Research On Shared Access Method For LTE And WiFi Heterogeneous Systems In Unlicensed Spectrum

In order to meet the high transmission rate service requirements of the wireless communication system,deploying the LTE(Long Term Evolution)system in the unlicensed spectrum can effectively alleviate the shortage of licensed spectrum resources and improve the available spectrum resources of the wireless communication system,thereby improving the system transmission rate.However,the unlicensed spectrum faces the problem of shared access under the coexistence of multiple systems.How to effectively coordinate the shared access unlicensed spectrum between the LTE and the WiFi system,ensure the fairness of shared access of multiple systems while deploying LTE and improve spectrum efficiency is an urgent problem.Therefore,this paper studies the LTE and WiFi sharing for unlicensed spectrum for the purpose of ensuring fairness in LTE and WiFi shared access unlicensed spectrum scenario and improving unlicensed spectrum utilization efficiency from the perspectives of frequency domain and time domain.The main contributions of the thesis are as follows.For the typical scenario of heterogeneous coexistence of LTE and WiFi in the unlicensed band,a frequency domain shared access method based on channel selection is proposed.The method analyzes and models the channel allocation problem based on game theory,and solves the problem by using the potential game method The simulation results show that the proposed algorithm can increase the average throughput of LTE users by 20%and increase the throughput of WiFi users by 10%compared with the existing algorithms.Then,for the dense deployment scenario of LTE and WiFi,a time-domain shared access method based on almost blank subframe(ABS)is further proposed.We analyze and model the behaviors of LTE and WiFi systems accessing channel based on queuing model,and the mean packet delay is taken as the performance index,and I propose a utility function that takes into account the shared access fairness and the overall user satisfaction.The ratio of blank subframes is adaptively adjusted as the traffic load changes by maximizing the utility function.The simulation shows that the proposed algorithm can reduce the WiFi delay by 20%-50%and guarantee the delay of LTE.In the last part an unlicensed frequency band coexistence hardware platform is designed and set up by universal software radio peripheral(USRP).The experimental results show that the throughput of the WiFi system can be improved when heterogeneous systems shared access to unlicensed spectrum,and the effectiveness of the proposed algorithm is further verified.The work of the research is summarized at the end.And we point out the direction for the further improvement.