Modified LMS algorithms for robust ADPCM

The robustness of adaptive differential pulse code modulation (ADPCM) systems versus transmission errors is addressed. To secure the stability of the decoder, it is necessary to modify the form of the LMS (least-mean-square) algorithm used to adapt the predictor. Solutions introducing soft constraints are investigated. The leakage algorithm is proved to be not fully satisfactory, and a new stabilizing algorithm is presented that makes it possible to achieve good performances. Compared to existing methods, the main advantage of this algorithm is its low computational complexity. Form a theoretical point of view, the effect of transmission errors is described by a set of nonlinear recurrent equations. An analysis is carries out in the deterministic second-order case.<
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