Research On RAW Grouping In IEEE 802.11ah For Industrial Internet Of Things

In the process of industrial intelligence,the Industrial Internet of Things is an important link to connect the physical and information world.Faced with the need to access large-scale,low-power devices in the Industrial Internet of Things,IEEE released the IEEE 802.11 ah protocol for information transmission in the Internet of Things,the protocol supports large-scale terminal devices in the Industrial Internet of Things for low-power,long-distance communication.In order to ensure transmission performance in dense networks,802.11 ah proposes a Restricted Access Window(RAW)mechanism at the Medium Access Control(MAC)layer,which aims to alleviate the transmission conflicts of large-scale nodes.However,there are still many problems with the standard RAW mechanism.This article studies the RAW grouping mechanism in the 802.11 ah protocol.First,to solve the problem that the standard RAW mechanism cannot adapt to the network environment to adjust the grouping,this paper proposes three RAW regrouping methods: Assignment Identifier(AID)reassignment method,AID group reassignment method,and RAW regrouping based on pseudo-random sequence method.The AID reassignment method achieves RAW regrouping by establishing a MAC address-AID mapping table and node reassociation process,but there is a problem of complete network disconnection during the reassociation process.The AID group reassignment method has been improved,and each group of nodes is reassociated according to the new RAW in batches,which greatly improves the channel utilization during the regrouping.However,the above two methods increase the regrouping overhead because the nodes need to be reassociated,and the RAW grouping mechanism also relies on the node's AID to be continuous,resulting in inflexible grouping,so a RAW regrouping implementation based on pseudo random sequence(RRI-PRS).In the associating phase,each node is assigned a pseudo-random sequence as an address code,and in the grouping phase,a grouped composite code is used to carry grouping information to achieve online regrouping of discontinuous AID nodes.Through NS3 simulation,it is shown that compared with the first two regrouping methods,the proposed RRI-PRS method hardly affects the network transmission performance when regrouping,and achieves online RAW regrouping.Second,in view of the unreasonable grouping caused by the standard RAW mechanism and the unbalanced load between groups,a RAW regrouping method based on excepted channel time(RR-ECT)is designed,which takes the channel utilization as the optimization goal.First,based on the theoretical analysis of the single-packet flow model and the saturated flow model,a competition success probability estimation method based on the regression model is proposed.Then calculate the expected channel time according to the probability of successful competition,group the nodes reasonably according to the expected channel time,adjust the duration of the RAW group,balance the load of each group,and reduce the collision probability of the nodes in the group;at the same time,weigh the packet overhead and channel utilization,optimize the numbers of RAW packets.Simulation results show that,due to the optimization of node grouping,RAW duration and number of groups,the proposed method significantly improves channel utilization and throughput and reduces network packet loss and delay in complex heterogeneous traffic networks.The paper has 34 drawings,8 tables,and 75 references.