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  • Compressive sensing based candidate detector and its applications to spectrum sensing and through-the-wall radar imaging.

     Lagunas Targarona, Eva
    Defense's date: 2014-03-07
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    L¿adquisició de dades es un tema fonamental en el processament de senyals. El teorema de Shannon-Nyquist hasigut la base dels mètodes convencionals de conversió analògic-digital. El teorema diu que per recuperar la informació,qualsevol senyal ha de ser mostrejada a una freqüència igual al doble de la màxima freqüència present a la senyal. Noobstant, aquest teorema assumeix el pitjor dels casos: quan les senyales ocupen tot l'espectre. En aquest context apareix lateoria del mostreig compressiu o Compressed Sensing (CS). CS ha suposat una autèntica revolució pel que fa al'adquisició i mostreig de dades analògiques en un esforç cap a resoldre la problemàtica de recuperar un procés continuocomprimible si únicament es realitza un número molt reduït de mesures del mateix. El requisit para l'èxit d'aquesta tècnicaés que la senyal ha de poder ser expressada de forma dispersa en algun domini. Això és, que la majoria dels seuscomponents siguin zero o es puguin considerar despreciables. L¿aplicació del mostreig compressiu suposa una nova líniagran interès investigador en àrees com la transmissió de dades, imatges mèdiques, biologia computacional, entre altres.A diferència de la majoria de publicacions relacionades amb CS, en aquesta tesi s'estudiarà CS aplicat a detecció,estimació i classificació de senyals, que no requereix la recuperació perfecta ni completa de la senyal. En concret, esproposa un nou detector basat en cert coneixement a priori sobre la senyal a detectar. La idea bàsica és escanejar el dominide la senyal amb una senyal anomenada candidata, que s'obté a partir de la informació que es té a priori de la senyal adetectar.El detector és aplicat a dos problemes particulars de detecció. En primer lloc, la teoria de CS és aplicada al sensatd'espectre. El principal problema radica en que les polítiques actuals d'assignació de bandes freqüencials són massaestrictes i no permeten l'ús òptim de l'espectre disponible. L'ús de l'espectre pot ser millorat si es possibilita que un usuarisecundari (sense llicència) pugui accedir a un canal desocupat per un usuari primari. La radio cognitiva és una solucióprometedora d¿aquest problema. Un requeriment essencial dels dispositius cognitius és la capacitat de detectar lapresència d'usuaris primaris. Un dels problemes que s'afronta en aquest context és la necessitat d'escanejar grans amplesde banda que requereixen freqüències de mostreig elevades. El detector proposat relaxa els requeriments de mostreig, itambé per proporcionar una estimació de la freqüència, potència i angle d'arribada dels usuaris primaris.La segona aplicació és en radars amb visió a través de paret (TWRI). Veure a través de les parets és possiblemitjançant l'enviament d'ones de radio, capaç de travessar objectes opacs, que reboten en els objectius i retornen alsreceptors. Aquest és un tipus de radar amb una gran varietat d'aplicacions, tant civils como militars. La resolució de lasimatges proporcionades per aquests radars millora quan s'usen grans amples de banda i més nombre d'antenes, el quedirectament implica la necessitat d'adquirir un major nombre de mostres i major volum de dades que processar. A vegades,reduir el nombre de mostres és interessant en TWRI des de un punt de vista logístic, ja que pot ser que algunes mostresfreqüencials o espacials siguin difícils o impossibles d'obtenir. En aquesta tesis focalitzarem el treball en la detecciód'estructures internes per reconstruir l'estructura de l'edifici. Les parets i/o díedres formats per la intersecció de dos paretsinternes formaran les nostres senyals candidates per al detector proposat. La validació de la proposta es durà a terme ambexperiments realitzats en el Radar Imaging Lab del Center for Advanced Communications, Villanova University, USA.

  • 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.

  • Design of an hybrid ground-space architecture based on individual on-board antenna power optimization for the forward link of a multi-beam broadband satellite system

     Joroughi, Vahid; Vazquez, Miguel Angel; Devillers, Bertrand; Pérez Neira, Ana Isabel
    AIAA International Communications Satellite Systems Conference
    Presentation's date: 2013-10
    Presentation of work at congresses

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    The multi-beam broadband satellite systems have been deployed to provide broadband services to their under-served geo-graphical area. In one hand, with assuming full frequency reuse among beams the resulting interference requires either a pre- or post-cancellation process. On other hand, by increasing the number of beams, the ground and space units must employ an extensive communication eort on the feeder link (i.e. the link between gateway and satellite) to exchange all of the feed signals, yet maintaining a low processing responsibility to the payload. Since the feeder link spectral resources are scarce, it is desirable to use an on-board beam generation process which leads to a signicant feeder link bandwidth reduction. In this context, a hybrid space/ground processing (i.e. both the gateway and the satellite digitally process the transmitted/received data) shall be employed. This work presents a design of the corresponding on-board beam generation process and precoding in the forward link (i.e. from gateway to users in coverage area) of satellite system. In order to eective limit inter-beam interference, this work also predicts a zero forcing precoding technique taking into account the per feed power constraint for practi- cal issues. To this end, we formulate the precoding problem with considering individual on-board feed in order to ecient and more realistic use of payload power resources. This is done by considering the zero forcing and its relation to the theory of generalized inverse in the linear algebra.

  • Antenna subset selection for spatial modulation: a novel and energy efficient single RF technique

     Ntontin, Konstantinos; Di Renzo, Marco; Pérez Neira, Ana Isabel; Verikoukis, Christos
    IEEE International Conference on Communications
    Presentation's date: 2013-06
    Presentation of work at congresses

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    In this paper, we propose a closed-loop and single RF multiple-input-multiple-output (MIMO) method, particularly suitable for the Uplink of cellular systems, which is based on the low-complexity and recently devised method of Spatial Modulation. By selecting a subset of the available transmit antennas to implement Spatial Modulation based on the instantaneous Bit Error Rate (BER), the proposed method achieves both multiplexing and transmit-diversity gains by utilizing only one RF chain. By taking into account the total power consumption at the transmit side, we numerically show that our proposed method is more energy efficient than the single RF transmit antenna selection method for the same target performance and several MIMO configurations and correlation values among the transmit antennas.

  • Forward link interference mitigation in mobile interactive satellite systems

     Henarejos, Pol; Vazquez, Miguel Angel; Cocco, Giuseppe; Pérez Neira, Ana Isabel
    AIAA International Communications Satellite Systems Conference
    Presentation's date: 2013-10
    Presentation of work at congresses

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    We present the results of the performance evaluation of polarization-time coding and soft interference cancellation in multi-beam satellite systems a ected by co-channel interference in realistic setups. The standard of Broadband Global Area Network service (BGAN) has been considered as reference for the physical layer and realistic interference and channel models have been adopted. The work has been carried out in the framework of the Next Generation Waveform for Increased Spectral E ciency (NGWISE) project founded by the European Space Agency (ESA).

  • Comparison of linear and widely linear processing in MIMO-FBMC systems

     Caus Lopez, Marius; Pérez Neira, Ana Isabel
    IEEE International Symposium on Wireless Communication Systems
    Presentation of work at congresses

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    This paper carries out a comparison between two multi-stream techniques aimed for filter bank multicarrier (FBMC) systems based on the offset quadrature amplitude modulation (OQAM). The first option performs linear processing (LP) and, therefore, it does not take into account the non-circularity property of the transmitted symbols. The second technique considers the FBMC specificities and performs widely linear processing (WLP). With the aim of predicting which solution gives the best performance we have conducted a theoretical analysis that reveals that the technique based on the LP is able to achieve the lowest sum mean square error (MSE) at high SINR in channels with high coherence bandwidth. This holds true when the number of streams (S), and the number of transmit antennas (NT) and receive antennas (NR) are related as follows S = NR = 3, NT = NR. The numerical results show that the LP also gives the best performance in terms of BER if the aforementioned inequality is satisfied and the channel coherence bandwidth is substantially larger than the subcarrier spacing. If not, then the LP exhibits an error floor and the WLP may give better performance, especially at low noise regime.

  • Multi-stream transmission in MIMO-FBMC systems

     Caus Lopez, Marius; Pérez Neira, Ana Isabel
    IEEE International Conference on Acoustics, Speech, and Signal Processing
    Presentation's date: 2013-05
    Presentation of work at congresses

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    This paper addresses the design of MIMO precoding and decoding techniques for the filter bank multicarrier (FBMC) modulation. Existing solutions give satisfactory performance in scenarios with high coherence bandwidth channels. With the aim of increasing the robustness against the channel frequency selectivity, we have rethought the problem, which results in a new subband processing. Simulation-based results show that the proposed solution can achieve similar bit error rates as the OFDMsolution, while the spectral efficiency is increased. These results are theoretically justified. As a conclusion, FBMC becomes attractive in frequency selective channels not only because it relaxes the frame synchronization with respect to OFDM, but also because it presents spatial multiplexing competitive results.

  • SDMA for FBMC with block diagonalization

     Caus Lopez, Marius; Pérez Neira, Ana Isabel; Moretti, Marco
    IEEE International Workshop on Signal Processing Advances in Wireless Communications
    Presentation's date: 2013-06
    Presentation of work at congresses

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    This paper deals with the design of MIMO pre-coding and decoding matrices for the filter bank multicarrier (FBMC) modulation. With the aim of increasing the system throughput we focus on the downlink of a multi-user communication system, where users share the same time slots and frequency resources. In this sense, we revisit the block diagonalization (BD) technique since it provides a good trade-off between complexity and performance. Based on the BD concept, we have formulated a new set of conditions that achieve interference-free data multiplexing in the FBMC context. In addition, we have carried out a theoretical analysis that reveals under what conditions MIMO-FBMC shows superior performance than MIMO-OFDM systems. Simulations results demonstrate that in the cases of study, the proposed solution slightly outperforms the classical BD technique, which can be combined with either OFDM or FBMC systems, in terms of bit error rate.

  • Design of an on-board beam generation process for the forward link of a multibeam broadband satellite system

     Joroughi, Vahid; Devillers, Bertrand; Vazquez, Miguel Angel; Pérez Neira, Ana Isabel
    IEEE Global Communications Conference
    Presentation's date: 2013-12
    Presentation of work at congresses

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    The multi-beam broadband satellite systems have been deployed to provide broadband services to their under-served geo-graphical area. In one hand, with assuming full frequency reuse among beams the resulting interference requires either a pre- or post-cancellation process. On other hand, by increasing the number of beams, the ground and space units must employ an extensive communication eort on the feeder link (i.e. the link between gateway and satellite) to exchange all of the feed signals, yet maintaining a low processing responsibility to the payload. Since the feeder link spectral resources are scarce, it is desirable to use an on-board beam generation process which leads to a signicant feeder link bandwidth reduction. In this context, a hybrid space/ground processing (i.e. both the gateway and the satellite digitally process the transmitted/received data) shall be employed. This work presents a design of the corresponding on-board beam generation process and precoding in the forward link (i.e. from gateway to users in coverage area) of satellite system. In order to eective limit inter-beam interference, this work also predicts a zero forcing precoding technique taking into account the per feed power constraint for practi- cal issues. To this end, we formulate the precoding problem with considering individual on-board feed in order to ecient and more realistic use of payload power resources. This is done by considering the zero forcing and its relation to the theory of generalized inverse in the linear algebra.

  • Performance analysis of multistream spatial modulation with maximum-likelihood detection

     Ntontin, Konstantinos; Di Renzo, Marco; Pérez Neira, Ana Isabel; Verikoukis, Christos
    IEEE Global Communications Conference
    Presentation's date: 2013-12
    Presentation of work at congresses

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    In this paper, we provide a theoretical analysis of the optimal Maximum-Likelihood (ML) detector for the recently proposed multistream Spatial Modulation (SM) concept for multiple-input-multiple-output (MIMO) systems. A Union Bound that is based on closed-form formulas is derived for the average bit error probability (ABEP) of the ML detection, which shows an excellent fit with respect to Monte Carlo simulations for the high signal-to-noise ratio (SNR) region. Furthermore, numerical results for different rates are provided regarding the comparison of the ABEP of multistream SM with ML detection with its recently proposed counterpart with suboptimal detection and with the ABEPs of other well-known MIMO schemes, such as conventional Spatial Multiplexing, Alamouti, and SM, which show its advantage over them. In addition, for the examined MIMO configuration and rates, the relative transmit energy efficiency gain of multistream SM with ML detection over the aforementioned methods is calculated for a low target ABEP.

  • Performance analysis of antenna subset selection in space shift keying systems

     Ntontin, Konstantinos; Di Renzo, Marco; Pérez Neira, Ana Isabel; Verikoukis, Christos
    IEEE International Workshop on Computer-Aided Modeling Analysis and Design of Communication Links and Networks
    Presentation's date: 2013-09
    Presentation of work at congresses

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    In this paper, we provide a performance analysis of closed-loop antenna subset selection in Space Shift Keying (SSK) systems. In particular, we provide a closed-form formula for the Symbol Error Rate (SER) of such systems, which is shown to closely match Monte Carlo simulations. Numerical results also verify the performance enhancement of this closed-loop scheme over the conventional open-loop SSK in the high Signal-to-Noise ratio (SNR) region due to the transmit-diversity gains. In addition, we provide the energy gain that the antenna selection scheme achieves over the open-loop SSK for a target SER.

  • Design of a hybrid ground/space architecture based on individual on-board feed power optimization for the forward link of a multi-beam broadband satellite system

     Joroughi, Vahid; Vazquez, Miguel Angel; Devillers, Bertrand; Pérez Neira, Ana Isabel
    AIAA International Communications Satellite Systems Conference
    Presentation's date: 2013-10
    Presentation of work at congresses

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    The multi-beam broadband satellite systems have been deployed to provide broadband services to their under-served geo-graphical area. In one hand, with assuming full frequency reuse among beams the resulting interference requires either a pre-or post-cancellation process. On other hand, by increasing the number of beams, the ground and space units must employ an extensive communication effort on the feeder link (i.e. the link between gateway and satellite) to exchange all of the feed signals, yet maintaining a low processing responsibility to the payload. Since the feeder link spectral resources are scarce, it is desirable to use an on-board beam generation process which leads to a significant feeder link bandwidth reduction. In this context, a hybrid space/ground processing (i.e. both the gateway and the satellite digitally process the transmitted/received data) shall be employed. This work presents a design of the corresponding on-board beam generation process and precoding in the forward link (i.e. from gateway to users in coverage area) of satellite system. In order to effective limit inter-beam interference, this work also predicts a zero forcing precoding technique taking into account the per feed power constraint for practical issues. To this end, we formulate the precoding problem with considering individual on-board feed in order to efficient and more realistic use of payload power resources. This is done by considering the zero forcing and its relation to the theory of generalized inverse in the linear algebra.

  • SDMA for filterbank with Tomlinson Harashima precoding

     Caus Lopez, Marius; Pérez Neira, Ana Isabel
    IEEE International Conference on Communications
    Presentation's date: 2013-06
    Presentation of work at congresses

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    Several studies have revealed that OFDM is outperformed in several areas by the filter bank based multicarrier (FBMC) modulation thanks to pulse shaping techniques. Nevertheless, the combination of FBMC with multi-antenna architectures is nontrivial. Aiming at making progress towards this direction we study MIMO precoding techniques for the MISO broadcast channel (MISO-BC). Due to its superior performance over linear precoding techniques we have focused on the spatial Tomlinson Harashima precoder (STHP). The analysis carried out in this paper concludes that the conventional STHP performs poorly when it is combined with FBMC systems since it is not able to cope with ISI and ICI. To combat the interferences we propose a novel subband processing based on the STHP concept. The numerical results show that FBMC and OFDM almost give the same performance in terms of BER. However, FBMC is able to achieve spectral efficiency values that are 31% higher in comparison to the ones obtained in OFDM when 20% of the symbol duration corresponds to the cyclic prefix

  • Efficient margin adaptive scheduling for MIMO-OFDMA systems

     Moretti, Marco; Pérez Neira, Ana Isabel
    IEEE transactions on wireless communications
    Date of publication: 2013-01
    Journal article

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  • Adaptive generalized space shift keying

     Ntontin, Konstantinos; Di Renzo, Marco; Pérez Neira, Ana Isabel; Verikoukis, Christos
    Eurasip journal on wireless communication and networking
    Date of publication: 2013-02-21
    Journal article

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    In this article, we propose a closed-loop precoding method for the Generalized Space Shift Keying (GSSK) modulation scheme, suitable for Multiple-Input-Single-Output (MISO) systems and denoted as adaptive GSSK (AGSSK), which achieves transmit-diversity gains in contrast to GSSK. For the case of a perfect feedback channel, we analytically show that for three and four antennas at the transmitter and rates 1 and 2 bits per channel use (bpcu), respectively, a full transmit-diversity can be achieved without reducing the achievable rate. For higher number of transmit antennas and rates, the performance of the proposed scheme degrades due to the smaller average minimum Euclidean distance as the rate increases. Due to this, we, furthermore, propose an enhancing method for AGSSK which relies on the use of time-orthogonal shaping filters for the different constellation points. For the enhanced method, named as AGSSK with time-orthogonal signal design (AGSSK-TOSD), we analytically prove that it offers transmit-diversity gains which are greater than the number of active transmit antennas for any number of transmit antennas and supported rate. This is attained without any antenna subset selection technique, which alleviates the processing burden on the terminal side. Monte Carlo simulations show that AGSSK significantly outperforms GSSK in terms of average bit error probability (ABEP) and, moreover, for medium to high rates and practical signal-to-noise ratio (SNR) regions AGSSK-TOSD outperforms well-known feedback-based multiple-antenna schemes. This advantage of AGSSK-TOSD is further substantiated with an energy effficiency comparison over the conventional schemes for a target (uncoded) ABEP.

  • Multi-stream transmission for highly frequency selective channels in MIMO-FBMC/OQAM systems

     Caus Lopez, Marius; Pérez Neira, Ana Isabel
    IEEE transactions on signal processing
    Date of publication: 2013-12-03
    Journal article

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    This paper addresses the joint design of MIMO precoding and decoding matrices for filter bank multicarrier (FBMC) systems based on OQAM, known as FBMC/OQAM. Existing solutions that support multi-stream transmission only give satisfactory performance in scenarios with high coherence bandwidth channels. To make progress towards the application of FBMC/OQAM to MIMO channels, we study the design of novel solutions that provide robustness against the channel frequency selectivity and support multi-stream transmission. To this end, two techniques have been devised under the criterion of minimizing the sum mean square error. The non-circular nature of the OQAM symbols has not been ignored, making evident the convenience of performing a widely linear processing. The first technique keeps the complexity at a reasonable level but in exchange the original problem is relaxed yielding a suboptimal solution. With the objective of performing closer to the optimum solution, the second option iteratively computes precoders and equalizers by resorting to an alternating optimization method, which is much more complex. We have demonstrated via simulations that the first technique nearly achieves the same results as the iterative design. Simulation results show that the proposed low-complexity solution outperforms existing MIMO-FBMC/OQAM schemes in terms of bit error rate. As for the comparison with OFDM, the numerical results highlight that FBMC/OQAM remains competitive, with and without perfect channel state information, while it provides spectral efficiency gains. Under highly frequency selective channels the proposed technique significantly outperforms OFDM.

  • Low-complexity interference variance estimation methods for coded multicarrier systems: application to SFN

     Caus Lopez, Marius; Pérez Neira, Ana Isabel; Renfors, Markku
    EURASIP Journal on Advances in Signal Processing
    Date of publication: 2013-10-27
    Journal article

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    For single-frequency network (SFN) transmission, the echoes coming from different transmitters are superimposed at the reception, giving rise to a frequency selective channel. Although multicarrier modulations lower the dispersion, the demodulated signal is sensitive to be degraded by inter-symbol interference (ISI) and inter-carrier interference (ICI). In view of this, we use channel coding in conjunction either with filter bank multicarrier (FBMC) modulation or with orthogonal frequency division multiplexing (OFDM). To deal with the loss of orthogonality, we have devised an interference-aware receiver that carries out a soft detection under the assumption that the residual interference plus noise (IN) term is Gaussian-distributed. To keep the complexity low, we propose to estimate the variance of the IN term by resorting to data-aided algorithms. Experimental results show that regardless of the method, FBMC provides a slightly better performance in terms of coded bit error rate than OFDM, while the spectral efficiency is increased when FBMC is considered.

  • A low-complexity method for antenna selection in spatial modulation systems

     Ntontin, Konstantinos; Di Renzo, Marco; Pérez Neira, Ana Isabel; Verikoukis, Christos
    IEEE communications letters
    Date of publication: 2013-11-13
    Journal article

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    In this Letter, a low-complexity Euclidean distance-based method for antenna subset selection in Spatial Modulation systems is presented. The proposed method avoids the high complexity of both the optimal exhaustive search and of a recently proposed Euclidean distance-based algorithm for performing the selection. Moreover, as the number of receive antennas increases and for practical signal-to-noise ratio (SNR) values, it offers better error performance than the conventional transmit antenna selection (TAS) algorithm. In addition, the benefits of the proposed selection scheme, as the number of receive antennas increases, are further substantiated by comparing its relative energy gain over the TAS method for a target uncoded Symbol Error Rate (SER).

  • 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.

  • 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.

  • Subcarrier allocation and power loading strategies for multi-user broadcast FBMC/OQAM systems

     Caus Lopez, Marius; Pérez Neira, Ana Isabel
    European Signal Processing Conference
    Presentation's date: 2012
    Presentation of work at congresses

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    With the objective of maximizing the sum-rate this paper tackles the subcarrier and the power allocation problems in the context of multi-user FBMC. Under highly frequency selective channels the demodulated data is affected by ISI and ICI. As a solution the band is partitioned into three sub- sets so that there is no overlapping between the subcarriers of the same subset. Then we propose a low complexity heuristic to carry out the resource allocation over each sub- set. Simulation-based results demonstrate that at low noise regime, the proposed solution is able to outperform the con- ventional approach

  • 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.

  • Closed-loop spatial modulation with antenna selection

     Wang, Jun-ling; Pérez Neira, Ana Isabel; Meiguo, Gao; Zhang, Qian; Xiaoyan, Bian
    International Conference on Signal Processing
    Presentation's date: 2012-10
    Presentation of work at congresses

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    The closed-loop scheme of spatial modulation (SM), which feeds back the selected transmit antenna subsets to the transmitter, is presented to overcome the constraint in SM that the number of transmit antennas has to be a power of two. This scheme outperforms the classic SM due to the limited feedback information. Motivated by reducing the receiver's complexity of this scheme, some mathematical characteristics of the joint transmit/receive antenna selection algorithm implemented in this paper are exploited.

    The closed-loop scheme of spatial modulation (SM), which feeds back the selected transmit antenna subsets to the transmitter, is presented to overcome the constraint in SM that the number of transmit antennas has to be a power of two. This scheme outperforms the classic SM due to the limited feedback information. Motivated by reducing the receiver's complexity of this scheme, some mathematical characteristics of the joint transmit/receive antenna selection algorithm implemented in this paper are exploited.

  • 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.

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    Adaptive generalized space shift keying (GSSK) modulation for MISO channels: a new method for high diversity and coding gains  Open access

     Ntontin, Konstantinos; Di Renzo, Marco; Pérez Neira, Ana Isabel; Verikoukis, Christos
    IEEE Vehicular Technology Conference
    Presentation's date: 2012-09-03
    Presentation of work at congresses

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    Generalized Space Shift Keying (GSSK) modulation is a recently proposed low-complexity concept for Multiple-Input- Multiple-Output (MIMO) wireless systems. GSSK modulation is a generalized version of Space Shift Keying (SSK) modulation, which provides a better spectral efficiency through multiple active antennas at the transmitter. An apparent weakness of GSSK modulation is that it does not exploit the transmit-antennas to achieve transmit-diversity. In this paper, we propose a precoding method for GSSK modulation, which simultaneously achieves high diversity and coding gains. The solution is based on: i) cophasing the active antennas of each spatial-constellation point; and ii) properly rotating the phases among spatial-constellation points. The new scheme requires Channel State Information at the Transmitter (CSIT), i.e., the channel phases of each wireless link, which can be obtained through a feedback channel. For the case of a perfect feedback channel, we analytically show that for three and four antennas at the transmitter a full transmit diversity can be achieved without reducing the achievable rate. Furthermore, for various MISO configurations and achievable rates we show through Monte Carlo simulations that our proposed scheme outperforms state-of-the-art open-loop GSSK schemes, in terms of both diversity and coding gain, when the number of bits allocated for the quantization of each channel phase is between 2 and 4.

  • Towards the performance and energy efficiency comparison of spatial modulation with conventional single-antenna transmission over generalized fading channels

     Ntontin, Konstantinos; Di Renzo, Marco; Pérez Neira, Ana Isabel; Verikoukis, Christos
    IEEE International Workshop on Computer-Aided Modeling Analysis and Design of Communication Links and Networks
    Presentation's date: 2012-09-17
    Presentation of work at congresses

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    In this paper, we present a performance and energy efficiency comparison of the recently devised single RF Multiple- Input-Multiple-Output (MIMO) concept of Spatial Modulation (SM) with the conventional single-antenna transmission method with receive Maximum Ratio Combining (MRC), which we denote as single-antenna/MRC, for different types of fading channels. In particular, the fading channels that are examined are: i) Rayleigh, ii) Nakagami- m , and iii) Weibull. Results that are based on Monte Carlo simulations show two main findings: i) the severity of fading has a big impact on the relative signal-to- noise (SNR) difference and energy efficiency gain between these two schemes for a target average bit error probability (ABEP); ii) the more severe the fading is, the more suitable SM tends to be with respect to the single antenna/MRC, according to the energy per bit required to achieve a particular low target ABEP.

  • Cooperative communications: from theory to experimental implementation

     Alonso Zárate, Jesús; Sanchez Recacha, Javier; Zorba Barah, Nizar; Pérez Neira, Ana Isabel; Verikoukis, Christos
    IEEE Global Communications Conference
    Presentation's date: 2012-12-03
    Presentation of work at congresses

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    Over the last years, cooperative communications have been studied from both fundamental and practical points of view. However, most of the existing studies of cooperative communications rely on math or computer simulation. In this paper, we describe the implementation of a cooperative communication strategy for wireless networks in a testbed based on Click Modular Router. We describe the methodology we have followed to reprogram the drivers controlling the data layer functions of off-the-shelf commercial Wireless Network Interface Cards (NICs). More precisely, we have implemented a Cooperative Automatic Retransmission (C-ARQ) scheme to show that the performance of wireless communications can be boosted by using an intermediate relay when the wireless channel between the source and the destination is in bad conditions. The results presented in this paper are promising, as they show that previous theory and simulation results presented in the literature can become true in a real implementation.

  • A suboptimal power allocation algorithm for FBMC/OQAM

     Caus Lopez, Marius; Pérez Neira, Ana Isabel
    IEEE International Workshop on Signal Processing Advances in Wireless Communications
    Presentation's date: 2012
    Presentation of work at congresses

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    This paper tackles the sum-rate maximization in FBMC systems. It is well-known that multipath fading destroys the orthogonality of the subcarriers, which brings a non-convex problem that can be interpreted as the maximization of a difference of concave functions. This reformulation enables using DC programming to find the global optimal but the complexity becomes unaffordable in the FBMC context. Aiming at reducing the complexity we have devised a new suboptimal algorithm. The idea consists in smartly partitioning the band into three subsets so that subcarrier signals belonging to the same subset do not overlap in the frequency domain. If subsets maximize sequentially their own rate the original problem is turned into three simpler problems. Simulation-based results show that the sum-rate is in the same order as the water-filling used in OFDM and a suboptimal solution based on DC programming. However, the addressed technique enables saving up to 25% of the power at SNR=22 dB.

  • Performance study of multiuser interference mitigation schemes for hybrid broadband multibeam satellite architectures

     Arnau, Jesus; Devillers, Bertrand; Mosquera, C.; Pérez Neira, Ana Isabel
    Eurasip journal on wireless communication and networking
    Date of publication: 2012-04-05
    Journal article

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  • 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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  • Transmitter-Receiver Designs for Highly Frequency Selective Channels in MIMO FBMC Systems

     Caus Lopez, Marius; Pérez Neira, Ana Isabel
    IEEE transactions on signal processing
    Date of publication: 2012-09-05
    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.

  • A discrete bit loading algorithm for FBMC/OQAM

     Caus Lopez, Marius; Pérez Neira, Ana Isabel; García Armada, Ana
    IEEE signal processing letters
    Date of publication: 2012-06
    Journal article

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    In this letter the discrete rate maximization problem is investigated for FBMC/OQAM. The analysis reveals that if there is crosstalk certain bit allocations violate the power constraints. Aiming at ensuring the feasibility along with alleviating the complexity we have devised a novel iterative algorithm, which always converges. Simulation-based results show that the proposed algorithm performs close to the upper bound for high-coherence bandwidth channels. Under highly frequency selective channels the existing algorithms are not able to guarantee the target SER whereas our approach guarantees the QoS.

  • Self-organized Femtocells: a Time Difference Learning Approach

     Galindo Serrano, Ana María
    Defense's date: 2012-06-11
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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  • GNSS Array-based Acquisition: Theory and Implementation  Open access

     Arribas Lázaro, Javier
    Defense's date: 2012-06-28
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    This Dissertation addresses the signal acquisition problem using antenna arrays in the general framework of Global Navigation Satellite Systems (GNSS) receivers. The term GNSS classi es those navigation systems based on a constellation of satellites, which emit ranging signals useful for positioning. Although the American GPS is already available, which coexists with the renewed Russian Glonass, the forthcoming European contribution (Galileo) along with the Chinese Compass will be operative soon. Therefore, a variety of satellite constellations and signals will be available in the next years. GNSSs provide the necessary infrastructures for a myriad of applications and services that demand a robust and accurate positioning service. The positioning availability must be guaranteed all the time, specially in safety-critical and mission-critical services. Examining the threats against the service availability, it is important to take into account that all the present and the forthcoming GNSSs make use of Code Division Multiple Access (CDMA) techniques. The ranging signals are received with very low precorrelation signal-to-noise ratio (in the order of ���22 dB for a receiver operating at the Earth surface). Despite that the GNSS CDMA processing gain o ers limited protection against Radio Frequency interferences (RFI), an interference with a interference-to-signal power ratio that exceeds the processing gain can easily degrade receivers' performance or even deny completely the GNSS service, specially conventional receivers equipped with minimal or basic level of protection towards RFIs. As a consequence, RFIs (either intentional or unintentional) remain as the most important cause of performance degradation. A growing concern of this problem has appeared in recent times. Focusing our attention on the GNSS receiver, it is known that signal acquisition has the lowest sensitivity of the whole receiver operation, and, consequently, it becomes the performance bottleneck in the presence of interfering signals. A single-antenna receiver can make use of time and frequency diversity to mitigate interferences, even though the performance of these techniques is compromised in low SNR scenarios or in the presence of wideband interferences. On the other hand, antenna arrays receivers can bene t from spatial-domain processing, and thus mitigate the e ects of interfering signals. Spatial diversity has been traditionally applied to the signal tracking operation of GNSS receivers. However, initial tracking conditions depend on signal acquisition, and there are a number of scenarios in which the acquisition process can fail as stated before. Surprisingly, to the best of our knowledge, the application of antenna arrays to GNSS signal acquisition has not received much attention. This Thesis pursues a twofold objective: on the one hand, it proposes novel arraybased acquisition algorithms using a well-established statistical detection theory framework, and on the other hand demonstrates both their real-time implementation feasibility and their performance in realistic scenarios. The Dissertation starts with a brief introduction to GNSS receivers fundamentals, providing some details about the navigation signals structure and the receiver's architecture of both GPS and Galileo systems. It follows with an analysis of GNSS signal acquisition as a detection problem, using the Neyman-Pearson (NP) detection theory framework and the single-antenna acquisition signal model. The NP approach is used here to derive both the optimum detector (known as clairvoyant detector ) and the sov called Generalized Likelihood Ratio Test (GLRT) detector, which is the basis of almost all of the current state-of-the-art acquisition algorithms. Going further, a novel detector test statistic intended to jointly acquire a set of GNSS satellites is obtained, thus reducing both the acquisition time and the required computational resources. The eff ects of the front-end bandwidth in the acquisition are also taken into account. Then, the GLRT is extended to the array signal model to obtain an original detector which is able to mitigate temporally uncorrelated interferences even if the array is unstructured and moderately uncalibrated, thus becoming one of the main contributions of this Dissertation. The key statistical feature is the assumption of an arbitrary and unknown covariance noise matrix, which attempts to capture the statistical behavior of the interferences and other non-desirable signals, while exploiting the spatial dimension provided by antenna arrays. Closed form expressions for the detection and false alarm probabilities are provided. Performance and interference rejection capability are modeled and compared both to their theoretical bound. The proposed array-based acquisition algorithm is also compared to conventional acquisition techniques performed after blind null-steering beamformer approaches, such as the power minimization algorithm. Furthermore, the detector is analyzed under realistic conditions, accounting for the presence of errors in the covariance matrix estimation, residual Doppler and delay errors, and signal quantization e ects. Theoretical results are supported by Monte Carlo simulations. As another main contribution of this Dissertation, the second part of the work deals with the design and the implementation of a novel Field Programmable Gate Array (FPGA)-based GNSS real-time antenna-array receiver platform. The platform is intended to be used as a research tool tightly coupled with software de ned GNSS receivers. A complete signal reception chain including the antenna array and the multichannel phase-coherent RF front-end for the GPS L1/ Galileo E1 was designed, implemented and tested. The details of the digital processing section of the platform, such as the array signal statistics extraction modules, are also provided. The design trade-o s and the implementation complexities were carefully analyzed and taken into account. As a proof-of-concept, the problem of GNSS vulnerability to interferences was addressed using the presented platform. The array-based acquisition algorithms introduced in this Dissertation were implemented and tested under realistic conditions. The performance of the algorithms were compared to single antenna acquisition techniques, measured under strong in-band interference scenarios, including narrow/wide band interferers and communication signals. The platform was designed to demonstrate the implementation feasibility of novel array-based acquisition algorithms, leaving the rest of the receiver operations (mainly, tracking, navigation message decoding, code and phase observables, and basic Position, Velocity and Time (PVT) solution) to a Software De ned Radio (SDR) receiver running in a personal computer, processing in real-time the spatially- ltered signal sample stream coming from the platform using a Gigabit Ethernet bus data link. In the last part of this Dissertation, we close the loop by designing and implementing such software receiver. The proposed software receiver targets multi-constellation/multi-frequency architectures, pursuing the goals of e ciency, modularity, interoperability, and exibility demanded by user domains that require non-standard features, such as intermediate signals or data extraction and algorithms interchangeability. In this context, we introduce an open-source, real-time GNSS software de ned receiver (so-named GNSS-SDR) that contributes with several novel features such as the use of software design patterns and shared memory techniques to manage e ciently the data ow between receiver blocks, the use of hardware-accelerated instructions for time-consuming vector operations like carrier wipe-o and code correlation, and the availability to compile and run on multiple software platforms and hardware architectures. At this time of writing (April 2012), the receiver enjoys of a 2-dimensional Distance Root Mean Square (DRMS) error lower than 2 meters for a GPS L1 C/A scenario with 8 satellites in lock and a Horizontal Dilution Of Precision (HDOP) of 1.2.

    Esta tesis aborda el problema de la adquisición de la señal usando arrays de antenas en el marco general de los receptores de Sistemas Globales de Navegación por Satélite (GNSS). El término GNSS engloba aquellos sistemas de navegación basados en una constelación de satélites que emiten señales útiles para el posicionamiento. Aunque el GPS americano ya está disponible, coexistiendo con el renovado sistema ruso GLONASS, actualmente se está realizando un gran esfuerzo para que la contribución europea (Galileo), junto con el nuevo sistema chino Compass, estén operativos en breve. Por lo tanto, una gran variedad de constelaciones de satélites y señales estarán disponibles en los próximos años. Estos sistemas proporcionan las infraestructuras necesarias para una multitud de aplicaciones y servicios que demandan un servicio de posicionamiento confiable y preciso. La disponibilidad de posicionamiento se debe garantizar en todo momento, especialmente en los servicios críticos para la seguridad de las personas y los bienes. Cuando examinamos las amenazas de la disponibilidad del servicio que ofrecen los GNSSs, es importante tener en cuenta que todos los sistemas presentes y los sistemas futuros ya planificados hacen uso de técnicas de multiplexación por división de código (CDMA). Las señales transmitidas por los satélites son recibidas con una relación señal-ruido (SNR) muy baja, medida antes de la correlación (del orden de -22 dB para un receptor ubicado en la superficie de la tierra). A pesar de que la ganancia de procesado CDMA ofrece una protección inherente contra las interferencias de radiofrecuencia (RFI), esta protección es limitada. Una interferencia con una relación de potencia de interferencia a potencia de la señal que excede la ganancia de procesado puede degradar el rendimiento de los receptores o incluso negar por completo el servicio GNSS. Este riesgo es especialmente importante en receptores convencionales equipados con un nivel mínimo o básico de protección frente las RFIs. Como consecuencia, las RFIs (ya sean intencionadas o no intencionadas), se identifican como la causa más importante de la degradación del rendimiento en GNSS. El problema esta causando una preocupación creciente en los últimos tiempos, ya que cada vez hay más servicios que dependen de los GNSSs Si centramos la atención en el receptor GNSS, es conocido que la adquisición de la señal tiene la menor sensibilidad de todas las operaciones del receptor, y, en consecuencia, se convierte en el factor limitador en la presencia de señales interferentes. Un receptor de una sola antena puede hacer uso de la diversidad en tiempo y frecuencia para mitigar las interferencias, aunque el rendimiento de estas técnicas se ve comprometido en escenarios con baja SNR o en presencia de interferencias de banda ancha. Por otro lado, los receptores basados en múltiples antenas se pueden beneficiar del procesado espacial, y por lo tanto mitigar los efectos de las señales interferentes. La diversidad espacial se ha aplicado tradicionalmente a la operación de tracking de la señal en receptores GNSS. Sin embargo, las condiciones iniciales del tracking dependen del resultado de la adquisición de la señal, y como hemos visto antes, hay un número de situaciones en las que el proceso de adquisición puede fallar. En base a nuestro grado de conocimiento, la aplicación de los arrays de antenas a la adquisición de la señal GNSS no ha recibido mucha atención, sorprendentemente. El objetivo de esta tesis doctoral es doble: por un lado, proponer nuevos algoritmos para la adquisición basados en arrays de antenas, usando como marco la teoría de la detección de señal estadística, y por otro lado, demostrar la viabilidad de su implementación y ejecución en tiempo real, así como su medir su rendimiento en escenarios realistas. La tesis comienza con una breve introducción a los fundamentos de los receptores GNSS, proporcionando algunos detalles sobre la estructura de las señales de navegación y la arquitectura del receptor aplicada a los sistemas GPS y Galileo. Continua con el análisis de la adquisición GNSS como un problema de detección, aplicando la teoría del detector Neyman-Pearson (NP) y el modelo de señal de una única antena. El marco teórico del detector NP se utiliza aquí para derivar tanto el detector óptimo (conocido como detector clarividente) como la denominada Prueba Generalizada de la Razón de Verosimilitud (en inglés, Generalized Likelihood Ratio Test (GLRT)), que forma la base de prácticamente todos los algoritmos de adquisición del estado del arte actual. Yendo más lejos, proponemos un nuevo detector diseñado para adquirir simultáneamente un conjunto de satélites, por lo tanto, obtiene una reducción del tiempo de adquisición y de los recursos computacionales necesarios en el proceso, respecto a las técnicas convencionales. El efecto del ancho de banda del receptor también se ha tenido en cuenta en los análisis. A continuación, el detector GLRT se extiende al modelo de señal de array de antenas para obtener un detector nuevo que es capaz de mitigar interferencias no correladas temporalmente, incluso utilizando arrays no estructurados y moderadamente descalibrados, convirtiéndose así en una de las principales aportaciones de esta tesis. La clave del detector es asumir una matriz de covarianza de ruido arbitraria y desconocida en el modelo de señal, que trata de captar el comportamiento estadístico de las interferencias y otras señales no deseadas, mientras que utiliza la dimensión espacial proporcionada por los arrays de antenas. Se han derivado las expresiones que modelan las probabilidades teóricas de detección y falsa alarma. El rendimiento del detector y su capacidad de rechazo a interferencias se han modelado y comparado con su límite teórico. El algoritmo propuesto también ha sido comparado con técnicas de adquisición convencionales, ejecutadas utilizando la salida de conformadores de haz que utilizan algoritmos de filtrado de interferencias, como el algoritmo de minimización de la potencia. Además, el detector se ha analizado bajo condiciones realistas, representadas con la presencia de errores en la estimación de covarianzas, errores residuales en la estimación del Doppler y el retardo de señal, y los efectos de la cuantificación. Los resultados teóricos se apoyan en simulaciones de Monte Carlo. Como otra contribución principal de esta tesis, la segunda parte del trabajo trata sobre el diseño y la implementación de una nueva plataforma para receptores GNSS en tiempo real basados en array de antenas que utiliza la tecnología de matriz programable de puertas lógicas (en ingles Field Programmable Gate Array (FPGA)). La plataforma está destinada a ser utilizada como una herramienta de investigación estrechamente acoplada con receptores GNSS definidos por software. Se ha diseñado, implementado y verificado la cadena completa de recepción, incluyendo el array de antenas y el front-end multi-canal para las señales GPS L1 y Galileo E1. El documento explica en detalle el procesado de señal que se realiza, como por ejemplo, la implementación del módulo de extracción de estadísticas de la señal. Los compromisos de diseño y las complejidades derivadas han sido cuidadosamente analizadas y tenidas en cuenta. La plataforma ha sido utilizada como prueba de concepto para solucionar el problema presentado de la vulnerabilidad del GNSS a las interferencias. Los algoritmos de adquisición introducidos en esta tesis se han implementado y probado en condiciones realistas. El rendimiento de los algoritmos se comparó con las técnicas de adquisición basadas en una sola antena. Se han realizado pruebas en escenarios que contienen interferencias dentro de la banda GNSS, incluyendo interferencias de banda estrecha y banda ancha y señales de comunicación. La plataforma fue diseñada para demostrar la viabilidad de la implementación de nuevos algoritmos de adquisición basados en array de antenas, dejando el resto de las operaciones del receptor (principalmente, los módulos de tracking, decodificación del mensaje de navegación, los observables de código y fase, y la solución básica de Posición, Velocidad y Tiempo (PVT)) a un receptor basado en el concepto de Radio Definida por Software (SDR), el cual se ejecuta en un ordenador personal. El receptor procesa en tiempo real las muestras de la señal filltradas espacialmente, transmitidas usando el bus de datos Gigabit Ethernet. En la última parte de esta Tesis, cerramos ciclo diseñando e implementando completamente este receptor basado en software. El receptor propuesto está dirigido a las arquitecturas de multi-constalación GNSS y multi-frecuencia, persiguiendo los objetivos de eficiencia, modularidad, interoperabilidad y flexibilidad demandada por los usuarios que requieren características no estándar, tales como la extracción de señales intermedias o de datos y intercambio de algoritmos. En este contexto, se presenta un receptor de código abierto que puede trabajar en tiempo real, llamado GNSS-SDR, que contribuye con varias características nuevas. Entre ellas destacan el uso de patrones de diseño de software y técnicas de memoria compartida para administrar de manera eficiente el uso de datos entre los bloques del receptor, el uso de la aceleración por hardware para las operaciones vectoriales más costosas, como la eliminación de la frecuencia Doppler y la correlación de código, y la disponibilidad para compilar y ejecutar el receptor en múltiples plataformas de software y arquitecturas de hardware. A fecha de la escritura de esta Tesis (abril de 2012), el receptor obtiene un rendimiento basado en la medida de la raíz cuadrada del error cuadrático medio en la distancia bidimensional (en inglés, 2-dimensional Distance Root Mean Square (DRMS) error) menor de 2 metros para un escenario GPS L1 C/A con 8 satélites visibles y una dilución de la precisión horizontal (en inglés, Horizontal Dilution Of Precision (HDOP)) de 1.2.

  • 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.

  • GRE3N-LINK-MAC. Conceptos radio generales para comunicaciones móviles eficientes energéticamente: aspectos de las capas de enlace y de acceso al medio

     Pérez Neira, Ana Isabel; Najar Marton, Montserrat; Caus Lopez, Marius; Lagunas Targarona, Eva; Pascual Iserte, Antonio
    Participation in a competitive project

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  • Network of Excellence in Wireless COMmunications #

     Pascual Iserte, Antonio; Pérez Neira, Ana Isabel; Najar Marton, Montserrat; Agusti Comes, Ramon; Umbert Juliana, Anna; Casadevall Palacio, Fernando-jose; Pérez Romero, Jordi
    Participation in a competitive project

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  • 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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  • Hybrid Space-Ground Processing for High-Capacity Multi-beam Satellite Systems

     Arnau Yañez, J; Bergmann, N; Candreva, E. A.; Corazza, G. E.; de Gaudenzi, R.; Devillers, Bertrand; Gappmair, W; Lombardo, F.; Mosquera, C.; Pérez Neira, Ana Isabel; Thibault, I.; Vanelli-Coralli, A.
    IEEE Global Communications Conference
    Presentation's date: 2011
    Presentation of work at congresses

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    Signal processing in satellite applications is usually performed either on-ground or on-board, i.e. at the gateway station or in the payload. Within the framework of the European Space Agency (ESA) SatNEx III study, a hybrid approach has been considered by splitting the processing between the satellite and the gateway, aiming to strike a better balance between performance and payload complexity. The design of a highcapacity multi-beam system has been carried out, to assess the potential applicability of a hybrid space-ground processing architecture (DIGISAT) for satellite broadband systems; this is achieved via hybrid space-ground beamforming, MIMO and MIMO-MUD, Precoding, as well as Digital Feeder link techniques.

  • Centralized vs distributed resource allocation in multi cell OFDMA systems

     Cicalò, Sergio; Tralli, Velio; Pérez Neira, Ana Isabel
    IEEE Vehicular Technology Conference
    Presentation's date: 2011
    Presentation of work at congresses

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    Radio Resource Management with Inter-cell Interference Coordination (ICIC), is a key issue under investigation for next generation wireless systems such as Long Term Evolution (LTE). Although centralized resource allocation (RA) and collaborative processing can optimally perform ICIC, the overall required complexity suggests the consideration of distributed techniques. In this paper we propose and compare a centralized RA strategy aimed at maximizing the sum-rate of a multi-cell clustered system in presence of power and fairness constraints, and a distributed RA strategy where inter-cell interference is partially coordinated through power planning schemes with preassigned power (an example is fractional frequency reuse). The distributed RA strategy reduces both signaling and feedback requirements, preserves intra-cell fairness and jointly works with a load balancing algorithm to support inter-cell fairness. We show in the results that the distributed RA with aggressive frequency reuse is able to approach the performance of the centralized RA when the number of users is large, while preserving the same level of fairness.

  • Power Balancing in FBMC-MISO Systems

     Caus Lopez, Marius; Pérez Neira, Ana Isabel
    European Signal Processing Conference
    Presentation's date: 2011-08-28
    Presentation of work at congresses

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  • Advanced interference mitigation techniques for the forward link of multi-beam broadband satellite systems

     Devillers, Bertrand; Pérez Neira, Ana Isabel
    Asilomar Conference on Signals, Systems & Computers
    Presentation's date: 2011-11-08
    Presentation of work at congresses

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    High throughput satellite systems are expected to rely in the user link on multi-beam architectures with small beam footprints and strong frequency reuse among beams, and will therefore operate in an interference limited regime. In this paper, the focus is set on the forward link of a multi-beam broadband satellite system, and linear precoding is considered to mitigate this increased level of interference among users. The contribution of the present work is twofold. First, assuming a single gateway scenario, we analytically prove the benefit of considering the precoding in the feed space, that is, not considering the presence of on-board beamforming. Second, for taking into account realistic feeder link bandwidth restrictions, we consider a multiple gateways scenario where each gateway is serving a cluster of adjacent cells. We propose an architecture which includes precoding in the feed space at each gateway, and derive a zero-forcing precoder design which mitigates both the inter and intra-cluster interfere ce.

  • Descentralized Beamforming for the Interference Channel

     Pérez Neira, Ana Isabel; Vázquez, Miguel A.
    Seminar at Technische Universität Vien
    Presentation's date: 2011-04
    Presentation of work at congresses

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  • Joint linear precoding and beamforming for the forward link of multi-beam broadband satellite systems

     Devillers, Bertrand; Pérez Neira, Ana Isabel; Mosquera, C.
    IEEE Global Communications Conference
    Presentation's date: 2011-12-08
    Presentation of work at congresses

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    Next generation high throughput satellite systems are expected to rely on the deployment of a high number of beams in the user link, and therefore operate in an interference limited regime. This paper builds on the combination of advanced interference mitigation techniques and on-ground beamforming to cope with this increased level of interference among users. Focussing on the forward link of a multi-beam broadband satellite system, we consider the joint design of linear precoding and on-ground beamforming at the gateway. This joint design is modeled, and different linear precoding techniques are considered for comparison. The provided simulation results quantify the performance gain generated by this joint design with respect to considering precoding for a fixed on-board beamforming. The robustness of the considered scheme to channel estimation errors is also analyzed.

  • Transmit and receive filters for MISO FBMC systems subjected to power constraints

     Caus Lopez, Marius; Pérez Neira, Ana Isabel
    IEEE International Conference on Acoustics, Speech and Signal Processing
    Presentation's date: 2011-05
    Presentation of work at congresses

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    Build upon the OFDM/OQAM scheme this paper addresses the design of linear transmit and receive filters. Aiming at enhancing the robustness against multipath fading, two novel techniques are proposed. The first one jointly designs transmit and receive filters under the MMSE criterion. The second scheme follows a ZF approach. In this case transmit and receive filters are independently devised. Pre-equalizers obtained by both strategies are subjected to power constraints. Simulation-based results show that the two proposed techniques benefit from having perfect channel knowledge at both ends of the link to outperform the Alamouti scheme. The best performance in terms of BER is given when transmit and receive filters are jointly designed.