Research On Co-existance Mechanism For LTE And WLAN In Unlicensed Frequency Bands

Nowadays,the number of mobile devices experiences explosive increase which consequently results in exponential increase on the mobile data rate.However,there is seldom vacant spectrum,especially in licensed frequency bands.Meanwhile,LTE(Long Term Evolution)technology has become one of the most deployed wireless communication technologies.Then expanding spectrum resource for LTE system becomes urgently important.One promising way is to use the unlicensed frequency bands for the LTE systems,which depends on the co-existence mechanism to mitigate the interference between LTE systems and the ones working on the unlicensed bands.This thesis focuses on the co-existence mechanisms for LTE and WLAN working on the unlicensed bands.In the introduction part,the background is introduced,and then follows the overview of the art of the state of the co-existence mechanisms between LTE and WLAN systems.In the third part,two types of interference avoidance mechanisms are developed.Firstly,a half-dynamic mechanism is designed,that is,the LTE frame is divided into listen subframe and transmission one.The ratio between these two kinds of subframes is adaptive to the channel occupacy rate in the last few frames.In order to enhance the spectrum efficiency and the fairness of both systems,a dynamic co-existance mechanism is proposed,which adaptively change the working mode regarding the channel occupancy condition.The fourth part addresses the channel selection mechanisms for coexisted LTE and WLAN systems.Two mechanisms are designed:single LTE station-based mechanism and multiple LTE station-based cooperation mechanism.In the single LTE station-based mechanism,the listen period is divided into several time slots which are randomly distributed in a frame.This design facilitates several LTE stations occupying the same channel can sense the channel state more accurately.When using multiple LTE station-based cooperation mechanism,multiple LTE stations cooperatively choose the suitable channel based on the channel state assembly provided by all LTE stations.More channel state information ensures the better performance.