| It is a serious challenge to implement protocol stack for the control plane because of the evolution of LTE network architecture. It is a realistic significance for us to implement correct, stable, highly efficient and good scalable protocol stack not only for promoting development of industrial, but also fully understanding the related standard protocols for future theoretical research.Firstly, the 3GPP radio access network standard protocols are fully understood. Protocol stack for the control plane is analyzed and for the user plane is read in detail. The system requirements and system characteristics of software system in control plane are described. The system requirements contain data transmission, interaction with other layers and signaling processing. The system characteristics contain standard, stability, portability, transactional, parallelism and real-time. Then, this paper designs two software architectures for the control plane at user equipment (UE) side in LTE radio access network according to system requirements and system characteristics. In the first architecture, one thread polls RRC (radio resource control) event queue and NAS (non-access stratum) event queue all the time. Signaling and event processing modules are designed by state machine. The modules of broadcast information and measurement use one thread separately. Network selection, cell selection and cell reselection are implemented as function of event processing. RRC exchanges information with physical layer by API primitive. In the second architecture, NAS and RRC use two threads to poll the queue separately. Access stratum (AS) abstract layer is designed between NAS and RRC to extent multi-mode protocol stack. Finally, the software system is finished in Linux kernel with RTAI patch environment. The software system can transplant many operating systems and physical layer platforms because of using operating system abstract layer and physical layer abstract layer. |
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