| As one of the key technologies of the 5th generation(5G)mobile communication,ultra-dense network(UDN)technology shortens the distance between access points and user equipment(UE)by deploying a large number of low-power nodes.Compared with the traditional macro base station deployment,ultra-dense network can not only enhance system throughput,improve the spectrum efficiency(SE)and energy efficiency(EE)of the local base station,but also provide a cell splitting gain for the network and solve the problem of coverage holes of the network,and users can access network anytime and anywhere.However,the increasing density of access points and the unplanned deployment of multiple types of access points in the ultra-dense network make the interference environment more complex,which hinders the development of resource management technologies in ultra-dense network.As the network architecture is moving toward the heterogeneous architecture,the cross-tier cooperation technology between tiers in the physical layer of heterogeneous ultra-network can not only reduce cross-tier interference,but also improve the throughput of the entire network through cross-tier cooperation.Based on the cross-tier cooperation technology in the physical layer of the heterogeneous network,this thesis studies the cross-tier cooperation resource allocation scheme for downlink transmission in the ultra-dense network.The innovations of this thesis are as follows:First,we propose a cross-tier cooperation resource allocation(CCRA)scheme over the heterogeneous ultra-dense network without quality of service(QoS)constraint to improve the whole system throughput.We first define the cooperation signal-to-interference-plus-noise ratio(SINR)threshold to classify the types of UEs,and the influence of the cooperation SINR threshold on the numbers of several types of UEs is analyzed by using stochastic geometry technology.We model this system throughput optimization problem as a non-convex resource allocation optimization problem and use dedicated channel technique to reduce cross-tier interference.At the same time,in order to reduce the computational complexity,we decompose this resource allocation problem into subcarrier allocation and power allocation,and we propose two algorithms to solve it.The simulation results show that using the proposed CCRA scheme in a dense environment can increase system throughput while ensuring lower cooperation costs.Second,we propose a QoS-based cross-tier cooperation resource allocation(QCCRA)transmission scheme over the ultra-dense network in case of QoS constraint.In order to mitigate the interference and improve the entire network throughput,a non-convex resource optimization problem is formulated.Specifically,the resource allocation process is decoupled into two parts,i.e.the subcarrier allocation and power allocation,and three algorithms are proposed to solve it.In the simulation results,we analyze the influence of the cooperation SINR threshold on the system throughput under different scenes of changing parameter,and provide a theoretical reference for how to set the cooperation SINR threshold value in the varying parameter scenes.And the performance of the proposed QCCRA scheme is compared with non-cooperation(NC)and full cooperation(FC)schemes.The simulation results show that the proposed QCCRA scheme can improve the system throughput under the premise of ensuring the minimum QoS requirement of each UE and obtain the advantages of the NC and FC schemes simultaneously.This thesis studies the resource management techniques under the ultra-dense network,and proposes two cross-tier cooperation resource allocation schemes without QoS constraint and with QoS constraint respectively,which solves the problem of system throughput loss caused by severe cross-tier and co-tier interference in our heterogeneous ultra-dense network model,and provides a theoretical reference for how to set the cooperation SINR threshold value in the varying parameter scenes. |
