The MAC Layer RAW Mechanism Research Of IEEE 802.11ah Protocol

With the rapid growth of Internet of Things(Io T)application such as smart home,smart grid and industrial sensor network,wireless networks with a large number of energy constrained low-power devices under the Internet of Things environment will show an explosive growth trend in the future.Therefore,IEEE 802.11 working group has developed a new amendment of the IEEE 802.11 ah protocol standard to support large-scale devices for long-distance and low-power communication.In a highly dense Io T environment,hundreds of devices complete for channels at the same time,which greatly increases the collision probability of network transmission and causes serious deterioration of network performance.Solving the channel access problem of large-scale devices is the core and key point of the research.Thefore,this paper focuses on the channel access mechanism of the Restricted Access Window(RAW)introduced by IEEE 802.11 ah protocol MAC layer.Firstly,the existing research using mathematical methods that simplify the analysis of IEEE 802.11 ah network performance and RAW grouping design can't fully reflect the performance in the actual network,so this paper uses the network simulation tool NS3 to study the IEEE 802.11 ah RAW grouping mechanism for the impact of network performance.By extending the Wi Fi module to support IEEE 802.11 ah RAW mechanism,and then comparing the RAW mechanism with the traditional DCF mechanism,the results show that the RAW mechanism can effectively improve the throughput of the network compared to DCF mechanism and reduce delay and energy loss.Then further study and analyze the impact of the number of RAW group and the number of slot in the group on the network performance.The results show that the RAW parameters need to be set reasonably according to the current network conditions.Unreasonable parameters settings will seriously affect the network performance and prevent network from working optimally.On the other hand,the channel access time of RAW group is evenly distributed in the original RAW mechanism,and the RAW group access time is not properly allocated according to the service requirement,so that the network cannot reach the optimal state.Therefore,this paper proposes a RAW grouping mechanism based traffic rate(TR-RAW).The devices are grouped by TR-RAW mechanism according to the service rate similarity of the devices,and then the time required for the group is adaptively calculated according to the service transmission requirements of the group.The dynamic RAW parameter set(RPS)configuration is performed between the Beacon frames to implement reasonable allocation of the RAW time slot resources,which is based on the calculation result of the group duration.Then NS3 simulation tool is used to simulated and verify the proposed TR-RAW mechanism.The simulation results show that the TR-RAW mechanism realizes the reasonable allocation of grouping duration according to the needs of the traffic transmission.TR-RAW mechanism can further improve throughput,reduce power consumption and latency compared to the original RAW mechanism that evenly distributed RAW group duration.Therefore,the proposed TR-RAW mechanism can better meet the needs of large-scale low-power devices for long-distance communication under the Io T environment.