Large-scale Access Control Mechanism In The Internet Of Things

The Internet of Things(Io T)will shape the future of wireless communications by allowing seamless connections among a wide range of devices.It is predicted that the number of connected devices will exceed 24.6 billion in 2025 and the Machine Type Communications(MTC)devices will account for nearly half of total connected devices.Large-scale MTC devices may be activated in a short time and apply for access to the Base Station(BS)simultaneously.When the number of devices far exceeds the scale that the access resources can carry,access congestion problems will inevitably arise.An effective way to tackle this problem is using an access class barring(ACB)mechanism with an ACB factor to defer some activated MTC devices transmitting their access requests.However,the conventional ACB scheme using a single fixed ACB factor yields an excessive delay and resource wastage in heavy-load scenarios.In response to the above problems,this thesis studies an access control method based on ACB mechanism and wireless access resource management.The main work of the thesis is summarized as follows:Firstly,a Dynamic ACB method with recycling idle preambles(DACB-Re)is proposed,in order to tackle the problem that there are idle preambles in the traditional authorized Random Access(RA)procedure.The two ACB factors are the Primary ACB(PACB)factor and the Secondary ACB(SACB)factor,which divide the ACB check into the PACB check and the SACB check that makes some devices utilize idle preambles to access the BS.Simulation results demonstrate that the DACB-Re method reduces the TST by 30%compared with the ACB scheme with one ACB factor.Secondly,the optimal values of the PACB factor and the SACB factor are derived,in order to minimize TST.And the TST performance of the DACB-Re method and the testbench schemes is also analyzed.Additionally,a dynamic update mechanism of the two factors is presented through estimating the number of contended devices.The theoretical analysis is consistent with the simulation results,which show that the TST of the DACB-Re method is about 30% lower than that of the dynamic ACB method with a single ACB factor.Also,simulation results show the DACB-Re method is robust to the estimation error.Lastly,a centralized overload control M2M-DACB access method is proposed based on the improved two-step handshake RA procedure,to tackle the problem of the large energy consumption of MTC equipment in the distributed overload control M2M-OSA method.The simulation results show that the proposed method can reduce the energy consumption of MTC equipment in the system under the premise that the TST performance of the two methods is very similar.