Whats is the difference between DC (Dual Connectivity) and CA (Carrier Aggregation)?

Hello Experts,
Whats is the difference between DC and CA?

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The differences between CA and DC are as follows:

  1. In CA all component carriers belong to the same eNodeB, but in DC, the aggregated carriers belong to different cells (where usually one cell is macro and the other is small). That’s why it is sometimes also referred to as inter-site carrier aggregation. The two eNodeBs are referred to as Master Cell Group (MCG) and Secondary Cell Group (SCG). Commonly it’s clear in case of EN DC option 3x
  2. In CA, only one UE identity is used in all component carriers. But in DC, UE is identified by different C-RNTIs in MCG and SCG.
  3. Only one PUCCH is used for uplink signaling messages across all component carriers in CA, and it is present in the Primary Component Carrier. In DC, however, separate PUCCHs are used in MCG and SCG.
    So, based on the differences we’ve seen so far between CA and DC, we can figure out in which scenario, which aggregation technology would be used.
    If the backhaul of the network is ideal between the nodes, then CA can be implemented. But if the backhaul is not ideal, for example, if there are large delays between the nodes, then the choice should be DC.
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  • 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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