Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Zugl.: Hamburg, Techn. Univ., Habil.-Schr., 2006 / Erscheinungsjahr auf der Haupttitels.: 2006

Zugl.: Bremen, Universiẗat, Diss., 2009.

Zugl.: Ilmenau, Techn. Univ., Diss., 2009

The increasing number of portable devices, such as Smart phones, laptops, tablets etc, has certainly pushed up the market of wireless communication systems. These high performance devices need to comply with the strict requirements in terms of energy consumption. Battery capacity progress is relatively slower compared with the technological evolution of devices. Therefore, energy consumption issues can be solved when innovations are introduced in the processor design and architecture side. This thesis focuses on the word-length optimization for algorithms that run on wireless receivers with multiple antennas (MIMO). The study was made for the signal’s quantization. Earlier experiments have shown that the signal conversion from floating–point to fixed–point representation requires unaffordable Bit-Error-Rate (BER) simulations that may last for hours or even for days. During this thesis, a new divide-and-conquer method has been developed. It faces the ‘quantization problem’ hierarchically by grouping signals and exploiting the correlation between quantization error and Gaussian additive noise. BER simulations were limited by involving noise simulations. This method was successfully applied to a highly adaptive digital signal processing (DSP) algorithm, improving the total simulation time up to 84%. / Η αυξανόμενος αριθμός των κινητών συσκευών, όπως τα Smart phones, laptops, tablets κλπ, έχει εκτοξεύσει υψηλά την αγορά των ασύρματων συσκευών επικοινωνίας. Αυτές οι συσκευές υψηλής τεχνολογίας πρέπει να συμμορφώνονται με τις αυστηρές απαιτήσεις στα πλαίσια της κατανάλωσης ενέργειας. Η πρόοδος της αύξησης της χωρητικότητας της μπαταρίας χαρακτηρίζεται σχετικά αργή συγκρινόμενη με την τεχνολογική εξέλιξη των συσκευών. Ως εκ τούτου, θέματα που αφορούν στην κατανάλωση ενέργειας αντιμετωπίζονται όταν πραγματοποιούνται καινοτομίες στον τομέα της σχεδίασης και αρχιτεκτονικής επεξεργαστών. Η παρούσα διατριβή εστιάζει στην βελτιστοποίηση των μηκών λέξεων (word-length optimization) για αλγορίθμους που τρέχουν σε ασύρματους δέκτες με πολλαπλές κεραίες (MIMO). Η μελέτη αφορά στην κβαντοποίηση σημάτων (signal quantization). Προηγούμενα πειράματα έδειξαν ότι η μετατροπή των σημάτων άπειρης ακρίβειας (floating-point) σε πεπερασμένης (fixed-point) απαιτεί χρονοβόρες Bit-Error-Rate (BER) προσομοιώσεις που μπορεί να διαρκέσουν πολλές ώρες ή ακόμη και ημέρες. Κατά την διάρκεια της διπλωματικής εργασίας, αναπτύχθηκε μία νέα divide-and-conquer μέθοδος. Αντιμετωπίζει το πρόβλημα της κβαντοποίησης ιεραρχικά ομαδοποιώντας τα σήματα και εκμεταλλεύοντας την συσχέτιση του σφάλματος κβαντοποίσης (quantization error) και του προσθετικού Γκαουσιανού θορύβου (AWGN). Οι BER προσoμοιώσεις περιορίστηκαν περιλαμβάνοντας προσομοιώσεις θορύβου (noise simulations). Αυτή η μέθοδος εφαρμόστηκε επιτυχώς σε πολύπλοκο αλγόριθμο υψηλής προσαρμοστικότητας για DSP, βελτιώνοντας τον συνολικό χρόνο προσομοίωσης έως και 84%.

Cooperative diversity exploits the broadcast nature of wireless channels and uses relays to improve link reliability. Most cooperative communication protocols are assumed to be synchronous in nature, which is not always possible in wireless communication. Also the relay nodes are assumed to be half duplex which in turn reduces the spectral efficiency. In this thesis, we first present a novel asynchronous cooperative communication protocol exploiting polarization diversity, which does not require synchronization at the relay node. Dual polarized antennas are employed at the relay node to achieve full duplex amplify-and-forward (ANF) communication. Hence the transmission duration is reduced which results into an increased throughput rate. Capacity analysis of the proposed scheme ascertains the high data rate as compared to conventional ANF. Bit error rate (BER) simulation also shows that the proposed scheme significantly outperforms both the non-cooperative single-input single-output and the conventional ANF schemes. Considering channel path loss, the proposed scheme consume less total transmission energy as compared to ANF and non-cooperative scheme in more practical distance range. Thus the proposed scheme is suitable for high rate and energy efficient relay-enabled communication. In addition to that, we also present a novel power allocation scheme for multiple relay nodes that results in efficient cooperative multiple-input multiple-output (MIMO) communication. Considering channel path loss, the total transmission energy is distributed between the source and the relay nodes. The energy distribution ratio between the relay and direct link is optimized such that the quality of received signal is maintained with minimum total transmission energy consumption. We calculate the energy distribution ratio analytically and verified it through computer simulation. With the new power allocation scheme, the system also obtains an increased channel capacity as compared to cooperative scheme with conventional equal power allocation and non-cooperative scheme. Optimal relay positioning with proposed energy allocation scheme is also explored to maximize the capacity.

La facilité de déploiement et la flexibilité des technologies sans fil ont permis une évolution considérable des normes IEEE 802.11. L'arrivée de la fibre optique à la maison a également motivé des études de recherche pour accroître les débits et la capacité. Dans ce contexte, la dernière norme IEEE 802.11ac ratifiée en 2014 a normalisé de nouvelles technologies pour atteindre des débits maximaux au-dessus de 1Obit/s. En particulier, 802 llac propose le Multiple Input Multiple Output Multi-Utilisateurs (MIMO-MU) et le Transmit Beamforming (TxBF). Ces technologies d'antennes intelligentes supposent un diagramme d'antenne d'émission qui dépend de la position des utilisateurs et des caractéristiques du canal de propagation multi-trajets correspondant. Cependant, les outils d'ingénierie et de planification radio actuels simulent une carte de couverture fixe et indépendante de tout traitement d'antennes adaptatives côté émission. Cette thèse étudie l'impact de ces techniques MIMO-MU et TxBF et propose des solutions adaptées pour l'ingénierie radio et l'optimisation du système ainsi que pour les outils de planification radio. En effet, la première partie de cette thèse consiste à affiner les gains de capacité en identifiant les configurations et les paramètres système optimaux. La deuxième partie aborde les gains de beamforming en termes du gain sur le rapport signal à bruit (SNR) et sur la réduction du niveau d'interférence pour avoir une modélisation réaliste de la couverture radio. / The deployment facility and flexibility of wireless technologies have allowed considerable evolution of IEEE 802 .11 standards. The arrival of the optical fiber to the home has further motivated the research studies to increase data rates and capacity. ln this context, the latest IEEE 802.l lac standard ratified in 2014 proposes new technologies to achieve maximum data rates above 1 Gbit/s. ln particular, 802.l lac includes the Multi-User Multiple Input Multiple Output (MU-MIMO) and Transmit Beamforming (TxBF). These smart antenna technologies assume a variable transmit antenna pattern in function of the users' position and the corresponding multipath propagation channel characteristics. However, the actual radio planning tools give a fixed coverage map in dependent of any adaptive or smart antenna processing. This thesis studies the impact of the MU-MIMO and TxBF techniques on radio engineering, system optimization as well as radio planning tools. Indeed, the first part of this thesis deals with refining the sum rate capacity gains by identifying interesting system configurations and optimal system parameters. The second part addresses the beamforming gains in terms of the Signal-to-Noise Ratio (SNR) gain and interference level to have realistic radio coverage modeling.

Made available in DSpace on 2014-06-11T19:22:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-03-28Bitstream added on 2014-06-13T20:29:03Z : No. of bitstreams: 1 guanais_dl_me_ilha.pdf: 1368426 bytes, checksum: 6f9d085c0dc031aa1fcd29a6d4256951 (MD5) / Neste trabalho, abordaremos um método sistemático para a construção de códigos espaço-temporal de treliça em sistema de comunicação sem fio que emprega a tecnologia MIMO quando submetidos em canais com desvanecimento do tipo quase-estático. O método é baseado na teoria de reticulados e explora conceitos de constelações rotacionais obtidas via partições de reticulados. Esta metodologia assegura a maior diversidade possível no processo de modulação utilizado / This paper proposes a systematic method for building Space-Time Trellis Codes in wireless communication system that employs MIMO when submitted in fading channels. The method is based on the theory of lattices that will combine concepts of rotated constellations and partition lattices. This methodology ensures the greatest possible diversity in the process of modulation used

Orientador: Jozue Vieira Filho / Coorientador: Edson Donizete de Carvalho / Banca: Francisco Villarreal Alvarado / Banca: Antônio Aparecido de Andrade / Resumo: Neste trabalho, abordaremos um método sistemático para a construção de códigos espaço-temporal de treliça em sistema de comunicação sem fio que emprega a tecnologia MIMO quando submetidos em canais com desvanecimento do tipo quase-estático. O método é baseado na teoria de reticulados e explora conceitos de constelações rotacionais obtidas via partições de reticulados. Esta metodologia assegura a maior diversidade possível no processo de modulação utilizado / Abstract: This paper proposes a systematic method for building Space-Time Trellis Codes in wireless communication system that employs MIMO when submitted in fading channels. The method is based on the theory of lattices that will combine concepts of rotated constellations and partition lattices. This methodology ensures the greatest possible diversity in the process of modulation used / Mestre

Orientador: Luís Geraldo Pedroso Meloni / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-16T11:37:29Z (GMT). No. of bitstreams: 1 Machado_RaquelGuerreiro_M.pdf: 2133776 bytes, checksum: 9563366e87c7b63b25e8e48bf81e0658 (MD5) Previous issue date: 2010 / Resumo: Na prática, quando um sistema faz uso de altas taxas de transmissão, os símbolos transmitidos são sujeitos a interferência inter-simbólica (ISI). Além disso, se existe movimento relativo entre o transmissor e receptor, tal movimentação provoca mudança no perfil do canal ao longo do tempo. Portanto, para que seja possível a implementação de sistemas sem-fio modernos que usem múltiplas antenas de transmissão e/ou recepção, é essencial que sejam desenvolvidos métodos que lidem com tais condições. Nesse contexto, este trabalho estuda a utilização da abordagem de estimação dos coeficientes de um canal MIMO com interferência inter-simbólica e variante no tempo e detecção de símbolos de forma conjunta. Com base na modelagem da dinâmica temporal dos coeficientes do canal e dos símbolos transmitidos, um vetor de estados é definido contendo ambas informações levando a uma não-linearidade na equação de observação do sistema proposto. Uma solução analítica para o problema de filtragem não-linear é então apresentada, bem como dois algoritmos que propõem soluções sub-ótimas. Por fim, simulações numéricas comprovam a superioridade da abordagem conjunta e mostram os desempenho dos dois algoritmos propostos para a solução do problema de estimação e detecção conjuntas em sistemas MIMO submetidos a canais sem-fio seletivos em frequência e variantes no tempo / Abstract: In practice, when a system uses high data transmission rates, the transmitted symbols are subjected to inter-symbol interference (ISI). Furthermore, if there exists a relative movement between the receiver and the transmitter, the wireless channel through which data is transmitted will vary in time. Therefore, in order to implement practical wireless systems that use multiple transmit and/or receive antennas, it is essential to devise methods to correctly detect symbols transmitted under such conditions. In this context, this dissertation studies the joint channel estimation and symbol detection approach. In establishing models for the temporal dynamic of the channel coefficients and transmitted symbols, an augmented state vector is defined containing both information, which leads to a non-linear observation equation. Then, an analytic solution is presented along with two sub-optimal algorithms. Finally, numeric simulations attest the superiority of the joint approach and confirm the performance of the algorithms for both the joint channel estimation and symbol detection approach in MIMO systems subject to frequency selective and time varying wireless channels / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica