Analysis And Design Of LTE And WiFi Coexistence Mechanism In The Unlicensed Spectrum

With the development of society and the progress of science and technology,the number of mobile terminals in wireless communication and the demand for multimedia applications traffic have increased unprecedentedly.Higher requirements for transmission rate,communication capacity and transmission time delay have been raised.Facing the challenges brought by the increasingly scarce spectrum resources,academia and industry have proposed a scheme to deploy LTE on the unlicensed band.This technology can not only expand the capacity of the cellular network,but also save the cost of spectrum resources.However,the media access control(MAC)layer and physical layer protocols of LTE and wireless fidelity(WiFi)are different.The fair and friendly coexistence between LTE and WiFi systems still faces many technical challenges.This thesis aims to address the above issues.First of all,we optimize and compare several solutions to operate LTE in the unlicensed band,which include duty-cycle muting(DCM)mechanism,listen-before-talk(LBT)mechanism,and LTE and WLAN aggregation(LWA)algorithm.After introducing and comparing the mechanisms of DCM,LBT and LWA,to obtain the maximum throughput of LTE and WiFi coexistence system,we optimize the three algorithms respectively by adjusting the key parameter of each mechanism.The simulation results further reveal the characteristics and applicable scenarios of DCM,LBT and LWA.Combining the advantages of DCM and LBT,we propose a novel adaptive access algorithm.The proposed mechanism can improve the utilization of the unlicensed band and reduce the interference of the WiFi system.In addition,by adjusting the size of the duty cycle and the size of backoff window,the algorithm can quickly switch between the two mechanisms,so it can overcome the limitations of the existing algorithms.The simulation results show that the hybrid adaptive access mechanism is superior to the two existing schemes in terms of the data transmission rates and the impact on the WiFi system.Finally,a noval bidirectional mobile offloading mechanism is developed.According to the load situation in LTE-U and WiFi networks,the proposed mechanism can unload users between LTE-U and WiFi system,and then by dynamically adjusting the allocation of the unlicensed band,the proposed bidirectional mobile offloading can improve the system throughput and achieve the load balance among different WiFi access points(APs)as well.The test results show that bidirectional mobile offloading is better than unidirectional mobile offloading in terms of higher system throughput and better load balance.