Research On Unlicensed Spectrum Access For 5G

With the rapid development of the mobile Internet,the data traffic of mobile communication networks has surged.However,the licensed spectrum resources below 6GHz are very scarce,which cannot continuously meet the demand for mobile data traffic.The Fourth Generation mobile communication system(4G)introduces Licensed Assisted Access(LAA)to offload the data traffic of the licensed spectrum to the unlicensed spectrum to increase network capacity.In order to further expand the spectrum,the Fifth Generation mobile communication system New Radio(5G NR)system began to pay attention to the unlicensed high frequency bands of 5GHz,6GHz and 60GHz millimeter wave(mmWave)Access.This thesis mainly studies the problems of NR in Unlicensed spectrum(NR-U)system in channel access:(1)The congestion of different nodes of the same RAT when accessing the NR-U channel results in a decrease in frequency utilization;(2)When NR-U adjusts CWS,the channel access delay is longer;(3)When the mmWave high frequency band is used in the unlicensed spectrum,the network coverage capability is lower,and the user access capability decreases.In response to the above problems,this thesis studies the unlicensed spectrum access technology for 5G,and the main research work and innovation points are summarized as follows:Aiming at the problem of low frequency utilization caused by the congestion of the same RAT nodes during NR-U channel access,an NR-U access technology based on Listen Before Talk(LBT)coordination is proposed.This scheme designs two coordination methods for network nodes of the same RAT,namely:dynamic coordination mode-Xn interface transmission and semi-static coordination mode-zero power CSI-RS transmission.Then,the Markov chain modeling analysis is performed on the NR-U channel access based on LBT coordination to deduce the system throughput and delay of LBT coordination access.Finally,through simulation analysis,it is concluded that through LBT coordination,the throughput of the entire coexistence system is significantly improved,and at the same time,selecting the appropriate number of LBT coordination effectively reduces the average delay of data transmission in the NR-U.Aiming at the high latency of NR-U during CWS adjustment,this thesis proposes a NR-U access scheme based on CWS adjustment of non-reference time slots.This scheme introduces and defines the non-reference time slot,and combines the feedback of the reference time slot and the feedback of the non-reference time slot,the CWS adjustment control is performed on four different data situations.Then,the transmission delay of the CWS adjustment technology based on the non-reference time slot is modeled and analyzed,and results that by introducing non-reference time slots for HARQ feedback,the transmission delay of the NR-U access delay of CWS adjustment based on non-reference time slots is 15.79%lower than that of the transmission delay under the traditional CWS adjustment scheme.Aiming at the problem of lower network coverage during unlicensed access in millimeter wave high-frequency bands,a licensed-assisted access technology based on k-means relay selection is proposed.In order to increase the coverage rate and transmission capacity of the network,a relay selection based on k-means is introduced,and the k-means algorithm is optimized in the way of actual communication nodes and range restrictions,and the unsupervised classification k-means algorithm is conditionally restricted.Simulation analysis shows that by jointly optimizing the transmission power of the 60GHz unlicensed node and the licensed relay node,the network coverage is extended to more than 87%.