Michael Joham
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Precoder Design in Multi-User FDD Systems with VQ-VAE and GNN Open
Robust precoding is efficiently feasible in frequency division duplex (FDD) systems by incorporating the learnt statistics of the propagation environment through a generative model. We build on previous work that successfully designed site…
Sum-Rate Optimisation of a Multi-User STAR-RIS-Aided System with Low Complexity Open
Reconfigurable intelligent surface (RIS) is a promising technology for future wireless communication systems. However, the conventional RIS can only reflect the incident signal. Hence, it provides a limited coverage, as compared to a simul…
Statistical Precoder Design in Multi-User Systems via Graph Neural Networks and Generative Modeling Open
This letter proposes a graph neural network (GNN)-based framework for statistical precoder design that leverages model-based insights to compactly represent statistical knowledge, resulting in efficient, lightweight architectures. The fram…
Decoupling Networks and Super-Quadratic Gains for RIS Systems with Mutual Coupling Open
We propose decoupling networks for the reconfigurable intelligent surface (RIS) array as a solution to benefit from the mutual coupling between the reflecting elements. In particular, we show that when incorporating these networks, the sys…
Robust Precoding for FDD MISO Systems via Minorization Maximization Open
In this work, we propose an approach to robust precoder design based on a minorization maximization technique that optimizes a surrogate function of the achievable spectral efficiency. The presented method accounts for channel estimation e…
Bilinear Precoder Based Efficient Rate Splitting Method in FDD Systems Open
In this work, we propose a low-cost rate splitting (RS) technique for a multi-user multiple-input single-output (MISO) system operating in frequency division duplex (FDD) mode. The proposed iterative optimisation algorithm only depends on …
Low Complexity Rate Splitting Approach in RIS-Aided Systems Based on Channel Statistics Open
Rate splitting multiple access (RSMA) and reconfigurable intelligent surface (RIS) are two prospective technologies for improving the spectral and energy efficiency in future wireless communication systems. In this work, we investigate a r…
Nonlinear Precoding in the RIS-Aided MIMO Broadcast Channel Open
We propose to use Tomlinson-Harashima Precoding (THP) for the reconfigurable intelligent surface (RIS)-aided multiple-input multiple-output (MIMO) broadcast channel where we assume a line of sight (LOS) connection between the base station …
A Versatile Pilot Design Scheme for FDD Systems Utilizing Gaussian Mixture Models Open
In this work, we propose a Gaussian mixture model (GMM)-based pilot design scheme for downlink (DL) channel estimation in single- and multi-user multiple-input multiple-output (MIMO) frequency division duplex (FDD) systems. In an initial o…
High-SNR Comparison of Linear Precoding and DPC in RIS-Aided MIMO Broadcast Channels Open
We compare dirty paper coding (DPC) and linear precoding methods in a reconfigurable intelligent surface (RIS)- aided high-signal-to-noise ratio (SNR) scenario, where the channel between the base station (BS) and the RIS is dominated by a …
Design of a Multi-User RIS-Aided System with Statistical Channel Knowledge Open
Reconfigurable intelligent surface (RIS) is a promising technology to enhance the spectral and energy efficiency in a wireless communication system. The design of the phase shifts of an RIS in every channel coherence interval demands a hug…
Channel-Adaptive Pilot Design for FDD-MIMO Systems Utilizing Gaussian Mixture Models Open
In this work, we propose to utilize Gaussian mixture models (GMMs) to design pilots for downlink (DL) channel estimation in frequency division duplex (FDD) systems. The GMM captures prior information during training that is leveraged to de…
An Efficient Rate Splitting Precoding Approach in Multi-User MISO FDD Systems Open
In this work, we develop an efficient precoding strategy for a multi-user multiple-input-single output (MU MISO) system operating in frequency-division-duplex (FDD) mode, where rate splitting multiple access (RSMA) is implemented. To this …
Diffusion-based Generative Prior for Low-Complexity MIMO Channel Estimation Open
This work proposes a novel channel estimator based on diffusion models (DMs), one of the currently top-rated generative models. Contrary to related works utilizing generative priors, a lightweight convolutional neural network (CNN) with po…
On the Asymptotic Mean Square Error Optimality of Diffusion Models Open
Diffusion models (DMs) as generative priors have recently shown great potential for denoising tasks but lack theoretical understanding with respect to their mean square error (MSE) optimality. This paper proposes a novel denoising strategy…
Performance Analysis of Systems with Coupled and Decoupled RISs Open
We analyze and compare different methods for handling the mutual coupling in RIS-aided communication systems. A new mutual coupling aware algorithm is derived where the reactance of each element is updated successively with a closed-form s…
Wireless Channel Prediction via Gaussian Mixture Models Open
In this work, we utilize a Gaussian mixture model (GMM) to capture the underlying probability density function (PDF) of the channel trajectories of moving mobile terminals (MTs) within the coverage area of a base station (BS) in an offline…
Limited Feedback on Measurements: Sharing a Codebook or a Generative Model? Open
Discrete Fourier transform (DFT) codebook-based solutions are well-established for limited feedback schemes in frequency division duplex (FDD) systems. In recent years, data-aided solutions have been shown to achieve higher performance, en…
Reverse Ordering Techniques for Attention-Based Channel Prediction Open
Channel state information (CSI) is crucial for enhancing the performance of wireless systems by allowing to adjust the transmission strategies based on the current channel conditions. However, obtaining precise CSI is difficult because of …
Highly Accelerated Weighted MMSE Algorithms for Designing Precoders in FDD Systems with Incomplete CSI Open
In this work, we derive a lower bound on the training-based achievable downlink (DL) sum rate (SR) of a multi-user multiple-input-single-output (MISO) system operating in frequency-division-duplex (FDD) mode. Assuming linear minimum mean s…
Alternating Minimization for Wideband Multiuser IRS-Aided MIMO Systems Under Imperfect CSI Open
This work focuses on wideband intelligent reflecting surface (IRS)-aided\nmultiuser MIMO systems. One of the major challenges of this scenario is the\njoint design of the frequency-dependent base station (BS) precoder and user\nfilters, an…
A Zero-Forcing Approach for the RIS-Aided MIMO Broadcast Channel Open
We present efficient algorithms for the sum-spectral efficiency (SE) maximization of the multi-user reconfigurable intelligent surface (RIS)-aided multiple-input multiple-output (MIMO) broadcast channel based on a zero-forcing approach. Th…
A Versatile Low-Complexity Feedback Scheme for FDD Systems via Generative Modeling Open
We propose a versatile feedback scheme for both single- and multi-user multiple-input multiple-output (MIMO) frequency division duplex (FDD) systems. Particularly, we propose utilizing a Gaussian mixture model (GMM) with a reduced number o…
Design of a Single-User RIS-Aided MISO System Based on Statistical Channel Knowledge Open
Reconfigurable intelligent surface (RIS) is considered a prospective technology for beyond fifth-generation (5G) networks to improve the spectral and energy efficiency at a low cost. Prior works on the RIS mainly rely on perfect channel st…