Near-Field Measurement System for the Upper Mid-Band

TL;DR

This paper introduces a low-cost near-field measurement system for the 6-24 GHz band, utilizing a novel reflection model and triangulation to accurately estimate MIMO channel parameters with minimal antennas.

Contribution

It proposes a new method for near-field parameter measurement using image point triangulation, enabling efficient MIMO channel analysis in the upper mid-band.

Findings

Accurate estimation of near-field paths using triangulation.

Effective measurement with only 2 transmit and 2 receive antennas.

Demonstrated feasibility with a prototype system.

Abstract

The upper mid-band (or FR3, spanning 6-24 GHz) is a crucial frequency range for next-generation mobile networks, offering a favorable balance between coverage and spectrum efficiency. From another perspective, the systems operating in the near-field in both indoor environment and outdoor environments can support line-of-sight multiple input multiple output (MIMO) communications and be beneficial from the FR3 bands. In this paper, a novel method is proposed to measure the near-field parameters leveraging a recently developed reflection model where the near-field paths can be described by their image points. We show that these image points can be accurately estimated via triangulation from multiple measurements with a small number of antennas in each measurement, thus affording a low-cost procedure for near-field multi-path parameter extraction. A preliminary experimental apparatus is presented comprising 2 transmit and 2 receive antennas mounted on a linear track to measure the 2x2 MIMO channel at various displacements. The system uses a recently-developed wideband radio frequency (RF) transceiver board with fast frequency switching, an FPGA for fast baseband processing, and a new parameter extraction method to recover paths and spherical characteristics from the multiple 2x2 measurements.