Research On Downlink User Access And Resource Allocation For Indoor Cell-Free VLC Network

Indoor visible light communication(VLC)network based on Cell-Free is user-centric,which cancels the division of VLC cell boundaries and effectively avoids the frequent handoff of users in the multi-VLC access points(APs)layout,so it has attracted the attention of scholars at home and abroad.However,the dense coverage of multiple VLC APs not only improves the service quality of user,but also leads to the problems of which AP users choose to access and the serious inter-cell interference.In addition,indoor VLC needs to consider the communication performance of VLC under noise and interference while meeting the illumination requirements,and the illumination uniformity is closely related to AP layout and resource allocation method.Based on the above problems,the downlink user access and resource allocation method for indoor Cell-Free VLC network is deeply studied in this thesis.In the third chapter,aiming at the problems of user access and indoor illumination nonuniformity in the scenario of limited bandwidth and diverse user demand for indoor CellFree VLC network,a user access algorithm based on user demand and network resource cooperating is designed to improve the user satisfaction and the sum user rate,and then the VLC AP transmit power is dynamically adjusted to optimize the indoor illumination uniformity.The priority level of user access to AP is determined by designing the weighting factors of supply and demand of user demand and available resources of VLC network,which realizes the access selection of user demand and network resource cooperating.Then,a joint optimization of illumination uniformity and rate for power allocation algorithm is used to dynamically adjust the transmit power of AP,which improves indoor illumination uniformity and the sum user rate.Simulation results show that the average user satisfaction and the sum user rate of the proposed user access algorithm are increased by 12.98% and 31.37% at most,respectively,while the sum user rate of the proposed power allocation algorithm is increased by 10.18% at most on the premise of meeting the indoor illumination uniformity.Therefore,the illumination quality and communication performance are improved.In the fourth chapter,aiming at the problems of the inter cell interference caused by spectrum multiplexing and low resource utilization of orthogonal spectrum allocation method,a time resource allocation algorithm based on cooperative AP clustering is designed to avoid interference between adjacent cells,and a subcarrier allocation algorithm based on interference toleration is proposed to mitigate the interference between non-adjacent cells.The core of the time resource allocation algorithm based on cooperative AP clustering is to optimize time fraction,where the reasonable allocation of the working time of each AP can avoid interference and improve the sum user rate.The subcarrier allocation algorithm based on interference toleration is to design the subcarrier association priority level of user and set the interference strength tolerance threshold,which increases the use efficiency of subcarrier resource of each AP and further reduces the interference caused by frequency multiplexing.Simulation results show that the average user satisfaction and the sum user rate of the proposed algorithm are increased by 5.37% and 19.70% at most,respectively,and the proposed algorithm can effectively reduce the inter-cell interference and improve the resource utilization.