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.

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.

The Lithium-ion battery is today used by close to every portable battery powered device, and this marked is constantly increasing because not only are the products the consumer have had for years getting more and more sophisticated, so he or she often “has” to replace yesterdays model with tomorrows. But as many products are furnished with new functions they use more power, hence their battery life is shortened. Because the Lithium-ion battery is so chemically advanced, it requires a sophisticated management system if it is to be fully utilized by the product. In this report, the parameters of the Lithium-ion battery which are the reason for this strict management are explained. The explanation does not look into the underlying chemistry for them because that is beyond the scope of this report. But sources for further reading on the subject are included. Different solutions for battery management are discussed and a Voltage-to-Frequency (VFC) converter is implemented in VHDL-AMS and simulated in ADVance-MS from Mentor[2]. The sources of error in the design are identified but dealt with in this report. This is not necessary before implementation in a CMOS-process has been shown possible. Simulations without component deviations are good, but once they are introduced, the converter shows that it is too sensitive for them. This can be solved utilizing digital error correction and calibration. After the ideal simulations are performed, transistor level simulations for the circuit are performed. Different solutions and requirements for the various components in the Voltage-to-Frequency converter are looked into with respect to the results found while simulating the ideal circuit. It was found that the comparator should have hysteresis to avoid unwanted chattering in its output signal. The architecture was chosen and the comparator was simulated. It was found that this architecture provided some offset-voltage, but this can easily be compensated by subtracting the offset from its reference voltage. Digital calibration can also here be utilized, but this is not looked into. Two high-gain op-amp architectures are looked into and simulated in this report, it was found that the two-stage used slightly more power than the two-stage op-amp with cascode-output, but they both provided approximately the same gain, even though the two-stage op-amp with cascode-output theoretically should provide about 100 times more gain. From this it is concluded that this architecture has a gain-limit independent of architecture used around 56dB. It is concluded that the Voltage-to-Frequency-architecture looked into is not suitable for implementation in this CMOS-process and that another architecture must be found if a Voltage-to-Frequency converter shall be made for the architecture.

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.

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.

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.

In this assignment the theoretical background for the nature of speckle is presented and practical work was done to reduce the speckle effect in a display system based on a laser source. This was done without any picture modulators, or any kind of line scan or flying spot scanning. Work was done to find the right setup to be able to as easy as possible characterize the statistics of the speckle in an image. A still image of an expanded laser spot worked as an image. A series of test sets were carried out to address the different factors which could make a difference on the speckle contrast and their role in such systems.

Polarization Effects in Wavelength Converters based on Semiconductor Optical Amplifiers

In this project it has been focused on the use of a 7.42 um, 4 mW Quantum Cascade Laser in trace gas detection spectroscopy. Norsk Elektro Optikk (NEO) is in possession of a Nanoplus G2102/DFB2/5-12 QCL laser, that can be used in spectroscopic detection of H2O, CO2 and SO2 It has been attempted to construct a setup that can be used for spectroscopic measurements using a self constructed current driver module to produce current pulses for the QCL. The QCL is operated in pulsed mode, with pulses of <500 ns width, and a 1 kHz pulse repetition frequency. Temperature control of the laser has been conducted with a LaserGas II SP monitor module, and temperature has been kept at 280 K during testing. Initially, various test have been conducted to ensure the general functionality of the driver module, and to avoid damage to the QCL. Two different solutions for the transmission line from the driver to the QCL have also been examined, and it has been concluded that the current pulses supplied to the laser are of good quality with minor broadening and short rise/fall times. Furthermore an I-V characteristic for the laser has been produced by incrementing the laser driving current, and measuring the corresponding laser voltage. Measurements of the laser output power have been conducted using a CaF2 collimating lens to focus the laser beam onto a PVI-2TE-8 Vigo photovoltaic detector from Vigo Systems S.A. It has proved difficult to obtain a good signal from the detector, with the maximum voltage measured across a 50Ω shunt resistor being 3 mV. This is 100-200 mV less than what should be expected. Various methods of noise reduction have been applied to improve the detected signal, none have however provided any noticeable improvements. Several possible reasons for the generally low output have been examined.

This Master’s thesis documents a new test method for detection of small delay faults in FPGA routing network. The main purpose of the test is accurate detection of faults in all parts of the network. The second aim is minimizing test application time. The work of the thesis consisted of four parts. First, a literature study was performed to get background knowledge of FPGA architecture and basics of testing. Second, detection accuracy was defined and measured in SPICE for test paths with different number of fan-out. Third, test configurations were developed. And finally, detection accuracies for the proposed test method were calculated. The SPICE measurements were performed on an interconnect model of FPGA. They revealed that detection accuracy of defects tested by branches of a test path is less than detection accuracy of defects tested by stems of a test path. In addition, it was observed that detection accuracy is best in the beginning of a test path. In the proposed test method detection accuracy is improved by testing all segments outside switch matrices by test path stems, and applying test patterns to all bidirectional segments in both directions. A comparison to two previous test methods showed that the proposed test method is more accurate while keeping the same number of test configurations. The detection accuracy can be improved further by allowing more test configurations.