Research On Performance And Energy Detection Threshold Optimization In LTE-LAA

With the continuous growth of mobile smart devices and their services,the future mobile communication technologies will face new challenges in terms of channel resource,service and business requirement.In order to obtain higher communication rate and better user experience,researchers propose to extend long term evolution(LTE)technology to 5GHz unlicensed spectrum,which is called licensed assisted access(LAA).This thesis mainly studies the coexistence of LTE and Wi-Fi systems on 5GHz unlicensed spectrum.Firstly,based on the characteristics of LAA coexistence scheme,this thesis considers the common capture effect in actual communication in the coexistence system,and constructs a two-dimensional discrete Markov model with capture effect.Secondly,in view of the impact of different energy detection thresholds for LAA and Wi-Fi systems on the performance of the coexistence system,an adaptive energy detection algorithm is proposed in this thesis to dynamically adjust the energy detection threshold of LAA,so as to reduce transmission collision and increase the fairness of coexistence networks.The main research work of this thesis is summarized as follows:Firstly,considering the possible capture effect in coexistence scenarios,two listen-before-talk(LBT)access mechanisms(namely Cat-3 and Cat-4)proposed by3 GPP are modeled as a two-dimensional discrete Markov model.Based on the proposed model,three transmission states(namely successful transmission,backoff and failed transmission)in Markov chain are explained and analyzed,and the closed form expression of signal transmission failure probability is derived.In order to further analyze the impact of capture effect on the performance of coexistence network,this thesis also compares and analyzes the impact of capture effect on the performance of coexistence system of two LBT access mechanisms.Simulation results verify the validity of the proposed Markov chain,and prove that the capture effect will affect the performance of the coexistence system to a certain extent.In addition,in the two LBT access mechanisms,Cat-3 is better than Cat-4 in throughput,and Cat-4 is better than Cat-3 in terms of LTE and Wi-Fi network fairness.Secondly,considering the impact of the fixed energy detection threshold scheme in the LAA on the performance of LAA and Wi-Fi coexistence,this thesis proposes an adaptive LBT energy detection threshold algorithm from the perspective of reducing transmission collisions.Based on this algorithm,LAA small base station(SBSs)can dynamically adjust the energy threshold of LAA according to certain fairness conditions and throughput thresholds.Moreover,in order to compare the adaptive energy threshold scheme with the traditional fixed energy threshold scheme,this thesis uses the network simulator-3(NS-3)flow monitoring module in the algorithm to monitor the performance of the coexistence network in real time.The simulation results show that the adaptive LAA energy threshold detection scheme is better than the fixed LAA energy threshold detection scheme in terms of throughput and delay.