Enhanced Carrier Aggregation (eCA) is a 3GPP release 13 enhancement to the carrier aggregation technology to increase the number of aggregated carriers from 5 to up to 32 carriers and dramatically improve the data rate experienced by the end users. This enhancement entails other modifications including transmission of uplink control information on a non-primary carrier (known as secondary PUCCH cell) and other related modifications.
The basic carrier aggregation (CA) feature was added to the LTE Release 10 enabling aggregation of up to 5 carriers of the same frame structure. Carrier aggregation was further enhanced in releases 11 and 12 enabling inter-band TDD CA with different UL-DL configurations, CA with multiple UL timing advances and aggregation of carriers with different frame structures.
With the LAA (Licensed-Assisted Access) in horizon during the LTE release 13 standard development, extending the LTE carrier aggregation feature towards capturing the spectrum opportunities of unlicensed spectrum in the 5GHz band created a lot of interest. 3GPP Release 13 introduced the carrier aggregation enhancement beyond 5 carriers and up to 32 carriers.
In legacy carrier aggregation, the transmission of uplink control information for all the aggregated carriers takes place on a physical uplink control channel (PUCCH) of a primary carrier. The increased number of aggregated carriers leads to overloaded PUCCH of the primary carrier. With the eCA technology, support of PUCCH on a secondary carrier in addition to the primary carrier was introduced.
With eCA, the carriers used by a wireless device, for the purpose of uplink control information transmission, are grouped into a primary PUCCH group whose control information are transmitted on the PUCCH of the primary carrier and a secondary PUCCH group whose control information are transmitted on the PUCCH of a secondary carrier (called PUCCH secondary carrier).
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