<p>This thesis describes the work on designing and testing an antenna solution for communications between cars. The antenna that is to be used is a so called ESPAR antenna or Electronically Steerable Passive Array Radiator using monopoles over a circular ground plane. Simulations were made on the following variations of the antenna: • The number of passive monopoles and the angle between them • The radius and height of the active and passive monopoles • The height of the skirt and the radius of the ground plane • Matching schemes The antenna that was decided to be the best for this application had these characteristics: - Ground plane radius 75 mm or half a wavelength - Skirt height of 37.5 mm or a quarter wavelengths - Six parasitic monopoles with a height of 39 mm equally spaced around an active monopole of 35 mm - Distance from active monopole to parasitic monopoles of a quarter wavelengths - Half power beam width of about 90 degrees and a front to back ratio of 16 dB - Gain of about 7.5 dB and an elevation angle of 25 degrees From these results a prototype of the antenna was constructed with different heights of the active and parasitic monopoles. The measurements showed less variation between the different configurations of the antenna than the simulations indicated. The largest difference was the elevation angle of the antenna. This was found to be about 0 degrees for all configurations which is an improvement of about 25 degrees from the simulated results. The best results was found to be with an antenna that has the same configurations as the simulated one described above but with a parasitic monopole height of 37 mm. The measurements showed the following specifications: - Gain of about 9.5 dB - HPBW of 80 degrees - FTBR of about 12 dB Because of certain elements in the construction of the antenna the measurements of the matching were inconclusive, and were not weighed heavily in this thesis.</p>

<p>Non-intrusive testing of pipelines has become a growing industry, and is expected to keep growing as the demands on quality control and safety keep increasing. In order to meet the oil industry’s demands for pipe monitoring of sub sea pipelines, the SmartPipe project was initiated by SINTEF in Trondheim, Norway. One of the primary objectives of the SmartPipe project is develop a system for in-service monitoring of the pipelines that are placed on the seabed by the offshore oil industry. This thesis presents a very early step in the research required for the development of such a system. The purpose of the presented work was to carry out introductory experimental work in order to find out whether it is possible to develop relatively simple techniques for in-service testing of sub sea steel pipes. A so-called pitch-catch setup and various wedges was used in order to test the area between a pair of 5 MHz ultrasound transducers. Measuring over a distance of 1.00 m, rather than just single points on the pipe, could provide more general information about the condition of the pipe. Tests with over 4 m distance between transducers were also carried out. Measurement stability and mechanical coupling are of crucial importance in ultrasonic test systems, and useful knowledge on the subjects has been gained and are documented in this thesis. Results from measurements indicate that comprehensible results can be attained even with very simple measurement setups. Especially when using special wedges for introduction of Rayleigh waves, the received signals had high amplitudes and the signal envelope had a simple shape. The effect that the damage to the pipe had on the Rayleigh waves, was found to be equally simple and predictable. Shear waves and longitudinal waves that are less sensitive to the surrounding medium, were also shown to be applicable in flaw detection. Results and discussion include both time domain, frequency domain and energy considerations.</p>

<p>In this thesis the performance of the ALOHA and CSMA MAC protocols are analyzed in spatially distributed wireless networks. The main measurement metric used is probability of outage, a metric that is referred to in most of the related research done in this field, but has not been treated in detail thus far. Some of the research done on other performance metrics such as transmission capacity, throughput, bit error rate, spatial reuse and delay are also noted and described briefly in this report. In our system model, users/packets arrive randomly in space and time according to a Poisson point process, and are thereby transmitted to their intended destinations using a fully distributed MAC protocol (either ALOHA or CSMA). Our model allows simultaneous transmissions between many transmitter-receiver pairs in the network. An SINR-based model is considered, and a packet transmission is encountered as successful if the received SINR is above a predetermined threshold value for the entire duration of the packet. Accurate bounds on the probability of outage, which is a function of the density of transmissions, are developed for both MAC protocols. The methods used to reach the obtained analytical results are presented in detail, and the analytical results are shown to follow the simulation results tightly. We also present the methods that were used to find expressions for the outage probability, which turned out to not be as successful as desired in terms of following the simulation results tightly for all densities. Furthermore, the derived bounds for the probability of outage are used to determine the performance advantage that CSMA provides over ALOHA and also to gain insight into the design of general MAC protocols for ad hoc networks. Our final comparison results show that CSMA performs better than unslotted ALOHA, and worse than slotted ALOHA in terms of probability of outage.</p>

<p>Conventional hearing aids perform badly in environments with reverberation and noise. In this paper the use of microphone arrays as hearing aids to increase directivity and signal-to-noise ratio (SNR) in a noisy environment are evaluated. A portable microphone array prototype is constructed to test beamforming algorithms in a real environment. Delay and sum beamforming, sub-band beamforming and an experimental type of binaural beamforming is implemented in real-time using the digital signal processor ADSP-BF533. Results from testing showed that a four microphone array using sub-band beamforming outperforms delay and sum beamforming using the same number of microphones. The results also showed that it is possible to obtain binaural impression of the array output and source localization using the proposed binaural technique called beamspreading.</p>

<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>