A robust ADPCM system using an error-correcting code

Effective utilization of an error-correcting code (ECC) is proposed in order to make a low-hit-rate adaptive differential PCM (ADPCM) system robust against bit errors in noisy channels, such as mobile radio. In 16 kb/s ADPCM systems, the inverse-quantizers with a small number (four) of levels lead to large offsets in stepsizes due to channel errors, and high-order all-pole predictors are very sensitive to them. For the purpose of solving these problems, we present a robust ADPCM system using an ECC, in which the reliability of words decoded by the ECC decoder is utilized to control the updating of the inverse-quantizer and also to stabilize the predictor in the receiver. Moreover, on condition that a sampling rate of the system is reduced from 8 to 6.4 kHz, the proposed system is compared with a forward adaptation system [8]. A computer simulation shows a maximum of 1.8 dB improvement over an usual system using the same ECC in segmental SNR for
BER\geq10^{-2}
.