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This thesis describes the construction and implementation of a microprocessor controlled recursive adaptive filter applied as a noise canceller. It describes the concept of the adaptive noise canceller, a method of estimating the received signal corrupted with additive interference (noise). This canceller has two inputs, the primary input containing the corrupted signal and the reference input consisting of the additive noise correlated in some unknown way to the primary noise. The reference input is filtered and subtracted from the primary input without degrading the desired components of the signal. This filtering process is adaptive and based on Widrow-Hoff Least-Mean-Square algorithm. Adaptive filters are programmable and have the capability to adjust their own parameters in situations where minimum piori knowledge is available about the inputs. For recursive filters, these parameters include feed-forward (non-recursive) as well as feedback (recursive) coefficients. A new design and implementation of the adaptive filter is suggested which uses a high speed 68000 microprocessor to accomplish the coefficients updating operation. Many practical problems arising in the hardware implementation are investigated. Simulation results illustrate the ability of the adaptive noise canceller to have an acceptable performance when the coefficients updating operation is carried out once every N sampling periods. Both simulation and hardware experimental results are in agreement.

Eleven experiments are reported which examine the effects of 90 dB (A) white noise on the processes which govern orienting of attention in visual space. The selectivity hypothesis argues that noise alters the priorities which govern stimulus selection so that subjectively dominant aspects of the environment are attended to more fully than those which are non-dominant. The applicability of this hypothesis is examined with regard to attentional orienting. Three experimental paradigms are used. The first involves a central cue presented immediately prior to target onset. In the absence of eye movements reaction times to expected targets are faster than to unexpected targets, but noise has no effects on performance. It is concluded that the power of the central alerting cue is focussing attention in a maximal fashion and noise has no further effect on policies of allocation. A second task design involves the presentation of positional information prior to a block of trials. Under such conditions subjects fail to maintain orienting as trials continue. Noise enhances the ability to maintain orienting over time. This effect is discussed in the light of the selectivity hypothesis. It is argued that the inability to maintain orienting is not due to the inhibition which arises as a result of successive responding. Rather it is due to the difficulty involved in maintaining an active orientation. The third paradigm involves orienting to specific locations on the basis of information stored in short-term memory. When recall of this information is aided by a visual warning signal occurring prior to target onset noise has no effect on performance. Without this signal, noise alters performance and these data are compared to predictions based upon the selectivity hypothesis. These effects are discussed in terms of a noise-induced change in the strategy of performance, rather than an effect which is mechanistic.

Approved for public release, distribution is unlimited / The performance of coherent and noncoherent RAKE receivers over a fading channel in the presence of pulse-noise interference and additive white Gaussian noise is analyzed. Coherent RAKE receivers require a pilot tone for coherent demodulation. Using a first order phase-lock-loop to recover a pilot tone with additive white Gaussian noise causes phase distortions at the phase-lock-loop output, which produce an irreducible phase noise error floor for soft decision Viterbi decoding. Both coherent and noncoherent RAKE receivers optimized for additive white Gaussian noise perform poorly when pulse-noise interference is present. When soft decision convolutional coding is considered, the performance degrades as the duty cycle of the pulse-noise interference signal decreases. The reverse is true for hard decision Viterbi decoding, since fewer bits experience interference and bit errors with high noise variance cannot dominate the decision statistics. Soft decision RAKE receiver optimized for pulse-noise interference and additive white Gaussian noise performed the best for both the coherent and noncoherent RAKE receivers. This receiver scales the received signal by the inverse of the variance on a bit-by-bit basis to minimize the effect of pulse-noise interference. The efficacy is demonstrated by analytical results, which reveal that this receiver reduces the probability of bit error down to the irreducible phase noise error floor when pulse-noise interference is present. This demonstrates how important it is to design the receiver for the intended operational environment. / Civilian, Department of Defense

Previous studies have demonstrated that in some instances certain types of auditory stimulation have facilitated a subject's ability at a visual task while in other instances, the subject's ability has been inhibited. The primary objective of this experiment was to investigate the effect of auditory stimulation upon a subject's performance on a visual discrimination task.

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Dans ce travail de recherche, on présente des développements spécifiques de diagnostiques optiques et leur application à l’étude aéroacoustique des jets rapides à haut nombre de Reynolds. Les résultats expérimentaux présentés ici résultent de visualisation par strioscopie et, de manière prépondérante dans ce manuscrit, de mesure de masse volumique par diffusion Rayleigh. Ces méthodes de caractérisation d’écoulement, appliquées aux jets subsoniques ou supersoniques, ont été associées à des mesures de bruit en champ lointain. La mesure par diffusion Rayleigh, qui repose sur la lumière diffusée par les molécules constituantes du gaz, et n’est donc pas intrusive. Des difficultés apparaissent néanmoins pour exploiter les résultats lorsque le milieu diffusant contient des poussières. Bien que l’air des écoulements obtenu en soufflerie soit filtré, la quantité résiduelle de poussières a rendu nécessaire le développement d’une méthode de nettoyage du signal en post-traitement. Le niveau des signaux obtenus par diffusion Rayleigh est très faible, et dominé par du bruit appelé shot noise. Un gain significatif sur le niveau de ce bruit a été obtenu en optimisant la chaîne d’acquisition après analyse des systèmes existants. De plus une méthode de traitement du signal dérivée d’une méthode existante a permis de calculer des spectres de masse volumique malgré le shot noise avec un seul capteur, là où il en fallait deux auparavant. Les profils de p obtenus par cette technique ont montré qu’il existe une loi de similarité permettant de superposer les profils mesurés à différentes positions axiales. Cette loi est identique pour les jets issus de trois tuyères aux géométries différentes, et à des nombres de Mach de 0.7 et 0.9. Une loi de similarité est également observée pour p’rms si les profils sont mesurés suffisamment loin de la tuyère. L’étude des spectres dans la couche de mélange a mis en évidence un maximum faiblement marqué autour d’une fréquence centrale comprise entre St = 0:2 et St = 2 dans les régions mesurées, plus marqué que dans les spectres de vitesse, et dont le comportement diffère selon l’état initialement laminaire ou turbulent du jet. L’évolution de la forme des spectres en fonction de la différence de masse volumique entre le jet et le milieu ambiant, ainsi qu’en fonction du nombre de Mach, a également été étudiée. Une loi permettant de superposer les spectres a été définie empiriquement sur la plage de variation des différents paramètres. Des mesures simultanées entre l’acoustique en champ lointain et la masse volumique dans l’écoulement ont été réalisées pour un jet à Mj = 0:9 et un jet à Mj = 1:32. Ces résultats ont permis l’estimation de cohérences spectrales et de moyennes conditionnelles. Les résultats obtenus mettent en évidence la présence de structures liées au rayonnement acoustique dans une région située proche de l’axe du jet en aval du cône potentiel. Pour finir, une étude a été réalisée sur le screech dans les jets supersoniques sous-détendus. Elle a permis d’identifier la position de la source de la rétroaction acoustique pour les modes A1, A2, et B, ainsi que la structure du cycle de la boucle qui détermine les changements de fréquences observés aux sauts de modes. / In this research study, developments of optical diagnosis techniques are presented, and are put into practice in an aeroacoustics study of high speed and high Reynolds jets. The results described here are obtained from Schlieren visualization, and in the majority from density measurements through Rayleigh scattering. These measurement methods are applied for subsonic and supersonic jets, and associated with far field acoustics measurements. Rayleigh scattering measurements rely on laser light scattered by the molecules constituting the flow, thus they are non-intrusive. However, some difficulties in interpreting the results arise when the flow contains dust particles. This problem is partly solved by using air filters in the wind tunnel, but some residual dust particles remain, thus a software based signal cleaning method has been developed and is applied to the signals during post-processing. Besides, the signals obtained from Rayleigh scattering are very weak, and dominated by a shot noise. The noise level has been significantly reduced following the optimization of the chain of acquisition in comparison with actual apparatus. Moreover, a method to compute spectra despite the shot noise level has been adapted from a classic method to be usable with a single sensor instead of two. The analysis of radial profiles of density measured with the Rayleigh scattering apparatus shows that a similarity law allows to superimpose radial profiles measured in jets exhausted from three different nozzles at Mach 0.9 and Mach 0.7. Another similarity law is observed for radial profiles of 0 rms when they are measured far enough form the nozzle. The analysis of density spectra in the mixing layer points out the presence of a local maximum of central frequency found between St = 0:2 and St = 2 depending on the probed location, which is not as clearly observed in velocity spectra. The spatial evolution of this maximum is found different whether the flow is initially laminar or turbulent at the nozzle exit. The dependence of spectra to the Mach number, and to the difference of density between the jet and the surrounding is also studied. A scaling law is empirically determined for the scope of the study. Simultaneous measurements of density and farfield acoustic acquired in a Mach 0.9, and a supersonic ideally expanded Mach 1.32 jets are processed to obtain coherence, and conditional averaging. The results emphasis the role of large structures downstream the end of the potential core in acoustic radiations. Finally, the screech in underexpended jets is studied. This work results in the identification of the acoustic feedback source location for A1, A2 and B modes, and in the characterization of the changes in the loop structure associated with mode switching.

Hil-Yee Chan, Walter. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 84-87). / Abstracts in English and Chinese. / Chapter Chapter 1 --- introduction --- p.3 / Chapter Chapter 2 --- Background Theory --- p.6 / Chapter 2.1 --- Maximally Flat Filter Response --- p.6 / Chapter 2.2 --- Equal-Ripple Filter Response --- p.8 / Chapter 2.3 --- Low-pass to Band-pass Transformation --- p.9 / Chapter 2.4 --- Impedance and Admittance Inverter --- p.10 / Chapter 2.5 --- Coupled-Resonator Filter --- p.14 / Chapter Chapter 3 --- Active Filter Employing Negative Resistance --- p.18 / Chapter 3.1 --- Lossy Coupled-Resonator Filter --- p.18 / Chapter 3.2 --- Common-source Capacitive Feedback Configuration --- p.21 / Chapter 3.3 --- Active LC-resonator --- p.23 / Chapter 3.4 --- Design Criteria of the Active Filter --- p.24 / Chapter Chapter 4 --- Intermodulation Analysis --- p.27 / Chapter 4.1 --- IM Distortion of the Negative Resistance Circuit --- p.27 / Chapter 4.2 --- Analysis of the Active Coupled-Resonator Filter --- p.30 / Chapter 4.3 --- IM Distortion Power of a Nth Order Active Filter --- p.32 / Chapter Chapter 5 --- Noise Analysis --- p.37 / Chapter 5.1 --- Noise Basics and Noise Figure --- p.37 / Chapter 5.2 --- Noisy Two-Ports --- p.41 / Chapter 5.3 --- Correlation Matrix Representation of Noisy Two-Ports --- p.44 / Chapter 5.4 --- Change of Representation --- p.46 / Chapter 5.5 --- Interconnection of Noisy Two-Ports --- p.47 / Chapter 5.6 --- Correlation Matrix of the Basic Two-Ports --- p.48 / Chapter 5.7 --- Extraction of the Noise Parameters of MESFET --- p.51 / Chapter 5.8 --- Noise Parameters of CFY30 --- p.53 / Chapter 5.9 --- Noise Figure of CFY30 --- p.56 / Chapter Chapter 6 --- Noise Analysis of Passive and Active Filter --- p.60 / Chapter 6.1 --- Noise Current Generated by the Negative Resistance Circuit --- p.60 / Chapter 6.2 --- Noise Figure of the Passive Filter --- p.63 / Chapter 6.3 --- Noise Figure of the Active Filter --- p.65 / Chapter 6.3.1 --- Noise Figure of a Second-order Active Filter --- p.65 / Chapter 6.3.2 --- Noise Figure of the Higher-order Active Filter --- p.68 / Chapter 6.4 --- Design consideration of Active Filter with Optimized Noise and Linearity Performance --- p.71 / Chapter Chapter 7 --- Design of 900MHz Hybrid Active Filter --- p.73 / Chapter 7.1 --- Schematic of Active Filter --- p.73 / Chapter 7.2 --- Design Variants --- p.75 / Chapter 7.3 --- Measurement Results --- p.75 / Chapter 7.3.1 --- Passive Filter --- p.75 / Chapter 7.3.2 --- Active Filter --- p.78 / Chapter Chapter 8 --- Conclusion and Future Work --- p.83 / Reference --- p.84 / Author's Publications --- p.88

Thesis. 1977. Ph.D. cn--Massachusetts Institute of Technology. Dept. of Physics / Vita. / Includes bibliographical references. / Ph.D.cn