# Hybrid Precoder and Combiner for Imperfect Beam Alignment in mmWave MIMO Systems

## TL;DR

This paper proposes a robust hybrid precoder and combiner design for mmWave MIMO systems that accounts for beam misalignment errors, improving performance stability in practical scenarios.

## Contribution

It introduces an error-statistics-based design approach and an iterative algorithm for robust hybrid precoding and combining in the presence of beam misalignment.

## Key findings

- Effective mitigation of beam misalignment effects
- Enhanced spectral efficiency with second-stage digital processing
- Numerical results confirm performance improvements

## Abstract

In this letter, we aim to design a robust hybrid precoder and combiner against beam misalignment in millimeter-wave (mmWave) communication systems. We consider the inclusion of the `error statistics' into the precoder and combiner design, where the array response that incorporates the distribution of the misalignment error is first derived. An iterative algorithm is then proposed to design the robust hybrid precoder and combiner to maximize the array gain in the presence of beam misalignment. To further enhance the spectral efficiency, a second-stage digital precoder and combiner are included to mitigate the inter-stream interference. Numerical results show that the proposed robust hybrid precoder and combiner design can effectively alleviate the performance degradation incurred by beam misalignment.