Control/User Plane Decoupled Architecture Utilizing Unlicensed Bands in LTE Systems

The explosive growth of wireless traffic demands and the shortage of licensed spectra motivate us to explore the utilization of unlicensed bands (including mmWave bands and opened licensed bands of other wireless systems for the future) in LTE systems, so-called LTE-U. However, since unlicensed spectra are normally distributed over high-frequency bands and may suffer from random and uncontrollable interference, there are many research challenges for LTE-U systems ahead. To tackle these challenges, we propose a C/U decoupled system architecture for LTE-U systems, which has the advantages of lower complexity, higher flexibility, higher reliability, and higher system capacity. Specifically, we first design a framework and the corresponding system procedures for our proposed C/U decoupled LTE-U systems, including network architecture, frame structure, and centralized resource management procedure. Then we put forward the corresponding enabling and supporting technologies to solve the research challenges, including frequent inter-microcell handoffs, available unlicensed spectrum harvesting, and quality of service guarantee for traffic with high reliability requirements. We also conduct a simulation study to demonstrate the performance gain of the unlicensed spectra transmissions in our proposed LTE-U systems. Finally, we discuss several remaining research challenges, which could be potential topics for future research.