A technique is provided for determining the configuration of a sub-frame having data symbols including cyclic-prefixes. In some communication standards such as the Long Term Evolution (LTE) standard, a plurality of possible configurations exist for a sub-frame, with each configuration being identifiable by a certain cyclic-prefix length. In an exemplary method realization, the technique includes receiving a data signal comprising the sub-frame, evaluating one or more hypotheses of the cyclic prefix length to produce one or more corresponding evaluation results, and, based on the evaluation results, deciding on a most-likely cyclic prefix length, according to which the sub-frame configuration is determined. The hypothesis evaluation may involve autocorrelation and cyclic accumulation of samples of the received data signal.