ta Rates with Carrier Aggregation Evolution LTE started with a 150 Mbps peak rate with 20 MHz bandwidth. In Release 10, the peak data rates were significantly upgraded by the introduction of carrier aggregation and higher-order MIMO. Mainstream carrier aggregation in 2016 delivered up to 450 Mbps on 3 X 20 MHz. 3GPP Release 10 defined a maximum capability up to 5 X 20 MHz with 8 X 8 MIMO, which gives 3 Gbps peak rate with 64-QAM. The data rate can be increased further with more spectrum and with more antennas. A higher number of antenna elements is feasible with comparatively large base sta- tion antennas; however, it is challenging to integrate more antennas into small devices. Therefore, data rates are more easily increased by using more spectrum rather than by using more device antennas. Release 13 enhances the possibilities of carrier aggregation to enable up to 32 component carriers, which makes higher data rates possible through 16 LTE-Advanced Evolution 3GPP Releases 8-9 LTE-Advanced 5 X 20 MHz 3GPP Releases 10-12 LTE-Advanced Pro 32 X 20 MHz 3GPP Releases 13 and beyond Figure 16.7 Evolution of carrier aggregation up to 32 component carriers. the use of more spectrum. In practice, the use of unlicensed spectrum enables LTE to benefit from even further carrier aggregation capabilities. Figure 16.7 illustrates carrier aggregation evolution. 16.3.2 Utilization of 5 GHz Unlicensed Band LTE networks have been deployed using licensed spectrum between 450 and 3600 MHz. The utilization of unlicensed bands in addition to licensed bands will enable capacity and peak data rate improvements for LTE-Advanced Pro. At the 5 GHz unlicensed band, there is plenty of spectrum available, suitable in particular for small cell deployments. This large pool of spectrum allows mobile broadband operators to take advantage of the carrier aggregation evolution provided by LTE-Advanced Pro. The evolution of LTE spectrum usage is shown in Figure 16.8, and the spectrum resources available in the unlicensed 5 GHz band are illustrated in 