Research On Decoupled Uplink And Downlink Association Scheme For 5G Heterogeneous Networks

Heterogeneous networks(HetNets),one of the key technologies of 5G networks,alleviate the surge of data business in hot spot regions while increasing the system capacity.However,with an explosion of uplink data traffic,HetNets is confronted with new challenges,among which user association is the primary issue to be solved.Therefore,decoupled UL and DL association(DUDA)scheme of 5G HetNets is discussed in the thesis,to effectively improve the transmission rate.The main research contents are as follows:Firstly,this thesis studies the cross layer DC-DUDA scheme for three-layer HetNets.DL or UL of user equipment is associated with the primary BS(P-BS)and the secondary BS(S-BS)at different tiers at the same time,but DL and UL access to different base stations.By combining DUDA technology,DL adopts the traditional maximum average received signal power(RSP)access policy,and UL accesses to the nearest base station via the minimum path loss association.Association probability and coverage probability of networks are obtained by stochastic geometry method,and the study shows that the coverage probability of networks is improved by the combination between DUDA and cross-tier DC.Secondly,the dual connectivity(DC)and Duda technologies are combined to analyze the two-tier HetNets.Dual-connectivity is used to allow UL or DL of users to associate two base stations,thus achieving the spectrum aggregation.This technology could not only unload traffic from the macro cell(MCell),but also improve the network throughput by separating the control plane and the user plane.On the other hand,DUDA technology is used to enable uplink(UL)and downlink(DL)to access to the base stations in different association ways.The study shows that the scheme may better solve the unbalanced load of UL and DL compared with the traditional coupled association.Finally,non-orthogonal multiple access(NOMA)is applied in DC-DUDA scheme regarding the limited frequency spectrum in HetNets to overcome the orthogonal channel constraint in the dual access technology.The total bandwidth is shared by the P-BS and S-BS links to obtain higher spectral efficiency.Besides,successive interference cancellation(SIC)is applied to eliminate the interference in NOMA.Simultaneously,orthogonal multiple access(OMA)is studied for a comparative analysis.The study shows that the average DUDA coverage probability is superior to the average coverage probability of coupled association.In addition,the spectrum effectiveness of P-BS in NOMA is superior to the P-BS in OMA.It is found that the transmission rate is higher and the spectral efficiency is higher.