# Improper Signaling for SISO Two-user Interference Channels with Additive Asymmetric Hardware Distortion

## TL;DR

This paper demonstrates that improper Gaussian signaling (IGS) can enhance the rate performance of two-user interference channels affected by asymmetric hardware distortion, through novel iterative optimization algorithms.

## Contribution

It introduces two new algorithms for optimizing IGS parameters in interference channels with asymmetric hardware impairments, outperforming existing methods.

## Key findings

- IGS improves rate performance in asymmetric HWD scenarios
- Proposed algorithms outperform proper Gaussian signaling
- Simplified algorithm reduces computational complexity

## Abstract

Hardware non-idealities are among the main performance restrictions for upcoming wireless communication systems. Asymmetric hardware distortions (HWD) happen when the impairments of the I/Q branches are correlated or imbalanced, which in turn generate improper additive interference at the receiver side. When the interference is improper, as well as in other interference-limited scenarios, improper Gaussian signaling (IGS) has been shown to provide rate and/or power efficiency benefits. In this paper, we investigate the rate benefits of IGS in a two-user interference channel (IC) with additive asymmetric HWD when interference is treated as noise. We propose two iterative algorithms to optimize the parameters of the improper transmit signals. We first rewrite the rate region as an pseudosignal-to-interference-plus-noise-ratio (PSINR) region and employ majorization minimization and fractional programming to find a suboptimal solution for the achievable user rates. Then, we propose a simplified algorithm based on a separate optimization of the powers and complementary variances of the users, which exhibits lower computational complexity. We show that IGS can improve the performance of the two-user IC with additive HWD. Our proposed algorithms outperform proper Gaussian signaling and competing IGS algorithms in the literature that do not consider asymmetric HWD.