The Global System for Mobile communications (GSM), which covers 54% of the world's mobile market, evolved into the General Packet Radio Service (GPRS). The thesis addresses interference suppression using new radio frequency (RF) and microwave design methods for GSM and GPRS. The overall outcome is interference reduction and enhanced network capacity, leading to superior quality of service (QoS) for wider area coverage. The main results can be summarized as follows * Design, manufacturing and characterisation measurements of new compact filters for GSM and GPRS base stations in order to reduce the out-of-band interference. It is shown that filters with novel microstrip resonators - dual mode filters and cross coupled filters - provide both a high degree of miniaturisation and narrow bandwidth. * Development of a new 3-D Finite-Difference Time-Domain (FDTD) design method for new microstrip filters. A non-homogeneous Perfectly Matched Layer (NH-PML) was implemented for Absorbing Boundary Conditions (ABC) to increase the accuracy of the FDTD method. Signal estimation techniques were developed to speed up FDTD computations. A novel design method based on neural networks (NN) and FDTD was implemented to reduce the total design time. * Investigation of High Temperature Superconductors (HTS) thin film resonators and antennas at microwave frequencies. High Q-factor HTS devices considerably enhance both the front-ends sensitivity and selectivity of wireless receivers. * Design, manufacturing and testing of radio frequency (RF) electronics for 16 elements GSM and GPRS Smart Antenna for multipath fading mitigation and for in-band interference including co-channel interference (CCI) suppression.

IEEE 802.16標準中，有所謂Multi-hop Relay (MR)的概念，其中存在很多問題需要解決，所以在IEEE 802.16j標準中提出中繼傳輸站(Relay Station，RS)來延伸原來的涵蓋範圍及解決遮蔽效應造成訊號衰弱的問題。但在MR中由於多了中繼傳輸站來傳遞資料，網路拓樸變得相對複雜，資料從發送端到接收端的路徑變長了，在資料大量傳輸的狀況下，會因干擾及壅塞的問題變得嚴重而導致整個網路效能低落。本研究提出一套具干擾感知的排程方法，可有效提升網路效能。本方法分為三個部分，首先在允入控制階段盡可能選取高調變的連線，其次利用空間距離的分群概念提出TZG (Time Zone Grouping)方法，以逆時針的方式區分不同RS傳輸的時區，最後以調整分區內non-real time服務的頻寬需求，減少RS在access zone頻寬的浪費。我們利用NS2進行模擬實驗分析，驗證所提出的方法在利用分區傳送避免碰撞下，UGS的delay time相較於未分群的方法可有效改善約33%，ertPS可改善約29%，rtPS可改善約20%，而系統throughout相較於其他僅選擇最大access link的頻寬需求作為access zone大小的方法最多可提升約15.5%的效能。 / As we know, there is Multi-hop Relay concept in standard of IEEE 802.16. But there are still many problems unsolved in WiMAX, so IEEE 802.16j propose a new station type, relay station, to extend signal coverage and improve the signal intensity which affected by shadow fading. Since there are many relay stations in the coverage of base station, data transmission and path routing become more complexity. At the same time, the transmissions become close, more interference and network congestion will decrease the efficiency of data transmission in the network. This research proposes a frame scheduling with interference aware, which consist of three parts. First, we make the better modulation of links get higher priority; Second, we use concept of distance to proposed Time Zone grouping (TZG), which set RS into different group in counterclockwise way to reduce interference; Third, adjusting bandwidth allocation in access zone to decrease bandwidth waste in access zone. We implement our algorithm in NS2 simulator, the result shows that our method can improve delay of UGS about 33%, ertPS about 20%, rtPS about 20% than RTDS(Real time Distributed Scheduling ), and the system throughput can grow about 15.5% than the mechanism that just choose maximum requirement in access link of all BS/RS as access zone.

This thesis investigates techniques and algorithms for mitigating radio frequency interference (RFI) affecting radio astronomy observations. In the past radio astronomy has generally been performed in radio-quiet geographical locations and unused parts of the radio spectrum, including small protected frequency bands. The increasing use of the entire spectrum and global transmitters such as satellites are forcing the astronomy community to begin implementing active interference cancelling. The amount of harmful interference affecting observations will also increase as future instruments such as the Square Kilometre Array (SKA) are required to use larger bandwidths to reach up to 100 times the current sensitivity levels, and as spectral line observations require observing in bands licensed to other spectrum users. Particular attention is paid to interference cancellation algorithms which make use of reference beams. This has proven to be successful in removing interference from the contaminated astronomical data. Reference antenna cancellers are closely analysed, leading to filters and techniques that can offer improved RFI excision for some important applications. It is shown that pre- and post-correlation reference antenna cancellers give similar results, and an important aspect of the cancellers is the use of a second reference signal when the reference interference-to-noise ratio is low. These modified filters can theoretically offer infinite interference suppression in the voltage domain, equivalent to that of post-correlation interference cancellers, and their internal structure can offer an understanding of the residual RFI and added receiver noise components of a variety of reference antenna techniques. The effect of variable geometric delays is also considered and various filters are compared as a function of the geometric fringe rate.

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

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

<p>This thesis describes the interference problem between IEEE 802.11 and Bluetooth. These well established communication standards are often used together simultaneously. Since both standards operate in the ISM-band at 2.45 GHz, they interfere with each other. In addition to this, interference from e.g. microwave ovens, heating processes, electric motors and cordless phones also occurs on the ISM-band. Due to this interference problem, a model has been developed in MATLAB to further investigate these interferences and the effects for the user.</p><p>The interference is modelled using the well known Class-A model for impulsive noise. The interference model is parameterized in the model and therefore the noise source(s) is described by a set of parameters derived from real measurements. Models for IEEE 802.11 legacy/b and Bluetooth are based on work published on the user community of MATHWORKS. To get a measure of performance, results from the model are presented as BER (Bit Error Rates) and PER (Packet Error Rates). When Bluetooth is used as a voice link, sound quality can also be performance evaluated directly by simply listening to a voice output file. To be able to track down a specific problem cause, measuring tools have also been included in the model to gain insight into what is causing bit/packet error.</p><p>A model describing the interference problem has been developed describing the real world usage of the standards by the use of state machines. Due to the complexity of the problem, and also for the model to be user friendly, this thesis is not composed of a thorough mathematical derivation describing BER probability for different modulation forms. The derivations for these has already been done and is therefore summarized and compared to when the model is validated. The model has been developed as a proof of concept for further work to fully support the current and coming IEEE standards for IEEE 802.11 and Bluetooth.</p>

<p>This is an essay about the political development of Iraq after the overthrow of the Baath regime by the coalition forces in 2003. Almost seven years later, the political scene is still characterised by chaos, even though the country entered a new phase with the adoption of democratic thinking and a new openness to the world. The unstable political situation is a product of inter-ethnic conflict and the interference by neighbouring countries. Iraq is up against two formidable tasks – building democracy and building a nation. The essay sets out to explore the prospects of this dual mission.</p><p>The essay breaks down into three distinct, theoretically motivated parts or sections. The first part is inspired by O’Donnell & Schmitter’s transition theory and revolves around Iraq’s transition from dictatorship to democracy. The second part sets out to evaluate the development of democracy in Iraq after Saddam Hussein in the light of the seven institutional criteria of <em>polyarchies</em> as identified by Robert Dahl. The third part evaluates Iraq in terms of Arendt Lijphart’s groundbreaking theory about consensus as a pre-condition for democracy in highly divided societies.</p><p>The investigation confirms the general picture of the political situation in Iraq as unstable but with one notable exception – the Kurdish region. The constitution testifies to the ambition to turn Iraq into a polyarchy with strong elements of consensual democracy, but the spirit of the constitution is frequently violated by government institutions and individual politicians. The consensual features have in fact served as safety valve for the ethnic and religious minorities of Iraq; but it is an open question whether they will survive the onslaught by Prime Minister Al-Maliki, a recent convert to the Westminster model. The unclear relationship between Islam and democracy also looms large in the background in a country like Iraq and must somehow be resolved by the governing elite.</p>

<p>Ultra wideband (UWB) communication systems refers to systems whose bandwidth is many times greater than the “narrowband” systems (refers to a signal which occupies only small amount of space on the radio spectrum). UWB can be used for indoor, communications for high data rates, or very low data rates for substantial link distances because of the extremely large bandwidth, immune to multi-path fading, penetrations through concrete block or obstacles. UWB can also used for short distance ranging whose applications include asset location in a warehouse, position location for wireless sensor networks, and collision avoidance.</p><p>In order to verify analytical and simulation results with real-world measurements, the need for experimental UWB systems arises. The Institute of Communications Engineering [IANT] has developed a low-cost experimental UWB positioning system to test UWB based positioning concepts. The mobile devices use the avalanche effect of transistors for simple generation of bi-phase pulses and are TDMA multi-user capable. The receiver is implemented in software and employs coherent cross-correlation with peak detection to localize the mobile unit via Time-Difference-Of-Arrival (TDOA) algorithms. Since the power of a proposed UWB system’s signal spread over a very wide bandwidth, the frequencies allocated to multiple existing narrowband systems may interfere with UWB spectrum. The goal of the filters discussed in this project is to cancel or suppress the interference while not distort the desired signal. To investigate the interference, we develop a algorithm to calculate the interference tones. In this thesis, we assume the interference to be narrowband interference (NBI) modeled as sinusoidal tones with unknown amplitude, frequency and phase. If we known the interference tones then it may be removed using a simple notched filter. Herein, we chose an adaptive filter so that it can adjust the interference tone automatically and cancel. In this thesis I tested adaptive filter technique to cancel interference cancellation (ie) LMS algorithm and Adaptive Noise Cancellation (ANC) technique. In this thesis performance of the both filters are compared.</p>

Comment les différents aspects d'une scène visuelle sont-ils encodés en mémoire visuelle à court-terme (MVCT) ? S'il est communément admis que la MVCT ne peut stocker simultanément qu'un nombre extrêmement limité d'informations, la question du format des représentations est actuellement loin d'être résolue. Cette thèse avait pour objectif d'étudier les influences de l'organisation perceptive des différents éléments d'une scène visuelle sur la capacité de stockage de la MVCT. Pour ce faire, dix expériences, utilisant le paradigme de détection de changement (c'est-à-dire en présentant deux séries de stimuli séparées par un court laps de temps et en demandant aux participants de détecter un éventuel changement entre ces deux séries) ont été réalisées. La principale manipulation expérimentale était la comparaison entre différentes organisations perceptives des stimuli dans le champ visuel. Les résultats de nos recherches ont contribué de façon significative à une meilleure compréhension de la façon dont les différents aspects d'une scène visuelle sont traités et encodés en MVCT et suggèrent l'existence de différents types de représentations organisées hiérarchiquement. Tout d'abord, les relations spatiales entre tous les éléments d'une scène visuelle seraient encodées sous la forme d'une configuration spatiale. Cette représentation configurale permettrait, dans un deuxième temps, l'analyse et l'encodage de l'identité individuelle des différents éléments. A ce niveau, nous avons montré que le nombre d'éléments pouvant être simultanément encodés et maintenus en MVCT pourrait dépendre considérablement de la manière dont ils sont présentés dans le champ visuel des participants. Ainsi, lorsque différents traits (couleur, forme, texture, orientation, etc.) occupent la même localisation spatiale, formant ainsi une même partie d'un objet, ils seraient traités et encodés aussi efficacement qu'un simple trait. Dans ce cas, la capacité de stockage de la MVCT doit être comprise en terme d'objets intégrés. Par contre, lorsque les traits d'un objet sont spatialement séparés les uns des autres, constituant différentes parties d'objets, le nombre d'éléments pouvant être simultanément encodés en MVCT est fonction du nombre de traits présents dans le champ visuel, et non du nombre d'objets. L'organisation perceptive des informations visuelles a donc une influence directe sur le nombre d'éléments pouvant être simultanément encodés en MVCT en modifiant la nature des représentations./ How are the different aspects of a visual scene encoded in visual short-term memory (VSTM)? Although it is acknowledged that only a small number of information can be simultaneously stored in VSTM, the format of representation is far to be understood. The goal of the present thesis was to study the perceptual influences of the items in a visual scene on the VSTM storage capacity. Ten experiments, using the change detection paradigm (i.e., two stimuli arrays were presented and separated by a short period of time, and the task was to detect a possible change between the two arrays) were conducted. The major experimental manipulation was to contrast different perceptual organisations of the stimuli in an array. The results of those experiments have significantly contributed to a better understanding about how the different aspects of a visual scene are processed and encoded in VSTM and suggest the existence of different types of representation, hierarchically organised. Firstly, the spatial relations between items in a visual scene would be encoded though spatial configuration. Then, this configural representation would allow the processing and the encoding of the identities of each individual item. Here, the number of items that can be simultaneously encoded in VSTM might greatly depend on the way they are presented in the visual field. Indeed, we provided evidence that visual features (colour, shape, texture, orientation), that share the same spatial location, are encoded in VSTM as accurately as single features. In that case, the VSTM storage capacity must be understood in terms of integrated objects rather than in terms of single features. In contrast, when visual features are spatially distributed over different spatial locations, the limitation in the storage capacity is function of the number of features. The perceptual organisation of the visual information has thus a direct influence on the number of items that can be simultaneously encoded in VSTM by modulating the nature of representations.

Robert J. McLaughlin. / "This report is based on a thesis submitted to the Department of Electrical Engineering, M.I.T., June 1958, in partial fulfillment of the requirements for the degree of Master of Science." / Bibliography: p. 33. / Army Signal Corps Contract DA36-039-sc-78108. Dept. of the Army Task 3-99-20-001 and Project 3-99-00-000.