Research On Key Technologies For Unlicensed Band Access

With the rapid development of mobile communication technology,the data traffic service has gradually become the main service of the fourth generation mobile communication LTE(Long Term Evolution)system,and the scarce licensed spectrum is insufficient to support such a large-scale data traffic service.Therefore,LTE proposes that Licensed-Assisted Access(LAA)technology offloads the traffic of the licensed band to the unlicensed band to alleviate the load pressure of the licensed band.lIn the fifth generation of mobile communication NR(New Radio)system,the unlicensed band technology will continue to be enhanced in order to provide a more efficient working mode and better service.This paper mainly considers the application scenarios of unlicensed bands,aiming to improve the efficiency of the use of unlicensed bands and provide lricher and better communication services.At present,the networking based on unlicensed fr-equency bands has the following key problems:LAA technology cannot guarantee delay performance when channel competition is fierce,and work efficiency needs to be improved;BWP(Bandwidth Part)technology in NR works with low efficiency when operating in unlicensed fr-equency bands.At the same time,the HARQ(Hybrid Automatic Repeat reQuest)feedback delay is large when the channel competition under the unlicensed band wideband carrier is fierce.In response to the above key issues,the main innovations of this paper are as follows:Aiming at the problem that LAA can not provide delay guarantee and low access probability when the channel competition is fierce,this paper designs a dynamic channel backoff mechanism based orn multi-channel,and reduces the average delay of channel access through dynamic channel backoff.In this paper,the Markov model is used to model tlhis mechanism,and the throughput performance and the average delay of the system are calculated.The simulation results show that the dynamic multi-channel backoff mechanism can significantly reduce the average delay of the LAA system on the basis of ensuring the fair coexistence of LAA and Wi-Fi.Aiming at the low efficiency and high latency of BWP technology iin NR unlicensed frequency band,this paper designs a timer-based BWP sxwitching technology.On the basis of keeping the default timer indicating normal operation,a new timer is introduced to indicate the channel condition,so that the user can actively switch to the BWP with better condition to continue data transmission when the channel condition is poor.Simulation results show that this mechanism can effectively reduce the average latency of the device when using BWP technology.Aiming at the large latency delay of uplink HARQ transmission under unlicensed wideband carrier in NR,this paper designs a mechanism for effective and timely feedback of HARQ data under unlicensed wideband carrier in NR.In the NR,the unlicensed wideband carrier need to implement LBT(Listen Before Talk)in multiple sub-bandwidths,considering the complexity of the device side and the base station side,designs a HARQ data transmission method for the wideband carrier.The simulation results show that the proposed method can significantly reduce the HARQ transmission delay under the wideband carrier when the channel conditions are poor.