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  • Beamforming Design and Power Control for Spectrum Sharing Systems  Open access

     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.

    In order to provide wireless services for the current demand of high data rate mobile applications, more spectrally efficient systems are needed. As a matter of fact, the current wireless systems are limited by a frequency splitting spectrum management which in one hand minimizes the multiuser interference but; on the other hand, it precludes the use of wider bandwidth signals. As a more aggressive frequency reuse is targeted (ideally, all transmitters might eventually share the same frequency band), the use of multiple antennas for interference reliving, jointly with a smart power allocation is compulsory. In addition, novel spectrum management regulatory policies are required for ensuring a peaceful coexistence between adjacent spectrum sharing networks and for promoting their development. The aim of this dissertation is provide a beamforming and power allocation design for these novel spectrum sharing systems which are meant to exponentially increase the spectral efficiency of the systems. A mathematical framework based on multicriteria optimization for analyzing the beamforming design is provided which serves as a fundamental tool for describing the state-of-the-art studies in multiantenna interference networks. Indeed, the achievable rates are described and several ways of computing the Pareto rate region of MISO interference channel (i.e. the communication model that represents the spectrum sharing network when the transmitters use multiple antennas) are studied. Nevertheless, as the system designer aims to work in a single efficient rate point, the sum-rate optimal beamforming design is studied. Curiously, it results that under some realistic assumptions on both the desired and interference power levels, the obtained beamformer is the reciprocal version of a known receiving one and it optimizes a notion of antenna directivity for multiuser communications. Neverthelss, it is important to remark that the higher transmit power is used, the more interference dominated is the medium, not only within the wireless network, but also to eventually adjacent networks that might suffer from inter-network interference. In order to cope with this problem, a spectrum licensing system is revisited, namely time-area-spectrum license. Under this spectrum management mechanism, a license holder is able to radiate signals under a certain portion of time, within a concrete area and in a given band. Moreover, the amount of signal strength within the area is constraint by a certain value. Since controlling the signal power levels in a given area is cumbersome, we propose to restrict the receive power as an estimation of the overall accumulated signal strength. Therefore, the optimal transmit beamformers and power allocations are studied. Concretely, the achievable rates are derived and an operational working point is envisaged. In addition, a suboptimal yet low computationally complex and decentralized beamforming design is presented and it shows a good performance in front of other decentralized designs.

  • 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.

  • 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.

  • 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.

  • 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

  • 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.

  • 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.

  • 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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  • 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.

  • 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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  • 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
    Presentation of work at congresses

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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.

  • Access to the full text
    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?

  • A Novel Architecture for the MIMO Multiuser Channel

     Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    ASMSSPSC 2010
    Presentation's date: 2010-09-13
    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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  • 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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    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.

  • 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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  • 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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  • 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.

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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.

  • 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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  • 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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  • 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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  • 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.

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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.

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    A robust maximin approach for MIMO communications with imperfect channel state information based on convex optimization  Open access

     Pascual Iserte, Antonio; Pérez Palomar, Daniel; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    IEEE transactions on signal processing
    Date of publication: 2006-01
    Journal article

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    This paper considers a wireless communication system with multiple transmit and receive antennas, i.e., a multiple-input-multiple-output (MIMO) channel. The objective is to design the transmitter according to an imperfect channel estimate, where the errors are explicitly taken into account to obtain a robust design under the maximin or worst case philosophy. The robust transmission scheme is composed of an orthogonal space–time block code (OSTBC), whose outputs are transmitted through the eigenmodes of the channel estimate with an appropriate power allocation among them. At the receiver, the signal is detected assuming a perfect channel knowledge. The optimization problem corresponding to the design of the power allocation among the estimated eigenmodes, whose goal is the maximization of the signal-to-noise ratio (SNR), is transformed to a simple convex problem that can be easily solved. Different sources of errors are considered in the channel estimate, such as the Gaussian noise from the estimation process and the errors from the quantization of the channel estimate, among others. For the case of Gaussian noise, the robust power allocation admits a closed-form expression. Finally, the benefits of the proposed design are evaluated and compared with the pure OSTBC and nonrobust approaches.

  • Differential Fuzzy Filtering for Adaptive Line Enhancement in Spread Spectrum Communications

     Pérez Neira, Ana Isabel; Joan, Bas; Lagunas Hernandez, Miguel Angel
    Signal processing
    Date of publication: 2006-04
    Journal article

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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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  • Statistical MIMO processing

     Lagunas Hernandez, Miguel Angel; Pérez Neira, Ana Isabel; Pascual Iserte, Antonio
    Second Internacional Symposium on Communications, Control and Signal Processing
    Presentation's date: 2006-03
    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
    Presentation of work at congresses

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  • 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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  • 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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  • 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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  • 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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  • A reduced complesity MIMO broadcast scheme: a way between opportunistic and dirty paper implementation

     Zorba Barah, Nizar; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    European Signal Processing Conference
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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.

  • Method and System for Robustly Transmitting the Minimum Power in Multi-User and Multi-Antenna Communications Systems with Imperfect Channel Knowledge

     Payaró Llisterri, Miquel; Pascual Iserte, Antonio; Lagunas Hernandez, Miguel Angel
    Date of request: 2006-06-28
    Invention patent

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    Convex optimization theory applied to joint transmitter-receiver design in MIMO channels - chapter 8  Open access

     Pérez Palomar, Daniel; Pascual Iserte, Antonio; Cioffi, John M; Lagunas Hernandez, Miguel Angel
    Date of publication: 2005-04-30
    Book chapter

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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 Pérez, Antoni; BAS, J
    Date of publication: 2005-04-22
    Book chapter

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  • Robust scheduling in MIMO-OFDM multi-user systems based on convex optimization

     Morell Pérez, Antoni; Pascual Iserte, Antonio; Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel Angel
    IEEE International Workshop on Computational Advances in Multi-Sensor Adaptive Processing
    Presentation's date: 2005-12
    Presentation of work at congresses

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