1. A trellis-based lock detector comprising: receiving means adapted for receiving an incoming signal, the incoming signal being at least one of the following: a digitally modulated informative signal, and a noise signal; observation means adapted for performing multi-symbol observations on the received signal; cumulative means adapted for acquiring cumulative observation data by recursively computing observation data corresponding to multi-symbol observations performed by the observation means; memory means adapted for storing cumulative observation data corresponding to multi-symbol observations performed by the observation means, in a traceback; and, a maximum likelihood sequence estimation device including an evaluating portion adapted for evaluating the cumulative observation data stored in the traceback matrix; and a decision portion adapted for making a decision on a status of the trellis-based lock detector by selecting from the group consisting of: a lock status, and unlock status, based on the evaluation of acquired cumulative observation data.