Exploiting Correlation Between Wideband and Differential CQIs for Adaptation and Feedback

Differential channel quality indicator (CQI) and wideband CQI are key components of the 4G and 5G standards. They enable a base station (BS) to acquire channel state information that is essential for rate adaptation and scheduling without overwhelming the uplink. We present a novel throughput-optimal rate adaptation rule, which exploits the correlation between the differential and wideband CQIs to improve throughput without any additional feedback, and a computationally efficient approach to evaluate it. We then propose a novel flexible-overhead differential CQI feedback scheme, in which the number of feedback bits can be subband-specific. The combination of the two approaches provides a new flexibility to the BS to control the feedback overhead and achieves a throughput comparable to conventional approaches with much less feedback.