超密集异构无线网络中负载均衡方案研究及能效优化

Ultra-dense heterogeneous networks (UDHNs) can alleviate the traffic congestion and enhance the network coverage by deploying ultra-dense small cells (Base Stations, BSs), which are the mainstream of change and development in future wireless networks. However, there exist the unbalanced load distribution caused by disparate BSs and the high energy consumption caused by the deployment of ultra-dense small cells in general UDHNs with a splitting function. In such networks, the macro BSs perform the control signaling and data transmission, but small BSs just be responsible for the data transmission. To deal with the aforementioned problems, this project will work on the study of offloading (load balancing) mechanisms and energy efficiency optimization, i.e., the one of energy-efficient offloading mechanisms for UDHNs. The detailed research content of this project includes the following two points: (1) under some aspects of energy-saving measures including resource partitioning, BS operation (Cell Sleeping), power control, etc., this project will focus on the design of purely energy-efficient and compromising offloading mechanisms for UDHNs, and thus achieve a goal of reducing the energy consumption and CO2 emission, cutting the network cost and enhancing the system performance; (2) this project will also carry out the performance analyses of energy-efficient offloading mechanisms according to the stochastic geometry (SG) theorem, investigate the impacts of BS density and function-splitting factor on the performance, and finally provide some guidance for the optimal network configuration. In these two aspects, the former concentrates on the design of offloading mechanisms, but the latter is concerned about performance analyses. In fact, they are interrelated and complementary components in the research.

超密集无线异构网络（UDHN）通过在热点区域部署大规模小基站以减轻网络拥挤及加强网络覆盖，是未来无线网络变革与发展的主流。但是，具备功能模块划分的UDHN广义架构（宏基站同时担任数据与控制业务，但小基站只负责数据业务）却存在因异构基站部署所带来的负载不平衡问题与超密集小基站部署所引入的高能耗问题。为处理这些问题，本课题拟开展负载均衡方案研究及能效优化工作，即能效型负载均衡方案研究：（1）课题将结合资源划分、小区睡眠与功率控制等节能措施，开展UDHN中能效型（包括纯能效型与折衷型）负载均衡方案研究，以达到节能减排、削减网络运营成本及强化系统性能的目标；（2）利用随机几何（SG）等手段实施能效型负载均衡方案的性能分析工作，调研小区密度与功能划分因子等关键网络参数在方案中的作用，最终为网络最优部署提供指导。在上述两大研究内容中，前者注重方案设计，后者倾向于性能分析，它们相互联系、互为一体。

针对超密集异构无线网络及它的特例（称为分层异构网络、异构网络或异构蜂窝网络）中负载失衡及高能耗问题，本课题开展了负载均衡方案研究及能效优化工作。具体研究内容如下：.（1）课题结合资源划分与功率控制等节能措施，开展了能效型（包括纯能效型与折衷型）负载均衡方案的研究。在开展过程中，课题进一步融入非正交多址接入（NOMA）、大规模多进多出（MIMO）、移动边缘计算（MEC）、码分多址接入（CMDA）与群簇等技术以达到降低干扰、增加用户接入及强化系统性能的目的。待融入上述技术后，课题结合时频资源划分、功率控制、功率分配、计算与频谱资源管理等手段，设计了最大化整体能效、和能效、频谱效益、加权频谱效益与能效、加权容量与功耗等优化目标的系列负载均衡方案。鉴于不同的方案中所涉及的优化问题形式各样，开发了基于对偶分解、定点迭代、联盟博弈、分数优化与智能集群等方法的诸多有效的卸载算法。显然，这些方案的定制不仅能为超密集异构无线网络及它的特例（称为分层异构网络、异构网络或异构蜂窝网络）中纯能效型与折衷型负载均衡方案的研发提供理论支撑与技术指导，而且还能实现节能减排、削减网络运营成本及强化系统性能的目标。.（2）针对所设计的负载均衡方案，课题也开展了相关的性能分析工作，利用仿真手段深入分析了用户密度（数）、小基站密度、发射功率与时频资源划分因子等重要网络参量对方案性能的影响，揭示了其在方案中的作用。此外，针对融入中继与车联网的系统，课题利用随机几何等方法分析了路径损耗指数、基站部署与功率分配率等关键网络参量对中断概率、连接概率及频谱效益的影响。通过这些数据仿真分析，既能直接地验证方案的可行性及有效性，又能为现实中的网络最优部署提供参考与指导。