M. Ghanassi, B. Champagne, and P. Kabal
"Steady-State Squared Error of the Fixed-Point LMS Algorithm", Signal Processing, vol. 87, no. 12, pp. 3226-3233, Dec. 2007.
This communication studies the quantization effects on the steady-state performance of a fixed-point implementation of the Least Mean Squares (LMS) adaptive algorithm. Based on experimental observations, we introduce a new intermediate mode of operation and develop a simplified theoretical approach to explain the behaviour caused by quantization effects in this mode. We also review the stall mode and provide a new expression that predicts the discontinuous behaviour of the steady-state mean squared error as a function of the input signal power. Combined with a previous analysis of quantization effects in stochastic gradient mode, this study provides analytical expressions for the steady-state mean squared error for the full range of step-size values. We present experimental results that are in a good agreement with theoretical predictions to validate our model.
A. M. Wyglinski, F. Labeau, and P. Kabal
"Loading Algorithm for Multicarrier Spatial Diversity Systems with Antenna Selection", IEEE Trans. Wireless Commun., vol. 6, no. 6, pp. 2060-2065, June 2007.
In this paper, a novel loading algorithm consisting of four variants is proposed for a multicarrier transceiver employing multiple antennas configured for spatial diversity. The primary objective of the proposed algorithm is to increase the overall throughput while ensuring the mean bit error rate (BER) is below a specified limit. To achieve this, spatial diversity is employed to improve the subcarrier signal-to-noise ratio (SNR) values. Simultaneously, (uniform or non-uniform) bit allocation, which is a function of subcarrier SNR, is performed to increase throughput. To reduce power consumption, spatial processing complexity, and hardware costs, antenna subset selection is also performed by the proposed algorithm to choose a set of active transmit/receive antennas. The results show that combining bit allocation with spatial diversity (employing antenna subset selection) can yield substantial throughput increases.
A. H. Nour-Eldin and P. Kabal
"Objective Analysis of the Effect of Memory Inclusion on Bandwidth Extension of Narrowband Speech", Proc. Interspeech (Antwerp, Belgium), pp. 2489-2492, Aug. 2007.
For the purpose of improving Bandwidth Extension (BWE) of narrowband speech, we continue our recent work on the positive effect of exploiting the temporal correlation of speech on the dependence between speech frequency bands. We have shown that such memory inclusion into MFCC speech parametrization translates into higher highband certainty. In the work presented herein, we employ VQ to estimate highband discrete entropies, thus refining our analysis of the effect of memory inclusion on increasing highband certainty. Moreover, we extend our previous analysis to LSF parameters. We further construct a BWE system that exploits our memory inclusion technique, thus translating highband certainty gains into practical BWE performance improvement as measured by the objective quality of reconstructed speech. Results show that memory inclusion decreases the log-Spectral Distortion of the extended highband speech by as much as 1 dB corresponding to more than 14% relative.
J. Thiemann and P. Kabal
"Reconstructing Audio Signals from Modified Non-Coherent Hilbert Envelopes", Proc. Interspeech (Antwerp, Belgium), pp. 534-537, Aug. 2007.
In this paper, we present a speech and audio analysis-synthesis method based on a Basilar Membrane (BM) model. The audio signal is represented in this method by the Hilbert envelopes of the responses to complex gammatone filters uniformly spaced on a critical band scale. We show that for speech and audio signals, a perceptually equivalent signal can be reconstructed from the envelopes alone by an iterative procedure that estimates the associated carrier for the envelopes. The rate requirement of the envelope information is reduced by low-pass filtering and sampling, and it is shown that it is possible to recover a signal without audible distortion from the sampled envelopes. This may lead to improved perceptual coding methods.