[Paper Review] Hybrid Beamforming for 5G and Beyond Millimeter-Wave Systems: A Holistic View

Jun Zhang, Xianghao Yu+1 more|arXiv (Cornell University)|Nov 7, 2019

Millimeter-Wave Propagation and Modeling51 references17 citations

TL;DR

This paper proposes a holistic framework for hybrid beamforming in 5G and beyond mm-wave systems, introducing a new taxonomy of hardware structures and evaluating trade-offs among hardware efficiency, computational efficiency, and spectral efficiency. The FPS group-connected structure emerges as a leading candidate, enabling near-fully-digital performance with minimal RF chains and fixed-phase-shifter hardware, achieving high spectral efficiency while maintaining low complexity.

ABSTRACT

Millimeter-wave (mm-wave) communication is a key technology for future wireless networks. To combat significant path loss and exploit the abundant mm-wave spectrum, effective beamforming is crucial. Nevertheless, conventional fully digital beamforming techniques are inapplicable, as they demand a separate radio frequency (RF) chain for each antenna element, which is costly and consumes too much energy. Hybrid beamforming is a cost-effective alternative, which can significantly reduce the hardware cost and power consumption by employing a small number of RF chains. This paper presents a holistic view on hybrid beamforming for 5G and beyond mm-wave systems, based on a new taxonomy for different hardware structures. We take a pragmatic approach and compare different proposals from three key aspects: 1) hardware efficiency, i.e., the required hardware components; 2) computational efficiency of the associated beamforming algorithm; and 3) achievable spectral efficiency, a main performance indicator. Through systematic comparisons, the interplay and trade-off among these three design aspects are demonstrated, and promising candidates for hybrid beamforming in future wireless networks are identified.

Motivation & Objective

• To address the high hardware cost and energy consumption of fully digital beamforming in mm-wave systems.
• To evaluate and compare hybrid beamforming structures based on hardware efficiency, computational efficiency, and spectral efficiency.
• To identify promising hybrid beamforming architectures that balance performance and practical constraints.
• To propose a flexible mapping strategy that enables trade-offs between complexity and spectral efficiency.
• To guide future research in CSI acquisition, deep learning integration, finite-precision ADCs, and algorithm-hardware co-design.

Proposed method

• Proposes a new taxonomy of hybrid beamforming hardware structures, including fully precoded, partially precoded, and group-connected architectures.
• Introduces a flexible mapping strategy that allows adjustable trade-offs between hardware complexity and spectral efficiency via a parameter η.
• Analyzes the FPS (Fully Precoded Structure) group-connected implementation, which uses a small number of fixed phase shifters and RF chains comparable to data streams.
• Evaluates algorithmic efficiency using existing techniques such as compressive sensing, codebook-based design, and manifold optimization.
• Compares hardware components and algorithmic complexity across different structures using Tables III and IV.
• Employs a pragmatic, multi-dimensional evaluation framework focusing on three key performance metrics: hardware cost, computational load, and spectral efficiency.

Experimental results

Research questions

• RQ1 How do different hybrid beamforming hardware structures compare in terms of hardware efficiency, computational complexity, and spectral efficiency?
• RQ2 What is the impact of analog network architecture on beamforming algorithm design and achievable spectral efficiency?
• RQ3 Can a flexible mapping strategy effectively balance hardware complexity and spectral performance in hybrid beamforming systems?
• RQ4 Which hybrid beamforming structure comes closest to achieving fully digital performance with minimal RF chains and phase shifter hardware?
• RQ5 What are the key challenges and future research directions for practical deployment of hybrid beamforming in mm-wave networks?

Key findings

• The FPS group-connected structure achieves spectral efficiency close to fully digital beamforming while using only a small number of RF chains and fixed-phase-shifter components.
• With the proposed mapping strategy, varying the parameter η enables effective trade-offs between hardware complexity and spectral efficiency.
• The FPS implementation is compatible with existing low-complexity algorithms such as compressive sensing and manifold optimization, enhancing its practicality.
• The study demonstrates that a limited number of fixed phase shifters (~10) are sufficient to achieve high spectral efficiency when combined with an optimal structure.
• The FPS group-connected structure stands out as the most promising candidate for 5G and beyond mm-wave systems due to its balance of performance and hardware efficiency.
• Future research should focus on CSI acquisition, deep learning-based algorithms, finite-precision ADCs, and algorithm-hardware co-design to enable practical deployment.