Yann Cocheril

Advantages of Simple MIMO Schemes for Robust or High Data Rate Transmission Systems in Underground Tunnels

Robust, reliable and high data rate transmission systems are key components of underground information systems particularly in the case of driverless ones. In this context, wireless systems must be able to maximize data rate and/or robustness while avoiding increases in transmitting power and/or in transmission bandwidth. MIMO techniques are today well known in the scientific community for indoor applications where the propagation channel experiences multipath effects. The work presented in this paper concerns the evaluation of conventional MIMO techniques such as the Alamouti code, spatial multiplexing, and linear precoding in tunnels environments usually considered as correlated channels. After the choice of the best suited channel model and antenna configuration, the simulation of the physical layer based on Wi-Fi IEEE802.11 a/g standards gives rise to the comparison of the MIMO algorithms.

On the Importance of the MIMO Channel Correlation in Underground Railway Tunnels

This paper deals with MIMO channel modeling according to the correlation level in underground railway tunnels for various antenna configurations for the transmitting and receiving arrays. MIMO channel matrices have been computed with a 3D ray-tracing based software at 2.4 GHz and 5.8 GHz in two different tunnel environments: 1) a 1-track empty tunnel with a square cross section, 2) a 1-track tunnel with a square cross section in which a train is parked between the transmitter and the receiver. In this paper, two different strategies are investigated to model the MIMO channel using the Kronecker and the Weichselberger correlation based channel models. The first one is to model the MIMO channel using a single model over the total tunnel length. The second one takes into account the correlation at the receiving side according to the transmitter-receiver distance. In the latter solution, it is possible to isolate specific areas in the tunnel with specific correlation properties and model them in an independent way to take them into account in a system simulation. In this paper, these two modeling strategies are compared in terms of channel capacity.

4×4 MIMO channel sounding in tunnels for train-to-wayside communications

This paper presents MIMO channel sounding measurements performed in the underground road tunnel of Roux, in south of France, at 5.8 GHz. Different scenarios for antennas (spacing and polarization) and moving vehicles speeds were carried out in the tunnel. The aim was to be as close as possible to scenarios one can encountered in railway environments. From these measurements, MIMO channel matrices are computed, in order to determine the correlation level of the channel and its capacity along the tunnel, according to different antenna spacing and polarization.

MIMO propagation channel characteristics in tunnels

This paper deals with MIMO channels modeling in tunnels. A full 3D ray-tracing based simulator is used to simulate the MIMO channel in a 1-track tunnel for various antennas configurations at the transmitter and at the receiver. A parametric study is described. The main purpose consists in determining correlation based MIMO channel statistical models and evaluating their performances in an empty tunnel. Channel models obtained with the Kronecker and the Weichselberger models are compared in terms of envelope of the matrix coefficients distribution and mean channel capacity. The best configurations which model correctly the channel while maximizing its capacity will be given.

Cooperative MIMO communications for transport applications

The success of MIMO technology has led to the concept of cooperative communications where multiple single-antenna nodes can share their antennas in order to create a distributed ¿virtual¿ MIMO system. The basic idea of Multiple Input Multiple Output systems is to create spatial diversity transmitting signals from different locations. This elementary concept is the basis of cooperative communications. In this paper, a brief state of the art of cooperative communications is first presented. The concept is then applied to a wireless transmission scenario between an urban bus and a control centre with a relay for video surveillance applications. We consider either theoretical or realistic propagation channels: 1) Rayleigh channels on all three links, or 2) a Rice channel between the relay and the destination and a suburban channel for the other links. It will be shown that cooperative communications prove to be particularly interesting to extend the coverage range.

A measurement-based channel model for vehicular communications in tunnels

In this paper, we present a new version of the iterative nonlinear least square approximation (INLSA) algorithm for the design of measurement-based channel simulators. The proposed method aims to match the time-variant impulse response (TVIR) of the simulation model to that of the measured channel. The propagation delays are discerned directly from the measurements, whereas the gains, the Doppler frequencies, and the phases are computed iteratively by minimizing a matching error norm. We evaluate the performance of the proposed method in terms of the approximation of the transfer function and correlation properties of the measured channel. We demonstrate how the resulting channel simulator can be deployed for a more reliable estimation of the channel statistics. The obtained results indicate that the proposed method allows a precise emulation of the measured channel impulse response. Its remarkable performance and simplicity makes the proposed method a powerful tool for designing realistic channel models.

3D Channel Simulations Including Scattering from Non-Gaussian Rough Surfaces

An original approach to characterize radio channel in indoor environments composed of rough surfaces is presented. It is based on algorithms developed for the image rendering field that are extended to the radio wave propagation. To simulate rough surfaces scattering, these algorithms need information about roughness. A possible solution consists of quantifying roughness by using statistical distributions of surface parameters, such as heights, slopes and local normals. In this paper, different theoretical statistical laws are presented and a fitting is realized with corresponding distributions of three real samples of wall roughcasts. For these cases, the best parameter to quantify the roughness is presented. Next, two algorithms which take roughness into account are detailed and compared with first results of channel simulations in indoor environments at 60 GHz.

Comparison between two original methods including scattering in 3D channel simulations

Two original methods to characterize the channel behavior in indoor environments composed of rough surfaces are presented and compared between themselves. They are based on algorithms developed for the image rendering field using Monte-Carlo methods to simulate the scattering phenomenon from rough surfaces. A previous study has shown which statistical parameters of real rough surfaces such as wall roughcasts have to be considered in order to have the more realistic scattering simulation as possible. Firstly, this paper presents in details the two studied methods. Secondly, we compare their performance and accuracy by simulating the radio channel for different rough indoor environments at 60 GHz

Influence of an accurate environment description for the indoor propagation channel modelling

The current wireless systems evolve towards multimedia applications demanding more and more high bit rate. Consequently, we observe an important rise in frequency. Then, it becomes necessary to study the influence of particular details of environment such as rough surfaces or small and complex scattering structures. Nowadays, ray tracing techniques, based on the geometrical optic (OG) and the uniform theory of diffraction (UTD), are the dominant techniques to predict the channel behaviour over a large bandwidth. Our study aims to improve the ray tracing power for the indoor propagation channel modelling by taking into account particular details of the environment

Performance of the max-d min precoder in impulsive noise for railway communications in tunnels

In this paper, we investigate the bit error rate (BER) performance of the max-dmin MIMO precoder in presence of impulsive noise in a railway tunnel. Measurements showed that the received signal at the antenna on the moving train roof near the catenary suffers from electromagnetic noise interference (EMI). This implies that the traditional Gaussian noise model is no longer valid and an impulsive noise model should be considered. Based on this observation, we analyze the performance of the max-dmin MIMO precoding technique, based on the minimum distance criterion, with impulsive noise modeled as an alpha-stable distribution. We present two points of interest: i) an approximation of the error probability of the max-dmin precoder, applied to the MIMO context in tunnel, in the presence of heavy tailed alpha-stable impulsive noise, and ii) the performance evaluation, in terms of bit error rate, of a complete communication system, considering a MIMO channel model in tunnel and impulsive noise, both obtained by measurements. Two soft detection techniques, providing the soft decisions to the channel decoder, are proposed, based on the approximation of the impulsive noise by either a Gaussian or a Cauchy law.