An adaptive delta modulator robust to transmission errors

A technique is described suitable to make a fully digital adaptive delta modulator robust to channel error rates even higher than those of a satellite link. It is shown that the addition of a bias term into the adaptation algorithm makes the two step-sizes at the transmitter and at the receiver converge after a channel error. The step-size adapter parameters are obtained by a compromise between the convergence time and the idle-channel; in fact both are increasing funtions of the bias term. Results of simulations at 32 kbit/sec are given in terms of signal to noise ratio. The halving time of the relative deviation between the transmitter and receiver step-sizes is given as an index of the validity of the algorithm. Finally the error recovery time is defined and experimentally measured.