This paper presents an adaptive maximum likelihood method for estimating the time difference of arrival of a source signal at two spatially separate sensors. It is well-known that the maximum likelihood technique achieves the Cramer-Rao lower bound for time delay estimation error for certain signal conditions. The /spl alpha/-/spl beta/ tracker is a heuristic mechanism that is heavily used in target tracking applications. In this work, we combine an adaptive realization of the maximum likelihood time delay estimator with the /spl alpha/-/spl beta/ tracker to obtain significant improvement in the performance of the tracker, Experimental results showing 2 to 8 dB improvement in the mean-square estimation error over the conventional /spl alpha/-/spl beta/ tracker for various signal-to-noise ratios are also included in the paper.

A new approach is presented to the digitization and compression of a class of voiceband modem signals. The approach, baseband residual vector quantization (BRVQ), relies heavily on the simple structure present in a modem signal. After the signal is converted to baseband, the magnitude sequence and the sequence of residuals obtained when the phase within each baud of the baseband signals is modeled by a straight line are separately vector quantized. Carrier frequency estimation and baud-rate classification schemes that were designed to carry out these operations are described. Experimental results show that the performance of the BRVQ system at and below 16 kb/s is better than that of a previously developed vector quantization scheme that has itself been shown to outperform traditional speech-compression techniques such as adaptive predictive coding, adaptive transform coding, and subband coding when these techniques are used to compress modem signals.>

A novel carrier frequency estimation scheme for a relatively broad class of voiceband data signals (modem signals) is presented. The class of signals being studied includes different types of phase-shift-keyed (PSK) and frequency-shift-keyed (FSK) signals. The frequency estimates are obtained averaging the estimates of the derivative of the instantaneous signal phase after discarding the estimates at the baud boundaries. Experimental results illustrate that the frequency estimates obtained are unbiased and have small variances. Results also show that the carrier frequency estimation scheme presented is superior to two other techniques in terms of both the mean and variance of the carrier frequency estimates.>

A novel approach to image compression using vector quantization of linear (one-step) prediction errors is presented in this paper. In order to minimize the image reconstruction error, we choose the optimum predictor coefficients (in a least-squares sense) that satisfy the additional constraint that the energy of the impulse response function of the inverse reconstruction filter is bounded by a small constant c. Further, the code vectors are selected such that the reconstruction error is minimized, rather than the quantization noise for the prediction error sequences. Examples demonstrating the excellent quality of the reconstructed images using our approach at bit rates below 0.65 bit/pixel are presented.