Research On The Massive Access Scheme Based On NB-IoT

Since the NB-IoT(Narrow-Band Internet of Things)technology was proposed,various technical standards have been gradually improved,and it has become one of the most potential technologies in the low-power wide-area Internet of Things.In the process of gradually achieving in-depth integration with various fields,NB-IoT devices will be deployed on a large scale.Considering the 180KHz limited spectrum resources of the NB-IoT system,resource competition may occur when a large number of devices are connected,causing the system to appear Access congestion leads to problems such as reduced network access and waste of resources.Therefore,this research attempts to start from the study of NB-IoT access solutions to relieve the pressure on the system caused by massive device access and improve system performance.First,this research considers the massive device access scenario of a single cell in the NB-IoT system,under the Beta distribution,a preamble secondary use access scheme is proposed.Propose the definition of energy consumption of each time slot device,and divide the devices into high energy consumption and low energy consumption device groups by using two grouping methods:average energy consumption and cumulative energy consumption;define the action set and state set according to The state-action pair of the current time slot calculates the reward value,and selects the action corresponding to the maximum reward value as the next time slot action to determine whether the number of preambles allocated to the high energy consumption device group in the next time slot needs to be increased or decreased.Consider Prioritize the allocation of preambles for high-energy-consuming device groups.Under the premise of ensuring the access of high-energy-consuming device groups,the conflicting preamble and remaining preambles in the high-energy-consuming device group are jointly allocated to the low-energy-consuming device group to realize the secondary use of the conflict preamble.The simulation results show that the performance of this scheme is better than that of the traditional random access scheme,and is better than the system performance under the ACB(Access Class Barring)mechanism.Then,based on the ACB mechanism,this paper proposes a preamble conflict mitigation access scheme.First,use the ACB mechanism to limit the number of access devices,configure retransmission counters for all devices that pass the ACB mechanism,and determine in each time slot whether the device to be connected to the time slot contains a retransmission device(whose retransmission counter is not zero),and if it does,it will retransmit based on the retransmission counter value.The transmission device is divided into two retransmission device groups T₂ and T₁,and the non-retransmission device is divided into a non-retransmission device group T₀.Considering that the preamble is allocated to the T₂ and T₁ first,the remaining available preamble is allocated to the T₀.When each group of preamble is allocated,it is different from the traditional allocation scheme that the devices that compete for the same preamble fail.The conflict avoidance preamble allocation scheme is adopted,and the number of retransmissions is the highest among competing devices allocated to the same preamble in each group.The device successfully obtains the preamble to ensure that the preamble allocated by the system is fully utilized,thereby improving system access performance.The simulation results show that this scheme can significantly improve the access success rate of the NB-IoT system,and the retransmission rate will not increase significantly with the increase of the number of access devices,that is,the system delay performance will not be sacrificed.After comparing the above two introduction schemes,it is found that the two schemes are more suitable for scenarios with higher requirements on the expected degree or device life,and can exert their performance better in scenarios with higher requirements for explosion-proof coefficient.