Research And Performance Evaluation Of Key Technologies For Ultra-dense Networks

In order to meet the growing traffic demand,ultra-dense network(UDN)is regarded as a crucial part of the future network by densely deploying various kinds of small cells to boost the network capacity.Considering the complex and dense deployment of UDN,how to utilize the limited wireless resources to increase the network capacity,satisfy the various and unbalanced traffic de-mands,and improve the user experiences at lower cost is a big challenge for UDN.To solve the above challenge,it is in dire need to investigate and optimize the key technologies that limit the UDN performance.This thesis extensively investigates the basic knowledge and existing re-search work of UDN,based on which,we conduct further researches and per-formance evaluations on the key technologies including green communication,interference management and mobility management under UDN scenario.The main contributions of this thesis are summarized as follows:1)In the research of the energy-consumption aware green communication technology for UDN,we propose an energy-consumption aware user associ-ation and cell sleeping strategy which aims to find the energy-efficient user association and cell sleeping solution with the users' minimum rate require-ments constraints.We formulate the minimum energy consumption optimiza-tion problem as a complex combination optimization problem based on the average channel state information.To tackle this problem,we propose an alter-nating method by decomposing the problem into two simple sub-problems:the energy-efficient user association sub-problem with fixed cell working condition and the energy-efficient cell sleeping sub-problem with fixed user association.The proposed strategy obtains a local optimal solution by iteratively solving the above two sub-problems.The simulation results show that the proposed strategy can achieve a more steady and outstanding energy-saving performance compared to the existing strategies.2)In the research of user satisfaction aware fair interference managemen-t technology for UDN,we propose a user satisfaction aware fair sub-channel assignment strategy which aims to find the optimal sub-channel assignment so-lution to improve the users' quality of service(QoS)satisfaction performances.We formulate the optimization problem as a max-min fairness problem with respect to the user's satisfaction degree and decompose the problem into t-wo simple sub-problems:the QoS-based user clustering sub-problem and the weighted multi-cluster sub-channel assignment sub-problem.By doing this,the problem can be transferred from the complicated sub-channel assignment problem between a large number of users to the weighted sub-channel assign-ment between a small number of user clusters.The simulation results show that the proposed strategy can flexibly adapt to the variations in the number of sub-channels,the number of users and interference levels,and achieve con-siderable promotion in the minimum user satisfaction degree,throughput and fairness performances.3)In the research of predictive mobility management technology for UD-N,we propose a universal predictive mobility management strategy for urban UDN with control/data plane separation.Considering the regularity of user's movement in urban UDN,the user always accesses into the small cells in a certain order.Thus,we can utilize the transition relationships between small cells and pre-configure the small cells with larger handover probabilities for the users to speed up the date plane handover process.The propose strategy adopts the probability suffix tree(PST)model to learn and analyze the transi-tion relationships between small cells and proposes a hybrid PST-based predic-tion algorithm to guide the predictive mobility management.To accommodate different versions of the users,we further propose two modified mobility man-agement procedures.Simulation results show that the proposed strategy can significantly improve the prediction accuracy and effectively speed up the data plane handover process at a lower cost of redundant small cell configurations.In the end of this thesis,we summarize the overall contributions and fur-ther outline the future research directions of UDN.