# Performance Analysis of Rate Splitting in Massive MIMO Systems with Low Resolution ADCs/DACs
## 1 Introduction  
In massive multiple-input multiple-output (MIMO), base stations (BSs) are equipped with a large number of antennas to simultaneously serve user terminals by spatial multiplexing [1]. Massive MIMO uses linear processing to achieve high spectral efficiency (SE) and energy efficiency (EE) [1, 2, 3]. Massive MIMO systems can operate in the time division duplex (TDD) mode, where the uplink (UL) is utilized for channel state information (CSI) estimation and the downlink (DL) for data transmission [4]. However, imperfect CSI obtained from UL training decreases the system performance. Rate-splitting (RS) is a promising multiple access scheme that received a surge of interest in recent years [5, 6, 7]. In RS multiple access, the transmitter splits each user's message into two parts namely: a common part and a private part [5]. The common messages are encoded into one stream using a public codebook. The private messages are encoded into individual streams. The common stream is superimposed with the private streams of all users. It is assumed that the receivers decode the common message with zero error probability and their corresponding private messages by applying successive interference cancellation (SIC). Both RS multiple access and nonorthogonal multiple access (NOMA) utilize SIC at the receivers [6, 7, 8]. However, RS multiple access is a generalized technique that includes NOMA as a special case [6, 7, 8]. The advantage of RS over NOMA lies in the fact that the RS scheme partially decodes interference and treats the remaining part as noise, while the NOMA scheme needs to fully decode the interference from other users. Therefore, the RS strategy is a robust interference management technique outperforming NOMAwith a lower computational complexity in various network settings [6, 7]. The RS scheme also improves the achievable degrees-of-freedom (DoF) compared to that of NOMA [9]. Rate-splitting was also shown to enhance the EE of DL MISO transmission [10, 11]. In massive MIMO systems, RS multiple access was first proposed in a frequency division duplex (FDD) system to mitigate the effects of imperfect CSI [12]. The authors derived the asymptotic sum-rate of the RS scheme. The RS scheme performs better than the conventional non-RS schemes in terms of SE. Based on the results, a novel hierarchical rate-splitting (HRS) scheme was proposed which exploits the DL channel statistics for additional rate performance. The authors of [13] extended the results of [12] to a TDD massive MIMO system, where the BS and users suffer from hardware impairments. Compared to that of the conventional non-RS scheme, the RS scheme is able to enhance the sum-rate, especially in the presence of hardware impairments caused by phase noise and amplified thermal noise [13]. Furthermore, RS multiple access is a robust strategy to combat the effects of residual self-interference (SI) and intracell pilot contamination in massive MIMO systems [14, 15]. To realize the SE and EE gains, massive MIMO systems are analyzed by assuming high-quality perfect hardware in the literature. However, the radio-frequency (RF) components suffer from high hardware cost and circuit power consumption due to the large number of antennas at the BSs. Analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) are the dominant power hungry components at the BS. The power consumption of ADCs and DACs grows exponentially as the number of quantization bits increases [16]. The use of low-resolution ADCs and DACs emerged as a possible solution to reduce the hardware cost and power consumption in massive MIMO transceiver designs [17]. Several works proposed and analyzed different architectures such as one bit, low bit resolution (e.g., 1-3 bits), and variable bit resolution for massive MIMO systems [18, 19, 20, 21, 22, 23]. In [18], the authors analyzed the DL achievable rate in a one-bit massive MIMO with matched filter (MF) precoding. The rate loss incurred can be compensated by using 2.5 times more antennas at the BS.