T.D. Abhayapala

Australian National University, Canberra, Australian Capital Territory, Australia

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Publications (235)221.38 Total impact

  • Aastha Gupta, T.D. Abhayapala
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    ABSTRACT: This paper presents a double sided conical sensor array for common array processing applications. We show that double sided cone arrays are specially suited for extraction of spherical harmonic components of three dimensional spatial wavefields. We use a less known orthogonal relationship of spherical Bessel functions to develop a novel analysis equation for spherical harmonic extraction. As an illustration, we design and simulate a 5th order spherical harmonic decomposition array using 89 microphones to operate over a frequency band of an octave.
    Acoustics Speech and Signal Processing (ICASSP), 2010 IEEE International Conference on; 04/2010
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    Wen Zhang, Thushara D Abhayapala, Rodney A Kennedy, Ramani Duraiswami
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    ABSTRACT: This paper studies head-related transfer function (HRTF) sampling and synthesis in a three-dimensional auditory scene based on a general modal decomposition of the HRTF in all frequency-range-angle domains. The main finding is that the HRTF decomposition with the derived spatial basis function modes can be well approximated by a finite number, which is defined as the spatial dimensionality of the HRTF. The dimensionality determines the minimum number of parameters to represent the HRTF corresponding to all directions and also the required spatial resolution in HRTF measurement. The general model is further developed to a continuous HRTF representation, in which the normalized spatial modes can achieve HRTF near-field and far-field representations in one formulation. The remaining HRTF spectral components are compactly represented using a Fourier spherical Bessel series, where the aim is to generate the HRTF with much higher spectral resolution in fewer parameters from typical measurements, which usually have limited spectral resolution constrained by sampling conditions. A low-computation algorithm is developed to obtain the model coefficients from the existing measurements. The HRTF synthesis using the proposed model is validated by three sets of data: (i) synthetic HRTFs from the spherical head model, (ii) the MIT KEMAR (Knowles Electronics Mannequin for Acoustics Research) data, and (iii) 45-subject CIPIC HRTF measurements.
    The Journal of the Acoustical Society of America 04/2010; 127(4):2347-57. DOI:10.1121/1.3336399 · 1.56 Impact Factor
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    R. Iqbal, T. Abhayapala, J. Ahmed, T. Lamahewa
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    ABSTRACT: The classical Clarke model of mobile radio reception assumes a constant mobile velocity. We, in this paper, relax the assumption of constant mobile velocity to allow the mobile to have constant acceleration and derive expression for the non-stationary autocorrelation function of the channel process in general 2-dimensional (2D) scattering environments. Under suitable assumptions, an expression for Wigner-Ville spectrum is obtained in isotropic scattering environment which suggests that the Wigner-Ville spectrum is a natural generalization of the Clarke's model to constant mobile acceleration scenario.
    Multitopic Conference, 2009. INMIC 2009. IEEE 13th International; 01/2010
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    ABSTRACT: This paper presents a generalized expression for space-time cross correlation between signals at receiver antennas on a moving mobile in 3D space. This expression, which is a function of scattering environment coefficients, antenna locations and velocity of the mobile unit, will be useful for designers of communication systems in understanding space time correlation under various channel environments. A series of simulations are carried out in order to analyze the novel expression derived in the paper.
    Information, Communications and Signal Processing, 2009. ICICS 2009. 7th International Conference on; 01/2010
  • S. M. A. Salehin, T. D. Abhayapala
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    ABSTRACT: We propose a method for estimating the fundamental frequency and localizing a pulsatic, quasiperiodic signal in a correlated mixture. The spectra of the correlated signal is obtained by using the short-time Fourier transform (STFT). For a quasiperiodic, pulsatic signal, the frequency signal variation over the frame index is itself quasiperiodic and pulsatic. In a mixture, the overlap of the spectra of the second signal can erase this quasiperiodic and pulsatic property for a subset of frequency indices. Applying singular value decomposition (SVD) with different frame lengths to these frequency index signals, we can determine the length for which the sum of the ratio of the first over the second singular values is maximum. From this frame length, the fundamental frequency can be calculated. To localize the pulsatic signal, we apply the inverse STFT to the frequency bins where the ratio of singular values are large to obtain a time domain signal. This time domain signal gives an approximation to the position of the pulsatic signal in the mixture.
  • Rauf Iqbal, Thushara Abhayapala, Javed Ahmed, Tharaka Lamaheway
    International Bhurban Conference on Applied Science and Technology; 01/2010
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    ABSTRACT: A three-dimensional single-input single-output Mobile-to-Mobile wireless channel model is developed in this paper by considering the underlying physics of free space wave propagation. Based on this channel model, the temporal correlation function for a general three dimensional scattering environment is derived. The temporal correlation function is characterized by the joint angular power distribution at the transmitter and receiver antennas and the speed of transmitter and receiver antennas. Using a von Mises-Fisher distribution as the angular power distribution, the usefulness of the derived temporal correlation function is discussed.
  • Source
    Mengqiu Zhang, Rodney A. Kennedy, Thushara D. Abhayapala, Wen Zhang
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    ABSTRACT: Principal component analysis (PCA) is known to be a powerful linear technique for data set dimensionality reduction. This paper focuses on revealing the essence of PCA to interpret the data, which is to identify the internal structure of the random process from a large experimental data set. We give an explanation of the PCA procedure performed on a generated data set to demonstrate the exact meaning of the dimensionality reduction. Especially, a method is proposed to precisely determine the number of significant principal components for a random process. Then, the internal structure of the random process can be modeled by analyzing the relation between the PCA results and the original data set. This is vital in the efficient random process modeling, which is finally applied to an application in HRTF Modeling.
  • Dumidu S. Talagala, Thushara D. Abhayapala
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    ABSTRACT: Human beings have a remarkable ability to determine the direction of arrival of a sound and to separate sounds of interest. Replicating this ability is a challenging problem in audio signal processing. In this paper we present a model for the head related transfer function (HRTF) developed with the localisation objective in mind. This is achieved by splitting the 3D localisation cues in terms of two functions which can be independently evaluated. We illustrate the theory for calculating these functions and validate the results against actual HRTF data. We find the model to be a close match for a significant number of potential source locations.
  • S.M.A. Salehin, T.D. Abhayapala
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    ABSTRACT: Photoacoustic imaging is a high resolution, biomedical imaging modality used for cancer detection and imaging biological tissues. Exact photoacoustic reconstruction methods were proposed for simple geometries in both time and frequency domain. However, for arbitrary geometries only time reversal methods were previously proposed. In this paper, we propose a frequency domain algorithm for photoacoustic image reconstruction given an arbitrary sensor geometry. The spatial source distribution is expanded using a 2D Fourier Bessel expansion and the proposed method estimates Fourier Bessel coefficients of this expansion using a least squares method at frequencies corresponding to the zeros of Bessel functions. The effectiveness of the proposed method was corroborated by numerical experiments.
    Signal Processing and Communication Systems (ICSPCS), 2010 4th International Conference on; 01/2010
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    Y.J. Wu, T.D. Abhayapala
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    ABSTRACT: Any attempt to create multiple independent soundfields in separate zones over an extended region of open space results in unintended interference in a given zones from other zones. In this paper, we design spatial band stop filters to suppress interzone interference in the regions of interests and pass the desired soundfields with no distortion. This is achieved by using the higher order spatial harmonics of one zone to cancel the undesirable effects of the lower order harmonics of the same zone on the other zones. We illustrate the work by designing and simulating a 2D two-zone soundfield.
    Applications of Signal Processing to Audio and Acoustics, 2009. WASPAA '09. IEEE Workshop on; 11/2009
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    ABSTRACT: This paper proposes an efficient rate one space-frequency block code (SFBC) for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. The proposed SFBC incorporates concept of matched rotation precoding (MRP) to achieve full transmit diversity and optimal system performance for arbitrary number of transmit antennas, subcarrier interval and subcarrier grouping. The MRP exploits the inherent rotation property of SFBC and has relaxed restrictions on subcarrier interval and subcarrier grouping, making it ideal for adaptive/time varying systems. The lowerbound of the coding gain for MRP is derived and shown that it is useful when designing a SFBC for practical scenarios, e.g. when transmitters have only partial knowledge of power delay profile or when the power delay profile has only a few dominant delayed paths. Simulation results show that the MRP can achieve a similar or better performance than existing SFBCs.
    Communications, 2009. ICC '09. IEEE International Conference on; 07/2009
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    R. Iqbal, P. Sadeghi, T.D. Abhayapala
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    ABSTRACT: In this paper, we consider a wireless communication scenario in which the channel output is marginally Gaussian, but not jointly Gaussian. In particular, we study the joint probability distribution of channel outputs in correlated Rayleigh fading channels in response to constant power signaling, such as M-ary phase shift keying (MPSK). We show that the distribution of the channel output at any given sampling time is marginally Gaussian. However, the joint distribution of a sequence of channel outputs cannot be jointly Gaussian. A consequence of this result is that the information rates stated to be exact in two recent contributions, are strict upper bounds to the achievable data rates. We examine the tightness of these upper bounds by comparing them with the MPSK upper bound under perfect channel state information (CSI) assumption. We find that the CSI upper bound is considerably tighter in slow fading channels, high signal-to-noise ratios, and low-dimension (such as binary) PSK signaling.
    Computer Science and Information Engineering, 2009 WRI World Congress on; 05/2009
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    R. Iqbal, T.D. Abhayapala, T.A. Lamahewa
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    ABSTRACT: Clarke's classical model of mobile-radio reception assumes isotropic-rich scattering around the mobile receiver antenna. The assumption of isotropic scattering is valid only in limited circumstances. Here, a generalised Clarke model is developed, which is applicable to mobile-radio reception in general scattering environments. The authors give expressions for the autocorrelation and power spectral density of the channel fading process and demonstrate the generality of the model by applying it to different non-isotropic scattering scenarios. Using the generalised model, the effect of mobile direction of travel and the non-isotropicity on the statistics of the channel fading process is analysed. It is also shown that if the mobile direction of travel is equiprobable in all directions, a non-isotropic scattering environment on average is as good as an isotropic scattering environment.
    IET Communications 05/2009; DOI:10.1049/iet-com.2008.0054 · 0.72 Impact Factor
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    Wen Zhang, Rodney A. Kennedy, Thushara D. Abhayapala
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    ABSTRACT: This paper introduces a continuous functional model for head-related transfer functions (HRTFs) in the horizontal auditory scene. The approach uses a separable representation consisting of a Fourier-Bessel series expansion for the spectral components and a conventional Fourier series expansion for the spatial components. Being independent of the data, these two sets of basis functions remain unchanged for all subjects and measurement setups. Hence, the model can transform an individualized HRTF to a subject specific set of coefficients. A continuous functional model is also developed in the time domain. We show the efficient model performance in approximating experimental measurements by using the HRTF measurements from a KEMAR manikin and the synthetic data from the spherical head model. The statistical results are determined from a 50-subject HRTF data set. We also corroborate the predictive capability of the proposed model. The model has near optimal performance, which can be ascertained by comparison with the standard principle component analysis (PCA) and discrete Karhunen-Loeve expansion (KLE) methods at the measurement points and for a given number of parameters.
    IEEE Transactions on Audio Speech and Language Processing 05/2009; 17:819-829. DOI:10.1109/TASL.2009.2014265 · 2.63 Impact Factor
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    S. Kodituwakku, R.A. Kennedy, T.D. Abhayapala
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    ABSTRACT: A novel sinhc kernel, which generates a Kaiser window based time-frequency distribution for non-stationary signal analysis is introduced. The Kaiser distribution belongs to the Cohen class of time-frequency distributions, and satisfies desirable distribution properties. By controlling the shape of the Kaiser window, auto-term resolutions and cross-term magnitudes can be successfully traded.
    Electronics Letters 03/2009; 45(4-45):235 - 236. DOI:10.1049/el:20093130 · 1.07 Impact Factor
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    Y.J. Wu, T.D. Abhayapala
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    ABSTRACT: Reproduction of a soundfield is a fundamental problem in acoustic signal processing. A common approach is to use an array of loudspeakers to reproduce the desired field where the least-squares method is used to calculate the loudspeaker weights. However, the least-squares method involves matrix inversion which may lead to errors if the matrix is poorly conditioned. In this paper, we use the concept of theoretical continuous loudspeaker on a circle to derive the discrete loudspeaker aperture functions by avoiding matrix inversion. In addition, the aperture function obtained through continuous loudspeaker method reveals the underlying structure of the solution as a function of the desired soundfield, the loudspeaker positions, and the frequency. This concept can also be applied for the 3-D soundfield reproduction using spherical harmonics analysis with a spherical array. Results are verified through computer simulations.
    IEEE Transactions on Audio Speech and Language Processing 02/2009; DOI:10.1109/TASL.2008.2005340 · 2.63 Impact Factor
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    ABSTRACT: This paper presents a novel matched rotation precoding (MRP) scheme to design a rate one space-frequency block code (SFBC) and a multirate SFBC for MIMO-OFDM systems with limited feedback. The proposed rate one MRP and multirate MRP can always achieve full transmit diversity and optimal system performance for arbitrary number of antennas, subcarrier intervals, and subcarrier groupings, with limited channel knowledge required by the transmit antennas. The optimization process of the rate one MRP is simple and easily visualized so that the optimal rotation angle can be derived explicitly, or even intuitively for some cases. The multirate MRP has a complex optimization process, but it has a better spectral efficiency and provides a relatively smooth balance between system performance and transmission rate. Simulations show that the proposed SFBC with MRP can overcome the diversity loss for specific propagation scenarios, always improve the system performance, and demonstrate flexible performance with large performance gain. Therefore the proposed SFBCs with MRP demonstrate flexibility and feasibility so that it is more suitable for a practical MIMO-OFDM system with dynamic parameters.
    Journal on Advances in Signal Processing 02/2009; DOI:10.1155/2009/231587 · 0.81 Impact Factor
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    S.M.A. Salehin, T.D. Abhayapala
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    ABSTRACT: This paper presents a localization algorithm to detect lung sounds using a circular array of microphones. We use the natural basis functions of propagation waves in height invariant wavefields to form a spatial minimum variance (MV) problem in eigen space. We also derive a Nyquist criteria for localizing sources within a circular region. This Nyquist criteria shows that the radius of the region where sources can be localized is inversely proportional to the frequency of sound. The modified Nyquist criteria can be used for determining the number of sensors required for a given frequency range and radius of region for which sources need to be localized. The results are corroborated by computer simulations.
    Signal Processing and Communication Systems, 2008. ICSPCS 2008. 2nd International Conference on; 01/2009
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    R.A. Kennedy, Wen Zhang, T.D. Abhayapala
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    ABSTRACT: The classical problem of extrapolation of a bandlimited signal from limited time domain data is revisited for signals defined on the sphere. That is, given limited or incomplete measurements of a low pass signal on the unit sphere, find the unique extrapolation to the complete unit sphere. Signals defined on the unit sphere arise in a number of applications, such as beam-patterns in azimuth and elevation and head related transfer functions. Our investigations explore the role of integral equation operators in characterizing the extrapolation problem which leads to an iterative algorithm analogous to that obtained in the time-frequency case.
    Signal Processing and Communication Systems, 2008. ICSPCS 2008. 2nd International Conference on; 01/2009

Publication Stats

2k Citations
221.38 Total Impact Points

Institutions

  • 1998–2014
    • Australian National University
      • College of Engineering & Computer Science
      Canberra, Australian Capital Territory, Australia
  • 2008
    • University of Melbourne
      • Department of Electrical and Electronic Engineering
      Melbourne, Victoria, Australia
  • 2006
    • Queen's University Belfast
      Béal Feirste, N Ireland, United Kingdom
  • 2004
    • National ICT Australia Ltd
      Sydney, New South Wales, Australia
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States
  • 2001–2004
    • Imperial College London
      • Department of Electrical and Electronic Engineering
      London, ENG, United Kingdom
  • 2003
    • University of Technology Sydney
      Sydney, New South Wales, Australia