LTE, and more recently LTE-A (Advanced), are driving the wireless technologies for the near future becoming, with no doubt, the basis to build up the 5G ecosystem that will enable data transfer at speed above 1 Gbps. LTE commercial networks have moved in only few years from initial Category (Cat.) 3 running at download speed of 100 Mbps, to Cat. 4 up to 150Mbps in a 20 MHz spectrum. 3GPP Release 10 has then introduced the Carrier Aggregation (CA) technology bringing benefits not only for higher data rate but also for reducing traffic load.
CA was first defined for Cat. 4 with limited 10+10 MHz bandwidth allocation, but it has been only with Cat. 6, with 20+20 MHz bandwidth allocation, that it has shown the compelling benefits of the technology raising the bar of the maximum downloading speed up to 300 Mbps. Since then, LTE-A has evolved towards higher data rate not just as results of aggregating more carriers but also by using enhanced modulation schemes, 256 QAM, as well as adding more MIMO streams, from 2x2 to 4x4 and above.
