# Performance Analysis of Rate Splitting in Massive MIMO Systems with Low Resolution ADCs/DACs
## 1 Introduction
The work in [19] considered active eavesdropping in a secure massive MIMO where the effects of ADC/DAC quantization are modeled by the additive quantization noise model (AQNM). The authors proposed the use of artificial noise (AN) to mitigate the effects of active eavesdropping. The results showed that optimal power allocation is necessary to reduce the rate loss caused by high QN and improve the secrecy of the system. The authors of [20] studied the performance of FD massive MIMO systems with low-resolution ADCs/DACs. By considering perfect CSI, closed-form expressions for the UL and DL achievable rates under Rayleigh fading were derived. The work in [20] was extended to Rician fading channels [21] where imperfect CSI case was also analyzed. In [22, 23], the impact of quantization on the SE and EE of FD massive MIMO systems was considered for Rician fading. However, the works in [21, 22, 23] did not account for the impact of low-resolution ADCs on the CSI estimation. Assuming perfect CSI and regularized zero-forcing (RZF) precoding, [PERSON] et al. analyzed the optimal user loading in a massive MIMO system where BS is equipped with low-resolution DACs and the users are equipped with finite resolution ADCs [24]. Conventional massive MIMO relies on linear precoding techniques such as MF, zero-forcing (ZF), and RZF precoding to achieve high SE and EE performance in multiuser systems [25]. Of the three, RZF precoding is the state-of-the-art since it offers the best performance since it boosts the desired signal energy and mitigates the interference to other users [25]. These linear precoding techniques were shown to mitigate the effects of the quantization noise (QN) to some extent [18, 20, 21, 24]. However, using low-resolution ADCs/DACs at the transceivers causes a rate loss. In conventional non-RS schemes, to cope with the high QN from low-resolution ADCs/DACs, the number of antennas needs to be increased, which causes a high complexity burden to the systems [18, 20, 21]. Comparatively, the RS scheme was shown to be a robust strategy to enhance the SE and mitigate interference in massive MIMO systems with imperfect CSI [12], hardware impairments [13], and residual SI [14], respectively. However, there were no studies on RS multiple access in massive MIMO with low-resolution ADCs/DACs. We propose RS multiple access as an effective alternative to this issue. By employing a properly designed RS scheme in massive MIMO systems with low-resolution ADCs/DACs, higher SE can be achieved compared to that of the conventional non-RS scheme, even with less number of antennas than that of the conventional scheme. In the paper, we consider the DL of a multiuser massive MIMO system where the BS is equipped with low-resolution ADCs and DACs. Different from [13], where a generalized hardware impairment model is investigated, we focus on the effect of QN due to the low-resolution quantization bits and its impact on the SE/EE. In contrast to existing works [21; 22; 23], we account for the impact of the low-resolution ADCs on the channel estimates in the UL training phase [26]. In the DL, the low-resolution DACs distort the transmit signal by introducing QN. We consider the MF beamformer and regularized zero-forcing (RZF) precoder for the common and private messages, respectively [12; 13; 14]. While the RZF precoder was investigated in massive MIMO systems with low-resolution ADCs/DACs [24], the results were only derived for perfect CSI. In contrast, the results in our work are derived for the imperfect CSI case. The main contributions of this work are summarized as follows:  
* We derive the signal-to-interference-and-noise ratios (SINRs) of the common and private messages of the RS scheme in the asymptotic regime. Numerical results demonstrate the effectiveness of the RS scheme to achieve higher SE than the non-RS scheme for 2-3 bit resolution ADCs/DACs. We show that the RS scheme with QN (e.g., 3 bits) outperforms the conventional non-RS scheme with no QN (i.e., ideal ADCs/DACs) with reduced number of antennas.