Evaluation And Optimization Of Coexistence Performance Of Sidelink Communication System In Unlicensed Bands

With the rapid development of mobile communication technology and mobile Internet technology,the ever-increasing number of mobile terminal equipment accesses makes the global mobile data traffic show an exponential growth trend.At the same time,the quality requirements of users for mobile communication are also increasing High,increasingly crowded licensed spectrum resources will face greater pressure.In order to relieve the resource shortage of the licensed frequency band,in the 4G LTE phase,3 GPP proposes to offload the data traffic of the licensed spectrum to the unlicensed spectrum.In the 5G NR,Further standardization of the use of unlicensed frequency bands forms 5G NR-U.D2D(Device-to-Device)communication technology is one of the key technologies in 4G mobile data offloading.It allows direct communication between devices near the terminal,and deploying D2D communication in unlicensed spectrum has also become a research hotspot in recent years.Deploying mobile communication systems in unlicensed spectrum needs to consider its impact on existing networks such as Wi-Fi.This paper will focus on the coexistence of Wi-Fi and side-link communication in unlicensed spectrum.For users who use unlicensed spectrum sidelink to communicate,this paper presents an unlicensed band resource allocation scheme,which enhances the transmission success rate of SL-U users and enhances the utilization of unlicensed spectrum through resource selection and reservation,combined with Channel Occupancy Time mechanism and blind retransmit mechanism.Then,aiming at optimizing the number of blind retransmissions of users in the coexistence system,a feedback based retransmission number optimization algorithm is proposed,which releases more wireless channel resources and mitigate the impact on Wi Fi users when the number of users in the system is small;Further,aiming at the complex scenario with a large number of users in the system,an optimization scheme of retransmission times based on centralized reinforcement learning algorithm is proposed,which can maximize the total throughput of the system and further improve the utilization of unlicensed spectrum.Aiming at the resource exclusion threshold in the unauthorized band resource selection scheme,this paper uses the distributed reinforcement learning algorithm to optimize the control.This scheme can further increase the utilization of the unlicensed spectrum by SL-U users and improve the efficiency of the coexistence system.