Spatial Bandwidth of Bilateral Near-Field Channels for Linear Large-Scale Antenna Array System
Zhen Wang, Yijin Pan, Jun-Bo Wang, Yijian Chen, Hongkang Yu
TL;DR
This work derives a closed-form, geometry-aware expression for the local spatial bandwidth of line-of-sight bilateral near-field channels between 3D linear large-scale antenna arrays, capturing how orientation and placement affect spatial bandwidth and EDoF. It introduces a practical K-number proxy, K2, proportional to the local bandwidth and array length, and shows that the maximum local bandwidth and EDoF are achieved when the transmit and receive arrays are coplanar with the receive array perpendicular to the centroids line. The maximum local bandwidth scales with the transmit-span angle via ωmax = 2k0 sin(α/2), and the peak K-number scales with Lp and α as K2^max = (k0 Lp/π) sin(α/2). The results provide actionable geometric design rules for achieving high spatial multiplexing in near-field LoS MIMO systems, highlighting the importance of array size and placement over raw antenna count.
Abstract
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.