Estudio de los efectos producidos por la modulación temporal aplicada a una agrupación de antenas en sistemas de transmisión digital

Programa Oficial de Doutoramento en Tecnoloxías da Información e as Comunicacións en Redes Móbiles. 5032V0[Resumo] Os selos de identidade das comunicacións móbiles e sen fíos de hoxe en día son a demanda continua e crecente de mobilidade, capacidade e fiabilidade, xunto cun firme e definitivo compromiso coa sustentabilidade. Baixo estas premisas, as antenas intelixentes –capaces de sensar a contorna electromagnética e adaptar de xeito eficaz as súas características de radiación– están chamadas a xogar un papel crucial nas ditas comunicacións. Neste senso, os estándares sen fíos actuais consideran técnicas multi-antena encamiñadas a explotar a diversidade espacial, o multiplexado espacial e o conformado de feixe, acadando así mellores niveis de fiabilidade e capacidade. Con todo, ditas vantaxes obtéñense a expensas dun incremento da complexidade do sistema, factor non sempre asumible en termos de tamaño e eficiencia enerxética. Consecuentemente, suscítanse unha serie de retos de cara a desenvolver tecnoloxías de antena axeitadas e capaces de dar resposta ás anteriores prestacións no espazo limitado que dita a mobilidade. O concepto de agrupación de antenas modulada temporalmente (TMAs, do inglés time-modulated arrays) é unha técnica multi-antena que achega unha simplificación hardware significativa: o seu diagrama de radiación contrólase mediante a sinxela aplicación de pulsos periódicos de duración variable ás excitacións individuais da agrupación. A natureza non lineal desta operación causa a aparición de diagramas de radiación nas frecuencias harmónicas dos pulsos periódicos aplicados. A técnica pode empregarse para mellorar a topoloxía do nivel dos lóbulos secundarios do diagrama de radiación na frecuencia central e/ou para explotar de xeito proveitoso os diagramas dos harmónicos, dotando á antena de capacidades de antena intelixente. Esta tese é o resultado dunha investigación das TMAs dende unha perspectiva interdisciplinaria, é dicir, non soamente dende a óptica do diagrama de radiación ou das agrupacións de antenas, senón tamén dende un punto de vista de procesado do sinal. Máis concretamente, a tese é unha análise en profundidade da aplicación das TMAs ás comunicacións dixitais, desenvolvida en catro etapas: 1) análise matemática da posibilidade de transmitir sinais dixitais mediante TMAs, identificando as restricións para salvagardar a integridade do sinal e cuantificando a potencia radiada, 2) caracterización da taxa de erro de bit dun sistema de comunicación dixital que incorpora un TMA en recepción explotando o seu modo fundamental e considerando canles con ruído branco Gaussiano, 3) estudo das prestacións das TMAs –explotando os harmónicos– na recepción de sinais de comunicación dixitais con diversidade angular en canles multitraxecto con esvaecemento, 4) caracterización de TMAs para conformado de feixe mediante o uso de pulsos de suma de cosenos ponderados no lugar de pulsos rectangulares, chegando ás denominadas TMAs melloradas, dotadas dunha resposta superior en termos de flexibilidade e eficiencia.[Resumen] Hoy en día, los sellos de identidad de las comunicaciones inalámbricas son la demanda continua y creciente de movilidad, capacidad y fiabilidad, junto con un firme y definitivo compromiso con la sostenibilidad. Bajo estas premisas, las antenas inteligentes –capaces de sensar el entorno electromagnético y adaptar de forma eficaz sus características de radiación– están llamadas a jugar un papel crucial en dichas comunicaciones. En este sentido, los estándares inalámbricos actuales consideran técnicas multiantena encaminadas a explotar la diversidad espacial, el multiplexado espacial o el conformado de haz, alcanzando así mejores niveles de fiabilidad y capacidad. Sin embargo, dichas ventajas se obtienen a expensas de un incremento de la complejidad del sistema, factor no siempre asumible en términos de tamaño y eficiencia energética. En consecuencia, se plantean una serie de retos en el desarrollo de tecnologías de antena adecuadas, capaces de dar respuesta a las anteriores prestaciones en el espacio limitado que dicta la movilidad. El concepto de agrupación de antenas modulada temporalmente (TMAs, del inglés time-modulated arrays) es una técnica multiantena que aporta una simplificación hardware significativa: su diagrama de radiación se controla mediante la sencilla aplicación de pulsos periódicos de duración variable a las excitaciones individuales de la agrupación. La naturaleza no lineal de esta operación causa la aparición de diagramas de radiación en las frecuencias armónicas de los pulsos periódicos aplicados. La técnica se puede utilizar para mejorar la topología del nivel de los lóbulos secundarios del diagrama de radiación en la frecuencia central y/o para explotar de forma beneficiosa los diagramas de armónicos, dotando a la antena de capacidades de antena inteligente. Esta tesis es el resultado de una investigación de las TMAs desde una perspectiva interdisciplinar, es decir, no solamente desde la óptica del diagrama de radiación o de las agrupaciones de antenas, sino también desde un punto de vista de procesado de señal. Más concretamente, la tesis es un análisis en profundidad de la aplicación de las TMAs a las comunicaciones digitales, desarrollada en cuatro etapas: 1) análisis matemático de la factibilidad de transmitir señales digitales mediante TMAs, identificando las restricciones para salvaguardar la integridad de la señal y cuantificando la potencia radiada, 2) caracterización de la tasa de error de bit de un sistema de comunicación digital que incorpora una TMA en recepción explotando su modo fundamental y considerando canales con ruido blanco Gaussiano, 3) estudio de las prestaciones de las TMAs –explotando los armónicos– en la recepción de señales digitales con diversidad angular en canales multitrayecto con desvanecimiento, 4) caracterización de TMAs para conformado de haz mediante el uso de pulsos de suma de cosenos ponderados en lugar de pulsos rectangulares, llegando a las denominadas TMAs mejoradas, dotadas de una respuesta superior en términos de flexibilidad y eficiencia.[Abstract] An ever-increasing demand for higher mobility, capacity and reliability, together with a definitive compromise with sustainability, are the hallmarks of mobile and wireless communications systems nowadays. Under these premises, smart antenna devices –capable of sensing the electromagnetic environment and suitably adapting its radiation features– are correspondingly called to play a crucial role. In this sense, today’s wireless standards consider multiple-antenna techniques in order to exploit space diversity, spatial multiplexing and beamforming to achieve better levels of reliability and capacity. Such advantages, however, are obtained at the expense of increased system complexity which may be unaffordable in terms of size and energy efficiency. Consequently, some technical challenges remain to develop the adequate antenna technologies capable of supporting the aforementioned features in a limited physical space that the mobility demand dictates. The concept of time-modulated array (TMA) is a feasible multi-antenna technique that provides a significant hardware simplification: its radiated power pattern is controlled by the simple application of variable-width periodical pulses to the individual array excitations. The nonlinear nature of such an array operation causes the appearance of radiation patterns at the harmonic frequencies of the applied periodic pulses. The technique can be used for improving the side-lobe level topology of the radiation pattern at the central frequency and/or to profitably exploit the harmonic patterns in order to supply smart antenna capabilities. This thesis is the result of an investigation of TMAs from an interdisciplinary perspective, i.e., not only under a radiation pattern or an antenna array outlook but also from a signal processing point of view. More specifically, the thesis deals with an in-depth analysis of the application of TMAs in digital communications developed in four stages: 1) mathematical analysis of the feasibility of transmission of digital signals over TMAs, identifying the restrictions to safeguard the integrity of the signal and quantifying the radiated power, 2) characterization of the bit error rate of a digital communication system that incorporates a receive-TMA exploiting its fundamental mode and considering additive white Gaussian noise channels, 3) study of the performance of TMAs –exploiting their harmonics– for the angle diversity reception of digital communication signals over multipath fading channels, 4) an approach to the characterization of beamforming TMAs which use sum of weighted cosines pulses instead of rectangular ones, leading to the so-called enhanced time-modulated arrays, which endows them with a better response in terms of flexibility and efficiency

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

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

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

Time-Modulated Arrays With Haar Wavelets

© 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/LAWP.2020.2986832[Abstract]. Time-modulated arrays (TMAs) can effectively perform beamsteering over the first positive harmonic pattern by applying progressively delayed versions of stair-step approximations of a sine waveform to the antenna excitations. In this letter, we consider synthesizing such stair-step sine approximations by means of Haar wavelets. Haar functions constitute a complete orthonormal set of rectangular waveforms, which have the ability to represent a given function with a high degree of accuracy using few constituent terms. Hence, when they are applied to the TMA synthesis, employing single-pole double-throw switches, such a feature leads to an excellent rejection level of the undesired harmonics as well as a bandwidth greater than that supported by conventional TMAs with on-off switches.This work has been funded by the Xunta de Galicia (ED431G2019/01), the Agencia Estatal de Investigación of Spain (TEC2016-75067-C4-1-R, RED2018-102668-T) and ERDF funds of the EU (AEI/FEDER, UE).Xunta de Galicia; ED431G2019/0

Time-modulated array beamforming with periodic stair-step pulses

© 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/. This version of the article: Maneiro-Catoira, R., Brégains, J., García-Naya, J. A., & Castedo, L. (2020). “Time-modulated array beamforming with periodic stair-step pulses”, has been accepted for publication in Signal Processing, 166(107247). The Version of Record is available online at https://doi.org/10.1016/j.sigpro.2019.107247.[Abstract]: Time-modulated arrays (TMAs) are able to improve the side-lobe level of the radiation pattern at the fundamental mode but cannot steer the beam at such a mode towards a given direction. Beam-steering is possible in a TMA, but only at the harmonic patterns and at the expense of a severe TMA efficiency reduction. In this work we propose a TMA approach that simultaneously performs both features over the same beam by using two sets of switches: (1) single-pole four-throw switches to generate periodic stair-step pulses suitable for efficiently synthesizing a uniform steerable beam over the first positive harmonic, and (2) single-pole single-throw switches to reconfigure the side-lobe level of the previous beam. Performance, small size, cost-effectiveness, and performance invariability with the carrier frequency are features that make this TMA approach a competitive solution for analog beamforming. Accordingly, the structure is an attractive proposal for the design of multibeam transceivers.This work has been funded by the Xunta de Galicia (ED431C 2016-045, ED431G/01), the Agencia Estatal de Investigación of Spain (TEC2016-75067-C4-1-R) and ERDF funds of the EU (AEI/FEDER, UE).Xunta de Galicia; ED431C 2016-045Xunta de Galicia; ED431G/0

Time-Modulated Phased Array Controlled With Nonideal Bipolar Squared Periodic Sequences

© 2019 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/LAWP.2019.2892657.[Abstract]: Bipolar (±1) sequences with no zero state suit particularly well for safeguarding the switched feeding network efficiency when applied to time-modulated arrays. During the zero state of a conventional time-modulating sequence, if a given array element is switched off, a certain amount of energy of the transmitted/received signal is wasted. We propose a novel single sideband time-modulated phased array (TMPA) architecture governed by realistic bipolar squared sequences in which the rise/fall time of the switches is considered. By using single-pole dual-throw switches and nonreconfigurable passive devices, the TMPA exploits, exclusively, the first positive harmonic pattern while exhibiting an excellent performance in terms of efficiency and control level of the undesired harmonics without using synthesis optimization algorithms (software simplicity).This work has been funded by the Xunta de Galicia (ED431C 2016-045, ED341D R2016/012, ED431G/01), the Agencia Estatal de Investigaci´on of Spain (TEC2015-69648-REDC, TEC2016-75067-C4-1-R) and ERDF funds of the EU (AEI/FEDER, UE).Xunta de Galicia; ED431C 2016-045Xunta de Galicia; ED341D R2016/012Xunta de Galicia; ED431G/0

Time-Modulated Multibeam Phased Arrays With Periodic Nyquist Pulses

© 2018 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/LAWP.2018.2880087.[Abstract]: We present a single sideband time-modulated multibeam phased array governed by periodic Nyquist pulsed signals. A Nyquist pulse is a physically realizable approach to the ideal sinc function. Hence, its low-pass spectrum suits particularly well for time-modulated arrays (TMAs) to perform harmonic beam steering. Contrarily to switched TMAs and standard solutions based on variable phase shifters, the performance and complexity of the proposed time modulation scheme is rather robust when increasing the number of multibeams.This work has been funded by the Xunta de Galicia (ED431C 2016-045, ED341D R2016/012, ED431G/01), the Agencia Estatal de Investigaci´on of Spain (TEC2015-69648-REDC, TEC2016-75067-C4-1-R) and ERDF funds of the EU (AEI/FEDER, UE).Xunta de Galicia; ED431C 2016-045Xunta de Galicia; ED341D R2016/012Xunta de Galicia; ED431G/0

Analog Beamforming Using Time-Modulated Arrays With Digitally Preprocessed Rectangular Sequences

© 2018 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/LAWP.2018.2797971.[Abstract]: Conventional time-modulated arrays are based on the application of variable-width periodical rectangular pulses (easily implemented with radio frequency switches) to the individual antenna excitations. However, a serious bottleneck arises when the number of exploited harmonic beams increases. In this context, the modest windowing features of the rectangular pulses produce an inflexible and ineffective harmonic beamforming. The use of other pulses, such as sum of weighted cosines, partially solves these issues at the expense of introducing additional non-timing variables. We propose the discrete-time preprocessing of rectangular pulses before being applied to the antenna to accomplish an agile, efficient, and accurate harmonic beamforming, while keeping the simplicity of the hardware structure.This work has been funded by the Xunta de Galicia (ED431C 2016-045, ED341D R2016/012, ED431G/01), the Agencia Estatal de Investigación of Spain (TEC2013-47141-C4-1-R, TEC2015-69648-REDC, TEC2016-75067- C4-1-R) and ERDF funds of the EU (AEI/FEDER, UE).Xunta de Galicia; ED431C 2016-045Xunta de Galicia; ED341D R2016/012Xunta de Galicia; ED431G/0

NLOS Identification and Mitigation Using Low-Cost UWB Devices

[Abstract] Indoor location systems based on ultra-wideband (UWB) technology have become very popular in recent years following the introduction of a number of low-cost devices on the market capable of providing accurate distance measurements. Although promising, UWB devices also suffer from the classic problems found when working in indoor scenarios, especially when there is no a clear line-of-sight (LOS) between the emitter and the receiver, causing the estimation error to increase up to several meters. In this work, machine learning (ML) techniques are employed to analyze several sets of real UWB measurements, captured in different scenarios, to try to identify the measurements facing non-line-of-sight (NLOS) propagation condition. Additionally, an ulterior process is carried out to mitigate the deviation of these measurements from the actual distance value between the devices. The results show that ML techniques are suitable to identify NLOS propagation conditions and also to mitigate the error of the estimates when there is LOS between the emitter and the receiver.Xunta de Galicia; ED431C 2016-045Xunta de Galicia; ED431G/01Agencia Estatal de Investigación de España; TEC2016-75067-C4-1-