Differential channel quality indicator (CQI) and wideband CQI are key components of the reduced feedback schemes employed in the 5G New Radio (NR) and 4G Long Term Evolution (LTE) standards. They enable a base station (BS) to acquire channel state information that is essential for rate adaptation and frequency-domain scheduling without overwhelming the uplink. We present a novel throughput-optimal rate adaptation rule that exploits the correlation between the differential and wideband CQIs to improve throughput without any additional feedback. It also shows that the prevalent conventional method that adds the two CQIs is sub-optimal. We then propose a novel flexible-overhead differential CQI feedback scheme, in which the number of bits for differential CQI can be different across the subbands. This provides a new flexibility to the BS to control the feedback overhead. It differs from the current rigid parameterization, in which a user always feeds back a 2-bit differential CQI for each subband. In various single-user and multi-user deployment scenarios involving small-scale fading, large-scale shadowing, and co-channel interference, the proposed approach achieves nearly the same throughput as the feedback scheme employed in 5G and LTE, but with much less overhead.

中文翻译：

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在4G / 5G OFDM系统中利用宽带CQI的相关性并使差分反馈开销灵活

差分信道质量指示符（CQI）和宽带CQI是5G新无线电（NR）和4G长期演进（LTE）标准中采用的缩减反馈方案的关键组件。它们使基站（BS）能够获取速率自适应和频域调度必不可少的信道状态信息，而不会占用上行链路的资源。我们提出了一种新颖的吞吐量最优速率自适应规则，该规则利用差分和宽带CQI之间的相关性来提高吞吐量，而无需任何其他反馈。它还表明，将两个CQI相加的流行传统方法不是最优的。然后，我们提出了一种新颖的灵活开销差分CQI反馈方案，其中差分CQI的位数可以在子带上不同。这为BS提供了新的灵活性来控制反馈开销。它与当前的刚性参数化不同，在刚性参数化中，用户始终为每个子带反馈2位差分CQI。在涉及小规模衰落，大范围阴影和同信道干扰的各种单用户和多用户部署方案中，提出的方法可实现与5G和LTE中采用的反馈方案几乎相同的吞吐量，但要少得多高架。