Obtaining low-latency results from window-aggregate queries can be critical to certain data-stream processing applications. Due to a DSMS's lack of control over incoming data (typically, because of delays and bursts in data arrival), timely results for a window-aggregate query over a data stream cannot be obtained with guarantees about the results' accuracy. In this thesis, I propose a technique, which I term prodding, to obtain early result estimates for window-aggregate queries over data streams. The early estimates are obtained in addition to the regular query results. The proposed technique aims to maximize the contribution to a result-estimate computation from all the stateful operators across a multi-level query plan. I evaluate the benefits of prodding using real-world and generated data streams having different patterns in data arrival and data values. I conclude that, in various DSMS applications, prodding can generate low-latency estimates to window-aggregate query results. The main factors affecting the degree of inaccuracy in such estimates are: the aggregate function used in a query, the patterns in arrivals and values of stream data, and the aggressiveness of demanding the estimates. The utility of the estimates obtained using prodding should be optimized by tuning the aggressiveness in result-estimate demands to the specific latency and accuracy needs of a business, considering any available knowledge about patterns in the incoming data.

No description available.

Denna rapport är baserad utifrån ett examensarbete utfört hos Skellefteå Kraft Fibernät. Syftet var att jämföra ett antal olika modeller av tjänstefördelare och hitta en alternativ CPE till den som idag används. För att jämföra enheterna genomfördes ett antal tester såsom throughputtest, multicasttest och betygsättning av installationsvänligheten. Den gjordes en del intressanta upptäckter såsom att en uppgradering av mjukvaran förbättrade throughput och att bara en CPE hade lager 3 funktioner. I diskussionen görs slutligen en rekommendation på CPE baserat på resultaten i rapporten. / This report is based on a final project carried out at Skellefteå Kraft Fibernät. The aim was to compare a number of different models of CPE's and find an alternative CPE to the one currently used today. In order to compare the devices, a number of tests were carried out such as a throughput-test, multicast-test and a evaluation of the ease of installation. It was made some interesting discoveries such as that a firmware upgrade improved throughput and that only one CPE had layer 3 functionality. In the discussion, a recommendation on CPE is finally made based on the results in the report.

In this thesis, two different topics are treated related to wireless communication. Part I presents three different reconfigurable MEMS integrated antennas for MIMO applications. Simulation and measurement results are presented along with brief discussions on the topic of antenna selection with reconfigurable antenna elements. Part II presents an estimator for the coupling matrix of an antenna array with two slightly different approaches. CRB is derived and discussed in terms of parameter cost. / <p>QC 20101119</p>

No description available.

The goal of this dissertation is to test the agenda-setting theories of John Kingdon and Frank Baumgartner/Bryan Jones in terms of applicability. Universal service policy and the 1996 Telecommunications Act serve as the test case. Case study methodology guides the dissertation and employs a variety of methods including the quantitative and qualitative techniques used by John Kingdon and by Frank Baumgartner/Bryan Jones. These methods involve content analysis and the coding of media articles, an analysis of congressional hearings and government reports, and a review of scholarly literature on topics related to the policy-making in general, and telecommunications policy development, in particular. Universal service was selected for legislative action because it was bound up with telecommunications legislation, which required revision. Although some policy-makers preferred a market solution (that is the elimination of subsidized telecommunication services), universal service remained part of the telecommunications policy revision. Reasons include a new issue definition accompanied by a compelling image (information superhighway), the support of rural senators, and presidential leadership. With regard to fundamental differences between the Kingdon and Baumgartner/Jones' theories Kingdon's premise regarding the impact of cyclical events and systematic indicators has more applicability than Baumgartner and Jones' punctuated equilibria model of policy change. In addition, unlike Kingdon's research results, which indicate the media have a minor role in agenda-setting, Baumgartner and Jones' media attention indicators of policy change demonstrated a similar pattern to the universal service media indicators. The influence of interest groups is another point of difference. The universal case as with Baumgartner and Jones' research results that interest groups were major actors in setting the policy agenda. The contribution of this dissertation is to suggest elements of a new integrated model for the study of agenda-setting that incorporates aspects of the work of Kingdon and Baumgartner/Jones. / Ph. D.

Networks which use real-time communication have high requirements on latency and packet loss. Improving one aspect may results in worse performance for another, and it can be difficult to prioritize one over the other as all the requirements need to be met in order for the network tooperate as expected. Many studies have investigated reducing the size of packet buffers to improve the latency. However, they have mainly focused on studying TCP traffic which may not be optimal for real-time traffic, where it instead could be more suitable to use UDP. We have performed an experiment where we compared the performance of real-time traffic over multiple different buffer sizes. We generated traffic using synchronized bursts of packets which were either sample value (SV) or IP packets, as defined by IEC 61850. We measured the packet loss and latency for situations where the traffic was either entirely composed of SV packets, or when it had mixed SV and IP traffic. For the mixed traffic, we also experimented with using different VLAN priorities for the two types of packets. We have determined deadline thresholds that show what size of packet buffer will start causing packets to miss their deadline, and what size will lead every packet in bursts oftraffic to miss their deadlines. We also found that increasing the priority of SV packets in mixed traffic can have either a positive or a negative impact on their performance, depending on how highly they are prioritized.

National Telecommunications policies have been differentiated together with the extension of international trade, increasing importance of information in trade and the convergence of telecommunications, broadcasting and computing sectors. with the influence of these global factors, the subject of this thesis is the study of Mexican and Turkish national telecommunications policies regarding with the deregulation in telecommmunications service sector.

Thesis (M.B.A.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 57).

Τα τελευταία χρόνια παρατηρείται μια ραγδαία ανάπτυξη στο κλάδο των τηλεπικοινωνιών και αυτό είναι ορατό στην καθημερινή ζωή μας. Η ψηφιακή μετάδοση και επεξεργασία των σημάτων σε συνδυασμό με την βελτίωση των μέσων μετάδοσης, της υποδομής και των τεχνικών διαμόρφωσης, δίνουν την δυνατότητα στους επιστήμονες να επικεντρωθούν όλο και περισσότερο στα θέματα τηλεπικοινωνιών, ειδικά των ασύρματων τηλεπικοινωνιών. Στις ασύρματες τηλεπικοινωνίες οι τεχνικές πολλαπλής πρόσβασης χρησιμοποιούνται για να επιτρέψουν σε πολλούς χρήστες να μοιραστούν ταυτόχρονα ένα περιορισμένο φάσμα συχνοτήτων. Το μοίρασμα του φάσματος είναι απαραίτητο προκειμένου να αυξήσουμε την χωρητικότητα ενός συστήματος, ενώ θα πρέπει να γίνει με τέτοιο τρόπο, ώστε να μην υπάρχει σημαντική υποβάθμιση της απόδοσης του συστήματος. Για να αντιμετωπιστεί αυτή η υποβάθμιση έχουν προταθεί διάφορες τεχνικές πολλαπλής πρόσβασης. Σε μια από αυτές τις τεχνικές το συνολικό φάσμα συχνοτήτων διαιρείται σε συχνοτικά μη-επικαλυπτόμενες υποζώνες, οι οποίες ανατίθενται στους επιμέρους χρήστες (πολλαπλή πρόσβαση με διαίρεση συχνότητας – FDMA). Σε αυτή την περίπτωση, όμως, έχουμε σπατάλη του εύρους ζώνης του καναλιού, αφού οι χρήστες δεν μπορούν να χρησιμοποιούν όλο το κανάλι, όλη την ώρα. Μια τεχνική που δίνει λύση στο παραπάνω πρόβλημα (πολλαπλή πρόσβαση με διαίρεση κωδικών - CDMA), χρησιμοποιεί ορθογώνιους κώδικες που ανατίθενται στους χρήστες, δίνοντας τους την δυνατότητα ταυτόχρονης μετάδοσης στο κανάλι για όση ώρα απαιτείται. Το βασικότερο πρόβλημα αυτής της τεχνικής είναι ότι η ιδιότητα της ορθογωνιότητας των κωδίκων χάνεται όταν χρησιμοποιούνται συχνοτικά επιλεκτικά κανάλια. Μια νέα τεχνική πολλαπλής πρόσβασης που προτάθηκε η οποία αποφεύγει τα παραπάνω προβλήματα είναι η πολλαπλή πρόσβαση με διαίρεση συχνότητας και αναδιάταξη δεδομένων (Interleaved FDMA). Η συγκεκριμένη τεχνική συνδυάζει χαρακτηριστικά από το FDMA και το CDMA. Συγκεκριμένα, συμπιέζει χρονικά την ακολουθία συμβόλων που πρόκειται να αποσταλεί, την επαναλαμβάνει (παρόμοια λειτουργία με το CDMA) και την μετατοπίζει συχνοτικά βασιζόμενη στον εκάστοτε χρήστη (παρόμοια λειτουργία με το OFDMA). Στον δέκτη οι ακολουθίες των χρηστών διαχωρίζονται χωρίς πρόβλημα ακόμα και όταν το κανάλι είναι συχνοτικά επιλεκτικό. Σε αυτή την περίπτωση εισάγεται διασυμβολική παρεμβολή με αποτέλεσμα να απαιτείται κάποια διαδικασία ισοστάθμισης. Η δομή με βάση την οποία έγινε η μελέτη της τεχνικής πολλαπλής πρόσβασης IFDMA είναι η εξής: 1. Αναφορά στις τρέχουσες τεχνικές πολλαπλής πρόσβασης και στα πλεονεκτήματα και τα μειονεκτήματα της κάθε τεχνικής. 2. Μελέτη της τεχνικής IFDMA και αναφορά στα προβλήματα που εμφανίζει πχ ισοστάθμιση. 3. Παρουσίαση της υλοποίησης της τεχνικής IFDMA και των λύσεων για τα προβλήματα που παρουσιάζει, τα πειραματικά αποτελέσματα που σχετίζονται με την υλοποίηση, καθώς και συγκριτικά αποτελέσματα με τις πιο γνωστές τεχνικές πολλαπλής πρόσβασης. 4. Συμπεράσματα της μελέτης και της σύγκρισης της τεχνικής IFDMA με τις γνωστές τεχνικές πολλαπλής πρόσβασης, καθώς και πιθανές μελλοντικές κατευθύνσεις. / In recent years, we have seen a rapid growth in the telecom industry and this is evident in our everyday lives. The digital transmission and processing of signals in conjunction with the improvement of the transmission, infrastructure and technical configuration means, gives scientists the opportunity to focus increasingly on telecommunications issues, specifically on wireless telecommunications. In wireless telecommunications, multiple access techniques are used, in order to allow multiple users to share simultaneously a limited range of frequencies. Spectrum splitting is necessary, in order to increase the capacity of a system and should be done in a way that results in no significant degradation of system performance. To overcome this degradation various multiple access techniques have been proposed. According to one of these techniques, the total frequency spectrum is divided in frequency of non-overlapping sub-bands which are assigned to individual users (multiple access frequency division - FDMA). In this case, however, we are wasting the bandwidth of the channel, since users can not use all the channel, all the time. A technique that solves the above problem (multiple access with codes - CDMA) uses orthogonal codes, assigned to users, allowing them to simulcast in the channel for as long as needed. The main problem of this technique is that the status of orthogonality is lost when frequency selective channels are used. A new multiple access technique proposed, which avoids these problems, is the multiple access with frequency division and reorganization of data (Interleaved FDMA). This technique combines features from FDMA and CDMA. Specifically, it compresses timewise the sequence of symbols to be sent, repeats it (an operation similar to CDMA) and shifts it, in terms of frequency range, based on each user (a function similar to OFDMA). In the receptor’s side, the sequences of users separate without problem, even when the channel is frequency selective. In this case, intersymbol interference is introduced, which, therefore, requires an equalization process. The structure, upon which the study of the multiple access technique IFDMA made, was: 1. Reference to the current multiple-access techniques and the advantages and disadvantages of each one of them. 2. Study of the IFDMA technique and reference to the problems that it presents e.g. equalization. 3. Presentation of the implementation of a) the IFDMA technique, b) solutions for the problems it displays, c) experimental results and d) the results from the comparison against the most popular multiple-access techniques. 4. Conclusions, stemming from the study and the comparison of the IFDMA technique with the known multiple-access techniques; possible future prospects.