Scenario 1: Macro and small cells on the same carrier frequency, connected via non-ideal backhaul.
Scenario 2: Macro and small cells on different carrier frequencies, connected via non-ideal backhaul.
Scenario 3: Only small cells on one or more carrier frequencies, connected via non-ideal backhaul.
The challenges posed by these scenarios are summarized in the table below.
To address these challenges, 3GPP’s RAN Working Group 2, is currently working towards a set of solutions, with the following design goals in mind:
The idea of ‘dual connectivity’ has more or less been accepted as the way forward. This term refers to operation where a given UE consumes radio resources provided by at least two different network points connected with non-ideal backhaul. Each eNB involved in dual connectivity for a UE may assume different roles and these roles do not necessarily depend on the eNB’s power class and can vary among UEs.
Within the dual-connectivity framework, there are two potential solutions being discussed:
Inter-node radio resource aggregation: This solution is aimed at improving per-user throughput by aggregating radio resources in more than one eNB for user plane data transmission.RRC Diversity: This solution is targeted at improving mobility robustness by transmitting handover related RRC signalling could from/to a potential target cell. The RRC diversity scheme could also be applied for handovers from the macro to pico cells, between macro or between pico cells.
Further details of these solutions can be found in TR36.842.