【摘要】 随着毫米波无线通信技术日趋成熟以及2019年世界无线电大会(WRC-19)正式将24.25–27.5、37–43.5、66–71 GHz等频段分配给国际移动通信系统,预计毫米波通信系统近期将陆续在世界范围内大规模商用部署。毫米波存在路径损耗大、难穿透等不利的传播特性,其覆盖范围受到很大限制。城市密集城区将是未来毫米波系统商用部署并发挥其大容量优势的主要应用场景。本文基于信道实测数据探明了在典型的密集城区场景和毫米波频段下信道多径分簇特性,为未来毫米波系统传输设计和覆盖优化提供了研究基础和实验依据。毫米波信道测量系统利用高性能矢量信号源和矢量信号分析仪搭建了射频前端可重构的双定向信道测量系统。在发送端使用宽波束喇叭天线实现扇区覆盖,其位置与现网4G基站的部署位置一致;在接收端通过连续旋转高增益喇叭天线获取接收信号的角度信息。该系统可灵活支持多频段多场景信道测量,实现空-时-频多维信道特性获取。我们在两种典型密集城区环境以及28和39 GHz两个典型5G毫米波确认频段开展了大量信道实测,构建了信道实测数据库。考虑毫米波信道存在稀疏特性,提出改进的两步KPower Means多径分簇算法,在提升分簇准确性的同时有效减少了算法迭代次数。基于实测和分簇结果,可进一步分析环境因素对信道特性的影响,并建立在城市密集城区视距(Lo S)和非视距(NLo S)场景下完备的多径簇统计信道模型。信道分簇统计建模结果表明:在密集城区场景通常存在5–8个多径散射簇,具体的簇数目与环境密切相关,多径主要由建筑物外表面的一次和二次反射及屋顶和侧边绕射引起;由于存在丰富的多径,在适当的系统配置下通过架高发射天线,毫米波系统在NLo S场景下的覆盖范围可达到200米以上;相比于全向信道而言,簇内时延和水平角度扩展远小于全向信道的结果,并且随着工作频率升高,两者均呈现减小趋势;当接收机或用户在同一水平维度时,全向和簇内接收俯仰角度扩展近似,并且随频率变化不明显;对于不同信道统计参数间的相关性进行了分析,本文统计结果表明簇内时延和三维角度扩展间的相关性较弱。综上,基于大量的信道实测数据及信道分簇结果,揭示了环境散射体与多径散射簇的映射关系,文中给出反射和绕射等传播机制对信道参数的影响,并在典型频段构建了适用于城市密集城区场景的三维信道统计模型,建模结果有效弥补了3GPP、ITU等模型因数据缺失所存在的不足。最后,结合测量和建模结果,为毫米波无线通信的物理层设计提供了参考。更多还原

【Abstract】 The deployment of millimeter-wave(mmWave) cellular systems in dense urban environments with an acceptable coverage and cost-efficient transmission scheme is essential for the rollout of fifth-generation and beyond technology. In this paper, cluster-based analysis of mmWave channel characteristics in two typical dense urban environments is performed. First, radio propagation measurement campaigns are conducted in two identified mmWave bands of 28 and 39 GHz in a central business district and a dense residential area. The customdesigned channel sounder supports high-efficiency directional scanning sounding, which helps collect sufficient data for statistical channel modeling. Next, using an improved auto-clustering algorithm, multipath clusters and their scattering sources are identified. An appropriate measure for inter-and intra-cluster characteristics is provided,which includes the cluster number, the Ricean K-factor, root-mean-squared(RMS) delay spread, RMS angular spread, and their correlations. Comparisons of these parameters across two mmWave bands for both line-of-sight(LoS) and non-light-of-sight(NLoS) links are given. To shed light on the blockage effects, detailed analysis of the propagation mechanisms corresponding to each NLoS cluster is provided, including reflection from exterior walls and diffraction over building corners and rooftops. Finally, the results show that the cluster-based analysis takes full advantage of mmWave beamspace channel characteristics and has further implications for the design and deployment of mmWave wireless networks.更多还原