A Wideband Capacity Maximization Approach for CSI Feedback in Frequency Selective Channels

In this paper we investigate the problem of precoder selection assuming compressed channel state information (CSI) feedback over sub-bands. Typically (e.g., in NR Rel-16) the problem is approached by a two-step solution: independent precoder optimization for each sub-band, followed by selection of the compression bases. We show that such conventional approach does not perform well in scenarios of medium/high frequency selectivity. Then, we derive an alternative approach, based on wideband capacity maximization, which provides superior performance under frequency-selective channels, while being compatible with the existing NR Rel-16 framework without any additional signaling. We finally propose an adaptive method in which the receiver dynamically selects the wideband or the sub-band optimization strategy, depending on the instantaneous channel condition. The proposed approach achieves consistent gains (up to 3dB) in all the considered test cases.