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8.3 DUAL CONNECTIVITY [3]In LTE, dual connectivity, also known as Inter-site CA, is being introduced in Rel-12 to achieve CAbetween sites. This is an attractive solution for Heterogeneous Networks (HetNets) with no ideal backhaulnetwork. Dual connectivity allows mobility management to be maintained on the macro layer whileaggregating small cells to provide extra user plane capacity, increasing the throughput. The conceptoptimizes performance by combining the benefits of macro cell coverage and small cell capacity. Basedon increasing the bandwidth through CA, inter-site CA can provide a cell edge gain of 50 percent even inloaded networks.Figure 27. Simultaneous Connection to the Macro and Pico layers.Figure 28 depicts how Dual Connectivity is achieved. The radio protocols of the user plane are splitbetween the Master eNB (MeNB), typically a macro cell, and the Secondary eNB (SeNB), typically a smallcell. This gives more flexibility to radio bearers carrying user data. They can either use resources of themacro cell only (depicted in grey), of the small cell only (depicted in cyan) or aggregate both (depicted inblue), depending on whether coverage, offload or throughput is to be favored.Figure 28. Dual Connectivity.4G Americas LTE Carrier Aggregation October 2014 46