Research On Fair Competition Mechanism Of Shared-channel Between LTE And Wi-Fi

To alleviate the problem of increasingly scarce spectrum resources and meet the growing mobile broadband traffic demands,3GPP(3rd Generation Partnership Project)launched a process on LTE-U(Long Term Evolution-Unlicensed)standardization in 2014,and listed LTE-U as an LTE enhanced mobile communication technology of the next generation in Release 13.LTE-U technology aims to improve the spectrum efficiency of the unlicensed spectrum and increase the system capacity and so on.Nowadays,extending LTE to the unlicensed frequency band has become one of the hotspots of 5G(5th Generation)communication standard.However,considering that the unlicensed spectrum has been shared by other incumbent communication systems,such as Wi-Fi,ZigBee,BlueTooth etc.,the primary target of using LTE system in the unlicensed frequency band is to tackle the coexistence problem of LTE system and other communication systems that have been deployed in the unlicensed frequency band.With respect to the 5GHz frequency bands,one main target is to guarantee the fair and friendly coexistence of LTE system with Wi-Fi system in the unlicensed frequency band.In this thesis,fair competition mechanisms of shared-channel in the unlicensed frequency band between LTE system and Wi-Fi system are studied.First of all,according to different network load strengths and different priorities of data services,we propose ALBT(Adaptive Listen Before Talk)mechanism based on EDCA(Enhanced Distributed Channel Access)mechanism.Secondly,by constructing the multi-objective optimization model of the coexistence scenario between LTE system and Wi-Fi system,PLBT(Particle Listen Before Talk)mechanism based on particle swarm optimization algorithm is proposed.The main contents and innovations of this thesis are as follows:1.According to different network load strengths and different priorities of data services,we propose an ALBT(Adaptive Listen Before Talk)mechanism based on EDCA mechanism in LTE system while keeping Wi-Fi system unchanged,in which LTE system can adjust the contention window value of backoff mechanism adaptively.Furthermore,ALBT mechanism can be divided into two aspects,the backoff mechanism after one success transmission and the backoff mechanism after one data collision.For the backoff mechanism after one success transmission,ALBT mechanism can adjust the contention window value of backoff mechanism adaptively in LTE system by setting the success multiplier factor MFsu which synthetically considers different conflict rates and different priorities of data services.However,for the backoff mechanism after one data collision,ALBT mechanism can adjust the contention window value of backoff mechanism adaptively in LTE system by setting the collision multiplier factor MFco which takes into account different numbers of active terminals and different priorities of data services.The simulation results indicate that the ALBT mechanism can effectively reduce the conflict rate between LTE system and Wi-Fi system.Moreover,it can ensure the smooth transmission of low priority services,but also improve the throughput of high priority services.2.PLBT mechanism based on particle swarm optimization algorithm is developed in this thesis.According to the coexistence situation of LTE system and Wi-Fi system and the limitation of single-objective optimization,we construct a multi-objective optimization model to optimize the LTE system throughput and the Wi-Fi system throughput simultaneously.PLBT mechanism can realize the adaptive backoff process by calculating the optimal contention window value based on the particle swarm optimization algorithm.PLBT mechanism ultilizes the dynamic weighted aggregation function to transform the multi-objective optimization problem into a single-objective optimization problem,which reduces the complexity of the algorithm.The simulation results show that the PLBT mechanism can effectively improve the coexistence performance of LTE system and Wi-Fi system,and makes the LTE system and Wi-Fi system share the channel in the unlicensed frequency band with a fair and friendly manner.