in TETRA systems.
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paper_title: Measurement Analysis and Channel Modeling for TOA-Based Ranging in Tunnels

paper_content:

A robust and accurate positioning solution is required to increase the safety in GPS-denied environments. Although there is a lot of available research in this area, little has been done for confined environments such as tunnels. Therefore, we organized a measurement campaign in a basement tunnel of Linkoping university, in which we obtained ultra-wideband (UWB) complex impulse responses for line-of-sight (LOS), and three non-LOS (NLOS) scenarios. This paper is focused on time-of-arrival (TOA) ranging since this technique can provide the most accurate range estimates, which are required for range-based positioning. We describe the measurement setup and procedure, select the threshold for TOA estimation, analyze the channel propagation parameters obtained from the power delay profile (PDP), and provide statistical model for ranging. According to our results, the rise-time should be used for NLOS identification, and the maximum excess delay should be used for NLOS error mitigation. However, the NLOS condition cannot be perfectly determined, so the distance likelihood has to be represented in a Gaussian mixture form. We also compared these results with measurements from a mine tunnel, and found a similar behavior.
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paper_title: Measurement and Analysis of Extra Propagation Loss of Tunnel Curve

paper_content:

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.
---
paper_title: Wideband analysis of large scale and small scale fading in tunnels

paper_content:

In this contribution, the analysis and the modeling of the large scale and small scale fading statistics in a semicircular tunnel is presented. The results are based on experimental data obtained during an extensive measurement campaign in the 2.8 - 5 GHz frequency range. Lastly, a simple model to characterize the statistics of the received signal in tunnels is presented.
---
paper_title: An Empirical Random-Cluster Model for Subway Channels Based on Passive Measurements in UMTS

paper_content:

Recently, a measurement campaign for characterizing the channels in underground subway environments was conducted in Shanghai, China. Downlink signals transmitted by 46 universal mobile telecommunication system cells deployed along a 34-km-long subway were collected. Channel impulse responses are extracted from the data received in the common pilot channels, based on which parameters of multipath components are estimated by using a high-resolution parameter algorithm derived using the space-alternating generalized expectation-maximization principle. Multiple time-evolving clusters are obtained, each representing the channel from a remote-radio-unit of a base station to the receiver. Based on a total of 98 time-evolving clusters, channels observed in the station scenario and the tunnel scenario are modeled separately for their distinctive behaviors in many aspects, particularly in the variations of clusters’ trajectories. Intracluster characteristics parameterized by cluster delay and Doppler frequency spreads, $K$ -factor, and dependences among these parameters are investigated. Intercluster parameters, including coexisting cluster number, delay offset, power offset, and cross correlations, are investigated for the station scenario. A path loss model is established for the tunnel scenario.
---
paper_title: Effect of Antenna Position and Polarization on UWB Propagation Channel in Underground Mines and Tunnels

paper_content:

Radio propagation in confined spaces is consequent upon reflections by the boundaries. In such cases, the relative position and polarization of antennas becomes important. This paper investigates the effect of antenna position and polarization on ultra-wideband radio propagation in underground mines and tunnels. Analysis is based on channel measurements, over 2.4 to 4 GHz frequency band, in three tunnels of varying cross-sectional dimensions and lengths. Effects of mounting antennas on ceiling versus walls and horizontal versus vertical polarization are compared in terms of path loss and time dispersion. Results show that average path loss is more sensitive to antenna position and polarization, than is time dispersion. The effect of polarization is found to be dependent upon antenna position. Horizontal polarization results in less average path loss when the antennas are mounted close to the ceiling, whereas vertical polarization results in less average loss when mounted close to a side wall. It is demonstrated that carefully considering antenna position and polarization can result in more efficient and cost-effective deployment of UWB systems in underground environments.
---
paper_title: Path loss modeling and fading analysis for channels with various antenna setups in tunnels at 30 GHz band

paper_content:

The high-speed railway (HSR) environment has unique characteristics in radio propagation. The research on radio channel in HSR plays a vital role in system design, especially for advanced mobile systems working in the millimetre-wave band. This paper presents the simulation in a typical straight and arched tunnel at 30 GHz band with a verified ray-tracing tool. The simulation results illustrate that the advanced mobile communication system with high gain directional antennas can support longer than 1 km communication links in the tunnel. In this paper, the channel characteristics of three different antenna setups are compared at frequencies ranging from 31.5 GHz∼33.5 GHz, e.g., path loss exponent, autocorrelation and decorrelation distance of shadow fading, etc. Additionally, these characteristics will be shown with statistic values that can easily reproduce the radio channel properties. Furthermore, the results will be utilized to guide further realistic measurement campaign and physical layer design for advanced mobile communication systems.
---
paper_title: Measurements of the propagation of UHF radio waves on an underground railway train

paper_content:

Measurements of the natural propagation of UHF radio waves on an underground train are reported. Of prime interest are the natural propagation attenuation and the median signal level behavior. The propagation attenuation rates or the median signal level behaviors are found to correlate with the train carriages and frequency. On the front carriage, the propagation attenuation rate is 54 dB/100 m at 465 MHz and reduced to 21 dB/100 m at 820 MHz. However, on the rear carriage, it becomes 14.8 dB/100 m at 465 MHz and 7.8 dB/100 m at 820 MHz. It is shown that higher frequency is beneficial to the natural propagation and the train body greatly affects the natural propagation. Furthermore, the values of the path loss exponent are also given.
---
paper_title: Measurement of Distributed Antenna Systems at 2.4 GHz in a Realistic Subway Tunnel Environment

paper_content:

Accurate characterization of the radio channel in tunnels is of great importance for new signaling and train control communications systems. To model this environment, measurements have been taken at 2.4 GHz in a real environment in Madrid subway. The measurements were carried out with four base station transmitters installed in a 2-km tunnel and using a mobile receiver installed on a standard train. First, with an optimum antenna configuration, all the propagation characteristics of a complex subway environment, including near shadowing, path loss, shadow fading, fast fading, level crossing rate (LCR), and average fade duration (AFD), have been measured and computed. Thereafter, comparisons of propagation characteristics in a double-track tunnel (9.8-m width) and a single-track tunnel (4.8-m width) have been made. Finally, all the measurement results have been shown in a complete table for accurate statistical modeling.
---
paper_title: On the Possibility of Interpreting Field Variations and Polarization in Arched Tunnels Using a Model for Propagation in Rectangular or Circular Tunnels

paper_content:

We investigate the possibility of using the modal theory of the electromagnetic propagation in rectangular or circular tunnels, to satisfactorily interpret experimental results, including polarization, in arched tunnels. This study is based on extensive measurement campaigns carried out in the 450 MHz-5 GHz frequency range.
---
paper_title: Analysis of radio wave propagation characteristics in rectangular road tunnel at 800 MHz and 2.4 GHz

paper_content:

We analyze radio wave propagation characteristics in tunnel using simulations by ray-tracing method and measurements for a newly constructed tunnel in Korea. As the simulation results using direct wave and 25 reflected waves and the measurement ones against the 14.7 meters wide, and 6.15 meters high, and 365 meters long tunnel is similar to each other, the radio wave propagation model for predicting received power in the tunnel can be applied to the other tunnels.
---
paper_title: Enhancement of rectangular tunnel waveguide model

paper_content:

The ray theory is applied to locate the break point to distinguish propagation regions for line-of-sight topographies in rectangular tunnels. It is found that path loss in tunnels differs greatly in the regions prior to and after the break point. Nevertheless at least two waveguide modes are needed to accurately model tunnel natural propagation. In addition, the errors in the formulas to calculate the losses due to roughness and tilt of the tunnel walls are corrected. As a result, the propagation loss prediction of the rectangular tunnel waveguide model is significantly enhanced.
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paper_title: Research of propagation characteristics of break point: near zone and far zone under operational subway condition

paper_content:

This paper focuses on three vital aspects in propagation characteristics inside tunnels: break point; near zone and far zone in a practical environment. Firstly, all the distinguishing features of radio channel in the areas before and after break point at different angles such as modal theory, ray-tracing theory, statistics and propagation model have been summarized. By collectively analyzing the research perspectives above, a panoramic view on the propagation characteristics of break point; far zone and near zone has been proposed. Based on a measurement carried out in Madrid operational subway environment at 2.4 GHz, some new radio channel characters of the break point; the regions before and after break point at higher frequency have been discussed and analyzed.
---
paper_title: Measurement of Distributed Antenna Systems at 2.4 GHz in a Realistic Subway Tunnel Environment

paper_content:

Accurate characterization of the radio channel in tunnels is of great importance for new signaling and train control communications systems. To model this environment, measurements have been taken at 2.4 GHz in a real environment in Madrid subway. The measurements were carried out with four base station transmitters installed in a 2-km tunnel and using a mobile receiver installed on a standard train. First, with an optimum antenna configuration, all the propagation characteristics of a complex subway environment, including near shadowing, path loss, shadow fading, fast fading, level crossing rate (LCR), and average fade duration (AFD), have been measured and computed. Thereafter, comparisons of propagation characteristics in a double-track tunnel (9.8-m width) and a single-track tunnel (4.8-m width) have been made. Finally, all the measurement results have been shown in a complete table for accurate statistical modeling.
---
paper_title: Broadband Channel Long Delay Cluster Measurements and Analysis at 2.4GHz in Subway Tunnels

paper_content:

The delay caused by the reflected ray in broadband communication has a great influence on the communications in subway tunnel. This paper presents measurements taken in subway tunnels at 2.4 GHz, with 5 MHz bandwidth. According to propagation characteristics of tunnel, the measurements were carried out with a frequency domain channel sounding technique, in three typical scenarios: line of sight (LOS), Non-line-of-sight (NLOS) and far line of sight (FLOS), which lead to different delay distributions. Firstly IFFT was chosen to get channel impulse response (CIR) h(t) from measured three-dimensional transfer functions. Power delay profile (PDP) was investigated to give an overview of broadband channel model. Thereafter, a long delay caused by the obturation of tunnel is observed and investigated in all the scenarios. The measurements show that the reflection can be greatly remained by the tunnel, which leads to long delay cluster where the reflection, but direct ray, makes the main contribution for radio wave propagation. Four important parameters: distribution of whole PDP power, first peak arriving time, reflection cluster duration and PDP power distribution of reflection cluster were studied to give a detailed description of long delay characteristic in tunnel. This can be used to ensure high capacity communication in tunnels.
---
paper_title: Measurement of Distributed Antenna Systems at 2.4 GHz in a Realistic Subway Tunnel Environment

paper_content:

Accurate characterization of the radio channel in tunnels is of great importance for new signaling and train control communications systems. To model this environment, measurements have been taken at 2.4 GHz in a real environment in Madrid subway. The measurements were carried out with four base station transmitters installed in a 2-km tunnel and using a mobile receiver installed on a standard train. First, with an optimum antenna configuration, all the propagation characteristics of a complex subway environment, including near shadowing, path loss, shadow fading, fast fading, level crossing rate (LCR), and average fade duration (AFD), have been measured and computed. Thereafter, comparisons of propagation characteristics in a double-track tunnel (9.8-m width) and a single-track tunnel (4.8-m width) have been made. Finally, all the measurement results have been shown in a complete table for accurate statistical modeling.
---
paper_title: Modeling and measurement of wireless channels for underground mines

paper_content:

This paper investigates wireless channel modeling for underground mines. The ray tracing and modal methods, which have been widely used for modeling radio propagation in tunnels, are applied to model wireless channels in underground mines. In addition, propagation measurements are taken in an underground hard rock mine at three different frequencies (455 MHz, 915 MHz, and 2.45 GHz). Simulation results based on the ray tracing and modal methods are compared to measurement results and show agreement. Challenges for modeling wireless channels in mines are discussed.
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paper_title: Theoretical and experimental approach of the propagation of high frequency waves in road tunnels

paper_content:

Characterization of high frequency electromagnetic wave propagation in tunnels has important applications in the field of mobile communication. In long tunnels, the amplitude of the electric field radiated by a retransmitting antenna can be easily calculated from ray theory. However, for short tunnels, one of the most critical points is either the radiation towards free space of a mobile station emitting in the tunnel or, on the contrary, the penetration of an external wave inside the tunnel. This coupling between the inside and the outside is treated through the uniform theory of diffraction. By comparing theoretical and experimental results, it is shown that this theory leads to adequate prediction of the field variation and allows the authors to point out the influence of parameters, such as the position of the mobile in the tunnel and the influence of the angle of incidence, on the entrance plane of an incoming external wave. >
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paper_title: A ray-tracing method for predicting delay spread in tunnel environments

paper_content:

Our model to predict the propagation is based on ray-tracing which uses an images algorithm to find paths between transmitter and receiver of a digital communication system. It accounts for all rays reaching the receiver location after an arbitrary number of reflections and includes the effect of the angle of incidence, the material dielectric constant, the antenna pattern and polarization, the wall roughness, and the tunnel cross section size. The simulation results in this paper are obtained by analyzing many fewer rays compared to other published results. The results illustrate that in an empty straight rectangular tunnel environment, propagation has a very short time delay spread. Meanwhile, the results have shown that rms delay spread for horizontally polarized transmit and receive antennas is more than for vertically polarized transmit and receive antennas, in which the attenuation constant is less when transmit and receive antennas are horizontally polarized than when they are vertically polarized. Finally, by using a specific pattern, the rms delay spread is decreased compared to an isotropic antenna.
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paper_title: Experimental Characterization of an UWB Propagation Channel in Underground Mines

paper_content:

An experimental characterization of the ultrawideband (UWB) propagation channel in an underground mine environment over the frequency range from 3 GHz to 10 GHz is reported in this paper. Two kinds of antennas, directional and omnidirectional, were used to investigate the effect of the antenna directivity on the path loss propagation and on the time dispersion parameters in both line-of-sight (LOS) and no-line-of-sight (NLOS) underground galleries. The measurement and simulation results show that the path loss exponents in an underground environment are larger than their counterparts in an indoor environment. In NLOS, the directional-directional (Direct-Direct) antenna combination showed better radiation efficiency for reducing the time dispersion parameters while the omnidirectional-omni directional (Omni-Omni) case resulted better performance in term of path loss. After extracting the channel parameters, a statistical modeling of the UWB underground channel based on data measurements was conducted.
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paper_title: Effect of antenna on propagation characteristics of electromagnetic waves in tunnel environments

paper_content:

The optimal radiation pattern and optimal position of the source antenna installed inside a tunnel is the concern of this paper. By comparing theoretical and experimental results, it is shown that the field distribution of the electromagnetic wave in tunnel environments is sensitive to the position of the transmitting antenna in the cross section of a tunnel. And compared with the Omni-directional antenna, the utilization of the vertical antenna with radiation pattern of sinn θ on the upper middle of the wall, or the horizontal antenna with radiation pattern of sinn ϕ on the middle of the side wall, could represent significant improvement of the standing wave graphics, as well as the propagation attenuation.
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paper_title: Influence of Dimension Change on Radio Wave Propagation in Rectangular Tunnels

paper_content:

Based on the propagation modal and the software simulation method, characteristics of radio wave propagation in rectangular tunnels are studied from the view of the size shift of the tunnel width and height. The results show that the influence of the height change on the vertical polarization mode is greater than on the horizontal polarization mode; that of the width change on the vertical polarization mode is less than on the horizontal polarization mode.
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paper_title: Propagation in tunnels: experimental investigations and channel modeling in a wide frequency band for MIMO applications

paper_content:

The analysis of the electromagnetic field statistics in an arched tunnel is presented. The investigation is based on experimental data obtained during extensive measurement campaigns in a frequency band extending from 2.8GHz up to 5GHz and for a range varying between 50m and 500 m. Simple channel models that can be used for simulating MIMO links are also proposed.
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paper_title: Subway tunnel guided electromagnetic wave propagation at mobile communications frequencies

paper_content:

A measurement campaign has been carried out in the Berlin subway to characterize electromagnetic wave propagation in underground railroad tunnels. The received power levels at 945 and 1853.4 MHz are used to evaluate the attenuation and the fading characteristics in a curved arched-shaped tunnel. The measurements are compared to ray-optical modeling results, which are based on ray density normalization. It is shown that the geometry of a tunnel, especially the cross-sectional shape and the course, is of major impact on the propagation behavior and thus on the accuracy of the modeling, while the material parameters of the building materials have less impact.
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paper_title: Channel modeling and analysis for wireless networks in underground mines and road tunnels

paper_content:

Wireless networks can greatly facilitate the communication in underground mines and road/subway tunnels, where the propagation characteristics of electromagnetic (EM) waves are significantly different from those in terrestrial environments. According to the structure of underground mines and road tunnels, two types of channel models can be utilized, namely, tunnel and room/pillar channel models. However, there exists no theoretical model for room-and-pillar channel in underground mines to date, and current existing tunnel channel models do not provide an analytical solution for both near and far regions of the sources. In this paper, the multimode model is proposed, which provides an analytical expression for the received power and the power delay profile at any position in a tunnel.Moreover, the multimode model is extended to characterize the room-and-pillar channel in the underground mines after combining it with the shadow fading model. The theoretical models are validated by experimental measurements. Based on the proposed channel models, the effects of various factors on the signal propagation are analyzed. The factors include: the operating frequency, the size of the tunnel or underground mine room, the antenna position and polarization, and the electrical parameters.
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paper_title: Propagation Character of Electromagnetic Wave of the Different Transmitter Position in Mine Tunnel

paper_content:

In order to analysis the propagation character of electromagnetic wave in the limited space of mine tunnel when the wireless sensor is set in different position, the electric-field intensity and magnetic-field intensity of horizontal polarization wave are obtained according to Maxwell equation and boundary condition of tunnel. The electric-field attenuation coefficient of horizontal and vertical polarization wave are deduced through the traveling-wave condition of limited space. The attenuation characters of different position transmitter in rectangular mine tunnels are simulated in an experiment tunnel.The results shows the attenuation of electric-field intensity is increase quickly in 50m.When the transmitter is more close to the wall of the mine tunnel, the mode of propagation is more complex and the attenuation is more serious, whereas in the middle of the mine tunnel, the attenuation rate of radio is the least. It is benefit to evaluate the channel of wireless sensor network in mine tunnel.
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paper_title: Influence of Mine Tunnel Wall Humidity on Electromagnetic Waves Propagation

paper_content:

High moisture in mine tunnel can cause the change of the permittivity and conductivity of tunnel walls, therefore influence the characteristics of electromagnetic waves propagation. This paper analyzes the mechanism of humidity influencing the permittivity and conductivity and attenuation of electromagnetic waves propagation in the circular tunnel and rectangular tunnel. The study result shows that, in the interest frequency range, the change of permittivity caused by humidity has little effect on propagation attenuation, but the effect on the conductivity change cannot be ignored. When the humidity is greater than a certain value, the attenuation will be increased significantly.
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paper_title: Analysis of radio wave propagation characteristics in rectangular road tunnel at 800 MHz and 2.4 GHz

paper_content:

We analyze radio wave propagation characteristics in tunnel using simulations by ray-tracing method and measurements for a newly constructed tunnel in Korea. As the simulation results using direct wave and 25 reflected waves and the measurement ones against the 14.7 meters wide, and 6.15 meters high, and 365 meters long tunnel is similar to each other, the radio wave propagation model for predicting received power in the tunnel can be applied to the other tunnels.
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paper_title: Radio Wave Attenuation Character in the Confined Environments of Rectangular Mine Tunnel

paper_content:

The radio waves are more complex in confined environments such as coal mine tunnels, in order to obtain the propagation character of radio wave in the confined environments of mine tunnel, the electric-field intensity and magnetic-field intensity of horizontal polarization wave are obtained according to Maxwell equation and boundary condition of tunnel. The attenuation coefficients of electric field in horizontal and vertical polarization are deduced through the traveling wave condition of confined space. The attenuation characters of different position transmitter in rectangular mine tunnels are simulated in an experiment tunnel. The results shows the attenuation of electric-field intensity is increase quickly in 50m.When the transmitter is more close to the wall of the mine tunnel, the mode of propagation is more complex and the attenuation is more serious, whereas in the middle of the mine tunnel, the attenuation rate of radio is the least. Factors that influence the attenuation character of radio waves in mine tunnel are analysed and simulated too, it is benefit to evaluate the wireless channel quality in mine tunnel.
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paper_title: A Novel Wideband MIMO Car-to-Car Channel Model Based on a Geometrical Semi-Circular Tunnel Scattering Model

paper_content:

In this paper, we present a wideband multiple-input multiple-output (MIMO) car-to-car (C2C) channel model based on a geometrical semi-circular tunnel (SCT) scattering model. From the geometrical SCT scattering model, a reference channel model is derived under the assumption of single-bounce scattering in line-of-sight (LOS) and non-LOS (NLOS) propagation environments. In the proposed reference channel model, it is assumed that an infinite number of scatterers are randomly distributed on the tunnel wall. Starting from the geometrical scattering model, the time-variant transfer function (TVTF) is derived, and its correlation properties in time, frequency, and space are studied. Expressions are presented for the space–time–frequency cross-correlation function (STF-CCF), the two-dimensional (2D) space CCF, the 2D time–frequency CCF (TF-CCF), the temporal autocorrelation function (ACF), and the frequency correlation function (FCF). Owing to the semi-circular geometry, we reduced the originally threefold integrals to double integrals in the computations of the correlation functions, which simplifies the numerical analysis considerably. From the TVTF characterizing the reference model, an efficient sum-of-cisoid (SOC) channel simulator is derived. Numerical results show that both the temporal ACF and the FCF of the SOC channel simulator match very well with those of the reference model. A validation of the proposed model has been done by fitting the delay spread of the reference model to that of the measured channel, which demonstrates an excellent agreement. The proposed channel simulator allows us to evaluate the performance of C2C communication systems in tunnel environments.
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paper_title: Channel modeling of wireless communication in underground coal mines

paper_content:

Communication systems relying on wireless technology can significantly improve the safety and production in underground mines; however, their unreliable operation in such high-stress environments is a significant obstacle to achieving this. Underground mine tunnels offers several distinctive features that are quite different from regular rail/road tunnels. While several studies have been performed on electromagnetic (EM) wave propagation in tunnel environments, there is limited understanding of the inter-working of tunnel dimension with long range tilt variations (a typically feature of coal mines) on the propagation characteristics of wireless radio waves. In this paper, we present and describe a new hybrid multimode model for wireless communication in underground coal mines; and analyze it with respect to important parameters such as operating frequency, mine tunnel size, and transmitter-receiver position. The characterization results suggest that the mine tunnel size and transmitter-receiver position affects the signal behavior significantly.
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paper_title: Modeling for MIMO wireless channels in mine tunnels

paper_content:

The electromagnetic waves propagation situation is very complex in mine tunnels, so it is important to establish an efficient MIMO channel model for applying wireless communication technology to coal mine underground. A stochastic MIMO channel model is proposed firstly based on wireless propagation environment in mine tunnels, and then two spatial correlative channel models are established through correcting channel matrices based on abundant scatter environment. In this paper, the singular values and the channel capacity obtained with a Rayleigh channel model are compared, and system performance of different channel models are simulated. The simulation results indicate that established channel models are feasible by comparing with measurements results to mine tunnels.
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paper_title: Ray-optical modeling of simulcast radio propagation channels in tunnels

paper_content:

Simulcast radio propagation channel characteristics inside tunnels are considered in this paper. Based on the image theory of ray optics, a simulcast radio propagation channel in a rectangular tunnel is exactly formulated. As only the field components of horizontal and vertical polarization are of interest in real implementation, the exact formulation is approximated to facilitate the numerical computation. The calculated simulcast radio propagation channels are comparable fairly to measurements at 900 MHz and 2.0 GHz. The validated ray-optical modeling approach is then applied to simulate simulcast radio propagation channel characteristics at 900 MHz and 2.0 GHz to gain deeper insight and better understanding of this type of channels in tunnels. Results show that large fluctuations occur in the capture regions of the distributed antennas for both 900 MHz and 2.0 GHz. The fluctuations in the simulcast regions are larger at 2.0 GHz than at 900 MHz. The root-mean-squared (rms) delay spread is greater in the simulcast regions than in the capture regions of the distributed antennas. This larger delay spread is mainly due to the delay introduced by the transmission medium. Large values of the rms delay spread can be avoided by a careful design of the distance between the distributed antennas.
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paper_title: Tunnel and Non-Tunnel Channel Characterization for High-Speed-Train Scenarios in LTE-A Networks

paper_content:

In this contribution, a measurement campaign for high- speed-train (HST) channel is introduced where the down- link signals of in-service Long Time Evolution-Advanced (LTE-A) network deployed along the HST railway between Beijing to Shanghai are acquired. Channel impulse responses (CIRs) are extracted from received signals, and concatenated power delay profiles (CPDPs) are illustrated. According to the delay trajectories of the CPDPs, measurement scenarios are categorized into non- tunnel and tunnel scenarios. The delay spread and K- factor are investigated for both scenarios. The results show that the two scenarios have distinguishable statistics in delay spread and K-factor.
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paper_title: GBSB MODEL for MIMO Channel AND its Space-time CORRELATION Analysis in Tunnel

paper_content:

Aiming at the special space in the tunnel, this paper assumes the geometric distribution of scatterers which is totally different from on the ground, puts forward a new GBSB model of MIMO channel and deduces the space-time correlation function of the model. The results of theoretical analysis and simulation show that the model can more accurately reflect the factors which impact the channel correlation in the tunnel.
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paper_title: In-Tunnel Vehicular Radio Channel Characterization

paper_content:

Inside a tunnel, electromagnetic wave propagation differs strongly from the well understood "open-air" situation. The characterization of the tunnel environment is crucial for deploying vehicular communication systems. In this paper we evaluate vehicle-to-vehicle (V2V) radio channel measurements inside a tunnel. We estimate the time-varying root mean square (rms) delay and Doppler spreads, as well as the excess delay and the maximum Doppler dispersion. The fading process in V2V communications is inherently non-stationary. Hence, we characterize the stationarity time, for which we can consider the fading process to be wide sense stationary. We show that the spreads, excess delay, and maximum Doppler dispersion are larger on average when both vehicles are inside the tunnel compared to the "open-air" situation. The temporal evolution of the stationarity time is highly influenced by the strength of time-varying multipath components and the distance between vehicles. Furthermore, we show the good fit of the rms delay and Doppler spreads to a lognormal distribution, as well as for the stationarity time. From our analysis we can conclude that the IEEE 802.11p standard will be robust towards inter-symbol and inter-carrier interference inside a tunnel.
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paper_title: Measurements and Modeling of Distributed Antenna Systems in Railway Tunnels

paper_content:

This paper covers some of the work carried out in the planning of the global system for mobile communication for railway (GSM-R) of the tunnels on the new high-speed trains in Spain. Solutions based on distributed antenna systems have been tested by installing several 900-MHz transmitters inside and outside of a 4000-m tunnel and measuring the propagation in different conditions. The measurements have been used to model the effects of tunnel propagation, including curves, trains passing from the outside to the inside, and the effect of two trains passing inside the tunnel. All cases have been tested by comparing solutions using isofrequency and multifrequency distributed transmitters inside the tunnel. The improvements of signal-to-noise ratio and the reduction of the blocking effects of two trains passing have demonstrated the advantages of using isofrequency distributed antenna systems in tunnels. Finally, a complete propagation model combining both modal analysis and ray tracing has been applied to predict the propagation loss inside and outside these tunnels, and results have been compared with the measurements. The model has proven to be very useful for radio planning in new railway networks.
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paper_title: Investigation on MIMO channels in subway tunnels

paper_content:

The purpose of this paper is to examine the possibilities of increasing the channel capacity in tunnels, and particularly in railway tunnels, due to the use of multiple-input-multiple-output techniques. Many measurement campaigns have been carried out, considering the complicated geometric structure of these tunnels. We determine the channel characteristics by making a statistical analysis of correlation matrices between antennas and singular values of the channel transfer matrix. A comparison between the theoretical and experimental results is also presented. A stochastic channel model is then proposed and validated.
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paper_title: Measurement of Distributed Antenna Systems at 2.4 GHz in a Realistic Subway Tunnel Environment

paper_content:

Accurate characterization of the radio channel in tunnels is of great importance for new signaling and train control communications systems. To model this environment, measurements have been taken at 2.4 GHz in a real environment in Madrid subway. The measurements were carried out with four base station transmitters installed in a 2-km tunnel and using a mobile receiver installed on a standard train. First, with an optimum antenna configuration, all the propagation characteristics of a complex subway environment, including near shadowing, path loss, shadow fading, fast fading, level crossing rate (LCR), and average fade duration (AFD), have been measured and computed. Thereafter, comparisons of propagation characteristics in a double-track tunnel (9.8-m width) and a single-track tunnel (4.8-m width) have been made. Finally, all the measurement results have been shown in a complete table for accurate statistical modeling.
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paper_title: Modeling and Understanding MIMO propagation in Tunnels

paper_content:

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.
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paper_title: A Novel Wideband MIMO Car-to-Car Channel Model Based on a Geometrical Semi-Circular Tunnel Scattering Model

paper_content:

In this paper, we present a wideband multiple-input multiple-output (MIMO) car-to-car (C2C) channel model based on a geometrical semi-circular tunnel (SCT) scattering model. From the geometrical SCT scattering model, a reference channel model is derived under the assumption of single-bounce scattering in line-of-sight (LOS) and non-LOS (NLOS) propagation environments. In the proposed reference channel model, it is assumed that an infinite number of scatterers are randomly distributed on the tunnel wall. Starting from the geometrical scattering model, the time-variant transfer function (TVTF) is derived, and its correlation properties in time, frequency, and space are studied. Expressions are presented for the space–time–frequency cross-correlation function (STF-CCF), the two-dimensional (2D) space CCF, the 2D time–frequency CCF (TF-CCF), the temporal autocorrelation function (ACF), and the frequency correlation function (FCF). Owing to the semi-circular geometry, we reduced the originally threefold integrals to double integrals in the computations of the correlation functions, which simplifies the numerical analysis considerably. From the TVTF characterizing the reference model, an efficient sum-of-cisoid (SOC) channel simulator is derived. Numerical results show that both the temporal ACF and the FCF of the SOC channel simulator match very well with those of the reference model. A validation of the proposed model has been done by fitting the delay spread of the reference model to that of the measured channel, which demonstrates an excellent agreement. The proposed channel simulator allows us to evaluate the performance of C2C communication systems in tunnel environments.
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paper_title: Characterization of Angular Spread in Underground Tunnels Based on the Multimode Waveguide Model

paper_content:

One of the biggest challenges facing wireless designers is determining how to configure multiple-input–multiple-output (MIMO) antennas in underground-environments, such as mines, so that they deliver best performance. Here, we showed that angular dispersion of the signal, a phenomenon that greatly impacts channel capacity, can be accurately predicted in both near-field and far-field of underground tunnels using a multimode waveguide. Not only this analytical model is much faster than other methods, but also it does not have other shortcomings of measurement-based modeling (e.g., poor resolution for far distances in the tunnel). Further, we characterized angular-spread for different tunnel sizes and showed that the power-azimuth-spectrum can be modeled by a zero-mean Gaussian distribution whose standard-deviation (angular-spread) is dependent on the tunnel dimension and the transmitter-receiver distance. Angular-spread is found to be a decreasing function of axial distance. After a certain distance, it becomes very small (about 4 $^{\circ}$ ) and independent of tunnel transverse dimension. Our results are useful for design of MIMO systems in underground tunnels and sufficient to permit the correlation-matrix required to extend the IEEE 802.11n MIMO channel model to underground environments.
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paper_title: A calculation model and characteristics analysis of radio wave propagation in rectangular shed tunnel

paper_content:

Shed tunnel belongs to a kind of heterogeneous tunnel of open cut tunnel, which has been widely used in the railway as well as highway construction. Geometrical optics method is adopted in this paper to study and present a simulation of radio waves propagation in rectangular shed tunnels. By comparing the received power under different polarization modes, frequencies and permittivities, we get some relevant conclusions that the near-field region signal in shed tunnel fade soon, and the vertical polarization radio wave propagate in the shed tunnel is greatly influenced by environment.
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paper_title: A multi-mode waveguide tunnel channel model for high-speed train wireless communication systems

paper_content:

The recent development of high-speed trains (HSTs) introduce new challenges to wireless communication systems for HSTs. For demonstrating the feasibility of these systems, accurate channel models which can mimic key characteristics of HST wireless channels are essential. In this paper, we focus on HST channel models for the tunnel scenario, which is different from other HST channel environments, such as rural area and viaducts. Considering unique characteristics of tunnel channel environments, we extend the existing multi-mode waveguide tunnel channel model to be time dependent, obtain the channel impulse responses, and then further investigate certain key tunnel channel characteristics such as temporal autocorrelation function (ACF) and power spectrum density (PSD). The impact of time on ACFs and PSDs, and the impact of frequency on the received power are revealed via numerical results.
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paper_title: Research on Doppler spread of multipath channel in subway tunnel

paper_content:

Radio wave propagation in subway tunnel differs strongly from other circumstances because of the multi-path characteristics and special structure. A real multi-path propagation model for radio transmission in typical rectangular subway tunnel is presented in this paper, and ray-tracing technologies and wireless statistical theory are used to analyze Doppler spread and Doppler shift. Simulation results based on Wireless Insite show that Doppler spread and Doppler shift in tunnel are depended strongly upon frequency and velocity. Higher frequency signals and higher train's velocity exhibit larger Doppler spread and Doppler shift. The simulation results in this paper provide a reference for the application of 4G and 5G technologies used in metro system.
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paper_title: A Modified Method for Predicting the Radio Propagation Characteristics in Tunnels

paper_content:

Paths between transmitter and receiver could be determined based on geometric optics in straight rectangular tunnels. Later on, the united theory of diffraction is used to calculate receiving power. This method could also be applied to other tunnels with different cross section. From the results of simulation and theory, this method has the same exactness as dedicated software, as well as lower complexity of computing.
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paper_title: A Study on Channel Modeling in Tunnel Scenario Based on Propagation-Graph Theory

paper_content:

A new approach based on conventional propagation graph channel modeling was proposed to haracterize the wireless channel in non-light of sight (NLOS) tunnel scenarios. The scattering points are regarded as several points sets, which are different from the propagation-graph theory, then the transfer probability among sets is introduced to adjust the channel impulse response (CIR) taps. The advantage of the proposed method is that wideband channel coefficients, CIR in delay, antennas' correlation coefficient, angle of arrival (AOA), angle of departure (AOD), channel capacity can be calculated analytically for these environments. The validation of the proposed method is performed by the reasonable distribution of the CIR taps, AOD and AOA. Finally some works are done to investigate the variation of tunnel channel coefficients when tunnel bending angle varies, and channel matrix degradation is adopted to explain it.
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paper_title: Graph Theoretic Models and Tools for the Analysis of Dynamic Wireless Multihop Networks

paper_content:

Wireless multihop networks are being increasingly used in military and civilian applications. Advanced applications of wireless multihop networks demand better understanding on their properties. Existing research on wireless multihop networks has largely focused on static networks, where the network topology is time-invariant; and there is comparatively a lack of understanding on the properties of dynamic networks with dynamically changing topology. In this paper, we use and extend a recently proposed graph theoretic model, i.e. evolving graphs, to capture the characteristics of such networks. We extend and develop the concepts of route matrix, connectivity matrix and probabilistic connectivity matrix as convenient tools to characterize and investigate the properties of evolving graphs and the associated dynamic networks. The properties of these matrices are established and their relevance to the properties of dynamic wireless multihop networks are introduced.
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paper_title: WINNER model for subway tunnel at 5.8 GHz

paper_content:

Modern subways operation relies on wireless systems based on IEEE802.11x modems deployed inside tunnels. Constraints on robustness and needs for high data rates led to the use of MIMO techniques. In order to evaluate performance of MIMO systems in dynamic configurations with moving trains, it is mandatory to develop adequate dynamic channel model. In this paper, the authors present a new WINNER based model for a subway tunnel at 5.8 GHz in a representative geometric configuration with two tracks and two crossing trains and a 4×4 MIMO system. The statistical behavior of the key parameters of the new WINNER scenario are derived from the complex impulse responses obtained with a 3D ray tracing simulator and given in this paper. Five clusters are considered. The total received power and the 4×4 MIMO channel capacity are compared with the ones derived from the 3D ray tracing simulator.
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paper_title: Physics-based ultra-wideband channel modeling for tunnel/mining environments

paper_content:

Understanding wireless channels in mining environments is critical for designing optimized wireless systems in these complex environments. In this paper, we propose a physics-based deterministic UWB channel model for characterizing wireless channels in mining/tunnel environments. Both the time domain Channel Impulse Response (CIR) and frequency domain channel transfer function for tunnel environments are derived in an analytical form. The derived CIR and transfer function are validated by RF measurements at different frequencies.
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paper_title: Computational Electrodynamics the Finite-Difference Time-Domain Method

paper_content:

Part 1 Reinventing electromagnetics: background history of space-grid time-domain techniques for Maxwell's equations scaling to very large problem sizes defense applications dual-use electromagnetics technology. Part 2 The one-dimensional scalar wave equation: propagating wave solutions finite-difference approximation of the scalar wave equation dispersion relations for the one-dimensional wave equation numerical group velocity numerical stability. Part 3 Introduction to Maxwell's equations and the Yee algorithm: Maxwell's equations in three dimensions reduction to two dimensions equivalence to the wave equation in one dimension. Part 4 Numerical stability: TM mode time eigenvalue problem space eigenvalue problem extension to the full three-dimensional Yee algorithm. Part 5 Numerical dispersion: comparison with the ideal dispersion case reduction to the ideal dispersion case for special grid conditions dispersion-optimized basic Yee algorithm dispersion-optimized Yee algorithm with fourth-order accurate spatial differences. Part 6 Incident wave source conditions for free space and waveguides: requirements for the plane wave source condition the hard source total-field/scattered field formulation pure scattered field formulation choice of incident plane wave formulation. Part 7 Absorbing boundary conditions for free space and waveguides: Bayliss-Turkel scattered-wave annihilating operators Engquist-Majda one-way wave equations Higdon operator Liao extrapolation Mei-Fang superabsorption Berenger perfectly-matched layer (PML) absorbing boundary conditions for waveguides. Part 8 Near-to-far field transformation: obtaining phasor quantities via discrete fourier transformation surface equivalence theorem extension to three dimensions phasor domain. Part 9 Dispersive, nonlinear, and gain materials: linear isotropic case recursive convolution method linear gyrontropic case linear isotropic case auxiliary differential equation method, Lorentz gain media. Part 10 Local subcell models of the fine geometrical features: basis of contour-path FD-TD modelling the simplest contour-path subcell models the thin wire conformal modelling of curved surfaces the thin material sheet relativistic motion of PEC boundaries. Part 11 Explicit time-domain solution of Maxwell's equations using non-orthogonal and unstructured grids, Stephen Gedney and Faiza Lansing: nonuniform, orthogonal grids globally orthogonal global curvilinear co-ordinates irregular non-orthogonal unstructured grids analysis of printed circuit devices using the planar generalized Yee algorithm. Part 12 The body of revolution FD-TD algorithm, Thomas Jurgens and Gregory Saewert: field expansion difference equations for on-axis cells numerical stability PML absorbing boundary condition. Part 13 Modelling of electromagnetic fields in high-speed electronic circuits, Piket-May and Taflove. (part contents).
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paper_title: GBSB MODEL for MIMO Channel AND its Space-time CORRELATION Analysis in Tunnel

paper_content:

Aiming at the special space in the tunnel, this paper assumes the geometric distribution of scatterers which is totally different from on the ground, puts forward a new GBSB model of MIMO channel and deduces the space-time correlation function of the model. The results of theoretical analysis and simulation show that the model can more accurately reflect the factors which impact the channel correlation in the tunnel.
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paper_title: Theory of the propagation of UHF radio waves in coal mine tunnels

paper_content:

The theoretical study of UHF radio communication in coal mines, with particular reference to the rate of loss of signal strength along a tunnel, and from one tunnel to another around a corner is the concern of this paper. Of prime interest are the nature of the propagation mechanism and the prediction of the radio frequency that propagates with the smallest loss. The theoretical results are compared with published measurements. This work was part of an investigation of new ways to reach and extend two-way communications to the key individuals who are highly mobile within the sections and haulageways of coal mines.
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paper_title: Energy efficiency of small cell backhaul networks based on Gauss–Markov mobile models

paper_content:

To satisfy the recent growth of mobile data usage, small cells are recommended to deploy into conventional cellular networks. However, the massive backhaul traffic is a troublesome problem for small cell networks, especial in wireless backhaul transmission links. In this study, backhaul traffic models are first presented considering the Gauss–Markov mobile models of mobile stations in small cell networks. Furthermore, an energy efficiency model of small cell backhaul networks with Gauss–Markov mobile models has been proposed. Numerical results indicate that the energy efficiency of small cell backhaul networks can be optimised by trade-off the number and radius of small cells in cellular networks.
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paper_title: A Hybrid Ray-Tracing/Vector Parabolic Equation Method for Propagation Modeling in Train Communication Channels

paper_content:

In recent years, various techniques have been applied to modeling radio-wave propagation in railway networks, each one presenting its own advantages and limitations. This paper presents a hybrid channel modeling technique, which combines two of these methods, the ray-tracing (RT) and vector parabolic equation (VPE) methods, to enable the modeling of realistic railway scenarios including stations and long guideways within a unified simulation framework. The general-purpose RT method is applied to analyze propagation in complex areas, whereas the VPE method is reserved for long and uniform tunnel as well as open-air sections. By using the advantages of VPE to compensate for the limitations of RT and vice versa, this hybrid model ensures improved accuracy and computational savings. Numerical results are validated with experimental measurements in various railway scenarios, including an actual deployment site of communication-based train control (CBTC) systems.
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paper_title: Radio Wave Propagation in Arched Cross Section Tunnels – Simulations and Measurements

paper_content:

For several years, wireless communication systems have been developed for train to infrastructure communication needs related to railway or mass transit applications. The systems should be able to operate in specific environments, such as tunnels. In this context, specific radio planning tools have to be developed to optimize system deployment. Realistic tunnels geometries are generally of rectangular cross section or arch-shaped. Furthermore, they are mostly curved. In order to calculate electromagnetic wave propagation in such tunnels, specific models have to be developed. Several works have dealt with retransmission of GSM or UMTS. Few theoretical or experimental works have focused on 2.4 GHz or 5.8 GHz bands. In this paper, we propose an approach to model radio wave propagation in these frequency bands in straight arch-shaped tunnels using tessellation in multi-facets. The model is based on a Ray Tracing tool using the image method. The work reported in this paper shows the propagation loss variations according to the shape of tunnels. A parametric study on the facets size to model the cross section is conducted. The influence of tunnel dimensions and signal frequency is examined. Finally, some measurement results in a straight arch-shaped tunnel are presented and analyzed in terms of slow and fast fading.
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paper_title: SBR image approach for radio wave propagation in tunnels with and without traffic

paper_content:

We propose a deterministic approach to model the radio propagation channels in tunnels with and without traffic. This technique applies the modified shooting and bouncing ray (SBR) method to find equivalent sources (images) in each launched ray tube and sums the receiving complex amplitude contributed by all images coherently. In addition, the vector effective antenna height (VEH) is introduced to consider the polarization-coupling effect resulting from the shape of the tunnels. We verify this approach by comparing the numerical results in two canonical examples where closed-form solutions exist. The good agreement indicates that our method can provide a good approximation of high-frequency radio propagation inside tunnels where reflection is dominant. We show that the propagation loss in tunnels can vary considerably according to the tunnel shapes and the traffic inside them. From the results we also find a "focusing" effect, which makes the power received in an arched tunnel higher than that in a rectangular tunnel. Besides, the deep fading that appears in a rectangular tunnel is absent in an arched tunnel. The major effect of the traffic is observed to be the fast fading due to the reflection/obstruction of vehicles. Additional considerations, such as time delay, wall roughness, and wedge diffraction of radio wave propagation in tunnels are left for future studies.
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paper_title: Ray-density normalization for ray-optical wave propagation modeling in arbitrarily shaped tunnels

paper_content:

This work is concerned with the calculation of natural electromagnetic (EM) wave propagation and the determination of the propagation channel characteristics in highway or railway tunnels in the ultrahigh-frequency (UHF) range and above (>300 MHz). A novel ray-tracing technique based on geometrical optics (GO) is presented. Contrary to classical ray tracing, where the one ray representing a locally plane wave front is searched, the new method requires multiple representatives of each physical EM wave at a time. The contribution of each ray to the total field at the receiver is determined by the proposed ray-density normalization (RBN). This technique has the further advantage of overcoming one of the major disadvantages of GO, the failure at caustics. In contrast to existing techniques, the new approach does not use ray tubes or adaptive reception spheres. Consequently, it does not suffer their restrictions to planar geometries. Therefore, it allows one to predict the propagation of high-frequency EM waves in confined spaces with curved boundaries, like tunnels, with an adequate precision. The approach is verified theoretically with canonical examples and by various measurements at 120 GHz in scaled tunnel models.
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paper_title: Ray optical modeling of wireless communications in high-speed railway tunnels

paper_content:

A new deterministic approach for wave propagation modeling in high-speed train tunnels is presented. The model is based on a new ray launching method and results in the polarimetric and complex channel impulse response as well as the Doppler diagram for radio links between on-train stations and tunnel-fixed stations. Different channel simulations under certain propagation conditions are presented.
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paper_title: Channel modeling and analysis for wireless networks in underground mines and road tunnels

paper_content:

Wireless networks can greatly facilitate the communication in underground mines and road/subway tunnels, where the propagation characteristics of electromagnetic (EM) waves are significantly different from those in terrestrial environments. According to the structure of underground mines and road tunnels, two types of channel models can be utilized, namely, tunnel and room/pillar channel models. However, there exists no theoretical model for room-and-pillar channel in underground mines to date, and current existing tunnel channel models do not provide an analytical solution for both near and far regions of the sources. In this paper, the multimode model is proposed, which provides an analytical expression for the received power and the power delay profile at any position in a tunnel.Moreover, the multimode model is extended to characterize the room-and-pillar channel in the underground mines after combining it with the shadow fading model. The theoretical models are validated by experimental measurements. Based on the proposed channel models, the effects of various factors on the signal propagation are analyzed. The factors include: the operating frequency, the size of the tunnel or underground mine room, the antenna position and polarization, and the electrical parameters.
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paper_title: Theory of the propagation of UHF radio waves in coal mine tunnels

paper_content:

The theoretical study of UHF radio communication in coal mines, with particular reference to the rate of loss of signal strength along a tunnel, and from one tunnel to another around a corner is the concern of this paper. Of prime interest are the nature of the propagation mechanism and the prediction of the radio frequency that propagates with the smallest loss. The theoretical results are compared with published measurements. This work was part of an investigation of new ways to reach and extend two-way communications to the key individuals who are highly mobile within the sections and haulageways of coal mines.
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paper_title: On wireless communication in tunnels

paper_content:

We review recent research work on wireless communication in straight and curved tunnels. Modal theory of fields in a circular tunnel excited by a linear source is given in detail. Closed form expressions for the propagation parameters of the dominant modes in circular and rectangular straight tunnels in the high frequencies are derived. We present field measurements in tunnels and interpret them in terms of the mode theory. The main characteristics of the dominant modes in a curved tunnel are studied.
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paper_title: Radio Wave Propagation Scene Partitioning for High-Speed Rails

paper_content:

Radio wave propagation scene partitioning is necessary for wireless channel modeling. As far as we know, there are no standards of scene partitioning for high-speed rail (HSR) scenarios, and therefore we propose the radio wave propagation scene partitioning scheme for HSR scenarios in this paper. Based on our measurements along the Wuhan-Guangzhou HSR, Zhengzhou-Xian passenger-dedicated line, Shijiazhuang-Taiyuan passenger-dedicated line, and Beijing-Tianjin intercity line in China, whose operation speeds are above 300 km/h, and based on the investigations on Beijing South Railway Station, Zhengzhou Railway Station, Wuhan Railway Station, Changsha Railway Station, Xian North Railway Station, Shijiazhuang North Railway Station, Taiyuan Railway Station, and Tianjin Railway Station, we obtain an overview of HSR propagation channels and record many valuable measurement data for HSR scenarios. On the basis of these measurements and investigations, we partitioned the HSR scene into twelve scenarios. Further work on theoretical analysis based on radio wave propagation mechanisms, such as reflection and diffraction, may lead us to develop the standard of radio wave propagation scene partitioning for HSR. Our work can also be used as a basis for the wireless channel modeling and the selection of some key techniques for HSR systems.
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paper_title: Computational Electrodynamics the Finite-Difference Time-Domain Method

paper_content:

Part 1 Reinventing electromagnetics: background history of space-grid time-domain techniques for Maxwell's equations scaling to very large problem sizes defense applications dual-use electromagnetics technology. Part 2 The one-dimensional scalar wave equation: propagating wave solutions finite-difference approximation of the scalar wave equation dispersion relations for the one-dimensional wave equation numerical group velocity numerical stability. Part 3 Introduction to Maxwell's equations and the Yee algorithm: Maxwell's equations in three dimensions reduction to two dimensions equivalence to the wave equation in one dimension. Part 4 Numerical stability: TM mode time eigenvalue problem space eigenvalue problem extension to the full three-dimensional Yee algorithm. Part 5 Numerical dispersion: comparison with the ideal dispersion case reduction to the ideal dispersion case for special grid conditions dispersion-optimized basic Yee algorithm dispersion-optimized Yee algorithm with fourth-order accurate spatial differences. Part 6 Incident wave source conditions for free space and waveguides: requirements for the plane wave source condition the hard source total-field/scattered field formulation pure scattered field formulation choice of incident plane wave formulation. Part 7 Absorbing boundary conditions for free space and waveguides: Bayliss-Turkel scattered-wave annihilating operators Engquist-Majda one-way wave equations Higdon operator Liao extrapolation Mei-Fang superabsorption Berenger perfectly-matched layer (PML) absorbing boundary conditions for waveguides. Part 8 Near-to-far field transformation: obtaining phasor quantities via discrete fourier transformation surface equivalence theorem extension to three dimensions phasor domain. Part 9 Dispersive, nonlinear, and gain materials: linear isotropic case recursive convolution method linear gyrontropic case linear isotropic case auxiliary differential equation method, Lorentz gain media. Part 10 Local subcell models of the fine geometrical features: basis of contour-path FD-TD modelling the simplest contour-path subcell models the thin wire conformal modelling of curved surfaces the thin material sheet relativistic motion of PEC boundaries. Part 11 Explicit time-domain solution of Maxwell's equations using non-orthogonal and unstructured grids, Stephen Gedney and Faiza Lansing: nonuniform, orthogonal grids globally orthogonal global curvilinear co-ordinates irregular non-orthogonal unstructured grids analysis of printed circuit devices using the planar generalized Yee algorithm. Part 12 The body of revolution FD-TD algorithm, Thomas Jurgens and Gregory Saewert: field expansion difference equations for on-axis cells numerical stability PML absorbing boundary condition. Part 13 Modelling of electromagnetic fields in high-speed electronic circuits, Piket-May and Taflove. (part contents).
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paper_title: Modeling radio wave propagation in tunnels with a vectorial parabolic equation

paper_content:

To study radio wave propagation in tunnels, we present a vectorial parabolic equation (PE) taking into account the cross-section shape, wall impedances, slowly varying curvature, and torsion of the tunnel axis. For rectangular cross section, two polarizations are decoupled and two families of adiabatic modes can be found explicitly, giving a generalization of the known results for a uniform tunnel. In the general case, a boundary value problem arises to be solved by using finite-difference/finite-element (FD/FE) techniques. Numerical examples demonstrate the computational efficiency of the proposed method.
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paper_title: Analysis of MIMO capacity in waveguide environments using practical antenna structures for selective mode excitation

paper_content:

Different realistic antenna configurations are studied and their impact on MIMO capacity is investigated in waveguide-like environments, such as hallways, tunnels or streets. Simulations are conducted for a 2/spl times/2 MIMO system using the the finite element method, which is particularly well suited for this kind of problem. First, each antenna is optimized independently from the other by optimizing its shape and location in a manner that insures optimal input impedance and excitation of a single mode. Subsequently, the two antennas are placed together and a final optimization is carried out to reduce their mutual coupling and improve the impedance matching. The results obtained for a 2/spl times/2 MIMO system clearly show the significance of practical antenna considerations on MIMO capacity in a waveguide environment.
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paper_title: A multi-mode waveguide tunnel channel model for high-speed train wireless communication systems

paper_content:

The recent development of high-speed trains (HSTs) introduce new challenges to wireless communication systems for HSTs. For demonstrating the feasibility of these systems, accurate channel models which can mimic key characteristics of HST wireless channels are essential. In this paper, we focus on HST channel models for the tunnel scenario, which is different from other HST channel environments, such as rural area and viaducts. Considering unique characteristics of tunnel channel environments, we extend the existing multi-mode waveguide tunnel channel model to be time dependent, obtain the channel impulse responses, and then further investigate certain key tunnel channel characteristics such as temporal autocorrelation function (ACF) and power spectrum density (PSD). The impact of time on ACFs and PSDs, and the impact of frequency on the received power are revealed via numerical results.
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paper_title: Channel modeling and analysis for wireless networks in underground mines and road tunnels

paper_content:

Wireless networks can greatly facilitate the communication in underground mines and road/subway tunnels, where the propagation characteristics of electromagnetic (EM) waves are significantly different from those in terrestrial environments. According to the structure of underground mines and road tunnels, two types of channel models can be utilized, namely, tunnel and room/pillar channel models. However, there exists no theoretical model for room-and-pillar channel in underground mines to date, and current existing tunnel channel models do not provide an analytical solution for both near and far regions of the sources. In this paper, the multimode model is proposed, which provides an analytical expression for the received power and the power delay profile at any position in a tunnel.Moreover, the multimode model is extended to characterize the room-and-pillar channel in the underground mines after combining it with the shadow fading model. The theoretical models are validated by experimental measurements. Based on the proposed channel models, the effects of various factors on the signal propagation are analyzed. The factors include: the operating frequency, the size of the tunnel or underground mine room, the antenna position and polarization, and the electrical parameters.
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paper_title: A Hybrid Ray-Tracing/Vector Parabolic Equation Method for Propagation Modeling in Train Communication Channels

paper_content:

In recent years, various techniques have been applied to modeling radio-wave propagation in railway networks, each one presenting its own advantages and limitations. This paper presents a hybrid channel modeling technique, which combines two of these methods, the ray-tracing (RT) and vector parabolic equation (VPE) methods, to enable the modeling of realistic railway scenarios including stations and long guideways within a unified simulation framework. The general-purpose RT method is applied to analyze propagation in complex areas, whereas the VPE method is reserved for long and uniform tunnel as well as open-air sections. By using the advantages of VPE to compensate for the limitations of RT and vice versa, this hybrid model ensures improved accuracy and computational savings. Numerical results are validated with experimental measurements in various railway scenarios, including an actual deployment site of communication-based train control (CBTC) systems.
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paper_title: A Novel Wideband MIMO Car-to-Car Channel Model Based on a Geometrical Semi-Circular Tunnel Scattering Model

paper_content:

In this paper, we present a wideband multiple-input multiple-output (MIMO) car-to-car (C2C) channel model based on a geometrical semi-circular tunnel (SCT) scattering model. From the geometrical SCT scattering model, a reference channel model is derived under the assumption of single-bounce scattering in line-of-sight (LOS) and non-LOS (NLOS) propagation environments. In the proposed reference channel model, it is assumed that an infinite number of scatterers are randomly distributed on the tunnel wall. Starting from the geometrical scattering model, the time-variant transfer function (TVTF) is derived, and its correlation properties in time, frequency, and space are studied. Expressions are presented for the space–time–frequency cross-correlation function (STF-CCF), the two-dimensional (2D) space CCF, the 2D time–frequency CCF (TF-CCF), the temporal autocorrelation function (ACF), and the frequency correlation function (FCF). Owing to the semi-circular geometry, we reduced the originally threefold integrals to double integrals in the computations of the correlation functions, which simplifies the numerical analysis considerably. From the TVTF characterizing the reference model, an efficient sum-of-cisoid (SOC) channel simulator is derived. Numerical results show that both the temporal ACF and the FCF of the SOC channel simulator match very well with those of the reference model. A validation of the proposed model has been done by fitting the delay spread of the reference model to that of the measured channel, which demonstrates an excellent agreement. The proposed channel simulator allows us to evaluate the performance of C2C communication systems in tunnel environments.
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paper_title: 3D Wideband Non-Stationary Geometry-Based Stochastic Models for Non-Isotropic MIMO Vehicle-to-Vehicle Channels

paper_content:

Actual vehicle-to-vehicle (V2V) channel measurements have shown that the wide-sense stationary (WSS) modeling assumption is valid only for very short time intervals. This fact motivates us to develop non-WSS V2V channel models. In this paper, we propose a novel three-dimensional (3D) theoretical non-WSS regular-shaped geometry-based stochastic model (RS-GBSM) and the corresponding sum-of-sinusoids (SoS) simulation model for non-isotropic scattering wideband multiple-input multiple-output (MIMO) V2V fading channels. The movements of the transmitter (Tx), scatterers, and receiver (Rx) result in the time-varying angles of departure (AoDs) and angles of arrival (AoAs) that make our models non-stationary. The proposed RS-GBSMs, combining line-of-sight (LoS) components, a two-sphere model, and multiple confocal elliptic-cylinder models, have the ability to study the impacts of vehicular traffic density (VTD) and non-stationarity on channel statistics, and jointly consider the azimuth and elevation angles by using the von Mises Fisher (VMF) distribution. The proposed RS-GBSMs are sufficiently generic and adaptable to model various V2V scenarios. Based on the proposed 3D non-WSS RS-GBSMs, important local channel statistical properties are derived and thoroughly investigated. The impacts of VTD and non-stationarity on these channel statistical properties are investigated by comparing them with those of the corresponding WSS model. The proposed non-WSS RS-GBSMs are validated by measurements in terms of the channel stationary time. Finally, numerical and simulation results demonstrate that the 3D non-WSS model is more practical to characterize real V2V channels.
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paper_title: A non-stationary geometry-based stochastic model for MIMO high-speed train channels

paper_content:

In this paper, a non-stationary wideband geometry-based stochastic model (GBSM) is proposed for multiple-input multiple-output (MIMO) high-speed train (HST) channels. The proposed model employs multiple confocal ellipses model, where the received signal is a superposition of the line-of-sight (LoS) and single-bounced rays. Because of the time-varying feature of angles of arrival (AoAs), angles of departure (AoDs), and LoS angle, the proposed GBSM has the ability to investigate the non-stationarity of HST environment caused by the high speed movement of the receiver. From the proposed model, the local spatial cross-correlation function (CCF) and the local temporal autocorrelation (ACF) are derived for different taps. Numerical results and analysis show that the proposed channel model is capable of characterizing the time-variant HST wireless channel.
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paper_title: Novel 3D Geometry-Based Stochastic Models for Non-Isotropic MIMO Vehicle-to-Vehicle Channels

paper_content:

This paper proposes a novel three-dimensional (3D) theoretical regular-shaped geometry-based stochastic model (RS-GBSM) and the corresponding sum-of-sinusoids (SoS) simulation model for non-isotropic multiple-input multiple-output (MIMO) vehicle-to-vehicle (V2V) Ricean fading channels. The proposed RS-GBSM, combining line-of-sight (LoS) components, a two-sphere model, and an elliptic-cylinder model, has the ability to study the impact of the vehicular traffic density (VTD) on channel statistics, and jointly considers the azimuth and elevation angles by using the von Mises Fisher distribution. Moreover, a novel parameter computation method is proposed for jointly calculating the azimuth and elevation angles in the SoS channel simulator. Based on the proposed 3D theoretical RS-GBSM and its SoS simulation model, statistical properties are derived and thoroughly investigated. The impact of the elevation angle in the 3D model on key statistical properties is investigated by comparing with those of the corresponding two-dimensional (2D) model. It is demonstrated that the 3D model is more accurate to characterize real V2V channels, in particular for pico cell scenarios. Finally, close agreement is achieved between the theoretical model, SoS simulation model, and simulation results, demonstrating the utility of the proposed models.
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paper_title: Road traffic density estimation in vehicular networks

paper_content:

Road traffic density estimation provides important information for road planning, intelligent road routing, road traffic control, vehicular network traffic scheduling, routing and dissemination. The ever increasing number of vehicles equipped with wireless communication capabilities provide new means to estimate the road traffic density more accurately and in real time than traditionally used techniques. In this paper, we consider the problem of road traffic density estimation where each vehicle estimates its local road traffic density using some simple measurements only, i.e. the number of neighboring vehicles. A maximum likelihood estimator of the traffic density is obtained based on a rigorous analysis of the joint distribution of the number of vehicles in each hop. Analysis is also performed on the accuracy of the estimation and the amount of neighborhood information required for an accurate road traffic density estimation. Simulations are performed which validate the accuracy and the robustness of the proposed density estimation algorithm.
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paper_title: GBSB MODEL for MIMO Channel AND its Space-time CORRELATION Analysis in Tunnel

paper_content:

Aiming at the special space in the tunnel, this paper assumes the geometric distribution of scatterers which is totally different from on the ground, puts forward a new GBSB model of MIMO channel and deduces the space-time correlation function of the model. The results of theoretical analysis and simulation show that the model can more accurately reflect the factors which impact the channel correlation in the tunnel.
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paper_title: A generic non-stationary MIMO channel model for different high-speed train scenarios

paper_content:

This paper proposes a generic non-stationary wideband geometry-based stochastic model (GBSM) for multiple-input multiple-output (MIMO) high-speed train (HST) channels. The proposed generic model can be applied on the three most common HST scenarios, i.e., open space, viaduct, and cutting scenarios. A good agreement between the statistical properties of the proposed generic model and those of relevant measurement data from the aforementioned scenarios demonstrates the utility of the proposed channel model.
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paper_title: Finite-State Markov Modeling for Wireless Channels in Tunnel Communication-Based Train Control Systems

paper_content:

Communication-based train control (CBTC) is being rapidly adopted in urban rail transit systems, as it can significantly enhance railway network efficiency, safety, and capacity. Since CBTC systems are mostly deployed in underground tunnels and trains move at high speeds, building a train–ground wireless communication system for CBTC is a challenging task. Modeling the tunnel channels is very important in designing the wireless networks and evaluating the performance of CBTC systems. Most existing works on channel modeling do not consider the unique characteristics of CBTC systems, such as high mobility speed, deterministic moving direction, and accurate train-location information. In this paper, we develop a finite-state Markov channel (FSMC) model for tunnel channels in CBTC systems. The proposed FSMC model is based on real field CBTC channel measurements obtained from a business-operating subway line. Unlike most existing channel models, which are not related to specific locations, the proposed FSMC channel model takes train locations into account to have a more accurate channel model. The distance between the transmitter and the receiver is divided into intervals and an FSMC model is applied in each interval. The accuracy of the proposed FSMC model is illustrated by the simulation results generated from the model and the real field measurement results.
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paper_title: A survey on vehicle-to-vehicle propagation channels

paper_content:

Traffic telematics applications are currently under intense research and development for making transportation safer, more efficient, and more environmentally friendly. Reliable traffic telematics applications and services require vehicle-to-vehicle wireless communications that can provide robust connectivity, typically at data rates between 1 and 10 Mb/s. The development of such VTV communications systems and standards require, in turn, accurate models for the VTV propagation channel. A key characteristic of VTV channels is their temporal variability and inherent non-stationarity, which has major impact on data packet transmission reliability and latency. This article provides an overview of existing VTV channel measurement campaigns in a variety of important environments, and the channel characteristics (such as delay spreads and Doppler spreads) therein. We also describe the most commonly used channel modeling approaches for VTV channels: statistical as well as geometry-based channel models have been developed based on measurements and intuitive insights. Extensive references are provided.
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paper_title: Vehicle-to-vehicle channel modeling and measurements: recent advances and future challenges

paper_content:

Vehicle-to-vehicle communications have recently received much attention due to some new applications, such as wireless mobile ad hoc networks, relay-based cellular networks, and intelligent transportation systems for dedicated short range communications. The underlying V2V channels, as a foundation for the understanding and design of V2V communication systems, have not yet been sufficiently investigated. This article aims to review the state-of-the-art in V2V channel measurements and modeling. Some important V2V channel measurement campaigns and models are briefly described and classified. Finally, some challenges of V2V channel measurements and modeling are addressed for future studies.
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paper_title: 3D non-stationary wideband circular tunnel channel models for high-speed train wireless communication systems

paper_content:

This paper proposes three-dimensional (3D) non-stationary wideband circular geometry-based stochastic models (GBSMs) for high-speed train (HST) tunnel scenarios. Considering single-bounced (SB) and multiple-bounced (MB) components from the tunnel's internal surfaces, a theoretical channel model is first established. Then, the corresponding simulation model is developed using the method of equal volume (MEV) to calculate discrete angular parameters. Based on the proposed 3D GBSMs, important time-variant statistical properties are investigated, such as the temporal autocorrelation function (ACF), spatial cross-correlation function (CCF), and space-Doppler (SD) power spectrum density (PSD). Results indicate that all statistical properties of the simulation model, verified by simulation results, can match well those of the theoretical model. The statistical properties of the proposed 3D GBSMs are further validated by relevant measurement data, demonstrating the flexibility and utility of our proposed tunnel GBSMs.
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paper_title: GBSB MODEL for MIMO Channel AND its Space-time CORRELATION Analysis in Tunnel

paper_content:

Aiming at the special space in the tunnel, this paper assumes the geometric distribution of scatterers which is totally different from on the ground, puts forward a new GBSB model of MIMO channel and deduces the space-time correlation function of the model. The results of theoretical analysis and simulation show that the model can more accurately reflect the factors which impact the channel correlation in the tunnel.
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paper_title: Communication in tunnel: Channel characteristics and performance of diversity schemes

paper_content:

This paper gives an overview of the theoretical and experimental approach which has been carried out in order to study the narrow band and wideband channel characteristics in a straight semi-arched tunnel. To improve the reliability of the link in terms of bit error rate and/or channel capacity, Multiple Input Multiple Output (MIMO) techniques have been proposed. Usually the efficiency of MIMO techniques is often compared to the performances of a Single Input Single Output (SISO) system, chosen as a reference. In this presentation, other diversity schemes at the receiving side as selection combining and maximum ratio combining are also considered since they have an easier implantation.
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paper_title: Wireless Communication for Heavy Haul Railway Tunnels Based on Distributed Antenna Systems

paper_content:

Radio-over-fiber (RoF) technology can improve reliability and quality of service (QoS) of railway communication systems effectively. This paper studies directional antenna radiating same direction and intercross base station redundant network these two coverage strategies of RoF in long heavy haul railway tunnels (more than 1 km). As RAUs (remote antenna unit) deployed in long tunnels, according to different coverage strategies, the number of RAUs is different, this will lead various handover mechanisms. Based on the channel modeling of simulator in this paper, coverage efficiency (power consumption of unit distance in tunnel) handover trigger probability and outage probability are adopted to compare the performance of these two coverage strategies. It can be concluded that when using directional antenna radiating same direction, due to the longer radiate distance R, it has better coverage efficiency, and the trigger probability almost reached 100% once entered the overlapping area, and the handover outage probability is clearly lower than using intercross base station antenna network, even if the train is fast.
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Title: Channel measurements and models for high-speed train wireless communication systems in tunnel scenarios: a survey

Section 1: Introduction
Description 1: Introduce the importance of HST wireless communication systems in tunnel scenarios and provide an overview of the paper.

Section 2: HST channel measurements in tunnel scenarios
Description 2: Review and classify recent HST tunnel channel measurements based on various parameters and statistics.

Section 3: Measurement setup
Description 3: Discuss details of the setups used in HST tunnel channel measurements, including antenna configurations and frequency bands.

Section 4: Large-scale vs. small-scale fading
Description 4: Explain large-scale and small-scale fading characteristics in HST tunnel scenarios.

Section 5: Far region vs. near region inside tunnel
Description 5: Describe the differentiation between far and near regions inside tunnels and their impact on channel characteristics.

Section 6: Typical propagation zones
Description 6: Discuss the different propagation zones in tunnels and how they affect propagation characteristics.

Section 7: Parameters influencing radio propagation inside tunnel
Description 7: Outline various parameters, such as tunnel size and shape, that affect radio propagation in tunnels.

Section 8: HST channel models in tunnel scenarios
Description 8: Present an overview of different HST tunnel channel models discussed in the literature.

Section 9: Network architectures for tunnels
Description 9: Discuss possible network architectures for providing wireless coverage inside tunnels.

Section 10: Modeling approaches of HST tunnel channel models
Description 10: Explain various modeling approaches for HST tunnel channel models, such as deterministic, stochastic, and hybrid models.

Section 11: Research directions in HST tunnel channel measurements and models
Description 11: Discuss future research directions in HST tunnel channel measurements and modeling.

Section 12: Conclusion
Description 12: Summarize the key points of the survey and highlight the importance of future work.