@article {651,
	title = {Spectral and Energy Efficiency Maximization of MISO STAR-RIS-Assisted URLLC Systems},
	journal = {IEEE Access},
	volume = {1},
	year = {2023},
	month = {July},
	pages = {70833-70852},
	doi = {10.1109/ACCESS.2023.3294092},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Jorswieck, Eduard}
}
@article {653,
	title = {SNR Maximization in Beyond Diagonal RIS-assisted Single and Multiple Antenna Links},
	journal = {IEEE Signal Processing Letters},
	volume = {30},
	year = {2023},
	month = {August},
	pages = {923-926},
	doi = {10.1109/LSP.2023.3296902},
	author = {Santamar{\'\i}a, Ignacio and Mohammad Soleymani and Jorswieck, Eduard and Guti{\'e}rrez, Jes{\'u}s}
}
@article {547,
	title = {Robust Improper Signaling for Two-user SISO Interference Channels},
	journal = {IEEE Transactions on Communications},
	volume = {67},
	year = {2019},
	month = {July},
	pages = {4709-4723},
	abstract = {It has been shown that improper Gaussian signaling (IGS) can improve the performance of wireless interference limited systems when perfect channel state information (CSI) is available. In this paper, we investigate the robustness of IGS against imperfect CSI on the transmitter side in a two-user single-input single-output (SISO) interference channel (IC) as well as in a SISO Z-IC, when interference is treated as noise. We assume that the true channel coefficients belong to a known region around the channel estimates, which we call the uncertainty region. Following a worst-case robustness approach, we study the rate-region boundary of the IC for the worst channel in the uncertainty region. For the two-user IC, we derive a robust design in closed-form, which is independent of the phase of the channels by allowing only one of the users to transmit IGS. For the Z-IC, we provide a closed-form design for the transmission parameters by considering an enlarged uncertainty region and allowing both users to employ IGS. In both cases, the IGS-based designs are ensured to perform no worse than proper Gaussian signaling. Furthermore, we show, through numerical examples, that the proposed robust designs significantly outperform non-robust solutions.},
	keywords = {Achievable rate region, imperfect CSI, improper Gaussian signaling, two-user interference channel, worst-case robustness.},
	doi = {10.1109/TCOMM.2019.2910549},
	author = {Mohammad Soleymani and Lameiro, Christian and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
@article {631,
	title = {Rate Splitting in MIMO RIS-assisted Systems with Hardware Impairments and Improper Signaling},
	journal = {IEEE Transactions on Vehicular Technology},
	volume = {72},
	year = {2023},
	month = {April},
	pages = {4580-4597},
	doi = {10.1109/TVT.2022.3222633},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Jorswieck, Eduard}
}
@article {660,
	title = {Optimization of Rate-Splitting Multiple Access in Beyond Diagonal RIS-assisted URLLC Systems},
	journal = {IEEE Transactions on Wireless Communications},
	year = {2023},
	doi = {10.1109/TWC.2023.3324190},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Jorswieck, Eduard and Clerckx,Bruno}
}
@article {645,
	title = {NOMA-based Improper Signaling for Multicell MISO RIS-assisted Broadcast Channels},
	journal = {IEEE Transactions on Signal Processing},
	volume = {71},
	year = {2023},
	pages = {963-978},
	doi = {10.1109/TSP.2023.3259145},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Jorswieck, Eduard and Rezvani, Sepehr}
}
@article {559,
	title = {Improper Signaling for SISO Two-user Interference Channels with Additive Asymmetric Hardware Distortion},
	journal = {IEEE Transactions on Communications},
	volume = {67},
	year = {2019},
	month = {December},
	pages = {8624-8638},
	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 pseudo-signal-to-interference-plus-noiseratio (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.},
	doi = {10.1109/TCOMM.2019.2939310},
	author = {Mohammad Soleymani and Lameiro, Christian and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
@article {620,
	title = {Improper Signaling for Multicell MIMO RIS-assisted Broadcast Channels with I/Q Imbalance},
	journal = {IEEE Transactions on Green Communications and Networking},
	volume = {6},
	year = {2022},
	month = {June},
	pages = {723-738},
	doi = {10.1109/TGCN.2021.3140150},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
@article {574,
	title = {Improper Gaussian Signaling for the K-user MIMO Interference Channels with Hardware Impairments},
	journal = {IEEE Transactions on Vehicular Technology},
	volume = {69},
	year = {2020},
	month = {October},
	pages = {11632-11645},
	doi = { 10.1109/TVT.2020.3015558},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
@article {562,
	title = {Ergodic Rate for Fading  Interference Channels with Proper and Improper Gaussian Signaling},
	journal = {Entropy},
	volume = {21},
	year = {2019},
	month = {September},
	doi = {https://doi.org/10.3390/e21100922},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Lameiro, Christian and Schreier, Peter J.}
}
@article {609,
	title = {Distributed algorithms for spectral and energy-efficiency maximization of K-user interference channels},
	journal = {IEEE Access},
	volume = {9},
	year = {2021},
	month = {July},
	pages = {96948-96963},
	abstract = {In this paper, we propose a cooperative distributed framework to optimize a variety of rate and energy-efficiency (EE) utility functions, such as the minimum-weighted rate or the global EE, in the K-user interference channel. We focus on the single-input multiple-output (SIMO) case, where each user, based solely on local channel state information (CSI), optimizes its transmit power and receive beamformer, although the framework can also be extended to the multiple-output multiple-input (MIMO) case. The distributed framework combines an alternating optimization approach with majorization minimization (MM) techniques, thus ensuring convergence to a stationary point of the centralized cost function. Closed-form power update rules are obtained for some utility functions, thus obtaining very fast convergence algorithms. The receivers treat interference as noise (TIN) and apply the beamformers that maximize the signal-to-interference-plus-noise (SINR). The proposed cooperative distributed algorithms are robust against channel variations and network topology changes and, as our simulation results suggest, they perform close to the centralized solution. As a benchmark, we also study a non-cooperative distributed framework based on the so-called "signal-to-leakage-plus-noise ratio" (SNLR) that further reduces the overhead of the cooperative version.},
	doi = {10.1109/ACCESS.2021.3094976},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
@conference {572,
	title = {Rate Region of the K-user MIMO Interference Channel with Imperfect Transmitters},
	booktitle = {European Signal Processing Conference (EUSIPCO 2020)},
	year = {2020},
	month = {August},
	pages = {1638-1642},
	address = {Amsterdamd, The Netherlands},
	abstract = {This paper studies the rate region of a multiple-input, multiple-output (MIMO) system with imperfect transmitters when interference is treated as noise at the receiver side. We consider a K-user MIMO interference channel (IC) in which the transmitters suffer from an additive hardware distortion (HWD) modeled as spatially uncorrelated Gaussian noise with covariance matrix proportional to the transmit covariance matrix. We employ the difference of convex programming (DCP) technique to solve the rate-region optimization problem and obtain its stationary points. Our proposed HWD-aware algorithm outperforms the HWD-unaware design that disregards HWD. Our results show that the performance of the K-user MIMO IC is highly affected by HWD, especially in high signal-to-noise-ratio scenarios.},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Maham, Behrouz and Schreier, Peter J.}
}
@conference {635,
	title = {Rate region of MIMO RIS-assisted broadcast channels with rate splitting and improper signaling},
	booktitle = {International ITG 26th Workshop on Smart Antennas},
	year = {2023},
	month = {March},
	address = {Braunschweig, Germany},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Jorswieck, Eduard}
}
@conference {664,
	title = {NOMA-based Improper Signaling for MIMO STAR-RIS-assisted Broadcast Channels with Hardware Impairments},
	booktitle = {IEEE Global Communications Conference (GLOBECOM)},
	year = {2023},
	month = {Dec.},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Jorswieck, Eduard}
}
@conference {666,
	title = {Maximization of Minimum Rate in MIMO OFDM RIS-assisted Broadcast Channels},
	booktitle = {IEEE International Workshop on Computational Advances in Multi-Sensor Adaptive Processing},
	year = {2023},
	month = {Dec.},
	address = {Los Sue{\~n}os, Costa Rica},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Sezgin, Aydin and Jorswieck, Eduard}
}
@conference {643,
	title = {Interference Leakage Minimization in RIS-assisted MIMO Interference Channels},
	booktitle = {IEEE International Conference on Acoustics Speech and Signal Processing},
	year = {2023},
	month = {June},
	address = {Rhodes, Greece},
	author = {Santamar{\'\i}a, Ignacio and Mohammad Soleymani and Jorswieck, Eduard and Mohammad Soleymani}
}
@conference {516,
	title = {Improper Signaling for OFDM Underlay Cognitive Radio Systems},
	booktitle = {IEEE Statistical Signal Processing Workshop (SSP)},
	year = {2018},
	month = {June},
	address = {Freiburg, Germany},
	abstract = {Improper signaling, where real and imaginary parts of the transmit
signal are correlated and/or have unequal power, has received a lot
of attention lately because it has been shown to increase achievable
rates in many interference-limited communication systems. In this paper, we study whether improper signaling can also benefit an orthogonal frequency-division multiplexing (OFDM) underlay cognitive radio (UCR) system. We assume that the primary user (PU) transmits proper signals, while the secondary user (SU) is allowed to employ improper signaling. We consider two different rate constraints for the rate of the PU: i) the total rate of the PU, and ii) the rate of the PU in each subband. We propose an algorithm to implement improper signaling for each constraint. In both cases, we show that the benefits of improper signaling are relatively small and decrease rapidly with increasing number of subbands. This rather negative result shows that the use of improper signaling in interference scenarios needs to be justified on a case-by-case basis.},
	author = {Mohammad Soleymani and Lameiro, Christian and Schreier, Peter J. and Santamar{\'\i}a, Ignacio}
}
@conference {648,
	title = {Energy-efficient Rate Splitting for MIMO STAR-RIS-assisted Broadcast Channels with I/Q Imbalance},
	booktitle = {31th European Signal Processing Conference (EUSIPCO)},
	year = {2023},
	month = {September},
	address = {Helsinki, Finland},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Jorswieck, Eduard}
}
@conference {554,
	title = {Energy-Efficient Improper Signaling for K-user Interference Channels},
	booktitle = {European Signal Processing Conference (EUSIPCO)},
	year = {2019},
	month = {September},
	abstract = {This paper investigates the energy efficiency (EE) of improper Gaussian signaling (IGS) in a K-user interference channel (IC). IGS allows unequal variances and/or correlation between the real and imaginary parts, and it has recently been shown to be advantageous in various interference-limited scenarios. In this paper, we propose an energy-efficient IGS design for the K-user IC, which is based on a separate optimization of the powers and complementary variances of the users. We compare the EE region achieved by the proposed scheme with that achieved by conventional proper signaling and show that IGS can significantly improve the EE region.},
	author = {Mohammad Soleymani and Lameiro, Christian and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
@conference {541,
	title = {Energy-Efficient Design for Underlay Cognitive Radio using Improper Signaling},
	booktitle = {IEEE Int. Conference on Acoustics, Speech, and Signal Processing (ICASSP)},
	year = {2019},
	month = {May},
	address = {Brighton, UK},
	abstract = {Improper Gaussian signaling (IGS) has been used as an effective interference management tool in interference limited systems. Improper Gaussian signals are correlated with their complex conjugates. In this paper, we investigate theoptimality of IGS from an energy efficiency (EE) perspective. First, we obtain closed form optimality conditions for
IGS.We then leverage these conditions to devise a bisection method that finds the optimal transmission parameters. Our results show that IGS can improve the EE of an underlay cognitive radio system.},
	author = {Mohammad Soleymani and Lameiro, Christian and Schreier, Peter J. and Santamar{\'\i}a, Ignacio}
}
