Power-amplifier efficiency is a significant issue for the overall efficiency of most wireless system. Therefore, currently there are different kind of Switched mode power amplifiers are developed which are showing very high efficiency also at higher frequencies but all of these amplifiers are subjected to drive with the constant envelope signals. Whereas, for the increasing demand of high data rate transmissions in wireless communication there are some new modulation schemes are introduced and which are generating no more a constant envelope signal but a high peak to average power signal. Therefore, recently a new technique is proposed called the burst mode operation for operating the switched mode power amplifiers efficiently while driven by a high peak to average power signal.   The purpose of this master thesis work was to review the theory of this burst mode operation and some basic investigations of this theory on switched mode power amplifiers were performed in simulation environments. The amplifiers of class D, inverse D, DE and J are studied. The thesis work was mainly carried out by ADS and partly in MATLAB SIMULINK environment. Since this burst mode operation is a completely new technique therefore a new Harmonic balance simulation setups in ADS and Microwave Office are developed to generate the RF burst signals.   A Class J amplifier based on LDMOS technique is measured by a 16 carrier multi-tone signal having peak to average power ratio of 7 dB and achieved the drain efficiency of 50% with -30 dBc linearity at 946 MHz.

Transport Control Protocol (TCP) is the dominant protocol in modern communication networks, in which the issues of reliability, flow, and congestion control must be handled efficiently. This thesis studies the impact of the next-generation bufferless optical burst-switched (OBS) networks on the performance of TCP congestion-control implementations (i.e., dropping-based, explicit-notification-based, and delay-based). The burst contention phenomenon caused by the buffer-less nature of OBS occurs randomly and has a negative impact on dropping-based TCP since it causes a false indication of network congestion that leads to improper reaction on a burst drop event. In this thesis we study the impact of these random burst losses on dropping-based TCP throughput. We introduce a novel congestion control scheme for TCP over OBS networks, called Statistical Additive Increase Multiplicative Decrease (SAIMD). SAIMD maintains and analyzes a number of previous round trip times (RTTs) at the TCP senders in order to identify the confidence with which a packet-loss event is due to network congestion. The confidence is derived by positioning short-term RTT in the spectrum of long-term historical RTTs. The derived confidence corresponding to the packet loss is then taken in to account by the policy developed for TCP congestion-window adjustment. For explicit-notification TCP, we propose a new TCP implementation over OBS networks, called TCP with Explicit Burst Loss Contention Notification (TCP-BCL). We examine the throughput performance of a number of representative TCP implementations over OBS networks, and analyze the TCP performance degradation due to the misinterpretation of timeout and packet-loss events. We also demonstrate that the proposed TCP-BCL scheme can counter the negative effect of OBS burst losses and is superior to conventional TCP architectures in OBS networks. For delay-based TCP, we observe that this type of TCP implementation cannot detect network congestion when deployed over typical OBS networks since RTT fluctuations are minor. Also, delay-based TCP can suffer from falsely detecting network congestion when the underlying OBS network provides burst retransmission and/or deflection. Due to the fact that burst retransmission and deflection schemes introduce additional delays for bursts that are retransmitted or deflected, TCP cannot determine whether this sudden delay is due to network congestion or simply to burst recovery at the OBS layer. In this thesis we study the behaviour of delay-based TCP Vegas over OBS networks, and propose a version of threshold-based TCP Vegas that is suitable for the characteristics of OBS networks. The threshold-based TCP Vegas is able to distinguish increases in packet delay due to network congestion from burst contention at low traffic loads. The evolution of OBS technology is highly coupled with its ability to support upper-layer applications. Without fully understanding the burst transmission behaviour and the associated impact on the TCP congestion-control mechanism, it will be difficult to exploit the advantages of OBS networks fully.

In this thesis, the pulse diversity technique in radar systems in high clutter environments is investigated. In this technique, different pulse compression methods are used in each pulse in the transmitted burst to increase the unambiguous range. In pulse diversity, the design of filters used in the receiver is as important as designing the transmitted waveform. At the output of pulse-burst filter that processes pulse-by-pulse, as many channels as the pulses in the burst occur. Each of these channels is matched to a certain range interval. In order to improve the detector performance, the phase codes used in the transmitted pulse-burst waveform and their corresponding filters must have good auto-correlation and cross-correlation properties, either individually or as their sum. In the literature some phase codes, having mentioned properties, are present. However, the performance of these codes in radar applications is not fully evaluated. The studies in the thesis show that the codes in the literature cannot be used directly in radar applications. In the scope of thesis, optimization criteria suitable for radar applications are defined and applied according to the mentioned requirements. Then, the obtained phase codes are tested in the radar simulator and the obtained results of the simulations are evaluated.

In this thesis, a feedback-based contention avoidance technique based on weighted Dijkstra algorithm is proposed to address the contention avoidance problem for Optical Burst Switching networks. Optical Burst Switching (OBS) has been proposed as a promising technique to support high-bandwidth, bursty data traffic in the next-generation optical Internet. Nevertheless, there are still some challenging issues that need to be solved to achieve an effective implementation of OBS. Contention problem occurs when two or more bursts are destined for the same wavelength. To solve this problem, various reactive contention resolution methods have been proposed in the literature. However, many of them are very vulnerable to network load and may suffer severe loss in case of heavy traffic. By proactively controlling the overall traffic, network is able to update itself in case of high congestion and by means of this method / contention avoidance can be achieved efficiently. The performance analysis of the proposed algorithm is presented through network simulation results provided by OMNET++ simulation environment. The simulation results show that the proposed contention avoidance technique significantly reduces the burst loss probability as compared to networks without any contention avoidance techniques.

In this thesis, burst distance is optimized to increase air defense capability for systems utilizing airburst munitions. A simulator program is created to use during the study by taking advantage of the MATLAB environment. While creating the simulator program, a munition path model is derived by using fourth order Runge-Kutta method. Then, simulations are conducted at different burst distances and related information are recorded. By using least square optimization method and gathered data, optimum burst distance is found. Moreover, the effects of several factors on optimum burst distances are analyzed, including: the weights of the objectives in the optimization, target dimensions, target range, wind, target position ambiguity, firing angle, and velocity ambiguity after burst. Furthermore, a firing method is proposed. The result of the proposed firing method and the optimum solution are compared and success is presented. To sum up, this study presents a way to find optimum burst distance, analyzes the factors that may affect optimum burst distance, and suggests a firing method for effective shots.

Airburst projectiles increase the effectiveness of air defense, by forming clouds of small pellets. In this work, in order to evaluate the effectiveness of airburst projectiles, Single Shot Kill Probability (SSKP) is computed at different burst distances by using three lethality functions defined from different measures of effectiveness. These different measures are target coverage, number of sub-projectile hits on the target and kinetic energy of sub-projectiles after burst. Computations are carried out for two different sub-projectile distribution patterns, namely circular and ring patterns. In this work, for the determination of miss distance, a Monte Carlo simulation is implemented, which uses Modified Point Mass Model (MPMM) trajectory equations. According to the results obtained two different distribution patterns are compared in terms of effectiveness and optimum burst distance of each distribution pattern is determined at different ranges.

The aim of this study was to investigate the effects of resin and fiber on the abrasion, impact and internal pressure resistances of fiber reinforced plastic composite pipes produced by continuous filament winding method. For this study, pipe samples were produced with different combinations of resin type, fiber type, fiber amount and fiber length. All the samples were tested in accordance with the related ISO (International Organization for Standardization), DIN (German Standardization Institution) and BSI (British Standards Institution) standards. Three types of resins were used as ortophthalic, isophthalic and vinylester / two types of fibers were used as E-glass and ECR-glass and one type of GLASSFLAKES was used as C-glass. It was observed that the type of resin did not have any significant effect on burst pressure. However, the vinylester resin had a considerable positive effect on the abrasion and impact resistances. Moreover, it was observed that the type of fiber did not have any significant effect on impact and internal pressure resistances, but the use of C-glass GLASSFLAKES resulted in a positive effect on the abrasion resistance. Additionally, it was found that the increase in the amount of glass fiber resulted in increase of burst pressure, impact and abrasion resistances. Finally, it was observed that the length of glass fiber did not have any significant effect on abrasion resistance, but the decrease in fiber length resulted in a higher internal pressure and impact resistances.

This thesis reports the design, construction, and the initial results obtained from a digital spectrograph for observations of radio burst emission from the Sun. One of the distinct advantages of radio spectral studies of the Sun during events such as solar flares, coronal mass ejections (CMEs), etc. is that it gives a straight forward estimate of the speed of the outflowing material into the outer atmosphere of the Sun and subsequently the interplanetary medium. It is well known that in the solar atmosphere, the electron density and consequently the plasma frequency gradually decreases with increasing distance from the center. Therefore in a time-frequency plane, the intensity of the associated radio emission should generally drift from high to low frequencies with time. From this, and from a knowledge of the height of the successive plasma levels in the solar atmosphere, one can deduce the speed of the outward moving disturbance. In this respect, a study of the radio bursts at decameter wavelengths is important since such radiation originates from the corona at heights ≥1.3 R⊙ (1 R⊙ = 6.96 x 10° km = radius of the Sun) from the center of the Sun, which are otherwise accessible only through the use of white light coronagraphs atop high altitude mountains and onboard space vehicles. The primary units of the instrument are (i) zero-crossing detector (ZCD), (ii) sampler and (iii) correlator. The function of the ZCD is to digitize the input signal waveform. In the present case, we use a one-bit quantizer, i.e., its output is either a '1' or '0' depending on whether the input is above or below the zero level, respectively. The digitized signals are then sampled at the Nyquist rate using the sampler. The output of the sampler is then passed through a set of shift registers, and finally fed to the correlator. The latter measures the correlation between the signals at its input as a function of the delay (introduced by the shift registers) between them. After successful completion of several static/dynamic tests in the laboratory, the system was moved to the Gauribidanur radio observatory (Latitude: 13°36’12”; Longitude:77°27’07”), and is presently used along with the existing radiohe-liograph to derive both the spectral and spatial information of the various radio emitting transient sources on the Sun, respectively. The R..F. signal (40-150 MHz) from one of the antenna groups of the ra-dioheliograph forms the input to the spectrograph. The signal from the field goes through a series of amplification and mixing operations to bring it down to an I.F. of 10 MHz with a bandwidth of 1 MHz, and then fed to the spectrograph. The present frequency range of the spectrograph is 40 MHz, and the data corresponding to the above band is obtained in steps of 1 MHz by switching the local oscillator through a GPIB interface, after each integration period. Each 1 MHz data is then Fourier tranformed to get its corresponding power spectrum. Successive data sets are then arranged in order according to the frequency of the local oscillator signal to get the spectrum corresponding to the entire 40 MHz band. The initial results obtained with our instrument are also presented.

La performance accrue des instruments dans une vaste gamme de longueur d'onde a montré qu'une grande partie des étoiles jeunes étaient entourées de matière sans doute répartie dans un disque. La détection de tels systèmes par imagerie directe est difficile du fait de la faible taille angulaire de ces objets, ainsi que de leur faible luminosité en comparaison avec l'étoile. Il semble aujourd'hui que près de 50 \% d'étoiles pré-séquence principale de faible masse, dites étoiles T Tauri, soient entourées d'un disque. Cette proportion est beaucoup moins évidente pour les étoiles plus massives, dites Herbig Ae, du fait de leur faible nombre et du faible nombre de détections directes.<br />Jusqu'à présent, seule l'interprétation de la distribution spectrale d'énergie (SED) de ces objets permettait d'inférer la structure géométrique des disques autour des étoiles Herbig Ae. Les modèles sont fortement dégénerés et il est primordial d'obtenir des images, seules preuves directes de la présence ou non de disque. <br />Cette thèse a permis de mettre en évidence l'apport de l'imagerie en infrarouge moyen pour lever une partie de la dégénérescence liée à l'interprétation de la SED et mieux contraindre, pour plusieurs objets, les paramètres des disques, comme le rayon externe minimal ou l'inclinaison. De plus, nous présentons un nouveau mode d'observation avec VISIR, l'instrument pour les observations en infrarouge moyen au VLT (ESO, Chili): le mode BURST. Ce mode permet d'atteindre la limite de résolution spatiale déterminée par la diffraction. Grâce à l'imagerie en infrarouge faite avec cet instrument, cette thèse a permis de déterminer, pour la première fois, la géométrie (structure évasée) d'un disque autour d'une étoile massive inférée au préalable par l'interprétation des SEDs.

Η οπτική μεταγωγή καταιγισμών (Optical Burst Switching) είναι ένα ελπιδοφόρο παράδειγμα μεταγωγής για την επόμενη γενεά του Διαδικτύου. Ένα βασικό πρόβλημα στα δίκτυα OBS είναι η δρομολόγηση και ο χρονοπρογραμματισμός των καταιγισμών στους συνδέσμους του δικτύου, ώστε να μειωθεί η απώλεια και η καθυστέρηση τους. Εδώ παρουσιάζουμε έναν βασισμένο στην πηγή αλγόριθμο δρομολόγησης και χρονοπρογραμματισμού πολλαπλών κριτηρίων για την επιλογή μονοπατιών (διαδρομών) που ακολουθούνται από τους καταιγισμούς. Ο αλγόριθμος επιπλέον υπολογίζει και το χρόνο στον οποίο πρέπει να αρχίσει η μετάδοση των καταιγισμών ώστε να φθάσουν στον προορισμό με την ελάχιστη καθυστέρηση. Τα διαγράμματα χρησιμοποίησης (utilization profiles) των συνδέσμων του δικτύου, η καθυστέρηση διάδοσης των συνδέσμων και οι παράμετροι των καταιγισμών (μέγεθος, offset time κ.α.) διαμορφώνουν τα δεδομένα εισόδου του αλγορίθμου. Το προτεινόμενο σχήμα εκμεταλλεύεται τα κενά (void filling) που προκύπτουν από τη χρήση του bandwidth σε κάθε σύνδεσμο ώστε να βρεθεί η καλύτερη διαθέσιμη διαδρομή. Όταν δεν υπάρχει καμία κατάλληλη διαδρομή τη χρονική στιγμή που ζητείται από τον καταιγισμό, ο αλγόριθμος καθορίζει επίσης το χρονικό διάστημα (Time Offset) που πρέπει να καθυστερήσουμε τον καταιγισμό στην πηγή έως ότου γίνει διαθέσιμη η καλύτερη δυνατή διαδρομή. / Optical burst switching (OBS) is considered a promising switching paradigm for the next generation Internet. A key problem in OBS networks is the routing and scheduling of the bursts on the network links, so as to reduce burst loss and delay. In this paper we present a source-based multicost routing and scheduling algorithm to select the paths to be followed by the bursts and the times when the bursts should start transmission from their source so as to arrive at their destination with minimum delay. The utilization profiles of the network links, the link propagation delays, and the parameters of the bursts that have to be scheduled form the inputs to the algorithm. The proposed scheme exploits gaps in capacity utilization so as to find the best available path. When there is no suitable path at the time it is requested, the algorithm also determines the amount of time the burst must be delayed at the source for the best path to become available.