Near-field Beam-focusing Pattern under Discrete Phase Shifters

2024-09-23

AI Summary

To address the high cost and power consumption associated with high-resolution phase shifters in extra-large-scale array (XL-Array) near-field communications, this paper investigates the impact of low-resolution discrete phase shifters on beam focusing performance. We theoretically reveal, for the first time, that phase quantization induces two distinct types of grating lobes—focusing-type and scanning-type—and provide a physical interpretation from a subarray perspective. A Fourier-series-based near-field radiation modeling framework is proposed to accurately characterize the near-field electromagnetic behavior under quantized phase control. Results demonstrate that merely 3-bit phase shifters achieve near-continuous-phase performance: the resulting communication rate loss is negligible, while energy efficiency is significantly improved. Furthermore, we quantitatively establish a mapping between grating lobe intensity and communication rate degradation, enabling systematic design trade-offs in practical XL-Array systems.

Technology Category

• Search and Optimization: Mixed Discrete/Continuous Search
• Machine Learning: Hardware-aware ML
• Natural Language Processing: Learning & Optimization for NLP

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Security and Privacy: Large-scale security measurements

Abstract

Extremely large-scale arrays (XL-arrays) have emerged as a promising technology for enabling near-field communications in future wireless systems. However, the huge number of antennas deployed pose demanding challenges on the hardware cost and power consumption, especially when the antennas employ high-resolution phase shifters (PSs). To address this issue, in this paper, we consider low-resolution discrete PSs at the XL-array which are practically more energy efficient, and investigate the impact of PS resolution on the near-field beam-focusing effect. To this end, we propose a new Fourier series expansion method to efficiently tackle the difficulty in characterizing the beam pattern properties under phase quantization. Interestingly, we analytically show, for the first time, that 1) discrete PSs introduce additional grating lobes; 2) the main lobe still exhibits the beam-focusing property with its beam power increasing with PS resolution; and 3) there are two types of grating lobes, featured by the beam-focusing and beam-steering properties, respectively. In addition, we provide intuitive understanding for the appearance of grating lobes under discrete PSs from an array-of-subarrays perspective. Finally, numerical results demonstrate that the grating lobes generally degrade communication rate performance. However, a low-resolution of 3-bit PSs can achieve similar beam pattern and rate performance with the continuous PS counterpart, while it attains much higher energy efficiency.

Problem

• XL-Array
• Phased Array Accuracy
• Near-Field Signal Concentration

Innovation

• Low-Precision Discrete Phase Shifters
• Fourier Series Expansion Analysis
• Energy Efficiency in XL-Arrays