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Due to their ability to provide a worldwide absolute outdoor positioning, Global Navigation Satellite Systems (GNSS) have become a reference technology in terms of navigation technologies. Transportation-related sectors make use of this technology in order to obtain a position, velocity, and time solution for different outdoor tasks and applications. However, the performance of GNSS-based navigation is degraded when employed in urban areas in which satellite visibility is not good enough or nonexistent, as the ranging signals become obstructed or reflected by any of the numerous surrounding objects. For these situations, Ultra-Wideband (UWB) technology is a perfect candidate to complement GNSS as a navigation solution, as its anchor trilateration-based radiofrequency positioning resembles GNSS's principle. Nevertheless, this fusion is vulnerable to interferences affecting both systems, since multiple signal-degrading error sources can be found in urban environments. Moreover, an inadequate location of the augmenting UWB transmitters can introduce additional errors to the system due to its vulnerability to the multipath effect. Therefore, the misbehavior of an augmentation system could lead to unexpected and critical faults instead of improving the performance of the standalone GNSS. Accordingly, this research work presents the performance improvement caused by the application of Fault Detection and Exclusion methods when applied to a UWB-augmented low-cost GNSS system in urban environments. [ABSTRACT FROM AUTHOR]

An adaptive feedforward amplifier is implemented for a Universal Mobile Telecommunication System (UMTS) downlink channel (2110-2170 MHz). An exhaustive characterization of the space of solution has corroborated the feedforward theoretical behavior. As a result, an alternative adjustment method is proposed, called 'maximum output,' which entails maximizing a specific designed objective function. Besides this, an adaptive control system, based on distortion signal minimization architecture, has been fabricated in order to apply the designed method. The overall system performance achieves significant improvements such as 16.7 dB on the third-order intermodulation product, measured with a 5-MHz separated two-tone signal, 15 dB on the adjacent channel leakage ratio level and 2.7 dB on the output power level, both of them obtained with UMTS test model 1 (64 channels). The maximum output control method allows fulfilling any standard linearity specification while power efficiency is maximized so the desired tradeoff between linearity and efficiency is achieved. Index Terms--Adaptable control system, feedforward amplifier, output improvement, power minimization, Universal Mobile Telecommunication System (UMTS), wide-band code division multiple access (WCDMA).

Railway applications are in continuous evolution with the aim of offering a more efficient, sustainable, and safer transportation system for the users. Generally, these applications are constantly exchanging information between the systems onboard the train and the trackside through a wireless communication. Nowadays, Global System for Mobile communications-Railway (GSM-R) is the technology used by European Train Control System (ETCS), but it is becoming obsolete. Therefore, alternatives for this technology have to be found for the different railway applications. Its natural evolution is to move forward with the latest technology deployed: Long-Term Evolution (LTE), which the Public Land Mobile Networks (PLMN) have already deployed. Therefore, testing the performance of this communication technology in the railway environment could be useful to assess its suitability and reduce the cost of railway network dedicated deployment. In order to do that, a methodology to characterize the communication environment is proposed. The main goal is to measure geolocated impairments of any communication channel in a railway environment being able to determine its behavior of the different communication technologies and find out possible coverage issues. Moreover, it could help in the selection of suitable communication technology for railway. This paper presents a brief description of the communication for railways and its QoS parameters for performance measuring. Afterward, the testing methodology is described, and then, the communication channel measurement campaign on a real track in Spain where the railway environment is variable is presented (tunnels, rural/urban area...). Finally, the measurements and results on this real track in Spain are shown. The results provide suitability of the 4G technologies based on the delay requirements for the implementation of ETCS over it. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]