Uplink Transmission And Coexistence Optimization Based On MulteFire Systems

Owing to the popularity of mobile and smart devices,the recent widespread adoption of wireless broadband has led to an explosive growth in the volume of mobile data traffic,and meanwhile has brought tremendous pressures and challenges to the current system.An increasing interest in operating cellular networks in unlicensed spectrum has risen to cope with this issue.Therefore,a new technology called MulteFire comes into being,which enables LTE-based technology to solely operate in unlicensed spectrum and combines the performance benefits of LTE technology with the simplicity of WiFi-like deployments.However,MulteFire is still at an embryonic stage,and a lot of standardized details are still under discussion.Thoughout this thesis,system performance is evaluated mainly from the aspect of throughput.Firstly,simulations of MulteFire technology in different scenarios are performed,and the results show the MulteFire advantages in throughput and coexistence.And then,we analyze the interference sources in MulteFire systems,propose and evaluate the optimized coexisting schemes.Finally,improved uplink transmission schemes are proposed to reduce the noticeable uplink loss,and their performance is evaluated via the system level as well as some link level simulation,which shows the validity and feasibility.The main contribution of this work is summarized as the follows:1.Elaborate and discuss the MulteFire enhancements.First,the MulteFire related contents such as network architecture,access mode,channels and reference signals are summarized.Besides,the block error rate performance of uplink control channel and physical broadcast channel is simulated.For a more comprehensive assessment of MulteFire systems,we then simulate and compare the throughput from different perspectives,including two transmission modes of pure downlink mode and mixed-downlink-uplink mode,two network deployment scenarios of pure MulteFire network and MulteFire-WiFi-hybrid network,as well as different contention window size and energy detection threshold configurations and so on.2.Study the coexistence optimization for MulteFire.Like other unlicensed technologies,one main research point of MulteFire is the coexistence optimization problem,especially in the case that uplink coexists with downlink.This thesis gives a brief analysis of interfenence in MulteFire network firstly,and it turns out that the interference casued by adjacent base stations occupied a high proportion.Therefore,the proposed schemes require the base station to broadcast the scheduling information in real time via a certain signal,so that the strong interfering stations can carry out interference avoidance strategies.The determination criterias for the strong interfering stations and avoidance strategies are the key factors of the optimized schemes.This thesis mainly adopts the following two avoidance strategies,i.e.mute single subframe and postpone the whole transmission burst directly,and it also considers either received power or signal to interference ratio as the basis of selecting strong interfering stations according to the difference of downlink or uplink.As for the simulation,we firstly evaluate the reference signal used to measure the interference energy to verify the feasibility of this method.Then we perform simualtions on different determination criterias and avoidance strategies,and the results show significant system throughput gain of each scheme,indicating the advantages and effectiveness of the proposed schemes.3.Optimize the MulteFire uplink transmission mode.To cope with the deterioration of MulteFire uplink performance,cross MCOT scheduling mode and grant-less uplink transmission mode are proposed and evaluated in this thesis.And the simulation results demonstrate that they do achieve a higher uplink performance with ignorable demage to MulteFire downlink and WiFi performance,especially for grant-less uplink mode.However,the implementation of grant-less uplink mode will lead to a lot of modifications and enhancements such as downlink and uplink control information,uplink channel access method,frame structure and scheduling process.The detailed description and discussion of overall design for grant-less uplink transmission mode,as well as simulations on different uplink transmission detection methods and channel access modes will be presented in this thesis.