The Research Of Link Maintenance And Directional CCA On 60GHz Millimeter WLAN

With the rapid development of WLAN technology,2.4GHz and 5GHz bands fail to meet the demand for the spectrum resources of high-speed wireless transmission.The key technologies of WLAN on 60GHz millimeter wave band become one of the popular research topics for future 5G communication.Compared with 2.4GHz and 5GHz band,60GHz band has wider channel and higher rate.However,it also encounters some problems,such as severe path loss and poor penetration.It has the characteristics of short transmission distance and directional transmission.Due to the high direction of 60GHz millimeter wave transmission,the hidden terminal and exposed terminal problems are facing new challenges.In addition,IEEE standard group is currently promoting the next generation of millimeter wave 60GHz band WLAN transmission standard IEEE 802.1 lay,as the evolution of the IEEE 802.11ad standard which was made in 2013.Compared with the IEEE 802.11ad standard,the IEEE802.11ay standard has higher transmission rate and certain mobility,it also supports multi user.Its key technologies include MU-MIMO and channel bonding.By using the channel bonding technology,the same pair of STA and AP nodes in the 802.11ay may use different bandwidth beamforming(beamformed)links to transmit.So the beamformed link maintenance and indication mechanism defined in IEEE 802.11ad can not meet the requirements of 802.11 ay.Based on the link maintenance mechanism defined in the IEEE 802.11ad standard,this thesis proposes an improved link maintenance scheme suitable for IEEE 802.1 lay,which can be used for the indication and maintenance of multiple links for one node.The specific improvement work includes several aspects.Firstly,a new beamlink maintenance element is defined to identify and distinguish the timer of different bandwidth bonding links.Secondly,we give the specific starting time of each timer according to the establishment of several different channel bonding link.In addition,we adpot the principle of timer freezing and decreasing based on link instead of node in 802.11ad standard.It can avoid the redoing BF training of all links when one beamformed link is out of work,thus reduce the unnecessary redo training overhead.The performance analysis and simulation results verify the effectiveness of the multi-timer mechanism presented in this paper.Aimed at the hidden terminal and the exposed terminal problems in the directional transmission scenario of 60GHz millimeter wave band WLAN,this thesis proposes a E-CCA(Enhanced CCA)scheme suitable for directional transmission to alleviate the hidden and exposed terminal.The main idea of this scheme includes combing the CCA detection and the directional CCA detection,as well as executing CCA operation at the sending node and the receiving node.The CCA configuration is associated with the beam direction,so that a CCA configuration has only one NAV regardless of existence of the number of node pairs.It is benefit to reduce redundancy of NAV setting and improve the efficiency.The dynamic threshold of omni directional CCA and directional CCA is set up to alleviate the problem of directional hidden terminal and exposed terminal according to the channel state.The simulation results show that the E-CCA scheme can reduce the packet loss rate and improve the average throughput of nodes.