Dual Connectivity in LTE small cell networks

Dual Connectivity in LTE network can significantly improve per-user throughput and mobility robustness by allowing users to be connected simultaneously to master cell group (MCG) and secondary cell group (SCG) via MeNB (master eNB) and SeNB (secondary eNB), respectively. The increase in per-user throughput is achieved by aggregating radio resources from at least two eNBs. Moreover, dual connectivity also helps in load balancing between MCG and SCG. However, it imposes several technical challenges. The main ones are buffer status report calculation and reporting, power headroom calculation and reporting, logical channel prioritization, user power saving operations such as discontinuous reception (DRX), and increased device complexity to support bearer split. The coordination between eNBs over X2 interface may be effective to resolve some of these issues. The higher delay due to non-ideal backhaul between MeNB and SeNB, however, limits an efficient coordination between these eNBs. In this paper, we explain and explore these technical challenges and investigate potential solution directions. We also provide a quantitative analysis of potential gains in terms of peruser throughput and load balancing that can be achieved by data bearer split in uplink at the cost of complex UE behaviors using a system level simulation study.