The introduction of M-Code to the GPS signal structure can redefine the accuracy of the broadcast ephemeris. Existing ephemeris generation systems use dual frequency observations, obtained through the tracking of existing precise codes on the L1 and L2 frequencies. These codes are modulated using Binary Phase Shift Key (BPSK) modulation. The modernization signal M-Code is modulated using Binary Offset Carrier (BOC) modulation. In this study pseudorange observables derived from the tracking of M-Code are proven to have greater accuracy than those from existing precise codes, given equivalent receiver designs and operating conditions. In addition, the error due to specular multipath is derived. These general models of noise and multipath can be applied to any BOC modulated signals, including Galileo and QZSS. When applied to M-Code, the models predict that the maximum multipath error in the pseudorange is reduced in magnitude by 50% compared to the existing precise codes. However the range of multipath delays for which M-Code observables exhibit multipath is approximately twice that associated with existing precise BPSK codes. Existing ephemeris generation processes use the ionosphere free combination and carrier phase smoothing of the pseudorange to form smoothed pseudoranges. The smoothed pseudoranges are then input as measurements to an ephemeris filter. The analytic models of multipath error in the pseudorange and carrier phase observables are applied to predict errors in the smoothed pseudorange. Multipath error, amplified by ionosphere free combination, causes a bias in the smoothed pseudorange when parameterized as a function of multipath delay. There are conditions under which the bias is zero mean, and in those conditions multipath is suppressed. The mechanism for those conditions is solved and discussed, for both BOC and BPSK signal tracking. The solution of carrier phase multipath for BOC modulated signals also admits solutions with a special quality not seen in the BPSK solution. There are multipath delays for which the carrier phase multipath is identically zero regardless of the multipath phase. The zero carrier phase multipath condition may be the most promising feature associated with observables derived from BOC modulated codes. / text

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Sensor arrays have been successfully applied to many engineering fields and the theoretical as well as applied aspects of senor array processing have received intensive research interest. Practically, sensor array systems usually suffer from uncertainties such as unknown gains and phases, mutual coupling, and look direction mismatch. In this thesis, problems of direction finding and beamforming in the presence of array uncertainties are addressed, and new algorithms to tackle these problems are developed. In certain applications, senor arrays are only partly calibrated. Hence, the exact responses of some sensors are unknown, which degrades the performance of traditional direction finding techniques. To tackle this problem, a new method for direction finding with partly calibrated uniform linear arrays (ULAs) is proposed. It generalizes the estimation of signal parameters via rotational invariance techniques (ESPRIT) by modeling the imperfection of the ULA as gain and phase uncertainties. For a fully calibrated array, it reduces to the standard ESPRIT algorithm. In this method, the direction-of-arrivals (DOAs), unknown gains and phases of the uncalibrated sensors can be estimated in closed-form without performing spectral grid search. Moreover, it can be further improved by a refining scheme proposed. Its superiority over existing methods is demonstrated by simulation results. Apart from unknown gains and phases, the mutual coupling caused by interactions among sensors also seriously deteriorate the performance of array processing techniques. In ULAs, the mutual coupling matrix (MCM) can be approximated as a banded symmetric Toeplitz matrix. Using this specific property, a new parameterization of the steering vector is proposed and the corresponding method for joint estimation of DOAs and MCM is derived. Compared with the conventional subarray-based method, the proposed one makes use of the whole array and achieves better performance especially for weak signals. On the other hand, the specific property is further employed to develop a new approach to calibrate the steering vector. By incorporating the calibrated steering vector with a diagonally loaded robust beamformer, a new adaptive beamformer for ULAs with mutual coupling is obtained. It is found that the resultant steering vector estimate considerably improves the robustness of the beamformer against mutual coupling. Another common uncertainty in sensor array systems is the look direction mismatch. Though numerous robust beamformers have been developed accordingly, most of them cannot offer sufficient robustness against large look direction errors. To this end, a new robust beamforming method which can flexibly control the magnitude response in the look direction is proposed. By linearizing the nonconvex constraints in the original problem, the resultant problem is convex and can be solved using second-order cone programming (SOCP). Moreover, to further improve the robustness against array covariance uncertainties, this method is extended by optimizing its worst-case performance. Unlike some conventional methods restricted to specific arrays, the proposed method is applicable to arbitrary array geometries. Simulation results show that the proposed method offers comparable performance to the optimal solution for uniform linear arrays, and also achieves good results under different array specifications and geometries. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Not available / text

Not available / text

Not available

The dissertation presents the design and development of a systematic signal analysis and representation framework beyond short-time Fourier power spectrum for sounds, in particular environmental sounds. This framework is consistent with the underlying assumptions of the analysis method and its elements are correlated with human perception. The sound signal has to conform to certain conditions for its power spectrum to have a physical and perceptual meaning. We contend that very few environmental sounds readily meet these criteria and argue that the quantities that are traditionally used to describe sounds need to be repurposed and, if necessary, redefined to represent sounds by non-Fourier means. We propose a perceptuo-analytic organization of sounds so that any environmental sound can be analyzed based on its signal characteristics and perception. We present environmental sound acquisition in the context of collection and annotation of a database for the footstep sounds, a common environmental sound, and show that it can be represented by these unconventional means and further analyzed to produce descriptions which are obscured with the traditional analysis. We present a novel application of extracting gait characteristics from the footstep sounds which is enabled by the proposed framework.

Active Noise Control (ANC) is an old concept which has generated increased interest over the past 10-15 years. Using the principle of destructive interference of waves, an inverse pressure wave - "anti-sound wave" is generated in order to attenuate the undesired noise. To achieve substantial cancellation of sound, performance of the cancelling sources must be accurately monitored and controlled. This has only become possible with the rapid development of digital signal processing theory and hardware. Most of the early work in the area of ANC has been done in duct silencing using single channel feed forward and feedback control arrangements. Providing that the sound wavelength is large enough (Le. frequency low enough) in comparison with the cross-sectional dimensions of the duct, spherical sound waves can be adequately approximated with plane waves. The problem is then reduced from three to two dimensions, which provides the possibilities for better understanding of the basic mechanisms of active noise cancellation and study of various adaptive control algorithms. The aim of the present work is to systematically investigate ANC methods for outdoor applications, through the development of Electronically Controlled Acoustic Shadow (ECAS) systems. In this work, the problem is fully three-dimensional. Multichannel ANC methods are proposed to be used, to reduce the noise emitted by large vibrating structures, such as power transformers, in the open air. The adopted approach is to design an active sound wall to create a controlled "anti-sound" shadow. In this way unwanted sound can be reduced in the direction of a complaint area. The potential applications for outdoor ANC systems are considerable. There is need to reduce low frequency sound, which is very hard to reduce using conventional methods - very heavy and expensive structures are required. This opens up the whole field of reducing noise from heavy rotating machinery, such as large generators/motors, factory machinery and mills (many of which have to operate 24 hours per day to remain competitive - which in turn causes noise problems). This work is divided into two main parts. First part considers computer modelling, simulations and theoretical investigation of Electronically Controlled Acoustic Shadows (ECAS) systems. It is demonstrated, that these shadows can be superior to acoustic shadows generated naturally by solid barriers. Detailed analysis predicts that deep shadows (> 1 00 dB) are po.ssible, indicating that practical shadows (>20 dB) are potentially achievable. The object of second part of the work is to investigate practical ECAS systems and establish their performance. In Chapters 2 and 3 (PART 1) the system performance at the fundamental, 100Hz frequency of transformer noise is analysed. To investigate the influence of a large number of parameters on the active wall performance, computer modelling of the primary and secondary (cancelling) sources is developed. The acoustic radiation from this primary source distribution is computed in the far field over a given control angle (both azimuthal and elevation angles). Angles between the 150 and 600 in azimuth and 150 to 300 in elevation are co~'sidered. Phase and amplitude of the secondary sources are than computed through the matrix algebra using exact solution of the least squares problem to minimise the sound at the sensor array. Using this modelling important properties of the acoustic shadows generated by active walls are established, and the basic theory to explain these shadows is formulated. No such theory existed previously. The concept of generating an acoustic shadow in the direction of the complaint area, has resulted in the acoustic properties of a 15°xI5° reference shadow being established in detail. It appears that any arbitrary shadow at this frequency can then be constructed by an addition of the~~ reference shadows, the shadow depth depending on the density of the cancellers per unit angle. Deep shadows in access of 100 dB are predicted, making practical shadows from real sources a possibility. It is now feasible to predict and optimise the future performance of proposed active wall configurations using the computer modelling and developed theory. Further. in the first part of the document (Chapter 4). acoustic interference across high frequency finite Source distributions is studied. The basic theory of non compact sources is considered and the possibility of continuous source representation with a finite number of discrete sources is discussed. The concept of non discreteness or poor discrete representation is established. Here, the .~coustic wavelength is considered small compared to the separation distance between discrete sources. The extent of the near field from these discrete source arrays is also established. where the simplified far field radiation equation breaks down. Finally, in Chapter 4. the optimisation and performance of cancelling arrays to create acoustic shadows from non compact. discrete representation of finite source distributions is investigated.

published_or_final_version / abstract / toc / Orthopaedics and Traumatology / Master / Master of Philosophy

published_or_final_version / Computer Science / Doctoral / Doctor of Philosophy