Intra-Beam Interference Mitigation for the Downlink Transmission of the RIS-Assisted Hybrid Millimeter Wave System

• Published in: Entropy (Basel, Switzerland) Vol. 26; no. 3; p. 253
• Main Authors: Zhao, Lou, Zhang, Yuliang, Zhang, Minjie, Liu, Chunshan
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 13.03.2024; MDPI
• Subjects: Algorithms; analog beamforming; Antenna arrays; Antennas; Antennas (Electronics); Beamforming; Communication; Communications systems; Design; Digital to analog converters; Downlinking; Energy consumption; Energy efficiency; Hybrid systems; Interference; intra-beam interference; low-resolution A/Ds; millimeter wave; Millimeter waves; Normal distribution; Numerical analysis; Pulse amplitude modulation; Random variables; reconfigurable intelligent surface; Signal processing; Simulation methods; Upper bounds; Wireless telecommunications equipment; low-resolution A/Ds; millimeter wave; analog beamforming; reconfigurable intelligent surface; intra-beam interference; energy efficiency
• ISSN: 1099-4300; 1099-4300
• DOI: 10.3390/e26030253

Millimeter-wave (mmWave) communication systems leverage the directional beamforming capabilities of antenna arrays equipped at the base stations (BS) to counteract the inherent high propagation path loss characteristic of mmWave channels. In downlink mmWave transmissions, i.e., from the BS to users, distinguishing users within the same beam direction poses a significant challenge. Additionally, digital baseband precoding techniques are limited in their ability to mitigate inter-user interference within identical beam directions, representing a fundamental constraint in mmWave downlink transmissions. This study introduces an innovative analog beamforming-based interference mitigation strategy for downlink transmissions in reconfigurable intelligent surface (RIS)-assisted hybrid analog-digital (HAD) mmWave systems. This is achieved through the joint design of analog beamformers and the corresponding coefficients at both the RIS and the BS. We first present derived closed-form approximation expressions for the achievable rate performance in the proposed scenario and establish a stringent upper bound on this performance in a large number of RIS elements regimes. The exclusive use of analog beamforming in the downlink phase allows our proposed transmission algorithm to function efficiently when equipped with low-resolution analog-to-digital/digital-to-analog converters (A/Ds) at the BS. The energy efficiency of the downlink transmission is evaluated through the deployment of six-bit A/Ds and six-bit pulse-amplitude modulation (PAM) signals across varying numbers of activated RIS elements. Numerical simulation results validate the effectiveness of our proposed algorithms in comparison to various benchmark schemes.