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  • Beamforming Design and Power Control for Spectrum Sharing Systems

     Vázquez Oliver, Miguel Ángel
    Defense's date: 2014-01-24
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    Per tal de proporcionar serveis sense fils per a la demanda actual de les aplicacions mòbils d'alta velocitat de dades, es necessiten sistemes amb major eficiència espectral. És una realitat que els sistemes inalambrics actuals estan limitats per una divisió de la gestió de l'espectre de freqüències que d'una banda minimitza la interferència multiusuari però, d'altra banda, impedeix l'ús de senyals amb amples de banda més amplis. Per a tal fi, es plantena una reutilització de freqüències més agressiva (idealment, tots els transmissors eventualment podrien compartir la mateixa banda de freqüència). Sota aquest context, l'ús de múltiples antenes per neutralitzar la interferència així com una assignació de potència intel·ligent és primordial. A més, es requereixen noves polítiques de regulacion de l'espectre per garantir una convivència pacífica entre les xarxes d'espectre compartit.L'objectiu d'aquesta tesi és proporcionar una conformacion de feix i assignació de potència d'aquests nous sistemes d'espectre compartit que estan destinats a augmentar exponencialment l'eficiència espectral. Es proporciona un marc matemàtic basat en la optimització multicriteri per analitzar la proposta de conformacion de feix, que serveix com una eina fonamental per a la descripció dels estudis inicials en sistemes interferents amb múltiples antenes. En altres paraules, la regió de taxes de comunicació per al sistema MISO interferent es descriu. A més la conformació de feix òptima en suma de taxes de comunicació s'estudia i un diseny subòptim es presenta.D'altra banda i per tal de fer front al problema d'alts nivells d'interferència en sistemes d'espectre compartit, un nova regulació de l'espectre es revisa. En virtut d'aquest mecanisme de gestió de l'espectre, un titular de la llicència és capaç d'irradiar sota una certa porció de temps, dins d'un àrea concreta i en una banda donada. Per dur això a terme, la quantitat de potència total (desitjada i interferent) dins la zona es limitada a un cert valor. Atès que el control dels nivells de potència en una àrea determinada és difícil, proposem restringir la potència de recepció com una estimació de la potència total acumulada . D'aquesta manera, s'estudien els conformadors de transmissió òptima i l'assignació de potències.

  • MIMO designs for filter bank multicarrier and multiantenna systems based on OQAM

     Caus Lopez, Marius
    Defense's date: 2013-12-18
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    Des de la perspectiva que les taxes de dades requerides per les comunicacions mòbils incrementaran progressivament, s'estima necessari realitzar investigacions per tal d'assolir els futurs objectius. Amb aquesta finalitat, les comunicacions ràdio estan recorrent a la utilització de modulacions multi-portadora i a la diversitat en espai. Fins avui la modulació "orthogonal frequency division multiplexing" (OFDM) és considerada com la tecnologia dominant. D'una banda la modulació OFDM permet la utilització de múltiples antenes d'una manera senzilla. D'altre banda, la baixa atenuació que OFDM exhibeix fora de la banda pas, posa de manifest que la sincronització ha d'estar molt ben ajustada. A més, el prefixe cíclic (PC) que evita la interferència entre blocs, redueix de manera substancial l'eficiència espectral. Amb l'objectiu de vèncer els inconvenients dels sistemes OFDM introduïm la modulació "filter bank multicarrier modulation based on OQAM" (FBMC/OQAM). Aquesta modulació no necessita cap PC i utilitza formes d'ona ben confinades en el domini temporal i freqüencial. Aquest aspecte esdevé crucial en xarxes de ràdio cognitiva i en sistemes de comunicació on els nodes no estan sincronitzats. En principi, la baixa atenuació que OFDM exhibeix fora de la banda de pas hauria de decantar la balança en favor de FBMC/OQAM. Tanmateix, la propietat que garanteix que la senyal transmesa pugui ser perfectament recuperada pel receptor, no es compleix quan hi ha propagació multicamí. Tret que el canal sigui equalitzat, això significa que hi ha interferència entre portadores. Aquesta observació posa de manifest que l'aplicació de FBMC/OQAM en arquitectures on hi ha diverses antenes esdevé un gran repte, ja que a mesura que s'afegeixen antenes s'incrementa la interferència. L'objectiu d'aquesta tesis és estudiar com la modulació FBMC/OQAM pot beneficiar-se de la diversitat en espai. El primer intent que s'ha fet per encarrilar la recerca en la direcció desitjada, ha estat dissenyar tècniques de processat de senyal en recepció. En aquest cas s'ha posat èmfasi en arquitectures "single-input-multiple-output" (SIMO). En el pas següent, s'ha investigat la possibilitat d'equalitzar el canal en la banda del transmissor. Tanmateix, s'ha considerat que només el transmissor està equipat amb múltiples antenes originant una configuració "multiple-input-single-output" (MISO). En aquest escenari la recerca no només està orientada a combatre el canal sinó també a distribuir la potència entre les sub-portadores. Finalment s'inclou el disseny conjunt del receptor i de l'emissor en un sistema de comunicacions "multiple-input-multiple-output" (MIMO). De la teoria que s'ha desenvolupat en aquesta tesis, és possible concloure que les tècniques concebudes en el context d'OFDM poden ser fàcilment adaptades als sistemes FBMC/OQAM, si la resposta freqüencial del canal es plana en la banda dels sub-canals. Tanmateix, la relació entre potència màxima i potència mitja o la sensibilitat a les desviacions de la portadora limiten el nombre de sub-portadores, de tal manera que la selectivitat en freqüència del canal pot ser perceptible. Llavors, la hipòtesis de resposta plana no es compleix i les característiques de la modulació FBMC/OQAM han de ser considerades. En aquesta situació, les tècniques proposades permeten que FBMC/OQAM sigui tan competitiu com OFDM. Depenent de les condicions de propagació i del nombre d'antenes resulta que FBMC/OQAM és la millor opció. Els resultats de les simulacions juntament amb l'anàlisi teòric que s'ha portat a terme, contribueixen a aconseguir avenços en l'aplicació de FBMC/OQAM en arquitectures amb múltiples antenes. Les tècniques de processat de senyal descrites en aquesta dissertació permeten explotar els potencials de FBMC/OQAM i MIMO, per millorar la fiabilitat de l'enllaç així com l'eficiència espectral.

  • Collaborative Beamforming Schemes for Wireless Sensor Networks with Energy Harvesting Capabilities  Open access

     Berbakov, Lazar
    Defense's date: 2013-07-11
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    In recent years, wireless sensor networks have attracted considerable attention in the research community. Their development, induced by technological advances in microelectronics, wireless networking and battery fabrication, is mainly motivated by a large number of possible applications such as environmental monitoring, industrial process control, goods tracking, healthcare applications, to name a few. Due to the unattended nature of wireless sensor networks, battery replacement can be either too costly or simply not feasible. In order to cope with this problem and prolong the network lifetime, energy efficient data transmission protocols have to be designed. Motivated by this ultimate goal, this PhD dissertation focuses on the design of collaborative beamforming schemes for wireless sensor networks with energy harvesting capabilities. On the one hand, by resorting to collaborative beamforming, sensors are able to convey a common message to a distant base station, in an energy efficient fashion. On the other, sensor nodes with energy harvesting capabilities promise virtually infinite network lifetime. Nevertheless, in order to realize collaborative beamforming, it is necessary that sensors align their transmitted signals so that they are coherently combined at the destination. Moreover, sensor nodes have to adapt their transmissions according to the amounts of harvested energy over time. First, this dissertation addresses the scenario where two sensor nodes (one of them capable of harvesting ambient energy) collaboratively transmit a common message to a distant base station. In this setting, we show that the optimal power allocation policy at the energy harvesting sensor can be computed independently (i.e., without the knowledge of the optimal policy at the battery operated one). Furthermore, we propose an iterative algorithm that allows us to compute the optimal policy at the battery operated sensor, as well. The insights gained by the aforementioned scenario allow us to generalize the analysis to a system with multiple energy harvesting sensors. In particular, we develop an iterative algorithm which sequentially optimizes the policies for all the sensors until some convergence criterion is satisfied. For the previous scenarios, this PhD dissertation evaluates the impact of total energy harvested, number of sensors and limited energy storage capacity on the system performance. Finally, we consider some practical schemes for carrier synchronization, required in order to implement collaborative beamforming in wireless sensor networks. To that end, we analyze two algorithms for decentralized phase synchronization: (i) the one bit of feedback algorithm previously proposed in the literature; and (ii) a decentralized phase synchronization algorithm that we propose. As for the former, we analyze the impact of additive noise on the beamforming gain and algorithm’s convergence properties, and, subsequently, we propose a variation that performs sidelobe control. As for the latter, the sensors are allowed to choose their respective training timeslots randomly, relieving the base station of the burden associated with centralized coordination. In this context, this PhD dissertation addresses the impact of number of timeslots and additive noise on the achieved received signal strength and throughput

    En los últimos años, las redes de sensores inalámbricas han atraído considerable atención en la comunidad investigadora. Su desarrollo, impulsado por recientes avances tecnológicos en microelectrónica y radio comunicaciones, está motivado principalmente por un gran abanico de aplicaciones, tales como: Monitorización ambiental, control de procesos industriales, seguimiento de mercancías, telemedicina, entre otras. En las redes de sensores inalámbricas, es primordial el diseño de protocolos de transmisión energéticamente eficientes ya que no se contempla el reemplazo de baterías debido a su coste y/o complejidad. Motivados por esta problemática, esta tesis doctoral se centra en el diseño de esquemas de conformación de haz distribuidos para redes de sensores, en el que los nodos son capaces de almacenar energía del entorno, lo que en inglés se denomina energy harvesting. En primer lugar, esta tesis doctoral aborda el escenario en el que dos sensores (uno de ellos capaz de almacenar energía del ambiente) transmiten conjuntamente un mensaje a una estación base. En este contexto, se demuestra que la política de asignación de potencia óptima en el sensor con energy harvesting puede ser calculada de forma independiente (es decir, sin el conocimiento de la política óptima del otro sensor). A continuación, se propone un algoritmo iterativo que permite calcular la política óptima en el sensor que funciona con baterías. Este esquema es posteriormente generalizado para el caso de múltiples sensores. En particular, se desarrolla un algoritmo iterativo que optimiza las políticas de todos los sensores secuencialmente. Para los escenarios anteriormente mencionados, esta tesis evalúa el impacto de la energía total cosechada, número de sensores y la capacidad de la batería. Por último, se aborda el problema de sincronización de fase en los sensores con el fin de poder realizar la conformación de haz de forma distribuida. Para ello, se analizan dos algoritmos para la sincronización de fase descentralizados: (i) el algoritmo "one bit of feedback" previamente propuesto en la literatura, y (ii) un algoritmo de sincronización de fase descentralizado que se propone en esta tesis. En el primer caso, se analiza el impacto del ruido aditivo en la ganancia y la convergencia del algoritmo. Además, se propone una variación que realiza el control de lóbulos secundarios. En el segundo esquema, los sensores eligen intervalos de tiempo de forma aleatoria para transmitir y posteriormente reciben información de la estación base para ajustar sus osciladores. En este escenario, esta tesis doctoral aborda el impacto del número de intervalos de tiempo y el ruido aditivo sobre la ganancia de conformación.

  • Nonlinear Simulation and Design of Microwave, Multi-Device Distributed Autonomous Circuits  Open access

     Acampora, Alessandro
    Defense's date: 2013-07-30
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    It is widely believed that many drawbacks in today's wireless communication paradigm might be relieved by enabling high carrier frequency transmission, and endowing both the network and the user equipment with some degree of reconfigurability. The urgency of a new framework in wireless digital transmission which should allow for higher bit rate, lower latency and tighter delay constraints, led us to investigate the fundamental building blocks which, at the circuital/device level, will foster a change towards more efficient communication schemes, delivering a more satisfactory end user experience. Specifically, this work deals with the inherently analog devices, found at the core of each transceiver module and capable of providing the carrier signal; these are the oscillators. In particular, two distinct classes of oscillators are regarded central to our contribution. One class is constituted by N-push oscillators, which thanks to coupling effect of N identical core oscillators allow N-fold harmonic generation (and thus high frequency transmission). The second class is constituted by wideband tunable oscillators, whose topology derives from a feedback distributed amplifier and therefore called distributed oscillators; by adequately altering the bias level at each section Distributed Voltage Controlled Oscillators can be implemented (which can scan a wide frequency range). The introductory part of this work, deals with their operation principles in great detail. As microwave oscillators are nonlinear devices, a full nonlinear analysis, synthesis, and optimization is considered for their implementation. Consequently, nonlinear numerical techniques have been reviewed in the second part of the thesis. Particularly, the role of Harmonic Balance simulations and the auxiliary generator/probe method for obtaining the oscillator solutions has been emphasized; the overall research goal of this dissertation is to show that the former techniques are very effective in obtaining detailed information about the periodic steady state behavior for the two class of circuits being investigated. A triple-push oscillator topology has been initially considered. Provided a certain phase distribution is maintained among the oscillating elements, the output power of the third harmonic increases while the lower order harmonics cancel out, which represents the default operating mode. Due to circuit symmetry, to the presence of delay in the coupling network and to unavoidable mismatches, unwanted oscillating modes might coexist with the intended one. A design strategy relying on the Harmonic Balance parametric analysis of the oscillating voltage at a selected node in the coupling network with respect to coupling phase and coupling strength is presented, to the aim of quenching undesired oscillation modes. Moreover the design of a four stage reverse mode distributed voltage controlled oscillator (DVCO) has been described. All the design steps have been reported, from a very idealized, purely behavioral design to a very concrete one, involving details derived from electromagnetic simulations. Harmonic Balance techniques were used to evaluate its tuning function, output power and DC current consumption, which have been completely characterized across the tuning bandwidth. Finally, a method for an optimized design with reduced variations in the output power has been presented. An alternative implementation, targeting wider tuning ranges/ higher oscillation frequencies was introduced. The measurements performed on the fabricated prototypes revealed good agreement with the simulation results, confirming the validity of the approach.

  • Application of Network Coding in Satellite Broadcast and Multiple Access Channels  Open access

     Cocco, Giuseppe
    Defense's date: 2013-02-12
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    Satellite broadcasting and relaying capabilities enable mobile broadcast systems over wide geographical areas, which opens large market possibilities for handheld, vehicular and fixed user terminals. The geostationary (GEO) satellite orbit is highly suited for such applications, as it spares the need for satellite terminals to track the movement of the spacecraft, with important savings in terms of complexity and cost. The large radius of the GEO orbit (more than 40000 km) has two main drawbacks. One is the large free space loss experienced by a signal traveling to or from the satellite, which limits the signal-to-noise ratio (SNR) margins in the link budget with respect to terrestrial systems. The second drawback of the GEO orbit is the large propagation delay (about 250 msec) that limits the use of feedback in both the forward (satellite to satellite terminal) and the reverse (satellite terminal to satellite) link. The limited margin protection causes loss of service availability in environments where there is no direct line of sight to the satellite, such as urban areas. The large propagation delay on its turn, together with the large terminal population size usually served by a GEO satellite, limit the use of feedback, which is at the basis of error-control. In the reverse link, especially in the case of fixed terminals, packet losses are mainly due to collisions, that severely limit the access to satellite services in case a random access scheme is adopted. The need for improvements and further understanding of these setups lead to the development of our work. In this dissertation we study the application of network coding to counteract the above mentioned channel impairments in satellite systems. The idea of using network coding stems from the fact that it allows to efficiently exploit the diversity, either temporal or spatial, present in the system. In the following we outline the original contributions included in each of the chapters of the dissertation. Chapter 3. This chapter deals with channel impairments in the forward link, and specifically with the problem of missing coverage in Urban environments for land mobile satellite (LMS) networks. By applying the Max-flow Min-cut theorem we derive a lower bound on the maximum coverage that can be achieved through cooperation. Inspired by this result, we propose a practical scheme, keeping in mind the compatibility with the DVB-SH standard. We developed a simulator in Matlab/C++ based on the physical layer abstraction and used it to test the performance gain of our scheme with a benchmark relaying scheme that does allow coding at packet level. Chapter 4. The second chapter of contributions is devoted to the information theoretical study of real-time streaming transmissions over fading channels with channel state information at the transmitter only. We introduce this new channel model and propose several transmission schemes, one of which is proved to be asymptotically optimal in terms of throughput. We also provide an upper bound on the achievable throughput for the proposed channel model and compare it numerically with the proposed schemes over a Rayleigh fading channel. Chapter 5. Chapter 5 is devoted to the study of throughput and delay in non-real-time streaming transmission over block fading channels. We derive bounds on the throughput and the delay for this channel and propose different coding techniques based on time-sharing. For each of them we carry out an analytical study of the performance. Finally, we compare numerically the performance of the proposed schemes over a Rayleigh fading channel. Chapter 6. In the last technical chapter we propose a collision resolution method for the return link based on physical layer network coding over extended Galois field (EGF). The proposed scheme extracts information from the colliding signals and achieves important gains with respect to Slotted ALOHA systems as well as with respect to other collision resolution schemes.

    Una de les característiques mes importants de les plataformes de comunicacions per satèl.lit és la seva capacitat de retransmetre senyals rebuts a un gran número de terminals. Això es fonamental en contextes com la difusió a terminals mòbils o la comunicació entre màquines. Al mateix temps, la disponibilitat d’un canal de retorn permet la creació de sistemes de comunicacions per satèl.lit interactius que, en principi, poden arribar a qualsevol punt del planeta. Els satèl.lits Geoestacionaris son particularment adequats per a complir amb aquesta tasca. Aquest tipus de satèl.lits manté una posició fixa respecte a la Terra, estalviant als terminals terrestres la necessitat de seguir el seu moviment en el cel. Per altra banda, la gran distància que separa la Terra dels satèl.lits Geoestacionaris introdueix grans retrassos en les comunicacions que, afegit al gran número de terminals en servei, limita l’ús de tècniques de retransmissió basades en acknowledgments en cas de pèrdua de paquets. Per tal de sol.lucionar el problema de la pèrdua de paquets, les tècniques més utilitzades son el desplegament de repetidors terrestres, anomenats gap fillers, l’ús de codis de protecció a nivell de paquet i mecanismes proactius de resolució de col.lisions en el canal de retorn. En aquesta tesi s’analitzen i s’estudien sol.lucions a problemes en la comunicació per satèl.lit tant en el canal de baixada com el de pujada. En concret, es consideren tres escenaris diferents. El primer escenari es la transmissió a grans poblacions de terminals mòbils en enorns urbans, que es veuen particularment afectats per la pèrdua de paquets degut a l’obstrucció, per part dels edificis, de la línia de visió amb el satèl.lit. La sol.lució que considerem consisteix en la utilització de la cooperació entre terminals. Una vegada obtinguda una mesura del guany que es pot assolir mitjançant cooperació en un model bàsic de xarxa, a través del teorema Max-flow Min-cut, proposem un esquema de cooperació compatible amb estàndards de comunicació existents. El segon escenari que considerem es la transmissió de vídeo, un tipus de tràfic particularment sensible a la pèrdua de paquets i retards endògens als sistemes de comunicació per satèl.lit. Considerem els casos de transmissió en temps real i en diferit, des de la perspectiva de teoria de la informació, i estudiem diferents tècniques de codificació analítica i numèrica. Un dels resultats principals obtinguts es l’extensió del límit assolible de la capacitat ergòdica del canal en cas que el transmissor rebi les dades de manera gradual, enlloc de rebre-les totes a l’inici de la transmissió. El tercer escenari que considerem es l’accés aleatori al satèl.lit. Desenvolupem un esquema de recuperació dels paquets perduts basat en la codificació de xarxa a nivell físic i en extensions a camps de Galois, amb resultats molt prometedors en termes de rendiment. També estudiem aspectes relacionats amb la implementació pràctica d’aquest esquema.

  • Analysis of information and power transfer in wireless communications

     Caspers, Erick; Ho Yeung, Sai; Sarkar, Tapan K.; Garcia-Lamperez, Alejandro; Salazar Palma, Magdalena; Lagunas Hernandez, Miguel Angel; Pérez Neira, Ana Isabel
    IEEE antennas and propagation magazine
    Date of publication: 2013-06
    Journal article

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    An analysis of wireless information compared to power transfer over the same channel, consisting of a transmitting and receiving antenna system, is discussed. This frequency-selective additive-white-Gaussian-noise channel displays a fundamental tradeoff between the rate at which energy and the rate at which reliable information can be transmitted over the same channel, as in an RFID system, a power-line communication system, or for an energy-harvesting system. The optimal tradeoffs between power transferred and the channel capacity due to Shannon (which is additive-white-Gaussian-noise limited), Gabor (which is interference limited), and Tuller (which is defined in terms of the signal and noise amplitudes, and not power) are compared, and the differences are discussed. The appropriate use of each of the channel-capacity formulations for a frequency-selective transmitting/receiving antenna system in wireless communication is then computed as an illustrative example, to describe the tradeoff between wireless power transfer and wireless information transfer over a transmitting/receiving antenna system.

    An analysis of wireless information compared to power transfer over the same channel, consisting of a transmitting and receiving antenna system, is discussed. This frequency-selective additive-white-Gaussian-noise channel displays a fundamental tradeoff between the rate at which energy and the rate at which reliable information can be transmitted over the same channel, as in an RFID system, a power-line communication system, or for an energy-harvesting system. The optimal tradeoffs between power transferred and the channel capacity due to Shannon (which is additive-white-Gaussian-noise limited), Gabor (which is interference limited), and Tuller (which is defined in terms of the signal and noise amplitudes, and not power) are compared, and the differences are discussed. The appropriate use of each of the channel-capacity formulations for a frequency-selective transmitting/receiving antenna system in wireless communication is then computed as an illustrative example, to describe the tradeoff between wireless power transfer and wireless information transfer over a transmitting/receiving antenna system.

  • Transmit beamforming for the MISO Interference Channel with asymmetric link gains

     Vázquez, Miguel Ángel; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    IEEE International Conference on Acoustics, Speech, and Signal Processing
    Presentation's date: 2012-03-25
    Presentation of work at congresses

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    This paper proposes a transmit beamforming technique to cope with the problem of the Multiple Input Single Out- put Interference Channel (MISO IC). In this scenario, the achievable sum-rate is highly conditioned by the inter-user interference. Furthermore, optimizing the sum-rate is known to be a cumbersome problem. In order to deal with this prob- lem, we approximate the sum-rate when the desired received signal power level is higher than the multiuser interference power level (i.e. when the Signal-to-Interference Ratio (SIR) is high). For that case, the sum-rate expression can be opti- mized distributively and it leads to a transmit beamformer that outperforms the existing decentralized techniques when the channel gains are asymmetric. Numerical simulations show the performance of the proposed technique which improves the existing decentralized designs for the MISO IC.

  • A unifying approach to transmit beamforming for the MISO interference channel

     Vázquez, Miguel Angel; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    International ITG Workshop on Smart Antennas
    Presentation's date: 2012
    Presentation of work at congresses

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    This paper addresses the problem of optimal beam- forming in the MISO interference channel. Different approaches are known to obtain the Pareto rate region. In this paper, several frameworks are thoroughly analyzed and compared. It is shown that there is an equivalence between all methods. Indeed, we show that they are different scalarization techniques of the same vector objective optimization problem. The results provide a bridge between the frameworks which were studied separately in the literature. Numerical simulations validate our theoretical findings

    This paper addresses the problem of optimal beam- forming in the MISO interference channel. Different approaches are known to obtain the Pareto rate region. In this paper, several frameworks are thoroughly analyzed and compared. It is shown that there is an equivalence between all methods. Indeed, we show that they are different scalarization techniques of the same vector objective optimization problem. The results provide a bridge between the frameworks which were studied separately in the literature. Numerical simulations validate our theoretical findings

  • Open spectrum communication systems and optimized downlink beamforming

     Vázquez, Miguel Ángel; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    International Wireless Communications and Mobile Computing Conference
    Presentation's date: 2012-08-27
    Presentation of work at congresses

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    This paper addresses the problem of transmit beamforming in open spectrum communication systems. In these scenarios, the operator or the data communication provider delivers a set of base stations to the final users under no radio planning strategy. In order to deal with such an uncoordinated communication system, this work presents a centralized algorithm for calculating the optimal precoding strategy the via semidefinite relaxation technique. The problem to be solved is a novel design of minimum norm beamformers under QoS and received power constraints. Numerical results will show the performance of the method.

  • Licensing open spectrum systems

     Vázquez, Miguel Angel; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    International Workshop on Cognitive Information Processing
    Presentation's date: 2012
    Presentation of work at congresses

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    This paper studies how the spectrum regulation could change in the future open spectrum communication systems. Due to their huge success in short-range communication systems (WiFi, Zigbee, ...), broader area telecommunication providers might mimic the open spectrum philosophy to their systems. Nevertheless, current wireless open spectrum systems are not designed for wide areas and they do not provide QoS to their users. This work proposes an alternative to the nowadays open spectrum systems in order to fulfill those requirements. Optimal power transmission strategies are derived. Numerical results show the performance of our proposal.

    This paper studies how the spectrum regulation could change in the future open spectrum communication systems. Due to their huge success in short-range communication systems (WiFi, Zigbee, ...), broader area telecommunication providers might mimic the open spectrum philosophy to their systems. Nevertheless, current wireless open spectrum systems are not designed for wide areas and they do not provide QoS to their users. This work proposes an alternative to the nowadays open spectrum systems in order to fulfill those requirements. Optimal power transmission strategies are derived. Numerical results show the performance of our proposal.

  • Confidential communication in downlink beamforming

     Vázquez, Miguel Ángel; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    IEEE International Workshop on Signal Processing Advances in Wireless Communications
    Presentation's date: 2012-06-17
    Presentation of work at congresses

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    This paper deals with the problem of secure transmission in downlinkbeamforming. In this scenario, a base station, which usually serves information to an amount of users, wants to transmit a confidential message to one of the users. Focusing on the beamforming solution, we derive all possible weighted solutions. With this, each non-intended receiver has an im- portance factor and, therefore, the resulting beamformer is able to properly reconfigure its secure transmission varying the weighting factors. This deri vation is done via multicrite- ria optimization, which allows us to transform a quasiconvex problem into a semidefinite one and, thus, reduce the compu- tational complexity. Numerical results show the performance of the method.

  • Generalized eigenvector for decentralized transmit beamforming in the MISO interference channel

     Vázquez, Miguel Ángel; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    IEEE transactions on signal processing
    Date of publication: 2012-11-30
    Journal article

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  • Low-complexity resource allocation with rate balancing for the MISO-OFDMA broadcast channel

     Henarejos, Pol; Pérez Neira, Ana Isabel; Tralli, Velio; Lagunas Hernandez, Miguel Angel
    Signal processing
    Date of publication: 2012-12
    Journal article

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    This paper presents a low-complexity algorithm for multiuser scheduling and resource allocation in the Multiple Input Single Output (MISO) downlink channel with Orthogonal Frequency Division Multiple Access (OFDMA). The goal of the algorithm is to maximize the sum-rate on the radio channel and to ensure that the rate assignment is suitably balanced among users. The proposed algorithm uses partial Channel State Information (CSI) and therefore has a reduced feedback requirement. It also allows an on-line implementation, based on an ergodic optimization framework with dual optimization and stochastic approximation. Performance and complexity reduction are quantified by considering comparison with other solutions in a realistic single-cell system configuration. It is shown that the algorithm is effective to balance average rate among users even in heterogeneous and non-stationary channel conditions with lower computational complexity and feedback requirements.

  • Feedback of Channel State Information in Multi-Antenna Systems Based on Quantization of Channel Gram Matrices  Open access

     Sacristan Murga, Daniel Francisco
    Defense's date: 2012-07-19
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    This dissertation deals with the proper design of efficient feedback strategies for Multiple-Input Multiple-Output (MIMO) communication systems. MIMO systems outperform single antenna systems in terms of achievable throughput and are more resilient to noise and interference, which are becoming the limiting factors in the current and future communications. Apart from the clear performance advantages, MIMO systems introduce an additional complexity factor, since they require knowledge of the propagation channel in order to be able to adapt the transmission to the propagation channel’s characteristics and achieve optimum performance. This channel knowledge, also known as Channel State Information (CSI), is estimated at the receiver and sent to the transmitter through a limited feedback link. In this dissertation, first, the minimum channel information necessary at the transmitter for the optimum precoding design is identified. This minimum information for the optimum design of the system corresponds to the channel Gram matrix. It is essential for the design of optimized systems to avoid the transmission of redundant feedback information. Following this idea, a quantization algorithm that exploits the differential geometry of the set of Gram matrices and the correlation in time present in most propagation channels is developed in order to greatly improve the feedback performance. This scheme is applied first to single-user MIMO communications, then to some particular multiuser scenarios, and finally it is extended to general multiuser broadcast communications. To conclude, the feedback link sizing is studied. An analysis of the tradeoff between size of the forward link and size of the feedback link isformulated and the radio resource allocation problem, in terms of transmission energy, time, and bandwidth of the forward and feedback links is presented.

    En un mundo cada vez más interconectado, donde hay una clara tendencia hacia un mayor número de comunicaciones inalámbricas simultáneas (comunicaciones M2M: Machine to Machine, redes de sensores, etc.) y en el que las necesidades de capacidad de transmisión de los enlaces de comunicaciones aumentan de manera vertiginosa (audio, video, contenidos multimedia, alta definición, etc.) el problema de la interferencia se convierte en uno de los factores limitadores de los enlaces junto con los desvanecimientos del nivel de señal y las pérdidas de propagación. Por este motivo los sistemas que emplean múltiples antenas tanto en la transmisión como en la recepción (los llamados sistemas MIMO: Multiple-Input Multiple-Output) se presentan como una de las soluciones más interesantes para satisfacer los crecientes requisitos de capacidad y comportamiento relativo a interferencias. Los sistemas MIMO permiten obtener un mejor rendimiento en términos de tasa de transmisión de información y a su vez son más robustos frente a ruido e interferencias en el canal. Esto significa que pueden usarse para aumentar la capacidad de los enlaces de comunicaciones actuales o para reducir drásticamente el consumo energético manteniendo las mismas prestaciones. Por otro lado, además de estas claras ventajas, los sistemas MIMO introducen un punto de complejidad adicional puesto que para aprovechar al máximo las posibilidades de estos sistemas es necesario tener conocimiento de la información de estado del canal (CSI: Channel State Information) tanto en el transmisor como en el receptor. Esta CSI se obtiene mediante estimación de canal en el receptor y posteriormente se envía al transmisor a través de un canal de realimentación. Esta tesis trata sobre el diseño del canal de realimentación para la transmisión de CSI, que es un elemento fundamental de los sistemas de comunicaciones del presente y del futuro. Las técnicas de transmisión que consideran activamente el efecto de la interferencia y el ruido requieren adaptarse al canal y, para ello, la realimentación de CSI es necesaria. En esta tesis se identifica, en primer lugar, la mínima información sobre el estado del canal necesaria para implementar un diseño óptimo en el transmisor, con el fin de evitar transmitir información redundante y obtener así un sistema más eficiente. Esta información es la matriz de Gram del canal MIMO. Seguidamente, se desarrolla un algoritmo de cuantificación adaptado a la geometría diferencial del conjunto que contiene la información a cuantificar y que además aprovecha la correlación temporal existente en los canales de propagación inalámbricos. Este algoritmo se implementa y evalúa primero en comunicaciones MIMO punto a punto entre dos usuarios, después se implementa para algunos casos particulares con múltiples usuarios, y finalmente se amplía para el caso general de sistemas broadcast multi-usuario. Adicionalmente, esta tesis también estudia y optimiza el dimensionamiento del canal de realimentación en función de la cantidad de recursos radio disponibles, en términos de ancho de banda, tiempo y potencia de transmisión. Para ello presenta el problema de la distribución óptima de dichos recursos radio entre el enlace de transmisión de datos y el enlace de realimentación para transmisión de información sobre estado del canal como un problema de optimización.

  • Resource Management in Multicarrier Based Cognitive Radio Systems  Open access

     Shaat, Musbah
    Defense's date: 2012-03-09
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    The ever-increasing growth of the wireless application and services affirms the importance of the effective usage of the limited radio spectrum. Existing spectrum management policies have led to significant spectrum under-utilization. Recent measurements showed that large range of the spectrum is sparsely used in both temporal and spatial manner. This conflict between the inefficient usage of the spectrum and the continuous evolution in the wireless communication calls upon the development of more flexible management policies. Cognitive radio (CR) with the dynamic spectrum access (DSA) is considered to be a key technology in making the best solution of this conflict by allowing a group of secondary users (SUs) to share the radio spectrum originally allocated to the primary user (PUs). The operation of CR should not negatively alter the performance of the PUs. Therefore, the interference control along with the highly dynamic nature of PUs activities open up new resource allocation problems in CR systems. The resource allocation algorithms should ensure an effective share of the temporarily available frequency bands and deliver the solutions in timely fashion to cope with quick changes in the network. In this dissertation, the resource management problem in multicarrier based CR systems is considered. The dissertation focuses on three main issues: 1) design of efficient resource allocation algorithms to allocate subcarriers and powers between SUs such that no harmful interference is introduced to PUs, 2) compare the spectral efficiency of using different multicarrier schemes in the CR physical layer, specifically, orthogonal frequency division multiplexing (OFDM) and filter bank multicarrier (FBMC) schemes, 3) investigate the impact of the different constraints values on the overall performance of the CR system. Three different scenarios are considered in this dissertation, namely downlink transmission, uplink transmission, and relayed transmission. For every scenario, the optimal solution is examined and efficient sub-optimal algorithms are proposed to reduce the computational burden of obtaining the optimal solution. The suboptimal algorithms are developed by separate the subcarrier and power allocation into two steps in downlink and uplink scenarios. In the relayed scenario, dual decomposition technique is used to obtain an asymptotically optimal solution, and a joint heuristic algorithm is proposed to find the suboptimal solution. Numerical simulations show that the proposed suboptimal algorithms achieve a near optimal performance and perform better than the existing algorithms designed for cognitive and non-cognitive systems. Eventually, the ability of FBMC to overcome the OFDM drawbacks and achieve more spectral efficiency is verified which recommends the consideration of FBMC in the future CR systems.

    El crecimiento continuo de las aplicaciones y servicios en sistemas inal´ambricos, indica la importancia y necesidad de una utilizaci´on eficaz del espectro radio. Las pol´ıticas actuales de gesti´on del espectro han conducido a una infrautilizaci´on del propio espectro radioel´ectrico. Recientes mediciones en diferentes entornos han mostrado que gran parte del espectro queda poco utilizado en sus ambas vertientes, la temporal, y la espacial. El permanente conflicto entre el uso ineficiente del espectro y la evoluci´on continua de los sistemas de comunicaci´on inal´ambrica, hace que sea urgente y necesario el desarrollo de esquemas de gesti´on del espectro m´as flexibles. Se considera el acceso din´amico (DSA) al espectro en los sistemas cognitivos como una tecnolog´ıa clave para resolver este conflicto al permitir que un grupo de usuarios secundarios (SUs) puedan compartir y acceder al espectro asignado inicialmente a uno o varios usuarios primarios (PUs). Las operaciones de comunicaci´on llevadas a cabo por los sistemas radio cognitivos no deben en ning´un caso alterar (interferir) los sistemas primarios. Por tanto, el control de la interferencia junto al gran dinamismo de los sistemas primarios implica nuevos retos en el control y asignaci´on de los recursos radio en los sistemas de comunicaci´on CR. Los algoritmos de gesti´on y asignaci´on de recursos (Radio Resource Management-RRM) deben garantizar una participaci´on efectiva de las bandas con frecuencias disponibles temporalmente, y ofrecer en cada momento oportunas soluciones para hacer frente a los distintos cambios r´apidos que influyen en la misma red. En esta tesis doctoral, se analiza el problema de la gesti´on de los recursos radio en sistemas multiportadoras CR, proponiendo varias soluciones para su uso eficaz y coexistencia con los PUs. La tesis en s´ı, se centra en tres l´ıneas principales: 1) el dise˜no de algoritmos eficientes de gesti´on de recursos para la asignaci´on de sub-portadoras y distribuci´on de la potencia en sistemas segundarios, evitando asi cualquier interferencia que pueda ser perjudicial para el funcionamiento normal de los usuarios de la red primaria, 2) analizar y comparar la eficiencia espectral alcanzada a la hora de utilizar diferentes esquema de transmisi´on multiportadora en la capa f´ısica del sistema CR, espec´ıficamente en sistemas basados en OFDM y los basados en banco de filtros multiportadoras (Filter bank Multicarrier-FBMC), 3) investigar el impacto de las diferentes limitaciones en el rendimiento total del sistema de CR. Los escenarios considerados en esta tesis son tres, es decir; modo de transmisi´on descendente (downlink), modo de transmisi´on ascendente (uplink), y el modo de transmisi´on ”Relay”. En cada escenario, la soluci´on ´optima es examinada y comparada con algoritmos sub- ´optimos que tienen como objetivo principal reducir la carga computacional. Los algoritmos sub-´optimos son llevados a cabo en dos fases mediante la separaci´on del propio proceso de distribuci´on de subportadoras y la asignaci´on de la potencia en los modos de comunicaci´on descendente (downlink), y ascendente (uplink). Para los entornos de tipo ”Relay”, se ha utilizado la t´ecnica de doble descomposici´on (dual decomposition) para obtener una soluci´on asint´oticamente ´optima. Adem´as, se ha desarrollado un algoritmo heur´ıstico para poder obtener la soluci´on ´optima con un reducido coste computacional. Los resultados obtenidos mediante simulaciones num´ericas muestran que los algoritmos sub-´optimos desarrollados logran acercarse a la soluci´on ´optima en cada uno de los entornos analizados, logrando as´ı un mayor rendimiento que los ya existentes y utilizados tanto en entornos cognitivos como no-cognitivos. Se puede comprobar en varios resultados obtenidos en la tesis la superioridad del esquema multiportadora FBMC sobre los sistemas basados en OFDM para los entornos cognitivos, causando una menor interferencia que el OFDM en los sistemas primarios, y logrando una mayor eficiencia espectral. Finalmente, en base a lo analizado en esta tesis, podemos recomendar al esquema multiportadora FBMC como una id´onea y potente forma de comunicaci´on para las futuras redes cognitivas.

  • Necessary and suffificient conditions for optimal beamforming in the MISO IC

     Vázquez, Miguel Angel; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    IEEE Communication Theory Workshop
    Presentation's date: 2011-06-20
    Presentation of work at congresses

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  • Regulation and research on wireless communications

     Lagunas Hernandez, Miguel Angel; Pérez Neira, Ana Isabel; Vázquez, Miguel Ángel
    IEEE Applied Electromagnetics Conference
    Presentation's date: 2011-12-18
    Presentation of work at congresses

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    This paper describes wh ich are the major changes would occur in regulation policies and role of the regulation bodies due to the advance of technology development, research and innovation in telecommunications. The so-called open spectrum, instead of free-sp ectrum, seems to offer great opportunities to all curren t players, from operators to technology providers. Open spectrum gives room also to new players mainly for those applications encompassed as short range communications scenarios. This paper remarks that in the vision of future radio co mmunications the regulator, in addition to its current duties, wil l assume an important role on conducting and funding research needed to properly face this new role. Finally an example is provided, which takes advantage of an included reference, in order to put in evidence how many fundamentals of current wireless research will be revisited with unexpected results.

  • Autonomous design for the MISO interference channel

     Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel; Vázquez, Miguel Ángel
    IEEE Applied Electromagnetics Conference
    Presentation's date: 2011-12-18
    Presentation of work at congresses

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    This paper investigates the power control and beamforming design in the MISO-IC (Multiple Input Single Output-Interference Channel) when constraints are placed at the receivers’ input power. In this way regulatory constraints are met and transmissions can coexist spatially. Dynamic and easy- to-implement distributed designs a re proposed; thus, using only local per user power measurements, which includes that of the intended signal as well as the undesired interference from other users plus receiver noise.

  • Space-time ML receiver and its reciprocal transmitter design for interference networks

     Vázquez, Miguel Angel; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    International ITG Workshop on Smart Antennas
    Presentation's date: 2011-02-23
    Presentation of work at congresses

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    This paper examines a type of linear beamforming for communications in interference networks. First, a receiver beamformer design is derived from a Maximum Likelihood (ML) framework with Automatic Gain Control (AGC) constraints. The studied beamformer keeps the complexity of the receiver low and it is able either to remove full coherent arrivals or to enhance them when required when different AGC constraints are used. Second, the reciprocal transmit beamformer which is of interest for the interference networks is obtained. This dual beamformer is derivated via revisting the idea of directivity for wireless multiuser communication scenarios. Furthermore, the duality in interference networks is reviewed. Numerical simulations demonstrate the effectiveness of the studied schemes.

  • Space-time-frequency candidate methods for spectrum sensing

     Lagunas Targarona, Eva; Najar Marton, Montserrat; Lagunas Hernandez, Miguel Angel
    European Signal Processing Conference
    Presentation's date: 2011-09
    Presentation of work at congresses

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    The basic idea behind Cognitive Radio (CR) is to allow unlicensed users to utilize licensed frequency bands when they do not interfere to the primary (licensed) users. Thus, an important requirement of CR systems is to sense the spectrum in order to obtain awareness about the spectrum usage. In this paper, a new spectral estimation procedure for monitoring the radio spectrum which exploits frequency, time and angle diversity is presented. The procedure is a feature-based method able to detect predetermined spectral shape, providing at the same time an estimate of its power level, an estimate of its frequency location and an estimate of its angle of arrival. The specific spectral shape is called the candidate spectrum and gives name to the different methods.

  • A novel non-iterative architecture for broadcast MIMO

     Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel; Devillers, Bertrand
    International Workshop on Cognitive Information Processing
    Presentation's date: 2010-06
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  • Spectrum Sensing for Cognitive Radio in Filter-Bank Multi-Carrier Communications Systems: The Candidate Estimate

     Lagunas Hernandez, Miguel Angel; Pérez Neira, Ana Isabel; Rojas, Miguel A.
    International Conference on Circuits, Systems, Signals
    Presentation's date: 2010
    Presentation of work at congresses

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    Joint temporal-spatial reference beamforming: EIG beamforming  Open access

     Lagunas Hernandez, Miguel Angel; Pérez Neira, Ana Isabel; Vázquez, Miguel Angel
    World Scientific and Engineering Academi and Society International Conference on Communications
    Presentation's date: 2010-07
    Presentation of work at congresses

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    Traditional methods for beamforming can be grouped in two families, the time reference beamformer and the spatial reference beamforming. Nevertheless, the increasing demand on receivers for location systems and high bandwidth over frequency selective fading able to properly manage multipath and co-channel interference motivates the need for versatile processing able to cope with both problems. This paper presents a new beamforming procedure, derived from a ML-like framework, which is able to either remove full coherent arrivals, as well as, to enhance them when required yet preserving the receiver architecture and low design complexity. The performance of the beamformer is also tested in the multiuser broadcast scenario.

  • A Novel Architecture for the MIMO Multiuser Channel

     Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    ASMSSPSC 2010
    Presentation's date: 2010-09-13
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    The challenge of the multiantenna-IC and practical solutions for the MISO case  Open access

     Pérez Neira, Ana Isabel; Vázquez, Miguel Ángel; Lagunas Hernandez, Miguel Angel
    International Symposium on Modeling and Optimization in Mobile, Ad Hoc and Wireless Networks
    Presentation's date: 2010-05-31
    Presentation of work at congresses

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    The interference channel (IC) models a network of simultaneous communication node pairs. Interference is not a fundamental limitation: IA (interference alignment) is cooperative and not selfish. It avoids MUD. What about intermediate SINR regime in a constant channel? (where the desired signal power is an issue). What about MIMO-IC?

  • The Physics and Mathematics of Multiantenna Systems and How to Improve their Performances (AP1006-0644)

     Pérez Neira, Ana Isabel; Sarkar, Tapan K.; Salazar, M.; Lagunas Hernandez, Miguel Angel
    IEEE Trans. on Antennas and Propagation
    Date of publication: 2010-06
    Journal article

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  • Decentralized parameter and random field estimation with wireless sensor networks

     Matamoros Morcillo, Javier
    Defense's date: 2010-05-06
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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  • Randomized space-time block coding for the multiple-relay channel  Open access  awarded activity

     Gregoratti, David
    Defense's date: 2010-06-22
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    En la última década, la cooperación entre usuarios ha generado un gran interés por la posibilidad de mejorar la velocidad de transmisión en las redes de comunicaciones inalámbricas. El objetivo es formar un array con las antenas de todos los dispositivos y, de esta forma, aplicar técnicas de procesado espacio-temporal. El esquema de cooperación más sencillo es el canal con relays: todos los terminales que escuchen una comunicación entre dos puntos pueden ayudar a la fuente retransmitiendo lo que hayan recibido.En un sistema realista, los relays no disponen de información sobre el canal en trasmisión. En este escenario, los códigos espacio-temporales (STC, del inglés space-time coding) son la alternativa más eficiente para aprovechar la diversidad introducida por los relays. Sin embargo, los STC clásicos están diseñados para un número limitado y fijo de antenas transmisoras y no se adaptan bien a sistemas cooperativos donde el número de relays puede ser elevado y, sobretodo, puede variar en el tiempo, según los usuarios entren o salgan de la red. El problema principal es la necesidad de usar un código nuevo cada vez que cambie la configuración de la red, generando un importante tráfico de señalización.Esta tesis analiza un código espacio-temporal a bloques de dispersión lineal (LD-STBC, del inglés linear-dispersion space-time block coding), aleatorio y distribuido: a cada relay se le asigna una matriz aleatoria que aplica una transformación lineal al vector que contiene los símbolos de la fuente. Cada matriz se genera de forma independiente y sin ninguna relación con el número de usuarios involucrados. De esta manera, el número de nodos puede variar sin necesidad de modificar los códigos existentes.La forma más intuitiva de construir matrices de dispersión lineal independientes es que sus elementos sean variables aleatorias independientes e idénticamente distribuidas (i.i.d.). Por esta razón, se estudia primero la eficiencia espectral obtenida por este tipo de LD-STBC. Es importante remarcar que la eficiencia espectral es una cantidad aleatoria, ya que es una función de los códigos aleatorios anteriormente descritos. Sin embargo, cuando las dimensiones de las matrices crecen infinitamente pero manteniendo constante la tasa del código (relación entre número de símbolos de la fuente sobre el número de símbolos de los relays), la eficiencia espectral converge rápidamente hacia una cantidad determinista. Este resultado se demuestra usando la teoría de las matrices aleatorias. Por esta razón, el sistema se analiza aproximando la eficiencia espectral con su limite. Por ejemplo, la comparación con el canal directo entre fuente y destino permite definir unas condiciones suficientes en donde el sistema con relays es superior a la comunicación punto a punto.Posteriormente se debe analizar la probabilidad de outage, es decir la probabilidad de que, debido a la baja calidad del canal, la eficiencia espectral sea menor que la velocidad de transmisión solicitada por el sistema. Como ya se ha mencionado anteriormente, los relays se introducen para aumentar la diversidad del canal y, con ella, el número de caminos independientes entre la fuente y el receptor, reduciendo la probabilidad de outage. Para los LD-STBC i.i.d. las prestaciones en términos de outage dependen del tipo de relay (amplify and forward o decode and forward) y son función de la tasa del código, que debe ser cuidadosamente elegida para maximizar el orden de diversidad sin desperdiciar demasiados recursos.Finalmente, en el último capítulo de la tesis se considera otro tipo de LD-STBC, distinto del i.i.d. analizado hasta ahora. En este caso, las matrices de dispersión lineal siguen siendo independientes la una de la otra pero se añade la restricción de que cada una tenga columnas (o filas, según la tasa del código) ortogonales. Así, se consigue que el código siga siendo flexible con respecto a las variaciones en el número de usuarios, pero su estructura permite reducir la interferencia generada por cada relay, como se puede notar comparando su eficiencia espectral con la eficiencia espectral obtenida por el código i.i.d. Cabe destacar que el análisis asintótico de estos códigos (llamados isométricos) se basa en herramientas matemáticas más sofisticadas que las anteriores y, por lo tanto, es necesario un estudio más profundo para poder entender cómo se comporta en términos de outage.

    In the last decade, cooperation among multiple terminals has been seen as one of the more promising strategies to improve transmission speed in wireless communications networks. Basically, the idea is to mimic an antenna array and apply distributed versions of well-known space-diversity techniques. In this context, the simplest cooperative scheme is the relay channel: all the terminals (relays) that overhear a point-to-point communication between a source and a destination may decide to aid the source by forwarding (relaying) its message.In a mobile system, it is common to assume that the relays do not have any information about the channel between them and the destination. Under this hypothesis, the best solution to exploit the diversity offered by multiple transmitting antennas is to use space-time coding (STC). However, classical STC's are designed for systems with a fixed and usually low number of antennas. Thus, they are not suitable for relaying in most mobile communications systems where the number of terminals is potentially large and may vary as users join or leave the network. For each new configuration, a new code has to be chosen and notified to the relays, introducing a set-up overhead of signaling traffic.In this dissertation we will propose and analyze a randomized distributed linear-dispersion space-time block code (LD-STBC): each relay is assigned a specific matrix which linearly transforms (left-multiplies) the column vector of source symbols. Each matrix is independently generated and does not depend on the total number of transmitters, which can thus change without interrupting data transmission for a new code--relay assignment.The more intuitive way to build independent linear-dispersion matrices is to fill them with independent and identically distributed (i.i.d.) random variables. Therefore, we will first consider these i.i.d. codes and characterize the resulting spectral efficiency. In order to analyze the performance achieved by the system, we consider a large-system analysis based on random matrix theory. We will show that the random spectral efficiency (function of the random linear-dispersion matrices) converges almost surely to a deterministic quantity when the dimensions of the code grow indefinitely while keeping constant the coding rate. Since convergence is very fast, the random spectral efficiency will be approximated by the deterministic limit in the subsequent analysis. By comparison with the direct link, sufficient conditions are derived for the superiority of relaying.Next, we will analyze the outage probability of the system, that is the probability that the spectral efficiency falls below a given target rate due to channel fading. The main purpose of diversity techniques is to introduce alternative paths from the source to the destination, so that data transmission does not fail when the direct link undergoes deep fading. We will show that the diversity behavior of LD-STBC relaying mainly depends on both the coding rate and the relaying strategy (amplify and forward or decode and forward). It is then important to choose the coding rate that maximizes the diversity order without wasting too many resources.To conclude the dissertation, we will consider a different code based on independent isometric Haar-distributed random linear-dispersion matrices. Thenew code maintains the flexibility of the previous one with respect to variations in the number of relays. However, the more complex structure of the codes allows a noticeable reduction of the interference generated by the relays. Unfortunately, isometric codes also require more sophisticated mathematical tools for their asymptotic analysis. For this reason, we simply introduce the problem by showing that it is possible to have some spectral-efficiency gain with respect to i.i.d. codes. The outage-probability analysis requires a more thorough understanding and will be the subject of future work.

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    DVB-T candidate power detector for cognitive radio  Open access

     Rojas, M.A.; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    European Signal Processing Conference
    Presentation's date: 2009-08-24
    Presentation of work at congresses

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    Dynamic detection of primary users is one of the main functions of spectrum sensing for Cognitive Radio (CR) communications aiming to increase the use of radio spectrum. In this work the performance of the so-called Candidate power detector is reported. The main objective of this detector is the proper spectrum labelling of primary users in cognitive radio scenarios. The Candidate detector is tuned in order to detect Digital Video Broadcasting Terrestrial (DVB-T) signals, providing accurate power level estimates and frequency location in presence of interference signals or secondary users transmissions. The advantages of the resulting candidate detector are shown with respect to the existing alternatives based on energy detection and cyclo-stationary based detectors.

  • A low complexity space-frequency multiuser resource allocation algorithm

     Pérez Neira, Ana Isabel; Henarejos, P.; Tralli, V.; Lagunas Hernandez, Miguel Angel
    International ITG Workshop on Smart Antennas
    Presentation's date: 2009-02
    Presentation of work at congresses

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  • Correlation Matching Approach for Spectrum Sensing in Open Spectrum Communications

     Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel; Rojas, M A; Stoica, P
    IEEE transactions on signal processing
    Date of publication: 2009-12
    Journal article

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    Spectrum labeling for cognitive radio systems  Open access

     Lagunas Hernandez, Miguel Angel; Pérez Neira, Ana Isabel; Stoica, Petre; Rojas, Miguel A.
    International Workshop on Cognitive Information Processing
    Presentation's date: 2008-10
    Presentation of work at congresses

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    A key challenge of the air interface of the cognitive radio is an accurate detection of weak signals of licensed users over a wide spectrum range. This paper describes a method for first detecting and next locating in frequency a given primary user, even when a non-candidate interference is located at the same frequency. The range of SNR that is covered proves that the estimate is efficient for realistic scenarios. In addition, the good performance is kept even for very short data records (50 symbols of the candidate signal). The proposed technique shows much better performance than energy detectors and less complexity than cyclo-stationary based ones.

  • Spectrum labeling for cognitive radio

     Lagunas Hernandez, Miguel Angel; Pérez Neira, Ana Isabel; Rojas, M A; Stoica, P
    International Workshop on Cognitive Information Processing
    Presentation's date: 2008-06-09
    Presentation of work at congresses

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  • Achievable Rates for Gaussian Channels with Multiple Relays  Open access

     del Coso Sánchez, Aitor
    Defense's date: 2008-09-12
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    Los canales múltiple-entrada-múltiple-salida (MIMO) han sido ampliamente propuestos para superar los desvanecimientos aleatorios de canal en comunicaciones inalámbricas no selectivas en frecuencia. Basados en equipar tanto transmisores como receptores con múltiple antenas, sus ventajas son dobles. Por un lado, permiten al transmisor: i) concentrar la energía transmitida en una dirección-propia determinada, o ii) codificar entre antenas con el fin de superar desvanecimientos no conocidos de canal. Por otro lado, facilitan al receptor el muestreo de la señal en el dominio espacial. Esta operación, seguida por la combinación coherente de muestras, aumenta la relación señal a ruido de entrada al receptor. De esta forma, el procesado multi-antena es capaz de incrementar la capacidad (y la fiabilidad) de la transmisión en escenarios con alta dispersión.Desafortunadamente, no siempre es posible emplazar múltiples antenas en los dispositivos inalámbricos, debido a limitaciones de espacio y/o coste. Para estos casos, la manera más apropiada de explotar el procesado multi-antena es mediante retransmisión, consistente en disponer un conjunto de repetidores inalámbricos que asistan la comunicación entre un grupo de transmisores y un grupo de receptores, todos con una única antena. Con la ayuda de los repetidores, por tanto, los canales MIMO se pueden imitar de manera distribuida. Sin embargo, la capacidad exacta de las comunicaciones con repetidores (así como la manera en que este esquema funciona con respeto al MIMO equivalente) es todavía un problema no resuelto. A dicho problema dedicamos esta tesis.En particular, la presente disertación tiene como objetivo estudiar la capacidad de canales Gaussianos asistidos por múltiples repetidores paralelos. Dos repetidores se dicen paralelos si no existe conexión directa entre ellos, si bien ambos tienen conexión directa con la fuente y el destino de la comunicación. Nos centramos en el análisis de tres canales ampliamente conocidos: el canal punto-a-punto, el canal de múltiple-acceso y el canal de broadcast, y estudiamos su mejora de funcionamiento con repetidores. A lo largo de la tesis, se tomarán las siguientes hipótesis: i) operación full-duplex en los repetidores, ii) conocimiento de canal tanto en transmisión como en recepción, y iii) desvanecimiento sin memoria, e invariante en el tiempo.En primer lugar, analizamos el canal con múltiples repetidores paralelos, en el cual una única fuente se comunica con un único destino en presencia de N repetidores paralelos. Derivamos límites inferiores de la capacidad del canal por medio de las tasas de transmisión conseguibles con distintos protocolos: decodificar-y-enviar, decodificar-parcialmente-y-enviar, comprimir-y-enviar, y repetición lineal. Asimismo, con un fin comparativo, proveemos un límite superior, obtenido a través del Teorema de max-flow-min-cut. Finalmente, para el número de repetidores tendiendo a infinito, presentamos las leyes de crecimiento de todas las tasas de transmisión, así como la del límite superior.A continuación, la tesis se centra en el canal de múltiple-acceso (MAC) con múltiples repetidores paralelos. El canal consiste en múltiples usuarios comunicándose simultáneamente con un único destino en presencia de N repetidores paralelos. Derivamos una cota superior de la región de capacidad de dicho canal utilizando, de nuevo, el Teorema de max-flow-min-cut, y encontramos regiones de tasas de transmisión conseguibles mediante: decodificar-y-enviar, comprimir-y-enviar, y repetición lineal. Asimismo, se analiza el valor asintótico de dichas tasas de transmisión conseguibles, asumiendo el número de usuarios creciendo sin límite. Dicho estudio nos permite intuir el impacto de la diversidad multiusuario en redes de acceso con repetidores.Finalmente, la disertación considera el canal de broadcast (BC) con múltiples repetidores paralelos. En él, una única fuente se comunica con múltiples destinos en presencia de N repetidores paralelos. Para dicho canal, derivamos tasas de transmisión conseguibles dado: i) codificación de canal tipo dirty paper en la fuente, ii) decodificar-y-enviar, comprimir-y-enviar, y repetición lineal, respectivamente, en los repetidores. Además, para repetición lineal, demostramos que la dualidad MAC-BC se cumple. Es decir, la región de tasas de transmisión conseguibles en el BC es igual a aquélla del MAC con una limitación de potencia suma. Utilizando este resultado, se derivan algoritmos de asignación óptima de recursos basados en teoría de optimización convexa.

    Multiple-input-multiple-output (MIMO) channels are extensively proposed as a means to overcome the random channel impairments of frequency-flat wireless communications. Based upon placing multiple antennas at both the transmitter and receiver sides of the communication, their virtues are twofold. On the one hand, they allow the transmitter: i) to concentrate the transmitted power onto a desired eigen-direction, or ii) tocode across antennas to overcome unknown channel fading. On the other hand, they permit the receiver to sample the signal on the space domain. This operation, followed by the coherent combination of samples, increases the signal-to-noise ratio at the input of the detector. In fine, MIMO processing is able to provide large capacity (and reliability) gains within rich-scattered scenarios.Nevertheless, equipping wireless handsets with multiple antennas is not always possible or worthwhile. Mainly, due to size and cost constraints, respectively. For these cases, the most appropriate manner to exploit multi-antenna processing is by means of relaying. This consists of a set of wireless relay nodes assisting the communication between a set of single-antenna sources and a set of single-antenna destinations. With the aid of relays, indeed, MIMO channels can be mimicked in a distributed way. However, the exact channel capacity of single-antenna communications with relays (and how this scheme performs with respect to the equivalent MIMO channel) is a long-standing open problem. To it we have devoted this thesis.In particular, the present dissertation aims at studying the capacity of Gaussian channels when assisted by multiple, parallel, relays. Two relays are said to be parallel if there is no direct link between them, while both have direct link from the source and towards the destination. We focus on three well-known channels: the point-to-point channel, the multi-access channel and the broadcast channel, and study their performance improvement with relays. All over the dissertation, the following assumptions are taken: i) full-duplex operation at the relays, ii) transmit and receive channel state information available at all network nodes, and iii) time-invariant, memory-less fading.Firstly, we analyze the multiple-parallel relay channel, where a single source communicates to a single destination in the presence of N parallel relays. The capacity of the channel is lower bounded by means of the achievable rates with different relaying protocols, i.e. decode-and-forward, partial decode-and-forward, compress-and-forward and linear relaying. Likewise, a capacity upper bound is provided for comparison, derived using the max-flow-min-cut Theorem. Finally, for number of relays growing to infinity, the scaling laws of all achievable rates are presented, as well as the one of the upper bound.Next, the dissertation focusses on the multi-access channel (MAC) with multiple-parallel relays. The channel consists of multiple users simultaneously communicating to a single destination in the presence of N parallel relay nodes. We bound the capacity region of the channel using, again, the max-flow-min-cut Theorem and find achievable rate regions by means of decode-and-forward, linear relaying and compress-and-forward. In addition, we analyze the asymptotic performance of the obtained achievable sum-rates, given the number of users growing without bound. Such a study allows us to grasp the impact of multi-user diversity on access networks with relays.Finally, the dissertation considers the broadcast channel (BC) with multiple parallel relays. This consists of a single source communicating to multiple receivers in the presence of N parallel relays. For the channel, we derive achievable rate regions considering: i) dirty paper encoding at the source, and ii) decode-and-forward, linear relaying and compress-and-forward, respectively, at the relays. Moreover, for linear relaying, we prove that MAC-BC duality holds. That is, the achievable rate region of the BC is equal to that of the MAC with a sum-power constraint. Using this result, the computation of the channel's weighted sum-rate with linear relaying is notably simplified. Likewise, convex resource allocation algorithms can be derived.

  • Dual polarizaton for mimo processing in multibeam satellite systems

     Zorba Barah, Nizar; Realp, Marc; Lagunas Hernandez, Miguel Angel; Pérez Neira, Ana Isabel
    International Workshop on Signal Processing for Space Communications
    Presentation of work at congresses

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    The performance of HSDPA-HDR in delay constrained applications: closed-form expressions  Open access

     Zorba Barah, Nizar; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    WSEAS International Conference on Communications
    Presentation's date: 2007-07
    Presentation of work at congresses

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    Scheduling in a Downlink channel based on partial Channel State Information at the Transmitter (CSIT) is carried out through an opportunistic technique. Within a more practical perspective, this paper first presents a transmission strategy where a minimum rate per user is required, which in a wireless fading scenario, can only be guaranteed under a certain system outage constraint. This minimum rate is demanded within a given time interval to satisfy maximum delay restrictions for the user application. Closed form expressions for maximum scheduling delay and maximum jitter are obtained, standing as possible Quality of Service (QoS) indicators for the system behaviour. The derived expressions are then tested via simulations in several transmission scenarios.

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    Candidate spectral estimation for cognitive radio  Open access

     Rojas, Miguel A.; Lagunas Hernandez, Miguel Angel; Pérez Neira, Ana Isabel
    World Scientific and Engineering Academi and Society International Conference on Communications
    Presentation's date: 2007-07
    Presentation of work at congresses

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    Introducing a different view point of traditional filter bank approach for spectral estimation it is derived a spectral estimation method able to detect a given spectral shape forming part or contributing to a given data record. The method provides an estimated power level of the spectral shape contribution to the data record, and peaks close to the frequency where the spectral shape is located. Basically, the filter-bank, instead of being tuned to a single carrier, is tuned to the spectral shape. The spectral shape used to tune the filter-bank is refereed as the candidate spectrum. The major motivation for this procedure was the proper spectrum labelling of licensed users and interferers in cognitive radio applications.

  • IMPACT OF CHANNEL STATE INFORMATION ON THE ANALYSIS AND DESIGN OF MULTIANTENNA COMMUNICATION SYSTEMS  Open access

     Payaró Llisterri, Miquel
    Defense's date: 2007-02-14
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    Al llarg d'aquesta última dècada, s'ha produit un creixement constant en la demanda d'elevades taxes de transmissió de dades que han de suportar les aplicacions sobre comunicacions sense fils. Entre les diferents solucions ideades per la comunitat recercaire per tal de fer front a aquesta nova demanda, la utilització de múltiples antenes s'erigeix com una de les millors candidates degut al fet que proporciona simultàniament una millora en les taxes de transmissió i en la fiabilitat en la recepció de les dades. L'ús d'antenes múltiples en un dels extrems de la comunicació data de la dècada dels seixanta, nogensmenys ha estat en aquests últims anys quan s'ha pogut provar, tant en els camps teòric com pràctic, tot el potencial que possibilita la presència de múltiples antenes en ambdós extrems de la comunicació.El disseny adequat de sistemes de comunicació amb múltiples antenes per satisfer aquesta demanda no només depèn de la funció de mèrit (o de la mètrica de rendiment) escollida, sinó que també es veu afectat per la quantitat i la qualitat de la informació de l'estat del canal que es troba disponible als extrems de la comunicació. Aquesta tesi tracta sobre l'anàlisi i el disseny d'arquitectures per sistemes de comunicació amb múltiples antenes i amb diferents nivells de quantitat i qualitat de la informació de l'estat del canal. La secció d'anàlisi es centra en l'estudi de la capacitat i les taxes de transmissió assolibles per aquests tipus de sistemes de comunicació i la part de disseny queda més encarada a la síntesi de sistemes de comunicació pràctics amb l'objectiu de maximitzar el rendiment d'acord amb la mètrica de rendiment escollida.Primerament, l'atenció es centra en sistemes de comunicació amb múltiples antenes per a un únic usuari amb informació perfecte de l'estat del canal, que suposa una idealització dels sistemes pràctics que s'empren en la realitat. En aquest context, es revisen resultats de capacitat que són ben coneguts, i es caracteritza, a més, un transmissor lineal dissenyat per tal de maximitzar la fiabilitat de l'enllaç sense fils amb múltiples antenes. Addicionalment, s'apunten una sèrie d'analogies entre el disseny del transmissor lineal òptim i la teoria de construcció de constel.lacions de símbols.En segon lloc, es roman en un escenari de comunicacions amb un únic usuari i es considera el cas on la informació sobre l'estat del canal és incompleta. En aquest cas, es presenta un anàlisi detallat sobre la capacitat a través de les formulacions ergòdica i composta (compound), les quals prenen significat depenent del model utilitzat per caracteritzar el canal. Mentres que en canals ràpidament variants la capacitat ergòdica és la mesura clau de les taxes de transmissió assolibles per qualsevol sistema de comunicació, en canals fixos o de variació lenta, és la capacitat composta, la que mesura la mínima taxa de transmissió assolible de forma sostinguda durant la transmissió del missatge.Seguidament, es considera el cas on la informació disponible sobre l'estat del canal és imperfecta. Precisament, es discorre sobre un sistema de comunicació pràctic anomentat Precodificador Espacial de Tomlinson i Harashima i s'estudien les seves potencialitats en termes de taxes de transmissió assolibles. Gràcies a l'arquitectura versàtil del Precodificador Espacial de Tomlinson i Harashima l'esmentat estudi es duu a terme tant per escenaris amb un únic usuari com per escenaris amb múltiples usuaris. Per aquests dos casos, es presenta així doncs un disseny que és robust a les incerteses de la informació de l'estat del canal i que té per objectiu minimitzar les pèrdues de taxa de transmissió d'informació.Finalment, restant en un escenari amb múltiples usuaris amb coneixement imperfecte de l'estat del canal, es presenta una arquitectura de transmissió que és robusta a les incerteses de la informació sobre l'estat del canal disponible tant en el transmisor com en el receptor. La variable per al disseny robust és la distribució de potència entre els símbols d'informació destinats a cada usuari, i el criteri d'optimització és minimitzar la potència total transmesa, tot garantint una determinada qualitat de servei per cada usuari i per qualsevol possible realització del canal que sigui compatible amb la informació disponible sobre l'estat del canal.

    During the last decade, there has been a steady increase in the demand of high data rates that are to be supported by wireless communication applications. Among the different solutions that have been proposed by the research community to cope with this new demand, the utilization of multiple antennas arises as one of the best candidates due to the fact that it provides both an increase in reliability and also in information transmission rate. Although the use of multiple antennas at the receiver side dates back from the sixties, the full potential of multiple antennas at both communication ends has been both theoretically and practically recognized in the last few years.The design of proper multi-antenna communication systems to satisfy the high data rates demand depends not only on the chosen figure of merit or performance metric, but also on the quantity and the quality of the channel state information that is available at the communication ends. In this dissertation we deal with the analysis and design of different architectures for multiple-antenna communication systems for various degrees of quality and quantity of channel state information. The analysis section is devoted to the study of capacity and achievable rates and the part that deals with design is aimed at the synthesis of practical communication systems that maximize a certain performance measure.Firstly, we focus our attention on multiple antenna single-user communication systems with perfect channel state information, which is an idealization of actual practical systems. In this context, we review well known capacity results and deal with the practical characterization of a linear transmitter that is designed to maximize the reliability of the wireless multi-antenna link. Some analogies between the optimal linear transmitter design and the theory of constellation construction are also pointed out.Secondly, we stay in a single-user scenario and we move onto the case where the channel state information is incomplete. In this case, a detailed capacity analysis is presented dealing with the ergodic and compound capacity formulations, which arise depending on the model utilized to characterize the channel. While in rapidly varying channels the ergodic capacity is a key measure of the rates that can be achieved by any communication system, in slow varying or fixed channels the compound capacity measures the minimum transmission rate that can be sustained during the transmission of the message.Next, we shift to the case where the available channel state information is imperfect. Precisely, we deal with a practical communication system called spatial Tomlinson-Harashima precoder and study its achievable rate capabilities. Due to the versatile architecture of the spatial Tomlinson-Harashima precoder we are able to perform the study for the single and multi-user scenarios. For both cases, a design is presented which is robust to the uncertainties of the channel state information and which is aimed at maximizing the transmission rate.Finally, staying in the multi-user scenario with imperfect channel state information, we present a transmission architecture that is robust to the uncertainties of the side information that is available at both the transmitter and the receiver. The robustness criterion is to minimize the transmitted power while guaranteeing a certain quality of service per user for every possible realization of the channel that is compatible with the available channel state information.

  • Technical report 1: Overview of MIMO techniques for wireless systems

     Pérez Neira, Ana Isabel; Ibars, C; Fernández, C; MESTRE, X; Lagunas Hernandez, Miguel Angel
    Date: 2007-03
    Report

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  • 4x4 MIMO-OFDM Demonstrator for WiFi/WiMax

     Mestre Pons, Xavier; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel; Pascual Iserte, Antonio; Ventura, Lluís M.
    NEWCOM. Workshop on Flexilbe Radios
    Presentation's date: 2007-02
    Presentation of work at congresses

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  • Robust design of spatial Tomlinson-Harashima precoding in the presence of errors in the CSI

     Payaró Llisterri, Miquel; Pascual Iserte, Antonio; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    IEEE transactions on wireless communications
    Date of publication: 2007-07
    Journal article

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  • Mutual information optimization and capacity evaluation in MIMO systems with magnitude knowledge and phase uncertainty

     Payaró Llisterri, Miquel; Pascual Iserte, Antonio; Lagunas Hernandez, Miguel Angel
    Circuits systems and signal processing
    Date of publication: 2007-08
    Journal article

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  • Robust Power Allocation Designs for Multiuser and Multiantenna Downlink Communication Systems through Convex Optimization

     Payaró Llisterri, Miquel; Pascual Iserte, Antonio; Lagunas Hernandez, Miguel Angel
    IEEE journal on selected areas in communications
    Date of publication: 2007-09
    Journal article

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    MIMO channel metrics  Open access

     Lagunas Hernandez, Miguel Angel; Saladrigas, I.; Pérez Neira, Ana Isabel
    International Conference on Computers and Devices for Communications
    Presentation's date: 2006-12-18
    Presentation of work at congresses

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    Space diversity processing when suitable either at the transmitter side or at the receiver side provides a reduction on the transmitted power for the same received signal quality. The paper discusses the importance of the channel entropy in order to design, derived directly from the channel sounder, first, a system able to decide whether it is worth that the transmitter knows the channel or not (CSIT or Channel State Information at the Transmitter). Second, a channel metric is proposed in order to classify the channel regardless of the Tx-Rx space processing to be used. Among other aspects, this channel classifier would help in designing a vector quantifier to feedback the channel state information to the transmitter when CSIT is required.

  • A convex optimization approach for the robust design of multiuser and multiantenna downlink communication systems

     Payaró Llisterri, Miquel; Pascual Iserte, Antonio; Yuan, Jinhong; Lagunas Hernandez, Miguel Angel
    IEEE Workshop on Signal Processing Advances in Wireless Communications
    Presentation's date: 2006-07
    Presentation of work at congresses

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  • Average Rate Behavior for Cooperative Diversity in Wireless Networks

     Jesus, Gomez; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    IEEE International Symposium on Circuits and Systems
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  • Antenna Arrays: What does it mean a good channel?

     Lagunas Hernandez, Miguel Angel; Pérez Neira, Ana Isabel
    European Conference on Antennas and Propagation
    Presentation of work at congresses

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  • Neuro-fuzzy logic in signal processing for communications:from bits to protocols

     Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel; Morell, A; Bas, J
    Date of publication: 2006-01
    Book chapter

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  • Optimum linear transmitter design for MIMO systems with two QPSK data streams

     Payaró Llisterri, Miquel; Pascual Iserte, Antonio; Lagunas Hernandez, Miguel Angel
    IEEE International Conference on Communications 2006
    Presentation's date: 2006-06
    Presentation of work at congresses

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  • Impact of a line of sight component on the performance of a MIMO system designed under statistical channel knowledge

     Pascual Iserte, Antonio; Payaró Llisterri, Miquel; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    IEEE Workshop on Signal Processing Advances in Wireless Communications
    Presentation's date: 2006-07
    Presentation of work at congresses

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