Research On Power Saving Mechanism Of MAC Layer In IEEE 802.11ah

With the rapid penetration of embedded devices,IoT are becoming the dominant communication paradigms in a wide range of emerging smart services,including smart metering,healthcare,internet of vehicles,agricultural monitoring and industrial automation.This new application and services of scalable smart systems have brought great challenges to the traditional communication technology,unified standards of IoT become the urgent needs of major manufacturers.IEEE 802.11 ah standard is proposed by IEEE 802.11 wireless LAN standards group to support IoT applications.IEEE 802.11 ah standard improves the PHY and MAC on the basis of IEEE 802.11 n and ac technologies.It works in the Sub-1GHz unauthorized frequency bands,supports a wide range of coverage that more than one kilometer,and supports a large number of densely deployed energy-limited terminal devices.It is one of the most competitive solution in the future field of IoT.Based on the enhancement of the IEEE 802.11 ah MAC layer power saving mechanism,this thesis proposes an improved scheme for the restricted access window(RAW)mechanism and grouping algorithm in IEEE 802.11 ah for the low power requirement of IoT applications.The main contents are as follows.The RAW slot adaptation algorithm increases the adaptive adjustment of the RAW slot duration based on the original RAW mechanism.For the purpose of maximizing RAW uplink energy efficiency,estimating the probability that the Station(STA)may be in different states with transmitting data in the RAW slot by applying the probability theory,comprehensively considering the transmission energy consumption and sleep energy consumption brought by STA communication,and constructing the energy efficiency objective function of slot duration.Then,using the simulate anneal algorithm to select the RAW slot duration when the energy efficiency is optimal under the dynamic change of the number of STAs.Simulation results show that the proposed mechanism can provide substantial improvement on uplink throughput and energy efficiency,meet the need of wide-scale low-power and high energy-efficient IoT applications.To solve the problem of hidden nodes in large scale networks,a STA regrouping algorithm is proposed under the contention based CASM/CA mechanism to minimize the transmission collisions caused by hidden nodes.Firstly,the hidden node relationship tableis constructed by detecting the hidden node relationship in the network using the time difference of PS-Pollframes transmission start time between STAs.Then,the expected traffic requirements of STA are integrated into the hidden node table to form a hidden traffic table with a comprehensive knowledge of the potential impact of hidden nodes.Finally,a Viterbi-like algorithm is appliedto allocate the STA into groups in order to minimize the intra-group hidden traffic and hence the potential collision in the whole network.Simulation results show that STA regrouping algorithm can effectively reduce network contention and improve system throughput and energy efficiency.