In order to acquire first subbands in at least a central band of a broad frequency band, in which subbands frames are transmitted by a base station (BSBB) of a broadband network (RBB) which is co-located with a network (RNB) having narrow subbands comprised in the broadband, a mobile (MBBB) which does not know the distribution of the subbands correlates subsequences of a generated reference signal with subsequences which are respectively detected in the subbands and compares correlation coefficients against a threshold. By knowing the distribution of the first subbands, the mobile is able to process the signaling transmitted by the base station, in order to access allocated resources, after a synchronization phase.