X 2 SU-MIMO, including dynamic rank adaptation. From the results in Figures 7.13 and 7.14 it is clearly observed that by enabling eICIC a much higher offered traffic can be tolerated with the same or better end-user throughput. Looking at Figure 7.13, it is observed that the offered traffic can be increased from 20 to 40 Mbps while still having a 5-percentile outage of 2 Mbps, thus corresponding to a 100% capacity gain from enabling eICIC. We need to note that the setting of pico cell RE and macro cell ABS muting is semi-static in these results, meaning that it is only adjusted as a function of the average offered traffic and is the same per layer. At low offered load, the results with and without eICIC are similar indicating that ABS is not used, and only moderate values of the pico cell RE are used. As the offered traffic is increased, it is observed that both the value of the pico cell RE and the usage of ABS increase to cope with the increased inter-layer interference. Fast Dynamic eICIC The results above illustrated that there is a need to adjust the number of ABS and the RE parameters dynamically according to the instantaneous UE locations and traffic patterns. We LTE Small Cell Optimization Distributed RRM Centralized RRM Fronthaul Macro Picos Macro Picos Figure 7.15 Architectures for HetNet radio resource management (RRM) will next consider network architectures and algorithms for dynamic eICIC configurations. The eICIC configurations are optimized jointly between macro and pico cells: Macro cell has the load information over multiple pico cells while the pico cell has the local load information. The architecture options from HetNet eICIC control is shown in Figure 7.15. The distributed solution has full RRM functionality in each pico cell and the inter-eNodeB coordination is done with X2 signalling. The distributed coordination can be slow (several seconds) or fast (milliseconds). The centralized approach uses baseband hotel where all the RRM functions including packet scheduling are located in the macro