Research On The Coexistence Fairness And System Performance Of LTE And Wi-Fi In Unlicensed Band

With the development of mobile Internet iindustry,the growth of data traffic brings unprecedented challenges to celluar system.LAA(Licensed Assisted Access)uses carrier aggregation technology to combine LTE in unlicensed spectrum(5 GHz)with LTE in licensed band,which supports a higher data rate and a better user experience.While,the performance of some other radio access technologies in unlicensed band such as Wi-Fi(Wireless Fidelity)is degraded seriously by LAA.Therefore,two aspects should be considered when dealing with the coexistence of LAA and Wi-Fi.On one hand,it is necessary to ensure the channel access fairness of LAA and Wi-Fi in unlicensed band.On the other hand,system performance should be improved based on the coexistenc fairness.Firstly,this paper introduces the deployment of LAA and Wi-Fi in unlicensed band and key technologies of both technologies.The Carrier Sense Multiple Access/Collision Avoidance mechanism in Wi-Fi system is included.Some researches on coexistence mechanism are also introduced.Then,the channel access models of LAA and Wi-Fi are proposed.Based on the models,the collision probability and the data transmission probability of LAA and Wi-Fi in the coexistence scenario are deduced.The influence of the size of the LAA contention window on the coexistence performance is analyzed,and the optimal theoretical window range is determined.Finally,an ALBT(Adaptive LBT)algorithm with contention window size adjustment is proposed.In this algorithm,the LAA node adaptively adjusts the contention window size according to the perceived slot utilization which reflects the load density of the real-time system.System-level simulation platform is established and the simulation is carried out to evaluate the performance of LAA and Wi-Fi in downlink transmission under indoor deployment.Compared with the fixed contention window size mechanism,simulation results show that ALBT algorithm can achieve at least 5%LAA-LTE performance gain in average user throughput with different load intensity.The delay performance of LAA and Wi-Fi can be effectively improved at the same time.