Dual connectivity in LTE HetNets with split control- and user-plane

Recently, a new network architecture with split control-plane and user-plane has been proposed and gained a lot of momentum in the standardisation of Long Term Evolution (LTE) Release 12. In this new network architecture, the control-plane, which transmits system information and handles user connectivity, and the user-plane, which manages user data, are split and no longer transmitted necessarily by the same network node. This dual connectivity confers a large flexibility to the system, and allows for a more energy efficient operation and enhanced mobility management. In this paper, we present a detailed description of our dual connectivity framework based on the latest LTE-Advanced enhancements, in which macrocell-assisted (MA) small cells use different channel state information-reference signals (CSI-RS) to differentiate among each other and allow User Equipment (UE) to take adequate measurements for cell (re)selection. Taking into account the limited number of available CSI-RSs, we study the assignment problem of CSI-RSs to MA small cells, analyse CSI-RS collision and confusion issues and present simulation results to demonstrate the flexibility of the proposed network architecture.