Research On Packet-access Method In Large-scale Machine Type Communications

Machine-to-Machine(M2M)communications will play an important role in the infrastructure of the Internet of Things in the future.With the development of communication technology,more and more Machine Type Devices(MTDs)need to be connected to the Base Station(BS).Since the preamble resources are limited,when the massive MTD requests to communicate with the BS at the same time,the existing random access mechanism can no longer satisfy such a large number of random access requests.There will be problems such as low random-access efficiency,high latency,and low resource utilization.In this paper,two random access mechanisms in Machine Type Communications(MTC)are proposed for these problems,the specific research contents are as follows:First,we introduced the random access process of M2 M communication,and analyzed the causes of random access congestion.Several standards for measuring the performance of random access mechanisms are introduced,and the advantages and disadvantages of several random access mechanisms are introduced in detail.Secondly,aiming at the congestion problem caused by large-scale equipments accessing the BS at the same time and the high access delay caused by the traditional backoff mechanism,a random access method based on different delay requirements for grouping devices is proposed.On the basis of the random access backoff mechanism,the devices in the cell are grouped according to the delay requirements,and different backoff models are introduced for the devices in different groups.The preambles are dynamically allocated according to the delay requirements of the devices in different groups,and the delay and throughput of the delay sensitive devices are analyzed.By maximizing throughput,the optimal backoff parameters are designed.The simulation results show that compared with the unified backoff mechanism,the proposed packet mechanism can not only meet the delay requirements of delay sensitive devices,but also improve the access efficiency.Finally,a random access method based on clustering and preamble reuse is proposed for the problem of low access efficiency and low preamble utilization caused by large-scale devices accessing BS at the same time.On the basis of the existing random access packet mechanism,the device is divided into several clusters according to the geographical location,and the access requests of devices in cluster is first sent to the cluster header and then forwarded to the BS by the cluster header.Then,the preamble reuse scheme is determined according to the clustering scheme,and the optimal intra-cluster access and outer-cluster access slot allocation scheme is designed by maximizing the access success probability.The simulation results show that when large-scale MTDs access the BS,the reasonable clustering scheme and the intra-cluster access time can not only improve the access success probability,reduce the access delay,but also improve the preamble utilization rate and reduce the possibility of preamble conflict.