Contextos universitarios transformadores: a nova normalidade académica. Leccións aprendidas e retos de futuro. V Xornadas de Innovación Docente

Colección: Contextos Universitarios Transformadores (CUT). Número

Hybrid Supervised-Unsupervised Channel Estimation Scheme with Dynamic Transmission of Pilots

The final publication is available at Springer via http://dx.doi.org/10.1007/s11063-010-9161-x[Abstract] Multiple-Input Multiple-Output (MIMO) digital communications standards typically include pilot symbols in the definition of the transmit signals with the purpose of acquiring the Channel State Information (CSI) using supervised algorithms at the receiver side. Such pilot symbols convey no information and, therefore, system throughput, spectral efficiency and transmit energy consumption are all penalized. In this article, we propose to acquire the CSI combining supervised and unsupervised algorithms. Our strategy avoids the periodical transmission of unnecessary pilots by using a simple decision criterion to determine the time instants when the performance obtained with an unsupervised algorithm degrades or, equivalently, the time instants when pilots are required. We show the performance of this scheme for MIMO systems with Decision-feedback equalizers at the receiver.Galicia. Consellería de Economía e Industria; 09TIC008105PRMinisterio de Ciencia e Innovación; TEC2007-68020-C04-01Ministerio de Ciencia e Innovación; TIN2009-0573Ministerio de Ciencia e Innovación; CSD2008-0001

Bit Error Probability and Capacity Bound of OFDM Systems in Deterministic Doubly-Selective Channels

© 2020 IEEE. This version of the article has been accepted for publication, after peer review. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. The Version of Record is available online at: https://doi.org/10.1109/TVT.2020.3011365[Abstract]: Doubly-selective channels, such as those that occur when the transmitter and the receiver move relative to each other at high speeds, are a key scenario for fifth generation (5G) cellular systems, which are mostly based in the use of the orthogonal frequency-division multiplexing (OFDM) modulation. In this paper, we consider an OFDM system using quadrature amplitude modulation (QAM) symbols and we show that, when transmitting over deterministic doubly-selective channels, the inter-carrier-interference (ICI) affecting a symbol can be well approximated by a complex-valued normal distribution. Based on this, we derive a lower bound for the link capacity using the Shannon-Hartley theorem. Finally, we provide an approximation of the bit error probability (BEP) using the well-known BEP expressions for Gray-coded QAM constellations over additive white Gaussian noise (AWGN) channels, and show numerical results that confirm that the proposed BEP expression approximates accurately the bit error ratio (BER) of the OFDM system for standardized channel models. The proposed closed-form analytical expressions for the capacity and the BEP do not only allow for discarding the need of computationally-costly Monte-Carlo system simulations, but also provide a theoretical framework to optimize the system parameters directly impacting on the achievable performance.Xunta de Galicia; ED431G2019/01This work has been funded by the Xunta de Galicia (ED431G2019/01), the Agencia Estatal de Investigación of Spain (TEC2016-75067-C4-1-R, PID2019-104958RB-C42), ERDF funds of the EU (AEI/FEDER, UE), and the National Natural Science Foundation of China (NSFC) under Grants no. 61850410529 and 61971313.China, National Natural Science Foundation of China (NSFC); 61850410529China, National Natural Science Foundation of China (NSFC); 6197131

Transmission of Still Images Using Low-Complexity Analog Joint Source-Channel Coding

[Abstract] An analog joint source-channel coding (JSCC) system designed for the transmission of still images is proposed and its performance is compared to that of two digital alternatives which differ in the source encoding operation: Joint Photographic Experts Group (JPEG) and JPEG without entropy coding (JPEGw/oEC), respectively, both relying on an optimized channel encoder–modulator tandem. Apart from a visual comparison, the figures of merit considered in the assessment are the structural similarity (SSIM) index and the time required to transmit an image through additive white Gaussian noise (AWGN) and Rayleigh channels. This work shows that the proposed analog system exhibits a performance similar to that of the digital scheme based on JPEG compression with a noticeable better visual degradation to the human eye, a lower computational complexity, and a negligible delay. These results confirm the suitability of analog JSCC for the transmission of still images in scenarios with severe constraints on power consumption, computational capabilities, and for real-time applications. For these reasons the proposed system is a good candidate for surveillance systems, low-constrained devices, Internet of things (IoT) applications, etc.Xunta de Galicia; ED431C 2016-045Xunta de Galicia; ED431G/01Agencia Estatal de Investigación de España; TEC2016-75067-C4-1-

Time Modulated Arrays: from their Origin to Their Utilization in Wireless Communication Systems

[Abstract] Time-modulated arrays (TMAs) are electromagnetic systems whose radiated power pattern is controlled by the application of variable-width periodical pulses to the individual elements. The nonlinear nature of the array operation causes the appearance of radiation patterns at the harmonic frequencies of such periodic pulses. The technique can be used for improving the side-lobe level (SLL) topology of the radiation pattern at the central frequency and/or to profitably exploit the harmonic patterns in order to supply smart antenna capabilities. Among the latter features, the TMA harmonic beamforming takes on special importance due to its attractive trade-off performance-hardware complexity. From this perspective, TMAs are sensors capable of transforming the spatial diversity of a communication channel into frequency diversity, thus improving the performance of a wireless communication. In addition to a walk through the origins of the concept, and a brief analysis of the mathematical fundamentals, this paper organizes the prolific state of the art of TMAs in two major thematic blocks: (1) TMA design from an antenna perspective; and (2) TMA design from a signal processing perspective.Ministerio de Economía, Industria y Competitividad; TEC2013-47141-C4-1-RMinisterio de Economía, Industria y Competitividad; TEC2015-69648-RED

A MATLAB Tool for Visualizing the 3D Polar Power Patterns and Excitations of Conformal Arrays

[Abstract] This paper describes the implementation of a MATLAB® tool to plot the three-dimensional polar radiation diagram generated by a conformal antenna array. A related tool has also been developed for visualizing the geometrical arrangement (positions and orientations) of the elements, as well as the relative values of the amplitudes and phases of their excitations. Supporting M-files are available.Xunta de Galicia; 09TIC008105PRMinisterio de Ciencia e Innovación; TEC2007-68020-C04-01Ministerio de Ciencia e Innovación; CSD2008-0001

Analog Video Encoding and Quality Evaluation

[Abstract] The most widespread analog video encoding systems in the literature are based on the use of the 2D and 3D DCT. These systems use both transformations indistinctly without assessing their suitability. In this paper, we present procedures to compress video using 2D and 3D-DCT and we evaluate the video quality for different compression levels.Xunta de Galicia; ED431C 2016-045Xunta de Galicia; ED431G/01Agencia Estatal de Investigación de España; TEC2016-75067-C4-1-

On the Feasibility of Time-Modulated Arrays for Digital Linear Modulations: a Theoretical Analysis

[Abstract] Wireless communications are widely based on linear digital modulation methods, which introduce the digital baseband information in the amplitude and/or in the phase of a carrier sinusoid. Time-modulated arrays, on the other hand, constitute an interesting technique capable of adapting the power radiation pattern of an antenna array. In this work, we study from a theoretical point of view the impact of time-modulated arrays on the transmission of linearly modulated digital communication signals. The work focuses on the requirements to safeguard the integrity of the signal and on the quantification of the useful power radiated within the desired band

Impact of Time-Modulated Arrays on the BER of Linear Digital Modulations

This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of Electromagnetic Waves and Applications on 21 Aug. 2015, available online: http://www.tandfonline.com/doi/full/10.1080/09205071.2015.1075908[Abstract] Time modulation provides a simple way to control the power radiation pattern of an antenna array. By appropriately selecting the parameters of a Time-Modulated Array (TMA) it is possible to obtain a reconfigurable pencil beam adequate for wireless communications. This work focuses on the impact of a TMA on the Bit Error Ratio (BER) performance of a wireless communication receiver with a linear digital modulation. We show how the BER of such a receiver is affected by the TMA synthesis variables.Ministerio de Economía y Competitividad; TEC2013-47141-C4-1-RXunta de Galicia; Grant 2012/28

A MATLAB Interface for Analyzing Conformal Arrays Composed of Polarized Heterogeneous Elements

[Abstract] As an extension and improvement of a previous work, this paper presents a graphical interface designed with MATLAB®, which is capable of representing both the spatial and electrical configurations of a conformal antenna array, as well as the different patterns radiated by the array. The tool considers the polarization of the elements of the array, which are not necessarily congruent to each other