305 research outputs found
Time keeping in myriad networks : theories, solutions and applications
Get PDFThesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2001.Includes bibliographical references (leaves 70-72).Distributed sensor networks make extensive use of a common time reference. In this work we address the problem of time dissemination in a packet switched network when the nodes are NOT generally all connected to an accurate, external time reference source. We thoroughly analyze Network Time Protocol - version 3 and identify its oversimplified clock modeling and its neglect of network delay variance (network jitter) as the primal causes for its inaccuracy. We explicitly address frequency skew in our clock model and propose a novel Kalman filtering technique for de-noising (remove of network jitter) during the NTP time synchronization process. The parameters of the Kalman linear estimator are optimal and they are computed online from the network environment, with a well-defined procedure. Our End-to-End technique decreases NTP rms error by two orders of magnitude and is compared with a software phased lock loop and a linear programming technique, with cross traffic exhibiting long-range dependence (fractional Brownian motion cross-traffic) or no dependence at all (white Gaussian case). We conclude with applications over packet switched networks that require time synchronization, like spatial filtering (beam-forming). The suite of algorithms and applications define a new class of packet switched networks, called Myriad Networks.by Aggelos Anastasiou Bletsas.S.M
Ολοκληρωμένη μικροκυματική μονάδα για επικοινωνίες 5ης γενιάς
No full textSummarization: In just the past year, preliminary interest and discussions about a possible 5G standard have evolved into a fullfledged conversation that has captured the attention and imagination of researchers and engineers around the world. This thesis presents an integrated front end module intended for use in 5th generation communications transceivers. The chip that has been designed includes a two stage cascode common source low noise amplifier and a five stack power amplifier. The low noise amplifier achieves a maximum small signal gain of 16.5dB and noise figure of 4.01dB, while the power amplifier achieves a maximum saturated power of 19dBm and a maximum power added efficiency of 30%. The total area of the testchip is roughly 3.3mm2 including the DC and RF testpads.Περίληψη: Τα τελευταία μόλις χρόνια, το αρχικό ενδιαφέρον και οι συζητήσεις για ένα πιθανό πρότυπο 5G έχουν μετατραπεί σε ένα μείζον ζήτημα που έχει τραβήξει την προσοχή και τη φαντασία των ερευνητών και μηχανικών ολόκληρου του πλανήτη. Αυτή η μεταπτυχιακή εργασία έχει ως στόχο να παρουσιάσει μια ολοκληρωμένη μονάδα front-end με εφαρμογή σε πομποδέκτες για τηλεπικοινωνίες 5ης γενιάς. Το τσιπ που σχεδιάστηκε περιλαμβάνει έναν δισταδιακό ενισχυτή χαμηλού θορύβου (LNA) και έναν 5-stack ενισχυτή ισχύος (PA). Ο LNA επιτυγχάνει μέγιστο κέρδος 16.5dB και noise figure (NF) 4.01dB, ενώ ο PA επιτυγχάνει μέγιστη ισχύ εξόδου 19dBm με απόδοση 30%. Η συνολική επιφάνεια του τσιπ είναι περίπου 3.3mm2 συμπεριλαμβάνοντας τις επαφές για DC και RF
Intelligent antenna sharing in cooperative diversity wireless networks
Get PDFThesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2005.Includes bibliographical references (p. 143-152).Cooperative diversity has been recently proposed as a way to form virtual antenna arrays that provide dramatic gains in slow fading wireless environments. However, most of the proposed solutions require simultaneous relay transmissions at the same frequency bands, using distributed space-time coding algorithms. Careful design of distributed space-time coding for the relay channel is usually based on global knowledge of some network parameters or is usually left for future investigation, if there is more than one cooperative relay. We propose a novel scheme that eliminates the need for space-time coding and provides diversity gains on the order of the number of relays in the network. Our scheme first selects the best relay from a set of M available relays and then uses this "best" relay for cooperation between the source and the destination. Information theoretic analysis of outage probability shows that our scheme achieves the same diversity-multiplexing gain tradeoff as achieved by more complex protocols, where coordination and distributed space-time coding for M relay nodes is required. Additionally, the proposed scheme increases the outage and ergodic capacity, compared to non-cooperative communication with increasing number of participating relays, at the low SNR regime and under a total transmission power constraint.(cont.) Coordination among the participating relays is based on a novel timing protocol that exploits local measurements of the instantaneous channel conditions. The method is distributed and allows for fast selection of the best relay as compared to the channel coherence time. In addition, a methodology to evaluate relay selection performance for any kind of wireless channel statistics is provided. Other methods of network coordination, inspired by natural phenomena of decentralized time synchronization, are analyzed in theory and implemented in practice. It was possible to implement the proposed, virtual antenna formation technique in a custom network of single antenna, half-duplex radios.by Aggelos Anastasiou Bletsas.Ph.D
Tool for optimized design of integrated RF CMOS low noise amplifiers
No full textDiploma ThesisSummarization: The demand for larger bandwidth in wireless communications, motivates the RF circuit designers to advance to higher frequencies in order to serve the rapidly growing market. CMOS technology has dominated in the design of radio frequency and analog integrated circuits. Using devices in the nanometer regime, provides the possibility for greater operation frequencies and ultimately faster data rates. Additionally, RF circuit design is increasingly taking advantage of the aggressive scaling of submicrometer CMOS technologies that make possible the integration of complete tele-communication systems in a single chip (SoC). Low noise amplifiers (LNA) are one of the most important blocks of any telecommunication system. Their importance lies on the fact that they impact the noise performance more than any of the other blocks in the receiver chain. The main purpose of the low noise amplifier is to increase the power of the attenuated input signal, while at the same time minimizing the noise added to the chain by the circuit itself. In the RF design procedure, a designer faces the problem of trade-offs in quantities like consumption, gain, linearity etc. The purpose of this thesis is the introduction of a theoretical model that defines the optimum operation of a LNA (figure-of-merit) and afterwards the introduction of a design methodology that approaches the theoretical response. The thesis also proposes the integration of a genetic algorithm in the design sequence, that finds actual optimum solutions using the procedures of natural selection, reproduction and mutation. Finally, the efficiency of the equation model and genetic algorithm combination is showcased with the design of an optimum 5 GHz common source LNA. The optimal LNA design is obtained in the region of moderate inversion, according to both the analytical model and the optimization procedure. Furthermore, the other LNA topologies such as cascode LNA and common gate LNA are also evaluated. This work provides valuable insight into the design trade-offs of the different LNA topologies
Evaluation of Kalman Filtering for Network Time Keeping
No full textSummarization: Time information is critical for a variety of
applications in distributed environments that facilitate pervasive
computing and communication. This work describes
and evaluates a novel Kalman filtering algorithm for endto-end
time synchronization between a client computer and
a server of “true” time [e.g., a Global Positioning System
(GPS) source] using messages transmitted over packetswitched
networks, such as the internet. The messages exchanged
have the network time protocol (NTP) format, and
the algorithm evaluated, is performed only at the client
side. The Kalman filtering algorithm is compared to two
other techniques widely used, based on linear programming
and statistical averaging, and the experiments involve independent
consecutive measurements (Gaussian case) or measurements
exhibiting long-range dependence (self-similar
case). Performance is evaluated according to the estimation
error of frequency offset and time offset between client
and server clock, the standard deviation of the estimates
and the number of packets used for a specific estimation.
The algorithms could exploit existing NTP infrastructure,
and a specific example is presented.Presented on: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Contro
Energy harvesting with a low-cost and high efficiency rectenna for low-power input
No full textIn this paper a low-complexity, low-cost and high efficiency rectenna is analyzed, fabricated and measured, for low input power. Even though the configuration employs a low-cost, lossy substrate and a low-complexity rectifier circuit with a single diode, the rectenna efficiency reaches 20% and 37% at -20 and -10 dBm, respectively. Measurements agree well with simulations.</p
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