Leandro de Haro

A survey on future railway radio communications services: challenges and opportunities

Radio communications is one of the most disruptive technologies in railways, enabling a huge set of value-added services that greatly improve many aspects of railways, making them more efficient, safer, and profitable. Lately, some major technologies like ERTMS for high-speed railways and CBTC for subways have made possible a reduction of headway and increased safety never before seen in this field. The railway industry is now looking at wireless communications with great interest, and this can be seen in many projects around the world. Thus, railway radio communications is again a flourishing field, with a lot of research and many things to be done. This survey article explains both opportunities and challenges to be addressed by the railway sector in order to obtain all the possible benefits of the latest radio technologies.

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The increasing interest in MIMO (Multiple-Input Multiple-Output) systems has given rise to a prolific research activity in recent years. Both theoretical and practical issues have been studied. However, so far few MIMO testbeds or prototypes have been built for DVB-T or future standards. In this paper, a novel 2 × 2 MIMO testbed specifically designed for evaluating the performances of a DVB-T2 MIMO system is presented. The description of signal processing is detailed including a new scheme to estimate the MIMO channel matrix. Finally, measurement results with different polarization schemes are presented for typical scenarios, obtaining higher capacity in LoS situations using polarization diversity.

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This paper proposes several configurations for multiple base stations in indoor MIMO systems and compares their performance. The results are based on channel measurements realized with a MIMO testbed. The receiver was moved along several routes and floors on an office building. Both outdoor and indoor locations are considered for the transmitters or base stations, which allow the analysis of not only indoor but also outdoor-to-indoor environment. The use of 2 base stations with different system level combinations of the two is analyzed. We show that the configuration with base station selection provides almost as good performance as a full water-filling scheme when the 2 base stations are placed at different locations. Also the spatial correlation properties for the different configurations are analyzed and the importance of considering path loss when evaluating capacity is highlighted.

2 MIMO DVB-T2 System: Design, New Channel Estimation Scheme and Measurements With Polarization Diversity

A novel multiport and multimode quasi analytical model is derived to analyze and to provide comprehensive guidelines to design reconfigurable multimode multiple-input multiple-output (MIMO) microstrip antennas. The model shows to be an efficient and accurate method to gain physical insight into the multimode MIMO microstrip behavior. Numerical and experimental examples illustrate the validity of the model and the usefulness of the design guidelines.

Measurements of MIMO indoor channels at 1800MHz with multiple indoor and outdoor base stations

This letter presents a deep insight on a real implementation of a train-to-wayside radio on subway tunnels that makes use of a 2 × 2 multiple-input-multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) setup. The main purpose of this letter is to study in detail the keyhole phenomenon of an MIMO-OFDM train-to-wayside communication system on a tunnel. MIMO keyholes are studied in different tunnels sections, and capacity results are provided. Moreover, we introduce the first keyhole measurements on a railway tunnel. Finally, we follow a quantitative approach to estimate keyhole probabilities on each tunnel stretch and capacity outage curves.

On the Analysis and Design of Reconfigurable Multimode MIMO Microstrip Antennas

A measurement campaign was carried out to analyse several possible transmitter locations for a 4×4 MIMO system. The receiver modules were moved along indoor routes, and both indoor and outdoor locations were considered for the transmitters. The spatial correlation, path loss and capacity were analysed. Also several options regarding signal combination at system level were studied, assuming two base stations with 2 antennas each. As a result, it is shown that the 2×4 configuration with base station selection and waterfilling scheme provides almost as good performance as a 4×4 full waterfilling scheme when the 2 base stations are spatially separated. This solution may be very interesting to reduce system complexity without significant loss of performance.

Keyhole Estimation of an MIMO-OFDM Train-to-Wayside Communication System on Subway Tunnels

This letter presents a deep insight on a real implementation of a train-to-wayside broadband radio on subway tunnels that makes use of a 2 ×2 MIMO-OFDM setup. A keyhole is a phenomenon that usually happens in tunnels and that seriously degrades channels capacity, even if both transmitter and receiver antennas are uncorrelated. The main purpose of this letter is to study in detail the influence of the polarization in the probability of having a keyhole on a MIMO-OFDM train-to-wayside communication system on a tunnel. MIMO keyholes are studied in four different polarization setups, six different tunnels cross-sections and, finally, capacity results are provided.

Measurements of MIMO capacity at 1800 MHZ with in- and outdoor transmitter locations

One of the key challenges in railway engineering is how to provide passengers an efficient, secure, and safe service. To achieve this, operators and stakeholders demand robust and high-capacity train-to-wayside broadband radio. Current radio technologies implement MIMO (Multiple-Input Multiple-Output) technology, whose use requires a good characterization of the propagation. In this paper, the results of an experimental campaign on MIMO propagation in subway tunnels are presented. The campaign makes use of an OFDM testbed at roughly 600 MHz, allowing the measurement of the channel transfer matrix under different conditions regarding polarization, antenna separation, tunnel cross section, power allocation algorithm, and so forth. Particular attention is paid to the probability of appearance of keyholes, which imply a severe degradation of the MIMO performance even when transmitter and receiver antennas are uncorrelated. The measurements are carried out using a train that travels at the normal operative velocities. As a result of the measurements, it has been found that the use of vertical polarization at both terminals is advantageous and that, on average but for a narrow margin, λ-spaced antennas outperform λ/2-spaced ones (90% capacities of 7.00 and 6.76 bps/Hz, resp.), although the latter show a lower probability of keyholes. However, keyhole probabilities are always below 2%, so their influence on the performance of the whole system is limited.

Influence of Polarization on Keyhole Probability on a MIMO-OFDM Train-to-Wayside System on Tunnels

The paper will describe the test-bed and the test realized to measure SMATV performances when a DVB-S2 signal is received. The possible long term instabilities are going to be studied to obtain a link margin in case the DVB-S2 would be received using SMATV networks..

Keyholes in MIMO-OFDM: Train-to-Wayside Communications in Railway Tunnels

This paper is focused on explaining the radiation test in temperature performed on the Engineering and Qualification Model of the Medium Gain Antenna Radiofrequency (MGA-RFA) Assembly of ESA’s BepiColombo mission. The goal of this program is to observe and study Mercury and its surroundings in a very demanding environment in terms of temperature and radiation. The MGA is an X-band two-axis steerable horn, which provides bidirectional communications between spacecraft and Earth as backup of the High Gain Antenna and also operates as primary communication link at several mission stages or conditions. The paper presents the measurement set-up for the qualification campaign of the antenna, where it was necessary to characterize the antenna in a representative thermal environment, and the results obtained from this test. Results of test up to 1508C show how gain and radiation pattern shapes are slightly affected by thermal stress, but without jeopardizing mission requirements. In addition, by analyzing correlation of this test with RF analysis in the same thermal conditions, it becomes possible to accurately extrapolate the MGA-RFA behavior up to temperatures of more than 5008C. This fact allowed the successful space qualification of this model.