Carrier aggregation is a technique used in wireless communication to increase the data rate per user. Thereby multiple frequency blocks (called component carriers) are assigned to the same user. The maximum possible data rate per user is increased the more frequency blocks are assigned to a user. The sum data rate of a cell is increased as well because of a better ressource utilization. In addition load balancing:p.42 is possible with carrier aggregation.
Types of carrier aggregation
Depending on the positions of the component carriers three cases of carrier aggregation are distinguished::p. 113
- The case where the component carriers are contiguous in the same frequency band is called intra-band contiguous carrier aggregation.
- If the component carriers are in the same frequency band but are separated by a gap the carrier aggregation is called intra-band non-contiguous.
- The most complex case is when the component carriers lie in different frequency band. This is called inter-band carrier aggregation.
There is no difference between these three cases from a baseband perspective. However, the complexity from an RF point of view is increased in the case inter-band carrier aggregation.
The chanel bandwidth for UMTS/HSPA+ is about 3.8 MHz with a carrier spacing of 5 MHz. Carrier aggregation is also called Dual Cell in the context of UMTS/HSPA+.
Through carrier aggregation (part of the UMTS extension HSPA+) two downlink carriers may be assigned to one user since Release 8. Release 10 supports four-carrier aggregation and eight-carrier-aggregation is supported since Release 11. 3GPP standardized carrier aggregation for HSPA+ for the uplink for up to two component carriers since Release 9.:p.157
LTE supports since its first release channel bandwidths of 1,4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. Since LTE-Advanced Rel. 10 any two channels (of possibly different bandwidths) may be aggregated and be assigned to a single user.:p.30 A difference between two aggregated 10MHz component carriers and a single ordinary 20MHz channel is that in the case of carrier aggregation the control information are transmitted on both component carriers.
LTE Advanced with carrier aggregation allows Gigabit LTE. This is made possible through higher order modulation (256QAM), carrier aggregation and 4x4 MIMO. Since LTE Release 10 up to 5 component carriers may be aggregated, allowing for transmission bandwidths of up to 100 MHz:p.113. Using five aggregated component carriers, MIMO and 256QAM allows theoretical data rates of up to 2 Gigabits per second.
- Dahlman, Erik; Parkvall, Stefan; Sköld, Johann (2014). 4G LTE / LTE-Advanced for Mobile Broadband. Elsevier. ISBN 9780124199859.
- Holma, Harri; Toskala, Antti; Tapia, Pablo (2012). LTE-Advanced: 3GPP Solution for IMT-Advanced. Wiley. ISBN 9781119974055.
- Holma, Harri; Toskala, Antti; Tapia, Pablo (2014). HSPA+ Evolution to Release 12. Wiley. ISBN 9781118503218.