Performance Study Of Co-Existence Between ELAA And WiFi Systems In Unlicensed Spectrum

With the rapid growth in the number of smart terminals,mobile data traffic has grown in an exponential manner in recent years.For wireless communication systems,the limited frequency resource retards capacity growth.In order to solve this problem,some network operators attempt to expand the available bandwidth by developing the unlicensed frequency band.Specifically,enhanced Licensed-Assisted Access(eLAA)was proposed in Release 14.It aggregates the licensed frequency band for Long Term Evolution(LTE)and the unlicensed frequency band for 5GHz.One of the key issues is to achieve a balanced coexistence between eLAA and WiFi.The main works are as follows:1.By comparing the two techniques(i.e.,LTE and WiFi),this paper summarizes their own characters and analyzes the differences in Media Access Control(MAC)layer protocols.Then this paper predicts the effects of deploying LTE in the unlicensed frequency band on WiFi systems,and the problems caused by the coexistence are also explored.In addition,this paper points out the weaknesses of the existing approaches without Listen Before Talk(LBT).2.This paper proposes a Maximum Channel Occupancy Time-based(MCOT-based)Adaptive Listen Before Talk(ALBT)coexistence approach.During the MCOT,cat-2 LBT protocol is adopted.However,cat-4 LBT protocol is adopted without the MCOT.Compared with the situation that only cat-4 LBT is implemented,the proposed approach can improve the terminal-access speed.On the other hand,the proposed approach outperforms the method that only cat-2 LBT is implemented in coexistence fairness.At last,simulation results demonstrate the theoretical analysis mentioned above.3.This paper proposes a LBT-based Dynamic Multi-subframe Scheduling(DMSS)approach.Specially,an uplink grant is allowed to schedule multiple subframe sources.In this way,the uplink grant overhead can be reduced obviously.In addition,a terminal can make another UL LBT attempt in the situation that the first UL LBT is fail.This multiple-attempt approach can make the full use of UL grant and increase the access ability of eLAA terminals.At last,simulation results prove that the proposed approach can improve the coexistence performance.