Two-Layer Microwave Linear Analog Computer (MiLAC)-aided Multi-user MISO Networks

TL;DR

This paper proposes a two-layer MiLAC architecture for multi-user MISO networks that achieves digital beamforming performance using purely analog microwave components, validated through theoretical proofs and numerical results.

Contribution

It introduces a novel two-layer MiLAC architecture with a closed-form mapping to digital beamforming, enabling analog beamforming to match digital performance in multi-user scenarios.

Findings

Two-layer MiLAC achieves the same sum-rate as digital beamforming.

Theoretical proof that lossless, reciprocal two-layer MiLAC can match digital performance.

Optimization framework for power and scattering matrices enhances performance.

Abstract

Microwave linear analog computer (MiLAC)-aided transmit beamforming, which processes transmitted symbols entirely in the analog domain, has recently emerged as a promising alternative to fully digital or hybrid beamforming architectures for single-user multi-antenna systems. However, recent studies have shown that deploying a single lossless and reciprocal MiLAC at the transmitter cannot achieve the same capacity as fully digital beamforming in multi-user scenarios. To address this limitation, we propose a novel two-layer MiLAC-aided beamforming architecture at the transmitter for a downlink multi-user multiple-input single-output (MISO) network. Leveraging microwave network theory, we first prove that lossless and reciprocal two-layer MiLAC-aided beamforming can achieve the same performance as digital beamforming, and we derive a closed-form mapping from digital beamforming to two-layer MiLAC analog beamforming. Furthermore, we formulate a sum-rate maximization problem and develop an efficient optimization framework to jointly optimize the power allocation and the scattering matrices for the proposed two-layer MiLAC architecture. Numerical results validate our theoretical findings and demonstrate that two-layer MiLAC achieves the same sum-rate performance as fully digital beamforming.