# RLS Precoding for Massive MIMO Systems with Nonlinear Front-End

## TL;DR

This paper introduces a distortion-aware RLS precoding scheme for massive MIMO systems with nonlinear RF front-ends, improving performance by jointly compensating channel effects and RF distortions using an efficient iterative algorithm.

## Contribution

It presents a novel RLS-based precoding method that accounts for RF nonlinearities and an efficient message passing algorithm for practical implementation.

## Key findings

- Significant performance improvement over existing methods.
- Effective compensation of RF chain nonlinearities.
- Low computational complexity of the proposed algorithm.

## Abstract

To keep massive MIMO systems cost-efficient, power amplifiers with rather small output dynamic ranges are employed. They may distort the transmit signal and degrade the performance. This paper proposes a distortion aware precoding scheme for realistic scenarios in which RF chains have nonlinear characteristics. The proposed scheme utilizes the method of regularized least-squares (RLS) to jointly compensate the channel impacts and the distortion imposed by the RF chains. To construct the designed transmit waveform with low computational complexity, an iterative algorithm based on approximate message passing is developed. This algorithm is shown to track the achievable average signal distortion of the proposed scheme tightly, even for practical system dimensions. The results demonstrate considerable enhancement compared to the state of the art.