Finite-Resolution Digital Beamforming for Multi-User Millimeter-Wave Networks

• Published in: IEEE transactions on vehicular technology Vol. 71; no. 9; pp. 9647 - 9662
• Main Authors: Nasir, Ali Arshad, Tuan, Hoang D., Dutkiewicz, Eryk, Hanzo, Lajos
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.09.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Analog to digital converters; Antenna arrays; Antenna design; Antennas; Array signal processing; Beamforming; Communication networks; Computational efficiency; digital beamforming; Iterative methods; low-resolution ADC; Millimeter wave communication; Millimeter waves; Millimeter-wave communications; Optimization; Simulation; Transmission line matrix methods; Transmitting antennas
• ISSN: 0018-9545; 1939-9359
• DOI: 10.1109/TVT.2022.3180786

Recent studies have shown that low-resolution analog-to-digital-converters and digital-to-analog-converters (ADCs and DACs) can make fully-digital beamforming more power efficient than its analog or hybrid beamforming counterpart over wide-band millimeter-wave (mmWave) channels. Inspired by this, we propose a computationally efficient fully-digital beamformer relying on low-resolution ADCs/DACs for multi-user mmWave communication networks. Both a generalized (unstructured) beamformer (GB) and a structured zero-forcing beamformer (ZFB) are proposed. For maintaining fairness among all users in the network, specifically tailored objective functions are considered under sum-power constraints, namely that of maximizing the geometric mean (GM) of users' rate and their max-min rate. These computationally challenging beamforming design problems are tackled by developing computationally efficient steep ascent algorithms, which have the radical benefit of relying on a closed-form solution at each iteration. Moreover, to facilitate the employment of low-cost amplifiers at each antenna, the GB design problem subject to the equal-gain transmission constraint is considered, which assigns equal transmit power to each transmit antenna. The proposed algorithms promise a user-rate distribution having a reduced deviation among the user-rates, i.e., improved rate-fairness. Our extensive simulation results show an approximately upto 45% reduction for the GM-rate of a 2-bit ADC (4-bin quantization) compared to the <inline-formula><tex-math notation="LaTeX">\infty</tex-math></inline-formula>-resolution ADC.