Backward adaptive lattice and transversl predictors for ADPCM

Abstract

Adaptive predictors are important components of high performance differential pulse code modulation (DPCM) systems. This work compares the noise-free and noisy channel performance of DPCM at 16 kilobits/sec for four backward adaptive predictors: (1) an adaptive gradient transversal predictor, (2) a Kalman transversal predictor, (3) an adaptive gradient lattice predictor, and (4) a least squares lattice predictor. Subjective performance comparisons for five sentences rate the least squares lattice best, followed in order by the Kalman transversal, the gradient lattice, and the gradient transversal. All adaptive predictors exceed the performance of a fixed predictor. Monte Carlo simulations reveal that the lattice predictors outperform the transversal predictors for bit error rates of 10-3or greater. A fully backward adaptive DPCM system is investigated which uses the least squares lattice predictor and limited channel coding and is shown to outperform delta modulation for noise-free channels and for noisy channels with bit error rates as high as 10-2.