Phase unwrapping of digital signals

In order to unwrap the phase of a digital signal, the signal's z-plane zeros, which lie close to the unit circle, are located by repeatedly expanding the z-plane in small steps and detecting a zero's crossing of the unit circle. This detection is accomplished by determining the step which gives rise to a maximum change in the phase at any frequency sampling point and across any segment of the unit circle. This method and its associated computer program have been rigorously tested, and the phase was successfully unwrapped in most cases, with the few exceptions involving sequences generated from high-density clusters of zeros.>