HARQ Timing Design Based On TD-LTE Access Technology In Unlicensed Spectrum

With the continuous development of communication industry,the wireless access rate demand for user experience is getting higher and higher.High-speed communication has become an indispensable part of society life.However,the spectrum resources are limited it is more and more difficult to obtain spectrum utilization although some mainstream wireless communication access system such as WCDMA and LTE have used related modulation and coding technology.The problem will be alleviated when the Licensed Assisted Access technology is projected for researching by The 3rd Generation Partnership Project.Licensed Assisted Access technology means deploying LTE system in the unlisenced spectrum with little affection to any other systems.LBT mechanism can solve the coexistence problems harmoniously between LTE system and other systems in unlisenced spectrum.The LBT mechanism means channel needs to be detected before LTE system uses the unlisenced spectrum resource.LTE system can not use it unless the interference in the channel is less than the threshold.However,it will bring some problems about HARQ mechanism when LTE system is deployed in the unlisenced spectrum with TDD mode.For instance,some HARQ processes can not retransmit data during channel detection which results in high HARQ process latency because of LBT mechanism’s existence.HARQ timing collision can also accur after the frame reconfiguration point when the radio frame configuration changes dynamically adapting to the unstable uplink and downlink traffic.In this thesis,the LBT mechanism in the unlisenced spectrum and the reason why the high latency of HARQ process generates is introduced first.According to this new problem,this thesis proposes a resource allocation method based on priority judgement.The priority of each process is determined by the number of of missing retransmission of each HARQ process and their latency.The limited resource will be allocated to higher priority processes when the channel is available.The system simulation result shows that the system average throughput with priority decision mechanism under low traffic is higher than before but the HARQ process average latency reduces little.The HARQ process average latency under high traffic has larger gain than low traffic while the system average throughput changes little even brings some negative gain.Morever,this thesis also analyzes the problem of HARQ timing collision when dynamic TDD technology is used in unlisenced spectrum and proposes a new scheme based on transitional radio frame according to existing solutions.Its core is to insert a transitional radio frame after the frame reconfiguration point so that the HARQ process timing can transit to reconfigurated frame in a simple way with little collision.The simulation results show that the scheme based on the transitional radio frame will bring a certain amount of gain on system average throughput under low traffic while the gain is not obvious under middle and high traffic.Compared with the simulation results of the existing solutions,the scheme based on the transitional radio frame does not have a great advantage in the result.However,the complexity of implementation and signaling load it brings gets lower.