PHY3 – MIMO, Beamforming and Channel Estimation
Thursday, 4 June 2026, 11:00-12:30, room Sala1 (1st floor)
Session Chair: Pawel Kryszkiewicz (Poznan Univ. Technology, PL)
Asymptotic Capacity Approximation and Simplified Optimization for MIMO-BD-RIS in Rician Fading
Fabien Héliot and Rahim Tafazolli (University of Surrey, United Kingdom (Great Britain))
This work studies the capacity limits of multi-input multiple-output (MIMO) systems using beyond diagonal (BD) reconfigurable intelligent surface (RIS), a.k.a., MIMO-BD-RIS systems, in Rician fading channels, when the number of transmit antennas, Nt, or receive antennas, Nr, is asymptotically large. More specifically, we first derive a novel asymptotic approximation of the MIMO-BD-RIS capacity for the large Nt or Nr regime that is then used to greatly simplify the optimization process of the BD-RIS reflection pattern in this scenario, since we prove that it simply boils down to solving a classic MIMO beamforming problem with extra constraints. Numerical simulations validate both the correctness of our capacity approximation for different types of BD-RIS reflection patterns as well as the effectiveness of our simplified MIMO-BD-RIS optimization method. They also show that the relative share of the capacity related to the BD-RIS reflection pattern optimization in the overall capacity decreases as the minimum value between Nt, Nr, and the number of RIS elements increases, making optimization less pertinent in this case.
DMA-Aided MU-MISO Systems for Power Splitting SWIPT via Lorentzian-Constrained Holography
Askin Altinoklu and Leila Musavian (University of Essex, United Kingdom (Great Britain))
This paper presents an optimal power splitting and beamforming design for co-located simultaneous wireless information and power transfer (SWIPT) users in Dynamic Metasurface Antenna (DMA)-aided multiuser multiple-input single-output (MISO) systems. The objective is to minimize transmit power while meeting users’ signal-to-interference-plus-noise ratio (SINR) and energy harvesting (EH) requirements. The problem is solved via an alternating optimization framework based on semi-definite programming (SDP), where metasurface tunability follows Lorentzian-constrained holography (LCH). In contrast to traditional beamforming architectures, DMA-assisted architectures reduce the need for RF chains and phase shifters; however, they require optimization under Lorentzian constraints that couple amplitude and phases. Hence, the proposed method integrates several LCH schemes, including the recently proposed adaptive-radius LCH (ARLCH), and evaluates nonlinear EH models and circuit noise effects. Simulation results show that the proposed design significantly reduces transmit power compared with baseline methods, highlighting the efficiency of ARLCH and optimal power splitting in DMA-assisted SWIPT systems.
Exploiting Beam-Squint for Fast Object Detection in Hybrid Beamforming ISAC Systems
Ozan Demirsoy (Hacettepe University, Turkey & ASELSAN Inc., Turkey); Omer Haliloglu (None); Cenk Toker (Hacettepe University, Turkey)
This paper investigates the beam-squint phenomenon in hybrid beamforming-based Integrated Sensing and Communication (ISAC) systems operating at millimeter-Wave (mmWave) frequencies. Instead of treating beam-squint as a performance degradation factor, it is exploited for sensing to accelerate beam scanning and enable computationally efficient range and angle estimation. An interleaved Orthogonal Frequency Division Multiplexing (OFDM) subcarrier allocation is adopted to jointly preserve range resolution and support simultaneous communication. The beam-squint induced frequency tapering effect, termed as the beam-squint window, is analytically formulated and exploited for coarse object localization. A two step estimation method is proposed, consisting of range and angle profiling, which is a computationally efficient alternative to MMSE estimation. Simulation results demonstrate that the proposed method significantly reduces required beam number in beam sweeping while providing satisfactory estimation accuracy, making it a practical and cost-effective solution for 6G and Beyond ISAC transceivers without additional True-Time Delay (TTD) hardware.
Precoding Design with Codebook-Based Effective CSI Feedback in MIMO Systems
Bikshapathi Gouda and Antti Arvola (University of Oulu, Finland); Juha Karjalainen (Nokia Bell Labs, Finland); Sami-Jukka Hakola (Nokia, Finland); Antti Tölli (University of Oulu, Finland)
We consider downlink multi-user multiple-input multiple-output (MIMO) precoding with limited channel state information (CSI) feedback. Conventional codebook-based schemes compress the physical channel at the user equipment (UE), which can cause a precoder–combiner mismatch when interference-aware combining is applied at the UE. We propose an effective CSI feedback (ECSI-FB) method in which each UE estimates its minimum mean-squared-error combiner from precoded pilots, forms the corresponding post-combining effective channel, and feeds back a compact quantized representation using the same beam-domain reporting structure as conventional codebook feedback. The base station (BS) reconstructs the effective CSI and iteratively refines its precoders via over-the-air signaling, thereby improving the alignment between precoding and combining under practical feedback constraints. Simulation results demonstrate fast convergence within about five iterations and up to 80% sum-rate improvement over conventional physical-channel feedback.
Weighted Sum Rate Maximization for ITS-Aided Arrays in Multi-User MIMO
Robbert Beerten (KU Leuven, Belgium); Wen Shang (King’s College London, United Kingdom (Great Britain)); Tugce Kobal (Nokia Bell Labs, United Kingdom (Great Britain))
This work explores the potential of integrating an Intelligent Transmissive Surface (ITS) into an antenna array to improve beamforming performance. We show that integrating a moderate number of passive refractive elements into a small antenna array can significantly improve the Weighted Sum Rate (WSR). We investigate the optimization of the WSR under two distinct operational constraints: a Radiated Power (RP) constraint and a Transmitted Power (TP) constraint. Our analysis reveals that the choice between these constraints significantly impacts the design parameters of the ITS-aided array. By contrasting these approaches, we explore critical design and material parameters, including the array geometry, surface loss, and illumination strategies.
