10 research outputs found

    Doctor of Philosophy

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    dissertationWireless communications pervade all avenues of modern life. The rapid expansion of wireless services has increased the need for transmission schemes that are more spectrally efficient. Dynamic spectrum access (DSA) systems attempt to address this need by building a network where the spectrum is used opportunistically by all users based on local and regional measurements of its availability. One of the principal requirements in DSA systems is to initialize and maintain a control channel to link the nodes together. This should be done even before a complete spectral usage map is available. Additionally, with more users accessing the spectrum, it is important to maintain a stable link in the presence of significant interference in emergency first-responders, rescue, and defense applications. In this thesis, a new multicarrier spread spectrum (MC-SS) technique based on filter banks is presented. The new technique is called filter bank multicarrier spread spectrum (FB-MC-SS). A detailed theory of the underlying properties of this signal are given, with emphasis on the properties that lend themselves to synchronization at the receiver. Proposed algorithms for synchronization, channel estimation, and detection are implemented on a software-defined radio platform to complete an FB-MC-SS transceiver and to prove the practicality of the technique. FB-MC-SS is shown through physical experimentation to be significantly more robust to partial band interference compared to direct sequence spread spectrum. With a higher power interfering signal occupying 90% of its band, FB-MC-SS maintains a low bit error rate. Under the same interference conditions, DS-SS fails completely. This experimentation leads to a theoretical analysis that shows in a frequency selective channel with additive white noise, the FB-MC-SS system has performance that equals that obtained by a DS-SS system employing an optimal rake receiver. This thesis contains a detailed chapter on implementation and design, including lessons learned while prototyping the system. This is to assist future system designers to quickly gain proficiency in further development of this technology

    Design and implementation of a downlink MC-CDMA receiver

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    Cette thèse présente une étude d'un système complet de transmission en liaison descendante utilisant la technologie multi-porteuse avec l'accès multiple par division de code (Multi-Carrier Code Division Multiple Access, MC-CDMA). L'étude inclut la synchronisation et l'estimation du canal pour un système MC-CDMA en liaison descendante ainsi que l'implémentation sur puce FPGA d'un récepteur MC-CDMA en liaison descendante en bande de base. Le MC-CDMA est une combinaison de la technique de multiplexage par fréquence orthogonale (Orthogonal Frequency Division Multiplexing, OFDM) et de l'accès multiple par répartition de code (CDMA), et ce dans le but d'intégrer les deux technologies. Le système MC-CDMA est conçu pour fonctionner à l'intérieur de la contrainte d'une bande de fréquence de 5 MHz pour les modèles de canaux intérieur/extérieur pédestre et véhiculaire tel que décrit par le "Third Genaration Partnership Project" (3GPP). La composante OFDM du système MC-CDMA a été simulée en utilisant le logiciel MATLAB dans le but d'obtenir des paramètres de base. Des codes orthogonaux à facteur d'étalement variable (OVSF) de longueur 8 ont été choisis comme codes d'étalement pour notre système MC-CDMA. Ceci permet de supporter des taux de transmission maximum jusquà 20.6 Mbps et 22.875 Mbps (données non codées, pleine charge de 8 utilisateurs) pour les canaux intérieur/extérieur pédestre et véhiculaire, respectivement. Une étude analytique des expressions de taux d'erreur binaire pour le MC-CDMA dans un canal multivoies de Rayleigh a été réalisée dans le but d'évaluer rapidement et de façon précise les performances. Des techniques d'estimation de canal basées sur les décisions antérieures ont été étudiées afin d'améliorer encore plus les performances de taux d'erreur binaire du système MC-CDMA en liaison descendante. L'estimateur de canal basé sur les décisions antérieures et utilisant le critère de l'erreur quadratique minimale linéaire avec une matrice' de corrélation du canal de taille 64 x 64 a été choisi comme étant un bon compromis entre la performance et la complexité pour une implementation sur puce FPGA. Une nouvelle séquence d'apprentissage a été conçue pour le récepteur dans la configuration intérieur/extérieur pédestre dans le but d'estimer de façon grossière le temps de synchronisation et le décalage fréquentiel fractionnaire de la porteuse dans le domaine du temps. Les estimations fines du temps de synchronisation et du décalage fréquentiel de la porteuse ont été effectués dans le domaine des fréquences à l'aide de sous-porteuses pilotes. Un récepteur en liaison descendante MC-CDMA complet pour le canal intérieur /extérieur pédestre avec les synchronisations en temps et en fréquence en boucle fermée a été simulé avant de procéder à l'implémentation matérielle. Le récepteur en liaison descendante en bande de base pour le canal intérieur/extérieur pédestre a été implémenté sur un système de développement fabriqué par la compagnie Nallatech et utilisant le circuit XtremeDSP de Xilinx. Un transmetteur compatible avec le système de réception a également été réalisé. Des tests fonctionnels du récepteur ont été effectués dans un environnement sans fil statique de laboratoire. Un environnement de test plus dynamique, incluant la mobilité du transmetteur, du récepteur ou des éléments dispersifs, aurait été souhaitable, mais n'a pu être réalisé étant donné les difficultés logistiques inhérentes. Les taux d'erreur binaire mesurés avec différents nombres d'usagers actifs et différentes modulations sont proches des simulations sur ordinateurs pour un canal avec bruit blanc gaussien additif

    Design of discrete-time filters for efficient implementation

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 325-333).The cost of implementation of discrete-time filters is often strongly dependent on the number of non-zero filter coefficients or the precision with which the coefficients are represented. This thesis addresses the design of sparse and bit-efficient filters under different constraints on filter performance in the context of frequency response approximation, signal estimation, and signal detection. The results have applications in several areas, including the equalization of communication channels, frequency-selective and frequency-shaping filtering, and minimum-variance distortionless-response beamforming. The design problems considered admit efficient and exact solutions in special cases. For the more difficult general case, two approaches are pursued. The first develops low-complexity algorithms that are shown to yield optimal or near-optimal designs in many instances, but without guarantees. The second focuses on optimal algorithms based on the branch-and-bound procedure. The complexity of branch-and-bound is reduced through the use of bounds that are good approximations to the true optimal cost. Several bounding methods are developed, many involving relaxations of the original problem. The approximation quality of the bounds is characterized and efficient computational methods are discussed. Numerical experiments show that the bounds can result in substantial reductions in computational complexity.by Dennis Wei.Ph.D

    SCADA and related technologies

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    Presented at SCADA and related technologies for irrigation district modernization, II: a USCID water management conference held on June 6-9, 2007 in Denver, Colorado.SCADA systems in irrigation districts have focused on remote monitoring and remote control. In many districts, the remote control is manual, but in others the automation of structures is enabled through the usage of distributed control for the automation of individual structures. This paper presents the concept of an expanded, "umbrella" SCADA system that will perform the standard functions of remote control and remote monitoring, and will also incorporate information flow in the field for operators. The umbrella SCADA system will mesh the equipment-equipment information into an equipment-program-personnel network

    SCADA and related technologies

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    Presented at SCADA and related technologies for irrigation district modernization, II: a USCID water management conference held on June 6-9, 2007 in Denver, Colorado.Northern Water (Northern Colorado Water Conservancy District) conducted field demonstrations and comparisons of flow monitoring equipment at 18 canal and ditch sites in the lower South Platter River Basin during the 2006 irrigation season. Equipment included data loggers from 8 different manufacturers, 16 different models of water level sensors from 12 manufacturers, and 4 different types of telemetry from 7 manufacturers. The data loggers that were demonstrated included four models of single-sensor with integrated data logger, four models of programmable multi-sensor data logger, and one model of basic, low-cost data logger without telemetry. Relative equipment costs for each data logger system are summarized in Table 6. The water level sensors tested included submersible pressure transducers, optical shaft encoders, ultrasonic distance sensors, bubbler level sensor, float and pulley with potentiometer, buoyancy sensor, and a laser distance sensor. Bench checks of sensor calibrations were accomplished by Northern Water staff before field installation, and again at the end of the irrigation season. Observed sensor accuracy was compared to that expected from manufacturer specifications. The telemetry systems tested in the field included license-free spread-spectrum radios from four manufacturers, licensed radio modems in the 450 MHz range, satellite radio modems to a web server, and cdma modems with static IP addresses. Increased mast height and high gain directional antenna improved radio telemetry as expected. Additionally, operational files were utilized to document telemetry performance when available. The purpose and intent of the equipment demonstration and comparison was not to identify a single best data logger, sensor, and/or telemetry system. Each has different features and strengths, as well as varying costs. For each specific flow monitoring application, different equipment may be preferred or better suited than other equipment. However, the 2006 demonstration and comparison should provide a reference point for those seeking to become more knowledgeable in equipment selection while avoiding unpleasant surprises

    Analogue filter networks: developments in theory, design and analyses

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    VLSI signal processing through bit-serial architectures and silicon compilation

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    TDRSS telecommunications study. Phase 1: Final report

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    A parametric analysis of the telecommunications support capability of the Tracking and Data Relay Satellite System (TDRSS) was performed. Emphasis was placed on maximizing support capability provided to the user while minimizing impact on the user spacecraft. This study evaluates the present TDRSS configuration as presented in the TDRSS Definition Phase Study Report, December 1973 to determine potential changes for improving the overall performance. In addition, it provides specifications of the user transponder equipment to be used in the TDRSS

    NASA Space Engineering Research Center Symposium on VLSI Design

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    The NASA Space Engineering Research Center (SERC) is proud to offer, at its second symposium on VLSI design, presentations by an outstanding set of individuals from national laboratories and the electronics industry. These featured speakers share insights into next generation advances that will serve as a basis for future VLSI design. Questions of reliability in the space environment along with new directions in CAD and design are addressed by the featured speakers
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