| With the proliferation of mobile devices and exponential growth of mobile data services,wireless networks are facing challenges of spectrum deficit and spectrum under-utilization.To solve this problem,Licensed-Assisted Access(LAA)has been standardized by 3GPP in Release 13 to address the scarcity of the licensed spectrum allocated for mobile communication systems.However,it is a very challenging problem to ensure fair coexistence between LAA and WiFi systems,especially in the channel environment unstable unlicensed band.In this paper,a fair downlink strategy is proposed for hybrid LAA WiFi and systems,aiming to tune the access probability ranges and assign optimal minimum contention window values for the LAA SBS according to resource availability and spectrum quality.The research is divided into three parts.Firstly,coexistence challenges caused by frequent collisions is posed,which result from the employment of different access mechanisms in unlicensed band.And a 3D-Markov-based analytical framework using listen-before-talk mechanism with dynamic contention window adaptation to solve the problem of contentions and collisions between LAA and WiFi systems in variable interference environments.Secondly,the packet loss due to channel error is analyzed without shielding the PHY layer characteristics of LAA.Based on the analytical model,we investigate the instantaneous rate of WiFi and LAA nodes in different coexistence scenarios combined with MAC and PHY layer transmission characteristics.Following that,a downlink fair strategy is proposed to guarantee the throughput performance of the coexisting WiFi system by limiting the LAA access probability within an explicit upper-lower bound.Finally,Hardware simulation results validate that the proposed dynamic contention window adaptation is effective in LAA and WiFi coexistence scenario,and can effectively improve system throughput from 11%to 13%.Finally,the research is concluded and the study direction is prospected. |
PDF Full Text Request