rdination The principle of coordinated muting by using almost blank subframes (ABS), as exploited for the eICIC concept as explained in Chapter 7, can in principle also be used for UDN deployments. However, only small cells that act as a dominant interferer for a victim user should start using ABS. Furthermore, the nearby small cells that also potentially act as aggressor node should ideally coordinate which subframes to mute (i.e. configure as ABS). The combinational problem of coordinated muting among small cells is specially challenging when one small cell is identified as being simultaneously aggressor and serving cell for a victim UE that experiences a dominant interferer from another small cell. Such coordination can be attained by pre-assigning some 'good' subframes and 'bad' subframes for the different small cells, where bad subframes are those that may be muted. The pattern of such pre-assigned subframes can either be set a priori or by using slowly adapting SON coordination algorithms. Furthermore, as for the eICIC concept, the users that are subject to significant time-variant interference fluctuations shall be configured with time-domain measurement restricts in coherence with their dominant interfering cells usage of ABS and normal transmissions to ensure good link adaptation and scheduling based on trustworthy CSI feedback. Following the concept originally presented in [10], the proactive time-domain ICIC scheme can be realized as follows. The muting actions are only taken if a small cell is identified as an aggressor to a victim user. Otherwise, normal transmission is used on all subframes. If the difference between the received signal from the serving cell and the user's dominant interfering cell is below a threshold (set to 10 dB), while the DIR is above 3 dB, the user is marked as a victim user. The cell that is the dominant interferer for the victim user is denoted as the aggressor cell, and is requested to mute. The muting action is reverted when the victim user that triggered the muting leave