Rate-Splitting to Mitigate Residual Transceiver Hardware Impairments in Massive MIMO Systems

Rate-splitting (RS) has recently been shown to provide significant performance benefits in various multiuser transmission scenarios. In parallel, the huge degrees-of-freedom provided by the appealing massive multiple-input multiple-output (MIMO) necessitate the employment of inexpensive hardware, being more prone to hardware imperfections, in order to be a cost-efficient technology. Hence, in this paper, we focus on a realistic massive multiple-input single-output broadcast channel hampered by the inevitable hardware impairments. We consider a general experimentally validated model of hardware impairments, accounting for the presence of multiplicative distortion due to phase noise, additive distortion noise and thermal noise amplification. Under both scenarios with perfect and imperfect channel state information at the transmitter (CSIT), we analyze the potential robustness of RS to each separate hardware imperfection. We analytically assess the sum-rate degradation due to hardware imperfections. Interestingly, in the case of imperfect CSIT, we demonstrate that RS is a robust strategy for multiuser MIMO in the presence of phase and amplified thermal noise, since its sum-rate does not saturate at high signal-to-noise ratio (SNR), contrary to conventional techniques. On the other hand, the additive impairments always lead to a sum-rate saturation at high SNR, even after the application of RS. However, RS still enhances the performance. Furthermore, as the number of users increases, the gains provided by RS decrease not only in ideal conditions, but in practical conditions with residual transceiver hardware impairments as well. Notably, although a deterministic equivalent analysis is employed, the analytical and simulation results coincide even for finite system dimensions. As a consequence, the applicability of these results also holds for current 'small scale' multiantenna systems.