Low-resolution digital-to-analog converter (DAC) has shown great potential in facilitating cost-and powerefficient implementation of massive multiple-input multiple-output (MIMO) systems. We investigate the performance of a massive MIMO downlink network with low-resolution DACs using regularized zero-forcing (RZF) precoding. It serves multiple receivers equipped with finite-resolution analog-to-digital converters (ADCs). By taking the quantization errors at both the transmitter and receivers into account under spatially correlated channels, the regularization parameter for RZF is optimized with a closed-form solution by applying the asymptotic random matrix theory. The optimal regularization parameter increases linearly with respect to the user loading ratio while independent of the ADC quantization resolution and the channel correlation. Furthermore, asymptotic sum rate performance is characterized and a closed-form expression for the optimal user loading ratio is obtained at low signal-to-noise ratio. The optimal ratio increases with the DAC resolution while it decreases with the ADC resolution. Numerical simulations verify our observations.
Index TermsMassive multiple-input multiple-output (MIMO), digital-to-analog converter (DAC), analog-to-digital converter (ADC), spatial correlation, user loading ratio.
I. INTRODUCTIONMassive multiple-input multiple-output (MIMO) has gained significant attention as a candidate technique for the next generation wireless system [2]- [4]. In massive MIMO, a large amount of antennas Part of this work was presented in [1] at the IEEE VTC-Fall in Toronto, Canada, Sept. 2017. 2 equipped at base station (BS) can provide high spectral and energy efficiencies [5]. Despite these merits of massive MIMO, it suffers from a challenging issue of high cost and power consumption for applications even at the BS. This is due to the fact that each antenna has to be driven by a separate radio-frequency (RF) chain.Considering that the power consumption of each RF chain can decrease dramatically by reducing the resolutions of digital-to-analog converters (DACs), one of the potential solutions is to employ lowresolution DACs for downlink transmissions [6]- [11]. More specifically in [6]-[8], nonlinear precoding schemes were proposed for massive MIMO downlink transmission with low-resolution DACs. In [6], a novel precoding technique using 1-bit DACs was presented to mitigate multiuser interference and quantization distortions. In [7], a computationally-efficient 1-bit beamforming algorithm, named POKEMON (short for PrOjected downlinK bEaMfOrmiNg), was proposed. The authors of [8] studied perturbation methods which minimize the probability of errors at receivers in a massive MIMO downlink with 1bit DAC. Alternatively, linear precoding techniques were studied for the downlink transmissions using low-precision DACs [9]- [11]. A linear precoding approach was studied in [9], where the output data of conventional linear precoders were directly quantized by low-resolution DACs. Considering 1-bit DACs and z...