[pt] Esta tese propõe novas melhorias para a codificação CELP a baixas taxas de bits. Primeiro, é proposto um algoritmo CELP em que a complexidade do procedimento de busca no dicionário adaptativo é grandemente reduzida, graças a uma modificação introduzida no modelo de síntese CELP. Resultados de simulação mostram que a qualidade da voz codificada com o algoritmo CELP proposto tem qualidade comparável àquela obtida com o algoritmo CELP convencional. As demais contribuições têm o propósito de melhorar a qualidade da voz codificada com o algoritmo CELP a baixas taxas de bits. Uma delas propicia uma codificação mais eficiente da envoltória espectral LPC da voz: é, especificamente, um esquema que combina quantização vetorial e interpolação interbloco dos parâmetros LSF. Com este esquema a envoltória espectral LPC codificada tem boa qualidade a uma taxa de bits tão baixa quanto 1 kb/s. A voz codificada com os algoritmos CELP apresenta freqüentemente distorções em sua envoltória espectral que são causadas por deficiências do sinal de excitação. Esta tese propõe um novo pós-filtro que reduz estas distorções e, com isso, melhora significativamente a qualidade subjetiva da voz codificada. A baixas taxas de bits a estrutura CELP convencional é incapaz de reproduzir com boa qualidade os ataques dos sons sonoros, que são cruciais para uma boa percepção da voz. Nesta tese é descrito um algoritmo CELP que dá prioridade a estes segmentos críticos. Cada bloco da voz é classificado em um dentre dezesseis padrões de sonoridade e cada padrão tem uma configuração de codificação e alocação de bits distintas. Resultados de simulação mostram que a qualidade da voz codificada a 4 kb/s com o algoritmo CELP proposto é significativamente melhor do que aquela conseguida com um codificador CELP convencional, também operando a 4 kb/s. / [en] This work presents new improvements to CELP speech coding at low bit rates. First, a CELP algorithm is proposed in wich the complexity of the adaptive codebook search is gratly decreased. This is achieved by means of a modified model of the CELP synthesizer. Simulation results show that the proposed algorithm can provide speech quality comparable to one obtained with the conventional CELP codec. The rest of contributions aim to improve the quality of speech codec at low bit rates with CELP algorithm. One of them is an efficient scheme for coding the LPC spectral envelope of speech for coding the LPC spectral envelope of speech. The proposed scheme combines vector quantization and interpolation of LSF parameters, and it provides a coded spectral envelope with very good quality at 1 kb/s. Speech coded with CELP codecs frequently displays distortions in its spectral envelope that are produced by deficient excitation. This thesis proposes a new postfilter that enhances the perceptual quality of codec speech by decreasin these distortions. This work presents new improvements to CELP speech coding at low bit rates. First, a CELP algorithm is proposed in wich the complexity of the adaptive codebook search is gratly decreased. This is achieved by means of a modified model of the CELP synthesizer. Simulation results show that the proposed algorithm can provide speech quality comparable to one obtained with the conventional CELP codec. The rest of contributions aim to improve the quality of speech codec at low bit rates with CELP algorithm. One of them is an efficient scheme for coding the LPC spectral envelope of speech for coding the LPC spectral envelope of speech. The proposed scheme combines vector quantization and interpolation of LSF parameters, and it provides a coded spectral envelope with very good quality at 1 kb/s. Speech coded with CELP codecs frequently displays distortions in its spectral envelope that are produced by deficient excitation. This thesis proposes a new postfilter that enhances the perceptual quality of codec speech by decreasin these distortions. Voiced onsets are crucial for a good perception of speech but, at low bit rates, the conventional CELP is unable to reproduce them with good quality. This work presents a CELP algorithm into one of a set of sixteen voicing patterns. A distinct coding configuration and bit allocation are applied to each pattern. Simulation results show that the quality of speech codec with the proposed 4 kb/s CELP codec is significantly bette than the one obtained with conventional 4 kb/s CELP codec.

The standard MIP mapping technique halves the resolution of textures for each level of the MIP chain. In this thesis the bits per pixel(bpp) is reduced as well. Normal maps are generally used with MIP maps, and todays industry standard for these are usually 24 bpp.The reduction is simulated as there is currently no support for the lower bpp in GPU hardware. Objectives: To render images of normal mapped objects with decreasing bpp for each level in a MIP chain and evaluate these against the standard MIP mapping technique using a subjective user study and an objective image comparison method. Methods: A custom software is implemented to render the images with quantized normal maps manually placed in a MIP chain. For the subjective experiment a 2AFC test is used, and the objective part consists of a PDIFF test for the images. Results: The results indicate that as the MIP level is increased and the bpp is lowered, users can increasingly see a difference. Conclusions: The results show that participants can see a difference as the bpp is reduced, which indicates normal mapping as not suitable for this method, however further study is required before this technique can be dismissed as an applicable method

Test Tools are very important in the design of a system. They generally simulate a working environment, only at a higher speed, or with less frequently occurring test cases. In the verification of protocols based on the Fibre Channel physical layer, this becomes a necessity, as errors can be non-existent or very unusual in normal operating environments. Most systems need to be able to handle these unexpected events nonetheless. Therefore, there is a need for a method of introducing these errors in a controlled way. A bit error generation and logging tool for two proprietary protocols based on the Fibre Channel physical layer has been developed. The hardware platform consists mainly of a Virtex II Pro FPGA with accompanying I/O support. Control of the hardware is handled by a graphical user interface residing on a PC. Communication between the hardware and the PC is handled with a UART. The final implementation can handle four parallel one way links, or two full duplex links, independently. This report describes the implementation and the necessary theoretical background for this.

Abstract An inevitable trend in wireless communications is the requirement for higher and higher data rates. At the same time, location awareness requires high accuracy for positioning ability. One option fulfilling both of these challenges is the use of an ultra wideband (UWB) physical layer technology due to its extremely large inherent bandwidth. From the two possible solutions to generate UWB signals, this thesis is focused on the singleband approach. This technique is closer to the original idea of impulse radio transmission than the other recently proposed multiband UWB approach. This thesis focuses on UWB coexistence with several selected radio systems; global positioning and cellular systems, and wireless local area networks. The topic was studied analytically and with experimental tests. The analytical part is divided into simulations and theoretical calculations. In the study, two different physical layer concepts, several modulation schemes and pulse waveforms have been used to find the best system performance under interference. From time hopping and direct sequence based approaches (TH and DS, respectively), the latter with binary pulse amplitude modulation was seen to outperform the former one in an interfered multipath channel if compared with bit error rate performance. Therefore, the theoretical calculations are addressed to the DS-UWB approach. The formulation defined makes it possible to rather easily calculate the upper bound for DS-UWB system performance in an AWGN channel and the results can be used to calculate reference bounds, for example, in receiver algorithm studies. The experimental part of the work focused on link level coexistence measurements between UWB and either IEEE802.11b or 3G networks. UWB can cause harmful performance degradation on the victim system if there are unrealistic numbers of active interferers in close vicinity of the victim receiver. However, increasing the separation between the UWB interferer and victim to 40 cm, or 70 cm, in the case of WLAN and 3G, respectively, the impact is insignificant. It was also shown that the activity factor of the UWB transmitter has a great impact on the victim system's performance degradation. UWB activity factors of less than about 5% can be tolerated by the studied victim systems.

In the field of communications, a high data rate and low multi-path fading is required for efficient information exchange. Orthogonal Frequency Division Multiplexing (OFDM) is a widely accepted IEEE 802.11n (and many others) standard for usage in communication systems operating in fading dispersive channels. In this thesis, we modeled the OFDM algorithm at the behavioral level in VHDL/Verilog that was successfully synthesized/verified on an FPGA. Due to rapid technology scaling, FPGAs have become popular and are low-cost and high performance alternatives to (semi-) custom ASICs. Further, due to reprogramming flexibility, FPGAs are useful in rapid prototyping. As per the IEEE standard, we implemented both transmitter and receiver with four modulation schemes (BPSK, QPSK, QAM16, and QAM64). We extensively verified the design in simulation as well as on Altera Stratix IV EP4SGX230KF40C2 FPGA (Terasic DE4 Development Board). The synthesized design ran at 100 MHz clock frequency incurring 54 µ sec. end-to-end latency and 8% logic utilization.

Safety-critical systems, especially those found in avionics and automotive industries, rely on machine arithmetic to perform their tasks: integer arithmetic, fixed-point arithmetic or floating-point arithmetic (FPA). Machine arithmetic exhibits subtle differences in behavior compared to the ideal mathematical arithmetic, due to fixed-size representation in memory. Failure of safety-critical systems is unacceptable, due to high-stakes involving human lives or huge amounts of money, time and effort. By formally proving properties of systems, we can be assured that they meet safety requirements. However, to prove such properties it is necessary to reason about machine arithmetic. SMT techniques for machine arithmetic are lacking scalability. This thesis presents approaches that augment or complement existing SMT techniques for machine arithmetic. In this thesis, we explore approximations as a means of augmenting existing decision procedures. A general approximation refinement framework is presented, along with its implementation called UppSAT. The framework solves a sequence of approximations. Initially very crude, these approximations are fairly easy to solve. Results of solving approximate constraints are used to either reconstruct a solution of original constraints, obtain a proof of unsatisfiability or to refine the approximation. The framework preserves soundness, completeness, and termination of the underlying decision procedure, guaranteeing that eventually, either a solution is found or a proof that solution does not exist. We evaluate the impact of approximations implemented in the UppSAT framework on the state-of-the-art in SMT for floating-point arithmetic. A novel method to reason about the theory of fixed-width bit-vectors called mcBV is presented. It is an instantiation of the model constructing satisfiability calculus, mcSAT, and uses a new lazy representation of bit-vectors that allows both bit- and word-level reasoning. It uses a greedy explanation generalization mechanism capable of more general learning compared to traditional approaches. Evaluation of mcBV shows that it can outperform bit-blasting on several classes of problems.

Bit-Patterned Media (BPM) has been recognised as one of the candidate technologies to achieve an areal density beyond 1Tb/in2 by fabricating single-domain islands out of continuous magnetic media. Though much attention has been focused on the fabrication of BPM, existing lithography techniques demonstrate difficulties in producing uniform islands over large areas cost effectively; the resulting fabricated islands often vary in position and size. The primary purpose of the research documented in this thesis is to investigate the issue of island geometry variations on the data recovery process from a perpendicular patterned media with head and media configurations optimised to achieve an areal density of 1Tb/in2. In order to achieve the research aim, a read channel model has been implemented as a platform to evaluate the read channel performance numerically. It can be also altered to investigate new read channel designs. The simulated results demonstrate that island geometry variations have a detrimental effect on read channel performance. It has shown that a BPM system can be tolerant to island position variations, but more effort needs to be paid to the effect that island size variations have on the read channel performance. A new read channel design revolving around the design of a modified trellis has been proposed for use in the Viterbi detector in order to combat the effect of island geometry variations. The modified trellis for island position variations results in extra states and branches compared to the standard trellis, while the modified trellis for island size variations results in only extra branches. The novel read channel designs demonstrate an improved read channel performance in the presence of island geometry variations even with increasing amounts of island position and size variations. There are two ways to obtain the read channel performance in terms of the bit-error-rate (BER): a) by running a numerical Monte-Carlo simulation to count the number of bits in error at the output of the read channel model and b) using an analytical approach to calculate the BER by approximating the noise into a known distribution. It is shown that both ways demonstrate very similar results, which indicates as long as the distribution of the noise present in read channel model is predictable, the analytical approach can evaluate the BER performance more efficiently, especially when the BER is low. However, the Monte-Carlo simulation is still useful for understanding of the correlation of the errors. Novel trellis proposed in this work will contribute to the commercial development of BPM in two ways: a) to improve the data recovery process in BPM systems, b) to allow a tolerance of 10% size variations for the existing fabrication techniques.

For the past 50 years, the magnetic storage industry has been the ultimate provider, covering the ever-expanding needs of digital mass storage. Up to now, scaling to smaller dimensions has been the core approach for achieving higher areal densities in conventional media. However, recent studies have shown that further miniaturisation is physically bound by superparamagnetic effects. Bit patterned media (BPM) is one of the most promising solutions for extending the areal densities beyond 1Tbit/in². The ability to magnetically characterise novel BPM is a key requirement for its future commercialisation. The work presented in this thesis describes the investigation of the Magneto-Optic Kerr Effect (MOKE) and the Anomalous Hall Effect (AHE) techniques, used in the characterisation of BPM samples. These samples were produced as part of this work using a customised subtractive fabrication process. Continuous thin magnetic films with Ptseed(10nm)/[Co(0.4nm)/Pt(1nm)]x15 composition and perpendicular anisotropy, were deposited using electron-beam (e-beam) evaporation, and subsequently patterned into magnetic nano-islands through means of e-beam lithography and Ar⁺ ion milling. In terms of the MOKE technique, a fully customised polar MOKE system has been developed and successfully used to observe the hysteretic behaviour of magnetic nano-island arrays with varying dimensions. An expected reduction in the MOKE signal due to pattering has been observed, as well as an additional signal reduction due to the scattering effect arising from the non-vertical sidewalls of the dome-shaped islands. In the case of islands with improved shape profile, the magnetic reversal of BPM arrays with islands sizes down to 35nm has been successfully detected, demonstrating a sensitivity of approximately 6x10⁻¹³emu for the MOKE system. In terms of the AHE technique, Au Hall crosses were deposited on top of the BPM arrays that had been previously characterised by MOKE, allowing the direct comparison and cross-verification of the results obtained by the two techniques. A revised Hall cross design, where the Hall crosses were generated by direct patterning of the Pt seed layer, has provided a significant improvement in AHE signal. This has allowed the detection of the magnetic reversal of individual sub-50nm magnetic islands, demonstrating a sensitivity of approximately 6.6x10⁻¹⁵emu for the AHE technique. The spatial sensitivity of these Hall cross structures has been experimentally determined, indicating a decrease in sensitivity with increasing distance from the cross centre and with decreasing island diameter. In conclusion, the sensitivity profile of Hall cross structures must be taken into account for the accurate interpretation of BPM characterisation results obtained by the AHE technique. Finally, some suggestions are outlined with regard to the future improvement of the developed characterisation techniques and the further continuation of the work presented in this thesis.

The work in this PhD thesis covers two strands of x-ray experiments: firstly, the characterisation of large arrays of dense structures by means of x-ray scattering, and, secondly, the investigation of hybrid anisotropy square structures with x-ray microscopy. The ability to accurately characterise large arrays of nanoscale magnetic structures is a key requirement for both scientific understanding and technological advance such as bit patterned recording media (BPM). In this work small angle x-ray scattering (SAXS) was investigated as a characterisation technique for large arrays of patterned structures. Dense arrays of magnetic nanostructures were prepared on x-ray transparent membranes and measured. The SAXS data was then modelled to obtain structure parameters such as the mean structure diameter, the diameter distribution and the mean position variance with statistical significance. Arrays (500 x 500 μm2) of nominally uniform nanostructures with centre-to-centre distances between 250 nm-50 nm were structurally characterised and compared to structure diameters obtained by optical scanning electron microscopy measurements. The mean structure diameter was found to be between 39 nm-15nm and agree within the errors with the diameter obtained from SEM measurements. This work provides accurate data on the distribution (variance) of nanostructure sizes which is key for modelling these arrays for applicationin BPM. In the second part of the work, the static and dynamic properties of patterned hybrid anisotropy square structures ([Co/Pd]-Py) were investigated by using time-resolved scanning transmission X-ray microscopy (STXM). In these patterned structures the magnetisation in the layers change both in magnitude and direction and gives rise to interesting new domain configurations. The reciprocal interaction between magnetic vortices in the Py layer and locally circular stripe domains in the Co/Pd was investigated and a mutual domain imprint between the layer was observed. In dynamic excitation experiments the precession of the vortex core is studied and showed good agreement with micromagnetic simulations made by Hrkac and Bryan. As demonstrated patterned hybrid anisotropy square structures have promising magnetic properties with potential applications in data storage (vortex switching) or spintronics (vortex oscillators).

In this thesis, drill bit buttons with cobalt, nickel and iron binders in different compositions have been tested against granite and sandstone and the wear and friction have been measured. Furthermore, the wear and degradation of the buttons have been categorized. Buttons with cobalt binder were tested against granite and sandstone and buttons with alternative binders (Ni, Fe, Co) were tested against granite. Cobalt buttons were used as a reference and the wear and friction of the alternative binders was compared to the reference. The amount of worn rock was also measured. Furthermore, post treated drill bit buttons with a composition of Fe-Ni-Co were compared to buttons with the same composition that had not been post treated The results show that buttons with an alternative composition of Fe-Co-Ni and Fe- Ni wears less than the cobalt reference. The post treatment process does not decrease the wear of the drill bit but lowers the deviation from the mean wear. The amount of worn rock does not differ between the samples except for between the post treated and not post treated buttons with a composition of Fe-Ni-Co. The post treated buttons produces more rock debris than the not post treated. No apparent difference could be seen on the surface of the tested buttons after the test. However, composition specific cracks could be found underneath the surface of the samples. EDS-analysis showed signals of oxygen inside of all of the investigated cracks. For some compositions at depths of 20 micrometers. The curves of friction shows similar appearance but the values of the coefficient of friction differs. No apparent correlation was found between the wear and friction of the samples. Furthermore, no apparent correlation was found between the hardness and the wear of the buttons.