Research On Wireless Coverage Extension Technology Based On Integration Of Access And Backhaul

With the official commercial use of 5G and the development of 6G research,various applications in the mobile Internet and the Internet of Things continue to emerge,which has brought about a surge in data traffic and an ultra-dense deployment model of base stations.In the past,wired fiber deployment was mainly used,but this method has high costs of deployment.With the development of millimeter waves,a large number of spectrum resources can be utilized,so millimeter waves can be used for wireless transmission to reduce costs and increase flexibility.The Integrated Access Backhaul(IAB)proposed by 3GPP is taking advantage of these advantages,using wireless backhaul instead of fiber deployment,and further designing the network architecture.For ultra-dense networks,the ultra-dense deployment of nodes and the IAB topology connection method have brought many problems,including including determining the network topology and base station deployment locations..In terms of topology design,it is necessary not only to meet the connection requirements of users,but also to reasonably arrange the deployment of link relays according to the resource allocation strategy.With the different needs of users,it is necessary to design a reasonable user access method and select an IAB node suitable for user connection.In addition,since the quality of the network and the demands of users are changing in real time,the fixed network topology is unreasonable,so each base station node needs to dynamically adjust the connection as the network changes.In the process of adjustment,node handover is also going on continuously.In order to ensure the handover efficiency,it is necessary to further design the handover method and conditions of handover,and these problems need to be studied and solved.First of all,this thesis studies the architecture of IAB,mainly from the analysis of the IAB network architecture,introduces the integration mode of the traditional network and the integration of access and backhaul,analyzes the characteristics of different modes Mainly introduce and analyze the latest IAB architecture,introduce the CU/DU separation mode inside the IAB node,describe the working mode and characteristics of this mode,and further introduce the integrated network topology of access and backhaul on this basis.Secondly,this thesis conducts a research on cell expansion with integrated access and backhaul.The traditional cell handover bias value is fixed and uniform,which cannot well adapt to the dynamic changes of the network environment and user requirements.We propose a cell range expansion mechanism to autonomously attract users to a specific base station for access,which reduces the number of users directly connected to the home base station to a certain extent and prevents the home base station from being overloaded.In this thesis,the traditional cell expansion scheme is innovated to improve the adaptive capability of the network.In the scheme of bias value design for cell expansion,independent distributed reinforcement learning is proposed to determine the bias value,thereby improving the coverage performance of the network.Specifically,independent distributed learning is adopted to reflect the plug-and-play characteristics of IAB nodes.Distributed learning has the characteristics of low coupling,and each base station can obtain maximum benefits for itself under certain circumstances.Using the DQN method to replace the Q learning method can to a certain extent solve the problem that the Q table in the Q learning is difficult to store due to the large number of states.The simulation results show that under the new cell selection strategy proposed in this thesis,the overall throughput of the system after training has been improved to a certain extent.Compared with the traditional connection strategy,it reduces the load of the high-power home base station,solves the overload problem of the high-power home base station,improves the user rate of the high-power home base station connection,and improves the rate of some users at the edge with low rate,thereby effectively improving Network coverage and stability.Finally,this thesis conducts research on cell handover in the integration of access and backhaul,and proposes a handover scheme for mobile IAB nodes and a recovery mechanism in the event of a backhaul link failure(RLF).In the IAB multi-hop network,the backhaul link failure(RLF)situation may occur.Since this situation may occur in each backhaul segment,for the failed links in different backhaul parts,on the basis of CHO handover,RLF recovery is proposed.The CHO trigger mechanism at the time is proposed,and a link measurement scheme is proposed to improve the hysteresis of node measurement information.The simulation results show that the proposed handover method can effectively solve the situation that the topological connection error occurs in the node handover when the RLF is restored,and the home base station cannot be returned.The new handover mechanism can reduce the average handover times and improve handover speed.