Durant ces dernières années, un grand intérêt a été accordé aux systèmes à antennes multiples à cause de leur capacité à augmenter les débits. Une multitude de codes Espace-Temps existent dans la littérature. Les codes Espace-Temps optimaux sont ceux qui satisfont lespropriétés suivantes: rendement plein, ordre de diversité maximal, gain de codage optimal. Malheureusement, les meilleurs codes existants souffrent de déterminants minimaux s'évanouissant lorsque l'efficacité spectrale augmente. Nous proposons deux nouvelles constructions de codes Espace-Temps ayant un rendement plein, une diversité pleine et des déterminantsminimaux ne s'évanouissant pas lorsque l'efficacité spectrale augmente.Nous nous basons dans nos constructions sur les algèbres cycliques de division de centre Q(i) et Q(j). Les premiers codes construits sont les "codes Quaternioniques". Il s'est avéré que la répartition non uniforme de lénergie dans la matrice mot de code pénalise leurs performances lorsque le nombre d'antennes à l'émission augmente. Pour pallier ce problème énergétique, nous avons construit une nouvelle famille de codes Espace-Temps, appelée "codes Parfaits". Ces derniers ont une efficacité énergétique qui se traduit par une distribution énergétique uniforme au sein du mot de code et des constellations transmises ne présentant aucune perte de forme par rapport aux constellations émises. Les codes Quaternioniques et les codes Parfaits atteignent le compromis gain de multiplexage-diversité optimal. La représentation en réseaux de points des codes Quaternioniques et des codes Parfaits permet leur décodage par les décodeurs de réseaux de points. Les décodeurs les plus connus dans la littérature sont le décodeur par sphères et le Schnorr-Euchner. Ces derniers sont utilisés pour décoder des réseaux de points infinis. Étant donné que nous considérons des constellations finies, des versions modifiées des deux algorithmes ont été proposées. La comparaison des complexités correspondants aux deux versions modifiées de ces décodeurs nous a permis de choisir le meilleur, à savoir, le Schnorr-Euchner. Le décodage des réseaux de points peut être considérablement accéléré en utilisant une réduction de réseaux de points. A ce jour, la réduction n'est appliquée qu'aux réseaux de points infinis . L'utilisation du schéma de codage/décodage en mod-Lamda rend l'application de la réduction possible en considérant des constellations finies. Nos nouvelles constructions de codes Espace-Temps se basent sur des réseaux de points algébriques. Nous proposons dans ce sens une nouvelle réduction algébrique adaptée aux réseaux de points algébriques pour les systèmes mono-antenne sur canal à évanouissements rapides. Cette méthode sera étendue au cas des systèmes à antennes multiples dans un proche avenir.

<p>The main issue in this thesis is to minimize the number of operations and the energy consumption per operation for the computation (arithmetic operation) part of DSP circuits, such as Finite Impulse Response Filters (FIR), Discrete Cosine Transform (DCT), and Discrete Fourier Transform (DFT) etc. More specific, the focus is on the elimination of most frequent common sub-expression (CSE) in binary, Canonic Sign Digit (CSD), Twos Complement or Sign Digit representation of the coefficients of non-recursive multiple input multiple output (MIMO)  FIR system , which can be realized using shift-and-add based operations only. The possibilities to reduce the complexity i.e. the chip area, and the energy consumption have been investigated.</p><p>We have proposed an algorithm which finds the most common sub expression in the binary/CSD/Twos Complement/Sign Digit representation of coefficients of non-recursive MIMO multiplier less FIR systems. We have implemented the algorithm in MATLAB. Also we have proposed different tie-breakers for the selection of most frequent common sub-expression, which will affect the complexity (Area and Power consumption) of the overall system. One choice (tie breaker) is to select the pattern (if there is a tie for the most frequent pattern) which will result in minimum number of delay elements and hence the area of the overall system will be reduced. Another tie-breaker is to choose the pattern which will result in minimum adder depth (the number of cascaded adders). Minimum adder depth will result in least number of glitches which is the main factor for the power consumption in MIMO multiplier less FIR systems. Switching activity will be increased when glitches are propagated to subsequent adders (which occur if adder depth is high). As the power consumption is proportional to the switching activity (glitches) hence we will use the sub-expression which will result in lowest adder depth for the overall system.</p>

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Leonard J. Cimini, Jr., Electrical and Computer Engineering. Includes bibliographical references.

A significant challenge for fourth generation cellular systems is the reliable delivery of high speed (up to 1 gigabit per second) data to mobile or nomadic users throughout a cluttered urban environment. The wireless channel is a difficult channel over which to achieve high rate reliable communications. The wireless channel suffers many impairments such as small-scale multipath fading, shadowing, high path loss, co-channel interference, and Doppler shift due to mobility of the terminals and mobility in the propagation environment. Since radio spectrum is a scarce resource it is necessary to build cellular networks with high spectral efficiency. Two promising methods to solve this problem are multihop (MH) relaying and multiple-input multiple-output (MIMO) antenna techniques. The most difficult mobile users to serve reliably are those close to cell edges and those shadowed by large objects such as buildings. With MH relaying, a number of simple and inexpensive wireless relays are deployed throughout the cell to relay transmissions around obstacles and to reduce the path loss to distant mobile users. Also, MH relaying enables the deployment of small subcells throughout the cell, increasing the system's area averaged spectral efficiency. Various MIMO techniques can be used in scattering channels to increase capacity and reliability of data links in a wireless network. MH relaying and MIMO are key inclusions in emerging cellular standards such as IEEE 802.16 and LTE-Advanced, so it is necessary to study how these may be used jointly in a cellular environment. We look at various techniques available in MH relaying and MIMO, and assess the benefits and difficulties of these techniques when used in cellular systems. We put together a realistic cellular system model, with typical cellular topologies and well-accepted propagation models, and assess the performance of a multihop MIMO system. We find that there are tradeoffs in using these techniques jointly since they provide gains by somewhat conflicting methods. MH relaying lowers path loss and mitigates scattering in the channel, while MIMO benefits from significant scattering. As a result, it is necessary to understand how to design a MH-MIMO network carefully in order to maximize the net benefit. / Communications

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

L’utilisation d’une chambre réverbérante pour modéliser un canal de communication sans fil a récemment été proposée. La chambre réverbérante est une cavité métallique fermée dans laquelle se trouve une pale mécanique en mouvement permettant de modifier les conditions aux limites et d’ainsi obtenir en moyenne une répartition uniforme des champs. Cette cavité métallique fermée présente de nombreux avantages pour modéliser un canal de communication. Citons principalement le fait que l’environnement est reproductible grâce au mouvement de la pale. L’étude détaillée du canal de communication sans fil à l’intérieur de cet environnement est le sujet de cette thèse. Nous développons à la fois une approche théorique et expérimentale (dans 3 chambres réverbérantes différentes). En particulier, on caractérise ce canal dans les dimensions temporelles, fréquentielles et spatiales afin de dériver ensuite un modèle de canal. Nous nous intéressons en particulier aux systèmes sans fil multi-antennes car ceux-ci exploitent les trois dimensions (temps, fréquence, position). Ensuite, nous comparons l’environnement en chambre réverbérante au cas d’un environnement confiné, à savoir une voiture. Nous testons également une chaîne complète de transmission OFDM et SC-FDE sur base du modèle de canal en chambre développé dans cette thèse. Enfin, nous présentons un nouveau système de test composé de deux chambres réverbérantes couplées à l’aide d’un guide d’ondes dont les dimensions transverses peuvent être changées. Grâce à ce guide d’ondes, le degré de liberté du canal multi-antennes peut être contrôlé.

The problem of detecting a vector of symbols, drawn from a finite alphabet and transmitted over a multiple-input multiple-output (MIMO) channel with Gaussian noise, is of central importance in digital communications and is encountered in several different applications. Examples include, but are not limited to; detection of symbols spatially multiplexed over a multiple-antenna channel and the multiuser detection problem in a code division multiple access (CDMA) system. Two algorithms previously proposed in the literature are considered and analyzed. Both algorithms have their origin in other fields of science but have gained mainstream recognition as efficient algorithms for the detection problem considered herein. Specifically, we consider the sphere decoder and semidefinite relaxation detector. By incorporating assumptions applicable in the communications context the performance of the two algorithms is addressed. The first algorithm, the sphere decoder, offers optimal performance in terms of its error probability. Further, the algorithm has proved extremely efficient in terms of computational complexity for moderately sized problems at high signal to noise ratio (SNR). Although it is recognized that the algorithm has an exponential worst case complexity, there has been a widespread belief that the algorithm has a polynomial average complexity at high SNR. A contribution made herein is to show that this is incorrect and that the average complexity, as the worst case complexity, is exponential in the number of symbols detected. Instead, another explanation of the observed efficiency of the algorithm is offered by deriving the exponential rate of growth and showing that this rate, although strictly positive for finite SNR, is small in the high SNR regime. The second algorithm, the semidefinite relaxation (SDR) detector, offers polynomial complexity at the expense of suboptimal performance in terms of error probability. Nevertheless, previous numerical observations suggest that error probability of the SDR algorithm is close to that of the optimal detector. Herein, the near optimality is of the SDR algorithm is given a precise meaning by studying the diversity of the SDR algorithm when applied to the (real valued) i.i.d.~Rayleigh fading channel and it is shown that the SDR algorithm achieves the same diversity order as the optimal detector. Further, criteria under which the SDR estimates coincide with the optimal estimates are derived and discussed. / Ett grundläggande problem som påträffats inom digital kommunikation är detektering av en symbolvektor, tillhörande ett ändligt symbolalfabet, som sänts över en MIMO (från engelskans multiple-input multiple-output) kanal med Gausiskt brus. Detta problem påträffas bland annat då symboler sänts över en trådlös kanal med flera antenner hos mottagaren och sändaren samt då flera användare i ett CDMA system simultant skall avkodas. In denna avhandling behandlas två mottagaralgoritmer konstruerade för detta ändamål. Algoritmerna har sin bakgrund i andra forskningsområden men kan i nuläget sägas vara mycket välkända inom kommunikationsområdet. De benämns vanligtvis som sfäravkodaren (eng. sphere decoder) samt den semidefinita relaxeringsdetektorn (eng. semidefinite relaxation detector). Algoritmerna analyseras i denna avhandling matematiskt genom att införa förenklande antaganden som är relevanta och applicerbara för de kommunikationsproblem som är av intesse. Den första algoritmen, sfäravkodaren, löser dessa detektionsproblem på ett optimalt sätt i betydelsen att den minimerar sannolikheten för att detektorn fattar ett felaktigt beslut rörande det sända meddelandet (symbolvektorn). Också vad gäller algoritmens komplexitet har simuleringar visat att den är oväntat låg, åtminstone vid höga signalbrusförhållanden (SNR). Trots att det är allmänt känt att algoritmen i sämsta fall har exponentiell komplexitet så har detta lett till den allmänt spridda uppfattningen att medelkomplexiteten (eller den förväntade komplexiteten) endast är polynomisk vid höga signalbrusförhållanden. Ett av huvudbidragen i denna avhandling är att visa att denna uppfattning är felaktig och att också medelkomplexiteten växer exponentiellt i antalet symboler som simultant detekteras. Ytterligare ett bidrag ligger i att ge en alternativ förklaring till den observerat låga medelkomplexiteten. Det visas att den exponentiella hastighet med vilken komplexiteten växer beror på signalbrusförhållande, och att den är låg för höga SNR. Den andra algoritmen, den semidefinita relaxeringsdetektorn, erbjuder polynomisk komplexitet vid en något högre felsannolikhet. Intressant nog har dock felsannolikheten tidigare, genom simuleringar, visat sig vara endast marginellt högre än felsannolikheten hos den optimala mottagaren. Bidraget som relaterar till den semidefinita relaxeringsmottagaren ligger i att både förklara och i att ge en specifik kvatifierbar mening åt uttalandet att felsannolikheten endast är marginellt högre. I syfte att åstadkomma detta studeras diversitetsordningen för detektorn, och det bevisas att diversitetsordningen för den semidefinita relaxeringsdetektorn är densamma som för den optimala mottagaren. Utöver detta karakteriseras också de krav som måste uppfyllas för att den detektorn skall finna den optimala lösningen. / QC 20100901

Technology Portfolios are essential to the evolution of large complex systems. In an effort to harness the power of new technologies, technology portfolios are used to predict the value of integrating them into the project. This optimization of the technology portfolio creates large complex design spaces; however, many processes operate on the assumption that their technology elements have no dependency on each other, because dependencies are not well defined. This independence assumption simplifies the process, but suggests that these environments are missing out on decision power and fidelity. Therefore, this thesis proposed a way to explain the variations in Portfolio recommendations as a function of adding dependencies. Dependencies were defined in accordance with their development effort figures of merit and possible relationships. The thesis then went on to design a method to integrate two dependency classes into the technology portfolio framework to showcase the effect of incorporating dependencies. Results indicated that Constraint Dependencies reduced the portfolio or stayed the same, while Value Dependencies changed the portfolio optimization completely; making the user compare two different optimization results. Both indicated that they provided higher fidelity with the inclusion of the information added. Furthermore, the upcoming NASA Near-Earth Asteroid Campaign was studied as a case study. This campaign is the plan to send humans to an asteroid by 2025 announced by President Obama in April 2010. The campaign involves multiple missions, capabilities, and technologies that must be demonstrated to enable deep-space human exploration. Therefore, this thesis capitalized on that intention to show how adopting technology in earlier missions can act as a feed-forward method to demonstrate technology for future missions. The thesis showed the baseline technology portfolio, integrated dependencies into the process, compared its findings to the baseline case, and ultimately showed how adding higher fidelity into the process changes the user's decisions. Findings concerning the Near-Earth Asteroid Campaign, the use of dependencies to add fidelity and implications for future work are discussed.

We consider the uplink of a multicell multiuser single-input multiple-output system where the channel experiences both small and large-scale fading. The data detection is done by using the linear zero-forcing technique, assuming the base station (BS) has perfect channel state information of all users in its cell. We derive  new, exact analytical expressions for the uplink rate, symbol error rate, and outage probability per user, as well as alower bound on the achievable rate. This bound is very tight and becomes exact in the large-number-of-antennas limit. We further study the asymptotic system performance in the regimes of high signal-to-noise ratio (SNR), large number of antennas, and large number of users per cell. We show that at high SNRs, the system is interference-limited and hence, we cannot improve the system performance by increasing the transmit power of each user. Instead, by increasing the number of BS antennas, the effects of interference and noise can be reduced, thereby improving the system performance. We demonstrate that, with very large antenna arrays at the BS, the transmit power of each user can be made inversely proportional to the number of BS antennas while maintaining a desired quality-of-service. Numerical results are presented to verify our analysis.

Multi-user wireless systems with multiple antennas can drastically increase the capac- ity while maintaining the quality of service requirements. The best performance of these systems is obtained at the presence of instantaneous channel knowledge. Since uplink-downlink channel reciprocity does not hold in frequency division duplex and broadband time division duplex systems, efficient channel quantization becomes important. This thesis focuses on different quantization techniques in a linearly precoded multi-user wireless system. Our work provides three major contributions. First, we come up with an end-to-end transceiver design, incorporating precoder, receive combining and feedback policy, that works well at low feedback overhead. Second, we provide optimal bit allocation across the gain and shape of a complex vector to reduce the quantization error and investigate its effect in the multiuser wireless system. Third, we design an adaptive differential quantizer that reduces feedback overhead by utilizing temporal correlation of the channels in a time varying scenario.