Bursting Discovered in Adaptive Signal Processing: Feedback to Blame

Bursting occurs in under-excited adaptive feedback controllers when the parameter estimates attain values that would destabilize the closed loop system were they not further adjusted. Most adaptive signal processing applications do not involve feedback of signals around the adaptive block, and hence are not susceptible to such 'closed loop' instabilities. One exception is the application of adaptive filters in phone lines, the adaptive hybrid, which does involve feedback. Bursting has been observed in adaptive hybrids. This paper compares two sets of situations. The behaviour of a single adaptive hybrid at one end of a phone line is shown to replicate the behaviour of a simple model reference adaptive controller. The use of adaptive hybrids at both ends of the phone line parallels a simple decentralized adaptive controller. The interplay between these two problem areas may shed light on both.