This functionality – known as Carrier Aggregation (CA) – is a core capability of LTE-Advanced.
CA permits LTE to achieve the goals mandated by IMT-Advanced while maintaining backward
compatibility with Release-8 and 9 LTE. Release-10 CA permits the LTE radio interface to be
configured with any number (up to five) carriers, of any bandwidth, including differing
bandwidths, in any frequency band. Carrier aggregation can be used for both FDD and TDD.
In the following chapter Release-10 principle is presented as well as the extension provided in
see the below figure for an example where FDD is used.
*Figure: Carrier Aggregation (FDD); The LTE-Advanced UE can be allocated DL and UL resources on the aggregated resource consisting of two or more Component Carriers (CC), the R8/R9 UEs can be allocated resources on any ONE of the CCs. The CCs can be of different bandwidths.*
LTE carrier aggregation basics
The target figures for data throughput in the downlink is 1 Gbps for 4G LTE Advanced. Even with the improvements in spectral efficiency it is not possible to provide the required headline data throughput rates within the maximum 20 MHz channel. The only way to achieve the higher data rates is to increase the overall bandwidth used. IMT Advanced sets the upper limit at 100 MHz, but with an expectation of 40 MHz being used for minimum performance. For the future it is possible the top limit of 100 MHz could be extended.
It is well understood that spectrum is a valuable commodity, and it takes time to re-assign it from one use to another in view - the cost of forcing users to move is huge as new equipment needs to be bought. Accordingly as sections of the spectrum fall out of use, they can be re-assigned. This leads to significant levels of fragmentation.
To an LTE terminal, each component carrier appears as an LTE carrier, while an LTE-Advanced terminal can exploit the total aggregated bandwidth.
Type of carrier aggregation:
The downlink and uplink can be configured completely independently, with only the limitation
that the number of uplink carriers cannot exceed the number of downlink carriers. Each
aggregated carrier is referred to as a component carrier, CC. The component carrier can have
a bandwidth of 1.4, 3, 5, 10, 15 or 20 MHz. With a maximum of five component carriers, the
maximum aggregated bandwidth is 100 MHz. 3 types of allocation have been defined in 3GPP
to meet different operator’s spectrum scenario.