LTE-Advanced carrier aggregation increases the effective bandwidth in order to improve upon the prior maximum carrier bandwidth limit of 20 MHz. Carrier aggregation achieves an increased network capacity by combining multiple carriers of various bandwidths to improve uplink and downlink transmission speeds.
Carrier Aggregation Results in More Speed
Carrier aggregation achieves much higher data rates and higher data capacity than the prior releases of LTE. Carrier aggregation can combine component carriers with various bandwidths such as 1.4, 3, 5, 10, 15 or 20 MHz to achieve bandwidths as high as 100 MHz.
Intra-Band Carrier Aggregation Simplifies Timing Synchronization
Carriers in the same band can be aggregated in LTE-Advanced. These carriers can be synchronized with a primary carrier or can be grouped in different carrier groups. Synchronizing intra-band carriers with one reference carrier simplifies timing synchronization in both downlink and uplink communications.
Carrier Aggregation Offers More Network Deployment Alternatives
Seamless coverage along with high throughput can be achieved by carrier aggregation. Carrier aggregation may employ many different deployment scenarios. Macro cell carriers providing large coverage areas can be aggregated with carriers of remote radio heads and repeaters offering efficient coverage areas for hot spots.
Inter-Band Carrier Aggregation Provides More Flexibility
Carriers in the different bands can be aggregated in LTE-Advanced. This provides flexibility to wireless operators to aggregate their non-contiguous spectrum in different bands and offer higher speeds and capacity to customers. Inter-band carrier aggregation employs a new technology that coordinates timing among the more complex transceiver architecture.
Dual connectivity (DC) enables simultaneous transmission and reception of data on multiple component carriers from two cell groups via two base stations: master cell group (MCG) via master node and secondary cell group (SCG) via secondary node. In addition to standalone deployment, where both cell groups use NR, DC also enables non-standalone deployments, where a wireless device can be connected to LTE and NR at the same time. In a non-standalone deployment, the MCG may use either LTE or NR.
Dual connectivity not only enhances user throughput by increasing the aggregated bandwidth, but also provides mobility robustness and supports load-balancing among the nodes in the network.
Enhanced Carrier Aggregation
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.
Carrier Aggregation Timeline
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.
Carrier Aggregation Beyond 5 Carriers
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.
PUCCH on Secondary Cell
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.
Primary and Secondary PUCCH Cell Group
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).