Research On Random Access And Congestion Controlling Of Massive Machine Type Communication

In massive Machine Type Communication,when a large number of Machine Type Communication Device(MTCD)floods into the LTE(Long Term Evolution)network in a short period of time,and a random access attempt is initiated at the same time,because of the available random access resources are limited,which will cause serious network congestion,resulting in low network access efficiency and an increase in average access delay,which has a serious impact on system access efficiency and user experience.In view of the above problems,this thesis proposes two random access mechanisms.(1)Aiming at the problem of overload caused by simultaneous initiation of access attempts,a random access scheme based on sliding window is proposed.In this scheme,the equipment enters the random access waiting queue according to the order of arrival,and will a fixed-size sliding window is imposed on the queue.Only the MTCD within the sliding window in a random access time slot is allowed to select random access resources and initiate random access attempts.This method can restrict the same random access the number of devices that initiate random access attempts at the same time in the access time slot,thereby reducing the competition for available random access resources and improving the overall efficiency of the system.(2)Aiming at the problem of limited available random access resources in the random access process,a DACB scheme based on factor graph preamble multiplexing is proposed from the perspective of increasing available random access resources.In this scheme,when the random access time slot arrives,all MTCDs that initiate random access attempts are allowed to randomly select two different preambles from the set of available preambles,and then multiply them with their respective factors to form one.The new preamble,and then send the newly generated preamble to the base station,the base station can use the excellent high autocorrelation and low cross-correlation of the preamble to detect this combined preamble,which is greatly increased by multiplexing the preamble.The number of available preamble resources;(3)A method for estimating the number of active MTCDs is proposed.Before the arrival of each random access slot,the base station first estimates the number of active MTCDs in the current random access slot according to the estimation method,and then dynamically adjusts the number of accesses based on this estimated value.This method can limit the number of MTCDs that initiate random access attempts at the same time when the access strength is too high,and reduce the probability of network congestion.