Enhancements on Type-II 5G New Radio Codebooks for UE Mobility Scenarios

This article focuses on potential enhancements of current 5G New Radio (NR) codebooks (CBs) for user equipment (UE) mobility scenarios. An overview of the incremental evolution of the 5G NR Type-II CBs is presented, and its inherent drawbacks in mobility scenarios are discussed. The current Type-II CBs fail to deliver adequate performance when used by moving UEs at medium to high speeds, mainly due to the current channel coherence time-based CSI measurement and reporting. Measured channel data from a number of real-world scenarios are analyzed by means of Doppler power spectrum and delay-Doppler power spectrum to verify the so-called channel stationarity time, which is several-fold higher than the channel coherence time. Based on the presented analysis, conclusions are drawn that for stationarity time-based CSI measurements and reporting, Doppler frequency components in addition to space and delay components can be exploited for Type-II CB enhancements. The enhanced Type-II CB achieves a drastic feedback reduction due to the sparse nature of the channel in the delay-Doppler domain and improved performance compared to the 5G NR Type-II CB.