Research On Wireless Backhaul Strategy And Resource Allocation In Ultra-dense Heterogeneous Networks

With the coming of the 5G era,there are not only massive applications and convenient lifestyles,but also a boost in traffic.Ultra-dense heterogeneous networks(UD-HetNets)intensively deploy small base stations(SBSs)in macro cells,shorten the distance between users and base stations(BSs).As the path loss and deep attenuation are reduced,the network capacity can be increased and UD-HetNets becomes an effective means to cope with massive traffic.However,the tremendous user data in the network still needs to be transmitted back to the core network,which puts great pressure on the backhaul.As a relatively new type of backhaul,wireless backhaul has the characteristics as economy,flexibility and convenient networking compared to wired backhaul.It is attracting more and more attentions.However,the wireless backhaul needs to occupy time-frequency resources to transmit data,which makes the already rare resources even scarcer.Since non-orthogonal multiple access(NOMA)technology has the characteristics of multiple connectivity and high resource efficiency,it can significantly improve the wireless backhaul performance of UD-HetNets.Hence,we focus on the wireless backhaul of UD-HetNets based on NOMA technology.Firstly,an overview of UD-HetNets is presented,where the evolution of UD-HetNets is reviewed.Then,three key technologies for UD-HetNets,which are wireless backhaul,resource allocation,and NOMA are introduced.At last,the main issues in UD-HetNets are presented.Secondly,in a two-layer heterogeneous networks(HetNets),a wireless backhaul scheme called the ONC wireless backhaul strategy,that automatically switches among three basic modes of orthogonal multiple access(OMA),NOMA and half-duplex cooperation NOMA(HD-CNOMA)is proposed.The purpose of the proposed strategy is to maximize the outage performance according to the variation of channel quality.Power allocation schemes with optimal outage performance in NOMA and cooperation non-orthogonal multiple access(CNOMA)modes are designed,respectively.Then,a closed form of the outage probability of the ONC strategy is derived.The simulation results show that the ONC strategy can obtain the best outage performance and increase the backhaul capacity,compared to wireless backhaul that only uses OMA,NOMA or CNOMA mode.Finally,based on the ONC wireless backhaul strategy,a resource allocation scheme for wireless backhaul in UD-HetNets is proposed,which is called the ONC-RA scheme.For the purpose of further improving the outage performance,the SBS clustering method based on the greedy algorithm is first proposed,and then a method of resources allocation to these clusters is proposed.We also deduced the order of resource allocation for optimal outage performance.Considering line-of-sight(LOS)and non-line-of-sight(NLOS)wireless communication scenarios,the Rice and Rayleigh fading channels are assumed,respectively.Under these channel modes,the ONC-RA scheme was simulated and verified,then compared with other schemes.The results show that the ONC-RA scheme has the best outage performance compared to the OMA,NOMA,full-duplex cooperation NOMA(FD-CNOMA)modes and the ONC wireless backhaul strategy based on average resource allocation.Moreover,it only sacrifices a little amount of backhaul capacity in exchange for a significant improvement in outage performance.