面向B5G的毫米波大规模MIMO低空无人机异构网信道模型及其回程应用

While the research on 5G networks is on its road, the idea of beyond 5G (B5G) ones has attracted the attention of researchers, which is the combination of 5G and low-altitude wireless communication networks. Therefore, to provide an effective solution for public-safety and emergency communication (PSEC), by using millimeter wave (mmW) and 5G techniques, this project proposes a novel B5G-origined and UAV-assisted wireless communication network (B5G-UAV-LAWC), and researches the following key problems. .1). Due to the employment of mmW and the complex radio environment in low altitude, in the considered B5G-UAV-LAWC systems the air-ground/ground-air (AG/GA) channels differ significantly from the traditional aeronautical communication ones as well as the terrestrial communication ones. Therefore, by first considering the case where the UAVs are equipped with single antenna, this project would focus on modeling the AG/GA channels of the line-of-sight (LoS) and no-line-of-sight (NLoS) transmission as well as their high-order statistics such as level cross rate (LCR) and average fading duration (AFD). Specially, the AG/GA channels would be investigated over the 28GHz, 38GHz, 60GHz, and 73GHz mmW bands. Then, with the obtained LoS and NLoS AG/GA channel models, an improved LoS communication model would be investigated by exploiting rich multipath components. An algorithm for adjusting the position of UAVs to maintain the LoS communication would be exploited, too. At the same time, with the autonomous capabilities of cognitive radio technique, this project would also consider an intelligent NLoS communication scheme using knife edge diffraction..2).In mmW, the radio signals are prone to severe propagation loss. Contrarily, due to the small wavelengths a large number of antennas can be packed in small space so that the huge beamforming can offset the frequency-dependent path loss. At the same time, because of the 3D property of UAVs’ aerial placement, the 3D mmW massive MIMO should be utilized in the B5G-UAV-LAWC systems. Therefore, the B5G-UAV-LAWC heterogeneous network would be further investigated by considering the fixed and distributed 3D massive MIMO antenna array, respectively. The fixed 3D massive MIMO considers the case where the massive MIMO base station (BS) is equipped on the same UAV, while the distributed 3D massive MIMO considers the case where the massive MIMO BS is formed by the large of antennas equipped on different UAVs. Then, using the results in 1), the project would investigate the AG/GA channel model over different mmW bands for the fixed and distributed 3D massive MIMO B5G-UAV-LAWC systems and investigate the high-order statistic of the obtained mmW 3D massive MIMO AG/GA channels. Finally, the project would focus on the channel hardening and favorable propagation of the novel mmW 3D massive MIMO AG/GA channels by modeling and establishing the respective measure models so that the hardening and favorable conditions would be derived. At the same time, by considering imperfect channel hardening and favorable propagation, the project would investigate the mathematical measure of network performance such as rate and resource allocation. .3). Considering the fact that multiple UAVs can be deployed in 3D aerial positions, the project would investigate effective LoS and NLoS wireless backhaul schemes by combining the mmW 3D massive MIMO, relay, and dual-connectivity. Besides this, the algorithms of establishing and adjusting optimal backhaul path would be investigated.

5G网络的研究正在如火如荼进行，兼容空间（低空）通信的超5G（B5G）技术同时也引起了研究人员的关注。项目提出基于毫米波三维大规模MIMO技术的面向B5G的无人机协助低空无线通信（B5G-UAV-LAWC）异构网络，拟研究以下问题：1）研究单天线配置的单UAV在毫米波不同频段上的空-地/地-空（AG/GA）视距和非视距信道模型及其高阶统计，提出利用多径分量建立视距传输和通过调整UAV位置保持视距通信的算法，提出利用认知无线电建立基于绕射信号的非视距传输；2）面向UAVs提出大规模MIMO固定和分布式配置模式，并就这两种模式在毫米波不同频段上研究3D大规模MIMO AG/GA信道，研究信道硬化和利好传输并建立各自的度量模型，在非理想信道条件下建立性能估计模型；3）研究UAVs与地面核心网回程，提出联合毫米波3D大规模MIMO与中继等技术的视距/非视距无线回程理论，探索最优中继回程路径算法。

为了解决目前公共安全应急通信系统与未来5G 网络及智能地面终端（GT）不相兼容问题，项目采用毫米波3D 大规模MIMO 等5G 关键技术，面向B5G 网络提出基于无人机协助的低空无线通信（B5G-UAV-LAWC）异构网络概念，为基于无人机协助的公共安全应急网络与5G 网络的融合提供理论基础和工程参考。.1、无人机协助的多用户MIMO毫米波网络混合预编码方案.针对无人机协助的毫米波网络下行链路多用户通信场景，在发射端使用混合预编码器，在接收端使用模拟合并器，设计了高可实现速率和能量效率的混合预编码方案。将预编码设计的多元联合优化问题分解为对子问题的优化求解。仿真表明，所提出的方案可有效减少用户间干扰，实现较高的频谱效率和能量效率。.2、基于空间Poisson点过程的无人机异构网络中断性能评估.考虑无人机空间分布特性给城市热点区域网络部署与设计带来的挑战，基于随机几何理论构建了空间无人机异构网络框架。首先，通过三维部署空中小基站和二维部署地面宏基站的方式对网络进行混合干扰建模，借助最大偏置接收功率级联准则来实现各基站的负载均衡；此外，考虑无人机通信特性，将空对地信道假设为Nakagami-m衰落模型；最后通过用户与各基站的级联概率以及通信距离的分布得出网络中断概率的数学解析表达式。.3、基于研究成果，在无人机毫米波网络中，提出一种位置信息辅助的基站与无人机间毫米波信道估计方法，实现了较高的天线增益并显著地减少了信道估计所用的时间。分析了CSI完善的情况下多小区UAV mm-Wave通信系统的吞吐量的渐近表达，并通过穷举搜索获得使吞吐量表达式最大化的最优天线阵列倾斜角，所提出的倾斜角优化方法可以有效提高系统的吞吐量。基于3-D PPP和2-D PPP构建了一个无人机辅助的混合异构网络模型，相较于传统无人机异构网络模型，该混合模型可以更好的描述真实场景，并且适当的提高路径损耗可以提升网络性能。基于3-D PPP构建了一个动态UAV网络模型，设计的三维动态无人机网络模型更接近实际场景，此外基于最近邻策略切换基站可以有效提高网络性能。

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