A method of implicit signaling to support In-Device coexistence interference avoidance is provided. A UE sends an IDC interference indication to an eNB. The indication indicates that a serving frequency becomes unusable due to a coexistence interference problem. The indication does not explicitly indicate a frequency index or a frequency location of the unusable serving frequency. The eNB determines the serving frequency as unusable in an implicit manner. The eNB also determines an implied unusable frequency region based on the received IDC indication. The implied unusable frequency region is between the serving frequency and the ISM band. In one advantageous aspect, the eNB configures a condition for the UE, such that the UE is refrained from sending IDC interference indications unless the condition is satisfied.