[en] The Vehicle-to-Everything (V2X) communication is a wireless technology aimed at enabling data exchanges between a vehicle and its surroundings, which is standardized and has great popularity in industry and academia. In the railway domain, even though the use of wireless communications for signalling purposes is not new, the use of a subset of V2X technologies for traffic safety-related services is currently under research since the current communication systems deployed do not provide the requirements demanded by these services. Thus, they allow increasing the safety, reliability and performance of this transportation medium. In this thesis we focus on the 802.11p/bd amendments where we evaluate their performance to support Train-to-Infrastructure (T2I) and Train-to-Train (T2T) communication links, that will enable traffic-safety related services and eventually the implementation of different degrees of automation in the railway. In addition, an adaptation of the Combtype Pilot-based Channel Estimation (CPCE) method is proposed for channel tracking for 802.11bd and improving its performance in scenarios with high Doppler spread. It is also benchmarked against the Midamble-based Channel Estimation (MCE) method which is the candidate method used in 802.11bd. In order to evaluate the performance of 802.11bd in railway, it is essential to consider the propagation characteristics of railway environments with dedicated channel models for simulation and testing. For the T2I propagation link, we have used a parametrizedWinner II channel model for simulation purposes, whereas for T2T a gap has been identified in the current state of the art. Therefore, an effort has been made in collaboration with the German's Research Center for Aeronautics and Space (DLR). Based on measurement campaign data, six Tapped Delay Line (TDL) channel models have been derived for T2T communications as well as their stochastic parameters. The proposed TDL channel models and the measured propagation characteristics have been used in a 802.11p/bd simulation framework in order to validate its performance as well as to evaluate the performance of the used communication protocols. The provided simulation results show a very good match between the proposed TDL channel models and the measurement data, indicating a good accuracy of the theoretical derivations and the simulation method. These channel models have been used to prove that CPCE achieves a higher performance that MCE. Moreover, the results show also that 802.11bd supports reliable V2X communications in railway environments.

[eu] Vehicle-to-Everything (V2X) komunikazioa haririk gabeko teknologia bat da, ibilgailu baten eta bere inguruaren artean datuak trukatzeko aukera ematen duena, estandarizatua eta industrian eta akademian ospe handia duena. Trenbide-jabarian, haririk gabeko komunikazioak seinaleztapenerako erabiltzea berria ez bada ere, gaur egun ikerketapean dago V2X teknologia erabiltzea trafiko-segurtasunerako, egungo komunikazio sistemek ez baitituzte zerbitzu horien eskakizunak betetzen. Horrela, garraiobide honen segurtasuna, fidagarritasuna eta errendimendua handitzeko aukera ematen dute. Tesi hau 802.11p/bd zuzenketetan oinarritzen da, non hauen errendimendua ebaluatzen den Train-to-Infrastructure (T2I) eta Train-to-Train (T2T) komunikazioak bermatzeko. Horrek, trafiko segurtasunarekin lotutako zerbitzuak eta trenbidean automozio maila desberdinak ezartzea ahalbidetuko du. Horrez gain, Comb-type Pilot-based Channel Estimation (CPCE) metodoaren egokitzapen bat proposatzen da 802.11bd-arekin kanalaren jarraipena egiteko eta Doppler altuko egoeretan bere errendimendua hobetzeko. Halaber, Midamble-based Channel Estimation (MCE) metodoarekin alderatzen da. 802.11bd errendimendua trenbidean ebaluatzeko, ezinbestekoa da trenbide inguruneetako hedapen ezaugarriak dituzten kanal dedikatuen modeloak kontuan hartzea, bai simulaziorako eta baita testeatzeko. T2I-aren hedapena simulatzeko,Winner II kanal eredu parametrizatu bat erabili da. T2Trako, berriz, ez da kanalaren modelorik aurkitu. Horregatik, Aeronautika eta Espazioko Alemaniako Ikerketa Zentroarekin (DLR) batera, sei Tapped Delay Line (TDL) modelo proposatu dira T2T komunikazioen neurketa kanpainanetan oinarrituta. Modelo hauek eta neurtutako hedapen parametroak erabili dira 802.11p/bd simulazio esparru batean protokoloaren errendimendua frogatzeko. Lortutako emaitzek, proposatutako TDL modeloen eta neurketen arteko antzekotasuna balioztatu dute. Modelo hauek, CPCE-k MCE-k baino errendimendu hobeagoa duela baieztatu dute. Gainera, lortutako emaitzek 802.11bd-ak trenbide inguruneetako V2X komunikazio fidagarriak mantentzeko gai direla adierazi dute.