Abstract
This paper investigates a multi-user massive multiple-input multiple-output (MU-mMIMO) hybrid precoding (HP) scheme using low-resolution phase shifters (PSs) and digital-to-analog converters (DACs). The proposed HP approach involves two stages: RF beamforming based on the slowly time-varying channel second-order correlation matrix, and baseband MU precoding based on the instantaneous effective baseband channel to mitigate MU-interference by a regularized zero-forcing (RZF) technique. We consider three HP design architectures: (i) HP using full-resolution PSs and DACs, with a baseband transfer block for constant-modulus RF beamformer, (ii) HP using $b$ -bit PSs and full-resolution DACs, with an orthogonal matching pursuit (OMP) based algorithm that can approach the optimal unconstrained RF beamformer, and (iii) HP using $b$ -bit PSs and $q$ -bit DACs, taking into account also DAC quantization noise. Illustrative results show that the proposed HP schemes with low-resolution PSs can approach the sum-rate of full-resolution PSs by using only 2-bit PSs, while offering higher energy efficiency. Furthermore, a study of sum-rate results for various PS and DAC quantization levels reveals that HP can achieve near-optimal performance with only 2-bit PSs and 5-bit DACs. Moreover, a comparison of the different array configurations, namely, uniform linear array (ULA), uniform circular array (UCA), uniform rectangular array (URA), and concentric circular array (CCA), indicates that URA and CCA outperform UCA and ULA in terms of spectral and energy efficiencies.
Highlights
M ULTIPLE-input multiple-output (MIMO) refers to utilizing multiple antennas at base station (BS) for improving data rates through spatial multiplexing in singleuser MIMO (SU-MIMO) and multi-user MIMO (MU-MIMO) operation modes [1]
We present the analysis of different 2D array structures (ULA, uniform rectangular array (URA), uniform circular array (UCA), and circular array (CCA)) in massive MIMO (mMIMO), where we compare the spatial, spectral and energy efficiencies by designing the hybrid precoding (HP) using low-resolution phase shifters (PSs) and quantized digital-to-analog converters (DACs)
We have presented the MU-mMIMO hybrid precoder (HP) design for low-resolution PSs and/or DACs, and investigated its performance using different 2D antenna array structures
Summary
M ULTIPLE-input multiple-output (MIMO) refers to utilizing multiple antennas at base station (BS) for improving data rates through spatial multiplexing in singleuser MIMO (SU-MIMO) and multi-user MIMO (MU-MIMO) operation modes [1]. Massive MIMO ( known as large-scale antenna systems, very large MIMO, hyper MIMO) uses a large number of antennas at BS, which significantly improves the spectral efficiency, simplifies the signal processing, and enhance the energy efficiency by directing the beams selectively to the users. HP is a two-stage precoder consisting of an analog RF beamforming stage and a digital baseband precoding stage, and with much-reduced system complexity/hardware cost, it can achieve the performance close to FDP which requires full instantaneous CSI. Most of the HP designs have assumed the use of full-resolution PSs and DACs to achieve a satisfactory performance close to FDP structures. The use of low-resolution PSs [23]–[31] and DACs/ADCs [32]–[37] allows a more viable HP to be designed.
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