Science and Development Network (SciDev.Net)
The 3GPP Long Term Evolution-Advanced (LTE-A) system extends the capabilities of 3rd Generation Partnership Project (3GPP) LTE Rel-8 with the support of carrier aggregation, where two or more component carriers are aggregated in order to support wider transmission bandwidths up to 100 MHz and for spectrum aggregation. A user terminal may simultaneously receive or transmit one or multiple component carriers depending on its capabilities. From the User Equipment (UE) perspective, the Layer 2 aspects of Hybrid automatic repeat request (HARQ) are similar to those of Rel-8. There is one transport block (in the absence of spatial multiplexing, or up to two transport blocks in the case of spatial multiplexing) and one independent HARQ entity per scheduled component carrier.