A Dual-Link Soft Handover Scheme for C/U Plane Split Network in High-Speed Railway

The heterogeneous network architecture based on control/user (C/U) plane split is a research hot spot in the fifth generation (5G) communication system. This new architecture for the high-speed railway (HSR) communication system can provide high quality of service (QoS) for the passengers, such as higher system transmission capacity, better transmission reliability, and lower co-channel interference. The relatively critical C plane is expanded and maintained in a reliable low-frequency band to guarantee transmission reliability, and the U plane is supported by the available high-frequency band to meet the increasing system capacity demands. However, there are still many problems to be solved in the C/U plane split network to ensure reliable transmission. In the HSR communication system, the C plane and the U plane are supported by the macro evolved NodeBs (eNBs) and the small eNBs, respectively. The handover between the different macro eNBs involves two types of handovers, which directly reduces its applicability and reliability in HSR. Therefore, a dual-link soft handover scheme for C/U plane split network in HSR is proposed in this paper. By deploying a train relay station (TRS) and two antennas in the train, the handover outage probability will be reduced. Moreover, the bi-casting is adopted to decrease the communication interruption time and the signaling flows of the intra-macro eNB handover and inter-macro eNB handover are designed in detail. Simulation results show that the proposed handover scheme can significantly reduce the outage probability and improve the handover success probability in the inter-macro eNB handover.