Design And Implementation Of EMM In NAS Layer Of Narrow-band Internet Of Things(NB-IoT) Protocol Stack

Narrow-Band Internet of Things(NB-IoT),as a new Low-Power Wide-Area Network(LPWAN)technology,has been widely applied in the field of Internet of things.EPS mobility management(EMM)is a sub layer of Non-Access Stratum(NAS)layer in NB-IoT protocol stack.EMM plays an important role in location information and mobility management of IoT terminals.However,with the rapid development of NB-IoT applications,in some areas where terminal devices and access sites are densely deployed,EMM congestion will be easily caused by access overload.How to optimize the access mechanism has become one of the main challenges.In view of the above situation,the NB-IoT radio access process is improved in this thesis,where an access congestion control algorithm based on machine learning running on the base station side has been designed.The congestion environment of wireless access network is periodically been learning by the base stations,and the access success coefficient will be predicted before each access cycle.And then this access parameters and resource configuration information will be broadcasted to the terminal from base station through the wireless channel,which will ensure that the terminal can make real-time selection of the target base station that is conducive to improving access performance,so as to reduce access collision.And based on the improved access mechanism,according to 3GPP standard protocol specification,EMM sublayer in NAS layer of NB-IoT protocol stack on terminal side is designed and implemented in detail,including the initial attach,security mode control,authentication and tracking-area update.In the end of the thesis,the test environment of EMM is implemented by building ARM hardware test platform and simulating channel based on MATLAB software.The basic functions of EMM sublayer protocol stack and the performance of congestion control algorithm are tested.The test results show that the functional modules of EMM protocol stack,such as state management,authentication,attachment request sending and attachment acceptance processing,meet the requirements of standard protocol.Compared with the latest version of the standard protocol,the congestion control performance is improved to some extent.The average number of terminal access collisions is reduced by 12.4%,and the average attachment delay is reduced by 11.3%,the expected design targets have been achieved.As the wireless access overload and EMM congestion have been reduced,there are some value for NB-IoT application of the research results of this thesis.