| With the rapid proliferation of smart devices and various advanced multimedia applications,consumers’demands of future wireless cellular communications,including the transmission rate,latency,and reliability,have increased significantly.The International Mobile Telecommunications Union-Radio Communications Sector(ITU-R)has established a peak rate requirement of 10 Gbit/s for the 5th generation(5G)communication.In order to meet this requirement,there is an increas-ing hope that the millimeter-wave band will be used for 5G communication systems.Compared to current communication systems operating on microwave bands,millimeter-wave bands offer vast spectrum resources and thus can meet future demands for ultra-high transmission rates.Despite its huge potentials and advantages,millimeter-wave cellular communications still face a number of key technique challenges,mainly including:(1)The networking for millimeter-wave cellular net-works.(2)User association and resource allocation for multi-band millimeter-wave heterogeneous networks.(3)User association for millimeter-wave networks with multi-connectivity.(4)Coexis-tence between millimeter-wave ultra reliable low latency communications(URLLC)and enhanced mobile broadband(eMBB).(5)Coexistence between millimeter-wave mobile broadband reliable low latency communications(BRULLC)and eMBB.This thesis conducts in-depth research on the above issues,aiming at establishing a comprehensive,top-down system for the resource manage-ment of mmWave communication networks.First,we introduce a novel hierarchical software-defined networking(SDN)architecture to facilitate the deployment of ultra-dense networks(UDNs)with both microwave base stations and millimeter-wave base stations.Aimed at reducing the cost of computational complexity and sig-naling overhead,the novel SDN architecture employs a semi-distributed design approach.Based on it,we propose three important technologies for the hierarchical SDN,including dynamic sub-ordinate SDN management,mobility management,and user-centric design,to further improve the performance of the UDNs.Simulation results show that the developed network architecture ex-hibits advantages in terms of computational complexity,load balancing,and power consumption compared to traditional network architectures.Secondly,considering different transmission characteristics of different millimeter-wave fre-quencies,we investigate the joint user association and resource allocation in multi-band millimeter-wave heterogeneous networks.According to whether a user can transmit on multiple millimeter-wave bands simultaneously,two different access schemes are considered:the single-band access scheme and the multi-band access scheme.For the single-band access scheme,we first derive the closed-form expression for the optimal time fraction allocation and then develop an iterative algorithm for joint user association and power allocation.For the multi-band access scheme,we develop a near-optimal solution based on the Markov approximation framework.Our analytical results reveal that different users can only access at most one band simultaneously although the multi-band access scheme allows a user to transmit on multiple bands.Finally,numerical results demonstrate that the multi-band access scheme performs better than the single-band access scheme,especially in the light load scenario.Thirdly,we develop a machine learning based user association algorithm for millimeter-wave communication networks with multi-connectivity,which does not require the channel informa-tion state(CSI).Specifically,we first formulate the millimeter-wave user association problem as a multi-label classification problem,which is then transformed into a series of single-label classifica-tion problems through efficient multi-label classification algorithms.To further reduce the amount of training samples,we utilize graphical model to represent the user association scenario and adopt novel feature extraction methods to obtain appropriate features from both geographical location information and topological information.Test results show that the proposed approach can achieve a good performance with only a few training samples and without the need of CSI.Fourthly,we develop a novel coexistence scheme for the millimeter-wave URLLC and eMBB,where URLLC users can reuse the spectrum resources of eMBB users to improve the spectrum efficiency of the coexistence system.Using the queueing theory and matrix geometry theory,we analyze the delay and reliability of millimeter-wave URLLC users while considering the multi-connectivity and the effects of blockages.Based on this,a resource management algorithm is developed to maximize the throughput of eMBB users while ensuring the QoS requirements of URLLC users.Simulation results show that compared to the conventional orthogonal coexistence scheme,the proposed scheme can effectively improve the throughput of eMBB users.Finally,we introduce a new type of service in the 6th generation(6G)communications,M-BRLLC,and utilize millimeter-wave communications to fulfill its requirements in terms of trans-mission rate,reliability,and latency.We develop a novel coexistence scheme for millimeter-wave MBRLLC and eMBB,where MBRLLC and eMBB users are scheduled during the same time s-cale.Based on this,a resource management problem is formulated to maximize the throughput of eMBB users while satisfying the QoS requirements of MBRLLC users.To solve it,we divide it into two subproblems,namely,MBRLLC user association problem and eMBB user association problem.For the former one,a design criterion for the multi-connectivity policy is first derived,by which a matching theory based user association algorithm is developed for MBRLLC users.For the latter one,the optimal solution is achieved by the improved Hungarian algorithm.Simulation results show that the proposed scheme can improve the throughput of eMBB users while increasing the number of MBRLLC users satisfying the QoS requirements.The research results in this thesis can provide a theoretical basis for investigating more com-plex millimeter-wave communication systems,as well as theoretical support and effective techni-cal solutions for the practical deployment and commercialisation of future millimeter-wave cellular communication systems. |
