Research On Massive Access In Narrowband Internet Of Things

With the advent and rapid standardization of NB-IoT,more and more LPWA(low-power wide-area)services will depend on NB-IoT.With burst and uncertainty of random access,supporting massive connections will cause challenges to wireless networks,then access congestion is inevitable.Therefore,it is very meaningful to study the massive access method in NB-IoT.This thesis mainly studies the problem of access congestion in NB-IoT.Based on the existing access control mechanisms and the different delay requirements of terminals,a dynamic access restriction method is proposed to control the number of random access terminals in NB-IoT.Firstly,according to different delay requirements,terminals are divided into two categories,and different access parameter generation methods are set for them.Secondly,the base station dynamically broadcasts an access barring factor according to the current requests and the target access congestion probability,allowing the terminal whose parameter is less than the barring factor to access.Finally,the performance of the scheme is verified by simulation.The results show that the proposed method can effectively improve the access success rate of delay-sensitive terminals and reduce the access delay greatly.In order to release access congestion,this thesis proposes a research direction that distributing access pressure to multiple access points.A joint access solution based on device clustering and data caching is proposed.Firstly,terminals in the same cell are divided into three coverage levels according to maximum coupling loss.Secondly,within the same coverage level,clusters are formatted according to location,and a leader node with caching is introduced as a relay node,and ordinary terminals access the base station through the relay nodes in the same cluster.Finally,determine the resource(both slots and preambles)allocation schemes by the traversal algorithm to acquire the highest success rate.Simulation shows that this scheme can both improve the access success rate and reduce the access delay effectively.