Nuestros investigadores

Saioa Arrizabalaga Juaristi

Publicaciones científicas más recientes (desde 2010)

Autores: Valdivia, L. J., (Autor de correspondencia); Adin, Íñigo; Añorga, Javier; et al.
ISSN 0748-8017  Vol. 35  Nº 2  2019  págs. 561 - 571
A malicious attack on a safety-critical system can derive in an undesired behavior of the system that may result in a failure. In this case, the reliability of the device is decreased, and it might affect directly to safety. Therefore, the security is also an essential issue to consider in the design of safety-critical systems. The main problem when safety and security are considered is to make them work together without interfering each other. A safety-critical device needs to be certified following standards like IEC-61508, and any security mechanisms must not affect this certification. This paper describes a system that integrates safety and security mechanisms to improve reliability without affecting safety certification. With the aim of reaching the required safety level, a redundant system is considered. This system is an n out of m distributed and synchronized voter. The synchronization method is based on the precision time protocol (IEEE-1588) allowing that all devices on a local network have the same time.
Autores: Añorga, Javier, (Autor de correspondencia); Arrizabalaga, Saioa; Sedano, Beatriz; et al.
ISSN 1380-7501  Vol. 77  Nº 7  2018  págs. 7977 - 8000
The popular Internet service, YouTube, has adopted by default the HyperText Markup Language version 5 (HTML5). With this adoption, YouTube has moved to Dynamic Adaptive Streaming over HTTP (DASH) as Adaptive BitRate (ABR) video streaming technology. Furthermore, rate adaptation in DASH is solely receiver-driven. This issue motivates this work to make a deep analysis of YouTube's particular DASH implementation. Firstly, this article provides a state of the art about DASH and adaptive streaming technology, and also YouTube traffic characterization related work. Secondly, this paper describes a new methodology and test-bed for YouTube's DASH implementation traffic characterization and performance measurement. This methodology and test-bed do not make use of proxies and, moreover, they are able to cope with YouTube traffic redirections. Finally, a set of experimental results are provided, involving a dataset of 310 YouTube's videos. The depicted results show a YouTube's traffic pattern characterization and a discussion about allowed download bandwidth, YouTube's consumed bitrate and quality of the video. Moreover, the obtained results are cross-validated with the analysis of HTTP requests performed by YouTube's video player. The outcomes of this article are applicable in the field of Quality of Service (QoS) and Quality of Experience (QoE) management. This is valuable information for Internet Service Providers (ISPs), because QoS management based on assured download bandwidth can be used in order to provide a target end-user's QoE when YouTube service is being consumed.
Autores: Goya, J., (Autor de correspondencia); De Miguel, G.; Arrizabalaga, Saioa; et al.
ISSN 1524-9050  Vol. 19  Nº 12  2018  págs. 4035 - 4042
The European Union (EU) is bolstering the railway sector with the aim of making it a direct competitor of the aviation sector. For that to occur, railway efficiency has to be improved by means of increasing capacity and reducing operational expenditure. Tracks are currently used below their maximum capacity. Given this fact and the EU's goals for the railway sector, research on solutions for on-board positioning system based on global navigation satellite systems (GNSS) have arisen in recent years. By taking advantage of GNSS, safety critical positioning systems will be able to use the infrastructure more efficiently. However, GNSS based positioning systems still cannot fulfill current normative validation processes, mainly, due to the fact that GNSS based positioning performance evaluation is not compatible with the key performance indicators (KPIs) used to assess railway systems performance: reliability, availability, maintainability, and safety. This paper proposes a methodology and unified key performance indicators (KPIs). Additionally, it shows real examples to address this issue. It aims to fill the gap between the current railway standardization process and any on-board positioning system.
Autores: Valdivia, Leonardo Jesús, (Autor de correspondencia); Adin, Íñigo; Arrizabalaga, Saioa; et al.
ISSN 1556-6072  Vol. 13  Nº 1  2018  págs. 48 - 55
Most critical applications today depend on computers, so a computer failure can cause financial disaster, serious injury, or even death. In this context, railways are considered a critical application, so they must meet the highest standards of availability and safety. Availability ensures continuous operation of the system, while a safe system must behave correctly in all operating and environmental conditions.
Autores: Adin, Íñigo; Arrizabalaga, Saioa; et al.
ISSN 0263-2241  Vol. 77  2016  págs. 124 - 131
The interoperability between on track balises and the on board Balise Transmission Module systems depends on both sides' susceptibility and allowed emissions. For that assessment, the document that governs the testing methodology, tools and procedures (Subset 116) needs to be completed prior to its publication. The present paper proposes an advance beyond the state of the art for the rolling stock emission assessment in terms of the test setup and of the post-processing procedure. The documentation commonly used in ERTMS-related issues has been analyzed and the common tools and procedures have been taken into consideration for the proposal presented by the authors. (C) 2015 Elsevier Ltd. All rights reserved.
Autores: Goya, J.; Zamora-Cadenas, Leticia; Arrizabalaga, Saioa; et al.
ISSN 1867-0717  Vol. 7  Nº 3  2015  págs. 1 - 18
Purpose This article focuses on a novel Advanced Train LocAtion Simulator (ATLAS) for on-board railway location using wireless communication technologies, such as satellite navigation and location based systems. ATLAS allows the creation of multiple simulation environments providing a versatile tool for testing and assessing new train location services. This enhancement reduces the number of tests performed in real scenarios and trains, reducing the cost and development time of new location systems as well as assessing the performance level for given tracks. Methods The simulation platform is based on modular blocks, where each block can be replaced or improved. The platform uses Monte Carlo Simulation to generate results with statistical significance. This implementation allows the modification of the development platform to cover multiple requirements, such as, ranging errors in the input parameters or including other positioning technologies. In this paper, the generated input parameter errors have been taken from the results of the field tests realized by the 3GPP ensuring the validity of the used parameter errors. However, these could be easily adapted by the user to particular characterized environments. Results Case studies for the validation of ATLAS will be also introduced, including preliminary results related to the use of Global System for Mobile communications in Railway (GSM-R) and Universal Mobile Telecommunications System (UMTS) technologies for positioning. The validation stage provides a way to test the platform functionalities and verify its flexibility. Conclusions The versatility of the platform to perform simulations using same configuration parameters for different case studies can be highlighted. Furthermore, first conclusions are drawn from the obtained results. The characterization of the infrastructure for the simulation and the performance improvement of the location systems in the tunnels (e.g., by including Inertial Measurement Unit (IMU)) are necessary to achieve accuracy levels that can be valid for ETCS level 3.