A Study On Coexistence Mechanisms And Resource Allocation Algorithms For LTE-U And WiFi Systems In Unlicensed Bands

With the popularization of smart mobile terminals and the diversification of mobile applications,the data traffic in cellular networks is increasing exponentially,and users' demand for spectrum is increasing day by day.Operators need to provide larger spectrum bandwidth to increase the capacity of the cellular system and meet the diverse service needs of users.Because a large number of available spectrum resources in unlicensed frequency bands are not fully utilized,3GPP has proposed the LTE-Unlicensed technology to provide additional spectrum bandwidth and improve the capacity of future cellular networks.However,LTE-U system and WiFi system in unlicensed frequency bands have completely different channel access mechanisms,which poses a major challenge for the friendly coexistence of the two systems in unlicensed frequency bands.Therefore,it is necessary to study efficient and reasonable coexistence mechanisms and resource allocation algorithms when the LTE-U system and the WiFi system coexist in unlicensed frequency bands to improve the overall performance of the LTE-U and WiFi coexistence network and meet the service requirements of LTE-U users and WiFi users.Based on the full investigation of domestic and foreign research on the coexistence of LTEU and WiFi systems in unlicensed frequency bands,this thesis conducts research on the fairness and resource allocation issues of LTE-U and WiFi systems coexisting in unlicensed frequency bands.A fairness-oriented carrier sensing adaptive transmission mechanism,an LTE-U system component carrier selection algorithm oriented to user throughput requirements,and an LTE-U system carrier power allocation algorithm oriented to user throughput requirements are proposed.First of all,this thesis focuses on the coexistence network scenario composed of an LTE-U system and a WiFi system in unlicensed frequency band,and studies the fairness of LTE-U system and WiFi system access in the coexistence network scenario.First,the user throughput and the coexistence fairness and fairness constraint conditions when an LTE-U system and a WiFi system coexist are analyzed.On this basis,the channel access problem of LTE-U users and WiFi users on the same carrier in the coexistence network is described,and a fairnessoriented carrier sensing adaptive transmission mechanism(Fairness-oriented CSAT,F-CSAT)is proposed.This mechanism takes into account the dynamic arrival and departure of users in the coexistence network,adaptively adjusts the LTE-U ON/OFF duty cycle in the CSAT cycle to meet the 3GPP requirements for coexistence fairness and Jain fairness index constraints,and maximize the total throughput of the coexistence network at the same time.Finally,the performance of the proposed F-CSAT mechanism is evaluated by simulation experiements.The simulation results show that compared with the fixed duty cycle mechanism,the F-CSAT mechanism can adaptively adjust the LTE-U ON/OFF duty cycle in the CSAT cycle,meet the coexistence fairness requirements of the coexistence network,and provide greater coexistence network throughput.Then,this thesis focuses on the coexistence network scenario composed of one LTE-U system and multiple WiFi systems in unlicensed frequency bands,and studies the problem of component carrier selection when LTE-U users access in the coexistence network scenario.First,the dynamic adjustment of the LTE-U ON/OFF duty cycle when an LTE-U system and a WiFi system coexist on a single carrier is analyzed.On this basis,the problem of component carrier selection when LTE-U users access in a coexistence network is described,and an LTEU system component carrier selection algorithm oriented to user throughput requirements is proposed.The algorithm takes into account the specific throughput requirements of LTE-U users,allows one LTE-U user to use multiple carriers,and also considers the dynamic arrival and departure of WiFi users and LTE-U users in the coexistence network.On the basis of ensuring the fairness of LTE-U and WiFi coexistence and the throughput requirements of existing LTE-U users in the network,one or more suitable carriers are selected for newly arrived LTE-U users according to their respective throughput requirements.Finally,simulation experiments evaluate the performance of the proposed component carrier selection algorithm.The simulation results show that compared with the two traditional carrier selection algorithms,this algorithm can obtain a larger average user utility value and better LTE-U user satisfaction.Finally,this thesis focuses on the coexistence network scenario composed of one LTE-U system and multiple WiFi systems in unlicensed frequency bands,and studies the carrier power allocation problem in the LTE-U system in the coexistence network scenario.First,it analyzes the impact of the difference in channel quality and LTE-U system channel occupation time of different carriers on the LTE-U system throughput.On this basis,the problem of carrier power allocation when LTE-U users access in the coexistence network is described,and an LTE-U system carrier power allocation algorithm oriented to user throughput requirements is proposed.This algorithm takes into account the difference in channel quality and the channel occupation time of the LTE-U system on different carriers.Based on the traditional water filling algorithm,under the limit of the total transmission power of the LTE-U base station,it performs an initial power allocation operation for all carriers in the LTE-U system.On this basis,the transmission power limit and minimum power requirement of the LTE-U base station on a single carrier are further considered,and the power allocation of all carriers is adjusted.Finally,simulation experiments evaluate the performance of the proposed carrier power allocation algorithm.The simulation results show that compared with the average power allocation algorithm,this algorithm can obtain a greater total throughput of the LTE-U system.