Achieving Quality Of Service And Optimization For LTE In Unlicensed Bands

The fifth-generation networks(5G)are expected to enable a huge data traffic and achieve better user satisfaction.At the same time,the coexistence of different access techniques poses a challenge for admission control and resource allocation.Due to the limited wireless resource in the licensed bandwidth,extending LTE links into the unlicensed bands has attracted considerable research interests as LTE in the unlicensed bands(LTE-U)is expected to offload dramatically increasing cellular traffic to the unlicensed bands.Thus,lots of works focused on the technology to enable the coexistence of LTE and Wi Fi on unlicensed band,including the LTE adaptation in MAC layer with Wi Fi and the performance analysis of both systems.In this thesis,we investigate how to achieve Quality-of-Service(Qo S)for the LTE system in unlicensed bands for LTE and Wi Fi heterogeneous wireless networks,as well as the performance of LTE-U operating in the vehicular networks.The main contributions of this thesis are listed as follows.Firstly,this thesis pays attention to the work about Licensed-Assisted-Access(LAA)to guarantee the Qo S for LTE devices coexisting with Wi Fi.LAA is one of the LTE-U technology defined by 3GPP and is used to assist the LTE service in the licensed band.In this part of work,the system model is establish based on the Markov Chain method under the scenario of LAA and Wi Fi heterogeneous networks in the unlicensed band,where LAA adopts the Listen before talk scheme to compete the transmission opportunity with Wi Fi stations.This thesis quantitatively analyzes the MAC delay for the incoming tagged LTE evolved Node Base Station(eNB)under the saturated Wi Fi traffic condition.Then,a delay-guaranteed admission control scheme is proposed to estimate whether the system should access the new incoming LAA eNB.This thesis introduces the exponential backoff mechanism for the delay analysis about LAA model and considers the freezing time of busy slots caused by collision or successful transmission.Validated by simulation results,our method provides essential insights into the system admission performance and fairness of access.Secondly,this thesis proposes the mechanism of Deterministic Carrier Aggregation(DCA)for LTE-U under the condition of unsaturated Wi Fi traffic,where the LTE eNB aggregates a predetermined number of channels in the unlicensed spectrum to achieve high data-rate communications.This thesis introduces the detailed MAC layer design of the mechanism,especially about the backoff process.The collision probability and channel occupation ratio are then analyzed for DCA to provide the performance estimation.Simulation results validate the effectiveness of DCA and the analytical results,when the eNB coexists with multiple Wi Fi systems under a wide range of traffic load conditions.DCA is particularly useful for applications requiring high bandwidth and enables efficient access control of mobile broadband applications in the LTE Unlicensed bands.Thirdly,we extend the LTE-Unlicensed technology to the vehicular networks.This thesis explores the scenario of LTE in the licensed and unlicensed bands for vehicular network communications.In this thesis,vehicle users adopt the LBT method to compete for resources in the unlicensed band,which is more effective than the traditional competition method of simply offloading traffic to the Wi Fi network or using only the LTE unlicensed band without changing the MAC protocol.The thesis distinguishes different users’ services and adopts users’ satisfaction indicators to measure the satisfaction of different services.Finally,with the goal of maximizing the experience quality of the entire system,the thesis jointly optimizes the licensed and unlicensed bands used by vehicle users and provides guidance on how to occupy the resources of licensed and unlicensed frequency bands.