Research On Detection And Avoidance Of Hidden Nodes Based In Wireless Network On Unlicensed Spectrum

In recent years,the data traffic of mobile communication networks has surged,and new services such as ultra-high-definition video and virtual reality have continuously emerged,constantly challenging the capacity limit of wireless networks.Spectrum resources below 6GHz are very scarce,which limits the increase in the capacity of mobile communication networks.To solve this problem,the 3rd Generation Partnership Project(3GPP)proposed the Licensed Assisted Access(LAA)technology to try to offload some mobile network data services to free non-licensed services.Increase network capacity on the spectrum.In order to further expand the spectrum,New Radio-based access to unlicensed spectrum(NR-U)technology considers the use of 60GHz millimeter wave frequency band.Different from the wireless access method of licensed spectrum,LAA adopts the traditional listen before talk(LBT)access mechanism,but this mechanism has limitations in the detection range.Hidden nodes outside the detection range of LBT will affect the edge of the LAA cell The user’s signal reception causes interference,and the user’s reception performance cannot be guaranteed.The NR-U technologies that works in the 60GHz millimeter wave frequency band generates a directional LBT mechanism to achieve spatial multiplexing.However,due to the single detection direction of this mechanism,more hidden node problems will generate.This thesis focuses on the above-mentioned hidden node problem in LAA and NR-U networks to carry out research on unauthorized hidden node detection and evasion technology.The main research work and innovation points are summarized as follows:(1)Aiming at the hidden node problem caused by the defects of the traditional LBT detection mechanism of the LAA network on 5GHz unlicensed frequency band,this thesis proposes a user-side auxiliary LBT mechanism,and realizes signaling interaction through the handshake mechanism between the LAA base station and the user,and then detects and avoids LAA cells Hidden nodes around edge users.The simulation results show that the proposed method achieves an increase of about 2 times the average arrival rate compared with the scene with hidden nodes.(2)Aiming at the hidden node problem caused by the single detection direction of directional LBT mechanism of the NR-U network on 60GHz unlicensed frequency band,this thesis proposes a paired LBT detection method,which requires two-way LBT detection on the base station and the user side,namely the transmitting(receiving)direction In the opposite direction,signaling interaction is realized through a handshake mechanism,and then hidden nodes around the base station and the user are detected and avoided.In addition,two optimization methods are given for the proposed paired LBT method:adjusting the threshold and beam width.The simulation results show that compared with the directional LBT,the paired LBT and the optimized paired LBT increase the total user arrival rate by 29.7%and 63.3%,respectively.(3)Aiming at the additional signaling overhead and access delay caused by auxiliary LBT and paired LBT,this thesis proposes a fast channel access method based on two-step random access and COT sharing technology.Through simulation calculation,it is obtained that when channel access priority is 3 and 4,The maximum access delay optimization of COT sharing mechanism is 1.591ms and 25.591ms,respectively.