LTE Advanced: 3GPP Solution for IMT-Advanced

4.2 Carrier Aggregation Principle

The Release 8 LTE downlink carrier maximum bandwidth is 20 MHz. This is well-suited to the most of the frequency bands for LTE deployment as the continuous allocation per operator in a given frequency band rarely exceeds 20 MHz. When seeking to introduce the data rate with larger bandwidth, one could have considered larger bandwidths but a lack of continuous spectrum would have limited the usability to a few frequency bands only. The solution was to use carrier aggregation where multiple carriers of 20 MHz (or less) would be aggregated for the same UE. The UE would be receiving carriers at the same time using of multiple frequency bands simultaneously. This kind of carrier aggregation where the carriers are on different frequency bands is considered inter-band carrier aggregation. Inter-band carrier aggregation of two cells of 10 MHz each is also an attractive use case from the operator point of view. It allows the operator to achieve similar UE peak data rates as in case of a single 20 MHz carrier but with fragmented spectrum. If an operator has room for more than 20 MHz in the same frequency band, then intra-band carrier aggregation can be also used, as shown in Figure 4.1. Further motivation with the existing 20 MHz bandwidth was to maintain the backwards compatibility with the earlier LTE Releases. An existing Release 8 UE may access the network using a single carrier only, while a Release 10 carrier aggregation capable UE may then use more ...