 cell. The pico cell is just RF head connected with fibre to the baseband hotel. The majority of existing eICIC studies have focused on slow distributed RRM where a number of small cells in the form of pico cells are deployed in the macro coverage area, that is, using self-organizing network (SON) type of algorithms based on long-term collection of the spatio-temporal load of network. Release 10 provides a mechanism to coordinate and exchange information of the eICIC configuration between eNodeBs, which is typically updated on a time scale of several seconds. It is a semi-static configuration. The classical distributed architecture with slow update frequency is used as the baseline reference in our analysis. We will show that a tighter inter-cell coordination can increase the performance of the network. It is possible to make fast coordination with distributed RRM by enhanced information exchange over X2 [8]. The fast coordination can also be obtained in the centralized RRM solution. In all these cases the RRM algorithms for both the macro and pico cells are implemented in the macro eNodeB. Slow and fast ABS adaptation are illustrated in Figure 7.16. Slow adaptation uses normal subframes and mandatory ABS subframes where the macro cell is not allowed to transmit data. The number of ABS subframes is changed only with X2 signalling. Fast ABS uses additionally optional ABS subframes, which can be used for the macro cell or the pico cell transmission. The decision can be done on the frame level by the macro cell. The fast RRM gives more flexibility to adapt the resource allocation to the instantaneous capacity requirements. UE can report CQI only during the normal subframes and during mandatory ABS subframes, but not during optional ABS subframes. All subframes cannot be optional ABS since some normal subframes and some mandatory ABS subframes are needed for UE CQI reporting. The UE CQI measurement configuration with fast ABS adaptation is illustrated in Figure 7.17. It is also implied that the small cell decides whi