<p>When estimating tissue velocities, the conventional autocorrelation method (AM) is only biased if the demodulation frequency is correctly estimated. While AM assumes the received centre frequency to be constant, the modified autocorrelation method (MAM) estimates the received centre frequency continuously from pulse to pulse. Although MAM has shown superior performance in simulation environments, it fails to show consistently better performance compared to AM when applied to experimental data. In order to investigate this lack of consistency, a model for simulation of signal from moving tissue was developed, including realistic aspects such as thermal noise, signal from clutter and aliasing. The simulation model was adapted using experimental tissue data and parameters from a true acquisition system. A 1st order FIR filter was applied for clutter rejection prior to velocity estimation. The investigations using simulation data shown faster performance degradation of MAM compared to AM when the amount of signal from clutter or thermal noise were increased independently. For clutter signal mimicking acoustic noise from reverberations, MAM went from significantly better under low-noise conditions to approaching AM performance when the signal-to-clutter ratio became lower than 10 dB. Analogously, MAM approached AM performance when the signal-to-noise ratio was lower than 15 dB. Velocity estimation of experimental data shown MAM's robustness to frequency dependent attenuation by means of frequency compensation, while AM suffered from bias effects due to erroneously estimated demodulation frequency. The frequency compensation did, however, not succeed to approve lower estimation variance in MAM compared to AM. Statistical analysis based on expected values from simulations, demonstrated correlation between the estimation error in AM and MAM.</p>

<p>A acquisition module for the OpenGNSS software receiver has been implemented as GNU Radio module. It has been tested and the functionality has been verified with both simulated and real signal. A number of proposals for future work and modifications to the GNU Radio framework has also been presented.</p>

<p>In this thesis, a measurement set-up has been developed to characterize high frequency medical ultrasound transducers using a pulse echo set-up. This work is a continuation of an earlier project. The aim of this project is to improve the instrumentation to get more reliable, repeatable and consistent results. The transducer used in this project was a 20MHz annular array transducer with 8 elements. Parameters such as the electroacoustic transfer function and reflection coefficients of element 1 and 2 have been found for a sinusoidal burst excitation and a Gaussian excitation, to give examples for the estimation of these parameters. Developing the right instrumentation for the pulse echo set-up and transducer for pulse echo measurements has been emphasised, where a transducer holder and reflector have been constructed for characterization of elements 1-5. A cylindrical water resistant reflector with a curved top was designed giving certain degrees of freedom as opposed to the pure spherical reflector concerning positioning of the reflector with respect to the transducer. A slanted bottom was included in the design of the reflector causing reflections from the bottom to diffract and thus stopping these from interfering with the reflections of interest happening at the top of the reflector surface. A transducer holder was also designed and custom made for the transducer used in the project, where both mechanical and electrical considerations have been taken, as the holder makes alignment of the transducer with respect to the reflector easier and coaxial cables have been introduced to get more control over the signals going to and from the transducer array. Coaxial cables were chosen as these are easy to model, and have clear specifications in addition to having the property of shielding noise signals. Alignment of the transducer has been emphasised to make radiation into the focus of the reflector easier, although the design of the reflector also allows the reflector to be tilted in the allocation of its focus point. By taking detailed lateral scans of echoes received by the transducer using a robot, in addition to varying the distance between the transducer and the reflector with an increment of 0.2 mm, the reflection coefficients were found to be very sensitive to lateral positioning, and to some extent sensitive to axial positioning of the transducer with respect to the reflector. The elimination of propagation delay due to the signals travel in waterpath and electrical transmission and reception chain leading to the transducer ports has also been compensated for, as these delays will effect the complex values of the transfer function. The electrical propagation delay is eliminated by using a simulation program, and analysis of the time between two consecutive echoes is done in order to find the physical time delay in the water path the pulses travelled. The electro acoustic transfer function has also been found for element 1 and element 2, but with a much greater time delay than what was expected. An uncertainty budget of the obtained parameters has also been done to see the impact of laboratory equipment on the meaurements. Estimation schemes to obtain reflection coefficients and the electro acoustic transfer function have been developed, which are repeatable for further characterization for the whole transducer array. Existing MATLAB codes have been modified in simulations and some new codes have been written for analyzing measurement based estimation of transfer functions, reflection coefficients and effects of various filters on their characteristics. Different types of filters have been used on the recorded echo signals to eliminate noise from the estimated reflection coefficients. A better control of the parasitic inductances due to the non coaxial cables in the system should perhaps be evaluated, and for further characterization of the transducer, the mechanical admittance can also be found by using the estimated reflection coefficients and electro acoustic transfer function.</p>

<p>The thesis concerns the design and prototype construction of a UHF half-duplex radio system, intended for use on board a small student satellite. The assignment is a continuance of a project assignment done during the fall of 2006, concerning the outline and specification of a new student satellite project at NTNU. The report details performance-deciding parameters of satellite communication systems operating at UHF frequencies, and fundamental information theory. Theory and application of RF design is discussed, along with complications in electronic engineering due to space environment factors. The report goes on to describe the design process and prototype development of a UHF transceiver intended for use in small, low power LEO satellites.</p>

<p>Mobility and freedom are two driving forces for research in wireless sensor networks. Recent advances in hardware development, offering low-cost, low-power sensor devices open up for an exciting research field where only the imagination can stop us from developing exiting and revolutionary applications. In the medical field sensor networks can be used to remotely monitor physiological parameters such as heartbeat or blood pressure or patients, and report to the hospital when some parameters are altered. This is a huge research field, and much research will be done in the coming years to cope with recently unsolved issues. This Master's thesis will present and describe a customized, tailor-made, and optimized cross-layer implementation of a communication protocol for medical purposes. The research platform is based on the IEEE802.15.4/ZigBee protocol that is widely popular for sensor networks applications. ZigBee based wireless sensor network finds interesting applications in medicine, and its flexibility, low cost, small hardware and low power consumption are promising features that could effectively serve medical applications. Extended testing was necessary to address the implementation issues as well as finding optimization opportunities. The protocol has several exiting features, and experiments so far reveal very promising results.</p>

<p>Cosine Modulated Filter Banks Systems in the Presende of Multipath Transmission</p>

<p>As broadcasted television is changing from analogue to digital transmission, the television industry has to adapt itself for a new reality. Digitization opens for a wide array of new ways of watching television, where interactivity and mobility are paramount. The difference in the experience lies in the interactive part, inviting the user to take part in what happens on the mobile screen. What the mobile telephone lacks in screen size it can now make up for with its interactive potential. Instead of just watching television, the user now interacts with it. As a result, the television experience can be tailored to suit consumers with different requirements. In this study I look at true-time broadcasted television to handheld devices over the standards achieved in Europe and Korea today, DVB-H and T-DMB, and how interactivity between content provider and end-user can be achieved. I also look into how metadata plays a crucial role in interactive television, and the means to utilize metadata to favor the end-user’s demands according to standards such as XML, MPEG and Tv-Anytime. By supplying metadata to i.e sport or reality shows, and hence creating interactivity between content provider and end-user, a new marked for television is made possible. Electronic program guides (EPGs), teletext and weather forecasts for handhelds are examples of ways that metadata can be utilized to create an interactive experience for the end-user.</p>

<p>Give an introduction to the proposed double CubeSat system and an overview of communication requirements and the propagation characteristics that influence the link budget. Based on the above findings, derive requirements for the ground station antenna. Emphasize simplicity and easy construction and propose an antenna system that may meet the requirements. Investigate it theoretically with available software to optimize its dimensions. A scale model of the antenna should finally be built and its main properties measured in an anechoic chamber.</p>

<p>Power amplifiers are nonlinear devices that traditionally have been tried linearized by means of predistortion. The nonlinear impact can be identified by sidelobes in the frequency domain. By accepting a certain sidelobe level, this implies that we also accept a somewhat nonlinear characteristic on the resulting cascade of our transmitter. The main question raised in this thesis is: How is the optimal nonlinear cascade that maximizes transmitted power defined when some given out-of-band spectral requirements are fulfilled? The problem has been limited such that examinations have been done on a single carrier system seen in context to a chosen set of out-of-band spectral requirements. The different nonlinear characteristics have been represented by means of B-splines. Thus, the results obtained are only the best set of parameters in the model utilized, and hence, only a sub-optimal solution to the problem. Results are presented for different spectral restrictions. Simulations performed suggest that a linear characteristic is the optimal, when restrictions are placed within the sidelobe level close to the mainlobe. When the first sidelobe is allowed to grow unlimited, a parameter set using 2-segments B-spline have proved to give the highest average transmitted</p>

<p>The evolution of services offered using communication technology has yielded a jungle of different services. Many of these services exhibits different QoS requirements; different requirements to delay, probability of packet-loss and throughput. Effectively this means they require different amounts of resources when handled in a network node. This thesis covers descriptions and simulations of four different scheduling algorithms deployed in a high-speed point-to-point radio-link scenario. The different algorithms examined in this thesis are the conventional First-In-First-Out (FIFO) algorithm, the Strict Priority (SP) queuing algorithm, the Deficit Round-Robin (DRR) algorithm and finally the Deficit Weighted Round-Robin (DWRR) algorithm. Theoretical presentations of each of the algorithms are followed by simulations which exhibits the characteristics of the different algorithms. Two of the mentioned algorithms (FIFO, DRR) does not offer capabilities of differentiation between different classified data-flows, while the two remaining algorithms (SP, DWRR) does. The simulations illustrates the advantages of deployment of scheduling algorithms capable of differentiating resource allocation with respect to the different QoS requirements of multiple data-flows. The simulation results reveals that when deployed in a high-speed point-to-point link, where low complexity is emphasized, the DWRR algorithm offers the most promising performances of the examined algorithms.</p>