abstract: The ability to identify unoccupied resources in the radio spectrum is a key capability for opportunistic users in a cognitive radio environment. This paper draws upon and extends geometrically based ideas in statistical signal processing to develop estimators for the rank and the occupied subspace in a multi-user environment from multiple temporal samples of the signal received at a single antenna. These estimators enable identification of resources, such as the orthogonal complement of the occupied subspace, that may be exploitable by an opportunistic user. This concept is supported by simulations showing the estimation of the number of users in a simple CDMA system using a maximum a posteriori (MAP) estimate for the rank. It was found that with suitable parameters, such as high SNR, sufficient number of time epochs and codes of appropriate length, the number of users could be correctly estimated using the MAP estimator even when the noise variance is unknown. Additionally, the process of identifying the maximum likelihood estimate of the orthogonal projector onto the unoccupied subspace is discussed. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2014

abstract: Multiple-input multiple-output systems have gained focus in the last decade due to the benefits they provide in enhancing the quality of communications. On the other hand, full-duplex communication has attracted remarkable attention due to its ability to improve the spectral efficiency compared to the existing half-duplex systems. Using full-duplex communications on MIMO co-operative networks can provide us solutions that can completely outperform existing systems with simultaneous transmission and reception at high data rates. This thesis considers a full-duplex MIMO relay which amplifies and forwards the received signals, between a source and a destination that do not a have line of sight. Full-duplex mode raises the problem of self-interference. Though all the links in the system undergo frequency flat fading, the end-to-end effective channel is frequency selective. This is due to the imperfect cancellation of the self-interference at the relay and this residual self-interference acts as intersymbol interference at the destination which is treated by equalization. This also leads to complications in form of recursive equations to determine the input-output relationship of the system. This also leads to complications in the form of recursive equations to determine the input-output relationship of the system. To overcome this, a signal flow graph approach using Mason's gain formula is proposed, where the effective channel is analyzed with keen notice to every loop and path the signal traverses. This gives a clear understanding and awareness about the orders of the polynomials involved in the transfer function, from which desired conclusions can be drawn. But the complexity of Mason's gain formula increases with the number of antennas at relay which can be overcome by the proposed linear algebraic method. Input-output relationship derived using simple concepts of linear algebra can be generalized to any number of antennas and the computation complexity is comparatively very low. For a full-duplex amplify-and-forward MIMO relay system, assuming equalization at the destination, new mechanisms have been implemented at the relay that can compensate the effect of residual self-interference namely equal-gain transmission and antenna selection. Though equal-gain transmission does not perform better than the maximal ratio transmission, a trade-off can be made between performance and implementation complexity. Using the proposed antenna selection strategy, one pair of transmit-receive antennas at the relay is selected based on four selection criteria discussed. Outage probability analysis is performed for all the strategies presented and detailed comparison has been established. Considering minimum mean-squared error decision feedback equalizer at the destination, a bound on the outage probability has been obtained for the antenna selection case and is used for comparisons. A cross-over point is observed while comparing the outage probabilities of equal-gain transmission and antenna selection techniques, as the signal-to-noise ratio increases and from that point antenna selection outperforms equal-gain transmission and this is explained by the fact of reduced residual self-interference in antenna selection method. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2018

abstract: As the number of devices with wireless capabilities and the proximity of these devices to each other increases, better ways to handle the interference they cause need to be explored. Also important is for these devices to keep up with the demand for data rates while not compromising on industry established expectations of power consumption and mobility. Current methods of distributing the spectrum among all participants are expected to not cope with the demand in a very near future. In this thesis, the effect of employing sophisticated multiple-input, multiple-output (MIMO) systems in this regard is explored. The efficacy of systems which can make intelligent decisions on the transmission mode usage and power allocation to these modes becomes relevant in the current scenario, where the need for performance far exceeds the cost expendable on hardware. The effect of adding multiple antennas at either ends will be examined, the capacity of such systems and of networks comprised of many such participants will be evaluated. Methods of simulating said networks, and ways to achieve better performance by making intelligent transmission decisions will be proposed. Finally, a way of access control closer to the physical layer (a 'statistical MAC') and a possible metric to be used for such a MAC is suggested. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2014

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / La ComÃdie Antique athÃnienne, dont le plus grand reprÃsentant est Aristophane, se caractÃrise essentiellement par le mÃlange des genres littÃraires et thÃÃtrales. Entre les genres qui participent de sa composition, il se met en Ãvidence le mime (ou la farse), un quatriÃme type de drame qui est peu connu et que, contrairement à la tragÃdie, la comedie et le drame satyrique, nâas pas Ãtà dÃveloppà en Attique, mais en rÃgion dorienne, et MÃgare Ãtait le lieu le plus important de son travail. Dans Les GuÃpes, ce mime est Ãvoquà par Xantias avec le ton pÃjoratif, mais, au bout de la piÃce, le personnage PhiloclÃon se transforme de faÃon vraiment ridicule en danceur farsesque, comme il faisaient les personnages des mimes. Le thÃÃtre farsesque de MÃgare est aussi Ãvoquà dans La Paix et Ãgalement exploità dans Les Acharniens, par le personnage du MÃgarien, et dans Les Grenouilles, par les personnages HÃraclÃs et Empousa. Ces personnages ont eu une participation rÃguliÃre dan le mime dorien. Comme le thÃme et les personnages, les âgrossiÃretÃsâ dâAristophane caractÃrisent chez le poÃte un ÃlÃment particulier, de ton farsesque, obscÃne, vulgaire et populaire, qui dispose Ãgalement ce quatriÃme genre dramatique. Cela lÃgitime la discussion sur les influences possibles de la farce dorienne sur la comÃdie dâ Aristophane. / A ComÃdia Antiga ateniense, cujo maior representante à AristÃfanes, à essencialmente caracterizada pela mistura de gÃneros literÃrios e teatrais. Entre os gÃneros que participam de sua composiÃÃo, destaca-se o mimo (ou farsa), um quarto tipo de drama do qual pouco se sabe e que, diferente da tragÃdia, da comÃdia e do drama satÃrico, nÃo se desenvolveu na Ãtica, mas em regiÃo dÃrica, atuando principalmente em MÃgara. Em Vespas, esse mimo à evocado de modo pejorativo por XÃntias, mas, ao final da peÃa, a personagem FiloclÃon ridiculamente se tranforma num verdadeiro danÃarino farsesco, semelhante ao que faziam as personagens daquele drama. O teatro farsesco de MÃgara à tambÃm mencionado em Paz, atravÃs da figura do poeta CÃrcino, e igualmente explorado em Acarnenses, na personagem do Megarense, e em RÃs, nas personagens HÃracles e Empusa. Estes tinham participaÃÃo assÃdua no mimo dÃrico. Assim como o tema e as personagens, as âgrosseriasâ de AristÃfanes caracterizam na obra do poeta um elemento peculiar, de tom farsesco, obsceno, vulgar e popular, que tambÃm caracteriza aquele quarto gÃnero dramÃtico. Isso legitima a discussÃo sobre as possÃveis influÃncias da farsa dÃrica sobre a comÃdia de AristÃfanes.

Abstract Radio link adaptation, multiple antenna techniques, relaying methods and dynamic radio resource assignment are among the key methods used to improve the performance of wireless communication networks. Opportunistic resource block (RB) allocation in downlink orthogonal frequency division multiple access (OFDMA) with limited feedback is considered. The spectral efficiency analysis of multiuser OFDMA with imperfect feedback path, multiple antenna methods and relaying methods is a particular focus. The analysis is derived for best-M feedback methods and for a RB-wise signal-to-noise ratio (SNR) quantization based feedback strategy. Practical resource fair round robin (RR) allocation is assumed at the RB assignment, i.e., each user gets the same portion of the available RBs. The fading of each RB is modelled to be independent and identically distributed (IID). This assumption enabled a communication theoretic approach for the performance evaluation of OFDMA systems The event probabilities related to the considered OFDMA systems are presented so that the feedback bit error probability (BEP) is a parameter in the expressions. The performance expressions are derived for the BEP in the case of binary phase-shift keying (BPSK) modulation and single antenna methods. Asymptotic BEP behavior is considered for the best-M feedback methods when the mean SNR tends to infinity. The system outage capacity and the average system spectral efficiency are investigated in the case of multiple antenna schemes. Antenna selection and space-time block coding (STBC) are considered in multiple antenna schemes when each RB is allocated exclusively to a single user. Simple OFDMA-spatial division multiple access (SDMA) schemes are also analyzed when zero forcing (ZF) detection is assumed at the receiver. Relay enhanced dynamic OFDMA with single and multiple antennas at each end is considered for fixed infrastructure amplify-and-forward (AF) relaying methods. The average spectral efficiency has been derived for the best-M and RB-wise one bit feedback schemes, antenna selection and STBC methods. The best choice for a combination of multiple antenna scheme and feedback strategy depends on several system parameters. The proposed analytical tools enable easy evaluation of the performance of the investigated schemes with different system parameters. The fundamental properties of the combinations of feedback and multiple antenna schemes are extensively studied through numerical examples. The results also demonstrate that the analytical results with idealized IID fading assumption are close to those obtained via simulations in a practical frequency selective channel when RBs are selected properly. Dynamic RB allocation is attractive for practical OFDMA systems since significant performance gain over random allocation can be achieved with a practical allocation principle, very low feedback overhead and an imperfect feedback channel.

The aim of the thesis is to find out the most suitable channel estimation algorithms for the existing MIMO-OFDM SDR platform. Starting with the analysis of several prevalent channel estimation algorithms, MSE performance are compared under different scenarios. As a result of the hardware independent analysis, the complexvalued matrix computations involved in the algorithms are decomposed to real FLoating-point OPerations (FLOPs). Four feasible algorithms are selected for hardware dependent discussion based on the proposed hardware architecture. The computational latency is exposed as a manner of case study.

Next generation wireless systems will support higher data rates, improved spectral efficiency, and less latency. Massive multiple-input multiple-output (MIMO) is proposed to satisfy these demands. In massive MIMO, many benefits come from employing hundreds of antennas at the base station (BS) and serving dozens of user terminals (UTs) per cell. As the number of antennas increases at the BS, the channel becomes sparse. By exploiting sparse channel in massive MIMO, compressive sensing (CS) methods can be implemented to estimate the channel. In CS methods, the length of pilot sequences can be shortened compared to pilot-based methods. In this paper, a novel channel estimation algorithm based on a CS method called elastic net is proposed. Channel estimation accuracy of pilot-based, lasso, and elastic-net based methods in massive MIMO are compared. It is shown that the elastic-net based method gives the best performance in terms of error for the less pilot symbols and SNR values.

Ce travail de thèse présente une stratégie de transmission exploitant la diversité spatiale pour la transmission d'images sur canal sans fil. On propose ainsi une approche originale mettant en correspondance la hiérarchie de la source avec celle des sous-canauxSISO issus de la décomposition d'un canal MIMO. On évalue les performances des précodeurs usuels dans le cadre de cette stratégie via une couche physique réaliste, respectant la norme IEEE802.11n, et associé à un canal de transmission basé sur un modèle de propagation à tracé de rayons 3D. On montre ainsi que les précodeurs usuels sont mal adaptés pour la transmission d'un contenu hiérarchisé. On propose alors un algorithme de précodage allouant successivement la puissance sur les sous-canaux SISO afin de maximiser la qualité des images reçues. Le précodeur proposé permet d'atteindre un TEB cible compte tenu ducodage canal, de la modulation et du SNR des sous-canaux SISO. A partir de cet algorithme de précodage, on propose une solution d'adaptation de lien permettant de régler dynamiquement les paramètres de la chaîne en fonction des variations sur le canal de transmission. Cette solution détermine la configuration de codage/transmission maximisant la qualité de l'image en réception. Enfin, on présente une étude sur la prise en compte de contraintes psychovisuelles dans l'appréciation de la qualité des images reçues. On propose ainsi l'intégration d'une métrique à référence réduite basée sur des contraintes psychovisuelles permettant d'assister le décodeur vers la configuration de décodage offrant la meilleure qualité d'expérience. Des tests subjectifs confirment l'intérêt de l'approche proposée. / This thesis presents a transmission strategy for exploiting the spatial diversity for image transmission over wireless channel. We propose an original approach based on the matching between the source hierarchy and the SISO sub-channels hierarchy, resulting from the MIMO channel decomposition. We evaluate common precoder performance in the context of this strategy via a realistic physical layer respecting the IEEE802.11n standard and associated with a transmission channel based on a 3D-ray tracer propagation model. It is shown that common precoders are not adapted for the transmission of a hierarchical content. Then, we propose a precoding algorithm which successively allocates power over SISO subchannels in order to maximize the received images quality. The proposed precoder achieves a target BER according to the channel coding, the modulation and the SISO subchannels SNR. From this precoding algorithm, we propose a link adaptation scheme to dynamically adjust the system parameters depending on the variations of the transmission channel. This solution determines the optimal coding/transmission configuration maximizing the image quality in reception. Finally, we present a study for take into account some psychovisual constraints in the assessment of the received images quality. We propose the insertion of a reduced reference metric based on psychovisual constraints, to assist the decoder in order to determine the decoding configuration providing the highest quality of experience. Subjective tests confirm the interest of the proposed approach.

Abstract Broadband single-carrier modulated signals experience severe multipath distortion when propagating through the physical medium. Correcting the distortion with channel equalization is the foremost task of the detector. Prior information about the transmitted signals in the form of channel decoder feedback can significantly enhance equalization accuracy. An algorithm that iteratively performs channel decoding and equalization with prior information is generally denoted a turbo equalizer. This thesis focuses on turbo equalization with prior information using the principle of interference cancellation followed by minimum mean squared error (MMSE) filtering. Receiver algorithms, receiver convergence, and coding and modulation in the context of MMSE turbo equalization are studied. Computationally efficient versions of the receiver algorithm through approximate time-average filtering, matched filtering, square-root time-variant filtering and frequency-domain filtering are studied. The frequency-domain turbo equalizer (FDTE) is found to exhibit both superior convergence and low computational complexity among the compared equalizer algorithms. Multi-dimensional extrinsic information transfer (EXIT) charts are introduced for the purpose of tracking the convergence of the turbo equalization of layered MIMO transmissions. Generic properties of the equalizer EXIT functions defining the equalizer convergence are analyzed. The principles for detector ordering, maximum sum-rate code design and maximum rate symmetric design are derived from the properties of the multidimensional EXIT functions. Semi-analytical EXIT charts are developed for the convergence analysis of the FDTE. The effects of channel parameters and the channel code are analyzed with semi-analytical methods. A new approach for the design of irregular low-density parity-check (LDPC) codes using a convergence outage principle is proposed. A performance gain is demonstrated in a single-input multiple output (SIMO) channel over non-optimized regular LDPC codes and irregular LDPC codes optimized for the AWGN channel. The outage convergence based design, which takes advantage of the semi-analytical convergence analysis method, is also extended to layered MIMO transmissions. Quadrature amplitude modulation using multilevel bit-interleaved coded modulation (MLBICM) is studied as an alternative to regular bit-interleaved coded modulation (BICM) for highly bandwidth-efficient transmission in MMSE turbo equalized systems. A linear bit-to-symbol mapping is introduced that enables the use of a computationally efficient MMSE turbo equalizer at the receiver. The proposed coded modulation is compared with BICM in channel measurement data based simulations and found to exhibit superior robustness against changes in spatial channel parameters. An automatic repeat request (ARQ) configuration using one ARQ controller for each equally performing group of code levels is proposed. The configuration takes advantage of the unequal error protection (UEP) property of the coded modulation. The semi-analytical convergence analysis is extended to the multilevel modulated case and applied in a channel measurement based convergence evaluation. The construction of the MLBICM is found to have an inherently better convergence behavior than BICM. Finally, the outage convergence based channel code design is extended to the layered MIMO multilevel signalling case.

Abstract The multiple–input multiple–output (MIMO) technique, applying several transmit and receive antennas in wireless communications, has emerged as one of the most prominent technical breakthroughs of the last decade. Wideband MIMO parameter estimation and its applications to the MIMO orthogonal frequency division multiplexing (MIMO–OFDM) channel estimation and mobile positioning are studied in this thesis. Two practical MIMO channel models, i.e., correlated-receive independent-transmit channel and correlated-transmit-receive channel, and associated space-time parameter estimation algorithms are considered. Thanks to the specified structure of the proposed training signals for multiple transmit antennas, the iterative quadrature maximum likelihood (IQML) algorithm is applied to estimate the time delay and spatial signature for the correlated-receive independent-transmit MIMO channels. For the correlated-transmit-receive MIMO channels, the spatial signature matrix corresponding to a time delay can be further decomposed in such a way that the angle of arrival (AOA) and the angle of departure (AOD) can be estimated simultaneously by the 2-D unitary ESPRIT algorithm. Therefore, the combination of the IQML algorithm and the 2-D unitary ESPRIT algorithm provides a novel solution to jointly estimate the time delay, the AOA and the AOD for the correlated-transmit-receive MIMO channels. It is demonstrated from the numerical examples that the proposed algorithms can obtain good performance at a reasonable cost. Considering the correlated-receive independent-transmit MIMO channels, channel coefficient estimation for the MIMO–OFDM system is studied. Based on the parameters of the correlated-receive independent-transmit MIMO channels, the channel statistics in terms of the correlation matrix are developed. By virtue of the derived channel statistics, a joint spatial-temporal (JST) filtering based MMSE channel estimator is proposed which takes full advantage of the channel correlation properties. The mean square error (MSE) of the proposed channel estimator is analyzed, and its performance is also demonstrated by Monte Carlo computer simulations. It is shown that the proposed JST minimum mean square error (MMSE) channel estimator outperforms the more conventional temporal MMSE channel estimator in terms of the MSE when the signals in the receive antenna array elements are significantly correlated. The closed form bit error probability of the space-time block coded OFDM system with correlation at the receiver is also developed by taking the channel estimation errors and channel statistics, i.e., correlation at the receiver, into account. Mobile positioning in the non-line of sight (NLOS) scenarios is studied. With the knowledge of the time delay, the AOA and the AOD associated with each NLOS propagation path, a novel geometric approach is proposed to calculate the MS's position by only exploiting two NLOS paths. On top of this, the least squares and the maximum likelihood (ML) algorithms are developed to utilize multiple NLOS paths to improve the positioning accuracy. Moreover, the ML algorithm is able to estimate the scatterers' positions as well as those of the MSs. The Cramer-Rao lower bound related to the position estimation in the NLOS scenarios is derived. It is shown both analytically and through computer simulations that the proposed algorithms are able to estimate the mobile position only by employing the NLOS paths.