This paper analyzes the spatial bandwidth of line-of-sight (LoS) channels in massive MIMO systems. For the linear large-scale antenna arrays (LSAA) of transceivers placed in random locations in 3D space, a simple but accurate closed-form expression is derived to characterize the spatial bandwidth. Subsequent analysis of the LSAA's spatial bandwidth properties is also provided, leading to the formulation of an approximate expression for the effective degrees of freedom (EDoF) of bilateral near-field channels. Interestingly, as proved in this work, when the transmit and receive arrays are coplanar, with the receive array positioned perpendicular to the axis joining the centroids of the transmit and receive arrays, the EDoF of the LoS channel is found to be approximately maximized.

翻译：本文分析了大规模MIMO系统中视距信道的空间带宽。针对收发端在三维空间中随机放置的线性大规模天线阵列，推导了一个简洁而精确的闭式表达式来表征其空间带宽。进一步分析了大规模天线阵列的空间带宽特性，并由此导出了双边近场信道有效自由度的近似表达式。有趣的是，本文证明当收发阵列共面且接收阵列垂直于收发阵列质心连线时，视距信道的有效自由度近似达到最大化。