Carrier Aggregation in LTE-Advanced

UMTS LTE system can support flexible bandwidth configuration up to 20 MHz. Currently, system enhancements are being considered to provide substantial improvements to LTE and allow it to meet or exceed IMT-Advanced requirements. One key enhancement feature is bandwidth extension via carrier aggregation to support deployment bandwidth up to 100 MHz. This will allow peak target data rates in excess of 1 Gbps in the downlink and 500 Mbps in the uplink to be achieved. Carrier aggregation is attractive because it allows operators to deploy a system with larger bandwidth by aggregating several smaller contiguous or non-contiguous carriers while providing backward compatibility to legacy users. For instance, an 80 MHz system can be constructed using contiguous or non-contiguous 4 × 20 MHz component carriers. Legacy users can then access the system using one of the component carriers. This paper provides an overview of carrier aggregation and discusses major technical issues including aggregation structure, scenarios, implementation, control signalling design and coexistence with legacy LTE systems.