"Tap Loading of Subcarrier Equalizers for Wireless Multicarrier Transceivers", IEEE Trans. Vehicular., vol. 57, no. 1, pp. 393-403, Jan 2008.
We present a novel algorithm for defining the lengths of subcarrier equalizers employed by wireless multicarrier transmission systems operating in frequency-selective fading channels. The equalizer lengths across the subcarriers are incrementally varied in a "greedy" fashion until the global cost function is below some prescribed threshold. By varying the equalizer lengths, the overall complexity of the equalization is constrained while the system meets a minimum error performance. Moreover, we investigate four strategies for terminating the proposed algorithm when an adequate number of equalizer taps have been allocated in this process. The results show that a system that employs variable-length equalizers defined by the proposed algorithm can achieve an improvement in error robustness of as much as an order of magnitude, relative to a system that employs constant-length equalizers with the same overall complexity
A. H. Nour-Eldin and P. Kabal
"Mel-Frequency Cepstral Coefficient-Based Bandwidth Extension of Narrowband Speech", Proc. Interspeech (Brisbane, Australia), pp. 53-56, Sept. 2008.
We present a novel MFCC-based scheme for the Bandwidth Extension (BWE) of narrowband speech. BWE is based on the assumption that narrowband speech (0.3–3.4 kHz) correlates closely with the highband signal (3.4–7 kHz), enabling estimation of the highband frequency content given the narrow band. While BWE schemes have traditionally used LP-based parametrizations, our recent work has shown that MFCC parametrization results in higher correlation between both bands reaching twice that using LSFs. By employing high-resolution IDCT of highband MFCCs obtained from narrowband MFCCs by statistical estimation, we achieve high-quality highband power spectra from which the time-domain speech signal can be reconstructed. Implementing this scheme for BWE translates the higher correlation advantage of MFCCs into BWE performance superior to that obtained using LSFs, as shown by improvements in log-spectral distortion as well as Itakura-based measures (the latter improving by up to 13%).
J. Thiemann and P. Kabal
"Using Salient Envelope Features for Audio Coding", AES 34th Int. Conf. (Jeju Island, South Korea), 6 pp., Aug. 2008.
In this paper, we present a perceptual audio coding method that encodes the audio using perceptually salient envelope features. These features are found by passing the audio through a set of gammatone filters, and then computing the Hilbert envelopes of the responses. Relevant points of these envelopes are isolated and transmitted to the decoder. The decoder reconstructs the audio in an iterative manner from these relevant envelope points. Initial experiments suggest that even without sophisticated entropy coding a moderate bitrate reduction is possible while retaining good quality.