89 research outputs found
Exploring the use of group delay for generalised VTS based noise compensation
In earlier work we studied the effect of statistical normalisation
for phase-based features and observed it leads to a significant
robustness improvement. This paper explores the extension
of the generalised Vector Taylor Series (gVTS) noise
compensation approach to the group delay (GD) domain. We
discuss the problems it presents, propose some solutions and
derive the corresponding formulae. Furthermore, the effects
of additive and channel noise in the GD domain were studied.
It was observed that the GD of the noisy observation is a convex
combination of the GDs of the clean signal and the additive
noise and also in the expected sense, channel GD tends to
zero. Experiments on Aurora-4 showed that, despite training
only on the clean speech, the proposed features provide average
WER reductions of 0.8% absolute and 4.1% relative compared
to an MFCC-based system trained on the multi-style
data. Combining the gVTS with a bottleneck DNN-based system
led to average absolute (relative) WER improvements of
6.0% (23.5%) when training on clean data and 2.5% (13.8%)
when using multi-style training with additive noise
Robust Phase-based Speech Signal Processing From Source-Filter Separation to Model-Based Robust ASR
The Fourier analysis plays a key role in speech signal processing. As a complex quantity, it can be expressed in the polar form using the magnitude and phase spectra. The magnitude spectrum is widely used in almost every corner of speech processing. However, the phase spectrum is not an obviously appealing start point for processing the speech signal. In contrast to the magnitude spectrum whose fine and coarse structures have a clear relation to speech
perception, the phase spectrum is difficult to interpret and manipulate. In fact, there is not a meaningful trend or extrema which may facilitate the modelling process. Nonetheless, the speech phase spectrum has recently gained renewed attention. An expanding body of work is showing that it can be usefully employed in a multitude of speech processing applications.
Now that the potential for the phase-based speech processing has been established, there is a
need for a fundamental model to help understand the way in which phase encodes speech information. In this thesis a novel phase-domain source-filter model is proposed that allows for deconvolution of the speech vocal tract (filter) and excitation (source) components through phase processing. This model utilises the Hilbert transform, shows how the excitation and vocal tract elements mix in the phase domain and provides a framework for efficiently
segregating the source and filter components through phase manipulation. To investigate the efficacy of the suggested approach, a set of features is extracted from the phase filter part for automatic speech recognition (ASR) and the source part of the phase is utilised for fundamental frequency estimation. Accuracy and robustness in both cases are illustrated and discussed. In addition, the proposed approach is improved by replacing the log with the generalised logarithmic function in the Hilbert transform and also by computing the group delay via regression filter.
Furthermore, statistical distribution of the phase spectrum and its representations along the feature extraction pipeline are studied. It is illustrated that the phase spectrum has a bell-shaped distribution. Some statistical normalisation methods such as mean-variance normalisation, Laplacianisation, Gaussianisation and Histogram equalisation are successfully applied to the phase-based features and lead to a significant robustness improvement.
The robustness gain achieved through using statistical normalisation and generalised logarithmic function encouraged the use of more advanced model-based statistical techniques such as vector Taylor Series (VTS). VTS in its original formulation assumes usage of the log function for compression. In order to simultaneously take advantage of the VTS and generalised logarithmic function, a new formulation is first developed to merge both into
a unified framework called generalised VTS (gVTS). Also in order to leverage the gVTS framework, a novel channel noise estimation method is developed. The extensions of the
gVTS framework and the proposed channel estimation to the group delay domain are then explored. The problems it presents are analysed and discussed, some solutions are proposed and finally the corresponding formulae are derived. Moreover, the effect of additive noise and
channel distortion in the phase and group delay domains are scrutinised and the results are utilised in deriving the gVTS equations. Experimental results in the Aurora-4 ASR task in an HMM/GMM set up along with a DNN-based bottleneck system in the clean and multi-style training modes confirmed the efficacy of the proposed approach in dealing with both additive and channel noise
On the usefulness of the speech phase spectrum for pitch extraction
© 2018 International Speech Communication Association. All rights reserved. Most frequency domain techniques for pitch extraction such as cepstrum, harmonic product spectrum (HPS) and summation residual harmonics (SRH) operate on the magnitude spectrum and turn it into a function in which the fundamental frequency emerges as argmax. In this paper, we investigate the extension of these three techniques to the phase and group delay (GD) domains. Our extensions exploit the observation that the bin at which F(magnitude) becomes maximum, for some monotonically increasing function F, is equivalent to bin at which F(phase) has maximum negative slope and F(groupdelay) has the maximum value. To extract the pitch track from speech phase spectrum, these techniques were coupled with the source-filter model in the phase domain that we proposed in earlier publications and a novel voicing detection algorithm proposed here. The accuracy and robustness of the phase-based pitch extraction techniques are illustrated and compared with their magnitude-based counterparts using six pitch evaluation metrics. On average, it is observed that the phase spectrum can be successfully employed in pitch tracking with comparable accuracy and robustness to the speech magnitude spectrum
Measurement, control and protection of microgrids at low frame rates supporting security of supply
Increasing penetrations of distributed generation at low power levels within electricity networks leads to the requirement for cheap, integrated, protection and control systems. To minimise unit cost, algorithms for the measurement of AC voltage and current waveforms should be implemented on a single microcontroller, which also carries out all other protection and control tasks, including communication and data logging. This limits the frame rate of the major algorithms, although ADCs can be over-sampled using peripheral control processors on suitable microcontrollers. Measurement algorithms also have to be tolerant of poor power quality which may arise, even transiently, within a microgrid, battlefield, or disaster-relief scenario. This thesis analyses the potential magnitude of these interfering signals, and presents suitably tolerant architectures and algorithms for measurements of AC waveforms (amplitude, phase and frequency). These algorithms are shown to be robust and accurate, with harmonic content up to the level of 53% THD, and with the major algorithms executing at only 500 samples per second. This is achieved by the careful optimisation and cascaded use of exact-time averaging techniques, which prove to be useful at all stages of the measurements: from DC bias removal to low-sample-rate Fourier analysis to sub-harmonic ripple removal. Algorithms for three-phase nodal power flow analysis are benchmarked on the Infineon TC1796 microcontroller and require less than 8% of the 2000μs frame time, leaving the remainder free for other algorithms. Furthermore, to optimise security of supply in a microgrid scenario, loss-of-mains must be detected quickly even when there is an accidental or deliberate balance between local active power generation and demand. The measurement techniques are extended to the detection of loss-of-mains using a new Phase Offset relay, in combination with a novel reactive power control technique to avoid the non-detection-zone. These techniques are tested using simulation, captured network transient events, and a real hardware microgrid including a synchronous generator and inverter
Applications of MATLAB in Science and Engineering
The book consists of 24 chapters illustrating a wide range of areas where MATLAB tools are applied. These areas include mathematics, physics, chemistry and chemical engineering, mechanical engineering, biological (molecular biology) and medical sciences, communication and control systems, digital signal, image and video processing, system modeling and simulation. Many interesting problems have been included throughout the book, and its contents will be beneficial for students and professionals in wide areas of interest
Non-Radiative Calibration of Active Antenna Arrays
Antenna arrays offer significant benefits for modern wireless communication systems
but they remain difficult and expensive to produce. One of the impediments of utilising
them is to maintain knowledge of the precise amplitude and phase relationships between
the elements of the array, which are sensitive to errors particularly when each element
of the array is connected to its own transceiver. These errors arise from multiple
sources such as manufacturing errors, mutual coupling between the elements, thermal
effects, component aging and element location errors. The calibration problem of
antenna arrays is primarily the identification of the amplitude and phase mismatch, and
then using this information for correction.
This thesis will present a novel measurement-based calibration approach, which uses a
fixed structure allowing each element of the array to be measured. The measurement
structure is based around multiple sensors, which are interleaved with the elements of
the array to provide a scalable structure that provides multiple measurement paths to
almost all of the elements of the array. This structure is utilised by comparison based
calibration algorithms, so that each element of the array can be calibrated while
mitigating the impact of the additional measurement hardware on the calibration
accuracy. The calibration was proven in the investigation of the experimental test-bed,
which represented a typical telecommunications basestation. Calibration accuracies of
±0.5dB and 5o were achieved for all but one amplitude outlier of 0.55dB. The
performance is only limited by the quality of the coupler design. This calibration
approach has also been demonstrated for wideband signal calibration
The role of specifications and contracts in outsourced product development in the automotive industry
D.B.A ThesisMuch attention has been paid to relationships between supplier and buyer finns, especially in
the field of product development and in particular in the automotive industry. There has been
a growing debate on the need to increase the responsibilities for suppliers and have a win-win
relationship with them instead of an adversarial relationship. Research has been extensive,
dealing with issues like location of suppliers, just in time, tiering of suppliers, etc., although
little attention has been paid to the issue of specifications and contracts which are an
important part of the product development process. The specification flow between the buyer
and suppliers is necessary in order to obtain the product. Specifications could be validated'
with the help of written contracts and thus can be seen as an important part of the contracts.
The objective of the study is to understand the role of specifications and contracts in these
companies and thus contribute to knowledge and the understanding of practitioners. One
automotive OEM located in Europe was used for the case study. One aircraft OEM, also
located in Europe, was used for supplementary data collection. In-depth interviews in five
first-tier suppliers, and an open ended questionnaire survey (internal and external) have been
used to provide complementary perspectives.
The research2 is guided by a qualitative inductive approach and is aimed at developing ideas
grounded in field observations. Strauss & Corbin's (1990) method for coding qualitative data
has been followed in order to model the role of specifications and contracts. Data was
gathered through semi-structured interviews with various managers in the OEMs and supplier
companies, participant and direct observation, internal documents, and questionnaires.
Specifications were identified to have a role in guiding outsourcing decisions, function as a
means of communication, help decide the time of involvement of the suppliers, help
differentiate suppliers, create visions for suppliers and help provide competitive advantage.
Contracts were identified to have a role in reaching agreements for continuing supply and
help assist in the validation of specifications.Dr Larry Burns, Vice President (R&D - General Motors):
Kjell Ake Eriksson,Auto OEM
A COLLISION AVOIDANCE SYSTEM FOR AUTONOMOUS UNDERWATER VEHICLES
The work in this thesis is concerned with the development of a novel and practical collision
avoidance system for autonomous underwater vehicles (AUVs). Synergistically,
advanced stochastic motion planning methods, dynamics quantisation approaches,
multivariable tracking controller designs, sonar data processing and workspace representation,
are combined to enhance significantly the survivability of modern AUVs.
The recent proliferation of autonomous AUV deployments for various missions such
as seafloor surveying, scientific data gathering and mine hunting has demanded a substantial
increase in vehicle autonomy. One matching requirement of such missions is
to allow all the AUV to navigate safely in a dynamic and unstructured environment.
Therefore, it is vital that a robust and effective collision avoidance system should be
forthcoming in order to preserve the structural integrity of the vehicle whilst simultaneously
increasing its autonomy.
This thesis not only provides a holistic framework but also an arsenal of computational
techniques in the design of a collision avoidance system for AUVs. The
design of an obstacle avoidance system is first addressed. The core paradigm is the
application of the Rapidly-exploring Random Tree (RRT) algorithm and the newly
developed version for use as a motion planning tool. Later, this technique is merged
with the Manoeuvre Automaton (MA) representation to address the inherent disadvantages
of the RRT. A novel multi-node version which can also address time varying
final state is suggested. Clearly, the reference trajectory generated by the aforementioned
embedded planner must be tracked. Hence, the feasibility of employing the
linear quadratic regulator (LQG) and the nonlinear kinematic based state-dependent
Ricatti equation (SDRE) controller as trajectory trackers are explored.
The obstacle detection module, which comprises of sonar processing and workspace
representation submodules, is developed and tested on actual sonar data acquired
in a sea-trial via a prototype forward looking sonar (AT500). The sonar processing
techniques applied are fundamentally derived from the image processing perspective.
Likewise, a novel occupancy grid using nonlinear function is proposed for the
workspace representation of the AUV. Results are presented that demonstrate the
ability of an AUV to navigate a complex environment.
To the author's knowledge, it is the first time the above newly developed methodologies
have been applied to an A UV collision avoidance system, and, therefore, it is
considered that the work constitutes a contribution of knowledge in this area of work.J&S MARINE LT
Integrated Data and Energy Communication Network: A Comprehensive Survey
OAPA In order to satisfy the power thirsty of communication devices in the imminent 5G era, wireless charging techniques have attracted much attention both from the academic and industrial communities. Although the inductive coupling and magnetic resonance based charging techniques are indeed capable of supplying energy in a wireless manner, they tend to restrict the freedom of movement. By contrast, RF signals are capable of supplying energy over distances, which are gradually inclining closer to our ultimate goal – charging anytime and anywhere. Furthermore, transmitters capable of emitting RF signals have been widely deployed, such as TV towers, cellular base stations and Wi-Fi access points. This communication infrastructure may indeed be employed also for wireless energy transfer (WET). Therefore, no extra investment in dedicated WET infrastructure is required. However, allowing RF signal based WET may impair the wireless information transfer (WIT) operating in the same spectrum. Hence, it is crucial to coordinate and balance WET and WIT for simultaneous wireless information and power transfer (SWIPT), which evolves to Integrated Data and Energy communication Networks (IDENs). To this end, a ubiquitous IDEN architecture is introduced by summarising its natural heterogeneity and by synthesising a diverse range of integrated WET and WIT scenarios. Then the inherent relationship between WET and WIT is revealed from an information theoretical perspective, which is followed by the critical appraisal of the hardware enabling techniques extracting energy from RF signals. Furthermore, the transceiver design, resource allocation and user scheduling as well as networking aspects are elaborated on. In a nutshell, this treatise can be used as a handbook for researchers and engineers, who are interested in enriching their knowledge base of IDENs and in putting this vision into practice
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