75 Mbps 10 MHz 150 Mbps 20 MHz 300 Mbps 150 Mbps 20 MHz 150 Mbps 20 MHz 450 Mbps 150 Mbps 20 MHz 150 Mbps 20 MHz Figure 2.12 Carrier aggregation capability development in the commercial networks and UEs aggregation in the downlink direction. In the markets where total of 60 MHz bandwidth is available for three-carrier aggregation, downlink peak data rates up to 450 Mbps were enabled in 2015 together with the availability of corresponding UEs. From the performance point of view, the carrier aggregation gives benefits in the full cell area. The cell edge area receiving transmission from the two or more separate frequencies allows to improve the cell edge performance, while also allowing to maximize the use of higher frequency band; since for the cases when uplink link budget is not sufficient on higher frequency band, the uplink connection can be covered by a lower frequency band while downlink is received from both. For range-limited scenarios, in general, single uplink is more preferable since the transmission power can be concentrated on a single frequency band alone. Figure 2.13 shows example performance with two-carrier aggregation. There is continuously increasing number of CA band combinations defined in 3GPP. The work on UE RF requirements was first started with limitation to two downlink only carriers. Depending on the bands to be aggregated together, there is some loss of the sensitivity due to the extra switch added in the receiver chain, to enable connecting the other receiver chain for other frequency band. There are 80 band combinations for two carriers aggregation defined in 3GPP in Release 12 until end of 2014, as given in [4]. There exists already several three- band combinations and during 2015 (Release 13) more cases are being added, including downlink band combinations with up to four different bands. The band combinations given in specifications [4] define for each band combination the possible relaxations in the reference sensitivity as well as transmit power allowed in the UE implementation. 