Analyzing the Performance of Dual Connectivity in Control/User-plane Split Heterogeneous Networks

The next generation heterogeneous networks are envisioned as multi-tier networks consisting of macro-cells, providing ubiquitous coverage and small cells, providing high data rate at hotspot areas to improve system capacity. In such heterogeneous networks, mobile terminals (MTs) experience frequent handovers causing high control overhead and link failure probability. To reduce control overhead and to ensure seamless mobility, logical separation between control plane and data plane has been evolved as a promising solution. In control/user-plane (C/U) split network architecture, macro-cell base stations provide control coverage using a low frequency band signal, whereas small cells provide high data rate transmissions to the MTs over high frequency band signals. While performing handovers over small cell base stations, throughput perceived by an MT may fall below the requested data rate. To improve the user perceived throughput at cell edges, recently dual connectivity (DC) has been proposed for long term evolution (LTE) cellular networks. However, analyzing the performance of DC in C/U split LTE heterogeneous networks is quite limited in the preceding literature. In this work, we analyze the performance of DC in C/U plane split network architecture explicitly considering data rate demands of the MTs, traffic arrival pattern, channel conditions as well as target call dropping probability. Our analyses reveal that the performance gain of DC over traditional hard handover is actually conditional on traffic load density in small cell base stations.