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Railways have already introduced satellite-based localization systems for non-safety related applications. Driven by economic reasons, the use of these systems for new services and, in particular, their introduction in signaling system is seriously investigated today and tested all around the world. Because of the weight of their history, their strong normative context and the high requested level of safety, the introduction is relatively slow. The aim of this paper is to provide a survey of past and current programs dealing with GNSS (Global Navigation Satellite Systems) as a basis to introduce main issues relative to context, standards, performance requirements and safety proofs. Links with aeronautical concepts are also presented, illustrating the transposable principles and the limits due to the land transport environment.

-Applications of GNSS (Global Navigation Satellite System) in land transportation systems are already extensively deployed and will certainly continue to grow especially in the framework of Intelligent Transport Systems. However, one of the best-known drawbacks of such a system is the lack of satellite visibility in dense urban areas as well as in some specific embedded railway environments. This restricts considerably GNSS use for extended safety related applications. In this paper, a new tool is proposed to predict the availability of a satellite constellation from the point of view of the land transportation user. Knowing the trajectory of a land vehicle, the tool predicts the number of satellites which will be received and produces a safety criterion able to qualify the GNSS localization result. A first version of the tool, already in operation, merges an image processing approach providing the knowledge of the land environment, and the output of a satellite tracking program predicting satellite positions in the sky. This allows us to determine, using a simple optical approach, the number of satellites received in line-of-sight or blocked, with regard to the nearby environment of the receiving antenna. Results obtained in railway as well as in road environments show that satellite signals received by multipath are often used by GNSS receivers in the localization process. Thus, propagation characteristics of the satellite signals in an urban canyon configuration were characterized to determine when a signal received by multipath is used by the receiver or not. A criterion related to the satellite elevation is defined to improve the overall performance of the predictive tool. Comparisons with real measurements are commented on. Both simulations and measurements are very similar.

Modulation type is one of the most important characteristics used in signal waveform identification. In this paper, an algorithm for automatic digital modulation recognition is proposed. The proposed algorithm is verified using higher-order statistical moments (HOM) of continuous wavelet transform (CWT) as a features set. A multilayer feed-forward neural network trained with resilient backpropagation learning algorithm is proposed as a classifier. The purpose is to discriminate among different M-ary shift keying modulation schemes and the modulation order without any priori signal information. Pre-processing and features subset selection using principal component analysis is used to reduce the network complexity and to improve the classifier's performance. The proposed algorithm is evaluated through confusion matrix and false recognition probability. The proposed classifier is shown to be capable of recognizing the modulation scheme with high accuracy over wide signal-to-noise ratio (SNR) range over both additive white Gaussian noise (AWGN) and different fading channels.

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Modern society demands cheap, more efficient, and safer public transport. These enhancements, especially an increase in efficiency and safety, are accompanied by huge amounts of data traffic that need to be handled by wireless communication systems. Hence, wireless communications inside and outside trains are key technologies to achieve these efficiency and safety goals for railway operators in a cost-efficient manner. This paper briefly describes nowadays used wireless technologies in the railway domain and points out possible directions for future wireless systems. Channel measurements and models for wireless propagation are surveyed and their suitability in railway environments is investigated. Identified gaps are pointed out and solutions to fill those gaps for wireless communication links in railway environments are proposed.

1 In this paper, a novel pilot-aided algorithm is developed for MIMO-OFDM systems operating in fast timevarying environment. The algorithm has been designed to work both with parametric L-path channel model (with known path delays) and equivalent discrete-time channel model to jointly estimate the multi-path Rayleigh channel complex amplitudes (CA) and Carrier Frequency Offset (CFO). Each CA timevariation within one OFDM symbol is approximated by a Basis Expansion Model (BEM) representation. An Auto-Regressive (AR) model is built for the parameters to be estimated. The algorithm performs estimation using Extended Kalman Filtering. The channel matrix is thus easily computed and the data symbol is estimated without Inter-sub-Carrier-Interference (ICI) when the channel matrix is QR-decomposed. It is shown that our algorithm is far more robust to high speed than the conventional algorithm, and the performance approaches that of the ideal case for which the channel response and CFO are known. . His main research interests are in mobile communications and carrier and symbol synchronization.Laurent Ros received the degree in electrical engineering from the "Ecole Supérieure d'Electricité" (Supélec), Paris, France, in 1992 and the Ph.D. degree in signal processing and communications from Grenoble Institute of Technology (Grenoble-INP), Grenoble, France, in 2001. From 1993to 1995 he was with France-Telecom R&D center, Lannion, France, where he worked in the area of very low frequency transmissions for submarine applications, in collaboration with Direction of Naval Construction, Toulon, France. From 1995 to 1999, he was a Research and Development team manager at Sodielec, Millau, France, where he worked in the design of digital modems and audio codecs for telecommunication applications. Since 1999, he has joined the Gipsalaboratory/DIS (ex "Laboratory of Image and Signal") and Grenoble-INP where he is currently an Associate Professor. His general research interests include statistical signal processing, synchronization and channel estimation problems for wireless communications.