d other factors considered in the eNodeB scheduler. The data are then preferably scheduled over the best-suited physical resource blocks from two LTE and LTE Advanced in Releases 8-11 CSI and ACK/NACK feedback from UEs Scheduler Uplink RX Downlink L1 Downlink L1 Resource block Carrier 1 Carrier 2 LTE RF bandwidth Use of resource blocks with good frequency domain CQI feedback Figure 2.11 Frequency domain scheduling with downlink carrier aggregation or more carriers. This provides extra frequency diversity and enables to increase the system capacity in addition to the peak data rates. Once the packet is placed on a particular carrier, the physical layer retransmissions are then taken care of by that particular carrier. The carrier aggregation in Release 10 has direct impact on the peak data rate. With the first phase carrier aggregation, the approach in 2013 was to reach maximum data rate of 150 Mbps, as in Release 8, with more fragmented spectrum availability when a single frequency band could not offer 20 MHz for a single operator and single radio technology. The following steps enabled then going beyond that, with first up to 300 Mbps in 2014 and during 2015 up to 450 Mbps downlink peak data rate as shown in Figure 2.12. The end user will benefit from the improved peak data rates and also the average data rate increases, depending on the load of the network. With fewer users, there is bigger impact than with very large number of users, since in the latter case the eNodeB scheduler anyway can choose from large pool of users which to schedule. Then the capacity increase from the extra frequency domain diversity is smaller. There can be intermediate steps in data rate as well. An European operator which typically would have spectrum in 1800 and 2600 MHz, would typically have no more than 10 with 800 MHz band, thus such an operator would likely utilize a total of 50 MHz of spectrum, resulting to a peak data rate of 375 Mbps when having UE capable for three-carrier LTE Small Cell Optimization 10 MHz 75 Mbps 150 Mbps 