Near- and Far-Field Communications with Large Intelligent Surfaces

Torres, Andrea de Jesus; Sanguinetti, Luca; Björnson, Emil

doi:10.48550/arxiv.2011.13835

Cited by 3 publications

(8 citation statements)

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“…For convenience, we use the term extremely large-scale array (XLarray) communications throughout the paper. In the extreme case when an infinite number of antenna elements are packed into a finite two-dimensional (2D) surface, XL-array converges to the emerging continuous electromagnetic (EM) surface, also known as large intelligent surfaces (LISs) [17]- [20] or holographic MIMO surface [21], [22].…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, their obtained results cannot be applied for XL-array systems, for which EM waves can only be captured/steered by discrete array elements that are separated by certain spaces (e.g., halfwavelength spacing for classical MIMO and sub-wavelength spacing for the discrete approximation of continuous surfaces). Besides, most existing works [11], [20] mainly consider the 2D channel modelling that only consider either the azimuth or elevation AoA/AoD, but not both as required for the more general three-dimensional (3D) channel modelling.…”

Section: Introductionmentioning

confidence: 99%

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Communicating with Extremely Large-Scale Array/Surface: Unified Modelling and Performance Analysis

Lu¹,

Zeng

2021

Preprint

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Wireless communications with extremely large-scale array (XL-array) correspond to systems whose antenna sizes are so large that conventional modelling assumptions, such as uniform plane wave (UPW) impingement, are longer valid. This paper studies the mathematical modelling and performance analysis of XL-array communications. By deviating from the conventional modelling approach that treats the array elements as sizeless points, we explicitly model their physical area/aperture, which enables a unified modelling for the classical discrete antenna arrays and the emerging continuous surfaces. As such, a generic array/surface model that accurately takes into account the variations of signal phase, amplitude and projected aperture across array elements is proposed. Based on the proposed model, a closed-form expression of the resulting signal-to-noise ratio (SNR) with the optimal single-user maximum ratio combining/transmission (MRC/MRT) beamforming is derived. The expression reveals that instead of scaling linearly with the antenna number M as in conventional UPW modelling, the SNR with the more generic model increases with M with diminishing return, which is governed by the collective properties of the array, such as the array occupation ratio and the physical sizes of the array along each dimension, while irrespective of the properties of the individual array element. In addition, we have derived an alternative insightful expression for the optimal SNR in terms of the vertical and horizontal angular spans, which are fully determined by the geometric angles formed by the array/surface and user location. Furthermore, we also show that our derived results include the far-field UPW modelling as a special case. One important finding during the study of far-field approximation is the necessity to introduce a new distance criterion to complement the classical Rayleigh distance, termed uniform-power distance (UPD), which concerns the signal amplitude/power variations across array elements, instead of phase variations as for Rayleigh distance. Extensive numerical results are provided to demonstrate the necessity of proper modelling for XL-array communications by comparing the proposed model with various benchmark models.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Communicating with Extremely Large-Scale Array/Surface: Unified Modelling and Performance Analysis

Lu¹,

Zeng

2021

Preprint

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“…More recently, near-field communications with antennas based on large intelligent surfaces (LISs), whose large aperture gives rise to near-field operation, was explored in [9]- [12]. In particular, [9] considered a single-user scenario, and characterized the pathloss and the available communication modes, while [10] studied a two-user uplink scenario in which the BS is equipped with an LIS. Both [9] and [10] studied ideal antenna architectures, where the transceiver has direct access to the signal observed at each element.…”

Section: Introductionmentioning

confidence: 99%

Beam Focusing for Near-Field Multi-User MIMO Communications

Zhang¹,

Shlezinger²,

Guidi³

et al. 2021

Preprint

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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 are such that users residing at the same angular direction can communicate reliably without interfering with each other, which is not achievable using conventional far-field beam steering.Index terms-Beam focusing, dynamic metasurface antennas, near-field multi-user communication.

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“…There are some preliminary efforts on the study of XL-MIMO communications without relying on the conventional UPW models [4], [5], [8]- [10]. For example, by deviating from the conventional approach that treats the array elements as isotropic and sizeless points, [4] proposed a new approach that takes into account the element's area/aperture, which enables the modelling of the variations of the projected aperture across array elements.…”

Section: Introductionmentioning

confidence: 99%

“…Based on this model, the signal-to-noise ratio (SNR) for single-user communication with the optimal maximalratio combining/transmission (MRC/MRT) beamforming was derived in closed-from. In [9], the power scaling laws and nearfield behaviours of single-user XL-MIMO communication was analyzed based on the two-dimensional (2D) channel modelling that only considers the azimuth AoA/AoD, and the extension to two-user system was studied in [10]. In [14], four antenna selection approaches were proposed to improve the energy efficiency for multi-user XL-MIMO communications.…”

Section: Introductionmentioning

confidence: 99%

Multi-User Communication with Extremely Large-Scale MIMO

Lu,

Zeng

2021

Preprint

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Extremely large-scale multiple-input multipleoutput (XL-MIMO) communication aims to further boost the antenna size significantly than current massive MIMO systems, for which conventional far-field assumption with uniform plane wave (UPW) model may become invalid. This paper studies the modelling and performance analysis for multi-user XL-MIMO communication. With the spherical wavefront phase modelling, and also by taking into account the variations of signal amplitude and projected aperture across array elements, the performance of the three typical beamforming schemes are analyzed, namely the maximal-ratio combining (MRC), zero-forcing (ZF), and minimum mean-square error (MMSE) beamforming. For the special case of two-users, we analytically show that the signal-to-interference-plus-noise ratio (SINR) of all the three beamforming schemes increases as the channels' correlation coefficient decreases. Furthermore, compared to existing UPW model where inter-user interference (IUI) can only be suppressed in angular domain, XL-MIMO enables a new degree-of-freedom (DoF) for IUI suppression by distance separation, even for users along the same direction. Simulation results are provided to validate the modelling and performance analysis of multi-user XL-MIMO communications.

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Near- and Far-Field Communications with Large Intelligent Surfaces

Cited by 3 publications

References 0 publications

Communicating with Extremely Large-Scale Array/Surface: Unified Modelling and Performance Analysis

Communicating with Extremely Large-Scale Array/Surface: Unified Modelling and Performance Analysis

Beam Focusing for Near-Field Multi-User MIMO Communications

Multi-User Communication with Extremely Large-Scale MIMO

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