A Study On Channel Access And Carrier Selection Mechanisms For LTE-U And WiFi Coexistence Network In Unlicensed Bands

With the continuous popularization of mobile terminals and the emergence of new mobile communication services,the mobile Internet has entered a new stage of growth,and the demand for mobile data services has exploded.At present,the Long Term Evolution-Unlicensed?LTE-U?technology is regarded as the most promising method for improving radio access network capacity and reducing operator costs.However,since the unlicensed bands belong to the Industrial Scientific and Medical?ISM?public spectrum bands,which are mainly used by WiFi systems,and LTE-U systems and WiFi systems have different channel access modes and operate independently,while there is no effective coordination mechanism to manage channel access between them,there exists great difficulties and challenges to mitigate interference and establish harmonious coexistence between the two systems.Based on investigating the literature of LTE-U and WiFi coexistence networks both at home and abroad,this thesis studies the channel access and carrier selection mechanism in the LTE-U and WiFi coexistence network in unlicensed bands,and proposes one channel access mechanism and two component carrier selection algorithms,which effectively solve the interference and collision problems in the LTE-U and WiFi coexistence network in unlicensed bands,and prompt network performance.Firstly,this thesis proposes an enhanced Listen-Before-Talk channel access mechanism for the hidden nodes issue in the LTE-U and WiFi coexistence network in unlicensed bands.Firstly,an enhanced LTE-U node structure is proposed,and a WiFi module is added to the LTE-U base station.The Radio Resource Control?RRC?layer and the Medium Access Control?MAC?layer function block of both LTE-U base stations and users are redifined,so that the LTE-U node and the WiFi node can be able to exchange information.The information content that needs to be exchanged between the e-MAC_WiFi in the WiFi module and the e-RRC in the LTE-U module are introduced,and the corresponding information format is further defined.Finally,based on the enhanced LTE-U node architecture,an enhanced Listen-Before-Talk?e-LBT?mechanism is proposed.It adds a Request to Send/Clear to Send?RTS/CTS?handshake procedure to the basic Listen Before Talk?LBT?mechanism to avoid hidden node problems in the coexisting network.Finally,the simulation performance comparison between e-LBT mechanism and basic LBT mechanism is given.The simulation results show that when there are many hidden nodes and data packet collisions in the LTE-U and WiFi coexistence network,e-LBT can effectively solve the hidden node problem,reduce packet collisions and improve system throughput.Then,this thesis proposes an unlicensed component carrier selection algorithm for throughput performance in the LTE-U and WiFi coexistence network in unlicensed bands.Firstly,an implementation of carrier-sense adaptive transmission mechanism is proposed to coordinate the transmission of LTE-U users and WiFi users on a single component carrier.The component carrier selection problem is then formulated as selecting a component carrier for the newly-arrived LTE-U user that provides the maximum throughput at the time of arrival of the new user,while ensuring the minimum throughput requirement of the WiFi network.Finally,an unlicensed component carrier selection?U-CCS?algorithm is proposed,which considers both carrier load and channel condition to select component carriers for newly-arrived LTE-U users.In addition,simulation experiments were performed to evaluate the performance of the U-CCS algorithm and compared it with other component carrier selection algorithms.The simulation results show that the minimum LTE-U user throughput and minimum WiFi user throughput of U-CCS algorithm are much larger than those of other component carrier selection algorithms.In addition,the U-CCS algorithm can guarantee the minimum throughput requirement of WiFi users and ensure the throughput balance between consecutively arriving LTE-U users.Finally,this thesis proposes a QoS-guaranteed component carrier selection algorithm for the quality of service?QoS?requirements of LTE-U users.LTE-U users are first categoried into two types:LTE-U type-1 users and LTE-U type-2 users.LTE-U type-1 users have specific minimum throughput requirements,while LTE-U type-2 users only accept best-effort services that the network can provide.An enhanced carrier sense adaptive transmission mechanism is then introduced to coordinate the transmission of LTE-U type-1 users,LTE-U type-2 users,and WiFi users on a single component carrier.On this basis,a QoS-guaranteed component carrier allocation?Q-CCS?algorithm is proposed,under the premise of guaranteeing LTE-U type-1 users'minmimu throughput requirement and WiFi users'minimum throughput requirement,to selects a component carrier for a newly-arrived LTE-U type-1 user or LTE-U type-2 user.Finally,the performance of the proposed mechanism is evaluated by simulation experiements.The simulation results show that compared with the random selection?RS?algorithm,the Q-CCS mechanism can achieve a large user utility value.