Research On Downlink Transmission Feedback Scheme For Standalone LTE-U Networks

In recent years,with the rapid development of mobile smart devices,network traffic increases explosively,which makes wireless communication networks more challenging to meet the capacity demand.With an increase of spectrum utilization over licensed spectrum,the limited licensed spectrum cannot satisfy the demand of network capacity.To this end,it is a viable choice to deploy long-term evolution(LTE)which has high spectrum utilization to unlicensed spectrum.Standalone LTE in unlicensed spectrum(LTE-U),which has the advantages of both LTE-like performance and Wi-Fi-like deployment simplicity,emerges as one of the related technologies.In this thesis,we focus on analyzing the throughput,optimizing the energy efficiency,and designing channel state information(CSI)feedback user selection of the standalone LTE-U networks.Firstly,we study downlink throughput of the standalone LTE-U networks,taking into account of rate adaption,channel feedback scheme,and frequency-domain scheduler.In specific,for the standalone LTE-U network with listen-before-talk(LBT)channel access mechanism,we propose an analytical model to analyze its downlink transmission throughput with random time-varying feedback delay.We firstly establish a model to analyze the probability mass function(pmf)of the random time-varying feedback delay for the standalone LTE-U networks.Then,under scenarios of independent and identically distributed users as well as non-independent and identically distributed users,the mathematical expressions of downlink throughput of the standalone LTE-U network with different subchannel gain feedback schemes and frequency-domain schedulers are derived.Simulation results not only verify the accuracy of the throughput analysis of the standalone LTE-U network but also show the relationships between its throughput and channel occupancy time ratio or time-varying feedback delay.Secondly,we analyze and optimize the energy efficiency(EE)of the users in the standalone LTE-U networks.Based on the analytical throughput derived in the second chapter,the energy efficiency under different schedulers and different channel gain feedback schemes is derived.Be-sides,taking greedy scheduler as an example,under the fairness constraint with Wi-Fi,we study the problem that how to fine tune the parameters of medium access control(MAC)protocol and channel gain feedback scheme to maximize the EE of the LTE-U users.Simulation results verify the accuracy of the analytical EE model and shed some light on the impact of the MAC protocol and the channel gain feedback scheme on the coexistence of the two networks and the EE of the users in the standalone LTE-U networks.Finally,we design a mechanism to select CSI feedback users in the standalone LTE-U net-works.To this end,for both cases in which a user is and is not selected to feed back CSI in the LTE-U base station's current channel access,we first analyze the user's expected throughput in the base station's next channel access.Then,for the sake of achieving proportional fairness of the expected throughput,an optimization problem of selecting users to feed back CSI in the stan-dalone LTE-U network is formulated.As the formulated problem is NP-hard,a suboptimal yet efficient solver based on decoupling and iteration methods is proposed.Simulation results vali-date the effectiveness of the proposed algorithm in improving the throughput of the network while maintaining a preferable fairness among users.