Design And Implemention Of Medium Control Access Layer In NB-IoT Terminal System

With the booming of communication technology,developing the Internet of Things(IoT)which is based on the Internet of Everything,has become an inevitable trend in the improvement of mobile communications.Narrowband IoT(NB-IoT)is a new communication technology based on cellular communication.It features wide coverage,low power consumption and massive access to meet the needs of low-speed IoT application scennarios.According to NB-IoT system's new functional requirements,its protocol stack architecture has been simplified and optimized.The Medium Access Control(MAC)layer which is a real-time scheduling control layer of the protocol stack has also been improved to accommodate new demands.This thesis relies on the industry-specific major project special research and development project "NB-IoT terminal IoT SOC development and application".Based on the Release 14 protocol,the main functions of the MAC layer in NB-IoT terminal system are studied,designed,and implemented.The main work and innovations are as follows:1.Starting from the MAC entity architecture of the terminal system,the main functions of MAC layer are studied in depth,which includes random access procedure,Hybrid Automatic Repeat reQuest(HARQ),resource scheduling,multiplexing of Service Data Unit(SDU),and demultiplexing of Protocol Data Unit(PDU).2.In order to improve the robustness and stability of the MAC layer,the MAC layer state machine is designed based on the finite state machine and the main functions of MAC layer,so that the work of each state can be kept as independent as possible.At the same time,in order to make the terminal communication process go smoothly,considering the information exchange between the MAC layer and other layers,and combining the MAC layer states,the primitive communication mechanism are designed to facilitate the communication among the layers of the protocol stack.Based on the former two,detailed processing flow and corresponding functions are designed for each process.3.According to the requirements and objectives of the project,a multi-core Digital Signal Processor(DSP)is used as a development platform to develop code by using the embedded C language.Based on the hardware interrupt function of DSP SYS/BIOS system,a subframe interrupt scheduling mechanism is designed to implement the MAC layer timer and real-time scheduling function.4.In order to verify the correctness and stability of the MAC layer implementation,50 test cases are written based on the test protocol for each process,testing 30 times for each.After continuous tests and improvements,the test cases of each process reached a pass rate of 100%,which verified that the functional implementation of the MAC layer conformed to the protocol consistency.