- Carrier aggregation (CA) allows a UE to simultaneous transmit and receive data on multiple component carriers from a single eNodeB where as Dual Connectivity (DC) allows a UE to simultaneously transmit and receive data on multiple component carriers from two cell groups via master eNodeB (MN) and secondary eNodeB (SN)
- CA can improves peak rates as well as user throughput at low load and DC can increase user throughput, provide mobility robustness, and support load-balancing among eNodeBs
- CA is for the scenarios where the backhaul between nodes is ideal, while DC is for non-ideal backhaul, e.g., relatively large delay between nodes.
- In CA implementation, user traffic is split between carriers in MAC layer, while in DC implementation, it is split in PDCP layer. In DC, the data bearer which is split in PDCP is called split bearer.
- CA and DC are not mutually exclusive; instead, they can be jointly implemented for the same UE e.g, there are multiple carriers in the master cell group (MCG) and multiple carriers in the secondary cell group (SCG)
- A DC UE has two identities: one C-RNTI in MCG and another C-RNTI in SCG, it has an always-active cell in MCG and another always-active cell in SCG, and it has separate PUCCH resource in MCG and SCG. In CA, there is only one common C-RNTI across all component carriers, and there is only one PUCCH which is on PCell.
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