Beam Focusing for Near-Field Multi-User MIMO Communications

By Haiyang Zhang, Nir Shlezinger, Francesco Guidi, Davide Dardari, M. Imani, Yonina C. Eldar. IEEE Transactions on Wireless Communications, 2021

519 citations recorded by the source corpus.

Large antenna arrays and high-frequency bands are two key features of future wireless communication systems. The combination of large-scale antennas with high transmission frequencies often results in the communicating devices operating in the near-field (Fresnel) region. In this paper, we study the potential of beam focusing, feasible in near-field operation, in facilitating high-rate multi-user downlink multiple-input multiple-output (MIMO) systems. As the ability to achieve beam focusing is dictated by the transmit antenna, we study near-field signalling considering different antenna structures, including fully-digital architectures, hybrid phase shifter-based precoders, and the emerging dynamic metasurface antenna (DMA) architecture for massive MIMO arrays. We first provide a mathematical model to characterize near-field wireless channels as well as the transmission pattern for the considered antenna architectures. Then, we formulate the beam focusing problem for the goal of maximizing the achievable sum-rate in multi-user networks. We propose efficient solutions based on the sum-rate maximization task for fully-digital, (phase shifters based-) hybrid and DMA architectures. Simulation results show the feasibility of the proposed beam focusing scheme for both single- and multi-user scenarios. In particular, the designed focused beams provide a new degree of freedom to mitigate interference in both angle and distance domains, which is not achievable using conventional far-field beam steering, allowing reliable communications for uses even residing at the same angular direction.

Subfields: Aerospace Engineering, Electrical and Electronic Engineering

View Paper: https://www.semanticscholar.org/paper/e90db272be81ffb09555e05c41a1404227d629ce

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Citations in the corpus

A Tutorial on Extremely Large-Scale MIMO for 6G: Fundamentals, Signal Processing, and Applications (2023, background): “However, in the far-field, the array response vector is only determined by the AoA/AoD rather than the distance.”
Flexible-Antenna Systems: A Pinching-Antenna Perspective (2024, unknown): “Assume that the n -th pinching antenna is set as ˜ ψ Pin n = ψ Pin n , i.e., the n -th pinching antenna is placed to be closest to U n , and the users are ordered according to their channel conditions in an ascending order, i.e., | h How this channel order can be realized will be discussed later.”
Near-Field MIMO Communications for 6G: Fundamentals, Challenges, Potentials, and Future Directions (2023, background): “Recent progress: Taking advantage of the capability of beamfocusing, the authors in [14] studied near-field multi-user transmission considering fully digital precoding, hybrid precoding, and transmissive reconfigurable metasurface (RMS). optimizing the sum rate in multi-user systems through…”
Holographic MIMO Communications: Theoretical Foundations, Enabling Technologies, and Future Directions (2022, background): “[224] specifically investigated beam focusing techniques in near-field to achieve significant rate improvement and reliable communications among UEs in the”
A Tutorial on Near-Field XL-MIMO Communications Toward 6G (2023, unknown): “The enhanced spatial resolution of XL-MIMO brings a new DoF for IUI suppression, i.e., the IUI can be suppressed not only by the angular separation as in the conventional far-ﬁeld UPW model, but also by the distance separation for users along the same direction [9], [74], [172].”