  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.
