Reliability evaluation of 5G C/U-plane decoupled architecture for high-speed railway

To facilitate the mobility of heterogeneous networks, control plane (C-plane) and user plane (U-plane) decoupled architecture is being considered by the fifth generation (5G) wireless communication network, in which relatively crucial C-plane is expanded and kept at dependable lower frequency bands to guarantee transmission reliability and the corresponding U-plane is moved to available higher frequency bands to boost capacity. Moreover, we apply this architecture to future professional high-speed railway wireless communication system to fulfill the wireless access desire of train passengers. However, for such emerging architecture, there still exist many problems to be solved to guarantee the reliable transmission. In this article, the problem of how to appropriately evaluate the transmission reliability of C/U-plane decoupled architecture is investigated. Due to the lack of ability to reflect the importance of C-plane, conventional outage probability cannot properly indicate the transmission reliability of C/U-plane decoupled architecture whose primary design consideration is that C-plane more heavily affects the transmission reliability thereby being kept at dependable lower frequency bands. Based on this, a novel indicator named unreliability factor (URF) is proposed. Theoretical analysis and simulation results demonstrate that URF can exactly highlight the effects of C-plane on the entire transmission process. Hence, it is more appropriate to employ URF as the indicator to evaluate the transmission reliability of C/U-plane decoupled architecture.