Design And Research Of ACB Mechanism Based On Collision Resolution And Dynamic Resource Allocation

With the rapid development of data services,wireless cellular networks need to carry more MTC(machine type communication)devices to meet the needs of large-scale Internet of things in the future.A large number of MTC devices access to wireless cellular network at the same time,which will cause serious congestion and system overload problems,and even in extreme cases,network services are not available.Due to the time extension and high access failure rate,the quality of service will eventually decline.In order to meet the large-scale deployment of Internet of things devices in the future and improve the communication quality,3GPP proposes congestion avoidance and overload control scheme,including ACB(access class barring)mechanism.This paper focuses on random access in massive machine communication scenarios,and improves ACB mechanism from two aspects: collision resolution of preamble and dynamic resource allocation based on SCMA(sparse code multiple access).In massive machine communication scenarios,when MTC devices initiate random access requests at the same time,the limited uplink channel resources lead to low access success probability of MTC devices.When the power consumption of each device is the same,the total energy required by all devices to transmit preamble is higher.To solve this problem,this paper proposes an optimal ACB factor design scheme based on preamble collision solution.When two devices select the same preamble sequence and meet the condition of a certain distance,the base station can judge the collision between the two devices according to the power delay spectrum.Based on the solution of preamble collision,the ACB mechanism is used to control the number of access devices,and the optimal ACB factor is derived by maximizing the number of successful access devices.Simulation results show that the proposed scheme can support more MTC devices than the traditional optimal ACB mechanism under the condition of sufficient uplink channel resources.Although this paper effectively improves the number of successful access devices and saves the total energy needed to send preamble,the random access performance is still constrained by the number of uplink channel resources.In the traditional orthogonal multiple access technology,due to the limited uplink channel resources,the device initiating random access fails due to the lack of PUSCH(physical uplink shared channel)resources,which leads to the low probability of successful access.When a large number of MTC devices initiate access requests at the same time,preamble collision intensifies and PUSCH resource utilization is low.In order to improve the random access performance,non orthogonal multiple access technology can be used to solve the problem of insufficient uplink channel resources.In this paper,combining the preamble collision resolution and dynamic resource allocation based on SCMA,we use preamble collision detection and increase the uplink channel resources by SCMA.Under the condition of accurately estimating the load,we dynamically allocate the uplink channel resources according to the load to maximize the number of successful access devices,and use ACB mechanism to control the number of access devices to reduce the collision probability.Simulation results show that the proposed scheme further improves the access success probability and PUSCH resource utilization,and reduces the collision probability.