3GPP-compliant single-user MIMO model for high-fidelity mobile network simulations

MIMO technology has been studied in textbooks for several decades and has been adopted in 4G and 5G systems. In particular, 3GPP 5G has adopted a hybrid beamforming architecture (with digital and analog parts) and a closed-loop MIMO mechanism, through which channel state information (CSI) is acquired at the gNB thanks to precoding matrix indicator (PMI) and rank indicator (RI) reports from the user. In the case of single-user MIMO (SU-MIMO), codebook-based precoding Type-I has been defined. Due to the recent evolution in 5G and beyond networks, designed to cover a wide range of use cases with every time more complex applications, it is essential to have network simulation tools (such as ns-3) that accurately model 5G network capabilities such as MIMO. Up to date, the well-known ns-3 simulator has been missing the inclusion of general and standard-compliant SU-MIMO models for 5G. To cover this gap, in this paper, we propose and implement a 3GPP-compliant closed-loop SU-MIMO simulation model and provide an exhaustive evaluation in the 5G-LENA module of ns-3. As per 3GPP 5G, we adopt a hybrid beamforming architecture, a closed-loop MIMO with PMI and RI reports aligned with 3GPP specifications, and codebook-based precoding following precoding Type-I. The simulation models are released as open-source and currently support up to 32 antenna ports and 4 streams per user. The simulation results presented in this paper help in testing and verifying the simulated models for different antenna configurations. Finally, we analyze the impact of realistic PHY modeling on the computational complexity and discuss some possible optimizations for large-scale network simulations.