Cross-Polarized Three-Dimensional Channel Measurement and Modeling for Small-Cell Street Canyon Scenario

In emerging heterogeneous networks, small-cell base stations deployed along urban streets can increase the network capacity for vehicular access significantly. To fully exploit the potential of full-dimensional multiple-input-multiple-output technologies, it is critical to understand the propagation characteristics of the small-cell vehicle-to-infrastructure (V2I) access channels. In this paper, a measurement campaign for the three-dimensional propagation with ±45° polarizations was conducted at 2.6 GHz in a typical urban street canyon environment. We utilized a sounder with two cross-polarized uniformed planar arrays. The transmitter was placed on the rooftop of a five-storey building and the receiver was placed at the 15th position along a street with the line of sight (LOS). The elevation/azimuth of arrival (EoA/AoA), power spectrum, and root-mean-square angular spread of arrival (ESA/ASA) of the multipath components were measured. We propose a dual-Laplace probability density function (PDF) model for the EoA distributions that have LOS clusters and ground reflections. We propose two models, the flat-bottom Laplace PDF and the superposed Laplace PDF, to describe the clustering behavior of the AoA distributions. We also propose the Lognormal models for the ESA and ASA distributions. Furthermore, it is found that polarization does not affect the EoA and AoA distributions, but has a significant impact on the ASA and ESA. The measurement results and channel models can help with the design and evaluation of the spatial transmission/multiplexing technologies in the small-cell V2I access.

I. Introduction

To SUPPORT the dramatically increasing multimedia and data traffic from vehicles, small cells in the emerging heterogeneous networks can significantly expand the capacity of vehicle-to-infrastructure (V2I) access in urban areas. Meanwhile, by employing planar antenna arrays on base stations (BSs), the full-dimensional multiple-input-multiple-output (FD-MIMO) can achieve a high-order spatial multiplexing gain by beamforming in both the azimuth and elevation domains [1]. The performance of beamforming in terms of link throughput and interference are determined by both the active antenna arrays and signal spatial propagation in radio channels. Therefore, sufficient knowledge and accurate models on the three-dimensional (3D) radio propagation characteristics are critical for the simulation and evaluation of FD-MIMO in the small-cell V2I scenario.