# A Hybrid Beamforming Receiver with Two-Stage Analog Combining and Low-Resolution ADCs

## TL;DR

This paper introduces a novel two-stage analog combining architecture for mmWave receivers that optimizes mutual information and effectively manages quantization errors using low-resolution ADCs.

## Contribution

It proposes a new two-stage analog combining solution and an algorithm to implement it under practical hardware constraints, enhancing mmWave receiver performance.

## Key findings

- Achieves optimal MI scaling with RF chains
- Maximizes MI for homogeneous MIMO channel singular values
- Validated by simulations showing improved MI performance

## Abstract

In this paper, we propose a two-stage analog combining architecture for millimeter wave (mmWave) communications with hybrid analog/digital beamforming and low-resolution analog-to-digital converters (ADCs). We first derive a two-stage combining solution by solving a mutual information (MI) maximization problem without a constant modulus constraint on analog combiners. With the derived solution, the proposed receiver architecture splits the analog combining into a channel gain aggregation stage followed by a spreading stage to maximize the MI by effectively managing quantization error. We show that the derived two-stage combiner achieves the optimal scaling law with respect to the number of radio frequency (RF) chains and maximizes the MI for homogeneous singular values of a MIMO channel. Then, we develop a two-stage analog combining algorithm to implement the derived solution under a constant modulus constraint for mmWave channels. Simulation results validate the algorithm performance in terms of MI.