6G超大规模天线信道波束域传播特性分析

为了探明6G超大规模天线信道在波束域的信道传播特性，重点开展了无线信道测量实验与测量数据分析.首先，在典型城市场景下，开展了sub-6 GHz频段配置超大规模均匀线阵的视距(light-of-sight, LoS)和非视距(non-LoS, NLoS)信道测量实验；其次，划分若干子阵列，并分别使用高分辨率参数提取算法估计多径幅度、时延和角度；然后，根据不同的子阵列角度分辨率构建虚拟波束，将对应不同虚拟波束角度的多径进行分组及叠加.通过比较不同子阵列在相同角度对应的虚拟波束系数，发现传统天线域的空间非平稳特性在波束域表现不明显.通过分析不同虚拟波束的信道系数，可观察到波束域稀疏特性，并且LoS场景的稀疏特性更加明显.针对不同场景下各虚拟波束的多径数目、功率和均方根时延扩展进行拟合分析，可知分别服从高斯分布、高斯分布、均匀分布.此外，分析发现LoS场景下虚拟波束间相关性较低，而NLoS场景下虚拟波束间相关性随波束分辨率提高而增大.

Beam domain propagation characteristics analysis of 6G ultra-massive MIMO channels

In order to fully explore the beam domain channel propagation characteristics, channel measurements and data analyses are conducted for the sixth-generation (6G) ultra-massive multiple-input multiple-output (MIMO) wireless channel. First, the line-of-sight(LoS) and non-LoS(NLoS) channel measurements in an urban scenario are conducted at sub-6 GHz frequency band with ultra-massive uniform linear array (ULA). Second, the ultra-massive ULA is divided into several sub-arrays. Multipath parameters including amplitude, delay, and angle of arrival, are estimated using the high-resolution algorithm. Then, virtual beams are constructed according to the angular resolution of sub-array. Multipaths that belong to different beam angles are grouped and added up. The channel coefficients of different sub-arrays in the same beam direction are compared to show that the non-stationary characteristics in antenna domain are less obvious in beam domain. By analyzing channel coefficients of different beams, obvious sparsity can be observed. The sparsity is more obvious in LoS scenario than that in NLoS scenario. Multipath numbers, powers, and root mean square delay spread (DS) of different virtual beams are also computed and fitted with Gaussian, Gaussian, and uniform distributions respectively. In addition, it is found that the cross-correlation coefficients of different virtual beams in LoS scenario are lower than those in NLoS scenario. The virtual beam resolution has great impact on the cross-correlation coefficients of different virtual beams in NLoS scenario.