PHY1 – Multiple Antenna Systems
Wednesday, 4 June 2025, 11:00-12:30, room 1.E
Session Chair: Erik G Ström (Chalmers University of Technology, SE)
C-RAN Architecture Modeling for Joint Precoder Signaling
Jarkko Kaleva and Antti Tölli (University of Oulu, Finland); Jarno Niemelä (Elisa Corporation, Finland)
Queuing and processing delays in Cloud Radio Access Network (C-RAN) infrastructure and Open Radio Access Network (O-RAN) interfaces significantly impact downlink distributed MIMO and coherent Multi-Transmission Reception Point (multi-TRP) joint transmission (JT) performance. This work introduces a novel queue-based signaling delay model for beamformer design control, enabling a more realistic evaluation of centralized and decentralized JT Multi-TRP methods. The proposed model captures accurate midhaul/fronthaul signaling delays inherent to C-RAN architectures, providing fine-grained insights into their effects on Multi-TRP JT coordination. The primary objective is to minimize the sum mean-squared error (MSE) within joint transmission clusters while incorporating network-induced signaling delays. The simulation results highlight the critical role of these delays in Multi-TRP JT performance and emphasize the need for delay-aware coordination strategies in next-generation wireless networks.
RIS Meets O-RAN: a Practical Demonstration of Multi-User RIS Optimization Through RIC
Ali Fuat Sahin (Istanbul Technical University, Turkey & TUBITAK BILGEM, Turkey); Onur Salan (Communications and Signal Processing Research (HİSAR) Laboratory, TÜBİTAK BİLGEM, Turkey); Ibrahim Hokelek (TUBITAK BILGEM, Turkey); Ali Gorcin (Istanbul Techical University, Turkey)
Open Radio Access Network (O-RAN) along with artificial intelligence, machine learning, cloud, and edge networking, and virtualization are important enablers for designing flexible and software-driven programmable wireless networks. In addition, Reconfigurable Intelligent Surfaces (RIS) represent an innovative technology to direct incoming radio signals toward desired locations by software-controlled passive reflecting antenna elements. Despite their distinctive potential, there has been limited exploration of integrating RIS with the O-RAN framework, an area that holds promise for enhancing next-generation wireless systems. This paper addresses this gap by designing and developing the RIS optimization xApps within an O-RAN-based real-time 5G environment. We perform extensive measurement experiments using an end-to-end 5G testbed including the RIS prototype in a multi-user scenario. The results demonstrate that the RIS can be effectively utilized to boost the received signal power of the selected user or provide fairness among the users. This is a promising result demonstrating that RIS can support high-level policies in a multi-user network scenario..
Investigation of Holographic Beamforming via Dynamic Metasurface Antennas in QoS Guaranteed Power Efficient Networks
Askin Altinoklu and Leila Musavian (University of Essex, United Kingdom (Great Britain))
This work focuses on designing a power-efficient network for Dynamic Metasurface Antennas (DMA)-aided multi-user multiple-input single-output (MISO) antenna systems. Power efficiency is achieved through holographic beamforming in a DMA-aided network, minimizing total transmission power while ensuring a guaranteed signal-to-noise-and-interference ratio (SINR) for multiple users in downlink. Unlike conventional MISO systems, which have well-explored beamforming solutions, DMA require specialized methods due to their unique physical constraints and wave-domain precoding capabilities. To achieve this, optimization algorithms relying on alternating optimization and semi-definite programming, are developed, including spherical-wave channel modelling of near-field communication. In this setup, the beamforming performance of DMA-aided precoding is analyzed in comparison to its optimal limits and traditional fully digital (FD) architectures, considering the effects of the Lorentzian constraints of metasurfaces and the degree of freedom (DoF) limitations due to a reduced number of RF chains. We demonstrate that the performance gap caused by DoF constraints becomes more significant as the number of users increases, highlighting the trade-offs of DMA in high-density wireless networks.
Quantized Precoding Under ACLR Constraints with FIR-DACs for Downlink MU-MIMO
Nicolas Schlegel (Institut Polytechnique Paris & Nokia Networks France, France); Chadi Jabbour (Telecom Paris, France); Alvaro Valcarce and Eric Wantiez (Nokia Bell Labs, France)
Scaling massive multiuser multiple-input multiple-output (MIMO) to larger antenna numbers constrains each chain in terms of power consumption and implementation. In this paper, the use of low resolution digital-to-analog converters (DACs) enabling these large scale arrays in downlink multiuser massive MIMO is studied with a focus on reaching adjacent channel leakage ratio (ACLR) targets. A quantization aware precoder with constraints on out-of-band (OOB) emissions is designed based on the multi-block alternate directions method of multipliers (ADMM) algorithm. With conventional DACs, simulation results indicate that these constraints do not provide sufficient ACLR. In response, Finite impulse response (FIR)- DACs are introduced as a reconfigurable alternative to analog filters. Numerical results show that ACLR targets can be reached, even at 1 bit, at a lower hardware cost than high resolution DACs.
Distributed Uplink Joint Transmission for 6G Communication
Kumar Sai Bondada, Usama Saeed, Yibin Liang, Daniel Jakubisin, Lingjia Liu and R. Michael Buehrer (Virginia Tech, USA)
This paper investigates the spectral efficiency achieved through uplink joint transmission, where a serving user and the network users (UEs) collaborate by jointly transmitting to the base station (BS). The analysis incorporates the resource requirements for information sharing among UEs as a critical factor in the capacity evaluation. Furthermore, coherent and non-coherent joint transmission schemes are compared under various transmission power scenarios, providing insights into spectral and energy efficiency. A selection algorithm identifying the optimal UEs for joint transmission, achieving maximum capacity, is discussed. The results indicate that uplink joint transmission is one of the promising techniques for enabling 6G, achieving greater spectral efficiency even when accounting for the resource requirements for information sharing.
