Comparing Type I and Type II Codebooks in 5G MIMO with Imperfect CSI at the Receiver

Abstract

Massive MIMO and beamforming are key enablers in 5G-NR, relying heavily on accurate CSI feedback to realize their potential. The 5G-NR standard includes Type I and Type II codebooks to facilitate CSI-based precoding, with Type II offering greater flexibility at the cost of higher complexity. This paper investigates the impact of imperfect CSI on the performance of these codebooks under realistic propagation conditions. By comparing BLER performance for different modulation schemes and channel profiles, we show that the advantage of Type II diminishes under high CSI error, especially in LOS scenarios. In contrast, under NLOS conditions, Type II consistently outperforms Type I when CSI quality is moderately preserved. These findings emphasize that the reliability of CSI acquisition plays a pivotal role in selecting the appropriate codebook, and that the robustness of Type I under imperfect CSI may be favorable in severely degraded conditions - a critical insight for future 6G codebook and beamforming design.