Carrier Aggregation(CA) is one of the most desired feature of LTE-Advanced. In LTE-A aggregation of carriers is used to increase the bandwidth and thereby increase data rates upto 1Gbps. Each aggregated carrier is referred to as Component Carrier(CC), can have BW of 1.4, 3, 5, 10, 15 or 20 MHz. LTE-Advanced allows aggregation of upto five component carriers to attain a maximum aggregated bandwidth of 100MHz.

As none of the service providers own 100MHz continuous carrier BW, three different carrier aggregation modes are supported

1. intra-band contiguous CA
2. intra-band noncontiguous CA
3. inter-band CA

CA is supported in both FDD and TDD modes.
In FDD the downlink(DL) and uplink(UL) can have different CCs, but UL is always lower or equal to DL. Also the CCs can have different carrier BW.
In TDD, the uplink and downlink CCs should be same and have same carrier BW.

Major design challenges on UE side in the design of transceiver circuits are due to support of aggregation of carriers in different frequency bands, higher bandwidths, tunable antennas, etc.,

The definitions used to define different CA combinations are

• Aggregated Transmission Bandwidth Configuration (ATBC) It is the total number of aggregated physical resource blocks(PRB)
• CA Bandwidth Class defined based on maximum of ATBC and maximum number of CCs.
  The classes releasedinR10andR11 are
  • Class A: ATBC ≤ 100, maximum number of CC = 1
  • Class B: ATBC ≤ 100, maximum number of CC = 2
  • Class C: 100 < ATBC ≤ 200, maximum number of CC = 2

In R12 and R13 are …

• CA Configurationindicates a combination of E-UTRA operating bands and CA bandwidth class.

Example
Release 10 table
Carrier Aggregation explained